N‐methyl‐D‐aspartate (NMDA) receptors are composed of subunits from two families: NR1 and NR2. We used a dual‐label in situ hybridization technique to assess the levels of NR1 and NR2A‐D messenger ribonucleic acid (mRNA) expressed in projection neurons and interneurons of the human striatum. The neuronal populations were identified with digoxigenin‐tagged complementary RNA probes for preproenkephalin (ENK) and substance P (SP) targeted to striatal projection neurons, and somatostatin (SOM), glutamic acid decarboxylase 67 kD (GAD67), and choline acetyltransferase (ChAT) targeted to striatal interneurons. Intense NR1 signals were found over all striatal neurons. NR2A signals were high over GAD67‐positive neurons and intermediate over SP‐positive neurons. ENK‐positive neurons displayed low NR2A signals, whereas ChAT‐ and SOM‐positive neurons were unlabeled. NR2B signals were intense over all neuronal populations in striatum. Signals for NR2C and NR2D were weak. Only ChAT‐positive neurons displayed moderate signals, whereas all other interneurons and projection neurons were unlabeled. Moderate amounts of NR2D signal were detected over SOM‐ and ChAT‐positive neurons; GAD67‐ and SP‐positive striatal neurons displayed low and ENK‐positive neurons displayed no NR2D hybridization signal. These data suggest that all human striatal neurons have NMDA receptors, but different populations have different subunit compositions that may affect function as well as selective vulnerability. J. Comp. Neurol. 419:407–421, 2000. © 2000 Wiley‐Liss, Inc.

Changes in mRNA levels of N-methyl-D-aspartate receptor (NR) subunits were studied in a rat model of withdrawal from forced ethanol ingestion over a period of 8 days. In part, this model may reflect the epsilon-type of human alcoholism according to Jellinek (College University Press, New Haven; 1972). The epsilon-type is characterized by dipsomania over a period of several days, recurring every few months and often followed by ethanol-induced seizures. Seizures may be modulated by an increased glutamatergic neurotransmission to excitatory or inhibitory neurons on the basis of a changed gene expression of NR subunits. This hypothesis promoted the present study. Film autoradiograms and emulsion-coated brain sections following labeling of cholinergic and GABAergic neuron populations were evaluated. NR subunit 1 (NR1) expression, studied with a probe recognizing all NR1 transcripts, was unchanged after withdrawal from chronic ethanol treatment compared to control animals. Using probes specific for different splice segments of NR1, however, we found that, in ethanol-treated rats, the expression of NR1-2 was decreased in all, and that of NR1-4 in all but one, areas investigated (only single label experiments were performed with NR1 splice variants). Withdrawing rats revealed a higher expression of NR subunit 2A (NR2A) mRNA in GABAergic neurons. No changes could be observed at the regional level. Conversely, NR2B mRNA was not substantially altered in cholinergic and GABAergic neurons, but showed a decrease over brain areas. For both, NR2C and NR2D, no ethanol-related changes of mRNA expression were observed. A link between such differential alterations in NR mRNA subunit expression and ethanol-induced seizures in withdrawing alcoholics of the epsilon-type seems possible.

Abstract:Epilepsy affects a huge number of patients by severe disruption of brain functions and is characterised by recurrent seizures, sometimes hard to be treated by medications.Seizure induced cellular consequences in ionic gradient and homeostasis are expected to result in electrophysiological differences between epileptic and non-epileptic neurons.In the following work we demonstrate these differences in layer III cortical pyramidal neurons sourced from epileptic and non-epileptic human patient tissue. Although visually indistinguishable and featuring similar membrane potentials and latency to first spikes upon whole cell patch stimulation, epileptic pyramidal neurons display a larger rheobase and a smaller membrane resistance, responding less efficiently to electrical stimulation than their peri-tumorous equivalents.This decreased excitability contradicts results in comparable animal models of epilepsy and was further corroborated by detailed analysis of spiking characteristics and phase plot analysis of these events. Both point to an overexpression of K + channels trying to compensate for the hyperexcited, epileptic network state. A computational model of a pyramidal neuron was utilized to give an estimate of the needful relative changes in K + and Na + conductances.not peer-reviewed)

A model of electrically evoked release of glutamate from rat hippocampus was developed and used to detect possible changes induced by lesions of hippocampal afferences. Neuronal glutamate in hippocampal slices was labelled by preincubation with [3H]glutamine. The slices were then superfused with physiological medium in the presence of the glutamate uptake inhibitor L-transpyrrolidine-2,4-dicarboxylic acid (100 microM or 3 microM) and stimulated twice electrically (S1, S2: 240 pulses, 3 Hz, 2 ms, 26-30 mA); various drugs were added before S2. In order to determine the basal and evoked outflow of [3H]glutamate only, the mixture of 3H-labelled compounds (glutamine, glutamate and GABA) was separated by ion exchange chromatography in superfusate fractions and slices. The electrically evoked overflow of [3H]glutamate was largely Ca2+-dependent and tetrodotoxin-sensitive and hence represented action potential-induced exocytotic release of [3H]glutamate. Evoked [3H]glutamate release was significantly increased by the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 microM), suggesting the presence of endogenous inhibitory adenosine, and reduced by the A1 receptor agonist N6-cyclopentyladenosine (1 microM, antagonized by DPCPX, 0.1 microM). There was no evidence for a cholinergic, serotonergic, or adrenergic modulation of the evoked release of [3H]glutamate: the corresponding selective agonists (or antagonists) were ineffective. After aspirative lesions of the septohippocampal pathways the hippocampal noradrenaline content was markedly increased, whereas cholinergic and serotonergic markers were reduced. The evoked release of [3H]glutamate in hippocampal slices of lesioned rats was significantly increased by a mechanism which still has to be determined, but which is not related to alterations in A1 receptor function. It is concluded that the present model was able to detect lesion-induced differences in electrically evoked release of [3H]glutamate, but the relationship of these differences to changes of noradrenergic, cholinergic or serotonergic hippocampal innervations remains to be established.