The projections of the ventral tegmental area and adjacent regions: A combined fluorescent retrograde tracer and immunofluorescence study in the rat

The principal features and mechanisms of dopamine modulation in the prefrontal cortex

Intracellular and extracellular electrophysiology of nigral dopaminergic neurons—1. Identification and characterization

Ventral tegmental (A10) system: neurobiology. 1. Anatomy and connectivity.

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 (I(h)), 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, I(h) size, or spontaneous firing rate. Although the absence of an I(h) reliably predicted that a VTA neuron was non-dopaminergic, and I(h)(-) neurons differ from I(h)(+) 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.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.2006.117069

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

Electrophysiological evidence for non-dopaminergic mesocortical and mesolimbic neurons in the rat.

Publisher Summary In the rat, the prefrontal cortex may be defined as the mesocortical zone receiving converging projections from the mediodorsal nucleus of the thalamus (MD) and from the dopamine (DA) cell group localized in the ventromedial mesencephalic tegmentum (VMT). It is composed of two subfields: a medial region, the pregenual medial wall of the hemisphere in reciprocal connection with the lateral part of the MD; and a lateral region on the dorsal bank of the rhinal sulcus, which is reciprocally connected with the medial part of the MD. A great number of cortical and subcortical structures receive efferents from prefrontal cortex and differences have been demonstrated anatomically as regards its medial and lateral projections. These projections involve other portions of the cortex (presubiculum, retrosplenial, perirhinal and entorhinal cortex) and subcortical structures related to the limbic system (midline thalamic nuclei, hypothalamus and the paramedian mesencephalic tegmentum) or the extrapyramidal system (striatum, substantia nigra (SN) and deep layers of the superior colliculus (CS)). The medial and lateral areas of the prefrontal cortex can also be distinguished on a functional basis because, in the rat, distinct behavioral deficits have been observed to result from their lesioning. This chapter reviews results from recent studies aimed at further characterization of the afferents to medial prefrontal cortex originating from the VMT, and the efferents from medial prefrontal cortex projecting to diencephalic and mesencephalic structures.

G. Chevalier

Papers

Electrophysiological evidence for non-dopaminergic mesocortical and mesolimbic neurons in the rat.

An electrophysiological analysis of some afferent and efferent pathways of the rat prefrontal cortex.