Cardiovascular responses to the injection of L-glutamate in the lateral hypothalamus of unanesthetized or anesthetized rats

The present experiment was designed to compare the cardiovascular effects of injections of 0.1 M L-glutamate (50, 100 or 500 nL) into the anterior (LHa), tuberal (LHt) or posterior (LHp) regions of the lateral hypothalamus (LH) of either unanesthetized or anesthetized male Wistar rats. In unanesthetized rats, L-glutamate caused significant depressor responses without significant heart rate (HR) effects. L-Glutamate caused similar depressor responses when injected into the different LH subregions. A positive trend was observed between depressor response intensity and injected volume. In urethane-anesthetized rats, L-glutamate caused either depressor responses or biphasic responses, characterized by a significant initial depressor component followed by a secondary pressor response which was significant only after the injection of L-glutamate in 500 nL. The depressor component was accompanied by significant bradycardia only when the LHa or LHt were stimulated. Similar depressor responses were observed after L-glutamate microinjection into the different LH subregions. A positive trend was observed between depressor response intensity and injected volume. The present results suggest that: 1) lateral hypothalamic L-glutamate-sensitive neurons are involved in cardiovascular control and may have a wide and homogeneous distribution throughout the LH; 2) these neurons are mainly associated to the expression of hypotensive responses in unanesthetized rats; and 3) bradycardiac responses are evidenced when L-glutamate is microinjected into the LHa and the LHt in urethane-anesthetized rats.