Number Of GABA Research Articles

The role of glutamate and GABA receptors in the anticonvulsive effects of levetiracetam and a 4-phenylpirrolidone derivative (GIZh-290) in rats

The method of radioligand binding ex vivo has been used to evaluate the involvement of the ionotropic and metabotropic glutamate and GABA receptors in the mechanism of anticonvulsant action of levetiracetam and the original compound GIZh-290 (2-oxo-4-phenylpyrrolidin-1-yl) acetic acid) in the rat brain. We found that at the peak of lithium-pilocarpine seizures, the Bmax value (the density of specific binding sites) decreases for [3H]-SR 95531, [3H](–)baclofen, [3Н](+)MK-801, and [3H]LY 354740 by 30–50% from the control level. The pre-treatment with levetiracetam (600 mg/kg) 40 minutes before pilocarpine kept the number of GABA- and NMDA-type receptors at the control level without affecting the metabotropic receptors. The administration of GIZh-290 (5.0 mg/kg), in contrast, maintained the density of GABAA receptors at the control level, while the density of other types of receptors remained decreased at the peak of seizures. Thus, the anticonvulsant effect of levetiracetam and GIZh-290 has different mechanisms.

Prenatal betamethasone does not affect glutamatergic or GABAergic neurogenesis in preterm newborns

Prenatal glucocorticoids (GCs) are routinely used for pregnant women in preterm labor to prevent respiratory distress syndrome and intraventricular hemorrhage in premature infants. However, the effect of antenatal GCs on neurogenesis in preterm neonates remains elusive. Herein, we hypothesized that prenatal GCs might suppress both glutamatergic and GABAergic neurogenesis in preterm rabbits and that this treatment would induce distinct changes in the expression of transcription factors regulating these developmental events. To test our hypotheses, we treated pregnant rabbits with betamethasone at E27 and E28, delivered the pups at E29 (term=32d), and assessed neurogenesis at birth and postnatal day 3. We quantified radial glia (Sox2+) and intermediate progenitor cells (Tbr2+) in the dorsal cortical subventricular zone to assess glutamatergic neuronal progenitors, and counted Nkx2.1+ and Dlx2+ cells in the ganglionic eminence to evaluate GABAergic neurogenesis. In addition, we assayed transcription factors regulating neurogenesis. We found that prenatal GCs did not affect the densities of radial glia and intermediate progenitors of glutamatergic or GABAergic neurons. The number of GABA+ interneurons in the ganglionic eminence was similar between the prenatal GC-treated pups compared to untreated controls. Moreover, the mRNA expression of transcription factors, including Pax6, Ngn1/2, Emx1/2, Insm1, Dlx1, Nkx2.1, and Gsh2, were comparable between the two groups. However, there was a transient elevation in Mash1 protein in betamethasone-treated pups relative to controls at birth. These data suggest that prenatal GC treatment does not significantly impact the balance of glutamatergic and GABAergic neurogenesis in premature infants.

Reduced GABA A receptors and benzodiazepine binding sites in the posterior cingulate cortex and fusiform gyrus in autism

Individuals with autism display deficits in the social domain including the proper recognition of faces and interpretations of facial expressions. There is an extensive network of brain regions involved in face processing including the fusiform gyrus (FFG) and posterior cingulate cortex (PCC). Functional imaging studies have found that controls have increased activity in the PCC and FFG during face recognition tasks, and the FFG has differential responsiveness in autism when viewing faces. Multiple lines of evidence have suggested that the GABAergic system is disrupted in the brains of individuals with autism and it is likely that altered inhibition within the network influences the ability to perceive emotional expressions. On-the-slide ligand binding autoradiography was used to determine if there were alterations in GABA A and/or benzodiazepine binding sites in the brain in autism. Using 3H-muscimol and 3H-flunitrazepam we could determine whether the number (B max), binding affinity (K d), and/or distribution of GABA A receptors and benzodiazepine binding sites (BZD) differed from controls in the FFG and PCC. Significant reductions were found in the number of GABA A receptors and BZD binding sites in the superficial layers of the PCC and FFG, and in the number of BZD binding sites in the deep layers of the FFG. In addition, the autism group had a higher binding affinity in the superficial layers of the GABA A study. Taken together, these findings suggest that the disruption in inhibitory control in the cortex may contribute to the core disturbances of socio-emotional behaviors in autism.

Cocaine causes deficits in radial migration and alters the distribution of glutamate and GABA neurons in the developing rat cerebral cortex.

Prenatal cocaine exposure induces cytoarchitectural changes in the embryonic neocortex; however, the biological mechanisms and type of cortical neurons involved in these changes are not known. Previously, we found that neural progenitor proliferation in the neocortical ventricular zone (VZ) is inhibited by cocaine; here, we examine the changes in cortical neurogenesis and migration of glutamate and GABA neurons induced by prenatal cocaine exposure. Pregnant rats received 20 mg/kg of cocaine intraperitoneally twice at an interval of 12 h during three periods of neocortical neurogenesis. Neocortical area and distribution of developing neurons were examined by counting Tuj1+, glutamate+, or GABA+ cells in different areas of the cerebral cortex. Cocaine decreased neocortical area by reducing the size of the Tuj1+ layer, but only when administered during early periods of neocortical neurogenesis. The number of glutamatergic neurons was increased in the VZ but was decreased in the outer cortical laminae. Although the number of GABA+ neurons in the VZ of both the neocortex and ganglionic eminences was unchanged, GABA+ cells decreased in all other neocortical laminae. Tangential migration of GABA+ cells was also disrupted by cocaine. These findings suggest that in utero cocaine exposure disturbs radial migration of neocortical neurons, possibly because of decreased radial glia guiding support through enhanced differentiation of neocortical VZ progenitors. Cocaine interrupts radial migration of both glutamatergic and GABAergic neurons within the neocortex, in addition to the tangential migration of GABAergic neurons from the subcortical telecephalon. This may result in abnormal neocortical cytoarchitecture and concomitant adverse functional effects.

Modulation of GABA release by nitric oxide in the chick retina: Different effects of nitric oxide depending on the cell population

γ-Aminobutyric acid (GABA) is considered to be the most important inhibitory neurotransmitter in the central nervous system, including the retina. It has been shown that nitric oxide (NO) can influence the physiology of all retinal neuronal types, by mechanisms including modulation of GABA release. However, until now, there have been no data concerning the effects on endogenous GABA release of NO produced by cells in the intact retina. In the present study, we have investigated how NO production induced by drugs influences the release of endogenous GABA in cells of the intact retina of mature chicken. Retinas were exposed to different drugs that affect NO production, and GABA remaining in the tissue was detected by immunohistochemical procedures. A specific nNOS inhibitor (7-NI) reduced the number of GABA + amacrine cells and cells in the ganglion cell layer (GCL) by 33% and 41%, respectively. A GABA transporter inhibitor blocked this effect. L-arginine (100 μM), the precursor of NO, induced increases of 62% and 34% in the number of GABA + amacrine cells and GCL cells, respectively. A sodium (Na +)-free solution, 7-NI and a PKG inhibitor prevented the effect of L-arginine (100 μM). However, a higher concentration of L-arginine (1 mM) induced a 35% reduction in the number of GABA + cells by a Na +-dependent mechanism that was restricted to the GCL population. NMDA, which stimulates NO production, increased GABA release as indicated by 53% and 38% reductions in the number of GABA + amacrine cells and GCL cells, respectively. This effect was blocked by 7-NI only in GCL cells. We conclude that basal NO production and moderate NO production (possibly induced by L-arginine; 100 μM) inhibit basal GABA release from amacrine cells and GCL cells. However, NMDA or L-arginine (1 mM) induce a NO-dependent increase in GABA release in GCL cells, possibly by stimulating higher NO production.

Interactions between the dopaminergic and GABAergic neural systems in the lateral anterior hypothalamus of aggressive AAS-treated hamsters

Adolescent exposure to anabolic–androgenic steroids (AAS) produces alterations to various neurochemical systems resulting in an elevated aggressive response. Both the GABAergic and dopaminergic neural systems are implicated in aggression control and are altered in the presence of AAS. The present studies provide a detailed report of the interaction between D2 receptors and GABAergic neurons in the lateral subdivision of the anterior hypothalamus (LAH), a brain region at the center of aggression control. Male Syrian hamsters were administered AAS throughout adolescence and their brains were processed for double-label immunofluorescence of GAD67 and D2 receptors. Results indicate an increase in the number of D2-ir and GAD67-ir cells in the LAH of AAS-treated animals. Although there were several cells in the LAH colocalized with both GAD67 and D2 receptors, there were no significant increases in the number of double-labeled GAD67/D2-ir neurons. Together, the data suggest the possibility of multiple GABAergic systems in the LAH allowing for differential inhibition of various neural systems. Given these changes in the number of GABAergic cells, it is likely that adolescent AAS exposure also alters the expression of GABAA receptors in brain areas innervated by the LAH. Thus, hamster brains were processed for immunohistochemistry and quantified for changes in GABAA-ir. Interestingly, adolescent exposure to AAS produced a significant decrease in the number of GABAA-ir elements in the LAH of aggressive hamsters. Taken together, results from the current studies provide a putative mechanism whereby dopamine stimulates aggression through removal of GABA inhibition in the LAH of AAS-treated animals.

Differential effects of diazepam treatment and withdrawal on recombinant GABA A receptor expression and functional coupling

Prolonged exposure to benzodiazepines, drugs known to produce tolerance and dependence and also to be abused, leads to adaptive changes in GABA A receptors. To further explore the mechanisms responsible for these phenomena, we studied the effects of prolonged diazepam treatment on the recombinant α 1β 2γ 2S GABA A receptors, stably expressed in human embryonic kidney (HEK) 293 cells. The results demonstrating that long-term (48 and 72 h) exposure of cells to a high concentration of diazepam (50 μM) enhanced the maximum number ( B max) of [ 3H]flunitrazepam, [ 3H]muscimol and [ 3H]t-butylbicycloorthobenzoate ([ 3H]TBOB) binding sites, without changing their affinity ( K d), suggested the up-regulation of GABA A receptors. As demonstrated by cell counting and WST-1 proliferation assay, the observed increase in receptor expression was not a consequence of stimulated growth of cells exposed to diazepam. Semi-quantitative RT-PCR and Western blot analysis, showing elevated levels of α 1 subunit mRNA as well as β 2 and γ 2 subunit proteins, respectively, suggested that prolonged high dose diazepam treatment induced de novo receptor synthesis by acting at both transcriptional and translational levels. The finding that the number of GABA A receptor binding sites returned to control value 24 h following diazepam withdrawal, makes this process less likely to account for the development of benzodiazepine tolerance and dependence. On the other hand, the results demonstrating that observed functional uncoupling between GABA and benzodiazepine binding sites persisted after the termination of diazepam treatment supported the hypothesis of its possible role in these phenomena.

Beta-amyloid peptide-induced modifications in α7 nicotinic acetylcholine receptor immunoreactivity in the hippocampus of the rat: Relationship with GABAergic and calcium-binding proteins perikarya

The effects of the injected beta-amyloid (Aβ) protein on the α7 subtype of nicotinic acetylcholine receptor protein (α7nAChR) in the hippocampus were studied in rats. Injections of Aβ into the retrosplenial cortex resulted in a decrease in α7nAChR-immunoreactivity in the hippocampus. Quantitative analysis revealed a significant reduction in α7nAChR-immunoreactivity in the dorsal part of the CA1 ipsilateral to the Aβ-injected side as compared to the corresponding hemisphere of non-treated control animals and with that seen in the contralateral hemisphere, which corresponds to the control (PBS)-injected side. A significant decrease in α7nAChR-immunoreactivity was also found in the dorsal part of the ipsilateral CA1 as compared with that in the ventral part of the CA1, in CA2, and in CA3 ipsilateral to the Aβ-injected side. The analysis also revealed a significant decrease in α7nAChR-immunoreactivity in the dentate gyrus ipsilateral to the Aβ-injected side as compared to the corresponding hemisphere of non-treated control animals and with that in the PBS-injected side co-localization studies showed that the α7nAChR protein is highly localized in GABA- and Parv-immunoreactive cells, while only few Calb-positive cells expressed immunoreactivity for α7nAChR. In addition, injections of Aβ protein resulted in a significant reduction in the number of GABA- and Parv-immunoreactive cells in the dorsal part of the ipsilateral CA1 as compared to the corresponding region of non-treated control animals and with that in the corresponding region of the PBS-injected side. Our findings suggest that Aβ induces a reduction in α7nAChR-containing cells, which may contribute to impairment of GABAergic synaptic transmission in the hippocampus.

Secreted factors from ventral telencephalon induce the differentiation of GABAergic neurons in cortical cultures

It is widely believed that the pyramidal cells and interneurons of the cerebral cortex are distinct in their origin, lineage and genetic make up. In view of these findings, the current thesis is that the phenotype determination of cortical neurons is primarily directed by genetic mechanisms. Using in vitro assays, the present study demonstrates that secreted factors from ganglionic eminence (GE) of the ventral telencephalon have the potency to induce the differentiation of a subset of cortical neurons towards gamma-aminobutyric acid (GABA)ergic lineage. Characterization of cortical cultures that were exposed to medium derived from GE illustrated a significant increase in the number of GABA-, calretinin- and calbindin-positive neurons. Calcium imaging together with pharmacological studies showed that the application of exogenous medium significantly elevated the intracellular calcium transients in cortical neurons through the activation of ionotropic glutamate receptors. The increase in GABA+ neurons appeared to be associated with the elevated calcium activity; treatment with blockers specific for glutamate receptors abolished both the synchronized transients and reduced the differentiation of GABAergic neurons. Such studies demonstrate that although intrinsic mechanisms determine the fate of cortical interneurons, extrinsic factors have the potency to influence their neurochemical differentiation and contribute towards their molecular diversity.

Expression of amino acid receptors and neural peptides in the weaver mouse brain

In the present study, we conducted: (i) in situ hybridization in order to investigate the expression of kainate and GABA A receptor subunits and the pre-proenkephalin and prodynorphin peptides in the brain of weaver mouse (a genetic model of dopamine deficiency) and (ii) immunocytochemistry in order to study the somatostatin-positive cells in weaver striatum. Our results indicated: (i) increases in mRNA levels of KA2 and GluR6 kainate receptor subunits, of α 4 and β 3 GABA A receptor subunits and of pre-proenkephalin and prodynorphin in 6-month-old weaver striatum; (ii) a decrease in α 1 and β 2 GABA A subunit mRNAs in 6-month-old weaver globus pallidus; (iii) increases in KA2, α 4 and β 3 and decreases in α 2 and β 2 mRNAs in the 6-month-old weaver somatosensory cortex; and (iv) an increase in somatostatin-immunopositive cells in 3-month-old weaver striatum. We suggest that: (i) in striatum, the alterations are induced by the induction of the transcription factor ΔfosB (for GluR6, pre-proenkephalin and prodynorphin mRNAs) and the suppression of transcription factors like NGF-IB (nerve growth factor inducible B; for the KA2 mRNA), in response to dopamine depletion; (ii) in striatum and cortex, the alterations in the expression of the GABA A subunits indicate an increase of extrasynaptic versus a decrease of synaptic GABA A receptors; and (iii) in globus pallidus, the increased striatopallidal GABAergic transmission leads to a decrease in the number of GABA A receptors. Our results further clarify the regulatory role of dopamine in the expression of amino acid receptors and striatal neuropeptides.

Neuron numbers in the sensory trigeminal nuclei of the rat: A GABA‐ and glycine‐immunocytochemical and stereological analysis

The volume, total neuron number, and number of GABA- and glycine-expressing neurons in the sensory trigeminal nuclei of the adult rat were estimated by stereological methods. The mean volume is 1.38+/-0.13 mm3 (mean+/-SD) for the principal nucleus (Vp), 1.59+/-0.06 for the n. oralis (Vo), 2.63+/-0.34 for the n. interpolaris (Vip), and 3.73+/-0.11 for the n. caudalis (Vc). The total neuron numbers are 31,900+/-2,200 (Vp), 21,100+/-3,300 (Vo), 61,600+/-8,300 (Vip), and 159,100+/-25,300 (Vc). Immunoreactive (-ir) neurons were classified as strongly stained or weakly stained, depending on qualitative criteria, cross-checked by a densitometric analysis. GABA-ir cells are most abundant in Vc, in an increasing rostrocaudal gradient within the nucleus. Lower densities are found in Vip and Vp. The mean total number of strongly labeled GABA-ir neurons ranges between 1,800 in Vp to 7,800 in Vip and 22,900 in Vc, and varies notably between subjects. Glycine-ir neurons are more numerous and display more homogeneous densities in all nuclei. Strongly labeled Gly-ir cells predominate in all nuclei, their total number ranging between 9,400 in Vp to 24,300 in Vip and 34,200 in Vc. A substantial fraction of immunolabeled neurons in all nuclei coexpress GABA and glycine. In general, all neurons strongly immunoreactive for GABA are small, while weakly GABA-ir cells which coexpress Gly are larger. In Vc, one-third of all neurons are immunoreactive: 16.6% of them are single-labeled for GABA and 31.6% are single-labeled for glycine. The remaining 51.8% express GABA and glycine in different combinations, with those showing strong double labeling accounting for 22.6%.

The inferior colliculus of the rat: Quantitative immunocytochemical study of GABA and glycine

Both GABA and glycine (Gly) containing neurons send inhibitory projections to the inferior colliculus (IC), whereas inhibitory neurons within the IC are primarily GABAergic. To date, however, a quantitative description of the topographic distribution of GABAergic neurons in the rat’s IC and their GABAergic or glycinergic inputs is lacking. Accordingly, here we present detailed maps of GABAergic and glycinergic neurons and terminals in the rat’s IC. Semithin serial sections of the IC were obtained and stained for GABA and Gly. Images of the tissue were digitized and used for a quantitative densitometric analysis of GABA immunostaining. The optical density, perimeter, and number of GABA- and Gly immunoreactive boutons apposed to the somata were measured. Data analysis included comparisons across IC subdivisions and across frequency regions within the central nucleus of the IC. The results show that: 1) 25% of the IC neurons are GABAergic; 2) there are more GABAergic neurons in the central nucleus of the IC than previously estimated; 3) GABAergic neurons are larger than non-GABAergic; 4) GABAergic neurons receive less GABA and glycine puncta than non-GABAergic; 5) differences across frequency regions are minor, except that the non-GABAergic neurons from high frequency regions are larger than their counterparts in low frequency regions; 6) differences within the laminae are greater along the dorsomedial–ventrolateral axis than along the rostrocaudal axis; 7) GABA and non-GABAergic neurons receive different numbers of puncta in different IC subdivisions; and 8) GABAergic puncta are both apposed to the somata and in the neuropil, glycinergic puncta are mostly confined to the neuropil.

Normalization of glutamate decarboxylase gene expression in the entopeduncular nucleus of rats with a unilateral 6-hydroxydopamine lesion correlates with increased gabaergic input following intermittent but not continuous levodopa

The expression of mRNA encoding for the 67 kilodalton isoform of glutamate decarboxylase (GAD67) was examined by in situ hybridization histochemistry in the entopeduncular nucleus (EP) of adult rats with a 6-hydroxydopamine unilaterally lesion of dopamine neurons. Our results provide original evidence that continuous or intermittent levodopa administration is equally effective at reversing the lesion-induced increase in GAD67 mRNA expression in the EP when compared with vehicle controls. To characterize the GABAergic interactions that may mediate levodopa-induced alterations in the EP, double-labeling in situ hybridization was conducted with a combination of GAD67 radioactive and preproenkephalin or preprotachykinin digoxigenin-labeled complementary RNA probes in the striatum. Levels of GAD67 mRNA labeling were significantly increased by intermittent, but not continuous levodopa. Analysis at the cellular level in a dorsal sector of the striatum revealed that GAD67 mRNA levels increased predominantly in preproenkephalin-unlabeled neuronal profiles, presumably striatal/EP neurons (+99.3%). Saturation analyses of 3H-flunitrazepam binding to GABA A receptors in the EP showed that the increase in GAD67 mRNA in preproenkephalin-unlabeled neurons by intermittent levodopa paralleled a significant decrease in number of GABA A receptors (Bmax) in the EP ipsilateral to the lesion. Continuous levodopa failed to alter striatal GAD67 mRNA levels, or the number or affinity of GABA A receptors when compared with vehicle-treated controls. These results suggest the normalization of GAD gene expression in the EP by intermittent levodopa involves an increase in GABAergic inhibition by striatonigral/EP neurons of the direct pathway. Conversely, the effects of continuous levodopa on GAD mRNA levels in the EP do not appear to be mediated by GABA.

BDNF up-regulates evoked GABAergic transmission in developing hippocampus by potentiating presynaptic N- and P/Q-type Ca2+ channels signalling.

Chronic application of brain-derived neurotrophic factor (BDNF) induces new selective synthesis of non-L-type Ca2+ channels (N, P/Q, R) at the soma of cultured hippocampal neurons. As N- and P/Q-channels support neurotransmitter release in the hippocampus, this suggests that BDNF-treatment may enhance synaptic transmission by increasing the expression of presynaptic Ca2+ channels as well. To address this issue we studied the long-term effects of BDNF on miniature and stimulus-evoked GABAergic transmission in rat embryo hippocampal neurons. We found that BDNF increased the frequency of miniature currents (mIPSCs) by approximately 40%, with little effects on their amplitude. BDNF nearly doubled the size of evoked postsynaptic currents (eIPSCs) with a marked increase of paired-pulse depression, which is indicative of a major increase in presynaptic activity. The potentiation of eIPSCs was more relevant during the first two weeks in culture, when GABAergic transmission is depolarizing. BDNF action was mediated by TrkB-receptors and had no effects on: (i) the amplitude and dose-response of GABA-evoked IPSCs and (ii) the number of GABA(A) receptor clusters and the total functioning synapses, suggesting that the neurotrophin unlikely acted postsynaptically. In line with this, BDNF affected the contribution of voltage-gated Ca2+ channels mediating evoked GABAergic transmission. BDNF drastically increased the fraction of evoked IPSCs supported by N- and P/Q-channels while it decreased the contribution associated with R- and L-types. This selective action resembles the previously observed up-regulatory effects of BDNF on somatic Ca2+ currents in developing hippocampus, suggesting that potentiation of presynaptic N- and P/Q-channel signalling belongs to a manifold mechanism by which BDNF increases the efficiency of stimulus-evoked GABAergic transmission.

Activity Deprivation Reduces Miniature IPSC Amplitude by Decreasing the Number of Postsynaptic GABAAReceptors Clustered at Neocortical Synapses

Maintaining the proper balance between excitation and inhibition is necessary to prevent cortical circuits from either falling silent or generating epileptiform activity. One mechanism through which cortical networks maintain this balance is through the activity-dependent regulation of inhibition, but whether this is achieved primarily through changes in synapse number or synaptic strength is not clear. Previously, we found that 2 d of activity deprivation increased the amplitude of miniature EPSCs (mEPSCs) onto cultured visual cortical pyramidal neurons. Here we find that this same manipulation decreases the amplitude of mIPSCs. This occurs with no change in single-channel conductance but is accompanied by a reduction in the average number of channels open during the mIPSC peak and a reduction in the intensity of staining for GABA(A) receptors (GABA(A)Rs) at postsynaptic sites. In addition, the number of synaptic sites that express detectable levels of GABA(A)Rs was decreased by approximately 50% after activity blockade, although there was no reduction in the total number of presynaptic contacts. These data suggest that activity deprivation reduces cortical inhibition by reducing both the number of GABA(A)Rs clustered at synaptic sites and the number of functional inhibitory synapses. Because excitatory and inhibitory synaptic currents are regulated in opposite directions by activity blockade, these data suggest that the balance between excitation and inhibition is dynamically regulated by ongoing activity.

Effect of embryonic knock-down of GABA A receptors on the levels of monoamines and their metabolites in the CNS of the mouse

In vitro evidence indicates that γ-aminobutyric acid (GABA), acting at GABA A receptors, exerts a positive trophic effect on monoaminergic neurons during embryogenesis. To determine whether in vivo antagonism of GABA A receptors during embryogenesis interferes with the development of monoaminergic neurons, we used mice in which the number of GABA A receptors was decreased by 50% by targeted deletion of the β 3 subunit gene of the GABA A receptor. Levels of serotonin, dopamine, norepinephrine, and the metabolites 3,4-deoxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid were measured in the brainstem, cortex, striatum and spinal cord of female adult homozygous null (β 3 −/−) and wild-type (β 3 +/+) mice, as well as progenitor C57BL/6J and Strain 129/SvJ mice. The level of norepinephrine in the spinal cord of β 3 −/− mice was 44% less than that of β 3 +/+ mice, and did not differ in the brainstem, cortex or striatum. This finding suggests that β 3 subunit-containing GABA A receptors mediate the trophic effects of GABA on a subpopulation of spinally-projecting noradrenergic neurons. In contrast, the levels of serotonin, dopamine or their metabolites were unaffected, suggesting that the development of serotonergic and dopaminergic neurons may require activation of only a small fraction of GABA A receptors or may not be dependent on β 3 subunit-containing GABA A receptors. Finally, Strain 129/SvJ and C57BL/6J mice differed with respect to the levels of dopamine and its metabolites in the brainstem, spinal cord and cortex. These differences may need to be considered when assessing the phenotype of gene-targeted mice for which these mice serve as progenitor strains.

GABAergic neurons of the laterodorsal and pedunculopontine tegmental nuclei of the cat express c-fos during carbachol-induced active sleep

The laterodorsal and pedunculopontine tegmental nuclei (LDT-PPT) are involved in the generation of active sleep (AS; also called REM or rapid eye movement sleep). Although the LDT-PPT are composed principally of cholinergic neurons that participate in the control of sleep and waking states, the function of the large number of GABAergic neurons that are also located in the LDT-PPT is unknown. Consequently, we sought to determine if these neurons are activated (as indicated by their c-fos expression) during active sleep induced by the microinjection of carbachol into the rostro-dorsal pons (AS-carbachol). Accordingly, immunocytochemical double-labeling techniques were used to identify GABA and Fos protein, as well as choline acetyltransferase (ChAT), in histological sections of the LDT-PPT. Compared to control awake cats, there was a larger number of GABAergic neurons that expressed c-fos during AS-carbachol (31.5±6.1 vs. 112±15.2, P<0.005). This increase in the number of GABA +Fos + neurons occurred on the ipsilateral side relative to the injection site; there was a small decrease in GABA +Fos + cells in the contralateral LDT-PPT. However, the LDT-PPT neurons that exhibited the largest increase in c-fos expression during AS-carbachol were neither GABA + nor ChAT + (47±22.5 vs. 228.7±14.0, P<0.0005). The number of cholinergic neurons that expressed c-fos during AS-carbachol was not significantly different compared to wakefulness. These data demonstrate that, during AS-carbachol, GABAergic as well as an unidentified population of neurons are activated in the LDT-PPT. We propose that these non-cholinergic LDT-PPT neurons may participate in the regulation of active sleep.

Research on the pharmacochemistry of some GABA and valproic acid derivatives

The role of GABA in epilepsy and especially in the action of various antiepileptics has been well established. We have reported the synthesis and pharmacochemical evaluation of a number of GABA and valproic acid derivatives and also the synthesis of two N-acyl-2-pyrrolidinone derivatives. We now report the pharmacochemical evaluation—anticonvulsant and antioxidant activity, and also study of lipophilicity—of the latter two in combination with the synthesis and evaluation of two novel ester derivatives (2-propylpentyl-3-pyridine carboxylate and 3-pyridinylmethyl 2-propylpentanoate), which contain the moieties of valproic acid and of 2-propyl-1-pentanol. Anticonvulsant activity was evaluated using the picrotoxin model and the antioxidant potential using the lipid peroxidation method. The study of lipophilicity was performed both by experimental (by reversed phase thin layer chromatography) and calculating (Rekker’s and Hansch/Leo’s fragmental and Suzuki/Kudo’s atom-based) methods; lipophilicity was also studied in combination with other physicochemical parameters of the above-mentioned compounds (van der Waals volume, van der Waals area, dipole moment, energy of formation, energy of hydration). In this study, we also include six other derivatives which we synthesized and tested in an earlier study. Only the two ester derivatives exhibited potent anticonvulsant and also antioxidant activity; the 2-pyrrolidinones did not exhibit significant activity in these experiments. In accordance with our earlier findings, the nicotinoyl and the nicotinyl moieties, in combination with considerable lipophilicity, seem to be suitable groups to confer activity in this type of compound. Good multiple correlation was derived between lipophilicity and energy of hydration and van der Waals volume of the compounds. Drug Dev. Res. 51:143–148, 2000. © 2001 Wiley-Liss, Inc.

Effects of chronic salicylate on GABAergic activity in rat inferior colliculus

It is well accepted that salicylate ototoxicity results in reversible tinnitus in humans. Salicylate-induced tinnitus may be an example of plasticity of the central auditory system and could potentially serve as a model to further understand mechanisms of tinnitus generation. This study examined levels of glutamic acid decarboxylase (GAD) and the binding characteristics of the GABA A receptor in auditory brainstem structures of Long–Evans rats chronically treated with salicylate. Western blotting revealed a significant 63% ( P<0.008) elevation of GAD levels in the inferior colliculus (IC) of salicylate-treated subjects. This occurred in subjects demonstrating behavioral evidence of tinnitus. Muscimol saturation analysis was indicative of a salicylate-related increase in receptor affinity. Linear regression of [ 3H]muscimol saturation analysis data revealed a significant ( P<0.05) reduction in K d values in whole IC (−48%), as well as in the central nucleus of IC (CIC, −58%) and combined external and dorsal cortex of IC (E/DCIC, −46%). The number of GABA A binding sites ( B max) were also significantly ( P<0.05) decreased. These changes were observed only in central auditory structures. This suggests that GAD expression and GABA A receptor binding characteristics may be altered with chronic exposure to sodium salicylate and these changes may represent aberrant plasticity clinically experienced as tinnitus.

Neurochemical determination of the location of NMDA and GABA receptors on rat striatal cholinergic neurons

This paper reports on the protocol for neurochemical determination of the location of various receptors on cholinergic neurons in various brain regions. We applied this protocol to investigate whether NMDA and GABA receptors are located on rat striatal cholinergic neurons. When striatal cholinergic neurons were selectively destroyed by intrastriatal injection of cholinergic neurotoxin, ethylcholine mustard aziridinium ion (AF64A), the number of NMDA and GABA A receptors decreased. However, no significant changes were observed on the number of GABA B receptors. These results suggest that NMDA and GABA A, but not GABA B receptors are located on cholinergic neurons in the striatum. These results also indicate the usefulness and scientific applicability of the present protocol. Themes: Neurotransmitters, modulators, transporters, and receptors Topics: Regional localization of receptors and transmitters