This is a summary of the virtual presentation given at the 2021 meeting of the Society for Research on the Cerebellum and Ataxias, https://www.meetings.be/SRCA2021/ , where the therapeutic potential of the CCK-CCK1R pathway for treating diseases involving Purkinje cell degeneration was presented. Spinocerebellar ataxia type 1 (SCA1) is one of a group of almost 50 genetic diseases characterized by the degeneration of cerebellar Purkinje cells. The SCA1 Pcp2-ATXN1[30Q]D776 mouse model displays ataxia, i.e. Purkinje cell dysfunction, but lacks progressive Purkinje cell degeneration. RNA-seq revealed increased expression of cholecystokinin (CCK) in cerebella of Pcp2-ATXN1[30Q]D776 mice. Importantly, the absence of Cck1 receptor (CCK1R) in Pcp2-ATXN1[30Q]D776 mice conferred a progressive degenerative disease with Purkinje cell loss. Administration of a CCK1R agonist to Pcp2-AXTN1[82Q] mice reduced Purkinje cell pathology and associated deficits in motor performance. In addition, administration of the CCK1R agonist improved motor performance of Pcp2-ATXN2[127Q] SCA2 mice. Furthermore, CCK1R activation corrected mTORC1 signaling and improved the expression of calbindin in the cerebella of AXTN1[82Q] and ATXN2[127Q] mice. These results support the Cck-Cck1R pathway is a potential therapeutic target for the treatment of diseases involving Purkinje neuron degeneration.

The intestinal hormone and neuromodulator cholecystokinin (CCK) receptors CCK1R and CCK2R act as a signaling hub in brain-gut axis, mediating digestion, emotion, and memory regulation. CCK receptors exhibit distinct preferences for ligands in different posttranslational modification (PTM) states. CCK1R couples to Gs and Gq, whereas CCK2R primarily couples to Gq. Here we report the cryo-electron microscopy (cryo-EM) structures of CCK1R-Gs signaling complexes liganded either by sulfated cholecystokinin octapeptide (CCK-8) or a CCK1R-selective small-molecule SR146131, and CCK2R-Gq complexes stabilized by either sulfated CCK-8 or a CCK2R-selective ligand gastrin-17. Our structures reveal a location-conserved yet charge-distinct pocket discriminating the effects of ligand PTM states on receptor subtype preference, the unique pocket topology underlying selectivity of SR146131 and gastrin-17, the conformational changes in receptor activation, and key residues contributing to G protein subtype specificity, providing multiple structural templates for drug design targeting the brain-gut axis.

The immune system in vertebrates senses exogenous and endogenous danger signals by way of complex cellular and humoral processes, and responds with an inflammatory reaction to combat putative attacks. A strong protective immunity is imperative to prevent invasion of pathogens; however, equivalent responses to commensal flora and dietary components in the intestine have to be avoided. The autonomic nervous system plays an important role in sensing luminal contents in the gut by way of hard-wired connections and chemical messengers, such as cholecystokinin (CCK). Here, we report that ingestion of dietary fat stimulates CCK receptors, and leads to attenuation of the inflammatory response by way of the efferent vagus nerve and nicotinic receptors. Vagotomy and administration of antagonists for CCK and nicotinic receptors significantly blunted the inhibitory effect of high-fat enteral nutrition on hemorrhagic shock-induced tumor necrosis factor-alpha and interleukin-6 release (P < 0.05). Furthermore, the protective effect of high-fat enteral nutrition on inflammation-induced intestinal permeability was abrogated by vagotomy and administration of antagonists for CCK and nicotinic receptors. These data reveal a novel neuroimmunologic pathway, controlled by nutrition, that may help to explain the intestinal hyporesponsiveness to dietary antigens, and shed new light on the functionality of nutrition.

To test the possible role of cholecystokinin (CCK) in the decrease of social exploration induced by intraperitoneal (IP) injection of lipopolysaccharide (LPS, 100 microg/kg), mice were pretreated with IP or intracerebroventricular (ICV) injection of the CCKA receptor antagonist L-364,718 (3 mg/kg and 10 microg/kg, respectively) and the CCKB receptor antagonist L-365,260 (1 mg/kg and 10 microg/kg, respectively). L-364,718 and L-365,260 did not alter LPS-induced decrease in social investigation, whatever the route of administration, suggesting that endogenous cholecystokinin does not mediate the effect of proinflammatory cytokines on social exploration in mice.

Cholecystokinin (CCK), a peptide hormone and one of the most abundant neuropeptides in vertebrate brain, mediates its actions via two G-protein coupled receptors, CCKAR and CCKBR, respectively active in peripheral organs and the central nervous system. Here, we demonstrate that the CCK receptors have a dynamic and largely reciprocal expression in embryonic and postnatal brain. Using compound homozygous mutant mice lacking the activity of both CCK receptors, we uncover their additive, functionally synergistic effects in brain development and demonstrate that CCK receptor loss leads to abnormalities of cortical development, including defects in the formation of the midline and corpus callosum, and cortical interneuron migration. Using comparative transcriptome analysis of embryonic neocortex, we define the molecular mechanisms underlying these defects. Thus we demonstrate a developmental, hitherto unappreciated, role of the two CCK receptors in mammalian neocortical development.

The peptide hormone cholecystokinin (CCK) exerts a wide range of digestive and CNS-related physiological signaling via CCK receptors in brain and gut. There is very limited information available on these receptors in Atlantic salmon. The aim of this study was to characterize CCK receptors in gut and brain of salmon. We have identified and cloned one CCK-1 receptor and duplicates of CCK-2 receptor in salmon. The phylogenetic analysis indicates the existence of one common ancestor gene for all CCK receptors. CCK-1R mRNA is highly expressed in pancreas followed by midgut, hindgut, gallbladder, and stomach indicating an involvement in pancreatic regulation and gallbladder contractions. CCK-2R1/gastrin mRNA is expressed at high levels in midgut and at relatively low levels in stomach, gallbladder, and pancreas. We postulate CCK-2R1/gastrin receptor to have gastrin-related functions because of its distribution and abundance in gastro-intestinal (GI) tissues. CCK-2R2 is relatively abundant in brain but has low expression levels in gut tissues supporting the hypothesis for involvement in the gut-brain signaling. Major functional motifs and ligand interaction sites in salmon are conserved with that of mammals. This information will be instrumental for comparative studies and further targeting receptor activation and selectivity of biological responses of CCK in salmon.

1. Gastrointestinal neuroendocrine (NE) cells synthesize, store and secrete gamma-aminobutyric acid (GABA). Recently, an autocrine-paracrine function of GABA has been proposed for secretion from NE cells. 2. To search for functional GABAA receptors in NE gut cells, we performed whole-cell and perforated-patch-clamp studies in the intestinal cholecystokinin (CCK)-secreting NE cell line STC-1. 3. Application of GABA evoked currents in STC-1 cells. These effects were mimicked by muscimol, an agonist of GABAA receptors, and blocked by picrotoxin or bicuculline, antagonists of GABAA receptors. The GABA- or muscimol-activated currents reversed near 0 mV, which under the recording conditions used was consistent with the activation of the GABAA receptor-Cl- channel complex. 4. In contrast to the effect on most neurons, GABA as well as muscimol led to a (reversible) depolarization of the membrane potential of STC-1 cells. Membrane depolarization in turn activated voltage-gated Ca2+ channels and increased intracellular Ca2+ concentrations in STC-1 cells. 5. In accordance with the observed membrane depolarization and activation of voltage-gated Ca2+ channels, both GABA and muscimol stimulated Ca2+-dependent CCK release. In contrast, bicuculline inhibited the GABA-induced secretion of CCK. 6. Using the reverse transcription-polymerase chain reaction (RT-PCR), mRNA of the GABAA receptor subunits alpha2, alpha3, alpha5, beta1, beta3 and delta could be detected in STC-1 cells. 7. In summary, we have shown that the CCK-secreting gut NE cell line STC-1 expresses functional GABAA receptors and that GABA stimulates CCK release. Thus, GABA is involved in the fine tuning of CCK secretion from the gut NE cell line STC-1.

Vincristine (VCR) is responsible for the onset of the VCR-induced peripheral neuropathy (VIPN), associated with neuropathic pain. Several reports have strongly linked the cholecystokinin type 2 receptor (CCK2R) to nociceptive modulation. Thus, our aim was to evaluate the effect of CCK2R blockade on the onset of VIPN, as well as its interaction on VCR anticancer efficacy. VCR was administrated in mice for 8 days (100 µg/kg/d, i.p.). Transcriptomic analysis of the dorsal root ganglia (DRG) was performed at day 7 in VCR and control mice. Proglumide (30 mg/kg/d), a CCK1R and CCK2R antagonist, and Ly225910 (1 mg/kg/d), a selective CCK2R antagonist, were administrated one day before and during VCR treatment. Tactile sensitivity was assessed during treatments. Immunofluorescence and morphological analyses were performed on the skin, DRG and sciatic nerve at day 7. The cytotoxicity of VCR in combination with proglumide/Ly225910 was evaluated in human cancer cell lines. Cck2r was highly upregulated in the DRG of VCR mice. Proglumide accelerated the recovery of normal sensitivity, while Ly225910 totally prevented the onset of allodynia and nerve injuries induced by VCR. Proglumide or Ly225910 in combination with VCR did not affect the cytotoxicity of VCR. Targeting CCK2R could therefore be an effective strategy to prevent the onset of VIPN.

Renal dopamine D1-like receptors (D1R and D5R) and the gastrin receptor (CCKBR) are involved in the maintenance of sodium homeostasis. The D1R has been found to interact synergistically with CCKBR in renal proximal tubule (RPT) cells to promote natriuresis and diuresis. D5R, which has a higher affinity for dopamine than D1R, has some constitutive activity. Hence, we sought to investigate the interaction between D5R and CCKBR in the regulation of renal sodium excretion. In present study, we found D5R and CCKBR increase each other's expression in a concentration- and time-dependent manner in the HK-2 cell, the specificity of which was verified in HEK293 cells heterologously expressing both human D5R and CCKBR and in RPT cells from a male normotensive human. The specificity of D5R in the D5R and CCKBR interaction was verified further using a selective D5R antagonist, LE-PM436. Also, D5R and CCKBR colocalize and co-immunoprecipitate in BALB/c mouse RPTs and human RPT cells. CCKBR protein expression in plasma membrane-enriched fractions of renal cortex (PMFs) is greater in D5R-/- mice than D5R+/+ littermates and D5R protein expression in PMFs is also greater in CCKBR-/- mice than CCKBR+/+ littermates. High salt diet, relative to normal salt diet, increased the expression of CCKBR and D5R proteins in PMFs. Disruption of CCKBR in mice caused hypertension and decreased sodium excretion. The natriuresis in salt-loaded BALB/c mice was decreased by YF476, a CCKBR antagonist and Sch23390, a D1R/D5R antagonist. Furthermore, the natriuresis caused by gastrin was blocked by Sch23390 while the natriuresis caused by fenoldopam, a D1R/D5R agonist, was blocked by YF476. Taken together, our findings indicate that CCKBR and D5R synergistically interact in the kidney, which may contribute to the maintenance of normal sodium balance following an increase in sodium intake.

The perisomatic domain of cortical neurons is under the control of two major GABAergic inhibitory interneuron types: regular-spiking cholecystokinin (CCK) basket cells (BCs) and fast-spiking parvalbumin (PV) BCs. CCK and PV BCs are different not only in their intrinsic physiological, anatomical and molecular characteristics, but also in their presynaptic modulation of their synaptic output. Most GABAergic terminals are known to contain GABAB receptors (GABABR), but their role in presynaptic inhibition and surface expression have not been comparatively characterized in the two BC types. To address this, we performed whole-cell recordings from CCK and PV BCs and postsynaptic pyramidal cells (PCs), as well as freeze-fracture replica-based quantitative immunogold electron microscopy of their synapses in the rat hippocampal CA1 area. Our results demonstrate that while both CCK and PV BCs contain functional presynaptic GABABRs, their modulatory effects and relative abundance are markedly different at these two synapses: GABA release is dramatically inhibited by the agonist baclofen at CCK BC synapses, whereas a moderate reduction in inhibitory transmission is observed at PV BC synapses. Furthermore, GABABR activation has divergent effects on synaptic dynamics: paired-pulse depression (PPD) is enhanced at CCK BC synapses, but abolished at PV BC synapses. Consistent with the quantitative differences in presynaptic inhibition, virtually all CCK BC terminals were found to contain GABABRs at high densities, but only 40% of PV BC axon terminals contain GABABRs at detectable levels. These findings add to an increasing list of differences between these two interneuron types, with implications for their network functions.

Neurogenesis in the adult rodent brain is largely restricted to the subependymal zone (SVZ) of the lateral ventricle and subgranular zone (SGZ) of the dentate gyrus (DG). We examined whether cholecystokinin (CCK) through actions mediated by CCK1 receptors (CCK1R) is involved in regulating neurogenesis. Proliferating cells in the SVZ, measured by 5-bromo-2-deoxyuridine (BrdU) injected 2 h prior to death or by immunoreactivity against Ki67, were reduced by 37 and 42%, respectively, in female (but not male) mice lacking CCK1Rs (CCK1R(-/-)) compared to wild-type (WT). Generation of neuroblasts in the SVZ and rostral migratory stream (RMS) was also affected, since the number of doublecortin (DCX)-immunoreactive (ir) neuroblasts in these regions decreased by 29%. In the SGZ of female CCK1R(-/-) mice, BrdU-positive (+), and Ki67-ir cells were reduced by 38 and 56%, respectively, while DCX-ir neuroblasts were down 80%. Subsequently, the effect of reduced SVZ/SGZ proliferation on the generation and survival of mature adult-born cells in female CCK1R(-/-) mice was examined. In the OB granule cell layer (GCL), the number of neuronal nuclei (NeuN)-ir and calretinin-ir cells was stable compared to WT, and 42 days after BrdU injections, the number of BrdU+ cells co-expressing GABA- or NeuN-like immunoreactivity (LI) was similar. Compared to WT, the granule cell layer of the DG in female CCK1R(-/-) mice had a similar number of calbindin-ir cells and BrdU+ cells co-expressing calbindin-LI 42 days after BrdU injections. However, the OB glomerular layer (GL) of CCK1R(-/-) female mice had 11% fewer NeuN-ir cells, 23% less TH-ir cells, and a 38% and 29% reduction in BrdU+ cells that co-expressed TH-LI or GABA-LI, respectively. We conclude that CCK, via CCK1Rs, is involved in regulating the generation of proliferating cells and neuroblasts in the adult female mouse brain, and mechanisms are in place to maintain steady neuronal populations in the OB and DG when the rate of proliferation is altered.

Cholecystokinin (CCK) is a gut hormone originally known for its effects on gallbladder contraction and release of digestive enzymes. CCK, however, also mediates satiety and stimulate insulin secretion. Knowledge of the distribution of CCK-producing enteroendocrine cells (I cells) in humans is sparse. The general notion, based on animal data, is that I cells are present mainly in the proximal small intestine. We examined the occurrence of I cells (immunohistochemically) and the expression of CCK messenger RNA (mRNA) as well as CCK1 and CCK2 receptor mRNA along the intestines in healthy individuals and patients with type 2 diabetes.

The combined use of gastrointestinal hormones for treating metabolic diseases is gaining increasing attention. It was documented previously that co-administration of a cholecystokinin receptor-1 receptor (CCK-1R) agonist with a glucagon-like peptide-1 receptor (GLP-1R) agonist exerted improved effects on metabolic improvements in obese rodents. Here, we reported a series of novel GLP-1R/CCK-1R co-agonists constructed by linking the C-terminus of a GLP-1R agonist (native GLP-1 or Xenopus GLP-1) to the N-terminus of a CCK-1R selective agonist NN9056. The stability of co-agonists was further enhanced by introducing an albumin binding motif. In vitro functional assays revealed that the co-agonists retained full agonism potency on GLP-1R and CCK-1R. Particularly, 2a and 2c showed higher hypoglycemic and insulinotropic activities than NN9056 and semaglutide. The glucose-lowering durations and PK profiles of 2a and 2c were comparable to those of semaglutide. Desirably, in diet induced obesity (DIO) mice, 2a and 2c exhibited superior metabolic benefits to NN9056 and semaglutide in reducing food intake, inducing body weight loss, and regulating lipid metabolism. In short- and long-term studies in diabetic db/db mice, 2a and 2c showed enhanced effects on HbA1c, glucose tolerance, and pancreas function restoration compared with semaglutide. Importantly, no side effects, toxicities, or pancreatic inflammation were caused by 2a and 2c treatments. These preclinical studies suggest that the pharmacological effects of CCK-1 and GLP-1 pathways can be harnessed in a single fusion peptide, yielding a promising combination therapy strategy for treating metabolic disorders.

Cholecystokinin (CCK) gene and its receptors play an important role in several biological processes including satiety signaling. Administration of exogenous or endogenously secreted CCK leads to decreased food intake in both rats and humans. Similarly, in rats pretreated with intraperitoneal CCK, antagonists of the CCKA receptor prevent decrease in food intake. The CCKB receptor plays an important role in anxiety and gastric acid secretion. We investigated the role of polymorphisms in the CCK gene (2 SNPs) and its receptors CCKA (4 SNPs) and CCKB (4SNPs, 1 microsatellite, CTn) in antipsychotic induced weight gain (n=215). Weight change (%) from baseline was compared across genotypic groups using analysis of covariance. In the European ancestry patients treated with clozapine or olanzapine a trend of association was observed with the SNP rs2929183 (p=0.10) in CCKBR gene. Carriers of the genotype AA (3.23%±4.8) gained less weight than the AG and GG genotypes (6.50%±6.5; p=0.035). A similar trend was observed for the CTn repeat, where carriers of the LL genotype gained less weight (3.73%±5.41) than the S allele carrying genotypes (6.29%±6.2, p=0.05). In the subjects of African ancestry we observed similar marginal association although with the opposite allele. However, none of these observations would survive corrections for multiple testing. None of the other polymorphisms in either CCK or CCKA receptor genes was associated with weight change (%). In conclusion, CCKB receptor gene may play a role in antipsychotic induced weight gain. However, these observations need to be replicated in a larger and independent sample set.

The gastrointestinal peptide hormones cholecystokinin and gastrin exert their biological functions via cholecystokinin receptors CCK1R and CCK2R respectively. Gastrin, a central regulator of gastric acid secretion, is involved in growth and differentiation of gastric and colonic mucosa, and there is evidence that it is pro-carcinogenic. Cholecystokinin is implicated in digestion, appetite control and body weight regulation, and may play a role in several digestive disorders.

Defensive rage behavior is mediated over a descending pathway from the medial hypothalamus to the dorsolateral midbrain periaqueductal gray (PAG) where further integration of this response takes place. The present study sought to determine the roles of CCK-A and CCK-B receptor activation in the PAG in modulating defensive rage behavior. The 'hissing' component of the defensive rage response was used throughout the experiment as the measure of defensive rage behavior. The basic design of the experiment involved placement of monopolar electrodes into the medial hypothalamus from which defensive rage could be elicited and cannula electrodes into the dorsal PAG for purposes of identifying defensive rage sites in this region and for microinjections of CCK compounds into these sites at a later time. Microinjections of the selective CCK-B receptor antagonist, LY288513 (1.05, 4.2, 17.0 nmol/0.25 microliter), into the PAG suppressed the hissing response in a dose- and time-dependent manner. Microinjections of the CCK-B agonist, pentagastrin, (0.5 and 1.0 nmol/0.25 microliter) facilitated the occurrence of defensive rage behavior. Moreover, administration of LY288513 (17 nmol/0.25 microliter) 55 min prior to pentagastrin (1.0 nmol/0.25 microliter) delivery blocked the facilitatory effects of pentagastrin. Administration of the CCK-A antagonist, PD140548 (34 nmol/0.25 microliter), into the PAG failed to alter response latencies for defensive rage behavior. In contrast, microinjections of the CCK-B antagonist, LY288513 (4.2, 17.0 nmol/0.25 microliter), facilitated the occurrence of predatory attack behavior elicited from the lateral hypothalamus. This finding demonstrates the specificity of the effects of CCK-B receptor blockade upon hissing. A combination of immunocytochemical and retrograde tracing procedures using microinjections of Fluoro-Gold (8%, 6 microliters) into the PAG were employed to identify the possible loci of CCK neurons that project to the PAG. The data revealed that neurons labeled for both CCK and Fluoro-Gold were located in the dorsolateral aspect of the midbrain tegmentum, identifying this region as a source of CCK inputs to the PAG. Overall, the findings demonstrate that CCK-B receptors in the PAG potentiate defensive rage behavior and likely suppress predatory attack.

Cholecystokinin octapeptide (CCK-8), the most potent endogenous anti-opioid peptide, has been shown to regulate the processes of morphine dependence. In our previous study, we found that exogenous CCK-8 attenuated naloxone induced withdrawal symptoms. To investigate the precise effect of exogenous CCK-8 and the role of cholecystokinin (CCK) 1 and/or 2 receptors in morphine dependence, a SH-SY5Y cell model was employed, in which the μ-opioid receptor, CCK1/2 receptors, and endogenous CCK are co-expressed.

Cholecystokinin (CCK) is a peptide hormone that induces bile release into the intestinal lumen which in turn aids in fat digestion and absorption in the intestine. While excretion of bile acids and cholesterol into the feces eliminates cholesterol from the body, this report examined the effect of CCK on increasing plasma cholesterol and triglycerides in mice. Our data demonstrated that intravenous injection of [Thr28, Nle31]-CCK at a dose of 50 ng/kg significantly increased plasma triglyceride and cholesterol levels by 22 and 31%, respectively, in fasting low-density lipoprotein receptor knockout (LDLR(-/-)) mice. The same dose of [Thr28, Nle31]-CCK induced 6 and 13% increases in plasma triglyceride and cholesterol, respectively, in wild-type mice. However, these particular before and after CCK treatment values did not achieve statistical significance. Oral feeding of olive oil further elevated plasma triglycerides, but did not alter plasma cholesterol levels in CCK-treated mice. The increased plasma cholesterol in CCK-treated mice was distributed in very-low, low and high density lipoproteins (VLDL, LDL and HDL) with less of an increase in HDL. Correspondingly, the plasma apolipoprotein (apo) B48, B100, apoE and apoAI levels were significantly higher in the CCK-treated mice than in untreated control mice. Ligation of the bile duct, blocking CCK receptors with proglumide or inhibition of Niemann-Pick C1 Like 1 transporter with ezetimibe reduced the hypercholesterolemic effect of [Thr28, Nle31]-CCK in LDLR(-/-) mice. These findings suggest that CCK-increased plasma cholesterol and triglycerides as a result of the reabsorption of biliary lipids from the intestine.

Aims: The behavior of pacemaker cardiomyocytes (PCs) in the sinoatrial node (SAN) is modulated by neurohormonal and paracrine factors, many of which signal through G-protein coupled receptors (GPCRs). The aims of the present study are to catalog GPCRs that are differentially expressed in the mammalian SAN and to define the acute physiological consequences of activating the cholecystokinin-A signaling system in isolated PCs. Methods and results: Using bulk and single cell RNA sequencing datasets, we identify a set of GPCRs that are differentially expressed between SAN and right atrial tissue, including several whose roles in PCs and in the SAN have not been thoroughly characterized. Focusing on one such GPCR, Cholecystokinin-A receptor (CCKAR), we demonstrate expression of Cckar mRNA specifically in mouse PCs, and further demonstrate that subsets of SAN fibroblasts and neurons within the cardiac intrinsic nervous system express cholecystokinin, the ligand for CCKAR. Using mouse models, we find that while baseline SAN function is not dramatically affected by loss of CCKAR, the firing rate of individual PCs is slowed by exposure to sulfated cholecystokinin-8 (sCCK-8), the high affinity ligand for CCKAR. The effect of sCCK-8 on firing rate is mediated by reduction in the rate of spontaneous phase 4 depolarization of PCs and is mitigated by activation of beta-adrenergic signaling. Conclusion: (1) PCs express many GPCRs whose specific roles in SAN function have not been characterized, (2) Activation of the cholecystokinin-A signaling pathway regulates PC automaticity.

Altered GABA-mediated inhibition is proposed to play a role in the pathogenesis of epilepsy. Previous studies have demonstrated a loss of somatostatin-containing GABAergic interneurons innervating granule cells in epileptic animals. However, the reorganization of synapses between interneurons and granule cells has not been investigated. We studied synapse organization in an animal model of temporal lobe epilepsy (TLE) using continuous hippocampal stimulation. The distribution of axon terminals and inhibitory synapses on granule cell dendrites was studied using a combination of immunohistochemistry and pre-embedding electron microscopy techniques. A whole-cell patch-clamp technique was applied to study the functional changes in GABAergic input from different interneurons. In epileptic animals, the density of cholecystokinin (CCK)-immunoreactive (IR) fibers and α2 subunit containing GABAA receptors in the inner molecular layer of the dentate gyrus was reduced. Quantitative immuno-electron microscopy study revealed that the ratio of CCK-containing symmetric synapses to the total symmetric synapses was reduced. The frequency of GABAergic synaptic currents (sIPSC) was decreased and their amplitude was increased. The inhibitory effect of the activation of cannabinoid 1 (CB1) receptors was also reduced in epileptic animals. Isolation of CCK- and parvalbumin (PV)-containing GABAergic inputs by N- and P/Q-type calcium channel blockers respectively suggested that GABA release from CCK-containing interneurons was selectively reduced in epileptic rats. This study found that there was a loss of CCK-containing GABAergic synapses to granule cells both morphologically and functionally. These studies add to our understanding of the mechanisms that contribute to altering GABAergic inhibition of granule cells in TLE.