The GHR-R antagonist JMV 2959 neither induces malaise nor alters the malaise property of LiCl in the adult male rat

The orexigenic peptide ghrelin (GHR) interacts with ghrelin receptors (GHR-Rs) to modulate brain reinforcement and feeding circuits. Pharmacological inactivation of GHR-Rs via administration of the drug JMV 2959 attenuates the rewarding/reinforcing effects of several drugs of abuse including alcohol, morphine, amphetamine and nicotine. One view of these results is that inactivation of GHR-Rs taps into brain reinforcement/feeding circuits acted upon by drugs of abuse. An alternate explanation is that JMV 2959 may induce malaise, which in turn may limit reinforcement as well as food ingestion. This is a variable of interest given that nicotine alone can induce malaise which may be enhanced by JMV 2959. In the present study, we assessed the capacity of JMV 2959 to produce malaise using a conditioned taste aversion (CTA) task. Adult male rats were allowed to consume a 0.1% sodium saccharin solution and then injected IP with either vehicle, 0.4 mg/kg nicotine, 3 mg/kg JMV 2959, a combination of 0.4 mg/kg nicotine and 3 mg/kg JMV 2959, or 32 mg/kg lithium chloride (a positive control known to support induction of CTA). Lithium chloride produced a robust avoidance of the saccharin solution in subsequent 2 bottle (water and saccharin) tests, whereas JMV 2959 alone did not induce CTA. The combination of JMV 2959 and nicotine induced a moderate degree of CTA that was similar to that produced by nicotine alone. These results suggest that JMV 2959 is unlikely to limit either reinforcement or food ingestion via induction of malaise.