Galanin Microinjection into the Rostral Ventrolateral Medulla of the Rat Is Hypotensive and Attenuates the Sympathetic Chemoreflex

Galanin is present in neurons in the brain that are important in the control of arterial pressure and intracisternal administration of galanin evokes hypotension, but the site of action is unknown. In urethane-anaesthetised, vagotomised mechanically ventilated Sprague Dawley rats (N=34), we investigated the effects of microinjecting galanin (1mM, 50nL, 50pmol) into the rostral ventrolateral medulla on resting splanchnic sympathetic nerve activity, arterial pressure, heart rate and phrenic nerve activity. Secondly, we determined the effect of microinjecting galanin into the rostral ventrolateral medulla on the cardiovascular response to stimulation of central and peripheral chemoreceptors, arterial baroreceptors and the somatosympathetic reflex. Galanin caused a prolonged reduction in resting splanchnic sympathetic nerve activity (-37.0 ± 7.2% of baseline), mean arterial pressure (-17.0 ± 3.5mmHg) and heart rate (25.0 ± 9.1bpm). Galanin increased the sympathoinhibitory response to aortic depressor nerve stimulation by 51.8%, had no effect on the somatosympathetic reflex, and markedly attenuated the effect of hypercapnia and hypoxia on arterial pressure (by 65% and 92.4% of control, respectively). These results suggest a role for galanin neurotransmission in the integration of the cardiovascular responses to hypoxia, hypercapnia and the sympathetic baroreflex in the rostral ventrolateral medulla. The data suggest that galanin may be an important peptide in the homeostatic regulation of chemosensory reflexes.