BRAIN RESEARCH ELSEVIER Brain Research 694 (1995) 223-232 Research report Time-course of the effects of anandamide, the putative endogenous cannabinoid receptor ligand, on extrapyramidal function J. Romero, R. de Miguel, E. Garcla-Palomero, J.J. Fernfindez-Ruiz *, J.A. Ramos 'Instituto Complutensede Drogodependencias', Departmentof Biochemistry, Faculty of Medicine, Complutense University, 28040-Madrid, Spain Accepted 21 June 1995 Abstract We have recently described the dose-response effect of anandamide (AEA), the N-amide derivative of arachidonic acid that acts as an endogenous ligand for the cannabinoid receptor, on extrapyramidal function. The present study has been designed to examine the time-course of this effect. To this end, adult male rats were submitted to an acute i.p. injection of AEA, A9-tetrahydrocannabinol (THC) or vehicle and examined at different times after drug administration. Animals were tested in an open-field test, then sacrificed and their striata used for analyses of dopaminergic indices. Results were as follows. The administration of AEA or THC produced the expected inhibition of motor behavior. Thus, the administration of AEA decreased the ambulation and the frequency of stereotypic movements (in particular, the number of rears) and increased the time spent by the rats in inactivity. These effects were evident at 10 and 30 min after the administration of the cannabinoid agonist, but mostly disappeared at 60 min. Interestingly, motor inhibition was observed again around 2 or 3 h after the administration of AEA. This was a small but persistent effect (decreased ambulation followed by increased inactivity), because it was observed until at least 6 h after AEA administration. The other cannabimimetic, THC, was always able of decreasing the ambulation and the frequency of rearing and grooming behavior, and of increasing the time spent in inactivity. This effect was usually something more marked than the effect of AEA, but the most characteristic fact was its persistence at all times studies, even at 6 h after administration. These motor disturbances were accompanied by changes in the activity of nigrostriatal dopaminergic neurons. Thus, the administration of AEA decreased the activity of tyrosine hydroxylase (TH) in the striatum at 10 and 30 min after treatment, suggesting a decreased nigrostriatal activity parallel to the motor deficit observed at these times. This was followed by an increase in TH activity and dopamine and L-3,4-dihydroxyphenylacetic acid contents at 60 min after treatment, which would likely reflect a compensatory stimulation of these neurons, whereas restoration of control values was found at 180 min after AEA administration, suggesting that the motor deficit observed at this time was not dependent on dopaminergic influence. Paradoxically, the administration of THC only produced changes in dopaminergic activity at 60 rain after treatment, similar to those seen with AEA, but was ineffective at the other times. In summary, AEA inhibits motor behavior in parallel to reductions in the activity of nigrostriatal dopaminergic neurons. However, this effect was of short duration, disappearing at 60 min after treatment, as compared with the inhibitory effect of THC on motor behavior which was observed at all times studied. Interestingly, a new AEA-induced inhibition of motor behavior, which was not accompanied by dopaminergic changes, appeared at longer times although its meaning remains to be determined. Keywords: Anandamide (arachidonylethanolamide); A9-Tetrahydrocannabinol; Cannabinoid receptor; Dopamine; Nigrostriatal dopaminergic neuron; Motor activity; Stereotypic behavior 1. Introduction Devane et al. [7] have recently described a candidate to be the endogenous ligand for the brain cannabinoid recep- tor, the N-ethanolamide of arachidonic acid called anan- damide (AEA). This compound has been reported to be capable of: (i) displacing the binding of radioactive * Corresponding author. Fax: (34) (1) 394-1691. 0006-8993/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0006-8993(95)00835-7 cannabinoid agonists to brain membranes [7]; (ii) activat- ing the molecular mechanism coupled to cannabinoid re- ceptors (inhibition of adenylate cyclase [33] and N-type calcium channels [19]); (iii) inhibiting the electrically evoked twitch response of the vas deferens [7]; and (iv) producing hypothermia, analgesia and hypoactivity [11], inhibition of prolactin secretion [29] and stimulation of adrenocorticotrophic hormone release [34]. All these ef- fects are characteristic of the exposure to psychotrophic cannabinoids, mainly A9-tetrahydrocannabinol (THC) (for review, see [9]), the prototypical car hinoid derived from