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.