An autoradiographic study of [H]AMPA receptor binding and in situ hybridization of AMPA sensitive glutamate receptor A (GluR-A) subunits following morphine withdrawal in the rat brain

Chronic treatment with opioids is well known to result in the development of physical dependence. More recently, glutamatergic mechanisms have been implicated in expression of the withdrawal syndrome from opioids. To better examine glutamatergic involvement, an autoradiographic study of [³H]AMPA receptor binding and an assessment of in situ hybridization of AMPA sensitive glutamate receptor A (GluR-A) subunits in the rat brain were each performed 7 h after withdrawal from morphine infusion. Animals were rendered dependent by intracerebroventricular (i.c.v.) infusion of morphine (26 nmol/μl/h) via osmotic minipumps for 3 days. Brain sections of 14-μm thickness were incubated with 15 nM [³H]AMPA for quantitation of binding to the AMPA receptor. The probe for in situ hybridization was labeled at its 3′ end using terminal deoxynucleotidyl transferase and [³⁵S]dATP. The highest degree of [³H]AMPA binding was shown in the hippocampus. The extent of [³H]AMPA binding was increased significantly in the cortex areas (18–21%), caudate-putamen (20%), and hippocampus (7–9%) of rats following withdrawal from morphine. The highest levels of mRNA for GluR-A, flop and flip subunits, were found in the dentate gyrus and in the CA3 region of the hippocampus, respectively. The levels of mRNA for the flop form of GluR-A were decreased in the CA3 of hippocampus (8%) of the rat brain. The levels of mRNA for the flip form of GluR-A were increased in the parietal cortex (7%) and the entorhinal cortex (8%). Increases in the binding of [³H]AMPA to its receptor may play an important role during withdrawal from morphine dependence.