Impaired wakefulness and rapid eye movement sleep in dopamine-deficient mice

Despite the established roles of the dopaminergic system in promoting arousal, the effects of loss of dopamine on the patterns of sleep and wakefulness remain elusive. Here, we examined the sleep architecture of dopamine-deficient (DD) mice, which were previously developed by global knockout of tyrosine hydroxylase and its specific rescue in noradrenergic and adrenergic neurons. We found that DD mice have reduced time spent in wakefulness. Unexpectedly, DD mice also exhibited a marked reduction in the time spent in rapid eye movement (REM) sleep. The electroencephalogram power spectrum of all vigilance states in DD mice were also affected. These results support the current understanding of the critical roles of the dopaminergic system in maintaining wakefulness and also implicate its previously unknown effects on REM sleep.

Specificity of Gβ and γ subunits to SNARE complex both at rest and after α2a adrenergic receptor stimulation

G proteins are major transducers of signals from G-protein coupled receptors (GPCRs). They are made up of α, β, and γ subunits, with 16 Gα, 5 Gβ and 12 Gγ subunits. Though much is known about the specificity of Gα subunits, the specificity of Gβγs by a given GPCR and those that activate each effector in vivo is not clear. In a previous paper, we were able to identify Gβ and Gγ interacting specifically neuronal α2a-adrenergic receptors (α2aARs). However, it still remains unclear how G protein specificity plays out in α2aAR-mediated effector interactions. This receptor is the major autoreceptor that acts as a brake to synaptic transmission in adrenergic neurons and the sympathetic nervous system, and as heteroreceptors on other neurons throughout the brain. Here, we examined the in vivo specificity of Gβγ to the soluble NSF attachment proteins (SNARE) complex upon presynaptic α2aAR activation in both adrenergic (auto-α2aARs) and non-adrenergic (heteroreceptor) neurons for the first time. To understand how this interaction underlies inhibition of synaptic transmission in diverse physiological functions such as spontaneous locomotor activity, anesthetic sparing, and working memory enhancement, we applied a quantitative MRM proteomic analysis of Gβ and Gγ subunits co-immunoprecipitation from transgenic FLAG-α2aARs and wildtype mice. We evaluated Gβ and Gγ subunit binding to the SNARE complex with and without activation of auto-α2aAR and hetero-α2aAR using epinephrine. Without epinephrine stimulation, Gβ1 and Gγ3 interact with SNARE. When auto-α2aARs are activated, Gβ1, Gβ2, and Gγ3 interact with SNARE. Further understanding of in vivo Gβγ specificity to various effectors offers new insights into the multiplicity of genes for Gβ and Gγ, and the mechanisms underlying GPCR signaling through Gβγ subunits to this interaction as a potential therapeutic target.SummarySpecific Gβγ dimers interact with SNARE complex following presynaptic α2aAR activation in both adrenergic and non-adrenergic neurons.

Hindbrain Catecholamine Neurons Modulate the Growth Hormone But Not the Feeding Response to Ghrelin

The gastrointestinal peptide, ghrelin, elicits feeding and secretion when administered systemically or centrally. Previous studies have suggested that hypothalamic projections of hindbrain catecholamine neurons are involved in both of these actions of ghrelin. The purpose of this study was to further assess the role of hindbrain catecholamine neurons in ghrelin-induced feeding and GH secretion and to determine the anatomical distribution of the catecholamine neurons involved. We lesioned noradrenergic and adrenergic neurons that innervate the medial hypothalamus by microinjecting the retrogradely transported immunotoxin, saporin (SAP) conjugated to antidopamine-β-hydroxylase (DSAP) into the paraventricular nucleus of the hypothalamus. Controls were injected with unconjugated SAP. We found that the DSAP lesion did not impair the feeding response to central or peripheral ghrelin administration, indicating that these neurons are not required for ghrelin’s orexigenic effect. However, the GH response to ghrelin was prolonged significantly in DSAP-lesioned rats. We also found that expression of Fos, an indicator of neuronal activation, was significantly enhanced over baseline levels in A1, A1/C1, C1, and A5 cell groups after ghrelin treatment and in A1, A1/C1, and A5 cell groups after GH treatment. The similar pattern of Fos expression in catecholamine cell groups after GH and ghrelin and the prolonged GH secretion in response to ghrelin in DSAP rats together suggest that activation of hindbrain catecholamine neurons by ghrelin or GH could be a component of a negative feedback response controlling GH levels.