Lateral septum stimulation disinhibits dopaminergic neurons in the antero-ventral region of the ventral tegmental area: Role of GABA-A alpha 1 receptors

• Published in: Neuropharmacology 2018-01, Vol.128, p.76-85
• Main Authors: Vega-Quiroga, Ignacio, Yarur, Hector E., Gysling, Katia
• Format: Article
• Language: English
• Subjects: Analysis of Variance; Animals; Baclofen; Benzylamines - pharmacology; Bicuculline; Biotin - analogs & derivatives; Biotin - metabolism; c-Fos; CGP-52432; Dextrans - metabolism; Dopamine - metabolism; Dopaminergic Neurons - physiology; Dose-Response Relationship, Drug; GABA Agents - pharmacology; Glutamic Acid - metabolism; Indiplon; In vivo microdialysis; Male; Neural Pathways - physiology; Phosphinic Acids - pharmacology; Proto-Oncogene Proteins c-fos - metabolism; Rats; Rats, Sprague-Dawley; Receptors, GABA-A - metabolism; Septal Nuclei - physiology; Tyrosine 3-Monooxygenase - metabolism; tyrosine hydroxylase; Ventral Tegmental Area - cytology
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/j.neuropharm.2017.09.034

The mechanisms commanding the activity of dopaminergic neurons of the ventral tegmental area (VTA) and the location of these neurons are relevant for the coding and expression of motivated behavior associated to reward-related signals. Anatomical evidence shows that several brain regions modulate VTA dopaminergic neurons activity via multiple mechanisms. However, there is still scarce knowledge of how the lateral septum (LS) modulates VTA activity. We performed in-vivo dual-probe microdialysis to measure VTA dopamine, glutamate and GABA extracellular levels after LS stimulation in the presence or absence of GABAergic antagonists. Anterograde tracing and immunohistochemical analysis was used to reveal the anatomical relationship between LS and VTA. LS stimulation significantly increased dopamine and GABA, but not glutamate, VTA extracellular levels. Intra VTA infusion of bicuculline, GABA-A receptor antagonist, inhibited the increase of dopamine but not of GABA VTA levels induced by LS stimulation. Intra VTA infusion of indiplon, selective positive allosteric modulator of GABA-A receptors containing alpha1 subunit, significantly increases VTA dopamine extracellular levels induced by LS. Combined c-Fos and tyrosine hydroxylase immunohistochemistry, revealed that LS stimulation increases the activity of dopaminergic neurons in the antero-ventral region of the VTA. Consistently, anterograde tracing with biotinylated dextran amine revealed the existence of fibers arising from the LS to the antero-ventral region of the VTA. Taken together, our results suggest that LS modulates dopaminergic activity in the antero-ventral region of VTA by inhibiting GABAergic interneurons bearing GABA-A receptors containing alpha1 subunit. •LS activates dopaminergic neurons by inhibiting VTA GABAergic interneurons containing GABA-A alpha1 receptors.•LS stimulation induces c-Fos expression in dopaminergic neurons of the antero-ventral region of the VTA.•LS connects to the antero-ventral region of the VTA.