Long-range projection neurons of the mouse ventral tegmental area: a single-cell axon tracing analysis

Abstract

Pathways arising from the ventral tegmental area (VTA) release dopamine and other neurotransmitters during the expectation and achievement of reward, and are regarded as central links of the brain networks that create drive, pleasure, and addiction. While the global pattern of VTA projections is well-known, the actual axonal wiring of individual VTA neurons had never been investigated. Here, we labeled and analyzed the axons of 30 VTA single neurons by means of single-cell transfection with the Sindbis-pal-eGFP vector in mice. These observations were complemented with those obtained by labeling the axons of small populations of VTA cells with iontophoretic microdeposits of biotinylated dextran amine. In the single-cell labeling experiments, each entire axonal tree was reconstructed from serial sections, the length of terminal axonal arbors was estimated by stereology, and the dopaminergic phenotype was tested by double-labeling for tyrosine hydroxylase immunofluorescence. We observed two main, markedly different VTA cell morphologies: neurons with a single main axon targeting only forebrain structures (FPN cells), and neurons with multibranched axons targeting both the forebrain and the brainstem (F + BSPN cells). Dopaminergic phenotype was observed in FPN cells. Moreover, four “subtypes” could be distinguished among the FPN cells based on their projection targets: (1) “Mesocorticolimbic” FPN projecting to both neocortex and basal forebrain; (2) “Mesocortical” FPN innervating the neocortex almost exclusively; (3) “Mesolimbic” FPN projecting to the basal forebrain, accumbens and caudateputamen; and (4) “Mesostriatal” FPN targeting only the caudateputamen. While the F + BSPN cells were scattered within VTA, the mesolimbic neurons were abundant in the paranigral nucleus. The observed diversity in wiring architectures is consistent with the notion that different VTA cell subpopulations modulate the activity of specific sets of prosencephalic and brainstem structures.

Parkinson Sac Domain Mutation in Synaptojanin 1 Impairs Clathrin Uncoating at Synapses and Triggers Dystrophic Changes in Dopaminergic Axons

“…As DAergic neurons of this system have different structural and functional features relative to DAergic neurons of the VTA (e.g. different axonal arborization size and pacemaking mechanism) (Aransay et al, 2015; Khaliq and Bean, 2010; Matsuda et al, 2009), a different susceptibility of these neurons to the mutation is plausible. At the light microscopic level, these structures were represented by focal and robust clusters of immunoreactivity for DAT, a plasma membrane protein of DAergic nerve terminals, and for the axonal plasma membrane SNARE SNAP25.…”

Amygdala Kisspeptin Neurons: Putative Mediators of Olfactory Control of the Gonadotropic Axis

“…Our current retrograde studies (not shown), using FluoroGold, indicate that at least some of the dopaminergic fibres originate in the midbrain dopaminergic population of the ventral tegmental area (VTA). Connections between the amygdala and the VTA have been described previously [45][46][47][48][49][50] . The VTA is a key brain area of the reward system [20] and has been linked with social behaviours, including affiliate behaviour and attachment [51] .…”

The Mesoaccumbens Pathway: A Retrograde Labeling and Single-Cell Axon Tracing Analysis in the Mouse

“…Several subdivisions have been identified within the rodent VTA; they include the PBP, PN, rVTA, VTT, and three midline subnuclei: the IF, RLi and CLi (Swanson, 1982; Ikemoto, 2007; Fu et al, 2012; see Aransay et al, 2015 for further discussion). Projections from VTA to Acb compose the so-called mesoaccumbens system in which dopaminergic axons modulate prefrontal, hippocampal and amygdaloid driving inputs at Acb (Brady and O’Donnell, 2004).…”

“…In addition, we used TH double-labeling to quantify the dopaminergic phenotype in mesoaccumbens neurons. Finally, we used the Sindbis-pal-eGFP vector (Furuta et al, 2001; Aransay et al, 2015) to visualize and reconstruct the complete axonal arborization of three mesoaccumbens neurons located in different VTA subdivisions.…”