Novel neurons in ventral tegmental area fire selectively during the active phase of the diurnal cycle.

Alice H. Luo, François E. Georges, Gary S. Aston-Jones
European Journal of Neuroscience. 2008-01-18; 27(2): 408-422
DOI: 10.1111/j.1460-9568.2007.05985.x

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1. Eur J Neurosci. 2008 Jan;27(2):408-22. doi: 10.1111/j.1460-9568.2007.05985.x.

Novel neurons in ventral tegmental area fire selectively during the active phase
of the diurnal cycle.

Luo AH(1), Georges FE, Aston-Jones GS.

Author information:
(1)Department of Psychiatry, University of Pennsylvania, Philadelphia, PA 19104,

The ventral tegmental area (VTA) contains dopamine (DA) and gamma-aminobutyric
acid (GABA) neurons involved in motivation and behavioral state. These phenomena
are also influenced by circadian factors. The goal of our studies was to examine
the impulse activity of neurochemically identified VTA neurons during dark
(active) vs light (rest) phases of the circadian cycle. Using extracellular
single-unit recordings with juxtacellular labeling in anesthetized rats, we found
multiple neuronal subpopulations including ‘novel neurons’ that selectively fired
during the dark phase. These novel neurons were electrophysiologically
categorized into two groups, ‘novel wide-spike’ and ‘novel thin-spike’ neurons.
Characterization of novel wide-spike neurons found they were consistently
non-dopaminergic and non-GABAergic [tyrosine hydroxylase (TH)(-), glutamic acid
decarboxylase (GAD)(-)]. However, they were inhibited by the D2 agonist
quinpirole, an effect that could be reversed by the D2 antagonist eticlopride.
Physiologically, they were fast firing (mean = 18.9 +/- 1.2 spikes/s), low
bursting neurons (median = 6.2 +/- 3.0% of spikes in bursts) with spike durations
> or = 2.0 ms, but slightly shorter than TH(+) neurons. They were also
consistently non-responsive to footpad stimulation. The novel thin-spike neurons
were neurochemically heterogeneous, and were located more ventrally than
thin-spike neurons found during the light phase. These findings reveal previously
unknown populations of VTA neurons whose activities are sensitive to diurnal
phase, and whose functions may be in the temporal regulation of arousal and
motivational processes.

DOI: 10.1111/j.1460-9568.2007.05985.x
PMID: 18215237 [Indexed for MEDLINE]

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