Neurotransmitters in Huntington's Chorea--a clinician's view

Somatostatin receptors in the central nervous system

Somatostatin was first identified chemically in 1973, since when much has been established about its synthesis, storage and release. It has important physiological actions, including a tonic inhibitory effect on growth hormone release from the pituitary. It has other central actions which are not well understood but recent cloning studies have identified at least five different types of cell membrane receptor for somatostatin. The identification of their genes has allowed studies on the distribution of the receptor transcripts in the central nervous system where they show distinct patterns of distribution, although there is evidence to indicate that more than one receptor type can co-exist in a single neuronal cell. Receptor selective radioligands and antibodies are being developed to further probe the exact location of the receptor proteins. This will lead to a better understanding of the functional role of these receptors in the brain and the prospect of determining the role, if any, of somatostatin in CNS disorders and the identification of potentially useful medicines.

Neural grafting in a rat model of Huntington's disease: progressive neurochemical changes after neostriatal ibotenate lesions and striatal tissue grafting

The acute and long-term changes following large neostriatal ibotenic acid lesions and intrastriatal striatal neuronal grafting have been studied neurochemically by determinations of the gamma-aminobutyrate (GABA) and acetylcholine-synthetic enzymes, glutamate decarboxylase and choline acetyltransferase, and of dopamine and its primary acidic metabolite, 3,4-dihydroxyphenylacetic acid. The neurochemical data have been matched with estimates of tissue volume changes and striatal graft development through tissue weight and protein content analysis and histological volumetric measurements. Injections of 20 micrograms ibotenic acid, deposited over four injection sites in the head of the caudate-putamen, had by one week caused a 70-85% reduction in glutamate decarboxylase and choline acetyltransferase activity. With time there was a progressive recovery of the specific enzyme activities in the lesioned areas (expressed per microgram protein or per mg wet weight) to 40-60% of control levels as determined at 20 weeks post-lesion in the caudate-putamen. This increase was, however, largely if not exclusively due to the long-term shrinkage of the lesioned caudate-putamen, amounting to 50-70% at 20 weeks. Thus, the total glutamate decarboxylase and choline acetyltransferase activity levels in the lesioned caudate-putamen remained virtually unchanged (between 15 and 25% of control) over the 20 week experimental period. Glutamate decarboxylase activity was also markedly reduced (35-70%) in the two primary striatal projection areas, globus pallidus and substantia nigra, and there were no signs of recovery over time. Striatal dopamine levels, which were acutely unaffected by the lesion, showed a slow decline so that the total dopamine content in the area was reduced by about 80% at 20 weeks. Suspended striatal neurons obtained from the striatal primordia of 14-15-day-old rat fetuses, injected into the previously lesioned caudate-putamen, survived and established a new striatum-like structure at the site of the ibotenic acid lesion. The final volume of the graft tissue reached up to about 10 mm3 in volume and reduced striatal atrophy on average from about 50 to 70% of normal control in the rats with lesions to about 30-40% in the animals with grafts. In the rats with grafts, there was a significant recovery of glutamate decarboxylase and choline acetyltransferase activities not only in the lesioned caudate-putamen, containing the graft (from 20-25% to 40-50%, when expressed as total enzyme activity levels), but also the glutamate decarboxylase activity in the globus pallidus, a structure located at a distance from the graft.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional neuronal replacement by grafted striatal neurones in the ibotenic acid-lesioned rat striatum

In rats, striatal neuronal destruction by so-called excitotoxic amino acids, kainic acid or ibotenic acid (IA) produce neuropathological and neurochemical changes in the basal ganglia which resemble those seen in patients with Huntington's chorea. Such lesioned animals show a behavioural syndrome which is reminiscent of the cardinal symptoms of the disease, accompanied by a substantial increase in local cerebral metabolic activity in several striatal target structures within the extrapyramidal motor system. The study was designed to explore the potential of grafted fetal striatal neurones implanted into the IA-lesioned striatum to compensate for the structural, neurochemical, metabolic and behavioural defects of IA-lesioned rats. Extending previous studies, we report here that such striatal implants can significantly ameliorate the lesion-induced locomotor hyperactivity and at least partly normalize the metabolic hyperactivity in the extrapyramidal neuronal system.

A polymorphic DNA marker genetically linked to Huntington's disease

Family studies show that the Huntington's disease gene is linked to a polymorphic DNA marker that maps to human chromosome 4. The chromosomal localization of the Huntington's disease gene is the first step in using recombinant DNA technology to identify the primary genetic defect in this disorder.