Brain serotonin depletion by lesions of the median raphe nucleus enhances the psychotomimetic action of phencyclidine, but not dizocilpine (MK-801), in rats.
We have previously shown that brain serotonin depletion by lesions of the median raphe nucleus (MRN) causes enhancement of phencyclidine-induced locomotor hyperactivity [S. Kusljic, D.L. Copolov, M. van den Buuse, Differential role of serotonergic projections arising from the dorsal and median raphe nuclei in locomotor hyperactivity and prepulse inhibition, Neuropsychopharmacology 28 (2003) 2138-2147]. In this study, we extend our previous work by (1) comparing the effect of phencyclidine with that of another NMDA receptor antagonist, dizocilpine (MK-801); (2) investigate behavioral changes in more detail; (3) assess in detail the effect of raphe lesions on regional serotonin levels in the brain. Male Sprague-Dawley rats received microinjection of the serotonergic neurotoxin 5,7-dihydroxytryptamine into the MRN or dorsal raphe nucleus (DRN). The effects of treatment with saline, phencyclidine and MK-801 on locomotor activity were determined 2 weeks after the surgery. MRN lesions caused serotonin depletion in the dorsal hippocampus, whereas DRN lesions caused serotonin depletion in the frontal cortex, striatum and ventral hippocampus. There was a significant increase in phencyclidine-induced locomotor hyperactivity in the MRN-lesioned group compared to sham-operated controls. Further analysis of behavior showed that phencyclidine-induced hyperambulation, but not stereotypy or rearing, was significantly higher in MRN-lesioned rats compared to controls. In contrast, there was no significant effect of the lesions on the psychotomimetic effect of MK-801. These results indicate that a hyposerotonergic state induced by destruction of projections from the MRN leads to altered brain circuitry that is responsible for the regulation of phencyclidine-but not MK-801-induced locomotor hyperactivity. Thus, MRN projections may play an inhibitory role in mechanisms involved in symptoms of schizophrenia.
Kusljic
Snezana
S
Behavioural Neuroscience Laboratory, Mental Health Research Institute of Victoria, Parkville, Australia.
Brosda
Jan
J
Norman
Trevor R
TR
van den Buuse
Maarten
M
D015116:5,7-Dihydroxytryptamine / Q000633:toxicity; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001921:Brain / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism; D001923:Brain Chemistry / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D016291:Dizocilpine Maleate / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006948:Hyperkinesis / Q000139:chemically induced* / Q000503:physiopathology; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D010622:Phencyclidine / Q000633:toxicity*; D011903:Raphe Nuclei / Q000187:drug effects* / Q000293:injuries / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000172:deficiency*; D018490:Serotonin Agents / Q000633:toxicity; D013997:Time Factors
D018691:Excitatory Amino Acid Antagonists; D018490:Serotonin Agents; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D016291:Dizocilpine Maleate; D010622:Phencyclidine