The effect of acute kainic acid treatment on mu-opioid receptors in rat brain

There is evidence that acute exposure to kainic acid (KA) induces the relea se of endogenous ligands for opioid receptors and that mu-opioid agonists i ntensify KA-induced neurodegeneration. The aim of the present study was to investigate any acute toxic effects of KA upon mu-opioid receptors labelled with [H-3]-DAMGO. 200-250 g rats were injected intraperitoneally with eith er saline or 16 mg/kg KA and brains were removed after 4 h. Membrane homoge nates were prepared from the cerebellum, cortex, hippocampus, medulla and p ens, midbrain and hypothalamus and striatum and in separate studies, from w hole brain. In addition, frozen coronal sections were processed for compara tive quantitative autoradiography. KA produced a two-fold increase in recep tor affinity for [H-3]-DAMGO in all regions and significant increases in re ceptor number in cortex, medulla and pens and striatum. Quantitative autora diography showed similar significantly increased mu-labelling of structures comprising these gross anatomical regions. The findings demonstrate region specific changes in rat brain mu-opioid receptors after acute KA treatment which may be functionally related to the convulsant effects of this excito toxin. (C) 1998 Elsevier Science B.V. All rights reserved.