GABAergic innervation in cerebral blood vessels: an immunohistochemical demonstration of L-glutamic acid decarboxylase and GABA transaminase

Amelioration of Cerebral Vasospasm and Secondary Injury by Vigabatrin After Experimental Subarachnoid Hemorrhage in the Rabbit

BACKGROUND

Vigabatrin, an antiepileptic drug, increases the level of gamma aminobutyric acid in the brain by inhibiting its catabolism. Because gamma aminobutyric acid has been proved to have vasodilatory effects, in the present study, we investigated the effect of vigabatrin to treat experimental subarachnoid hemorrhage (SAH)-induced vasospasm.

METHODS

A total of 30 New Zealand white rabbits were divided into 3 groups of 10 each: the control group, SAH group, and vigabatrin group. Experimental SAH was established by injection of autologous arterial blood into the cisterna magna. In the vigabatrin group, the rabbits were administered vigabatrin for 3 days after induction of the SAH. The first dose of vigabatrin was given 2 hours after SAH induction. A daily dose of 500 mg/kg vigabatrin was administered intraperitoneally. After 3 days, the rabbits were sacrificed, and the brains were removed, together with the cerebellum and brainstem. The basilar artery wall thickness and lumen areas were measured. The neuronal degeneration in the hippocampus (CA1, CA3, and dentate gyrus) was also evaluated.

RESULTS

The arterial wall thickness of the vigabatrin group was less than that in the SAH group (P < 0.001), and the mean luminal area of the vigabatrin group was greater than that in the SAH group (P < 0.001). Additionally, the hippocampal neuronal degeneration score of the vigabatrin group was lower than that of the SAH group (P < 0.001).

CONCLUSION

These findings have indicated that vigabatrin has a vasodilatory effect in an experimental SAH model in the rabbit. Moreover, it showed a neuroprotective effect in the hippocampal neurons against secondary injury induced by SAH.

Expression and distribution of GABA and GABAB-receptor in the rat adrenal gland

The inhibitory effects of gamma-aminobutyric acid (GABA) in the central and peripheral nervous systems and the endocrine system are mediated by two different GABA receptors: GABAA-receptor (GABAA-R) and GABAB-receptor (GABAB-R). GABAA-R, but not GABAB-R, has been observed in the rat adrenal gland, where GABA is known to be released. This study sought to determine whether both GABA and GABAB-R are present in the endocrine and neuronal elements of the rat adrenal gland, and to investigate whether GABAB-R may play a role in mediating the effects of GABA in secretory activity of these cells. GABA-immunoreactive nerve fibers were observed in the superficial cortex. Some GABA-immunoreactive nerve fibers were found to be associated with blood vessels. Double-immunostaining revealed GABA-immunoreactive nerve fibers in the cortex were choline acetyltransferase (ChAT)-immunonegative. Some GABA-immunoreactive nerve fibers ran through the cortex toward the medulla. In the medulla, GABA-immunoreactivity was seen in some large ganglion cells, but not in the chromaffin cells. Double-immunostaining also showed GABA-immunoreactive ganglion cells were nitric oxide synthase (NOS)-immunopositive. However, neither immunohistochemistry combined with fluorescent microscopy nor double-immunostaining revealed GABA-immunoreactivity in the noradrenaline cells with blue-white fluorescence or in the adrenaline cells with phenylethanolamine N-methyltransferase (PNMT)-immunoreactivity. Furthermore, GABA-immunoreactive nerve fibers were observed in close contact with ganglion cells, but not chromaffin cells. Double-immunostaining also showed that the GABA-immunoreactive nerve fibers were in close contact with NOS- or neuropeptide tyrosine (NPY)-immunoreactive ganglion cells. A few of the GABA-immunoreactive nerve fibers were ChAT-immunopositive, while most of the GABA-immunoreactive nerve fibers were ChAT-immunonegative. Numerous ChAT-immunoreactive nerve fibers were observed in close contact with the ganglion cells and chromaffin cells in the medulla. The GABAB-R-immunoreactivity was found only in ganglion cells in the medulla and not at all in the cortex. Immunohistochemistry combined with fluorescent microscopy and double-immunostaining showed no GABAB-R-immunoreactivity in noradrenaline cells with blue-white fluorescence or in adrenaline cells with PNMT-immunoreactivity. These immunoreactive ganglion cells were NOS- or NPY-immunopositive on double-immunostaining. These findings suggest that GABA from the intra-adrenal nerve fibers may have an inhibitory effect on the secretory activity of ganglion cells and cortical cells, and on the motility of blood vessels in the rat adrenal gland, mediated by GABA-Rs.

Autonomous vascular networks synchronize GABA neuron migration in the embryonic forebrain

GABA neurons, born in remote germinative zones in the ventral forebrain (telencephalon), migrate tangentially in two spatially distinct streams to adopt their specific positions in the developing cortex. The cell types and molecular cues that regulate this divided migratory route remains to be elucidated. Here we show that embryonic vascular networks are strategically positioned to fulfill the task of providing support as well as critical guidance cues that regulate the divided migratory routes of GABA neurons in the telencephalon. Interestingly, endothelial cells of the telencephalon are not homogeneous in their gene expression profiles. Endothelial cells of the periventricular vascular network have molecular identities distinct from those of the pial network. Our data suggest that periventricular endothelial cells have intrinsic programs that can significantly mold neuronal development and uncovers new insights into concepts and mechanisms of CNS angiogenesis from both developmental and disease perspectives.

The effect of thiocolchicoside on cerebral vasospasm following experimental subarachnoid hemorrhage in the rabbit

BACKGROUND

This study investigated the effects of thiocolchicoside to prevent cerebral vasospasm in a rabbit model of subarachnoid hemorrhage.

METHODS

Twenty-four adult male New Zealand white rabbits were randomly divided into three groups of eight rabbits each: group 1 (control), group 2 (subarachnoid hemorrhage), group 3 (treatment). Thiocolchicoside (4 mg/kg, intraperitoneally) was administered just before intracisternal blood injection and continued for 72 h once a day in the same dose for group 3. Animals were killed 72 h after subarachnoid hemorrhage. Basilar artery cross-sectional areas and arterial wall thicknesses were measured in all groups.

RESULTS

Intraperitoneal administration of thiocolchicoside was found to attenuate cerebral vasospasm after subarachnoid hemorrhage in rabbits. Thiocolchicoside treatment was determined to be effective in increasing the luminal area and reducing the wall thickness of the basilar artery.

CONCLUSIONS

Our findings, for the first time, showed that TCC can prevent vasospasm induced by SAH. Our results also showed that GABAergic activity may play an important role in cerebral vasospasm etiopathogenesis. In conclusion, the thiocolchicoside treatment might be beneficial in preventing vasospasm after subarachnoid hemorrhage, thus showing potential for clinical application.

Abnormal cholinergic and GABAergic vascular innervation in the hypothalamic arcuate nucleus of obesetub/tubmice

Tubby and tubby-like proteins (TULPs) are encoded by members of a small gene family. An autosomal recessive mutation in the mouse tub gene leads to blindness, deafness, and maturity-onset obesity. The mechanisms by which the mutation causes the obesity syndrome has not been established. We compared obese tub/tub mice and their lean littermates in order to find abnormalities within the mediobasal hypothalamus, a region intimately associated with the regulation of body weight. Using an antiserum to the vesicular acetylcholine transporter (VAChT), a marker for cholinergic neurons, many unusually large VAChT-immunoreactive (-ir) nerve terminals, identified by colocalization with the synaptic vesicle protein synaptophysin, were demonstrated in the hypothalamic arcuate nucleus of obese tub/tub mice. Double-labeling showed that VAChT-ir nerve endings also contained glutamic acid decarboxylase (GAD), a marker for gamma-aminobutyric acid (GABA) neurons. The VAChT- and GAD-ir nerve terminals were in close contact with blood vessels, identified with antisera to platelet endothelial cell adhesion molecule-1 (PECAM; also called CD31), laminin, smooth muscle actin (SMA), and glucose transporter-1 (GLUT1). Such large cholinergic and GABAergic nerve terminals surrounding blood vessels were not seen in the arcuate nucleus of lean tub/+ mice. The presence of abnormal cholinergic/GABAergic vascular innervation in the arcuate nucleus suggests that alterations in this region, which contains neurons that receive information from the periphery and which relays information about the energy status to other parts of the brain, may be central in the development of the obese phenotype in animals with an autosomal recessive mutation in the tub gene.

Relationship of spikes, synaptic activity, and local changes of cerebral blood flow

The coupling of electrical activity in the brain to changes in cerebral blood flow (CBF) is of interest because hemodynamic changes are used to track brain function. Recent studies, especially those investigating the cerebellar cortex, have shown that the spike rate in the principal target cell of a brain region (i.e. the efferent cell) does not affect vascular response amplitude. Subthreshold integrative synaptic processes trigger changes in the local microcirculation and local glucose consumption. The spatial specificity of the vascular response on the brain surface is limited because of the functional anatomy of the pial vessels. Within the cortex there is a characteristic laminar flow distribution, the largest changes of which are observed at the depth of maximal synaptic activity (i.e. layer IV) for an afferent input system. Under most conditions, increases in CBF are explained by activity in postsynaptic neurons, but presynaptic elements can contribute. Neurotransmitters do not mediate increases in CBF that are triggered by the concerted action of several second messenger molecules. It is important to distinguish between effective synaptic inhibition and deactivation that increase and decrease CBF and glucose consumption, respectively. In summary, hemodynamic changes evoked by neuronal activity depend on the afferent input function (i.e. all aspects of presynaptic and postsynaptic processing), but are totally independent of the efferent function (i.e., the spike rate of the same region). Thus, it is not possible to conclude whether the output level of activity of a region is increased based on brain maps that use blood-flow changes as markers.

GABA immunoreactivity in the human cerebellar cortex: a light and electron microscopical study

The distribution of gamma-aminobutyric acid (GABA) in surgical samples of human cerebellar cortex was studied by light and electron microscope immunocytochemistry using a polyclonal antibody generated in rabbit against GABA coupled to bovine serum albumin with glutaraldehyde. Observations by light microscopy revealed immunostained neuronal bodies and processes as well as axon terminals in all layers of the cerebellar cortex. Perikarya of stellate, basket and Golgi neurons showed evident GABA immunoreactivity. In contrast, perikarya of Purkinje neurons appeared to be negative or weakly positive. Immunoreactive tracts of longitudinally- or obliquely-sectioned neuronal processes and punctate elements, corresponding to axon terminals or cross-sectioned neuronal processes, showed a layer-specific pattern of distribution and were seen on the surface of neuronal bodies, in the neuropil and at microvessel walls. Electron microscope observations mainly focussed on the analysis of GABA-labelled axon terminals and of their relationships with neurons and microvessels. GABA-labelled terminals contained gold particles associated with pleomorphic vesicles and mitochondria and established symmetric synapses with neuronal bodies and dendrites in all cortex layers. GABA-labelled terminals associated with capillaries were seen to contact the perivascular glial processes, basal lamina and endothelial cells and to establish synapses with subendothelial unlabelled axons.

GABA immunoreactivity in the olfactory bulbs of the adult sea lamprey Petromyzon marinus L

The distribution of gamma-aminobutyric acid (GABA) immunoreactivity in the olfactory bulbs of the adult sea lamprey was studied using an antibody against this transmitter. Five types of GABA-immunoreactive (GABAir) cells were observed. Medium-sized GABAir cells (periglomerular cells) were located around the olfactory glomeruli and occasionally within them. In the inner cellular layer of the bulbs and around the olfactory ventricles, two types of GABAir perikarya were present: some medium-sized GABAir cells and numerous small GABAir cells (granules). In the walls of the olfactory ventricle, some medium-sized GABAir cells of cerebrospinal fluid-contacting type were observed. At the entrance of the olfactory nerves, medium-sized GABAir bipolar cells were present, mostly located between the olfactory nerve and the glomerular layer or close to the meninges, but some in the intracranial portion of the olfactory nerve. GABAir processes were present in all layers of the olfactory bulb. In addition there were also GABAir cells in the dorsal interbulbar commissure. The distribution of GABA observed in the olfactory system of lampreys indicates that this transmitter plays a major role in the modulation of bulbar circuits. The presence of granular and periglomerular cells in lampreys indicates that these two intrinsic GABAergic neurons of the olfactory bulbs are shared by most vertebrates, although lampreys have additional GABAir cell types.

Glutamic acid decarboxylase-positive neuronal cell bodies and terminals in the human cerebellar cortex

The distribution of gamma-aminobutyric acid (GABA) in the human cerebellar cortex was studied using immunohistochemistry for glutamic acid decarboxylase (GAD), the enzyme that catalyses GABA synthesis. Observations by light microscopy revealed, in all layers of the cerebellar cortex, strong, punctate positivity for GAD, related to putative GABAergic nerve terminals, as well as a diffuse cytoplasmic immunoreactivity within neuronal cell bodies. GAD-positive nerve terminals were found in close relationship with the walls of the cerebellar cortex microvessels. Observations by electron microscopy revealed positive nerve terminals in contact with the astrocyte perivascular sheath of capillaries. GAD immunoreactivity was also detected within astroglial perivascular endfeet and endothelial cells. The findings provide further insights into the GABAergic synapses of the circuitry of the human cerebellar cortex. The detection of 'vascular' GAD immunoreactivities suggests that GABAergic mechanisms may regulate cerebellar microvessel function.

Confocal imaging of intracellular chloride in living brain slices: measurement of GABAA receptor activity

We have developed a method using UV laser-scanning confocal microscopy and the fluorescent chloride ion indicator, 6-methoxy-N-ethylquinolinium chloride (MEQ), to image GABA-mediated changes in intracellular chloride (Cli-) in individual neurons of the rat acute brain slice. After bath-loading slices with the cell-permeant form (reduced) of MEQ, there was intense fluorescence within neurons of diverse morphologies in the hippocampus, neocortex and cerebellum. MEQ fluorescence localized to the cytosolic compartment of both the somata and proximal dendrites. MEQ fluorescence was calibrated using the ionophores nigericin and tributyltin in the presence of varying extracellular Cl- concentrations. Neuronal MEQ fluorescence was inversely related to intracellular Cl-, with a Stern-Volmer constant of 16 M-1 (50% quench by 61 mM Cl-). Application of GABA in the perfusate produced a concentration-dependent decrease in MEQ fluorescence (EC50 = 40 microM) that was blocked in the presence of the Cl- channel antagonist, picrotoxin. Bath perfusion of hippocampal slices with modulators of the GABAA receptor, pentobarbital and diazepam, potentiated the GABA-mediated response by 85 and 44%, respectively. A regional comparison identified larger GABA responses for both cerebellar Purkinje and granule cells relative to pyramidal neurons of the hippocampus and neocortex and to hippocampal interneurons. Pressure ejection of the GABAA agonist, muscimol (40 microM), from a micropipet onto individual hippocampal neurons allowed the measurement of rapid responses (1-5 s), compared to those obtained with bath application. Thus, optical imaging of [Cl-]i using MEQ and UV-laser-scanning confocal microscopy provides investigators with a new method to study GABAA pharmacology in neighboring neurons and perhaps even in the soma versus dendrites simultaneously, within living brain slices.

Embryonic and postnatal expression of four gamma-aminobutyric acid transporter mRNAs in the mouse brain and leptomeninges

The distribution of gamma-aminobutyric acid (GABA) transporter mRNAs (mGATs) was studied in mouse brain during embryonic and postnatal development using in situ hybridization with radiolabeled oligonucleotide probes. Mouse GATs 1 and 4 were present in the ventricular and subventricular zones of the lateral ventricle from gestational day 13. During postnatal development, mGAT1 mRNA was distributed diffusely throughout the brain and spinal cord, with the highest expression present in the olfactory bulbs, hippocampus, and cerebellar cortex. The mGAT4 message was densely distributed throughout the central nervous system during postnatal week 1; however, the hybridization signal in the cerebral cortex and hippocampus decreased during postnatal weeks 2 and 3, and in adults, mGAT4 labeling was restricted largely to the olfactory bulbs, midbrain, deep cerebellar nuclei, medulla, and spinal cord. Mouse GAT2 mRNA was expressed only in proliferating and migrating cerebellar granule cells, whereas mGAT3 mRNA was absent from the brain and spinal cord throughout development. Each of the four mGATs was present to some degree in the leptomeninges. The expression of mGATs 2 and 3 was almost entirely restricted to the pia-arachnoid, whereas mGATs 1 and 4 were present only in specific regions of the membrane. Although mGATs 1 and 4 may subserve the classical purpose of terminating inhibitory GABAergic transmission through neuronal and glial uptake mechanisms, GABA transporters in the pia-arachnoid may help to regulate the amount of GABA available to proliferating and migrating neurons at the sub-pial surface during perinatal development.

Attenuation by valproate of c-fos immunoreactivity in trigeminal nucleus caudalis induced by intracisternal capsaicin

1. Valproic acid, useful in the treatment of migraine, is an inhibitor of gamma aminobutyric acid (GABA) aminotransferase and activator of glutamic acid decarboxylase. Its mechanism in migraine remains obscure. The effects of valproic acid (2-propylpentanoic acid) were examined on the number of cells expressing c-fos-like immunoreactivity (c-fos-LI), a marker of neuronal activation, within the trigeminal nucleus caudalis (lamina I, IIo, TNC) 2 h after intracisternal injection of the irritant, capsaicin (0.1 ml; 15.25 micrograms ml-1), in urethane-anaesthetized Hartley guinea-pigs. Positive cells were counted in eighteen sections (50 microns) at three representative levels (rostral, middle and caudal) within lamina I, IIo of the TNC in 90 animals. 2. Numerous cells were labelled after capsaicin instillation (244 +/- 25; 1 ml; 15.25 mM) but not after capsaicin vehicle (11 +/- 1). Positive cells were also found within the medial reticular nucleus, the area postrema and the nucleus of the solitary tract. A similar distribution has been demonstrated previously after application of intracisternal irritants such as autologous blood or carrageenin. 3. Valproate (> or = 10 mg kg-1, i.p.) reduced labelled cells by 52% (P < 0.05) in lamina I, IIo but not within the area postrema, the nucleus of the solitary tract or the medial reticular nucleus. A similar finding was obtained previously after administration of sumatriptan, dihydroergotamine or the NK1 receptor antagonist RPR 100,893. 4. Pretreatment with bicuculline (30 micrograms kg-1; i.p.), a GABAA antagonist, but not phaclofen (1 mg kg-1) a GABAB antagonist, reversed the effect of valproate and increased c-fos positive cells within lamina I, IIo. Somewhat paradoxically, bicuculline by itself (30 micrograms kg-1 i.p.) decreased the number of labelled cells suggesting that more than a single GABAergic mechanism can suppress c-fos expression. 5. We conclude that the mechanism of action of valproate is mediated via GABAA receptors. Since valproate decreases both c-fos expression and as previously shown, neurogenic inflammation within the meninges, the GABAA receptor complex might provide an important target for drug development in migraine and related headaches.

gamma-Aminobutyric acid (GABA) metabolism in mammalian neural and nonneural tissues

4-Aminobutyric acid (GABA), a major inhibitory neurotransmitter of mammalian central nervous system, is found in a wide range of organisms, from prokaryotes to vertebrates. GABA is widely distributed in nonneural tissue including peripheral nervous and endocrine systems. GABA acts on GABAA and GABAB receptors. GABAA receptors are ligand-gated chloride channels modulated by a variety of drugs. GABAB receptors are essentially presynaptic, usually coupled to potassium or calcium channels, and they function via a GTP binding protein. In neural and nonneural tissues, GABA is metabolized by three enzymes--glutamic acid decarboxylase (GAD), which produces GABA from glutamic acid, and the catabolic enzymes GABA-transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH). Production of succinic acid by SSADH allows entry of the GABA carbon skeleton into the tricarboxylic acid cycle. Alternate sources of GABA include putrescine, spermine, spermidine and ornithine, which produce GABA via deamination and decarboxylation reactions, while L-glutamine is an additional source of glutamic acid via deamination. GAD from mammalian brain occurs in two molecular forms, GAD65 and GAD67 (referring to subunit relative molecular weight (Mr) in kilodaltons). These different forms of GAD are the product of different genes, differing in nucleotide sequence, immunoreactivity and subcellular localization. The presence and characteristics of GAD have been investigated in a wide variety of nonneural tissues including liver, kidney, pancreas, testis, ova, oviduct, adrenal, sympathetic ganglia, gastrointestinal tract and circulating erythrocytes. In some tissues, one form (GAD65 or GAD67) predominates. GABA-T has been located in most of the same tissues, primarily through histochemical and/or immunochemical methods; GABA-T is also present in a variety of circulating cells, including platelets and lymphocytes. SSADH, the final enzyme GABA catabolism, has been detected in some of the tissues in which GAD and GABA-T have been identified, although the presence of this enzyme has not been in mammalian pancreas, ova, oviduct, testis or sympathetic ganglia.

Peripheral GABAA receptor-mediated effects of sodium valproate on dural plasma protein extravasation to substance P and trigeminal stimulation

1. The GABA transaminase inhibitor and activator of glutamic acid decarboxylase, valproic acid is being used for the treatment of migraine. Its mechanism of action is unknown. We tested the effects of sodium valproate and GABAA-agonist muscimol on dural plasma protein ([125I]-bovine serum albumin) extravasation evoked by either unilateral trigeminal ganglion stimulation (0.6 mA, 5 ms, 5 Hz, 5 min) or substance P (SP) administration (1 nmol kg-1,i.v.) in anaesthetized Sprague-Dawley rats. 2. Intraperitoneal (i.p.) injection of sodium valproate or muscimol, but not baclofen (< or = 10 mg kg-1, i.p.) dose-dependently reduced dural plasma protein extravasation caused either by electrical trigeminal stimulation (ED50: 6.6 +/- 1.4 mg kg-1, i.p., and 58 +/- 18 micrograms kg-1, i.p. for valproate or muscimol, respectively) or by intravenous substance P administration (ED50: 3.2 +/- 1.4 mg kg-1, i.p. and 385 +/- 190 micrograms kg-1, i.p. for valproate or muscimol, respectively). 3. Valproate (6.6 mg kg-1, i.p.) or muscimol (58 micrograms kg-1, i.p.) had no effect on mean arterial blood pressure or heart rate when measured for 30 min after i.p. administration. 4. The GABAA-antagonist bicuculline (0.01 mg kg-1, i.p.) completely reversed the effect of valproate and muscimol on plasma extravasation following electrical stimulation or substance P administration, whereas the GABAB-receptor antagonist, phaclofen (0.01-1 mg kg-1, i.p.) did not. Bicuculline or phaclofen, given alone, did not alter the plasma extravasation response after either electrical stimulation or SP administration. 5. Valproate decreased plasma extravasation following substance P administration in adult animals, neonatally treated with capsaicin by a bicuculline-reversible mechanism. This suggests that GABAA receptors are not found primarily on those afferent neurones or fibres which are sensitive to capsaicin treatment in neonatal rats.6. We conclude that sodium valproate blocks plasma extravasation in the meninges through GABAA mediated postjunctional receptors probably within the meninges. The dosages required are comparable to those used clinically. Agonists and modulators at the GABAA receptor may become useful for the development of selective therapeutic agents for migraine and cluster headache.

Cerebral pial arterial innervation with special reference to GABAergic innervation

Glutamic acid decarboxylase (GAD)-immunoreactive (I) nerve fibers were observed to run parallel to other autonomic nerve fibers, especially vasoactive intestinal polypeptide (VIP)- and calcitonin gene-related peptide (CGRP)-I nerve fibers at the light microscopic level. At the ultrastructural level, GAD-immunoreactivities co-localized with CGRP immunoreactivities in nerve terminals, but not with choline acetyltransferase, VIP, tyrosine hydroxylase and neuropeptide Y immunoreactivities. GAD immunoreactivities were observed in the trigeminal ganglion, some of which were co-localized with CGRP-immunoreactivities. In the proximal portion of the internal carotid artery, GAD-I adventitial ganglion cells were observed and some were also immunoreactive for CGRP. These results strongly suggest that the origin of GABAergic innervation of the major cerebral pial arteries of the cat is mainly in the trigeminal ganglion, and partly in the adventitial ganglia of the internal carotid artery.