The ventral tegmental area revisited: is there an electrophysiological marker for dopaminergic neurons?

Journal of Physiology - Tập 577 Số 3 - Trang 907-924 - 2006
Elyssa B. Margolis1, Hagar Lock2, Gregory O. Hjelmstad3,1, Howard L. Fields3,1
1Ernest Gallo Clinic & Research Center, University of California, San Francisco, Emeryville, CA 94608, USA
2Neuronal Development and Regeneration Group, Parc Cientific de Barcelona, Josep Samitier, 1-5, Spain
3Department of Neurology and Wheeler Center for the Neurobiology of Addiction, University of California, San Francisco, CA 94143-0114, USA

Tóm tắt

The ventral tegmental area (VTA) and in particular VTA dopamine (DA) neurons are postulated to play a central role in reward, motivation and drug addiction. However, most evidence implicating VTA DA neurons in these functions is based on indirect electrophysiological characterization, rather than cytochemical identification. These physiological criteria were first established in the substantia nigra pars compacta (SNc), but their validity in the VTA is uncertain. In the current study we found that while 88 ± 2% of SNc neurons labelled by the neuronal marker NeuN were co‐labelled for the catecholamine enzyme tyrosine hydroxylase (TH), a much smaller percentage (55 ± 2%) of VTA neurons co‐expressed TH. In addition, using in vitro whole‐cell recordings we found that widely accepted physiological criteria for VTA DA neurons, including the hyperpolarization‐activated inwardly rectifying non‐specific cation current (Ih), spike duration, and inhibition by DA D2 receptor agonists, do not reliably predict the DA content of VTA neurons. We could not distinguish DA neurons from other VTA neurons by size, shape, input resistance, Ih size, or spontaneous firing rate. Although the absence of an Ih reliably predicted that a VTA neuron was non‐dopaminergic, and Ih(−) neurons differ from Ih(+) neurons in firing rate, interspike interval (ISI) standard deviation, and ISI skew, no physiological property examined here is both sensitive and selective for DA neurons in the VTA. We conclude that reliable physiological criteria for VTA DA neuron identification have yet to be determined, and that the criteria currently being used are unreliable.

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Journal of Physiology

Tập 577 Số 3

907-924

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