The release in vivo of [3-H] acetylcholine from cat caudate nucleus and cerebral cortex by atropine, pentylenetetrazol, K-+ -depolarization and electrical stimulation

Acetylcholine content and distribution in rat cortical synaptosomes after in vivo exposure to quinolinic acid

In this study, changes in the concentration and subcellular distribution of rat cortical synaptosomal acetylcholine (ACh) was investigated after a single injection of quinolinic acid (QUIN) into the nucleus basalis magnocellularis (nbM). In the P2 fraction of normal animals the ACh concentration was 235 +/- 18 pmol/mg protein. Of this, 64 +/- 10% was recovered in the particulate (P3) fraction and 24 +/- 1% in the soluble (S3) fraction. Cortical synaptosomes (P2) prepared 0.5 h after injecting either 600 or 1000 nmol of QUIN contained significantly higher concentrations of ACh (372 +/- 127 and 496 +/- 77 pmol/mg protein, respectively) when compared to the amount of ACh in control animals. The ACh concentration in the P2 fraction was still elevated 3 h after injecting 600 nmol QUIN, however, synaptosomal ACh decreased significantly 3 h after rats were treated with 1000 nmol QUIN. Determination of subcellular ACh 0.5 h after injecting QUIN revealed that neither dose of QUIN produced a change in the distribution of ACh between P3 and S3. However, 3 h after injecting QUIN, a shift in the subcellular distribution of ACh to the cytoplasmic fraction (S3) was observed with 1000 nmol QUIN. These results show that QUIN-induced depolarization of nbM neurons which project to the cortex produce both dose-dependent and time-dependent changes in synaptosomal ACh concentration and subcellular distribution.

CNS stimulation and PGE2 release. III. Pentamethylenetetrazole-induced seizures

Measurement of prostaglandin E2 (PGE2) in the ventriculocisternal perfusate of the halothane anesthetized, artificially ventilated cat has revealed low but measurable levels of the prostanoid (64 +/- 5 pg/min). Administration of pentamethylenetetrazole (PTZ) resulted in a rapid appearance of paroxysmal bursting, the magnitude and duration of which was dose dependent. During the 30-min interval after seizure initiation, PGE2 secretion rates into the ventriculocisternal perfusate rose by five- to sevenfold. Though the initial rate of PGE2 secretion correlated closely with the initial magnitude of bursting, there were significant differences, viz. the time courses. Thus, after a low dose of PTZ (200 mg/kg) the increase and return to normal of PGE2 secretion was time locked with the onset and offset of seizures. In contrast, after high doses of PTZ (250 mg/kg i.v.), seizure activity returned to near baseline by 90 min, while the levels of PGE2 secretion remained elevated for periods in excess of 150 min. Pretreatment with clonazepam (CLP: 3 mg/kg i.v. infusion) blocked seizures otherwise induced by PTZ (250 mg/kg) and the increase in PGE2 secretion. CLP administration 60 min after the initiation of seizures, blocked further seizure activity but did not alter the elevated secretion of PGE2. We thus believe these data jointly support the hypothesis that under intense paroxysmal bursting there is a change in neuronal state such that large stores of free fatty acids are available either because they have accumulated during the seizure because of a continued Ca2+ influx or the presence of large and continuing concentrations of Ca2+ accumulating in the cytosol secondary to energy failure.

Atropine infusions near the sexually dimorphic area of the gerbil hypothalamus facilitate hormonal induction of scent marking

The sexually dimorphic area (SDA) of the gerbil hypothalamus contains cells in which acetylcholinesterase activity is stimulated by testosterone. These cells are probably cholinoceptive. Because cholinoceptive cells and the SDA are both implicated in hormonal control of gerbil scent marking, marking was studied in castrated males given a low dose of testosterone systemically, and atropine, a cholinergic antagonist, near the SDA. Controls received saline near the SDA or atropine in the thalamus. Subjects were also tested for male sexual behavior, since it is also affected by the SDA. Infusing 25-35 micrograms atropine methyl nitrate near the SDA twice a week facilitated marking but did not affect mating. Experimental males marked more, whereas controls marked less, while receiving infusions, than they did before castration. The two control groups did not differ from each other. After infusions stopped, marking by experimental males decreased, though residual effects were detected in one test setting. The data suggest that a cholinoceptive system in or near the SDA participates in hormonal control of gerbil scent marking.

Local cholinergic mechanisms participate in the increase in cortical cerebral blood flow elicited by electrical stimulation of the fastigial nucleus in rat

We sought to determine whether the increase in regional cerebral blood flow (rCBF) elicited within the cerebral cortex (CX) by electrical stimulation of the fastigial nucleus (FN) of the cerebellum is: prevented by local application of the muscarinic cholinergic receptor antagonist, atropine and temporally correlated with a stimulus-locked release of acetylcholine (ACh) from the cortical surface. Rats were anesthetized, paralyzed, ventilated, with arterial blood gases controlled and arterial pressure maintained within the autoregulated range. Bilateral craniotomies were performed over a standardized region of the sensory motor CX and superfusion devices stereotaxically positioned on the cortical surface. Cortical surface temperature, as well as pH, pCO2 and pO2 of the solutions applied to the cortex were also carefully controlled. rCBF was measured in dissected regions of frontal (FCX), parietal (PCX), and occipital cortices (OCX), caudate nucleus (CN), and hippocampus (HIPP) by the Kety principle using [14C]iodoantipyrine as indicator. Resting rCBF (ml/100 g/min) in unoperated control animals ranged from 70 +/- 5 in HIPP to 95 +/- 7 in PCX and was unaffected by bilateral craniotomies and placement of superfusion devices containing Kreb's bicarbonate buffer (vehicle) on the cortical surface. Local application of atropine (ATR, 100 microM) to the right PCX via the superfusion device did not affect resting rCBF. With FN stimulation rCBF increased bilaterally and symmetrically in all areas up to 227% in PCX. ATR application attenuated by 59% the FN-elicited increase in rCBF on the ipsilateral frontoparietal CX, without affecting blood flow in adjacent structures. ATR did not affect cortical cerebrovasodilation produced by hypercarbia (arterial pCO2 = 59.0 +/- 1.4 mm Hg). FN-stimulation resulted in a small (22%) but significant (P less than 0.05, n = 9) reduction in the release of [3H]ACh from the cortical surface, while supramaximal depolarization with 55 mM K+ increased [3H]ACh release by 251%. These studies indicate that: increases in cortical rCBF elicited by FN stimulation, but not hypercarbia, are in large part mediated by local muscarinic cholinergic receptors; resting rCBF is not tonically affected by muscarinic receptor activation; and the release of ACh from the cortical surface is, in general, reduced during FN-stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Control of the release of newly synthetized 3H-5-hydroxytryptamine by nicotinic and muscarinic receptors in rat hypothalamic slices

The effects of various cholinergic agonists and antagonists on the spontaneous release of newly synthetized 3H-5-HT were examined in rat hypothalamic slices. 3H-5-HT was measured in incubating medium at the end of a 30 min incubation carried out with L-3H-tryptophan in the presence of the various drugs tested. ACh (10(-5) M) in the presence of eserine (2 X 10(-4) M), and carbachol (10(-5) M) stimulated the release of 3H-5-HT. In contrast, oxotremorine (10(-5) M) reduced the 3H-amine release. The effect of carbachol was blocked by two nicotinic blockers, mecamylamine (10(-6) M) and d-tubocurarine (10(-6) M). It was not reduced by the muscarinic antagonists, atropine (10(-6) M) and scopolamine (10(-6) M). In fact, each of two antagonists added alone to the incubating medium enhanced 3H-5-HT release. The scopolamine (10(-6) M) stimulating effect on 3H-5-HT release was suppressed by d-tubocurarine (10(-6) M). Finally, the inhibiting effect of oxotremorine on 3H-5-HT release was not prevented by d-tubocurarine (10(-6) M) but was in the presence of atropine (10(-6) M) or scopolamine (10(-6) M). In the concentrations used in the release study, the cholinergic agonists and antagonists had no effect on the total formation of 3H-5-HT and 3H-5-HIAA from L-3H-tryptophan and on the accumulation of L-3H-tryptophan in tissues. In these concentrations, except for eserine, they did not affect the uptake of exogenous 3H-5-HT in hypothalamic synaptosomes (P2 fraction). These results suggest that cholinergic receptors of the muscarinic and nicotinic type are involved in the control of 3H-5-HT release; since the stimulation of the muscarinic and nicotonic cholinergic receptors resulted in an inhibition and an activation of 3H-5-HT release, respectively. As in the case of peripheral noradrenergic and central dopaminergic neurons the cholinergic receptors could be localized on serotoninergic terminals.

Changes in regional brain acetylcholine levels during drug-induced convulsions

Acetylcholine (ACh) levels were determined in the brain of rats killed by decapitation or focussed microwave radiation during drug-induced convulsions. During metrazol or strychnine-induced convulsions a diffuse decrease in ACh levels was found in rats killed by decapitation. When the rats were killed by radiation and the brain was only divided into three large regions, strychnine caused no changes in ACh levels; metrazol caused a decrease in the cerebral cortex and lower brainstem. When discrete brain regions were investigated in rats killed by radiation, metrazol-induced convulsions were associated with a decrease in ACh level in all regions dissected and strychnine-induced convulsions with a decrease in the hippocampus and caudate nucleus only. Picrotoxin-induced convulsions were associated with a decrease in ACh level in the cerebral cortex, hippocampus, midbrain and medulla-pons, those induced by bicuculline with an increase in ACh level in the frontal cortex, hippocampus, midbrain and medulla-pons, by dimefline with an increase in the frontal cortex, midbrain and medulla-pons and a decrease in the caudate nucleus. The experiments show that each type of convulsant affects ACh levels in discrete brain regions in a different way.

Release of exqenous glycine in the pigeon optic tectum during stimulation of a midbrain nucleus

A pathway having an affinity for glycine has been investigated in the pigeon optic lobe; it originates in the nucleus isthmi pars parvocellularis (Ipc) and terminates in the tectum, In an attempt to obtain evidence that glycine plays a role as a transmitter in this system, the effect of electrical stimulation on release of labeled substances previously injected in the tectum was tested. By perfusing the upper strata of the optic tectum with a push-pull cannula the release of radioactive glycine was shown to be markedly increased by electrical stimulation of Ipc, but not by stimulation of other sites. Ipc stimulation did not affect the efflux of exogenous leucine or urea, whereas a GABA release was observed. With K+ (40 mM) stimulation all amino acids tested were released. It is suggested that the Ipc neuron terminals in the tectum take up glycine and release it upon stimulation of the Ipc nucleus.