CARDIOVASCULAR AND RESPIRATORY EFFECTS OF STIMULATION OF CELL-BODIES OF THE PARABRACHIAL NUCLEI IN THE ANESTHETIZED RAT

1. In order to assess the importance of the parabrachial nuclei in mod ulating cardiorespiratory activity, electric current or microinjection s of glutamate were used to stimulate discrete regions of the parabrac hial nuclei in anaesthetized rats. 2. Stimulation of cell bodies in th e medial region of the parabrachial nuclei and in the Kolliker-Fuse nu clei, caused an expiratory facilitatory response. This consisted mainl y of a decrease in respiratory rate as measured by observing phrenic n erve activity. 3. Stimulation of cell bodies in the lateral region of the parabrachial nuclei caused an inspiratory facilitatory response. T his consisted mainly of an increase in respiratory rate. 4. At the maj ority of sites (16 out of 20) where changes In respiratory rate were e licited by glutamate injection or electrical stimulation an increase i n blood pressure was observed. The coexistence of increases in blood p ressure and heart rate indicates the presence of inhibition of the hea rt rate component of the baroreflex and/or an increase in cardiac symp athetic drive. 5. The expiratory facilitatory response was not evoked reflexly by the rise in blood pressure since it was still present afte r administration of guanethidine, which abolished the rise in blood pr essure. 6. The interactions between the parabrachial nuclei and the me dullary respiratory complex in eliciting these changes are discussed.