Sympathetic nervous system activation by glutamate injections into the paraventricular nucleus

The purpose of the present study was to determine the overall cardiovascular and sympathetic nervous system responses to stimulation of neuronal cell bodies in the paraventricular neucleus (PVN) of the hypothalamus. Bilateral microinjections (50 nl) of monosodium glutamate or sodium acetate were made into the PVN of conscious unrestrained rats. Blood pressure, heart rate and plasma concentrations of norepinephrine and epinephrine were measured. The injection of sodium acetate as an osmotic control was without effect on any of the recorded variables. In contrast, the injections of glutamate were associated with a rapid increase in both blood pressure and heart rate. At doses of 15, 25, and 50 nmol blood pressure increased by13 ± 2, 14 ± 3and16 ± 1mmHg while heart rate increased by64 ± 15, 73 ± 8 and50 ± 8 bpm. These responses were associated with increases in plasma norepinephrine concentrations of51 ± 8, 100 ± 16and62 ± 13pg/ml while epinephrine concentrations rose by42 ± 17, 58 ± 18and38 ± 17pg/ml. The responses of glutamate (25 nmol) were not affected by blockade of vascular vasopressin receptors with d(CH 2 ) 5 Tyr(Me)AVP (10 μg/kg) (blood pressure: pre5 ± 3vs post13 ± 3mmHg, heart rate pre77 ± 9bpm vs post91 ± 7bpm, plasma norepinephrine: pre106 ± 22vs post121 ± 28pg/ml and plasma epinephrine: pre61 ± 25vs post34 ± 30pg/ml. These findings indicate that stimulation of neuronal cell bodies in the PVN of conscious rats causes an increase in sympathoadrenal outflow resulting in an increase in blood pressure and heart rate. Vasopressin release into the systemic circulation does not appear to play a major role in the cardiovascular responses associated with PVN stimulation.