Crustaceans and insects share many similarities of brain organization suggesting that their common ancestor possessed some components of those shared features. Stomatopods (mantis shrimps) are basal eumalacostracan crustaceans famous for their elaborate visual system, the most complex of which possesses 12 types of color photoreceptors and the ability to detect both linearly and circularly polarized light. Here, using a palette of histological methods we describe neurons and their neuropils most immediately associated with the stomatopod retina. We first provide a general overview of the major neuropil structures in the eyestalks lateral protocerebrum, with respect to the optical pathways originating from the six rows of specialized ommatidia in the stomatopod's eye, termed the midband. We then focus on the structure and neuronal types of the lamina, the first optic neuropil in the stomatopod visual system. Using Golgi impregnations to resolve single neurons we identify cells in different parts of the lamina corresponding to the three different regions of the stomatopod eye (midband and the upper and lower eye halves). While the optic cartridges relating to the spectral and polarization sensitive midband ommatidia show some specializations not found in the lamina serving the upper and lower eye halves, the general morphology of the midband lamina reflects cell types elsewhere in the lamina and cell types described for other species of Eumalacostraca.

Retrograde tract tracing studies have indicated that dorsal root ganglion cells from T8 to L2 innervate the rat's left kidney. Electrophysiology studies have indicated that putative second-order sympathetic afferents are found in the dorsal horn at spinal segments T10 to L1 in laminae V-VII. Here, the spread of pseudorabies virus through renal sensory pathways was examined following 2-5 days post-infection (PI) and the virus was located immunocytochemically using a rabbit polyclonal antibody. Two days PI, dorsal root ganglion neurons (first-order sympathetic afferents) were infected with PRV. An average of 1.2, 0.8, 2.1 and 4.4% of the infected dorsal root ganglion neurons were contralateral to the injected kidney at spinal segments T10, T11, T12 and T13, respectively. Four days PI, infected neurons were detected within laminae I and II of the dorsal horn of the caudal thoracic and upper lumbar spinal cord segments. The labeling patterns in the spinal cord are consistent with previous work indicating the location of renal sympathetic sensory pathways. The nodose ganglia were labeled starting 4 days PI, suggesting the involvement of parasympathetic sensory pathways. Five days PI, infected neurons were found in the nucleus tractus solitarius. In the present study, it was unclear whether the infected neurons in the nucleus tractus solitarius are part of sympathetic or parasympathetic afferent pathways or represent a convergence of sensory information. Renal denervation prevented the spread of the virus into the dorsal root ganglia and spinal cord. Sectioning the dorsal roots from T10-L3 blocked viral spread into the spinal cord dorsal horn, but did not prevent infection of neurons in dorsal root ganglion nor did it prevent infection of putative preganglionic neurons in the intermediolateral cell column. The present results indicated that renal afferent pathways can be identified after pseudorabies virus infection of the kidney. Our results suggest that renal afferents travel in sympathetic and parasympathetic nerves and that this information may converge at the NTS.

A predominant complaint in patients with neuropathic pain is spontaneous pain, often described as burning. Recent studies have demonstrated that negative reinforcement can be used to unmask spontaneous neuropathic pain, allowing for mechanistic investigations. Here, ascending pathways that might contribute to evoked and spontaneous components of an experimental neuropathic pain model were explored. Desensitization of TRPV1-positive fibers with systemic resiniferatoxin (RTX) abolished spinal nerve ligation (SNL) injury-induced thermal hypersensitivity and spontaneous pain, but had no effect on tactile hypersensitivity. Ablation of spinal NK-1 receptor-expressing neurons blocked SNL-induced thermal and tactile hypersensitivity as well as spontaneous pain. After nerve injury, upregulation of neuropeptide Y (NPY) is observed almost exclusively in large-diameter fibers, and inactivation of the brainstem target of these fibers in the nucleus gracilis prevents tactile but not thermal hypersensitivity. Blockade of NPY signaling within the nucleus gracilis failed to block SNL-induced spontaneous pain or thermal hyperalgesia while fully reversing tactile hypersensitivity. Moreover, microinjection of NPY into nucleus gracilis produced robust tactile hypersensitivity, but failed to induce conditioned place aversion. These data suggest that spontaneous neuropathic pain and thermal hyperalgesia are mediated by TRPV1-positive fibers and spinal NK-1-positive ascending projections. In contrast, the large-diameter dorsal column projection can mediate nerve injury-induced tactile hypersensitivity, but does not contribute to spontaneous pain. Because inhibition of tactile hypersensitivity can be achieved either by spinal manipulations or by inactivation of signaling within the nucleus gracilis, the enhanced paw withdrawal response evoked by tactile stimulation does not necessarily reflect allodynia.

Modulation of salt appetite involves interactions between the circumventricular organs (CVOs) receptive areas and inhibitory hindbrain serotonergic circuits. Recent studies provide support to the idea that the serotonin action in the lateral parabrachial nucleus (LPBN) plays an important inhibitory role in the modulation of sodium appetite. The aim of the present work was to identify the specific groups of neurons projecting to the LPBN that are activated in the course of sodium appetite regulation, and to analyze the associated endocrine response, specifically oxytocin (OT) and atrial natriuretic peptide (ANP) plasma release, since both hormones have been implicated in the regulatory response to fluid reestablishment. For this purpose we combined the detection of a retrograde transported dye, Fluorogold (FG) injected into the LPBN with the analysis of the Fos immunocytochemistry brain pattern after sodium intake induced by sodium depletion. We analyzed the Fos-FG immunoreactivity after sodium ingestion induced by peritoneal dialysis (PD). We also determined OT and ANP plasma concentration by radioimmunoassay (RIE) before and after sodium intake stimulated by PD. The present study identifies specific groups of neurons along the paraventricular nucleus, central extended amygdala, insular cortex, dorsal raphe nucleus, nucleus of the solitary tract and the CVOs that are activated during the modulation of sodium appetite and have direct connections with the LPBN. It also shows that OT and ANP are released during the course of sodium satiety and fluid reestablishment. The result of this brain network activity may enable appropriate responses that re-establish the body fluid balance after induced sodium consumption.

The prevalence of lower urinary tract storage disorders such as overactive bladder syndrome and urinary incontinence significantly increase with age. Previous studies have demonstrated age-related changes in detrusor function and urothelial transmitter release but few studies have investigated how the urothelium and sensory pathways are affected. The aim of this study was to investigate the effect of ageing on urothelial-afferent signalling in the mouse bladder. Three-month-old control and 24-month-old aged male mice were used. In vivo natural voiding behaviour, sensory nerve activity, urothelial cell function, muscle contractility, transmitter release and gene and protein expression were measured to identify how all three components of the bladder (neural, contractile and urothelial) are affected by ageing. In aged mice, increased voiding frequency and enhanced low threshold afferent nerve activity was observed, suggesting that ageing induces overactivity and hypersensitivity of the bladder. These changes were concurrent with altered ATP and acetylcholine bioavailability, measured as transmitter overflow into the lumen, increased purinergic receptor sensitivity and raised P2X3 receptor expression in the urothelium. Taken together, these data suggest that ageing results in aberrant urothelial function, increased afferent mechanosensitivity, increased smooth muscle contractility, and changes in gene and protein expression (including of P2X3). These data are consistent with the hypothesis that ageing evokes changes in purinergic signalling from the bladder, and further studies are now required to fully validate this idea.

Afferent and efferent neural elements of the retina and central ganglia in the freshwater snail Planorbarius corneus were labelled using retrograde transport of neurobiotin through the optic nerve. Axons of at least some photoreceptor cells become direct contributors to the optic nerve as no synaptic junctions could be detected. The processes enter the cerebral ganglion and form a dense bundle of thin afferent fibres, the so-called optical neuropil. Efferent neurons were revealed in all ganglia, except the buccal ones. Some of the ascending axons branch in the cerebral ganglia, cross the cerebro-cerebral commissure, reach the contralateral eye and form arborizations in the eye cup. Some efferent neurons send axons to different peripheral nerves as well: n.n. intestinalis, pallialis dexter, pallialis sinister internus et externus. Serotonin- and FMRF-amide-ergic fibres were revealed in the optic nerve. These fibres belong to those central neurons which send their axons to the ipsilateral eye only. They form abundant varicoses in the eye cup and nuclear layer of the retina, and possibly help to regulate retinal sensitivity to light.

The nucleus of the solitary tract (NTS) receives viscerosensory information from the vagus nerve to regulate diverse homeostatic reflex functions. The NTS projects to a wide network of other brain regions, including the paraventricular nucleus of the hypothalamus (PVN). Here we examined the synaptic characteristics of primary afferent pathways to PVN-projecting NTS neurons in rat brainstem slices.Expression of the Transient Receptor Potential Vanilloid receptor (TRPV1+ ) distinguishes C-fiber afferents within the solitary tract (ST) from A-fibers (TRPV1-). We used resiniferatoxin (RTX), a TRPV1 agonist, to differentiate the two. The variability in the latency (jitter) of evoked excitatory postsynaptic currents (ST-EPSCs) distinguished monosynaptic from polysynaptic ST-EPSCs. Rhodamine injected into PVN was retrogradely transported to identify PVN-projecting NTS neurons within brainstem slices. Graded shocks to the ST elicited all-or-none EPSCs in rhodamine-positive NTS neurons with latencies that had either low jitter (<200 µs - monosynaptic), high jitter (>200 µs - polysynaptic inputs) or both. RTX blocked ST-evoked TRPV1 + EPSCs whether mono- or polysynaptic. Most PVN-projecting NTS neurons (17/21 neurons) had at least one input polysynaptically connected to the ST. Compared to unlabeled NTS neurons, PVN-projecting NTS neurons were more likely to receive indirect inputs and be higher order. Surprisingly, sEPSC rates for PVN-projecting neurons were double that of unlabeled NTS neurons. The ST synaptic responses for PVN-projecting NTS neurons were either all TRPV1+ or all TRPV1-, including neurons that received both direct and indirect inputs. Overall, PVN-projecting NTS neurons received direct and indirect vagal afferent information with strict segregation regarding TRPV1 expression.

Previous study has shown that colitis-induced increases in calcitonin gene-related peptide (CGRP) immunoreactivity in bladder afferent neurons result in sensory cross-sensitization. To further determine the effects of colitis on CGRP expression in neurons other than bladder afferents, we examined and compared the levels of CGRP mRNA and immunoreactivity in the lumbosacral dorsal root ganglia (DRG) and spinal cord before and during colitis in rats. We also examined the changes in CGRP immunoreactivity in colonic afferent neurons during colitis. Results showed increases in CGRP mRNA levels in L1 (2.5-fold, p<0.05) and S1 DRG (1.9-2.4-fold, p<0.05). However, there were no changes in CGRP mRNA levels in L1 and S1 spinal cord during colitis. CGRP protein was significantly increased in L1 (2.5-fold increase, p<0.05) but decreased in S1 (50% decrease, p<0.05) colonic afferent neurons, which may reflect CGRP release from these neurons during colitis. In L1 spinal cord, colitis caused increases in the number of CGRP nerve fibers in the deep lamina region extending to the gray commissure where the number of phospho-Akt neurons was also increased. In S1 spinal cord, colitis caused the increases in the intensity of CGRP fibers in the regions of dorso-lateral tract, and caused the increases in the level of phospho-Akt in the superficial dorsal horn of the spinal cord. In spinal cord slice culture, exogenous CGRP increased the phosphorylation level of Akt but not the phosphorylation level of extracellular-signal regulated kinase ERK1/2 even though our previous studies showed that colitis increased the phosphorylation level of ERK1/2 in L1 and S1 spinal cord. These results suggest that CGRP is synthesized in the DRG and may transport to the spinal cord where it initiates signal transduction during colitis.

The limited success of translating basic animal findings into effective clinical treatments of pain can be partly ascribed to the use of sub-optimal models. Murine models of pain often consist in recording (1) threshold responses (like the tail-flick reflex) elicited by (2) non-nociceptive specific inputs in (3) anaesthetized animals. The direct cortical recording of laser-evoked potentials (LEPs) elicited by stimuli of graded energies in freely-moving rodents avoids these three important pitfalls, and has thus the potential of improving such translation. Murine LEPs are classically reported to consist of two distinct components, reflecting the activity of Aδ- and C-fibre afferent pathways. However, we have recently demonstrated that the so-called "Aδ-LEPs" in fact reflect the activation of the auditory system by laser-generated ultrasounds. Here we used ongoing white noise to avoid the confound represented by the early auditory response, and thereby comprehensively characterized the physiological properties of C-fibre LEPs recorded directly from the exposed surface of the rat brain. Stimulus-response functions indicated that response amplitude is positively related to the stimulus energy, as well as to nocifensive behavioral score. When displayed using average reference, murine LEPs consist of three distinct deflections, whose polarity, order, and topography are surprisingly similar to human LEPs. The scalp topography of the early N1 wave is somatotopically-organized, likely reflecting the activity of the primary somatosensory cortex, while topographies of the later N2 and P2 waves are more centrally distributed. These results indicate that recording LEPs in freely-moving rats is a valid model to improve the translation of animal results to human physiology and pathophysiology.

Immunocytochemical technique was used to compare the content of substance P (SP), Met-enkephalin (Met-Enk) and neurotensin (NT) on two sides of the lumbar dorsal horn of rats in which the unilateral dorsolateral funiculus was transected while formalin (0.2 ml, 5%) was injected equally into two hindpaws. The results showed that the SP-like immunoreactivity (SP-LI) and Met-Enk-LI were significantly higher and the NT-LI was significantly lower in the superficial laminae of dorsal horn on the side ipsilateral to the intact DLF than that on the opposite side, implying that peripheral noxious inputs can activate the supraspinal descending inhibitory systems which in turn modulate the transmission of noxious message at the spinal level by changing the activities of related peptidergic neurons.

Prior experiments have shown that a region of the medial and inferior vestibular nuclei contributes to cardiovascular and respiratory regulation. In addition to labyrinthine inputs, the majority of neurons in this region of the vestibular nuclei receive signals from the skin, muscle, and viscera, although the pathways conveying these nonlabyrinthine inputs to the vestibular nucleus neurons are unknown. To gain further insight into the afferent pathways to this functionally distinct subdivision of the vestibular complex, we combined monosynaptic mapping with viral transneuronal tracing in the ferret. First order afferent projections were defined by retrograde transport of the beta-subunit of cholera toxin (CTbeta), and the extended polysynaptic circuitry was defined in the same animals by injection of a recombinant of pseudorabies virus Bartha (PRV) into the contralateral vestibular nuclei. Neurons containing CTbeta or infected by retrograde transneuronal transport and replication of PRV were distributed throughout the spinal cord, but were 10 times more prevalent in the cervical cord than the lumbar cord. The labeled spinal neurons were most commonly observed in Rexed's laminae IV-VI and the dorsal portions of laminae VII-VIII. Both the CTbeta and PRV injections also resulted in labeling of neurons in all four vestibular nuclei, the prepositus hypoglossi, the reticular formation, the inferior olivary nucleus, the medullary raphe nuclei, the spinal and principal trigeminal nuclei, the facial nucleus, and the lateral reticular nucleus. Following survival times >/=3 days, PRV-infected neurons were additionally present in nucleus solitarius and the gracile and cuneate nuclei. These data show that an anatomical substrate is present for somatosensory and visceral inputs to influence the activity of cells in the autonomic region of the vestibular nuclei and suggest that these signals are primarily transmitted through brainstem relay neurons.

Background: Clinical investigation indicates a high level of co-morbidity between bladder overactivity and irritable bowel syndrome. The cross-sensitization of afferent pathways has been demonstrated to be the main reason for the cross-organ sensitization, but the underlying mechanism is unclear. Methods: A single dose of 2, 4, 6-trinitrobenzene sulfonic acid (TNBS) was applied to induce the colitis rat models by intracolonic administration. All rats were randomly divided into three groups: control, TNBS-3-day, and TNBS-7-day groups. Western blot and immunofluorescent staining were performed to detect the expression of the P2X3 receptor. The spontaneous contractions of the detrusor strip were measured to evaluate the detrusor contractility function. The micturition function was measured by a cystometry experiment. The intercontractile interval (ICI) and maximum bladder pressure (BP) were recorded. Results: The distal colon from colitis showed serious tissue damage or chronic inflammation after TNBS instillation (p < 0.01). However, there were no detectable histological changes in bladder among groups (p > 0.05). TNBS-induced colitis significantly increased P2X3 receptor expression on the myenteric and submucosal plexus of the distal colon and urothelium of the bladder, especially at day 3 post-TNBS (p < 0.05). Meanwhile, the expression of the P2X3 receptor on DRG neurons was increased in TNBS-induced colitis (p < 0.01). The detrusor strip of rats exhibited detrusor overactivity after days 3 and 7 of TNBS administration (p < 0.01), but inhibition of the P2X3 receptor had no effect (p > 0.05). Moreover, the rats with colitis exhibited the micturition pattern of bladder overactivity, manifested by decreased ICI and increased maximum BP (p < 0.05). Interestingly, inhibition of the P2X3 receptor by intrathecal injection of A-317491 alleviated bladder overactivity evoked by TNBS-induced colitis (p < 0.05). Conclusion: The upregulation of the P2X3 receptor in an afferent pathway involved in bladder overactivity evoked by TNBS-induced colonic inflammation, suggesting that the P2X3 receptor antagonist may be an available and novel strategy for the control of bladder overactivity.

The solitary tract nucleus (NTS) conveys visceral information to diverse central networks involved in homeostatic regulation. Although afferent information content arriving at various CNS sites varies substantially, little is known about the contribution of processing within the NTS to these differences. Using retrograde dyes to identify specific NTS projection neurons, we recently reported that solitary tract (ST) afferents directly contact NTS neurons projecting to caudal ventrolateral medulla (CVLM) but largely only indirectly contact neurons projecting to the hypothalamic paraventricular nucleus (PVN). Since intrinsic properties impact information transmission, here we evaluated potassium channel expression and somatodendritic morphology of projection neurons and their relation to afferent information output directed to PVN or CVLM pathways. In slices, tracer-identified projection neurons were classified as directly or indirectly (polysynaptically) coupled to ST afferents by EPSC latency characteristics (directly coupled, jitter < 200 micros). In each neuron, voltage-dependent potassium currents (IK) were evaluated and, in representative neurons, biocytin-filled structures were quantified. Both CVLM- and PVN-projecting neurons had similar, tetraethylammonium-sensitive IK. However, only PVN-projecting NTS neurons displayed large transient, 4-aminopyridine-sensitive, A-type currents (IKA). PVN-projecting neurons had larger cell bodies with more elaborate dendritic morphology than CVLM-projecting neurons. ST shocks faithfully (> 75%) triggered action potentials in CVLM-projecting neurons but spike output was uniformly low (< 20%) in PVN-projecting neurons. Pre-conditioning hyperpolarization removed IKA inactivation and attenuated ST-evoked spike generation along PVN but not CVLM pathways. Thus, multiple differences in structure, organization, synaptic transmission and ion channel expression tune the overall fidelity of afferent signals that reach these destinations.

Somatosensory information can be modulated at the spinal cord level by primary afferent depolarization (PAD), known to produce presynaptic inhibition (PSI) by decreasing neurotransmitter release through the activation of presynaptic ionotropic receptors. Descending monoaminergic systems also modulate somatosensory processing. We investigated the role of D1-like and D2-like receptors on pathways mediating PAD in the hemisected spinal cord of neonatal mice. We recorded low-threshold evoked dorsal root potentials (DRPs) and population monosynaptic responses as extracellular field potentials (EFPs). We used a paired-pulse conditioning-test protocol to assess homosynaptic and heterosynaptic depression of evoked EFPs to discriminate between dopaminergic effects on afferent synaptic efficacy and/or on pathways mediating PAD, respectively. DA (10 μM) depressed low-threshold evoked DRPs by 43 %, with no effect on EFPs. These depressant effects on DRPs were mimicked by the D2-like receptor agonist quinpirole (35 %). Moreover, by using selective antagonists at D2-like receptors (encompassing the D2, D3, and D4 subtypes), we found that the D2 and D3 receptor subtypes participate in the quinpirole depressant inhibitory effects of pathways mediating PAD.

Neuromuscular electrical stimulation (NMES) increases the excitability of corticospinal (CS) pathways by altering circuits in motor cortex (M1). How NMES affects circuits interposed between the ascending afferent volley and descending CS pathways is not known. Presently, we hypothesized that short-latency afferent inhibition (SAI) would be reduced and afferent facilitation (AF) enhanced when NMES increased CS excitability. NMES was delivered for 40 min over the ulnar nerve. To assess CS excitability, motor evoked potentials (MEPs) were evoked using transcranial magnetic stimulation (TMS) delivered at 120% resting threshold for first dorsal interosseus muscle. These MEPs increased by ∼1.7-fold following NMES, demonstrating enhanced CS excitability. SAI and AF were tested by delivering a "conditioning" electrical stimulus to the ulnar nerve 18-25 ms and 28-35 ms before a "test" TMS pulse, respectively. Conditioned MEPs were compared to unconditioned MEPs evoked in the same trials. TMS was adjusted so unconditioned MEPs were not different before and after NMES. At the SAI interval, conditioned MEPs were 25% smaller than unconditioned MEPs before NMES but conditioned and unconditioned MEPs were not different following NMES. At the AF interval, conditioned MEPs were not different from unconditioned MEPs before NMES, but were facilitated by 33% following NMES. Thus, when NMES increases CS excitability there are concurrent changes in the effect of afferent input on M1 excitability, resulting in a net increase in the excitatory effect of the ascending afferent volley on CS circuits. Maximising this excitatory effect on M1 circuits may help strengthen CS pathways and improve functional outcomes of NMES-based rehabilitation programs.

Tamsulosin, an α1-adrenoceptor antagonist, and sildenafil, a phosphodiesterase (PDE) inhibitor, are reported to improve lower urinary tract symptoms including overactive bladder (OAB). This study is aimed at investing the effects of tamsulosin and sildenafil and comparing the degree of the suppressive effects on the afferent pathways of micturition between them using an animal model of OAB, the spontaneously hypertensive rat (SHR).

Bladder pain of unknown etiology has been associated with co-morbid conditions and functional abnormalities in neighboring pelvic organs. Mechanisms underlying pain co-morbidities include cross-sensitization, which occurs predominantly via convergent neural pathways connecting distinct pelvic organs. Our previous results showed that colonic inflammation caused detrusor instability via activation of transient receptor potential vanilloid 1 (TRPV1) signaling pathways, therefore, we aimed to determine whether neurogenic bladder dysfunction can develop in the absence of TRPV1 receptors.

Recent studies have demonstrated the importance of local protein synthesis for neuronal plasticity. In particular, local mRNA translation through the mammalian target of rapamycin (mTOR) has been shown to play a key role in regulating dendrite excitability and modulating long-term synaptic plasticity associated with learning and memory. There is also increased evidence to suggest that intact adult mammalian axons have a functional requirement for local protein synthesis in vivo. Here we show that the translational machinery is present in some myelinated sensory fibers and that active mTOR-dependent pathways participate in maintaining the sensitivity of a subpopulation of fast-conducting nociceptors in vivo. Phosphorylated mTOR together with other downstream components of the translational machinery were localized to a subset of myelinated sensory fibers in rat cutaneous tissue. We then showed with electromyographic studies that the mTOR inhibitor rapamycin reduced the sensitivity of a population of myelinated nociceptors known to be important for the increased mechanical sensitivity that follows injury. Behavioural studies confirmed that local treatment with rapamycin significantly attenuated persistent pain that follows tissue injury, but not acute pain. Specifically, we found that rapamycin blunted the heightened response to mechanical stimulation that develops around a site of injury and reduced the long-term mechanical hypersensitivity that follows partial peripheral nerve damage--a widely used model of chronic pain. Our results show that the sensitivity of a subset of sensory fibers is maintained by ongoing mTOR-mediated local protein synthesis and uncover a novel target for the control of long-term pain states.

Precise alignment of pre- and postsynaptic elements optimizes the activation of glutamate receptors at excitatory synapses. Nonetheless, glutamate that diffuses out of the synaptic cleft can have actions at distant receptors, a mode of transmission called spillover. To uncover the extrasynaptic actions of glutamate, we localized AMPA receptors (AMPARs) mediating spillover transmission between climbing fibers and molecular layer interneurons in the cerebellar cortex. We found that climbing fiber spillover generates calcium transients mediated by Ca2+-permeable AMPARs at parallel fiber synapses. Spillover occludes parallel fiber synaptic currents, indicating that separate, independently regulated afferent pathways converge onto a common pool of AMPARs. Together these findings demonstrate a circuit motif wherein glutamate 'spill-in' from an unconnected afferent pathway co-opts synaptic receptors, allowing activation of postsynaptic AMPARs even when canonical glutamate release is suppressed.

The maintenance of the intestinal epithelium is of great importance for the survival of the organism. A possible nervous control of epithelial cell renewal was studied in rats and mice.