The cardiovascular effects of the injection of an enkephalin analogue, [d-ala2-met5]enkephalinamide (DAME) into the pressor area of the rostral ventrolateral medulla were studied in urethane-anesthetized and decerebrate rats. The excitatory amino acid l-glutamate was used to identify the ventrolateral medulla. The pressor responses to l-glutamate were elicited from an area that included the nucleus reticularis gigantocellularis, the medial aspect of the nucleus reticularis parvocellularis and the dorsal portion of the nucleus reticularis lateralis. Injection (0.1μl volume) of DAME (2.5-500.0 ng/site) into the ventrolateral medulla elicited a dose-related decrease in arterial blood pressure and heart rate and attenuated the carotid occlusion response (COR). Control injections (0.1-0.2 μl vol) of saline into the same area failed to produce any response. The specificity of this opiate response was tested with naloxone HC1, an opiate antagonist, which prevented, as well as reversed, the action of DAME both by intravenous (i.v.) administration and by injection into the ventrolateral medulla. It was concluded that the ventrolateral medulla plays a role in the generation of vasomotor tone and that stimulation of opiate receptors in this area by an enkephalin analogue produced hypotension, bradycardia and modification of cardiovascular reflexes.
All Science Journal Classification (ASJC) codes
- Cellular and Molecular Neuroscience
- carotid occlusion
- opiate receptors
- vasopressor neurons
- ventrolateral medulla