Facilitation of self-stimulation behavior following intracerebral microinjections of opioids into the ventral tegmental area.
The intracerebral microinjection technique was used to localize sites in the brain where morphine facilitated the self-stimulation rate at hypothalamic electrode sites. Bilateral injections of morphine (2 x 1 microgram) into the ventral tegmental area and substantia nigra produced the strongest enhancement at the shortest latencies. At these sites, bilateral injections of 200 ng of morphine also produced a significant enhancement whereas a dose of 50 ng was below threshold for the rate increasing effect. The enhancement by morphine was effectively antagonized by naloxone (5 mg/kg). When injected bilaterally into the same area, D-Ala2-Met5-enkephalinamide (2 x 1 microgram) also induced a strong enhancement of self-stimulation lasting for 70 minutes. A possible dopaminergic substrate for the opiate induced behavioral stimulation is discussed.
D000818:Animals; D001921:Brain / Q000033:anatomy & histology; D004745:Enkephalins / Q000494:pharmacology; D007031:Hypothalamus / Q000502:physiology; D007276:Injections, Intraventricular; D008297:Male; D008845:Microinjections; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009294:Narcotics / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D012653:Self Stimulation / Q000187:drug effects*; D013997:Time Factors
D004745:Enkephalins; D009294:Narcotics; D009270:Naloxone; D009020:Morphine