Abstract
Duloxetine is a dual serotonin (5-HT)/norepinephrine (NE) reuptake blocker with antidepressant potential. In the present in vivo electrophysiological study, the changes in the function of the rat 5-HT and NE systems after 2- and 21-day administration of duloxetine (20 mg/kg/day) were assessed in the dorsal hippocampus and the dorsal raphe nucleus (DRN). The firing rate of DRN neurons was decreased after 2 days of duloxetine, but returned to the control level after 21-day administration. This recovery of firing rate was presumably due to the desensitization of the DRN somatodendritic 5-HT1A autoreceptors found after long-term duloxetine administration. Overall serotonergic tone was assessed by examining the ability of the 5-HT1A antagonist WAY 100635 to alter hippocampal firing. WAY 100635 increased hippocampal firing rates in 21-day treated rats to a greater extent than in 2-day treated or control rats, suggesting that long-term administration induced an increase in endogenous levels of 5-HT in postsynaptic regions. This increase in 5-HT levels was accompanied by selective changes in the 5-HT and NE systems induced by long-term duloxetine administration,i.e., the desensitization of the alpha-2 adrenergic heteroreceptor on 5-HT terminals and the continued blockade of the 5-HT transporters. In contrast, the sensitivity of thealpha-2 adrenergic and terminal 5-HT1Bautoreceptors, as well as that of the postsynaptic 5-HT1Areceptor after 21-day treatment was unchanged. Therefore, this study demonstrates that duloxetine increases serotonergic tone in a limbic forebrain structure and may therefore be effective in the treatment of depression.
Footnotes
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Send reprint requests to: Dr. Lynne Rueter, Neurobiological Psychiatry Unit, McGill University, 1033 Pine Avenue West, Montréal, Québec, Canada H3A 1A1.
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↵1 This work was supported in part by the Medical Research Council of Canada (Grants MT-6444 and MA-11014) and the Fonds de la Recherche en Santé du Québec. L.R. is the recipient of a Fellowship from the Royal Victoria Hospital Research Institute (Montréal, Canada). P.B. is the recipient of a Medical Research Council of Canada Scientist Award.
- Abbreviations:
- 5-HT
- 5-hydroxytryptamine (serotonin)
- NE
- norepinephrine
- SSRI
- selective serotonin reuptake inhibitor
- LSD
- lysergic acid diethylamide
- DRN
- dorsal raphe nucleus
- MAOI
- monoamine oxidase inhibitor
- SIL
- silence
- ANOVA
- analysis of variance
- Received August 6, 1997.
- Accepted January 9, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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