INFLUENCE OF MEDIAN RAPHE NUCLEUS LESIONS ON NEUROLEPTIC-INDUCED CATALEPSY AND ON THE ANTICATALEPTIC EFFECT OF BUSPIRONE

Catalepsy induced by neuroleptics in rats can be modified by 5-hydroxy tryptaminergic (5-HTergic) manipulation. For example, buspirone (BUS) and other central 5-HT1A receptor ligands reduce neuroleptic-induced c atalepsy (NIC). The dorsal (DRN) and median (MRN) raphe nuclei are rep orted to be important sources of 5-HTergic projections to the basal ga nglia, the site of action of neuroleptics in producing NIC. A previous study showed that lesion of DRN did not affect NIC or the anticatalep tic effect of BUS. The present study was designed to evaluate the part icipation of MRN in NIC and in the anti-NIC effect of BUS. Twenty-four male Wistar rats (N = 6/group) weighing 220-250 g were used. Electrol ytic lesion of MRN was carried out in anesthetized rats along with sha m operations (electrode inserted but no current applied). Ten days lat er, the rats were injected with BUS (5 mg/kg, ip) or saline (I ml, ip) . Catalepsy was induced 20 min later with haloperidol (H; 1 mg/kg, ip) and measured at 30-min intervals by means of a bar test. The Costall & Naylor method of scoring (range 0-5 points) was used. Saline-injecte d MRN-lesioned rats displayed significantly lower catalepsy scores tha n sham-lesioned rats (1.5 +/- 0.2 vs 3.8 +/- 0.3 at 90 min after H). I n sham-lesioned rats, BUS significantly reduced the catalepsy scores i n comparison with saline-treated animals (1.3 +/- 0.2 vs 3.8 +/- 0.3 a t 90 min after H). However, BUS was not able to further reduce NIC in the MRN-lesioned animals. The present results show that MRN integrity is important for the production of NIC in rats and suggest that the MR N is the site where BUS acts to produce its anticataleptic effect.