Journal
SYNAPSE
Volume 68, Issue 10, Pages 454-467Publisher
WILEY
DOI: 10.1002/syn.21757
Keywords
diurnal rhythm; firing activity; amphetamine; apomorphine; cosinor
Categories
Funding
- Fonds de la Recherche en Sante du Quebec (FRSQ)
- Canadian Institutes of Health Research (CIHR) [PPP-81421, PP2-90159]
- Canadian Foundation for Innovation (CFI) [23381]
- Ministere du Developpement Economique de l' Innovation et de l'Exportation (MDEIE) [230301]
- McGill University Health Center (MUHC)
- McGill University (William Dawson Scholar Fund)
- Mexican National Council for Science and Technology (CONACYT) [193202/302017, 223534]
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Direct evidence that dopamine (DA) neurotransmission varies during the 24 h of the day is lacking. Here, we have characterized the firing activity of DA neurons located in the ventral tegmental area (VTA) using single-unit extracellular recordings in anesthetized rats kept on a standard light-dark cycle. DA neuronal firing activity was measured under basal conditions and in response to intravenous administration of increasing doses of amphetamine (AMPH: 0.5, 1, 2, 5 mg/kg), apomorphine (APO: 25, 50, 100, 200 mg/kg) and melatonin (MLT: 0.1, 1, 10 mg/kg) at different time intervals of the light-dark cycle. DA firing activity peaked between 07: 00 and 11: 00 h (3.5 +/- 0.3 Hz) and between 19:00 and 23:00 h (4.1 +/- 0.7 Hz), with lowest activity occurring between 11:00 and 15:00 h (2.4 +/- 0.2 Hz) and between 23:00 and 03:00 h (2.6 +/- 0.2 Hz). The highest number of spontaneously active neurons was observed between 03:00 and 06:00 h (2.5 +/- 0.3 neurons/track), whereas the lowest was between 19:00 and 23:00 h (1.5 +/- 0.2 neurons/track). The inhibitory effect of AMPH on DA firing rate was similar in both phases. The inhibitory effect of low dose of APO (25 mu g/kg, dose selective for D-2 autoreceptor) was more potent in the dark phase, whereas APO effects at higher doses were similar in both phases. Finally, MLT administration (1 mg/kg) produced a moderate inhibition of DA cell firing in both phases. These experiments demonstrate the existence of an intradiurnal rhythmic pattern of VTA DA neuronal firing activity and a higher pharmacological response of D-2 autoreceptors in the dark phase. (C) 2014 Wiley Periodicals, Inc.
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