AIDA, a class I metabotropic glutamate-receptor antagonist limits kainate-induced hippocampal dysfunction.

PURPOSE: In the developing animal, intraperitoneal injections of kainic acid (KA) lead to a prolonged initial seizure followed by chronic recurrent seizures and long-term hippocampal dysfunction. We investigated whether the class I metabotropic glutamate receptor (mGluR) antagonist 1-aminoindan-1,5-dicarboxylic acid (AIDA) is neuroprotective in the KA model of epilepsy. METHODS: Immature rats aged postnatal day 20 (P20) and P30 were injected with fixed volumes of KA, KA + AIDA, AIDA, or saline. We monitored recurrent seizures. Thirty days later, we tested hippocampal function with the Morris water-maze test or prepared hippocampal slices to record extracellularly evoked and spontaneous potentials from the CA1 area. In a third group, we performed neuronal counts. RESULTS: In both age groups, acute seizures were similar in KA and KA + AIDA groups. Rare spontaneous recurrent seizures occurred only in KA-injected rats. The KA P20 group performed significantly worse than controls in the water-maze test. The KA + AIDA group showed impaired performance on day 1, but learning improved substantially, reaching control values in the remaining 3 days. The P30 KA rats performed worse than controls on all trial days, whereas the KA + AIDA rats improved by day 3, but did not reach control values. Electrophysiologic recordings showed small but consistent differences between KA and control animals, suggestive of an adaptive modification in the gamma-aminobutyric acid (GABA)ergic system, reversed by AIDA. On histology, we observed a loss of CA1 interneurons in both ages. Cell loss was reversed by the use of AIDA. CONCLUSIONS: Blockade of the class I mGluR during KA-induced seizures in the developing brain limits seizure-induced hippocampal dysfunction.

Pentylenetetrazol-induced seizures in immature rats provoke long-term changes in adult hippocampal cholinergic excitability.

PURPOSE: We previously demonstrated that the anticholinesterase eserine provokes interictal-like discharges in the CA3 area of hippocampal slices from rats in which generalized seizures had been induced by pentylenetetrazol (PTZ) when immature. In this study, we investigated several factors as the possible mechanism for this effect, including age at convulsions. METHODS: Rats were injected with PTZ on postnatal day (P) 18-20 or >P60, and neuronal activity was recorded intra- and extracellularly from CA3 5-10 or >40 days later. In additional experiments, convulsions were triggered by kainate or were blocked by pentobarbital. Hippocampal (a) acetylcholine (ACh) innervation density was measured by immunocytochemistry, and ACh and gamma-aminobutyric acid (GABA) contents were determined by high-performance liquid chromatography (HPLC)-electrospray ionization. RESULTS: The excitatory effect of eserine was the most consistent in slices from rats PTZ-treated when immature and after the long interval, whereas the reverse was true in rats treated as adults. This effect was dependent on the occurrence of a seizure and was less prevalent when the seizure had been provoked by kainate. Adult animals PTZ-treated at P20 did not differ from control in (a) poly- or monosynaptic GABAA and GABAB CA3 inhibitory postsynaptic potentials (IPSPs); (b) density of ACh innervation; or (c) tissue content of ACh and GABA. CONCLUSIONS: A PTZ-induced generalized seizure in immature rat provokes endogenous ACh-induced interictal-like discharges in adult hippocampal CA3. This effect is only transiently observed if the seizure was induced in adult. It does not appear to be related to a change in GABAergic inhibition, in density of ACh innervation, or in ACh or GABA content.

Identification of a novel gene (HSN2) causing hereditary sensory and autonomic neuropathy type II through the Study of Canadian Genetic Isolates.

Hereditary sensory and autonomic neuropathy (HSAN) type II is an autosomal recessive disorder characterized by impairment of pain, temperature, and touch sensation owing to reduction or absence of peripheral sensory neurons. We identified two large pedigrees segregating the disorder in an isolated population living in Newfoundland and performed a 5-cM genome scan. Linkage analysis identified a locus mapping to 12p13.33 with a maximum LOD score of 8.4. Haplotype sharing defined a candidate interval of 1.06 Mb containing all or part of seven annotated genes, sequencing of which failed to detect causative mutations. Comparative genomics revealed a conserved ORF corresponding to a novel gene in which we found three different truncating mutations among five families including patients from rural Quebec and Nova Scotia. This gene, termed "HSN2," consists of a single exon located within intron 8 of the PRKWNK1 gene and is transcribed from the same strand. The HSN2 protein may play a role in the development and/or maintenance of peripheral sensory neurons or their supporting Schwann cells.