Search

Basal forebrain tissue fragments taken from embryonic day 15 were separated into primary astrocytes and primary neurons in culture and grafted to rats with alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid lesions to the nucleus basalis and medial septal regions. The two cell types were compared in two experimental paradigms for their behavioural, biochemical and histochemical effects; standard transplants of whole basal forebrain and sham transplants served as positive and negative controls, respectively. Each transplant cell type was characterised by in vitro immunocytochemistry to assess content and purity. Memory deficits produced by the lesions in a spatial win-stay T-maze task (Experiment 1) and a spatial plus associative radial maze task (Experiment 2) were significantly improved by the astrocyte, but not by the neuronal, primary cell transplants. The astrocyte graft groups performed as well as standard cholinergic rich basal forebrain groups, reaching control levels on both tasks, while the neuronal transplant groups were not significantly different to lesioned (sham transplanted) rats. There was no recovery in choline acetyltransferase activity in brain regions containing astrocyte grafts whereas activity in the neuronal graft regions was increased (often to control levels), similar to recovery produced by basal forebrain grafts. Grafts in all groups survived, transplanted neurons displaying similar morphology and placement in the host brain to unseparated basal forebrain grafts, while astrocytes showed evidence of migration. The cultured astrocytes were estimated to be > 95% pure, showing positive staining for all astrocyte markers and an absence of staining for neuronal markers. The results indicate that the restoration of cognitive function following fetal grafting is not dependent upon a restoration of cholinergic neuronal activity but is more likely mediated via diffuse graft-host communication, with trophic secretion a probable factor. This study emphasizes the usefulness of astrocytes in the repair of central nervous system injury and has implications for therapeutic potential.

In a number of recent studies attempts have been made to determine the subcellular origin of the released transmitter by comparison of the ratio of the radioactivity (14C/3H) of true and false transmitters between those released by stimulation and the subcellular fractions. It is shown that use of the isotopic or pseudo-molar ratios will lead to incorrect conclusions because varying degrees of isotopic dilution render the ratio meaningless. The only correct basis for comparison is the true molar ratio.

Oral administration of ethanol (20% v/v) to male Sprague-Dawley rats for different periods of time up to 28 weeks resulted in profound reductions of acetylcholine content, in vitro synthesis and release of acetylcholine, choline uptake, activities of choline acetyltransferase, acetylcholinesterase and pyruvate decarboxylase, content of noradrenaline, serotonin and, to a lesser extent, dopamine throughout the brain. Changes were fully and partially reversible by a 4 weeks' ethanol-free period following a treatment of 8 and 18 weeks, respectively. They remained persistent, however, after 28 weeks of treatment. Performance in an eight arm-radial maze revealed a severe impairment in both spatial and non-spatial reference and working memory. A similar pattern of memory impairment was obtained after ibotenate lesion of the cholinergic basal forebrain projection system. In order to test whether this memory impairment depends on cholinergic deafferentation of the cortex, cholinergic-rich fetal basal forebrain cell suspensions were transplanted into cortex, hippocampus or both these sites in ethanol treated rats. Cholinergic-rich transplants, but not cholinergic-poor transplants, were effective in ameliorating impaired memory function and measures of cholinergic activity in the basal forebrain projection system. The behavioural efficacy of the basal forebrain grafts was well correlated with measures of both transplant volume and the degree to which they restored acetylcholine content at the transplant site; these transplants had no effect, however, on brain monoamine levels. The effects of the cholinergic-rich transplants into cortical and hippocampal sites were additive in their amelioration of performance in the radial maze. Similarly, ibotenate lesions of the sites of origin of the cholinergic projections to neocortex (in the region of the nucleus basalis magnocellularis) and hippocampus (the medial septal areas and nucleus of the diagonal band), respectively, were additive in their deleterious effects on maze performance. There were no qualitative differences in the susceptibility of the four different types of memory performance measured (spatial and non-spatial reference and working memory) to the effects of ethanol, ibotenate lesions of the cholinergic projection system, or cholinergic-rich brain tissue transplants. Thus, overall, the results indicate that the forebrain cholinergic system acts as a whole, without major functional differences between the projections originating in the medial septal area/diagonal band complex and the basal nucleus, and that it discharges a very general function in cognitive processes.(ABSTRACT TRUNCATED AT 400 WORDS)

3,3-Dimethylbutanol (Dimbunol), a competitive inhibitor of choline dehydrogenase (CDH), and ethylcholine mustard aziridinium (ECMA), an effective irreversible inhibitor of both CDH and choline transport, were investigated for their effects upon the uptake and metabolism of [3H]choline in mice. Thirty minutes after Dimbunol administration (i.p. 0.5 mmoles/kg) a reduction in the rate of choline oxidation was accompanied by an inhibition of choline phosphorylation in the kidney. Choline had accumulated to 5-fold the control level. After ECMA (i.v. 4 mumoles/kg), kidney choline was elevated 18-fold and both oxidation and phosphorylation rates were severely inhibited. In the liver Dimbunol inhibited oxidation and phosphorylation of choline and generated a 2-fold rise in tissue choline. Ethylcholine mustard aziridinium inhibited both oxidation and phosphorylation in the liver to the same extent as in the kidney but produced only a 3-fold elevation of choline. Dimbunol failed to elevate serum choline 30 min after administration and brain choline and acetylcholine levels were also unchanged. Serum choline was doubled by ECMA. These studies suggest that both transport across the renal tubules and oxidation may be important in choline regulation, that high levels of choline may accumulate in the liver and kidney which are not available for acetylcholine synthesis but that longer term studies on the effects of Dimbunol might reveal useful ways of facilitating sustained elevation of serum choline in precursor therapy.