Drug and Alcohol Dependence 50 (1998) 241–249 Autoradiographic analysis of cannabinoid receptor binding and cannabinoid agonist-stimulated [ 35 S]GTP S binding in morphine-dependent mice Julia ´n Romero a, *, J. Javier Ferna ´ndez-Ruiz a , Gema Vela b , Mariano Ruiz-Gayo b , J. Angel Fuentes b , J. Antonio Ramos a a Instituto Complutense de Drogodependencias, Department of Biochemistry, Faculty of Medicine, Complutense Uniersity, 28040 Madrid, Spain b Department of Pharmacology, Faculty of Pharmacy, Complutense Uniersity, 28040 -Madrid,.Spain Received 16 September 1997; received in revised form 13 February 1998; accepted 13 February 1998 Abstract The present study was designed to test the possible existence of changes in brain cannabinoid receptors in morphine-dependent mice. To this end, we compared cannabinoid receptor binding and WIN 55,212-2-stimulated [ 35 S]guanylyl-5-O-( -thio)-triphos- phate ([ 35 S]GTP S) binding in several brain regions of mice chronically exposed to morphine or saline. The existence of opiate dependence in morphine-injected mice was assessed by analyzing the well-known jumping behavior induced by the blockade of opioid receptors with naloxone, whereas these animals were unresponsive to the blockade of cannabinoid receptors with SR141716. The different structures analyzed exhibited similar cannabinoid receptor binding levels in morphine-dependent and control mice, with the only exception of the globus pallidus, which exhibited a very small, but statistically significant, increase. In addition, the activation of cannabinoid receptors with WIN 55,212-2 increased [ 35 S]GTP S binding in most of the structures examined. The increase was of similar magnitude in morphine-dependent and control mice, except in the substantia nigra, where morphine-dependent mice exhibited lesser [ 35 S]GTP S binding levels in basal conditions, although a significantly higher WIN 55,212-2-stimulated binding. Other structures, such as the central gray substance, where there was a poor agonist-induced stimulation in control mice, exhibited, however, higher levels of WIN 55,212-2-stimulated [ 35 S]GTP S binding in morphine-depen- dent mice, whereas these animals tended to exhibit a higher [ 35 S]GTP S binding levels in basal conditions, although a lesser and not statistically significant WIN 55,212-2-stimulated binding, in the deep layers of the cerebral cortex. Thus, the data support the potential existence of a specific effect of morphine in the coupling of cannabinoid receptors to GTP-binding proteins, rather than on receptor binding, although this was observed only in the substantia nigra and central gray substance. © 1998 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Cannabinoid receptor binding; Cannabinoid agonist-stimulated [35S]GTP S binding; Autoradiography; Cannabinoids; 9-Tetrahydrocannabinol; Opiates; Morphine dependence 1. Introduction Opiates and cannabinoids are among the most widely consumed drugs of abuse in humans. Several studies have demonstrated that both types of drugs share several pharmacological properties, which include anal- gesia, hypothermia, sedation, hypotension, inhibition of both intestinal motility and locomotor activity (Kay- * Corresponding author: Tel.: +34 1 3941450; fax: +34 1 3941691; e-mail: jjfr@eucmax.sim.ucm.es. 0376-8716/98/$19.00 © 1998 Elsevier Science Ireland Ltd. All rights reserved. PII S0376-8716(98)00036-2