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Systemic and microiontophoretic administration of morphine differentially effect ventral pallidum/substantia innominata neuronal activity
Author(s) -
Napier T. Celeste,
Chrobak James J.,
Yew Jay
Publication year - 1992
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/syn.890120306
Subject(s) - substantia innominata , morphine , (+) naloxone , systemic administration , opioid , pharmacology , ventral pallidum , neuroscience , electrophysiology , chemistry , anesthesia , medicine , globus pallidus , psychology , receptor , central nervous system , in vivo , biology , cholinergic neuron , acetylcholine , basal ganglia , microbiology and biotechnology
Abstract In vivo electrophysiological recording techniques were employed to examine responses of ventral pallidum/substantia innominata (VP/SI) neurons to systemic and local administration of morphine. Using a cumulative dosing protocol, intravenous administration (0.1–30 mg/kg i. v.) produced a suppression of firing in 82% of neurons tested. The suppression was dose‐related and blocked by the opioid antagonist, naloxone. In contrast, microiontophoretic applications of morphine resulted in current‐related suppression (32% of neurons tested) or excitation (26%). Concurrent application of naloxone attenuated or blocked both effects of local morphine applicatio. It was demonstrated that acute tolerance did not develop with repeated morphine exposures following either systemic or local administration. The present findings establish the sensitivity of VP/SI neurons to morphine and provide functional relevance at the level of a single neuron for opioid peptides and their receptors in this region. As reported for most other opioid receptive brain areas, neuronal rate suppression was the predominate response observed, and it is proposed that excitations to iontophoresed morphine reflect a disinhibitory phenomenon. The differntial morphine‐induced rate changes, and number of responding neurons, observed with systemic vs. iontophoretic morphine administration suggest that extra‐VP/SI regions that also are opioid sensitive can subsequently direct neuronal responsivensess to opioids within the VP/SI. © 1992 Wiley‐Liss, Inc.