Concentration‐dependent activation of dopamine receptors differentially modulates GABA release onto orexin neurons

Abstract

Dopamine (DA) and orexin neurons play important roles in reward and food intake. There are anatomical and functional connections between these two cell groups: orexin peptides stimulate DA neurons in the ventral tegmental area and DA inhibits orexin neurons in the hypothalamus. However, the cellular mechanisms underlying the action of DA on orexin neurons remain incompletely understood. Therefore, the effect of DA on inhibitory transmission to orexin neurons was investigated in rat brain slices using the whole-cell patch-clamp technique. We found that DA modulated the frequency of spontaneous and miniature IPSCs (mIPSCs) in a concentration-dependent bidirectional manner. Low (1 μM) and high (100 μM) concentrations of DA decreased and increased IPSC frequency, respectively. These effects did not accompany a change in mIPSC amplitude and persisted in the presence of G-protein signaling inhibitor GDPβS in the pipette, suggesting that DA acts presynaptically. The decrease in mIPSC frequency was mediated by D2 receptors whereas the increase required co-activation of D1 and D2 receptors and subsequent activation of phospholipase C. In summary, our results suggest that DA has complex effects on GABAergic transmission to orexin neurons, involving cooperation of multiple receptor subtypes. The direction of dopaminergic influence on orexin neurons is dependent on the level of DA in the hypothalamus. At low levels DA disinhibits orexin neurons whereas at high levels it facilitates GABA release, which may act as negative feedback to curb the excitatory orexinergic output to DA neurons. These mechanisms may have implications for consummatory and motivated behaviours.

Electrophysiological Properties of Melanin-Concentrating Hormone and Orexin Neurons in Adolescent Rats

“…Orexin neurons were spontaneously active (Figure 6A ), as previously reported (Eggermann et al, 2003 ; Linehan et al, 2015 ). Among the age groups examined (4 weeks n / N = 58/18, 7 weeks n / N = 40/12, and 14 weeks n / N = 42/14), there was no age-dependent change in the RMP ( p = 0.5400, one-way ANOVA), AP frequency ( p = 0.0836, two-way RM ANOVA), first spike latency ( p = 0.6239, two-way RM ANOVA) or threshold p = 0.0851, one-way ANOVA; Figures 6B–E ).…”

“…Once whole cell access was achieved, a series of 600 ms hyperpolarizing and depolarizing current injections were applied to cells in 50 pA increments. Unique electrophysiological responses to these current injections were used to identify MCH and orexin neurons as described previously (Linehan et al, 2015 ; Belanger-Willoughby et al, 2016 ) and to assess active membrane properties. Briefly, MCH neurons are relatively hyperpolarized and silent at rest, and lack H-current.…”

“…Following the recording, the neurochemical phenotype was confirmed in a subset of recorded neurons filled with biocytin using triple staining for biocytin, MCH and orexin A, as previously described (Linehan et al, 2015 ; Belanger-Willoughby et al, 2016 ). Briefly, brain slices were fixed in 10% formalin overnight, and then incubated in a cocktail of rabbit anti-MCH IgG (1:2000; H-070-47, Phoenix Pharmaceuticals, Burlingame, CA, USA) and goat anti-orexin A IgG (1:2000; sc8070, Santa Cruz Biotechnology Inc., Dallas, TX, USA) for 3 days.…”

Short‐term high‐fat diet primes excitatory synapses for long‐term depression in orexin neurons

“…; Linehan et al . ). Specifically, orexin neurons display spontaneous firing, uniphasic after‐hyperpolarizing potential, H‐current and rebound depolarization following relief from hyperpolarization.…”

Involvement of orexin/hypocretin in the expression of social play behaviour in juvenile rats

“…Individual differences in social play expression have been documented both within (Pellis and Mckenna, 1992;Poole and Fish, 1976;Taylor, 1980) and between (Northcutt and Nwankwo, 2018;Siviy, Love, DeCicco, Giordano, & Seifert, 2003) rat strains, and one neural system that has been implicated in these differences is the dopamine system (Pellis and Mckenna, 1992;Siviy, Crawford, Akopian, & Walsh, 2011). The ORX system has reciprocal functional connections with the mesolimbic dopamine system (e.g., Korotkova, Sergeeva, Eriksson, Haas, & Brown, 2003;Linehan, Trask, Briggs, Rowe, & Hirasawa, 2015;Vittoz, Schmeichel, & Berridge, 2008), and it is anatomically positioned to directly influence its functioning. ORX neurons project to the ventral tegmental area (Fadel and Deutch, 2002;Peyron, et al, 1998), which has ORX1Rs (Ch'ng and Lawrence, 2015) through which ORX can act on dopaminergic and GABAergic neurons (Korotkova, et al, 2003).…”