Studies to investigate the role of 5-HT(2C) receptors on cocaine- and food-maintained behavior.

Abstract

The present series of studies were designed to investigate the 5-HT(2C) receptor agonist Ro 60-0175 on cocaine- and food-maintained behavior in the rat. Ro 60-0175 (0.1-3 mg/kg, s.c.) reduced cocaine (15 mg/kg, i.p.)-induced hyperactivity. This inhibitory effect of Ro 60-0175 (1 mg/kg, s.c.) was completely blocked by pretreatment with the selective 5-HT(2C) antagonist SB 242,084 (0.5 mg/kg, i.p.). In further studies, Ro 60-0175 (1-3 mg/kg, s.c.) reduced responding for both food (45-mg Noyes pellet) and cocaine (0.25 mg/infusion) maintained under identical schedules of reinforcement (fixed ratio (5), time out 1 min, 60-min duration). The effect on food-maintained responding was blocked by SB 242,084 (0.5 mg/kg, i.p.). Ro 60-0175 (0.3-3 mg/kg, s.c.) also reduced the breakpoint for cocaine self-administration under a progressive ratio schedule of reinforcement. After a period of extinction training, where cocaine solution was substituted with saline, an acute priming injection of cocaine (15 mg/kg, i.p.) but not Ro 60-0175 (1 mg/kg, s.c.) reinstated cocaine responding. In this model of relapse, Ro 60-0175 (1-3 mg/kg, s.c.) pretreatment attenuated the priming effect of acute cocaine injection. In a final series of studies to examine the cataleptogenic properties of Ro 60-0175, very mild indices of catalepsy were observed at the 3 mg/kg dose only. These catalepsy scores were significantly lower than that produced by haloperidol (0. 5 mg/kg, s.c.). In further tests of motor function using the Rotarod, deficits were again seen at the 3 mg/kg dose, but not at lower doses. Taken together, these studies suggest that, in addition to reducing food intake, 5-HT(2C) receptor agonists reduce cocaine-reinforced behavior. This would be consistent with electrophysiological and biochemical evidence suggesting an important modulatory influence of 5-HT(2C) receptor activation on mesolimbic dopamine function.

• Authors: A J Grottick, P J Fletcher, G A Higgins
• Journal: The Journal of pharmacology and experimental therapeutics (J Pharmacol Exp Ther) Vol. 295 Issue 3 Pg. 1183-91 (Dec 2000) ISSN: 0022-3565 [Print] United States
• PMID: 11082456 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• 6-chloro-5-methyl-1-((2-(2-methylpyrid-3-yloxy)pyrid-5-yl)carbamoyl)indoline
• Aminopyridines
• Ethylamines
• Indoles
• Receptor, Serotonin, 5-HT2C
• Receptors, Serotonin
• Ro 60-0175
• Cocaine

Topics

• Aminopyridines (pharmacology)
• Animals
• Catalepsy (chemically induced)
• Cocaine (pharmacology)
• Conditioning, Psychological (drug effects)
• Ethylamines (pharmacology)
• Food
• Indoles (pharmacology)
• Male
• Motor Activity (drug effects)
• Nucleus Accumbens (physiology)
• Rats
• Rats, Sprague-Dawley
• Receptor, Serotonin, 5-HT2C
• Receptors, Serotonin (physiology)
• Reinforcement Schedule
• Ventral Tegmental Area (physiology)