Antagonism of apomorphine-induced pecking in pigeons

Central nervous system stimulants, tranquillizers and other central nervous system depressants, antiemetics, antihistamine drugs and autonomic blocking agents were examined for their ability to prevent the pecking response in pigeons induced by apomorphine (250 mug/kg intramuscularly). Reduction in the proportion of positive responses or significant increase in the latent period of pecking were taken as the criterion of effectiveness. Protection was afforded by caffeine, lysergic acid diethylamide, morphine, rauwolscine, triflupromazine and yohimbine. In addition, a significant increase in latent period was produced by artane, pentobarbitone, benactyzine, 2-bromolysergic acid diethylamide, cyclizine, diphenhydramine, ergotoxine, hyoscine, promethazine, 5-(2-chloroethyl)-4-methylthiazole and trimethobenzamide. Most of these drugs influenced the pecking and emetic responses to apomorphine in an identical manner. It is possible that identical receptors may be concerned with apomorphine pecking (in pigeons) and emesis (in other species).

Neurogenic control of peripheral resistance in renal hypertension

The increased peripheral resistance responsible for hypertension associated with unilateral renal ischemia and contralateral nephrectomy, is abolished after destruction by pithing of the central nervous system of dogs and rats, or after inactivation of the inhibitory carotid sinus reflex in dogs. The tissue catecholamine content of renal hypertensive rats was in the same range as in the normotensive animals. These results suggest that the increased peripheral resistance in hypertension is neurogenically mediated and that the increased resistance is due to an increased response of the resistance vessels to normal neurogenic stimulation.

PULMONARY AND CENTRAL NERVOUS SYSTEM DAMAGE IN RATS EXPOSED TO HYPERBARIC OXYGEN AND PROTECTION THEREFROM BY GAMMA-AMINOBUTYRIC ACID

Male Wistar rats were exposed to oxygen at 6 atmospheres absolute pressure for periods of 30 and 40 minutes and the effect of the intraperitoneal administration of γ-aminobutyric acid (GABA) (20 mmoles/kg) and glucose (15 mmoles/kg) on the toxic effects of OHP was studied. GABA protected the animals against both gross lung damage and convulsions, but glucose was without effect. Since the accumulation of fluid in the peritoneal cavity was similar for GABA and glucose injections, it would appear that the protective action of GABA was not due to this influx of fluid into the peritoneal cavity brought about by the injected material. All animals having gross pulmonary pathology had suffered severe seizures during the exposure to OHP, but severe convulsions can occur without the incidence of pulmonary pathology. The significance of these observations is discussed.

REVERSAL OF THE EFFECT OF ALPHA-METHYLDOPA BY MONOAMINE OXIDASE INHIBITORS

L-α-Methyldopa, which normally causes sedation, induces a strong central excitation in mice pretreated with a monoamine oxidase inhibitor after a lag of a few hours. It is concluded that this excitation is caused by accumulation of free catecholamines liberated by amines which are slowly formed by decarboxylation of α-methyldopa. The hypotensive and sedative effects of α-methyldopa given alone are attributed to the slow release of catecholamines and subsequent breakdown by monoamine oxidase so that a partial depletion of catecholamines ensues.

SOME PHARMACOLOGICAL PROPERTIES OF THIOPROPERAZINE AND THEIR MODIFICATION BY ANTI-PARKINSONIAN DRUGS

The pharmacological properties of a phenothiazine derivative thioproperazine have been compared with those of chlorpromazine, and the modifications by some anti-Parkinsonian drugs of its actions on the central nervous system have been studied. Thioproperazine was less potent than chlorpromazine in lowering blood pressure and antagonizing adrenaline in the cat, in depressing respiratory rate in the rabbit, in producing hypothermia and analgesia and in reducing the minimum anaesthetic dose of hexobarbitone in mice, and in protecting rats from convulsions induced by tryptamine. It was roughly equipotent to chlorpromazine in reducing locomotor activity of mice. Thioproperazine was more potent than chlorpromazine in protecting grouped mice from the acute toxicity of dexamphetamine, in preventing the acute behavioural disturbances produced by dexamphetamine in the rat, in producing a state of experimental catatonia in the rat and in preventing the emetic action of apomorphine in the dog. Hyoscine, benztropine or promethazine greatly reduced the ability of thioproperazine to prevent behavioural changes due to dexamphetamine in the rat and also abolished symptoms of experimental catatonia produced by thioproperazine. In contrast, the antiapomorphine activity of thioproperazine in the dog was not reduced to any extent by hyoscine or benztropine.

FURTHER OBSERVATIONS ON THE STRUCTURE OF MYELIN SHEATHS IN THE CENTRAL NERVOUS SYSTEM

Direct evidence has been presented to confirm the existence of a spiral in the myelin sheaths of the central nervous system. An account of some of the variations in structure of central myelin sheaths has been given and it has been shown that the radial component of myelin sheaths has the form of a series of rod-like thickenings of the intraperiod line. These thickenings extend along the intraperiod line in a direction parallel to the length of the axon. The relative position of the internal mesaxon and external tongue of cytoplasm has been determined in a number of transverse sections of sheaths from the optic nerves of adult mice, adult rats, and young rats. In about 75 per cent of the mature sheaths examined, these two structures were found within the same quadrant of the sheath, so that the cytoplasm of the external tongue process tends to lie directly outside that associated with the internal mesaxon. The frequency with which the internal mesaxon and external tongue lie within the same quadrant of the sheath increases both with the age of the animal and with the number of lamellae present within a sheath. The possible significance of these findings is discussed.

A PROPOSED COMMON MECHANISM OF ACTION FOR GENERAL AND LOCAL ANAESTHETICS IN THE CENTRAL NERVOUS SYSTEM

Procaine and several general anaesthetics block production of action potentials in frog skeletal muscle fibres by a single mechanism of action, which suggests that there might be a common basic mechanism of action on neurones in the central nervous system. Procaine or cinchocaine given alone to intact white mice produced "excitement" and convulsions but when given 60 min after phenobarbitone they caused central nervous depression. Large, convulsant doses of procaine or cinchocaine abolished the righting reflex in mice previously treated with small, subanaesthetic doses of phenobarbitone. In contrast, leptazol only antagonized the depression produced by phenobarbitone. When applied directly to neuronally isolated slabs of cat cerebral cortex, procaine or pentobarbitone reduced the sizes of the surface negative and surface positive responses to direct electrical stimulation of the cortex. Leptazol had the opposite effect. When given systemically, procaine only increased the electrical threshold for the surface positive response recorded from the isolated slab; ether either increased or did not change this threshold, and leptazol either decreased or did not change it. These results are consistent with the suggestion that general and local anaesthetics have a fundamentally similar action on neurones in the central nervous system.