Wake-related activity of tuberomammillary neurons in rats

410

309

Recent evidence suggests that dopamine plays an important role in arousal, but the location of the dopaminergic neurons that may regulate arousal remains unclear. It is sometimes assumed that the dopaminergic neurons in the ventral tegmental area that project to the prefrontal cortex and striatum may regulate the state of arousal; however, the firing of these dopaminergic neurons does not correlate with overall levels of behavioral wakefulness. We identified wake-active dopaminergic neurons by combining immunohistochemical staining for Fos and tyrosine hydroxylase (TH) in awake and sleeping rats. Approximately 50% of the TH-immunoreactive (TH-ir) cells in the ventral periaqueductal gray matter (vPAG) expressed Fos protein during natural wakefulness or wakefulness induced by environmental stimulation, but none expressed Fos during sleep. Fos immunoreactivity was not seen in the substantia nigra TH-immunoreactive cells in either condition. Injections of 6-hydroxydopamine into the vPAG, which killed 55-65% of wake-active TH-ir cells but did not injure nearby serotoninergic cells, increased total daily sleep by ϳ20%. By combining retrograde and anterograde tracing, we showed that these wake-active dopaminergic cells have extensive reciprocal connections with the sleep-wake regulatory system. The vPAG dopaminergic cells may provide the long-sought ascending dopaminergic waking influence. In addition, their close relationship with the dorsal raphe nucleus will require reassessment of previous studies of the role of the dorsal raphe nucleus in sleep, because many of those experiments may have been confounded by the then-unrecognized presence of intermingled wake-active dopaminergic neurons.

Section: Vpag Th-ir Neurons Express Fos After Forced Wakefulnesssupporting

confidence: 92%

Identification of Wake-Active Dopaminergic Neurons in the Ventral Periaqueductal Gray Matter

Lü

Jhou²,

Saper³

2006

410

309

“…Both propofol and pentobarbital cause a sleep-like pattern of neuronal activity in the TMN and VLPO (Nelson et al, 2002(Nelson et al, , 2003Ko et al, 2003;Takahashi et al, 2006), consistent with the reduction in brain histamine levels during anesthesia (Mammoto et al, 1997). Moreover, injection of the GABA A receptor agonist muscimol into the TMN caused LORR, whereas the GABA A receptor antagonist gabazine antagonized LORR (Nelson et al, 2002(Nelson et al, , 2003.…”

Section: Introductionmentioning

confidence: 64%

The Involvement of Hypothalamic Sleep Pathways in General Anesthesia: Testing the Hypothesis Using the GABA_AReceptor β₃N265M Knock-In Mouse

Zecharia¹,

Nelson²,

Gent³

et al. 2009

119

The GABA A receptor has been identified as the single most important target for the intravenous anesthetic propofol. How effects at this receptor are then translated into a loss of consciousness, however, remains a mystery. One possibility is that anesthetics act on natural sleep pathways. Here, we test this hypothesis by exploring the anesthetic sensitivities of GABAergic synaptic currents in three specific brain nuclei that are known to be involved in sleep. Using whole-cell electrophysiology, we have recorded GABAergic IPSCs from the tuberomammillary nucleus (TMN), the perifornical area (Pef), and the locus ceruleus (LC) in brain slices from both wild-type mice and mice that carry a specific mutation in the GABA A receptor ␤ 3 subunit (N265M), which greatly reduces their sensitivity to propofol, but not to the neurosteroid alphaxalone. We find that this in vivo pattern of anesthetic sensitivity is mirrored in the hypothalamic TMN and Pef nuclei, consistent with their role as direct anesthetic targets. In contrast, anesthetic sensitivity in the LC was unaffected by the ␤ 3 N265M mutation, ruling out this nucleus as a major target for propofol. In support of the hypothesis that orexinergic neurons in the Pef are involved in propofol anesthesia, we further show that these neurons are selectively inhibited by GABAergic drugs in vivo during anesthesia, and that a modulation in the activity of Pef neurons alone can affect loss of righting reflex. Overall, our results support the idea that GABAergic anesthetics such as propofol exert their effects, at least in part, by modulating hypothalamic sleep pathways.

“…Noradrenergic, orexinergic, cholinergic, and dopaminergic wake neuron identifiers were labeled with Alexa Fluor 488 (green; Invitrogen, Carlsbad, CA), and c-fos was tagged with Alexa Fluor 594 (red). Because the primary antibody labeling histaminergic neurons (anti-HDC) was generated in the rabbit, c-fos for HDC labeled neurons was examined using DAB-nickel for c-fos labeling first, followed by rabbit anti-HDC and DAB labeling for both the ventral and caudal tuberomammillary nuclei, as previously delineated in the rat (Ko et al, 2003). In all cases, cells were deemed c-fos positive if c-fos labeling was evident in the nucleus.…”

Section: Methodsmentioning

confidence: 99%

Selective Loss of Catecholaminergic Wake–Active Neurons in a Murine Sleep Apnea Model

Zhu¹,

Fenik²,

Zhan³

et al. 2007

165

117

The presence of refractory wake impairments in many individuals with severe sleep apnea led us to hypothesize that the hypoxia/ reoxygenation events in sleep apnea permanently damage wake-active neurons. We now confirm that long-term exposure to hypoxia/ reoxygenation in adult mice results in irreversible wake impairments. Functionality and injury were next assessed in major wake-active neural groups. Hypoxia/reoxygenation exposure for 8 weeks resulted in vacuolization in the perikarya and dendrites and markedly impaired c-fos activation response to enforced wakefulness in both noradrenergic locus ceruleus and dopaminergic ventral periaqueductal gray wake neurons. In contrast, cholinergic, histaminergic, orexinergic, and serotonergic wake neurons appeared unperturbed. Six month exposure to hypoxia/reoxygenation resulted in a 40% loss of catecholaminergic wake neurons. Having previously identified NADPH oxidase as a major contributor to wake impairments in hypoxia/reoxygenation, the role of NADPH oxidase in catecholaminergic vulnerability was next addressed. NADPH oxidase catalytic and cytosolic subunits were evident in catecholaminergic wake neurons, where hypoxia/reoxygenation resulted in translocation of p67 phox to mitochondria, endoplasmic reticulum, and membranes. Treatment with a NADPH oxidase inhibitor, apocynin, throughout hypoxia/reoxygenation exposures conferred protection of catecholaminergic neurons. Collectively, these data show that select wake neurons, specifically the two catecholaminergic groups, can be rendered persistently impaired after long-term exposure to hypoxia/reoxygenation, modeling sleep apnea; wake impairments are irreversible; catecholaminergic neurons are lost; and neuronal NADPH oxidase contributes to this injury. It is anticipated that severe obstructive sleep apnea in humans destroys catecholaminergic wake neurons.