Abstract
The dorsomedial hypothalamic nucleus (DMH) mediates the cardiovascular response to acute stress. The cardiovascular response to the DMH-evoked response is dependent upon neurons in the brain stem where contains 5-HT1A receptor subtype. In the present study, we investigated whether intravenous (iv) injection of the selective 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) affected the cardiovascular response to the DMH-evoked response and sympathetic responses to chemo- and baro-receptor reflexes. In urethane-anaesthetized rats, bicuculline microinjections (10 pmol) into the DMH caused increases in mean arterial pressure (MAP; 17±2 mmHg), heart rate (HR; 85±15 bpm) and renal sympathetic nerve activity (RSNA; 48±5% of baseline). Iv injection of 8-OH-DPAT (0.1 mg/kg) resulted in small decreases in resting MAP (∼10 mmHg) and HR (∼30 bpm) and had no effect on resting RSNA, but greatly reduced the increases in MAP, HR and RSNA evoked by DMH activation. Subsequent injection of the selective 5-HT1A antagonist WAY-100635 completely restored the DMH-evoked cardiovascular response to that observed before 8-OH-DPAT injection. Injection of 8-OH-DPAT did not alter either the increase in RSNA evoked by chemoreceptor stimulation or the cardiac-related component of RSNA response. The results indicate that activation of 5-HT1A receptor blocks the cardiovascular response evoked from the DMH, but does not affect sympathetic vasomotor tone or chemoreceptor and baroreceptor reflexes. [Jpn J Physiol 55 Suppl:S188 (2005)]
