Changes of micro-opioid receptors and GABA in visual cortex of chronic morphine treated rats.
Electrophysiological and biochemical studies have indicated that GABAergic modulation is involved in the opioid-induced altering of response properties of visual cortical cells and impairing of short-term synaptic plasticity in the geniculo-cortical visual pathway. The aim of the current study was to examine whether there were changes in the localization and density of micro-opioid receptor subtype (MOR1) and GABA in the visual cortex of morphine-dependent and abstinent rats. Immunofluorescence histochemical method was applied to display MOR1 and GABA distribution. We found that MOR1-like immunoreactive neurons were significantly lowered in layer I-VI of visual cortex of rats sacrificed immediately after the last injection (defined as morphine-dependent (MD)) than saline-control group. In rats sacrificed just before the last injection (defined as morphine-abstinent (MA)), the density of micro-opioid receptor was higher than that in dependent group in layer I-V neurons of visual cortex, but remained lower than those in control group. Three hours after the last morphine injection (defined as 3h after morphine-abstinent (3h)), MOR1-like immunoreactive neurons in layer I and layer IV of visual cortex were still significantly lower than control. As to GABA-like immunoreactive neurons, they were significantly decreased in abstinent group compared to dependent group. These results provide morphological evidence that opioid-induced altering of response properties of visual cortical cells might be due to the change of visual cortical GABAergic system induced by opioid via mu-opioid receptor, which result in disinhibition of visual cortex projection neurons and their abnormal firing.
Li
Yanfei
Y
Hefei National Laboratory for Physical Sciences at Microscale and School of Life Science, University of Science and Technology of China, Hefei, Anhui, PR China.
He
Lihua
L
Chen
Qin
Q
Zhou
Yifeng
Y
D000818:Animals; D002452:Cell Count / Q000379:methods; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D013997:Time Factors; D014793:Visual Cortex / Q000187:drug effects* / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D009294:Narcotics; C485765:Oprm1 protein, rat; D017450:Receptors, Opioid, mu; D005680:gamma-Aminobutyric Acid; D009020:Morphine