title: Altered responsiveness of serotonin receptor subtypes following long-term cannabinoid treatment.
abstract: This study examined the effects of long-term cannabinoid administration on the responsivity of 5-HT1A and 5-HT2A receptors, which have been implicated in depression. Animals received 12 d administration of the potent cannabinoid receptor agonist HU-210 (100 microg/kg), following which they were monitored on their behavioural, physiological and hormonal responses to a single challenge of a 5-HT1A and 5-HT2A receptor agonist, 8-OH-DPAT (0.3 mg/kg) and DOI (1 mg/kg) respectively. Chronic HU-210 treatment lead to a significant enhancement of DOI-induced wet-dog shakes, but a reduction of DOI-induced back muscle contractions. DOI-induced corticosterone release was unaffected by HU-210 treatment. The hyperthermic response to DOI appeared to be potentiated by long-term HU-210 treatment, as 50% of these subjects died from an apparent serotonin syndrome with core temperatures exceeding 43 degrees C. The 8-OH-DPAT-induced hypothermic response and elevation of corticosterone were both significantly attenuated by long- term HU-210 treatment. These data imply that chronic cannabinoid treatment may up-regulate 5-HT2A receptor activity while concurrently down-regulating 5-HT1A receptor activity, a finding similar to that sometimes observed in depression. This may partially explain the association between excessive cannabis consumption and the induction of affective disease.
authors.affiliation: Department of Psychology, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Matthew N
authors.initials: MN
authors.lastname: Hill
authors.forename: Jane C
authors.initials: JC
authors.lastname: Sun
authors.forename: Maric T L
authors.initials: MT
authors.lastname: Tse
authors.forename: Boris B
authors.initials: BB
authors.lastname: Gorzalka
mesh_terms: D000818:Animals; D002186:Cannabinoids / Q000008:administration & dosage*; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D013759:Dronabinol / Q000008:administration & dosage / Q000031:analogs & derivatives*; D008297:Male; D051381:Rats; D020318:Rats, Long-Evans; D044282:Receptor, Serotonin, 5-HT1A / Q000096:biosynthesis / Q000378:metabolism*; D044402:Receptor, Serotonin, 5-HT2A / Q000096:biosynthesis / Q000378:metabolism*; D058829:Serotonin 5-HT1 Receptor Antagonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D013997:Time Factors; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
chemical_list: D002186:Cannabinoids; D044402:Receptor, Serotonin, 5-HT2A; D058829:Serotonin 5-HT1 Receptor Antagonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D044282:Receptor, Serotonin, 5-HT1A; D013759:Dronabinol; C062018:HU 211