Facilitation of self-stimulation of ventral tegmentum by microinjection of opioid receptor subtype agonists.
Intracranial self-stimulation (ICSS) evoked from the ventral tegmental area-substantia nigra (VTA-SN) and lateral hypothalamus-medial forebrain bundle (LH-MFB) was assessed following microinjections of mu (Tyr-D-Ala2-N-Me-Phe4-Gly5ol: DAGO), delta-(D-Ala2, D-Met5)-enkephalin: DADME) or kappa (Dynorphin-B or Rimorphin) opioid receptor subtype agonists or saline into either VTA-SN or LH-MFB. The current intensity was fixed at an optimum level to obtain 60-70% of the maximum asymptotic response rate. DAGO (5 micrograms/0.5 microliters), DADME (2 micrograms/0.5 microliters) or Dynorphin B (0.5 microgram/0.5 microliters) injected into VTA-SN facilitated the self-stimulation rates of VTA-SN by 27%, 32%, and 59%, respectively. These microinjections did not alter the self-stimulation of LH-MFB when effects of these injections were still persisting in VTA-SN. Similar doses of these opioid receptor agonists injected into LH-MFB had no significant effect on the self-stimulation rates of either LH-MFB or VTA-SN. The facilitatory effects of DADME were completely abolished by naloxone (30 mg/kg IP). Taken together, these results suggest that all three opioid receptor subtypes of ventral tegmentum and not of lateral hypothalamus are involved in the electrically evoked self-stimulation of VTA-SN.
Singh
J
J
Department of Neurophysiology, National Institute of Mental Health and Neuro Sciences, Bangalore, India.
Desiraju
T
T
Nagaraja
T N
TN
Raju
T R
TR
D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001931:Brain Mapping; D004305:Dose-Response Relationship, Drug; D004399:Dynorphins / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D004723:Endorphins / Q000494:pharmacology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology; D007026:Hypothalamic Area, Lateral / Q000187:drug effects* / Q000502:physiology; D008297:Male; D008474:Medial Forebrain Bundle / Q000187:drug effects / Q000502:physiology; D009042:Motivation; D009270:Naloxone / Q000494:pharmacology; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000145:classification / Q000187:drug effects* / Q000502:physiology; D012653:Self Stimulation / Q000187:drug effects* / Q000502:physiology; D013378:Substantia Nigra / Q000187:drug effects / Q000502:physiology; D013681:Tegmentum Mesencephali / Q000187:drug effects* / Q000502:physiology; D017557:Ventral Tegmental Area / Q000187:drug effects / Q000502:physiology
D000700:Analgesics; D004723:Endorphins; D004745:Enkephalins; D011957:Receptors, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; D004744:Enkephalin, Methionine; C013801:enkephalin-Met, Ala(2)-; D004399:Dynorphins; C036200:rimorphin