Adenyl cyclase activity in rat pineal gland: effects of chronic denervation and norepinephrine

Adenyl cyclase activity in the pineal gland of rats was determined by measuring the rate of formation of radioactive cyclic 3',5'-adenosine monophosphate from (14)C-labeled adenosine triphosphate. Norepinephrine added in vitro to pineal homogenates enhanced this activity, while denervation of the pineal gland by superior cervical ganglionectomy did not significantly reduce it. The enzyme in these denervated glands was more responsive to the stimulatory effects of norepinephrine.

Effects of exogenous serotonin on paleocortical excitability

Exogenous serotonin, in doses to 1 mg/kg i.v., has been found not to affect the excitability of the neurons in the amygdala to hippocampus multineuronal pathway of the limbic system. This is viewed as evidence in support of the hypothesis that injected serotonin does not exert its central effects through a direct synaptic action.

Distribution of intracarotidly injected serotonin in the brain

Cross circulation experiments, according to the technique of Heymans and Heymans and Swiss and Maison, have been used to study the distribution of serotonin (2–4 mg) injected in the internal carotid artery of the recipient rabbit. Approximately 1% of the injected neurohormone has been recovered from different parts of brain while more than 50% of the injected serotonin is present in the venous jugular blood of the recipient. Some of the injected serotonin reaches the general circulation probably through the sinus vertebralis longitudinalis causing hypotension. Pretreatment with Marsilid does not change the rate of serotonin entrance in nervous tissues although the increase of serotonin content in brain of animals treated with Marsilid is confirmed.