Molecular, Morphological, and Functional Characterization of Corticotropin-Releasing Factor Receptor 1-Expressing Neurons in the Central Nucleus of the Amygdala.

The central nucleus of the amygdala (CeA) is a brain region implicated in anxiety, stress-related disorders and the reinforcing effects of drugs of abuse. Corticotropin-releasing factor (CRF, Crh) acting at cognate type 1 receptors (CRF1, Crhr1) modulates inhibitory and excitatory synaptic transmission in the CeA. Here, we used CRF1:GFP reporter mice to characterize the morphological, neurochemical and electrophysiological properties of CRF1-expressing (CRF1+) and CRF1-non-expressing (CRF1-) neurons in the CeA. We assessed these two neuronal populations for distinctions in the expression of GABAergic subpopulation markers and neuropeptides, dendritic spine density and morphology, and excitatory transmission. We observed that CeA CRF1+ neurons are GABAergic but do not segregate with calbindin (CB), calretinin (CR), parvalbumin (PV), or protein kinase C-δ (PKCδ). Among the neuropeptides analyzed, Penk and Sst had the highest percentage of co-expression with Crhr1 in both the medial and lateral CeA subdivisions. Additionally, CeA CRF1+ neurons had a lower density of dendritic spines, which was offset by a higher proportion of mature spines compared to neighboring CRF1- neurons. Accordingly, there was no difference in basal spontaneous glutamatergic transmission between the two populations. Application of CRF increased overall vesicular glutamate release onto both CRF1+ and CRF1- neurons and does not affect amplitude or kinetics of EPSCs in either population. These novel data highlight important differences in the neurochemical make-up and morphology of CRF1+ compared to CRF1- neurons, which may have important implications for the transduction of CRF signaling in the CeA.

The role of serotonin(2) receptors in mediating cocaine-induced convulsions.

Previous research in our laboratory suggests that serotonin (5-HT) neurotransmission mediates the expression of cocaine-induced convulsions. The role of 5-HT in mediating this toxic effect of cocaine appears to be due to activation of 5-HT(2) receptors, because cocaine-induced convulsions are blocked by the 5-HT(2) antagonists cinanserin, ketanserin, and pirenperone. The present study utilized a number of compounds that display a high affinity for 5-HT(2) receptors to further examine the role of these sites in mediating this toxic effect of cocaine. Cocaine-induced convulsions were observed following pretreatment with various doses of the following 5-HT(2) antagonists: mianserin, metergoline, MDL 11939, and methiothepin. In addition, 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine (NAN 190) was tested to examine the influence of 5-HT(1) sites and the agonist compound 1-(3-triflurormethylphenyl)piperazine (TFMPP) was examined to further explore the role of 5-HT(1) and 5-HT(2) sites. Each 5-HT(2) antagonist attenuated cocaine-induced convulsions. Conversely, NAN 190 did not alter this toxic effect of cocaine. In addition, TFMPP significantly potentiated cocaine-induced convulsions. The results from this study support the hypothesis that 5-HT neurotransmission, acting primarily at 5-HT(2) receptors, plays an important role in mediating cocaine-induced convulsions.

Serotonin(2C) receptors appear to mediate genetic sensitivity to cocaine-induced convulsions.

RATIONALE: C57BL/6ByJ (6ByJ) and C57BL/6J (6J) mice differ in their sensitivity to cocaine-induced convulsions, with CD(50) values being 100 and 70 mg/kg, respectively. This genetic sensitivity to cocaine-induced convulsions is probably related to 5-HT(2) receptors, since the density of these sites and the concentration of 5-HT(2) antagonists required to block cocaine-induced convulsions is lower in 6J mice relative to 6ByJ mice. OBJECTIVE: Although 5-HT(2) receptors appear to play a role in mediating genetic sensitivity to cocaine-induced convulsions, the role of 5-HT(2) receptor subtypes in this effect of cocaine has not been examined. METHODS: The present study compared the effects of the preferential 5-HT(2C) agonists m-chlorophenylpiperazine (mCPP) and 6-chloro-2-(1-piperazinyl)pyrazine (MK212) on cocaine-induced convulsions in 6ByJ and 6J mice. General activity was also measured following pretreatment with mCPP and MK212. RESULTS: Both mCPP and MK212 potentiated cocaine-induced convulsions and the effect of these agonists was more robust in 6ByJ mice relative to 6J mice. CONCLUSION: The findings from this study support previous research suggesting that 5-HT(2) receptors play a role in mediating cocaine-induced convulsions, and extend previous research by suggesting that the 5-HT(2C) receptor subtype mediates cocaine-induced convulsions and genetic sensitivity to this toxic effect of cocaine.

Coloboma hyperactive mutant mice exhibit regional and transmitter-specific deficits in neurotransmission.

The mouse mutant coloboma (Cm/+), which exhibits profound spontaneous hyperactivity and bears a deletion mutation on chromosome 2, including the gene encoding synaptosomal protein SNAP-25, has been proposed to model aspects of attention-deficit hyperactivity disorder. Increasing evidence suggests a crucial role for SNAP-25 in the release of both classical neurotransmitters and neuropeptides. In the present study, we compared the release of specific neurotransmitters in vitro from synaptosomes and slices of selected brain regions from Cm/+ mice with that of +/+ mice. The release of dopamine (DA) and serotonin (5-HT) from striatum, and of arginine vasopressin and corticotropin-releasing factor from hypothalamus and amygdala is calcium-dependent. Glutamate release from and content in cortical synaptosomes of Cm/+ mice are greatly reduced, which might contribute to the learning deficits in these mutants. In dorsal striatum of Cm/+ mutants, but not ventral striatum, KCl-induced release of DA is completely blocked and that of 5-HT is significantly attenuated, suggesting that striatal DA and 5-HT deficiencies may be involved in hyperactivity. Further, although acetylcholine failed to induce hypothalamic corticotropin-releasing factor release from Cm/+ slices, restraint stress increased plasma corticosterone levels in Cm/+ mice to a significantly higher level than in +/+ mice, suggesting an important role for arginine vasopressin in hypothalamic-pituitary-adrenal axis activation. These results suggest that reduced SNAP-25 expression may contribute to a region-specific and neurotransmitter-specific deficiency in neurotransmitter release.

Modulation of locomotor activity by NMDA receptors in the nucleus accumbens core and shell regions of the rat.

Two subdivisions of the nucleus accumbens (NAC), the core and the shell, have been recently identified on the basis of immunohistochemical differences and neural connections. A major neural input to the NAC is provided by glutamatergic afferents of allocortical origin and there is evidence that glutamate can modulate psychomotor activation and drug reinforcement. This study was undertaken to explore whether selective pharmacological blockade of NMDA neurotransmission within the core and the shell region affected differentially spontaneous and cocaine-induced locomotor activity. We report that intra-NAC microinfusion of aminophosphonovaleric acid (AP-5) (0.75-3.0 micrograms/side, 1.5-6.0 micrograms total dose) within the core but not the shell region reduced cocaine-induced locomotion in a dose-dependent manner. In contrast, microinfusion of the same doses of AP-5 within the shell region caused a dose-dependent increase of spontaneous locomotion, while microinfusion within the core region was ineffective. These results indicate that blockade of NMDA receptors in the core and the shell of the NAC elicited different effects on spontaneous and cocaine-induced locomotion. This suggests that these substructures may subserve different functions within the integrated output of the NAC, functions that may vary according to the state of arousal.