Decreased adenosine receptor binding in dystonic brains of the dt(sz) mutant

In patients with paroxysmal non-kinesigenic dyskinesias, episodes of dystonia can be provoked by stress and also by methylxanthines (e.g. caffeine), which inhibit adenosine A(1)/A(2A) receptors. In the dt(sz) mutant hamster, a model of this movement disorder, adenosine A(1) receptor antagonists were previously found to worsen dystonia, while adenosine A(1) and A(2A) receptor agonists exerted pronounced beneficial effects. Therefore, in the present study, adenosine receptor A(1) and A(2A) binding was determined by autoradiographic analyses in dt(sz) hamsters under basal conditions, i.e. in the absence of a dystonic attack, and in a group of mutant hamsters which exhibited severe stress-induced dystonic attacks prior to kill. In comparison with non-dystonic control hamsters, [(3)H]DPCPX (8-cyclopentyl-1,3-dipropylxanthine) binding to adenosine A(1) receptors and [(3)H]CGS 21680 (2p-(2carboxyethylphen-ethylamino-5'-N-ethlycarboxamindoadenosine) binding to adenosine A(2A) receptors were significantly lower throughout the brain of dystonic animals. Under normal resting conditions, mutant hamsters showed significant decreases in adenosine A(1) (-12 to-42%) and in A(2A) (-19 to-34%) receptor binding compared with controls. Stressful stimulation increased adenosine A(1) and A(2A) receptor binding in almost all brain regions in both control and dystonic hamsters. The stress-induced increase was more marked in mutant hamsters, leading to a disappearance of differences in most regions compared with stimulated controls, except the striatum. In view of previous findings of striking beneficial effects of adenosine A(1) and A(2A) receptor agonists and of striatal dysfunctions in the dt(sz) mutant, the reduced adenosine receptor binding may be an important factor in the pathogenesis of paroxysmal dystonia.     

Tyrosine hydroxylase immunoreactivity and [3H]WIN 35,428 binding to the dopamine transporter in a hamster model of idiopathic paroxysmal dystonia.

Recent pharmacological studies and receptor analyses have suggested that dopamine neurotransmission is enhanced in mutant dystonic hamsters (dt(sz)), a model of idiopathic paroxysmal dystonia which displays attacks of generalized dystonia in response to mild stress. In order to further characterize the nature of dopamine alterations, the present study investigated possible changes in the number of dopaminergic neurons, as defined by tyrosine hydroxylase immunohistochemistry, as well as binding to the dopamine transporter labelled with [3H]WIN 35,428 in dystonic hamsters. No differences in the number of tyrosine hydroxylase-immunoreactive neurons were found within the substantia nigra and ventral tegmental area of mutant hamsters compared to non-dystonic control hamsters. Similarly, under basal conditions, i.e. in the absence of a dystonic episode, no significant changes in [3H]WIN 35,428 binding were detected in dystonic brains. However, in animals killed during the expression of severe dystonia, significant decreases in dopamine transporter binding became evident in the nucleus accumbens and ventral tegmental area in comparison to controls exposed to the same external stimulation. Since stimulation tended to increase [3H]WIN 35,428 binding in control brains, the observed decrease in the ventral tegmental area appeared to be due primarily to the fact that binding was increased less in dystonic brains than in similarly stimulated control animals. This finding could reflect a diminished ability of the dopamine transporter to undergo adaptive changes in response to external stressful stimulation in mutant hamsters. The selective dopamine uptake inhibitor GBR 12909 (20 mg/kg) aggravated dystonia in mutant hamsters, further suggesting that acute alterations in dopamine transporter function during stimulation may be an important component of dystonia in this model.     

Evidence for striatal dopaminergic overactivity in paroxysmal dystonia indicated by microinjections in a genetic rodent model

Mutant dystonic hamsters (dt(sz)), a model of primary paroxysmal dystonia, display attacks of generalized dystonia in response to mild stress in an age-dependent manner. Recent studies in dystonic hamsters have revealed decreased densities of dopamine D(1) and D(2) in the dorsal striatum. This finding has been interpreted as a down-regulation in response to enhanced dopamine release because systemic treatments with neuroleptics reduced the severity of dystonia while levodopa exerted prodystonic effects. Therefore, in the present study we investigated the effects of amphetamine as well as of selective D(1) or D(2) receptor agonists and antagonists on the severity of dystonia after systemic administrations and after microinjections into the dorsal striatum. Amphetamine and the dopamine D(2) agonist quinpirole increased the severity of dystonia after systemic and striatal injections, while the dopamine D(1) agonist SKF 38393 exerted only moderate prodystonic effects after systemic administration of a high dose but not after striatal injections. These results suggest that a predominant overstimulation of D(2) receptors is pathogenetically involved in the dystonic syndrome. Combined systemic or striatal administrations of the D(1) and D(2) receptor agonists did not reveal synergistic prodystonic effects at the examined doses. The selective D(1) antagonist SCH 23390 as well as the D(2) antagonist raclopride tended to decrease the severity of dystonia after systemic administration but failed to exert significant effects after striatal injection. The coadministration of ineffective doses of the antagonists SCH 23390 and raclopride, however, exerted an enormous antidystonic efficacy after both systemic and striatal injections.Since striatal injections of compounds which enhance dopaminergic activity aggravated dystonia, while coinjections of dopamine D1 and D2 receptor antagonists reduced the severity of dystonia, the present findings clearly support the hypothesis that striatal dopaminergic overactivity plays a crucial role for the manifestation of dystonic attacks in the hamster model of paroxysmal dystonia.     

Preferential release of neuroactive amino acids from the ventrolateral medulla of the rat in vivo as measured by microdialysis

The basal overflow of extracellular endogenous amino acids was measured from the ventrolateral medulla of urethane anaesthetized rats in vivo by microdialysis. Inclusion of a mercury salt, p-chloromercuriphenylsulphonic acid, in the dialysate (Krebs' solution), results in a preferential increase in the overflow of aspartate, glutamate, glycine and GABA. A smaller increase in the overflow of the glutamate precursor and metabolite, glutamine, was also found. There was no significant change in the basal extracellular levels of taurine, asparagine, alanine, serine, ornithine or lysine. Inclusion of a specific GABA uptake inhibitor, nipecotic acid, in the dialysate results in an immediate, dose dependent increase in the overflow of GABA, and to a lesser extent, taurine. Since it is likely that mercury salts increase neurotransmitter release by increasing free intracellular calcium ion concentrations, it is suggested that these results provide further evidence for a physiologically relevant neurotransmitter role for aspartate, glutamate, glycine and GABA in the ventrolateral medulla.     

The release of endogenous amino acids from the rat visual cortex.

The release of endogenous taurine, GABA, glycine, aspartate, glutamate, glutamine and alanine from the rat visual cortex was measured using a cortical cup technique. The electrocorticogram (ECoG) was monitored throughout most experiments. 2. Spreading depression, evoked by the dropwise placement of 10% KCl solution on to the brain outside the cup was associated with a significant increase in the release of GABA and glutamine but a marked fall in that of glutamate. The evoked release of GABA and glutamate but not of glutamine was Ca2+ dependent. 3. A solution containing 50 mM-K+ placed within the cup elicited a significant increase in the release of taurine and GABA, whereas 100 mM-K+ additionally released aspartate and glutamate. The K+-evoked release of these amino acids with the exceptions of taurine and glutamine was Ca2+-dependent. 4. Three series of experiments were carried out in which the preparations were stimulated electrically. Bipolar stimulation (100 Hz, 1 msec pulse width, 2-5 mA for 5 min) with the electrode within the cup was followed by significant increases in taurine, GABA and glutamate release; using a 5 mA current, there was an additional release of aspartate and alanine. Only the evoked release of GABA and glutamate was Ca2+ dependent. 5. In the second and third series of experiments, the electrode was sited adjacent to the cup or on the contralateral cortex respectively. Following stimulation (100 Hz, 1 msec pulse width, 2-5 mA for 5 min) there was a significant increase in taurine and GABA release and a significant fall in the release of aspartate and glutamate. With the exception of taurine, these changes in release were Ca2+ dependent. Reducing the stimulus current to 1-5 mA or the period of stimulation to 2-5 min initiated similar but statistically insignificant changes in release. A range (10-100 Hz) of stimulation frequencies was examined: the evoked release of GABA was linearly related to frequency whereas that of taurine was frequency-independent. The fall in aspartate and glutamate release was maximal at a frequency of about 50 Hz. 6. The results are discussed in relation to (a) the possible sites of release of the amino acids and (b) the proposed neurotransmitter roles of the physiologically active amino acids.     

Striatal microinjections of nitric oxide synthase inhibitors and L-arginine fail to exert effects on paroxysmal dystonia in the dtsz mutant

Primary dystonia is a common movement disorder with an unknown pathophysiology, but basal ganglia dysfunctions seem to play a critical role. Previous studies in the dtsz mutant hamster, an animal model of primary paroxysmal dystonia, demonstrated a deficit of striatal gamma-amino-butyric acid (GABA) containing interneurons, which normalized at the age of the spontaneous remission of the symptoms. Whereas the reduction of striatal parvalbumin-reactive interneurons is thought to be critically involved in the pathogenesis of dystonia in the hamster mutant, the impact of a reduced density of nitric oxide synthase (NOS) reactive interneurons within the striatum is still unclear. Beside GABA, these interneurons contain somatostatin, neuropeptide Y, nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and neuronal NOS, an enzyme which produces NO after the activation of the interneurons. In order to clarify if the reduced density of NOS-reactive interneurons contributes by an altered striatal production of nitric oxide (NO) to the occurrence of dystonic attacks in the hamster mutant, we performed microinjections of the NOS inhibitors 7-nitroindazole (7-NI) and Nomega-propyl-L-arginine (NPLA) and of the precursor of NO, L-arginine, into the striata of dtsz hamsters. Neither 7-NI (0.1 and 0.4 microg per hemisphere) and NPLA (2.5, 5 and 7.5 microg per hemisphere) nor L-arginine (9 and 18 microg per hemisphere) exerted any effects on the severity of dystonic movements in the dtsz mutant. Therefore, a critical involvement of striatal changes of NO in the pathophysiology of dystonic attacks in the dtsz hamster cannot be confirmed by the results of these pharmacological examinations. In view of the ontogenetic reduction of the other types of GABAergic interneurons, the deficit of NOS-reactive interneurons is possibly due to the same underlying unknown mechanism, but is less important for the pathophysiology of primary paroxysmal dystonia in the dtsz hamster mutant.     

Regional decreases in NK-3, but not NK-1 tachykinin receptor binding in dystonic hamster (dt(sz)) brains

Although the pathophysiology of primary dystonias is currently unknown, it is thought to involve changes in the basal ganglia-thalamus-cortex circuit, particularly activity imbalances between direct and indirect striatal pathways. Substance P, a member of the tachykinin family of neuropeptides, is a major component in the direct pathway from striatum to basal ganglia output nuclei. In the present study quantitative autoradiography was used to examine changes in neurokinin-1 (NK-1) and neurokinin-3 (NK-3) receptors in mutant dystonic hamsters (dt(sz)), a well characterized model of paroxysmal dystonia. NK-1 receptors were labeled in 10 dystonic brains and 10 age-matched controls with 3 nM [(3)H]-[Sar(9), Met(O(2))(11)]-SP. NK-3 binding sites were labeled in adjacent sections with 2.5 nM [(3)H]senktide. NK-1 binding was found to be unaltered in 27 brain areas examined. In contrast, NK-3 binding was significantly reduced in layers 4 and 5 of the prefrontal (-46%), anterior cingulate (-42%) and parietal (-45%) cortices, ventromedial thalamus (-42%) and substantia nigra pars compacta (-36%) in dystonic brains compared to controls. The latter effects may be particularly relevant in view of evidence that activation of NK-3 receptors on dopaminergic neurons in the substantia nigra pars compacta can increase nigrostriatal dopaminergic activity. Since previous studies indicated that a reduced basal ganglia output in mutant hamsters is based on an overactivity of the direct pathway which also innervates substantia nigra pars compacta neurons, the decreased NK-3 binding could be related to a receptor down-regulation.The present finding of decreased NK-3 receptor density in the substantia nigra pars compacta, thalamic and cortical areas substantiates the hypothesis that disturbances of the basal ganglia-thalamus-cortex circuit play a critical role in the pathogenesis of paroxysmal dystonia.     

Changes in the concentration of amino acids in the hippocampus of pentylenetetrazole-kindled rats

It is not well recognized how disturbances in the local metabolism of some amino acids, especially glutamate and GABA, may lead to seizures. In the presented study, we have examined changes in the hippocampal steady state concentrations of amino acids involved in pentylenetetrazole-kindled and freely moving rats. It was found that in the kindled animals, the concentration of alanine, arginine, glutamate, aspartate and taurine was increased in the interictal period of seizures compared to the control group, whereas kindling reduced the extracellular levels of GABA. No differences between kindled and not-kindled animals in the glycine, histidine and glutamine levels were present. There also appeared an over fourfold increase of the Glu/GABA ratio, a theoretical marker of the neuronal excitation level, in the kindled animals. A multivariate classification tree analysis showed that the hippocampal concentration of taurine, together with GABA and Glu, had the relatively largest prediction accuracy in discriminating between kindled and non-kindled animals, suggesting a specific role of these amino acids in the shaping of a new equilibrium between excitatory and inhibitory processes in the hippocampus of kindled animals.     

Hydrogen sulfide exposure alters the amino acid content in developing rat CNS

Hydrogen sulfide is a widespread environmental pollutant that may produce severe effects on the developing nervous system. Putative amino acid neurotransmitter levels in the rat cerebrum and cerebellum were determined to evaluate the effects of exposure to hydrogen sulfide during perinatal development. The levels of aspartate, GABA, glutamate, glycine and taurine were quantitated using high-performance liquid chromatography. With the exception of glycine, all of the amino acids examined were affected by the treatment. On day 21 postnatal, which was the last day of the exposure, aspartate, glutamate and GABA in the cerebrum and aspartate and GABA in the cerebellum were significantly depressed. The observed alterations in the amino acid levels during this critical phase of development may have chronically affected the activity of the neurotransmitters, their receptor sensitivity or their individual target areas. The consequence of one or a combination of such alterations may lead to behavioral and structural abnormalities.     

Immunocytochemical localization of amino acid neurotransmitter candidates in the ventral horn of the cat spinal cord: a light microscopic study

The distribution of immunoreactivities to six amino acids, possibly related to synaptic function, was investigated in the motor nucleus of the cat L7 spinal cord (laminae VII and IX) using a postembedding peroxidase-antiperoxidase technique. Consecutive 0.5 m transverse sections of plastic-embedded tissue were incubated with antisera raised against protein-glutaraldehyde conjugates of -aminobutyric acid (GABA), glycine, aspartate, glutamate, homocysteate, and taurine. This method allowed localization of the different immunoreactivities in individual cell profiles. The results showed that all these amino acids, except homocysteate, could be clearly detected in either neuronal or glial elements in the ventral horn. In cell bodies of neurons in lamina VII, immunoreactivity was observed for aspartate, glutamate, GABA, and glycine. Adjacent section analysis revealed that combinations of immunoreactivity for glycine/glutamate/aspartate, GABA/glycine/glutamate/aspartate and glutamate/aspartate, respectively, may occur in one and the same cell. In the motor nuclei (lamina IX), immunoreactivity to amino acids was observed in two types of neuron. Large cells, probably representing -motoneurons, were harboring immunoreactivity to both glutamate and aspartate, while a few small neurons in this area displayed a colocalization of glycine, glutamate, and aspartate. Dendrites and axons in the motor nuclei cocontained glycine/glutamate/aspartate, GABA/glycine/glutamate/aspartate, and glutamate/aspartate immunoreactivities. In both laminae VII and IX, taurine-like immunoreactivity was absent in neuronal cell bodies, but highly concentrated in perivascular cells and small cells with a morphology resembling that of glial cells. A punctate immunolabeling, in all probability representing labeling of nerve terminals, could be demonstrated in the ventral horn for GABA, glycine, and glutamate, but not with certainty for aspartate or taurine. A quantitative estimate of the covering of cell bodies of -motoneuron size by immunoreactive puncta revealed that glycine immunoreactive terminal-like structures were most abundant (covering 26–42% of the somatic membrane), while glutamate immunoreactive terminals were seen least frequently (5–9% covering). GABA-immunoreactive terminals covered from 10 to 24% of the soma surface. A colocalization of GABA and glycine immunoreactivities in putative nerve terminals could be shown both in the neuropil and in close relation to cell bodies of motoneurons. These results suggest that among the studied amino acids probably only three, namely GABA, glycine, and glutamate, can be considered to be neurotransmitter candidates in the ventral horn of the cat spinal cord.     

Extracellular levels of amino acids in striatum and globus pallidus of 6-hydroxydopamine-lesioned rats measured with microdialysis

Extracellular aspartate, glutamate, glutamine, taurine and GABA concentrations were measured by microdialysis in the rat striatum and globus pallidus after a unilateral 6-hydroxydopamine lesion of the dopamine system. The basal and potassium-evoked overflow of GABA was increased in the ipsilateral striatum, but the evoked overflow was decreased in both contralateral striatum and pallidum. Both basal and evoked overflow of glutamate was increased in ipsilateral striatum. The basal overflow of aspartate was significantly increased in the ipsilateral side. Basal glutamine on the other hand was decreased in the ipsilateral side. Taurine remained unchanged in both regions. These results suggest that dopamine is involved in the regulation of transmission by GABA and glutamate. Since glutamine might be the precursor to glutamate, the change in glutamate might affect the glutamine level. The changed aspartate level has no obvious explanation.     

Inhibition of aspartate release from the retina of the anaesthetised rabbit by stimulation with light flashes.

Rabbits were anaesthetised and the cornea, iris, lens and vitreous were removed from eyes to form an eye-cup which was filled with Krebs-bicarbonate Ringer. The medium in the eye-cup was replaced at 10-min intervals and the amino acids in each resulting sample were assayed. Exposure of the dark-adapted retina to flashes of light (3 Hz) did not alter the efflux of glutamate glutamine, alanine, glycine or GABA. The efflux of taurine and ACh was greatly increased by light flashes, but in contrast, the release of aspartate was reduced by more than 50%, a result consistent with the suggestion that aspartate may be a photoreceptor transmitter substance.     

Levels of neurotransmitter amino acids in the cerebrospinal fluid of patients with acute ischemic insult

The dynamics of excitatory (glutamate, aspartate) and inhibitory (GABA, glycine) neurotransmitter amino acid contents in the cerebrospinal fluid were studied in 110 patients with hemispheric ischemic insult. These studies revealed significant increases in the levels of glutamate and aspartate in the first six hours of illness, and the level and duration of these changes correlated with the severity of the insult. Peak GABA and glycine levels were seen at the end of the first day after strokes, reflecting the delayed activation of the mechanisms of protective inhibition. The insufficiency of GABAergic mediation in strokes located in the hemispheres to a significant extent mirrored the severity of clinical features and the potential of restorative processes. Early significant biochemical criteria were identified for objective assessment of the severity of brain ischemia, and these had pronostic value for the course and outcome of strokes. The most unfavorable prognostic signs were the presence of low (or undetectable) GABA levels in the first days after insult and progressive increases in aspartate levels to the third day on the background of sharp reductions in glutamate levels (after initial elevation on the first day). Translated from Zhurnal Nevrologii i Psikhiatrii imeni S. S. Korsakova, Vol. 99, No. 2, pp. 34–38, February, 1999.     

Are amino acid patterns necessarily abnormal in epileptic brains? studies on the genetically seizure-susceptible rat

Free amino acid concentrations have been compared in brain regions from genetically seizure-susceptible and seizure-resistant rats. No significant differences were found in either the inferior colliculus, a region of low electroshock threshold in seizure-susceptible animals, or in the ?, a region of high electroshock threshold. No changes were found in the ratios between glutamate, glutamaine, taurine, GABA or glycine. These findings invalidate the universality of the hypothesis linking seizure susceptibility to imbalances in glutamate: glutamine ratio. It has been proposed that the anticonvulsant action of taurine is due to rectification of abnormal glutamate levels. Taurine is a potent anticonvulsant in the seizure-susceptible rat, yet no imbalances of glutamate content are present.     

Regional alterations in brain amino acids after administration of the N-methyl-D-aspartate receptor antagonists MK-801 and CGP 39551 in rats.

The effects of the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and the novel competitive NMDA receptor antagonist CGP 39551 on levels of 11 amino acids, including several excitatory and inhibitory neurotransmitters, were studied in 12 brain regions of rats. Both drugs were administered at doses which produced comparable behavioural effects (ataxia, hyperactivity). Amino acids were determined in brain tissue by high-performance liquid chromatography after o-phthaldialdehyde precolumn derivatization. MK-801 (0.1 mg/kg, i.p.) moderately increased the concentration of glutamate and GABA in several brain regions. Other amino acids (glutamine, taurine, asparagine, alanine, serine) were only altered in single brain regions, or were not altered at all (aspartate, glycine, threonine, arginine). In contrast to MK-801, CGP 39551 (10 mg/kg, i.p.) increased glutamate levels only in the cerebellum, and produced no significant alterations in levels of GABA. The data demonstrate differences in alterations of amino acid levels in response to competitive and non-competitive NMDA receptor antagonists and support the assumption that competitive NMDA antagonists may be more selective than non-competitive antagonists.     

Regional distribution and extracellular levels of amino acids in rat central nervous system

The extracellular levels of aspartate, glutamate, serine, glutamine, glycine, alanine and GABA were studied in vivo with the microdialysis technique in 15 different regions of the rat brain. The effect of high K+ on the overflow of these amino acids was also studied. These results were compared with those from a regional dissection of 17 brain regions in which the tissue content of the same amino acids was determined. The in vivo data showed an unevenly distributed KCl response of aspartate, glutamate, taurine and GABA, all of which are putative neurotransmitters. It was not possible to predict the response to high K+ from the magnitude of the unstimulated overflow. Glutamine overflow was inversely related to that of glutamate during the high K+ stimulus, which is consistent with glutamine being the main precursor of glutamate. Only for GABA and alanine was overflow proportional to the tissue level in the different regions studied.     

Expression of cholecystokinin, somatostatin, thyrotropin-releasing hormone, glutamic acid decarboxylase and tyrosine hydroxylase genes in the central nervous motor systems of the genetically dystonic hamster

In the dt ^sz mutant hamster with idiopathic generalized dystonia, functional abnormalities of several neurotransmitters have been suggested to play a role in the development of symptoms. In the present study, we have used histochemistry with ³⁵S-ATP labeled oligonucleotides to determine whether these abnormalities are associated with modulation in the expression of neurotransmitter genes in motor regions. We examined the expression of genes encoding cholecystokinin (CCK), somatostatin (SRIF), thyrotropin-releasing hormone (TRH), glutamic acid decarboxylase (GAD), tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP43) in the cortex and basal ganglia of dystonic hamsters and of non-dystonic control hamsters of a related inbred line and of a non-related outbred line. The distribution of these mRNAs in normal hamster brain was similar to that in normal rat brain. In all cortical regions studied (frontal, parietal and piriformis), the expression of CCK was similar in dystonic and inbred controls but was significantly greater than in outbred controls. In the anterior thalamus, CCK expression was lower in dystonic hamsters than in both control groups. SRIF expression was significantly decreased in the cortex and striatum of dystonic animals than in inbred and outbred control hamsters. GAD expression was lower in the striatum and substantia nigra, pars reticulata of dystonic than in outbred hamsters, but similar values were found in all groups in the other regions studied. TH was lower in the substantia nigra of dystonic than in inbred controls. No changes were found in GAP43 expression. This study demonstrates that changes in modulation of the expression of some peptides and neurotransmitter enzymes can be found in the dystonic hamster, which is in contrast to other animal models such as the dystonic rat, where no such changes have been found. The present data are consistent with previous findings in dt ^sz hamsters that suggest a dysfunction within the basal ganglia-thalamocortical circuits. Received: 29 June 1998 / Accepted: 17 May 1999     

A significant reduction of putative transmitter amino acids in cerebrospinal fluid of patients with Parkinson's disease and spinocerebellar degeneration.

We evaluated the concentrations of the putative transmitter amino acids in the cerebrospinal fluid, and found a significant reduction of glutamate, aspartate, gamma-aminobutyric acid (GABA), and glycine concentrations in parkinsonian patients. There was no difference in amino acid concentrations between parkinsonian patients receiving L-DOPA and those not receiving L-DOPA. A similar decrease of glutamate and aspartate concentrations was found in patients with spinocerebellar degeneration. Concentrations of asparagine, glycine and taurine were also significantly decreased in patients with late cortical cerebellar atrophy.     

Regional heterogeneity in the distribution of neurotransmitter markers in the rat hippocampus.

A detailed neurochemical analysis of the distribution of markers for the most relevant neurotransmitter systems within the rat hippocampal formation has been performed. The hippocampi, obtained from unfrozen brains of male Sprague-Dawley rats were subdissected into tissue parts containing mainly CA1, CA3 or the dentate gyrus, respectively. Each part was further divided into ventral and dorsal halves. In these six hippocampal subregions the concentrations of noradrenaline, dopamine, serotonin, 3-methoxy-4-hydroxyphenylglycol, 5-hydroxyindoleacetic acid and the putative neurotransmitter amino acids glutamate, aspartate, GABA, glycine and taurine, and the levels of somatostatin and neuropeptide Y and the activities of choline acetyltransferase, acetylcholinesterase and glutamate decarboxylase were measured. A marked heterogeneity in the subregional distribution of markers for various neurotransmitter systems within the hippocampal formation was observed. Each neuronal marker was characterized by an individual pattern of distribution. Most of the markers showed a concentration-gradient, increasing from dorsal to ventral; only taurine was more abundant in the dorsal than in the ventral parts and no dorsoventral difference was seen for aspartate, glycine and neuropeptide Y. The highest molar ratios of total 3-methoxy-4-hydroxyphenylglycol to noradrenaline and 5-hydroxyindoleacetic acid to serotonin were found in the dorsal hippocampus. The levels of noradrenaline, GABA and glutamate decarboxylase activity were highest in the dentate gyrus and lowest in CA1. The concentrations of somatostatin were highest in CA1; those of serotonin were highest in CA3. Highest activities of choline acetyltransferase and acetylcholinesterase were found in the dentate gyrus; lowest activities were found in CA3. In CA3 the lowest values of glutamate, aspartate, taurine and somatostatin were also found. The heterogeneity in the distribution of individual neurochemical markers allows insights into possible functional differences of hippocampal subregions and provides a relevant basis for future neurochemical investigations in this brain area.     

Aspartate, glutamate and gamma-aminobutyric acid depolarize cultured astrocytes

Cultures of differentiated, glial fibrillary acidic protein-positive astrocytes from early postnatal rat cerebral hemispheres respond with depolarization of 2-36 mV to glutamate, gamma-aminobutyric acid (GABA) and aspartate but not to glycine or taurine. While GABA resulted in a transient depolarization, the effect of glutamate and aspartate persisted during the application. Since neurons were not present in these cultures a contribution of transmitter-mediated K+ release from adjacent neurons could be excluded. The depolarization triggered by these neurotransmitters is therefore an intrinsic reaction of astrocytes.