[Effects of 17 alpha-hydroxy-progesterone on cortico-caudate transmission in rats]

Estrogen and progesterone have known effects on the endocrine control of sexual functions, however there is renewed interest on their potential action on extrahypothalamic sites. Previous results obtained in this laboratory, showed that estradiol has an inhibitory effect on cortico-caudate transmission. In this study the action of 17 alpha-Hydroxy-Progesterone on cortico-caudate transmission was assessed. Intact, ovariectomized female rats and intact male Sprague-Dawley rats were anesthetized with chloral hydrate (40 mg/100 g i.p.) and 17 alpha-Hydroxy-Progesterone (10 microliters of a 2.5 mg/ml solution) was administered via a right jugular catheter. Conventional electrophysiological recordings were made in the caudate nucleus by means of glass electrodes, and the motor cortex was electrically stimulated by means of metal electrodes, insulated except at the tip. Excitatory responses were analyzed by a computer, adding successive sweeps to build Post-stimulus time histograms. Injection of 17 alpha-Hydroxy-Progesterone produced an increase in the magnitude of the response in the majority of neurons tested (95%). In some cells this increase was followed by a decrease (35%), and in one case the excitatory response was decreased. These changes started 5 to 10 minutes after the injection, and lasted for about one hour, when the excitatory response returned to control values. These results show that progesterone can modulate cortico-caudate transmission in the rat, and suggest that due to the short latency of this effect, this could be exerted through a non-genomic mechanism of action.