Effect of thyrotropin-releasing hormone, luteinizing hormone-releasing hormone, and somatostatin on neuronal activity of brain stem reticular formation and hippocampus in the female rat

Abstract

Changes in the multiunit activity of the brain stem reticular formation and dorsal hippocampus were studied in environmentally habituated, freely moving, regularly cyclic female rats with chronically implanted “macro” and “semimicro” depth electrodes. Cortical electroencephalograms and multiunit activity were recorded continuously. An inverse relationship was observed between the brain stem reticular formation and the dorsal hippocampus multiunit activity. The multiunit activity in the brain stem reticular formation was variably high during attentive behavior, stable and low under slow-wave sleep, and reached very high values in paradoxical sleep (REM). Conversely, the dorsal hippocampus multiunit activity was high during slow-wave sleep and variably low during attentive behavior or REM sleep. Samples of raw multiunit activity were tape-recorded during slow-wave sleep for analysis of interspike intervals of amplitude-discriminated cell discharges prior to and after hormonal treatments. The analysis revealed that intraperitoneal injection of either thyrotropin-releasing hormone ( 3 μ g 100 g body weight) or luteinizing hormone-releasing hormone (500 ng/rat) resulted in a rapid decrease in interspike intervals of amplitude-discriminated spikes in the brain stem reticular formation and a concomitant increase in intervals between hippocampal cell discharges. Somatostatin ( 3 μ g 100 g body weight), on the other hand, resulted in a general depression of firing rates of neurons in both the brain stem reticular formation and the dorsal hippocampus. In the administered doses, none of the hormones interfered with the regular vaginal cycle of the rats.