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Ventral tegmental area (VTA) dopamine (DA) neurons are implicated in reward processing, motivation, reward prediction error, and in substance use disorder. Recent studies have identified distinct neuronal subpopulations within the VTA that can be clustered based on their molecular identity, neurotransmitter profile, physiology, projections and behavioral role. One such subpopulation is characterized by expression of the NeuroD6 gene, and projects primarily to the nucleus accumbens medial shell. We recently showed that optogenetic stimulation of these neurons induces real-time place preference while their targeted deletion of the Vmat2 gene caused altered response to rewarding substances, including ethanol and psychostimulants. Based on these recent findings, we wanted to further investigate the involvement of the NeuroD6-positive VTA subpopulation in reward processing. Using the same NeuroD6(Cre+/wt);Vmat2(flox/flox) mice as in our prior study, we now addressed the ability of the mice to process sucrose reward. In order to assess appetitive behavior and motivation to obtain sucrose reward, we tested conditional knockout (cKO) and control littermate mice in an operant sucrose self-administration paradigm. We observed that cKO mice demonstrate higher response rates to the operant task and consume more sucrose rewards than control mice. However, their motivation to obtain sucrose is identical to that of control mice. Our results highlight previous observations that appetitive behavior and motivation to obtain rewards can be served by distinct neuronal circuits, and demonstrate that the NeuroD6 VTA subpopulation is involved in mediating the former, but not the latter. Together with previous studies on the NeuroD6 subpopulation, our findings pinpoint the importance of unraveling the molecular and functional role of VTA subpopulations in order to better understand normal behavior and psychiatric disease.

The subthalamic nucleus (STN) is critical for the execution of intended movements. Loss of its normal function is strongly associated with several movement disorders, including Parkinson's disease for which the STN is an important target area in deep brain stimulation (DBS) therapy. Classical basal ganglia models postulate that two parallel pathways, the direct and indirect pathways, exert opposing control over movement, with the STN acting within the indirect pathway. The STN is regulated by both inhibitory and excitatory input, and is itself excitatory. While most functional knowledge of this clinically relevant brain structure has been gained from pathological conditions and models, primarily parkinsonian, experimental evidence for its role in normal motor control has remained more sparse. The objective here was to tease out the selective impact of the STN on several motor parameters required to achieve intended movement, including locomotion, balance and motor coordination. Optogenetic excitation and inhibition using both bilateral and unilateral stimulations of the STN were implemented in freely-moving mice. The results demonstrate that selective optogenetic inhibition of the STN enhances locomotion while its excitation reduces locomotion. These findings lend experimental support to basal ganglia models of the STN in terms of locomotion. In addition, optogenetic excitation in freely-exploring mice induced self-grooming, disturbed gait and a jumping/escaping behavior, while causing reduced motor coordination in advanced motor tasks, independent of grooming and jumping. This study contributes experimentally validated evidence for a regulatory role of the STN in several aspects of motor control., De två första författarna delar förstaförfattarskapet.

Dopamine (DA) neurons of the ventral tegmental area (VTA) continue to gain attention as far more heterogeneous than previously realized. Within the medial aspect of the VTA, the unexpected presence of TrpV1 mRNA has been identified. TrpV1 encodes the Transient Receptor Potential cation channel subfamily V member 1, TRPV1, also known as the capsaicin receptor, well recognized for its role in heat and pain processing by peripheral neurons. In contrast, the brain distribution of TrpV1 has been debated. Here, we hypothesized that the TrpV1+ identity defines a distinct subpopulation of VTA DA neurons. To explore these brain TrpV1+ neurons, histological analyses and Cre-driven mouse genetics were employed. TrpV1 mRNA was most strongly detected at the perinatal stage forming a band of scattered neurons throughout the medial VTA, reaching into the posterior hypothalamus. Within the VTA, the majority of TrpV1 co-localized with both Tyrosine hydroxylase (Th) and Vesicular monoamine transporter 2 (Vmat2), confirming a DA phenotype. However, TrpV1 also co-localized substantially with Vesicular glutamate transporter 2 (Vglut2), representing the capacity for glutamate (GLU) release. These TrpV1+/Th+/Vglut2+/Vmat2+ neurons thus constitute a molecularly and anatomically distinct subpopulation of DA-GLU co-releasing neurons. To assess behavioral impact, a TrpV1Cre-driven strategy targeting the Vmat2 gene in mice was implemented. This manipulation was sufficient to alter psychomotor behavior induced by amphetamine. The acute effect of the drug was accentuated above control levels, suggesting super-sensitivity in the drug-na ve state resembling a “pre-sensitized” phenotype. However, no progressive increase with repeated injections was observed. This study identifies a distinct TrpV1+ VTA subpopulation as a critical modulatory component in responsiveness to amphetamine. Moreover, expression of the gene encoding TRPV1 in selected VTA neurons opens up for new possibilities in pharmacolog

The distribution pattern and functional role of brain neurons expressing the Transient receptor vanilloid-1 (Trpv1) gene, which in the sensory nervous system regulates body temperature, heat and pain, have remained obscure. Two studies using both in situ hybridization to detect endogenous Trpv1 mRNA and a floxed reporter allel in Trpv1-Cre mice, have detected sparse expression in the caudal aspect of the hypothalamus and the ventral tegmental area of the midbrain. This area has during recent years been associated with aversion processing via glutamatergic neurons expressing the Vesicular glutamate transporter 2 (Vglut2) gene. Glutamatergic neurons of this area thus seem to be selectively correlated with aversion, while dopaminergic neurons in the ventral midbrain have long been associated with reward processing. A previous study from our laboratory found that the Trpv1-positive neuronal population consisted of both glutamatergic and dopaminergic neurons. It was therefore of particular interest to study this population further. Would this small but distinct hypothalamic-mesencephalic neuronal group of neurons regulate any specific type of behaviour if selectively activated? The results presented show that Trpv1 mRNA is primarily detected at the perinatal stage forming a band of neurons stretching from the posterior hypothalamus through to, and including, the ventral tegmental area. In the mature mouse, application of optogenetic constructs to the Trpv1-Cre-positive population enabled the analysis of both projection pattern and behavioural role of the Trpv1 neurons. These rare neurons, forming a hypothalamic-mesenecphalic continuum, project to several areas of the limbic system including the hippocampus, septum, nucleus accumbens and the preoptic area. When optogenetically activated, Trpv1-Cre mice show normal movements in the open field test, but display progressive avoidance behaviour in an optogenetic real-time place preference test. The results identify a new neur

The subthalamic nucleus is important achieve intended movements. Loss of its normal function is strongly associated with several movement disorders. Classical basal ganglia models postulate that two parallel pathways, the direct and indirect pathways, exert opposing control over movement, with the subthalamic nucleus part of the indirect pathway through which competing motor programs are prevented. The subthalamic nucleus is regulated by both inhibitory and excitatory projections but experimental evidence for its role in motor control has remained sparse. The objective here was to tease out the selective impact of the subthalamic nucleus on several motor parameters required to achieve intended movement, including locomotion, balance and motor coordination. Optogenetic excitation and inhibition using both bilateral and unilateral stimulations of the subthalamic nucleus were implemented in freely-moving mice. The results demonstrate that selective optogenetic inhibition of the subthalamic nucleus enhances locomotion while its excitation reduces locomotion. These findings lend experimental support to basal ganglia models in terms of locomotion. However, further analysis of subthalamic nucleus excitation revealed grooming and disturbed gait. Selective excitation also caused reduced motor coordination, independent of grooming, in advanced motor tasks. This study contributes experimental evidence for a regulatory role of the subthalamic nucleus in motor control.

Activation of the subthalamic nucleus (STN) is associated with the stopping of ongoing behavior via the basal ganglia. However, we recently observed that optogenetic STN excitation induced a strong jumping/escaping behavior. We hypothesized that STN activation is aversive. To test this, place preference was assessed. Optogenetic excitation of the STN caused potent place aversion. Causality between STN activation and aversion has not been demonstrated previously. The lateral habenula (LHb) is a critical hub for aversion. Optogenetic stimulation of the STN indeed caused firing of LHb neurons, but with delay, suggesting the involvement of a polysynaptic circuit. To unravel a putative pathway, the ventral pallidum (VP) was investigated. VP receives projections from the STN and in turn projects to the LHb. Optogenetic excitation of STN-VP terminals caused firing of VP neurons and induced aversive behavior. This study identifies the STN as critical hub for aversion, potentially mediated via an STN-VP-LHb pathway.