The site of origin of the seizure discharge produced by tubocurarine acting from the cerebral ventricles

Involvement of M1 muscarinic receptors in the initiation of cholinergically induced epileptic seizures in the rat brain

The present study was designed to determine the types of acetylcholine receptors involved in the initiation of epileptic seizures from the zona incerta and surrounding structures by cholinergic stimulation in rats. Unilateral intracerebral microinjection of the mixed muscarinic and nicotinic agonist carbachol (3 micrograms) produced generalized seizures in 12 of 20 rats studied. Local pretreatment with equimolar doses of acetylcholine receptor antagonists was used as a method of determining the receptor type involved in the initiation of cholinergically induced seizures in the rat diencephalon. Pretreatment with the M1 muscarinic receptor antagonist, pirenzepine (7 micrograms), abolished carbachol-induced seizures in 91% of the animals tested. The M2 muscarinic receptor antagonist, methoctramine (12 micrograms) and the nicotinic receptor antagonist, mecamylamine (3 micrograms), were relatively ineffective in antagonizing seizures in 9% and 27%, respectively. The results suggest that M1 muscarinic receptors are preferentially involved in the initiation of generalized epileptic seizures in the basal diencephalon of the rat.

Reversal of the central hypotensive effect of clonidine by intracisternal curare-like agents

Administration of tubocurarine, pancuronium, gallamine, or decamethonium into the cisterna magna of chloralosed dogs induced a rise in blood pressure. Clonidine (3 micrograms/kg) administered into the cisterna magna after tubocurarine, pancuronium, or gallamine significantly increased blood pressure; no significant change was found after decamethonium. The pressor response to clonidine after tubocurarine was antagonized by injection of the alpha 1-adrenoceptor-blocking agents AR-C 239 or prazosin into the cisterna magna at low doses prior to injection of clonidine. Yohimbine, a preferential alpha 2-adrenoceptor-blocking agent was ineffective. It is suggested that the pressor response to intracisternal clonidine after intracisternal tubocurarine is due to stimulation of alpha 1-adrenoceptor stimulation.

Central cardiovascular actions of d-tubocurarine and inhibition of the hypotensive effect of clonidine

Intracisternal (i. cist.) administration of d-tubocurarine (0.025-0. 100 mg. kg-1) in alpha-chloralose-anaesthetized dogs caused a dose-related increase in blood pressure associated with seizures. When injected in dogs pretreated with guanethidine (15 mg. i.v.), d-tubocurarine elicited the same effect while bilateral adrenalectomy abolished the pressor response. The hypotensive effect of clonidine (0.003 mg. kg-1 i. cist.) was reversed when clonidine was given after the alkaloid. These results suggest possbile interactions of the drugs at central GABA-ergic, glycinergic or cholinergic synapses.

Effects of propylbenzilylcholine mustard on injection into the liquor space of cats

In unanaesthetized cats the effects were examined of propylbenzilylcholine mustard (PrBCM) on injection into the cannulated cerebral ventricles and cisterna magna. Extreme motor excitation, vocalization, shivering leading to fever, tachypnoea, panting, piloerection and salivation were produced on ventricular, vigorous scratching bouts on cisternal, injections. The sites of these actions are discussed. None of the effects was produced by atropine similarly injected. All effects were suppressed by anaesthetizing doses of pentobarbitone sodium injected intraperitoneally.

Sleep induced by small doses of tubocurarine injected into cerebral ventricles of dog

In unanaesthetized dogs, sleep with the typical sleep pattern in the E.E.G. was produced with (+)-tubocurarine when injected in a small dose (500 ng) into, or perfused in low concentration (100 ng/ml) through the cerebral ventricles.

Blood pressure effects obtained by drugs applied to the ventral surface of the brain stem

1. In cats anaesthetized with pentobarbitone sodium the effect on arterial blood pressure was examined of substances applied bilaterally to the exposed ventral surface of the brain stem by means of Perspex rings placed lateral to the pyramids and caudal to the trapezoid bodies. Routinely, atropine methyl nitrate, which does not pass the blood-brain barrier, was injected I.V.2. The cholinomimetic substances carbachol and physostigmine, and the amino acids glycine and GABA, caused a fall in arterial blood pressure.3. Atropine produced a small but definite rise in arterial blood pressure, antagonized the depressor effects of the cholinomimetic substances, but not those of the amino acids.4. Strychnine, leptazol and tubocurarine, caused a rise in arterial blood pressure.5. The depressor and pressor effects are due to changes in vasomotor tone. They are central effects brought about by penetration of the substances into the brain tissue from the ventral surface of the brain stem. They are not due to their absorption into the blood stream.6. The depressor effects of the cholinomimetic substances may imitate the action of cholinergic neurones, and those of the amino acids that of central inhibitory neurones ending on cells near the ventral surface of the brain stem and exerting an inhibitory influence on vasomotor tone. The pressor effects of strychnine and tubocurarine may in part result from ;disinhibition', i.e. from an antagonistic action produced by these drugs on the amino acids released from the central inhibitory neurones.

Direct and indirect activation of the hippocampus by tubocurarine

1. In cats anaesthetized with intravenous chloralose, tubocurarine was either perfused through the inferior horn of a lateral ventricle or applied by micro-injection into the hippocampus, and the electrical activity was recorded from the surfaces of the occipital cortices and from the cannulae used for the perfusion or injection which, insulated except at their tips, served as recording electrodes as well.2. With both methods, the hippocampus became activated by tubocurarine acting directly on the hippocampus. The activation resulted in an abnormal spike discharge interrupted from time to time by short bursts of fast activity, termed episodes, followed by periods of electrical silence during which no abnormal activity was recorded. This abnormal discharge was recorded in all leads. The spikes were negative when recorded from the surface of the hippocampus, but changed polarity when the electrode was lowered and penetrated the pyramidal cell layer, and on further lowering the electrode the positive spikes increased in voltage up to 15 mV and then decreased.3. With both methods, signs of indirect activation of the hippocampus were observed when the tubocurarine set up foci of excitation in one of the following three areas of cerebral cortex which lie ventral to the hippocampus, the Area entorhinica, the Area perirhinica and the Area post-splenialis. The foci of excitation resulted in a continuous discharge of negative spikes which were recorded in the leads from these areas only. A characteristic feature of the indirect hippocampal activation arising from the continuous discharge set up in the Area post-splenialis was the periodicity. Activation lasting 20-60 sec occurred every few minutes or at shorter intervals, often leading to an episode.

Microinjections of tubocurarine, leptazol, strychnine and picrotoxin into the cerebral cortex of anaesthetized cats

1. In cats anaesthetized with intravenous chloralose, microinjections of tubocurarine, leptazol, strychnine or picrotoxin, in a volume of 1 mul, were made into the grey matter of the cerebral cortex and the electrical activity was recorded from the site of injection with the microinjection cannula which, insulated except at its tip, served as recording electrode.2. Routinely the injections were made into the gyrus splenialis or into the underlying gyrus cinguli close to the mid-line, because the injections would then most likely be in grey and not in white matter. Injected in this way all four drugs set up foci of excitation which gave rise to synchronous firing of a large number of neurones with the result that high voltage negative spikes were recorded from the microinjection cannula.3. On injection into the gyrus splenialis the threshold dose was about 0.04 mug for picrotoxin, about 0.2 mug for tubocurarine, about 5 mug for strychnine and 25 to 50 mug for leptazol. Following the injection of larger doses the spike discharge continued for a few hours after picrotoxin and tubocurarine, for over an hour after strychnine, but for a few minutes only after leptazol. On injection into the gyrus cinguli the threshold doses were slightly greater and with larger doses the spikes occurred at greater frequency but were of lower voltage than in the gyrus splenialis.4. With large doses of picrotoxin injected into the gyrus splenialis the spikes developed an after-positivity and an after-discharge which sometimes passed into a short period of fast activity.5. The foci of excitation set up by the drugs were restricted to the site of injection because on raising or lowering the microinjection cannula the spikes recorded from it quickly decreased in voltage and then disappeared. When the injections were made close to a sulcus and the microinjection cannula, on being lowered, traversed the sulcus, the spikes changed their polarity.6. The spike discharge appears to be a consistent response to the injections of the drugs into grey matter of any part of the cerebral cortex since it was also obtained on their injection into the pyriform cortex, amygdala and area retrolimbica anterior, but not on their injection into white matter or caudate nucleus, thalamus or hypothalamus.

Site of origin of the abnormal discharge in the electrocorticogram produced by tubocurarine perfused through the anterior horn of a lateral ventricle

1. In cats anaesthetized with chloralose, perfusion of tubocurarine through the anterior horn of a lateral cerebral ventricle produces a rhythmic discharge of high voltage negative spikes recorded from an electrode inserted into this horn. The discharge spreads to the cerebral cortex where it gives rise to synchronous surface negative deflexions of low voltage. They have previously been described as ;slow waves'.2. The discharge results from an excitatory action of tubocurarine on the anterior limbic area, which is a cortical structure in the medial wall of the anterior horn lying rostral to the septum pellucidum.

The effect of (+)-tubocurarine chloride and of acute hypotension on electrocortical activity of the cat

1. The effects of I.V. injection of tubocurarine (3 mg/kg) and of acute hypotension upon electrocortical activity of cats under sodium pentobarbitone were analysed. Technical artifacts associated with changes in brain volume were minimized.2. Initially, the superficial cortical response was reduced by tubocurarine either insignificantly or by 34% or less. Cats bled before injection of tubocurarine showed initially a similar reduction but, occasionally, a severe delayed reduction was found. Any fall in the superficial cortical response started during the secondary rise in B.P., many seconds after the B.P. had reached its lowest initial level. By contrast, spontaneous electrocortical activity was reduced approximately when the peak initial fall of B.P. occurred and it started to recover during the secondary rise in B.P. Reduction of the superficial cortical response could still be elicited after spindling had been suppressed by deep barbiturate anaesthesia. The initial thalamocortical afferent component in somatosensory area I, which was evoked by dorsal column stimulation, was less reduced by injection of tubocurarine than were the post-synaptic positive-negative components.3. The depressant effects of injected tubocurarine upon the superficial cortical response and spindle activity were approximated by rapid arterial bleeding.4. The superficial cortical response was reduced following virtual arrest of the cerebral circulation by acute exsanguination or by acute oil embolization. Such reduction most likely does not depend on systemic transport of inhibitory substances to the brain.5. After injection of tubocurarine the rate of outflow from the superior sagittal sinus was variably reduced during the initial fall in B.P., and often showed a variable, secondary increase. A net deficit in cerebral blood flow was usually present during the period of 80 sec after injection.6. The variability in the effects of injected tubocurarine upon electrocortical activity is attributed to the variability of the net deficit in cerebral blood flow.

A NEW CONCEPT OF TEMPERATURE CONTROL IN THE HYPOTHALAMUS

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