Previous studies using genetic and lesion approaches have shown that the neuropeptide urocortin 1 (Ucn1) is involved in regulating alcohol consumption. Ucn1 is a corticotropin releasing factor (CRF) -like peptide that binds CRF1 and CRF2 receptors. Perioculomotor urocortin-containing neurons (pIIIu), also known as the non-preganglionic Edinger-Westphal nucleus, are the major source of Ucn1 in the brain and are known to innervate the lateral septum. Thus, the present study tested whether Ucn1 could regulate alcohol consumption through the lateral septum. In a series of experiments Ucn1 or CRF was bilaterally injected at various doses into the lateral septum of male C57BL/6J mice. Consumption of 20% volume/volume ethanol or water was tested immediately after the injections using a modification of a 2-h limited access sweetener-free "drinking-in-the-dark" procedure. Ucn1 significantly suppressed ethanol consumption when administered prior to the third ethanol drinking session (the expression phase of ethanol drinking) at doses as low as 6 pmol. Ethanol intake was differentially sensitive to Ucn1, as equivalent doses of this peptide did not suppress water consumption. In contrast, CRF suppressed both ethanol and water intake at 40 and 60 pmol, but not at lower doses. Repeated administration of Ucn1 during the acquisition of alcohol consumption showed that 40 pmol (but not 2 or 0.1 pmol) significantly attenuated ethanol intake. Repeated administration of Ucn1 also resulted in a decrease of ethanol intake in sham-injected animals, a finding suggesting that the suppressive effect of Ucn1 on ethanol intake can be conditioned. Taken together, these studies confirm the importance of lateral septum innervation by Ucn1 in the regulation of alcohol consumption.

It is well established that social recognition memory is mediated, in part, by arginine vasopressin (AVP). AVP cells within the bed nucleus of the stria terminalis (BST) and medial amygdala (MeA) send AVP-ergic projections to the lateral septum (LS). We have demonstrated that progesterone treatment decreases AVP immunoreactivity within the BST, the MeA and the LS, and that progesterone treatment impairs social recognition. These data suggested that progesterone may impair social recognition memory by decreasing AVP. In the present experiment, we hypothesized that infusions of AVP into the LS would rescue the progesterone-induced impairment in social recognition within adult male rats. One week after adult male rats underwent cannula surgery, they were given systemic injections of either a physiological dose of progesterone or oil control for 3 days. Four hours after the last injection, we tested social recognition memory using the social discrimination paradigm, a two-trial test that is based on the natural propensity for rats to be highly motivated to investigate novel conspecifics. Immediately after the first exposure to a juvenile, each animal received bilateral infusions of either AVP or artificial cerebrospinal fluid into the LS. Our results show that, as expected, control animals exhibited normal social discrimination. In corroboration with our previous results, animals given progesterone have impaired social discrimination. Interestingly, animals treated with progesterone and AVP exhibited normal social discrimination, suggesting that AVP treatment rescued the impairment in social recognition caused by progesterone. These data also further support a role for progesterone in modulating vasopressin-dependent behavior within the male brain.

The topographic distribution of calretinin-immunoreactive neurons was studied in the medial septum diagonal band of Broca complex of the rat, in relation to the localization of other neurochemically identified cell groups containing choline acetyltransferase, parvalbumin or calbindin D28k. Double-labelling experiments revealed that these four antigen-containing cells formed distinct dorsoventrally running lamellae overlayed on top of each other similar to onion leaves. There was only a slight overlapping of the various cell groups. None of the four antigens were co-localized in the same cells. The lamella occupied by calretinin-positive neurons is situated at the border of the medial septum and the intermediolateral septal nucleus, and shows some overlap with the area occupied by cholinergic neurons. Retrograde transport of horseradish peroxidase from the hippocampus combined with immunostaining for calretinin revealed that calretinin-containing neurons do not participate in the septohippocampal projection. The lack of projection to the amygdala was also confirmed. Thus, calretinin-containing neurons represent a distinct cell group in the medial septal region, which either projects to subcortical areas, or may function as interneurons relaying hippocampal feedback to the medial septal projection neurons.

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-β and tau proteins, which are believed to lead to neural damage that translates into brain dysfunction and cognitive deficits. Brain dysfunction can be evaluated by measuring single-neuron activity (spikes), global neural activity (local field potentials, LFPs) and the interaction between them. Considering that the dynamic interactions between the hippocampal pyramidal cells and lateral septum are important for proper structure function, we used the complete septo-hippocampal preparation from 30-day-old controls and J20-AD transgenic mice to record changes in spiking activity from the lateral septum and its relationship with LFP activity from the CA1 area. The cross-correlation analysis revealed that young J20 transgenic mice exhibit a significant reduction in coupling between lateral septum single-cell activity and neural network activity from the hippocampal CA1. Consistently, phase-lock analysis between lateral septum single-cell activity and CA1 neural network activity showed lower values in J20 transgenic mice. Similarly, the LFP- LFP coherence between CA1 and septum in the theta range showed lower values in J20 animals. Importantly, alterations were found before any detectable signs of cognitive deficits. Our data indicate that the disruption in the communication between hippocampus and rostral lateral septum is an early event in AD pathology and may contribute to the deficits observed during AD.

Reward-mediated associative learning is important for recognizing the significance of environmental cues. Such learning involves convergence of multimodal sensory inputs with circuits involved in affective and memory processes. Dopamine-dependent plasticity in the striatum plays a pivotal role, but the wider circuits engaged in cue-reward association are poorly understood. To identify candidate structures that may be of particular interest for further detailed electrophysiological and functional analysis, we quantified c-Fos expression in a selection of brain structures. c-Fos is a well-known marker of cell activation with additional potential importance for synaptic plasticity. We compared c-Fos expression between animals exposed to 100 pairings of a novel conditioned stimulus with a subsequent reward, and control animals exposed to the same number of cues and rewards, but where the cues and rewards occurred at random with respect to each other. We found significant increases in c-Fos expression in the superior colliculus in the group exposed to cue-reward pairing. This is consistent with previous recordings in conscious animals, showing modulation of phasic visual responses of single collicular neurons depending on their association with reward. Further, the data also suggest the possibility that the thalamic paraventricular nucleus and septal nuclei may be selectively activated during cue-reward association learning. Little is known of the neurophysiological responses in these structures during such tasks, so the present results suggest they would be targets of interest for future single-neuron recording experiments, designed to confirm whether the neurons show learning-specific modulation.

Pituitary adenylate-cyclase activating polypeptide (PACAP) has been implicated in the (patho)physiology of stress-adaptation. PACAP deficient (PACAP(-/-)) mice show altered anxiety levels and depression-like behavior, but little is known about the underlying mechanisms in stress-related brain areas. Therefore, we aimed at investigating PACAP(-/-) mice in light-dark box, marble burying, open field, and forced swim paradigms. We also analyzed whether the forced swim test-induced c-Fos expression would be affected by PACAP deficiency in the following stress-related brain areas: magno- and parvocellular paraventricular nucleus of the hypothalamus (PVN); basolateral (BLA), medial (MeA), and central (CeA) amygdaloid nuclei; ventral (BSTv), dorsolateral (BSTdl), dorsomedial (BSTdm), and oval (BSTov) nuclei of the bed nucleus of stria terminalis; dorsal (dLS) and ventral parts (vLS) of lateral septal nucleus, central projecting Edinger-Westphal nucleus (EWcp), dorsal (dPAG) and lateral (lPAG) periaqueductal gray matter, dorsal raphe nucleus (DR). Our results revealed that PACAP(-/-) mice showed greatly reduced anxiety and increased locomotor activity compared with wildtypes. In forced swim test PACAP(-/-) mice showed increased depression-like behavior. Forced swim exposure increased c-Fos expression in all examined brain areas in wildtypes, whereas this was markedly blunted in the DR, EWcp, BSTov, BSTdl, BSTv, PVN, vLS, dPAG, and in the lPAG of PACAP(-/-) mice vs. wildtypes, strongly suggesting their involvement in the behavioral phenotype of PACAP(-/-) mice. PACAP deficiency did not influence the c-Fos response in the CeA, MeA, BSTdm, and dLS. Therefore, we propose that PACAP exerts a brain area-specific effect on stress-induced neuronal activation and it might contribute to stress-related mood disorders.

Rats were injected with 3,4-methylenedioxymethamphetamine ("Ecstasy") and assessed for changes in locomotor activity and for the expression of the immediate early gene c-fos throughout the brain. A dose-dependent increase in locomotor activity was seen with 3,4-methylenedioxymethamphetamine (0, 5 and 20 mg/kg) that continued for at least 2 h following administration. Dose-dependent increases in c-fos expression were seen in much of the cortex, forebrain, brainstem and cerebellum in rats given 3,4-methylenedioxymethamphetamine. Expression was pronounced in 5-hydroxytryptamine terminal regions including the medial prefrontal cortex, caudate-putamen, nucleus accumbens, olfactory tubercle, islands of Calleja, lateral septum, paraventricular hypothalamus and paraventricular thalamus. High levels of c-fos expression were also seen in the supraoptic and median preoptic nuclei, regions involved in the control of fluid balance and body temperature, respectively. This is potentially important since deaths in 3,4-methylenedioxymethamphetamine users have been linked to hyperthermia and hyponatremia. In the brainstem, two regions of high c-fos expression were Barrington's nucleus, which is involved in micturition, and the pontine reticular nucleus oralis, a region involved in motor control of mastication. Activation of this latter structure may partly explain the bruxism (grinding of the jaw) reported by human 3,4-methylenedioxymethamphetamine users. Robust c-fos expression was seen in the cerebellum, particularly in the flocculus, and this may explain the reported deleterious effects of 3,4-methylenedioxymethamphetamine on balance and co-ordination. Significant c-fos expression was also seen in the ventral tegmental area, amidst the cell bodies of mesolimbic and mesocortical dopamine neurons, and in the median and dorsal raphe, where the serotonergic innervation of the forebrain originates. Double-labelling of fos-positive neurons with 5-hydroxytryptamine showed that only a small number of serotonergic neurons in the raphe expressed c-fos following 3,4-methylenedioxymethamphetamine. The widespread distribution of 3,4-methylenedioxymethamphetamine-induced c-fos expression seen in this study can be linked to the profound alterations in physiological function, mood and behaviour produced by this drug.

With the use of a rabbit polyclonal antiserum against a conserved region (54-118) of C-peptide of human preproinsulin-like peptide 7, referred to herein as C-INSL7, neurons expressing C-INSL7-immunoreactivity (irC-INSL7) were detected in the pontine nucleus incertus, the lateral or ventrolateral periaqueductal gray, dorsal raphe nuclei and dorsal substantia nigra. Immunoreactive fibers were present in numerous forebrain areas, with a high density in the septum, hypothalamus and thalamus. Pre-absorption of C-INSL7 antiserum with the peptide C-INSL7 (1 microg/ml), but not the insulin-like peptide 7 (INSL7; 1 microg/ml), also known as relaxin 3, abolished the immunoreactivity. Optical imaging with a voltage-sensitive dye bis-[1,3-dibutylbarbituric acid] trimethineoxonol (DiSBAC4(3)) showed that C-INSL7 (100 nM) depolarized or hyperpolarized a small population of cultured rat hypothalamic neurons studied. Ratiometric imaging studies with calcium-sensitive dye fura-2 showed that C-INSL7 (10-1000 nM) produced a dose-dependent increase in cytosolic calcium concentrations [Ca2+]i in cultured hypothalamic neurons with two distinct patterns: (1) a sustained elevation lasting for minutes; and (2) a fast, transitory rise followed by oscillations. In a Ca2+-free Hanks' solution, C-INSL7 again elicited two types of calcium transients: (1) a fast, transitory increase not followed by a plateau phase, and (2) a transitory rise followed by oscillations. INSL7 (100 nM) elicited a depolarization or hyperpolarization in a small population of hypothalamic neurons, and an increase of [Ca2+]i with two patterns that were dissimilar from that of C-INSL7. [125I]C-INSL7 bindings to rat brain membranes were inhibited by C-INSL7 in a dose-dependent manner; the Kd and Bmax. values were 17.7 +/- 8.2 nM and 45.4 +/- 20.5 fmol/mg protein. INSL7 did not inhibit [125I]C-INSL7 binding to rat brain membranes, indicating that C-INSL7 and INSL7 bind to distinct binding sites. Collectively, our result raises the possibility that C-INSL7 acts as a signaling molecule independent from INSL7 in the rat CNS.

The distribution and density of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites have been investigated in the brain of the primates Jacchus callithrix (marmoset) and Macaca fascicularis (macaque) using [(125)I]-PACAP27 as a radioligand. PACAP binding sites were widely expressed in the brain of these two species with particularly high densities in the septum, hypothalamus and habenula. A moderate density of recognition sites was seen in all subdivisions of the cerebral cortex with a heterogenous distribution, the highest concentrations occurring in layers I and VI while the underlying white matter was almost devoid of binding sites. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed intense expression of the mRNAs encoding the short and hop-1 variants of pituitary adenylate cyclase-activating polypeptide-specific receptor (PAC1-R) in the cortex of both marmoset and macaque, whereas vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide mutual receptor, subtype 1 (VPAC1-R) and vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide mutual receptor, subtype 2 (VPAC2-R) mRNAs were expressed at a much lower level. In situ hybridization histochemistry showed intense expression of PAC1-R and weak expression of VPAC1-R mRNAs in layer IV of the cerebral cortex. Incubation of cortical tissue slices with PACAP induced a dose-dependent stimulation of cyclic AMP formation, indicating that PACAP binding sites correspond to functional receptors. Moreover, treatment of primate cortical slices with 100 nM PACAP significantly reduced the activity of caspase-3, a key enzyme of the apoptotic cascade. The present results indicate that PACAP should exert the same neuroprotective effect in the brain of primates as in rodents and suggest that PAC1-R agonists may have a therapeutic value to prevent neuronal cell death after stroke or in specific neurodegenerative diseases.

A comprehensive three-dimensional digital atlas database of the C57BL/6J mouse brain was developed based on magnetic resonance microscopy images acquired on a 17.6-T superconducting magnet. By using both manual tracing and an atlas-based semi-automatic segmentation approach, T2-weighted magnetic resonance microscopy images of 10 adult male formalin-fixed, excised C57BL/6J mouse brains were segmented into 20 anatomical structures. These structures included the neocortex, hippocampus, amygdala, olfactory bulbs, basal forebrain and septum, caudate-putamen, globus pallidus, thalamus, hypothalamus, central gray, superior colliculi, inferior colliculi, the rest of midbrain, cerebellum, brainstem, corpus callosum/external capsule, internal capsule, anterior commissure, fimbria, and ventricles. The segmentation data were formatted and stored into a database containing three different atlas types: 10 single-specimen brain atlases, an average brain atlas and a probabilistic atlas. Additionally, quantitative group information, such as variations in structural volume, surface area, magnetic resonance microscopy image intensity and local geometry, were computed and stored as an integral part of the database. The database augments ongoing efforts with other high priority strains as defined by the Mouse Phenome Database focused on providing a quantitative framework for accurate mapping of functional, genetic and protein expression patterns acquired by a myriad of technologies and imaging modalities.

The elicitation and reduction of fear were indexed with fear-potentiated startle and corticosterone release and induction of the immediate-early gene c-fos as a marker of neural activity in male Sprague-Dawley rats. Conditioning consisted of pairing one stimulus with footshock, which was withheld when the conditioned stimulus was preceded by a different modality stimulus, the conditioned inhibitor. On the test day, approximately 60% of the rats were used for c-fos in situ hybridization, and were presented with either the conditioned stimulus alone, the conditioned inhibitor alone, a compound of the two stimuli, or no stimuli, and killed 30 min following the presentation of 10 such stimuli. The remaining rats were tested with the fear-potentiated startle paradigm. Rats displayed reliable fear-potentiated startle and corticosterone release to the conditioned stimulus, and both measures were reduced when the conditioned stimulus was preceded by the conditioned inhibitor. The ventral bed nucleus of the stria terminalis, septohypothalamic nucleus, some tegmental nuclei, and the locus coeruleus had particularly high c-fos induction in rats that received the conditioned inhibitor, providing one of the first functional indication that these nuclei might be important in behavioural or endocrine inhibition. Conditioning specific c-fos induction in the three groups that received a stimulus on the test day was observed in many hypothalamic areas, the medial geniculate body and the central gray, structures previously involved in fear and anxiety. The cingulate, infralimbic and perirhinal cortex, nucleus accumbens, lateral septum, dorsal endopiriform nucleus, and ventral tegmental area had higher c-fos induction in rats presented with the fearful conditioned stimulus, confirming previous studies. The amygdala and hippocampus of conditioned rats did not show higher c-fos induction than in rats repeatedly exposed to the context. Many regions displayed c-fos messenger RNA induction in the control condition, suggesting that processes other than fear and anxiety participate in c-fos induction.

Understanding the molecular mechanisms that promote stress resilience might open up new therapeutic avenues to prevent stress-related disorders. We recently characterized a stress and glucocorticoid-regulated gene, down-regulated in renal cell carcinoma - DRR1 (Fam107A). DRR1 is expressed in the mouse brain; it is up-regulated by stress and glucocorticoids and modulates neuronal actin dynamics. In the adult mouse, DRR1 was shown to facilitate specific behaviors which might be protective against some of the deleterious consequences of stress exposure: in the hippocampal CA3 region, DRR1 improved cognitive performance whereas in the septum, it specifically increased social behavior. Therefore DRR1 was suggested as a candidate protein promoting stress-resilience. Fam107B (family with sequence similarity 107, member B) is the unique paralog of DRR1, and both share high sequence similarities, predicted glucocorticoid response elements, heat-shock induction and tumor suppressor properties. So far, the role of Fam107B in the central nervous system was not studied. The aim of the present investigation, therefore, was to analyze whether Fam107B and DRR1 display comparable mRNA expression patterns in the brain and whether both are modulated by stress and glucocorticoids. Spatio-temporal mapping of Fam107B mRNA expression in the embryonic and adult mouse brain, by means of in situ hybridization, showed that Fam107B was expressed during embryogenesis and in the adulthood, with particularly high and specific expression in the forming telencephalon suggestive of an involvement in corticogenesis. In the adult mouse, expression was restricted to neurogenic niches, like the dentate gyrus. In contrast to DRR1, Fam107B mRNA expression failed to be modulated by glucocorticoids and social stress in the adult mouse. In summary, Fam107B and DRR1 show different spatio-temporal expression patterns in the central nervous system, suggesting at least partially different functional roles in the brain, and where the glucocorticoid receptor (GR)-induced regulation appears to be a unique property of DRR1.

Rats repeatedly exposed to restraint show a reduced hypothalamic-pituitary-adrenal axis response upon restraint re-exposure. This hypothalamic-pituitary-adrenal axis response habituation to restraint does not generalize to other novel stressors and is associated with a decrease in stress-induced c-fos expression in a number of stress-reactive brain regions. We examined whether habituation to repeated restraint is also associated with adaptation of immediate early gene expression in brain regions that process and relay primary sensory information. These brain regions may not be expected to show gene expression adaptation to repeated restraint because of their necessary role in experience discrimination. Rats were divided into a repeated restraint group (five 1-hour daily restraint sessions) and an unstressed group (restraint naïve). On the sixth day rats from each group were either killed with no additional stress experience or at 15, 30 or 60 min during restraint. Immediate early gene expression (corticotrophin-releasing hormone heteronuclear RNA, c-fos mRNA, zif268 mRNA) was determined by in situ hybridization. A reduction in stress-induced hypothalamic-pituitary-adrenal axis hormone secretion (plasma corticosterone and adrenocorticotropic hormone) and immediate early gene expression levels in the paraventricular nucleus of the hypothalamus, the lateral septum and the orbital cortex was observed in repeated restraint as compared with restraint naïve animals. This reduction was already evident at 15 min of restraint. Unexpectedly, we also found in repeated restraint rats a reduction in restraint-induced c-fos expression in primary sensory-processing brain areas (primary somatosensory cortex, and ventroposteriomedial and dorsolateral geniculate nuclei of thalamus). The overall levels of hippocampal mineralocorticoid receptor heteronuclear RNA or glucocorticoid receptor mRNA were not decreased by repeated restraint, as may occur in response to severe chronic stress. We propose that repeated restraint leads to a systems-level adaptation whereby re-exposure to restraint elicits a rapid inhibitory modulation of primary sensory processing (i.e. sensory gating), thereby producing a widespread attenuation of the neural response to restraint.

The sexually dimorphic area of the gerbil hypothalamus is essential for male sex behavior. To determine which aspects of mating activate its cells, or cells near or connected to it, we visualized c-Fos in the brains of male gerbils that had been exposed to various types of sex-related stimuli or that had displayed various aspects of sex behavior. Five groups of males were placed in familiar arenas containing sex-related odors. All subjects had previously mated in these arenas. For four groups, a female was introduced and remained with the male until he ejaculated, intromitted, mounted or sniffed her. Males in the fifth group remained in the arena alone. Males in a sixth group were placed in a clean arena in another room. These males were also familiar with this arena but had never encountered a female there. The seventh group remained in their home cages. The posterodorsal preoptic nucleus, the lateral part of the posterodorsal medial amygdala, the medial part of the sexually dimorphic area and the parvicellular part of the subparafascicular nucleus of the thalamus expressed c-Fos after ejaculation. Whether these cells triggered ejaculation or responded to it is not clear. The latter two areas also expressed c-Fos whenever males were exposed to the sex arena, but the sexually dimorphic area pars compacta did not express c-Fos under any condition. The medial core of the nucleus accumbens, the ventrolateral septum, the caudomedial bed nucleus of the stria terminalis, the medial/central part of the posterodorsal medial amygdala and the lateral part of the sexually dimorphic area also expressed c-Fos when males entered the sex arena. The ventrolateral part of the ventromedial nucleus of the hypothalamus expressed c-Fos whenever males were with females. None of the 31 areas studied responded to mounting or intromission, but the zona incerta, the amygdalohippocampal area, the lateral part of the sexually dimorphic area and the area lateral to the medial part of the sexually dimorphic area showed progressive increases in c-Fos expression as mating progressed. The area dorsal to the medial part of the sexually dimorphic area, the paraventricular nucleus of the hypothalamus, the ventral premammillary nucleus and the retrorubral field showed the same level of c-Fos expression when males were exposed to the non-sexual context as when they were exposed to the sexual one. While a projection to the retrorubral field from the sexually dimorphic area is critical for male sex behavior, the retrorubral field did not show a sex-related c-Fos response. The data suggest that brain regions involved in male sex behavior are involved in different aspects of it and that this can also apply to different subsets of cells in each area. The data also indicate that cells involved in mating do not necessarily show mating-related patterns of c-Fos expression. Thus, while c-Fos is useful for identifying areas involved in mating, or other behaviors, its characteristics could cause relevant areas to be overlooked.

Women with temporal lobe epilepsy have a higher incidence of reproductive disorders, which have been linked to alterations in the pulsatile release of gonadotropin-releasing hormone (GnRH). These experiments tested the hypothesis that the number of GnRH neurons is reduced in an animal model of temporal lobe epilepsy. The effects of pilocarpine-induced status epilepticus (SE) and the subsequent spontaneous recurrent eizures on the number of GnRH-positive neurons were studied in adult female mice. Systemic injections of pilocarpine were used to induce SE, and diazepam was administered 90 min after the first seizure. Control mice received all drugs except pilocarpine. The mice were euthanized either 1 week or 3 months after SE (i.e. after spontaneous recurrent seizures were observed). Even though the estrous cycle was disrupted after SE, and hippocampal damage was detected in both the CA1 and CA3 regions, pilocarpine-treated mice did not show a significant decrease in total or regional numbers of GnRH-immunopositive neurons. Therefore, these data do not support the hypothesis that a reduction in the number of GnRH neurons is responsible for the disruption of the estrous cycle after pilocarpine-induced epilepsy, which suggests that other mechanisms contribute to female reproductive disorders associated with chronic epilepsy.

The distribution of arginine vasopressin-associated neurophysin (neurophysin II) immunoreactivity was investigated in normal and mutant house mice during development and after various gonadal steroid manipulations. During postnatal development of normal mice dense networks of neurophysin II immunoreactivity in the lateral septal nucleus and lateral habenular nucleus appeared earlier in male than in female mice, with an adult pattern of immunoreactivity being attained by 8 weeks and 12 weeks of age, respectively. The neurophysin II immunoreactivity in the male was denser than that in female mice. After gonadectomy of adult normal mice there was a gradual loss of neurophysin II immunoreactivity in the lateral septum and lateral habenula over a period of 15 weeks. In hypogonadal mice, a mutant in which gonadal development is arrested postnatally due to a deficiency in hypothalamic gonadotrophin releasing hormone, no immunoreactive neurophysin II could be detected in the lateral septum or lateral habenula. A pattern of neurophysin II immunoreactivity similar to that in normal control mice was observed in hypogonadal mice which had been implanted for 4 weeks with silicone elastomer capsules containing testosterone or oestradiol-17 beta, but not 5 alpha-dihydrotestosterone or progesterone. Stimulation of gonadal development and endogenous steroid production in hypogonadal mice by third ventricular grafts of preoptic area tissue from normal neonatal animals also produced a normal pattern of neurophysin II immunoreactivity in the lateral septum and lateral habenula. In the androgen-insensitive testicular feminized mouse immunoreactive neurophysin II was undetectable in the lateral septum and lateral habenula. Treatment of testicular feminized mice with oestradiol-17 beta, but not progesterone, produced a normal pattern of neurophysin II immunoreactivity. The main immunohistological findings were confirmed by radioimmunoassay of tissue extracts which showed that the concentration of arginine vasopressin in lateral septum was far greater in normal males than females and was undetectable in hypogonadal mice; no oxytocin could be detected in the septum of normal or hypogonadal mice. These results show that the expression of neurophysin II immunoreactivity in the lateral septum and lateral habenula of the mouse brain is dependent on the presence of aromatizeable androgens or oestrogens.

GABAergic neurons of the medial septum of the basal forebrain make up a substantial portion of the septo-hippocampal pathway fibers, and are known to modulate hippocampal amino acid neurotransmission and support cognitive function. Importantly, these neurons are also implicated in age-related cognitive decline. Hypothalamic orexin/hypocretin neurons innervate and modulate the activity of these basal forebrain neurons and also provide direct inputs to the hippocampus. However, the precise role of orexin inputs in modulating hippocampal amino acid neurotransmission--as well as how these interactions are altered in aging--has not been defined. Here, orexin A (OxA) was administered to CA1 and the medial septum of young (3-4 months) and aged (27-29 months) Fisher 344 Brown Norway rats, and hippocampal GABA and glutamate efflux was analyzed by in vivo microdialysis. Following CA1 infusion of OxA, extracellular GABA and glutamate efflux was increased, but the magnitude of orexin-mediated efflux was not altered as a function of age. However, medial septum infusion of OxA did not impact hippocampal efflux in young rats, while aged rats exhibited a significant enhancement in GABA and glutamate efflux compared to young counterparts. Furthermore, immunohistochemical characterization of the medial septum revealed a significant decrease in parvalbumin (PV)-positive cell bodies in aged animals, and a significant reduction in orexin fiber innervation to the remaining GABAergic cells within the septum, while orexin innervation to the hippocampus was unaltered by the aging process. These findings indicate that: (1) OxA directly modulates hippocampal amino acid neurotransmission in young animals, (2) Aged animals show enhanced responsivity to exogenous OxA activation of the septo-hippocampal pathway, and (3) Aged animals undergo an intrinsic reduction in medial septum PV-immunoreactivity and a decrease in orexin innervation to remaining septal PV neurons. Alterations in orexin regulation of septo-hippocampal activity may contribute to age-related dysfunctions in arousal, learning, and memory.

Principal neurons in the hippocampus and prefrontal cortex of the rat have been identified as targets for glucocorticoids involved in the hypothalamic-pituitary-adrenocortical stress response. Alterations in mRNA expression for glucocorticoid receptors in each of these regions have been shown to affect the negative feedback response to corticosterone following an acute stressor. Both decreases in forebrain glucocorticoid receptors and in the efficiency of adrenocortical feedback have been observed in normal aging, and have been selectively induced with experimental lesions or manipulations in neurotransmitter systems. The current study investigated the possibility that a loss of cholinergic support from cells in the basal forebrain, a hallmark of aging, contributes to the selective age-related loss of glucocorticoid receptor mRNA expression at cholinoceptive target sites that include the hippocampus and medial prefrontal cortex. Lesions of the basal forebrain cholinergic system in young adult rats were made by microinjections of the immunotoxin 192 IgG-saporin into the medial septum/vertical limb of the diagonal band and substantia innominata/nucleus basalis. Basal levels of circulating glucocorticoids were unaffected by the lesions. Analysis of both mineralocorticoid and glucocorticoid receptor mRNA expression revealed a significant decrease in glucocorticoid receptor mRNA in the hippocampus and medial prefrontal cortex, with spared expression at subcortical sites and no detectable change in mineralocorticoid receptor mRNA in any of the examined regions. Thus, rats with lesions of the basal forebrain cholinergic system recapitulate some of the detrimental effects of aging associated with glucocorticoid-mediated stress pathways in the brain.

Cholinergic neurotransmission in the hippocampus is involved in cognitive functions, including learning and memory. Strategies to enhance septohippocampal cholinergic neurotransmission may therefore be of therapeutic value to limit cognitive decline during cholinergic dysfunction. In addition to current strategies being developed, such as the use of acetylcholinesterase inhibitors, enhancing acetylcholine (ACh) release may be critical for optimal cholinergic neurotransmission. Vesicular acetylcholine transporter (VAChT) activity limits the rate of formation of the readily releasable ACh pool. As such, we sought to determine the influence of increased VAChT expression on the septohippocampal cholinergic system. To do this, we used the B6.eGFPChAT congenic mouse, which we show contains multiple gene copies of VAChT. In this transgenic mouse, the increased VAChT gene copy number led to an increase in VAChT gene expression in the septum and a corresponding enhancement of VAChT protein in the hippocampal formation. VAChT overexpression enhanced the release of ACh from ex vivo hippocampal slices. From these findings, we conclude that VAChT overexpression is sufficient to enhance ACh release in the hippocampal formation. It remains to be established whether, in cases of cholinergic deficits, increasing VAChT expression would re-establish adequate levels of cholinergic neurotransmission, thereby providing a valid therapeutic target.

Vasopressin (VP), oxytocin (OXT) and vasoactive intestinal polypeptide (VIP) in the brain modulate physiological and behavioral processes in many vertebrates. Day-active tree shrews, the closest relatives of primates, live singly or in pairs in territories that they defend vigorously against intruding conspecifics. However, anatomy concerning peptidergic neuron distribution in the tree shrew brain is less clear. Here, we examined the distribution of VP, OXT and VIP immunoreactivity in the hypothalamus and extrahypothalamic regions of tree shrews (Tupaia belangeri chinensis) using the immunohistochemical techniques. Most of VP and OXT immunoreactive (-ir) neurons were found in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus. In addition, VP-ir or OXT-ir neurons were scattered in the preoptic area, anterior hypothalamic areas, dorsomedial hypothalamic nucleus, stria terminalis, bed nucleus of the stria terminalis and medial amygdala. Interestingly, a high density of VP-ir fibers within the ventral lateral septum was observed in males but not in females. Both VP-ir and VIP-ir neurons were found in different subdivisions of the suprachiasmatic nucleus (SCN) with partial overlap. VIP-ir cells and fibers were also scattered in the cerebral cortex, anterior olfactory nucleus, amygdala and dentate gyrus of the hippocampus. These findings provide a comprehensive description of VIP and a detailed mapping of VP and OXT in the hypothalamus and extrahypothalamic regions of tree shrews, which is an anatomical basis for the participation of these neuropeptides in the regulation of circadian behavior and social behavior.