Early changes in acetylcholine pools in the hippocampus of the rat brain after septal lesions

Effect of atropine and gammahydroxybutyrate on ischemically induced changes in the level of radioactivity in [3H]inositol phosphates in gerbil brain in vivo

Brain ischemia in gerbils was induced by ligation of both common carotid arteries for 1 min or 10 min. Sham-operated animals served as controls. Intracerebral injection of [3H]inositol into gerbil brain 16 hr before ischemic insult resulted in equilibration of the label between inositol lipids and water-soluble inositol phosphate. A short ischemic period (1 min) resulted in a statistically significant increase in the radioactivity of inositol triphosphate (IP3) and inositol monophosphate (IP), by about 48% and 79%, respectively, with little change in that of the intermediate inositol biphosphate (IP2), which increased by about 16%. When the ischemic period was prolonged (10 min), an increase in the radioactivity of inositol monophosphate exclusively, by about 84%, was observed. The level of radioactivity in inositol phosphates IP2 and IP3 decreased by about 50%, probably as a consequence of phosphatase activation by the ischemic insult. The agonist of the cholinergic receptor, carbachol, injected intracerebrally (40 micrograms per animal) increased accumulation of radioactivity in all inositol phosphates. The level of radioactivity in IP3, IP2, and IP was elevated by about 40, 23, and 147%, respectively. The muscarinic cholinergic antagonist, atropine, injected intraperitoneally in doses of 100 mg/kg body wt. depressed phosphoinositide metabolism in control animals. The level of radioactivity in water-soluble inositol metabolites in the brain of animals pretreated with atropine was evidently about 32% lower than in untreated animals. Pretreatment with atropine decreased the radioactivity of all inositol phosphates in the brain of animals subjected to 1-min ischemia and the radioactivity of IP in the case of 10-min brain ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic enzymes in neocortex, hippocampus and basal forebrain of non-neurological and senile dementia of Alzheimer-type patients

Choline acetyltransferase (ChAT) activity and acetylcholinesterase (AChE) staining were examined in different cortical regions, hippocampal formation and basal forebrain of non-neurological controls and of patients afflicted with senile dementia of Alzheimer type (SDAT). Both enzymes showed a clear topographical distribution in the various regions studied. In SDAT cases, ChAT activity was reduced by 0-60% in the neocortex and by up to 97% in the hippocampus depending on the area and layer examined. In the nucleus of the diagonal band of Broca (NDB) and the medial septal nucleus (MSN), the activity was decreased by 65% and 55%, respectively; no significant change was found in the lateral septal nucleus (LSN), nucleus basalis of Meynert (NBM), substantia innominata (SI) and globus pallidus (GP). Comparable changes were seen in AChE staining. The results indicate that degeneration or dysfunction of cholinergic neurons in the medial septal area and possibly neocortex is an important characteristic of SDAT.

Cholinergic pharmacology of mammalian hippocampal pyramidal cells

Responses of CAl pyramidal cells to cholinergic compounds were recorded with intracellular microelectrodes in guinea-pig hippocampal slices. Perfusion of slices with medium containing the muscarinic antagonists atropine or scopolamine (10(-7)-10(-6)M) blocked all actions of acetylcholine. Properties of control neurons and those from separate populations of neurons impaled in slices exposed to muscarinic blocking agents were compared. 1-2 h of perfusion with atropine-containing media significantly decreased membrane input resistance from 37.6 +/- 8.7 (S.D.) M omega (n = 74) to 21.9 +/- 7.7 (S.D.) M omega (n = 24) without producing significant changes in membrane potential. Muscarinic antagonists also reduced or eliminated the anomalous inward rectification normally seen in hippocampal pyramidal neurons. Exposure of slices to 10(-5)-10(-6)M eserine for about 1 h produced changes in neuronal membrane input resistance and potential and slow after hyperpolarizations similar to those elicited by application of acetylcholine. Bethanechol mimicked the actions of acetylcholine but was effective at lower concentrations and had longer lasting effects on afterhyperpolarizations. Nicotine produced an excitatory response in only one of 7 neurons. These experiments demonstrate that the actions of acetylcholine on hippocampal CAl neurons result from interaction with muscarinic receptors. Acetylcholine has modulatory effects on cell membrane properties which may be mediated through tonic release mechanisms.

Decreased 3H-L-quinuclidinyl benzilate binding and muscarine receptor subsensitivity after chronic gamma-butyrolactone treatment

A significant decrease in the number of 3H-quinuclidinyl benzilate (3H-QNB) binding sites in striatal membranes was observed in rats exposed to gamma-butyrolactone (GBL) during 3 weeks. This decrease in 3H-QNB binding was not due to a direct effect of GBL on muscarine receptors since no alterations of binding were produced by high concentrations of GBL or of its active metabolite gammahydroxybutyric acid (GHB) when added in vitro. Challenge doses of pilocarpine were less effective in producing catalepsy and tremors in rats chronically treated with GBL. It is proposed that the partial inhibition of the nigro-striatal dopaminergic pathway produced by chronic GBL treatment leads to a persistent activation of the intrastriatal cholinergic interneurons, which are tonically inhibited by dopaminergic nigrostriatal neurons. The activation of striatal cholinergic interneurons results in a decreased number of muscarine receptors and in a lower sensitivity to cholinomimetic agents. Moreover, tolerance to the anesthetic effect of GBL was found to occur after chronic treatment with this drug. The brain levels of GHB at the time of regaining of the righting reflex were 50% higher in GBL pretreated animals then in controls. Indicating the tolerance to GBL-induced "sleep" is due to a decrease sensitivity of the effector to GHB rather than to a faster inactivation of elimination of the drug.

Alteration of acetylcholine synthesis in mouse brain cortex in mild hypoxic hypoxia

Acetylcholine synthesis in four brain regions (cerebral neocortex, hippocampus, septum and striatum) of the mouse during mild hypoxic hypoxia was measured by using [U-14C]glucose and [2H4]choline. At the same time, concentrations of norepinephrine and dopamine in four brain regions (cerebral neocortex, hippocampus, striatum and hypothalamus) were also estimated. During 12% O2 hypoxia, concentrations of acetylcholine in the striatum were significantly decreased (P less than 0.05), whereas [2H4]acetylcholine, lactate and glucose did not alter in any regions studied. During 12% O2 hypoxia, concentrations of choline and [2H4]choline were significantly increased in all regions examined (P less than 0.05), except the [2H4]choline inthe striatum. Radioactivity (dpm/100 mg protein) and specific activity (dpm/nmol) of acetylcholine were significantly decreased in the cerebral neocortex, hippocampus and septum (P less than 0.01) during 12% O2 hypoxia. A particularly marked decrease was found in the hippocampus, strongly suggesting that cholinergic terminals are particularly sensitive to hypoxia. In addition, these data also suggest that the acetylcholine synthesis from glucose might be more sensitive to hypoxia than that from choline. During 12% O2 hypoxia, concentrations of catecholamine did not alter in any regions examined, whereas during 9% O2 hypoxia dopamine was significantly decreased in the cerebral neocortex and hippocampus (P less than 0.05).

Effect of hypnotic and anxiolytic agents on regional concentration of acetylcholine in rat brain

Pentobarbital (30 and 60 mg/kg) and chloral hydrate (300 and 600 mg/kg) administered in anesthetic/hypnotic doses produced significant increases in acetylcholine concentration in the cerebral cortex, striatum, hippocampus and brainstem. Hypnotic/anxiolytic agents like diazepam, flurazepam (100 mg/kg each) and triazolam (30 mg/kg) significantly increased the acetylcholine concentration only in the cerebral cortex and striatum. Alprazolam and ketazolam had no significant effect on regional distribution of acetylcholine in the brain. The results have been discussed with respect to the role of central cholinergic system in anesthetic and hypnotic actions of these drugs.

Effect of anesthetic doses of gamma-hydroxybutyrate on the acetylcholine content of rat brain

Gamma-hydroxybutyrate administered in anesthetic doses produces a time dependent increase in the levels of rat barin acetylcholine. A maximal increase in whole brain and subcortical levels of acetylcholine is observed about 15 min after administration of the lactone form of the drug. A similar GHB-induced increase in acetylcholine is observed in the striatum and a 75% increase in the hippocampus 15 min after administration of the drug. A good temporal correlation was not obtained between the increase in acetylcholine and the depth of anesthesia produced by the drug. Gamma-hydroxybutyrate did not cause a significant change in the striatal or hippocampal levels of choline. Possible mechanisms involved in the production of this increase in acetylcholine are discussed.

Effects of anesthetics and septal lesions and stimulation on 3H-acetylcholine formation in rat hippocampus

The rate of 3H-acetylcholine (ACh) formation from i.v. injected 3H-choline was studied in the rat hippocampus after various treatments which alter the activity of cholinergic septal hippocampal neurons. Administration of pentobarbital and placement of acute septal lesion reduced the formation of 3H-ACh but did not change 3H-choline content. Chloral hydrate administration reduced the formation of 3H-ACh and also increased 3H-choline content. The chloral hydrate induced increase in 3H-choline occurred also in animals with chronic septal lesions. Electrical stimulation of the septum caused an increase in both 3H-ACh and 3/-choline. Chronic septal lesion caused a reduction in both radioactive and endogenous ACh, but did not affect radioactive or endogenous choline. These findings suggest that there are multiple pools of choline in the brain and that the precursor pool for ACh synthesis is difficult to measure. Overall, the parameter that best correlated with cholinergic activity was the level of 3H-ACh. Possible mechanisms, for this finding are discussed.