METHODS FOR PERFUSING DIFFERENT PARTS OF THE CAT'S CEREBRAL VENTRICLES WITH DRUGS

Experimental hydrocephalus and hydrosyringomyelia. Computertomographic studies

Two methods were used to induce a model of experimental hydrocephalus and hydrosyringomyelia in the cat: a) injection of kaolin into the cisterna magna and b) closure of the lateral apertures of the fourth ventricle with cotton swabs. The pathological changes in the brain ventricles and the central canal of the spinal cord were monitored and documented at regular intervals by computed tomography (CT). The CT method is particularly advantageous for studies of this kind because the animals can be examined frequently without risking disturbances in cerebro-spinal fluid dynamics or tissue damage that would result from introduction of contrast media into the ventricular system. Our results and others reported earlier suggest that the dilated central canal acts as a kind of spontaneous CSF deviation route from the ventricles to the subarachnoid space. In spite of the tendency of the animals to recover in a clinical sense, the internal CSF space continued to expand; in cats the disease is progressive, a fact that is readily evident in follow-up CTs. This characteristic indicates that the spontaneous "shunt system" from the fourth ventricle through the dilated central canal to the spinal CSF spaces does not function well enough. Possible explanations for hydrocephalus compensation and the development of hydrosyringomyelia in experimental animals are discussed.

The dopamine autoreceptor agonist B-HT 920 inhibits in vivo dopamine release into the cerebroventricular system of cats

In anesthetized cats the dopamine autoreceptor agonist B-HT 920 (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]-azepine), 1 mg/kg i.v., greatly decreased the amount of dopamine in cerebroventricular perfusates. This effect was antagonized by a low dose (50 micrograms/kg i.v.) of haloperidol, but not by the alpha 2-adrenoceptor blocker idazoxan. Our observations provide evidence that B-HT 920 inhibits brain dopamine release in vivo and may be therapeutically valuable in diseases presumed to be accompanied by a predominance of brain dopamine activity, such as Huntington's disease, mania and schizophrenia.

Factors influencing the cholinesterases of cerebrospinal fluid in the anaesthetized cat

Both acetylcholinesterase and non-specific cholinesterase are found in cerebrospinal fluid and blood plasma of the cat; the ratio of activities acetylcholinesterase/non-specific cholinesterase is about 1.5 in cerebrospinal fluid and 0.15 in plasma. A search was made for factors capable of influencing the concentration of the two cholinesterases in cerebrospinal fluid. Either the ventricular system was perfused with artificial cerebrospinal fluid from a lateral ventricle to the aqueduct, or the atlanto-occipital membrane was punctured and cerebrospinal fluid was collected continuously from the cisterna magna. Factors studied included: (a) procedures affecting the composition or formation of cerebrospinal fluid, such as changes in the ionic constituents of the perfusate, the inhibition of cerebrospinal fluid formation by acetazolamide or ouabain, or the rapid intra-carotid infusion of hypertonic urea; (b) arousal (noise or stimulation of the central ends of the sciatic nerves), or deepening of anaesthesia; (c) changes in blood pressure; (d) central stimulants and depressants, pyrogens, prostaglandins, antagonists of acetylcholine. Whereas most procedures or drugs tested increased the concentration of acetylcholinesterase, some central depressants (e.g. chlorpromazine) reduced, while another (ether) increased the appearance of acetylcholinesterase in the cerebrospinal fluid. The effect of ether was, in all probability, due to damage to the blood-brain barrier. A rise in acetylcholinesterase concentration was obtained upon stimulation of the central ends of the sciatic nerves; this was inhibited by atropine but not by N-methylatropine, indicating that the rise was due to increased nervous activity and not to the circulatory effects of the stimulation, since the changes in blood pressure caused by the stimulation remained the same after atropine administration. Amphetamine or leptazol raised the levels of acetylcholinesterase but it was not possible to determine whether this was due only to increased central nervous activity, since there was invariably leakage through the blood-brain barrier which by itself would be sufficient to produce the effect. A rise in the level of acetylcholinesterase was seen after administration of pyrogen; this was apparently not a simple effect of warming the body, but due to the action of the pyrogen on centers concerned with temperature control, since warming the animal by external heat failed to produce a similar change.(ABSTRACT TRUNCATED AT 400 WORDS)

Drug administration into the third ventricle of the brain of anesthetized and conscious cats

A method is described for the administration of drugs into the third ventricle of the brain of conscious and anesthetized cats. Noradrenaline administered by this route produced cardiovascular stimulant effects as against depressor effects when administered into a lateral cerebral ventricle. The pressor responses evoked by third ventricular administration of noradrenaline were antagonized by spinal section in anesthetized cats and by hexamethonium in conscious animals. Conscious cats were more sensitive to the pressor effects of third ventricular noradrenaline than chloralose-anesthetized animals.

Release of transmitters into the perfused third cerebral ventrical of the cat

1. The third cerebral ventricle of cats treated with nialamide and anaesthetized with chloralose was perfused, and the effluent was tested for 5-hydroxytryptamine (5-HT) and also for acetylcholine (ACh) when the perfusion fluid contained neostigmine.2. Under ;resting' conditions a 25 min sample of effluent contained from < 1 to 6 ng 5-HT; the release remained steady during many hours of perfusion. It was necessary to watch out for traces of blood which might contribute to the 5-HT content and which were only visible after centrifugation.3. A number of regions in the ventral mid-brain and hind-brain were stimulated, including the two most anterior nuclei of the raphe, nucleus linearis rostralis and intermedius. Release of 5-HT (rarely more than 2 ng) was only obtained on stimulation of these two nuclei, whereas ACh was released by stimulating many points, such as the reticular formation or the decussation of the superior cerebellar peduncles, but not the two raphe nuclei.4. Low frequencies of stimulation were more effective at releasing 5-HT, and high frequencies at releasing ACh.5. Since the amount of 5-HT released on stimulation was rarely more than 2 ng, a powerful re-uptake process was suspected and confirmed by the use of chlorimipramine. Intravenous, intraperitoneal and intraventricular use of this drug temporarily increased the basal release to values ranging from 20 to 50 ng in 25 min samples, and about trebled the release on stimulation of either of the linear nuclei.6. Intravenous administration of chlorimipramine (10 mg/kg) caused the disappearance of electrical responses evoked in the brain stem by afferent sensory stimuli.

Effect of cycloheximide and actinomycin D on Na pump density in Hela cells

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Release of 5-hydroxytryptamine from caudate nucleus and septum

1. The anterior horn of one lateral ventricle was perfused in anaesthetized cats treated with inhibitors of monoamine oxidase, and the effluent was tested for 5-hydroxytryptamine (5-HT).2. The basal release of 5-HT varied from 0.25 to 4 ng in 25 min, and was usually about 1 ng.3. The basal release rose and fell with body temperature.4. Electrical stimulation for 15 min of the nucleus linearis intermedius or of the nucleus linearis rostralis caused a release of 5-HT which rarely outlasted the collection period of 25 min.5. Low frequencies (0.5/sec) were, per stimulus, more effective than high frequencies in releasing 5-HT. Over a 15 min period of stimulation, however, the highest total yield was at 20/sec; it fell abruptly at still greater frequencies.6. No release was obtained if the stimulating electrode was positioned in a variety of brain structures outside the two linear nuclei.7. The experiments indicate that 5-HT acts as a transmitter of impulses in neurones originating in the linear nuclei and terminating in caudate nucleus and septum.

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.

Central effects of picrotoxin when acting from the liquor spaces in anaesthetized cats

1. Picrotoxin was perfused through different parts of the cerebral ventricles in cats anaesthetized with chloralose, and applied topically to the upper cervical cord in cats anaesthetized with intraperitoneal pentobarbitone sodium. With both methods, picrotoxin produced effects similar to those produced by tubocurarine; but it was active in weaker concentrations.2. Perfused through the third ventricle, picrotoxin caused shivering resulting in a rise of rectal temperature, increased motor excitability, muscle jerks, tachypnoea, mydriasis, and withdrawal of the nictitating membranes. The effects were due to an action on structures in the walls of the ventral half of the ventricle, because they occurred only on perfusion of tubocurarine through this half and not on its perfusion through the dorsal half of the third ventricle. Noradrenaline perfused through the third ventricle abolished the shivering and the rise in temperature, but did not affect the motor hyperexcitability or the muscle jerks, whereas pentobarbitone sodium similarly perfused abolished these effects as well.3. Perfused through the inferior horn of a lateral ventricle, picrotoxin caused excitation of the hippocampus. This resulted in a rhythmic discharge of high voltage negative spikes in the electrocorticogram taken from the occipital cortices. The spikes developed after-positivity with after-discharges and were interrupted from time to time by bursts of fast activity termed episodes. This abnormal discharge was recorded also from the perfusion cannula which was inserted into the inferior horn and acted as a lead from the surface of the hippocampus.4. Perfused through the anterior horn of a lateral ventricle picrotoxin caused a rhythmic discharge of negative spikes which was recorded from the anterior horn cannula and resulted from excitation of the grey matter in the anterior limbic area which forms part of the medial wall of the horn.5. Applied to the surface of the upper cervical cord, picrotoxin produced scratching movements.

Perfusion from cerebral ventricle to cisterna magna in the unanaesthetized cat. Effect of calcium on body temperature

1. A method is described for the perfusion of the liquor space from a lateral cerebral ventricle to the cisterna magna in the unanaesthetized cat. Perfusions were carried out for 30-40 min using various physiological salt solutions whilst rectal temperature was recorded.2. When the salt solution used contained calcium in the physiological concentration, rectal temperature remained unchanged, but when it contained no calcium an intense hyperthermia developed during the perfusion. The finding that calcium must be present in the perfusion fluid for preventing temperature from rising may lead to a new understanding of the working of the ;set-point' in the control of body temperature and of the mechanism of action of pyrogens.3. Independent of the nature of the perfusion fluid a long-lasting late rise in temperature developed after a perfusion. This happened regularly when the infusion needle was inserted only into the hub of the ventricular cannula, but rarely when the needle was extended beyond the tip of the cannula shaft and the cannula had been flushed out during the preceding days. It is therefore thought that an unknown pyrogenic factor present in the lumen of the cannula and washed into the ventricle with the perfusion fluid is responsible for this effect.4. The effluent collected from the cisterna contracted the fundus strip of the rat stomach. As the contractions were little affected by BOL, they are attributed mainly to an action of prostaglandin E(1) and not to an action of 5-HT. There was no difference in the biological activity of the effluent whether the perfusion fluid contained calcium or not.

Release to the cerebral ventricles of substances with possible transmitter function in the caudate nucleus

1. One caudate nucleus of the anaesthetized cat was superfused by perfusing the anterior horn of one lateral cerebral ventricle. The perfusates were examined for their content in acetylcholine (ACh), dopamine, homovanillic acid (HVA) and 5-hydroxytryptamine (5-HT), at rest and after a variety of stimuli.2. When prostigmine was added to the perfusion fluid, ACh appeared in the effluent; its concentration tended to rise in the course of an experiment. Various afferent stimuli, all of which caused evoked responses recorded from the contra-lateral caudate nucleus, increased the ACh content of the effluent. Effective stimuli were noise and electrical stimulation of afferent nerves or of certain regions of the brain including the ipsi-lateral substantia nigra.3. The dopamine content of the effluent was extremely low (of the order of 50 pg/min) at rest, but, on occasion, rose sharply when the substantia nigra was stimulated electrically with trains of pulses repeated once every 3 sec. The results were inconsistent.4. Since dopamine in tissue is rapidly transformed enzymically into HVA, the appearance of this acid in the perfusate was examined.5. At rest, HVA was found to appear in the effluent at a rate of 2-8 ng/min. Its concentration was rapidly depressed by increasing the depth of anaesthesia.6. Stimulation of the substantia nigra for periods of 3 or 4 min caused an increment in the HVA content of the effluent lasting 1 hr or more. It was frequently seen when two points of the substantia nigra were stimulated simultaneously, less regularly with only one stimulating electrode, and rarely if this was placed in the most caudal part of the substantia nigra.7. These results strongly support the view that there is a dopaminergic nigro-striatal pathway. The following assumption would explain the erratic appearance of dopamine and the long duration of increments in HVA: many of the axons originating in the substantia nigra end either in the putamen or in parts of the caudate nucleus which are far away from the ventricular surface; any dopamine released from these axons will not reach the ventricular surface at all, and HVA will, at best, reach it very slowly.8. Small amounts of 5-HT appeared in the ventricular perfusate, and the quantity rose after the administration of monoamine oxidase inhibitors. It was not increased by the type of stimuli used in this work to elicit the release of ACh or HVA.

Effect of monoamineoxidase inhibitors on 5-hydroxytryptamine output from perfused cerebral ventricles of anaesthetized cats

1. In cats anaesthetized with pentobarbitone sodium, intraperitoneal injections of four inhibitors of monoamine oxidase (MAO) were shown to increase the 5-hydroxytryptamine (5-HT) in the effluent from the perfused cerebral ventricles.2. Weight for weight, tranylcypromine was found to be about twice as potent as pheniprazine, eight times as potent as nialamide and sixty times as potent as pargyline.3. The effect of tranylcypromine was also examined after reserpine had been injected into the cerebral ventricles or after p-chlorophenylalanine, given intraperitoneally. In both conditions tranylcypromine retained its ability to increase the 5-HT output from the perfused cerebral ventricle, but the effect was attenuated, more after p-chlorophenylalanine than after reserpine.4. Evidence is put forward that in both conditions the brain is not completely depleted of its 5-HT, but that the 5-HT is only reduced, more after p-chlorophenylalanine than after reserpine.

Norepinephrine: release from brain by d-amphetamine in vivo

After injection of H(3)-norepinephrine into the left lateral cerebral ventricle of cats, the lateral and third cerebral ventricles were perfused with an artificial cerebrospinal fluid. Addition of d-amphetamine to the perfusion fluid caused a significant increase in the concentration of H(3)-norepinephrine in the effluent.

Effect on temperature of 5-hydroxytryptamine injected into the cerebral ventricles of cats

1. In unanaesthetized cats the effect on rectal temperature was examined of 5-HT injected through a Collison cannula chronically implanted into the left lateral ventricle. The response depended on the amount of 5-HT injected and on the solvent employed.2. An intraventricular injection of 200 mug 5-HT creatinine sulphate dissolved in 0.9% NaCl solution resulted in a long-lasting rise often interrupted initially by a transient fall in temperature.3. This fall became more prominent with larger doses of 5-HT; even more when the 5-HT was dissolved in distilled water, and then the hyperthermic effect was attenuated.4. It is concluded that intraventricular 5-HT raises rectal temperature in cats when the amount is not too large, and that a hypothermic effect when it occurs results from paralysis of cells in the anterior hypothalamus which are excited by small doses. This would be similar to the actions of acetylcholine in the perfused superior cervical ganglion of the cat, where small doses excite but large doses paralyse the ganglion cells.5. An intraventricular injection of distilled water produced a steady rise in temperature which is attributed to release of 5-HT.

Release by tubocurarine of dopamine and homovanillic acid from the superfused caudate nucleus

1. The release of dopamine and its metabolite homovanillic acid from the ;superfused' caudate nucleus was studied in the cat. Fluorimetric assay of the two compounds was carried out on 30 min samples of artificial cerebrospinal fluid perfused through the anterior horn of one lateral ventricle.2. When tubocurarine 0.5 or 1 x 10(-4) g/ml. was added to the perfusion fluid, amounts of dopamine of the order of 0.1 ng/min, and very much larger quantities of homovanillic acid (up to 8 ng/min) appeared in the perfusing fluid.3. No release of dopamine was obtained under conditions when tubocurarine failed to produce any clinical signs or when gallamine was substituted for tubocurarine.

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.

Body temperature responses in cats and rabbits to the monoamine oxidase inhibitor tranylcypromine

1. In unanaesthetized cats tranylcypromine (1-10 mg/kg) had scarcely any effect on rectal temperature when injected intraperitoneally, yet such injections prevented the deep and long-lasting fall in rectal temperature which normally occurs when the cat is anaesthetized by intraperitoneal pentobarbitone sodium or intravenous chloralose. The anaesthesia itself, however, was not affected. In some of the experiments with pentobarbitone sodium rectal temperature even rose to fever level.2. In anaesthetized as well as in unanaesthetized cats injections of tranylcypromine (0.1-1 mg) into the cerebral ventricles caused a rise in rectal temperature.3. In rabbits, rectal temperature was scarcely affected when surgical anaesthesia was produced by intravenous infusions of pentobarbitone sodium under the same condition in which, in cats, intraperitoneal pentobarbitone sodium produced a deep and long-lasting fall in temperature, i.e. when no external heat was applied but excessive dissipation of heat was prevented by placing the rabbit on a cotton-wool pad. However, when it was placed on the metal surface of an operating table, the anaesthesia was associated with a deep fall in rectal temperature.5. In anaesthetized and unanaesthetized rabbits tranylcypromine had no effect on rectal temperature when injected intraperitoneally (10 mg/kg) or into the cerebral ventricles (1 mg).5. These results are discussed in relation to the theory that the three monoamines in the hypothalamus, 5-hydroxytryptamine (5-HT), adrenaline and noradrenaline, act as central transmitters in temperature regulation.