Thyrotropin-releasing hormone: neurogenesis of actions in the pentobarbital narcotized rat

Possible neuroanatomical substrates mediating some of the effects seen with thyrotropin-releasing hormone (TRH) in the pentobarbital (PB) narcotized rat were examined. This was accomplished by microinjecting picomole concentrations of TRH into 20 different brain sites. The behavioural effects examined were the capacity of TRH to antagonize PB-induced narcosis and hypothermia as well as TRH-induced shaking behavior. Microinjection of TRH into the septum was found to be significantly more effective in the reversal of PB narcosis than any other site examined. In contrast, the temperature and shaking response were evoked with approximately equal efficacy by TRH microinjection into a number of brain sites; including the preoptic/anterior hypothalamus, medial thalamus, thalamic, periventricular gray, interpeduncular nucleus and locus ceruleus. These results demonstrate the septal region to be the site of action for TRH reversal of PB narcosis and suggest the involvement of the septohippocampal system. In addition, they indicate that the neurogenesis of the shaking response is similar to that of the temperature response and that this differs from the neurogenesis of the analeptic response.