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bioRxiv2019

Dysfunction of ventral tegmental area GABA neurons causes mania-like behavior

The ventral tegmental area (VTA), an important source of dopamine, regulates goal- and reward-directed and social behaviors, wakefulness and sleep. Hyperactivation of dopamine neurons generates behavioral pathologies. But any roles of non-dopamine VTA neurons in psychiatric illness have been little explored. Lesioning or chemogenetically inhibiting VTA GABAergic (VTAVgat) neurons generated persistent wakefulness with mania-like qualities: locomotor activity was increased; sensitivity to D-amphetamine was heightened; immobility times decreased on the tail suspension and forced swim tests; and sucrose preference increased. Furthermore, after sleep deprivation, mice with lesioned VTAVgat neurons did not catch up on the lost NREM sleep, even though they were starting from an already highly sleep-deprived baseline, suggesting that the sleep homeostasis process was bypassed. The mania-like behaviors, including the sleep loss, were reversed by the mood-stabilizing drug valproate, and re-emerged when valproate treatment was stopped. Lithium salts, however, had no effect. The mania like-behaviors partially depended on dopamine, because giving D1/D2/D3 receptor antagonists partially restored the behaviors, but also on VTAVgat projections to the lateral hypothalamus (LH). Optically or chemogenetically inhibiting VTAVgat terminals in the LH elevated locomotion and decreased immobility time during the tail suspension and forced swimming tests. VTAVgat neurons are centrally positioned to help set an animals (and humans) level of mental and physical activity. Inputs that inhibit VTAVgat neurons intensify wakefulness (increased activity, enhanced alertness and motivation), qualities useful for acute survival. Taken to the extreme, however, decreased or failed inhibition from VTAVgat neurons produces mania-like qualities (hyperactivity, hedonia, decreased sleep).

neuroscience↗

bioRxiv2019

Galanin neurons in the hypothalamus link sleep homeostasis, body temperature and actions of the alpha2 adrenergic agonist dexmedetomidine

Sleep deprivation induces a characteristic rebound in NREM sleep accompanied by an immediate increase in the power of delta (0.5 - 4 Hz) oscillations, proportional to the prior time awake. To test the idea that galanin neurons in the mouse lateral preoptic hypothalamus (LPO) regulate this sleep homeostasis, they were selectively genetically ablated. The baseline sleep architecture of LPO-{Delta}Gal mice became heavily fragmented, their average core body temperature permanently increased (by about 2{degrees}C) and the diurnal variations in body temperature across the sleep-wake cycle also markedly increased. Additionally, LPO-{Delta}Gal mice showed a striking spike in body temperature and increase in wakefulness at a time (ZT24) when control mice were experiencing the opposite - a decrease in body temperature and becoming maximally sleepy (start of "lights on"). After sleep deprivation sleep homeostasis was largely abolished in LPO-{Delta}Gal mice: the characteristic increase in the delta power of NREM sleep following sleep deprivation was absent, suggesting that LPO galanin neurons track the time spent awake. Moreover, the amount of recovery sleep was substantially reduced over the following hours. We also found that the 2 adrenergic agonist dexmedetomidine, used for long-term sedation during intensive care, requires LPO galanin neurons to induce both the NREM-like state with increased delta power and the reduction in body temperature, characteristic features of this drug. This suggests that dexmedetomidine over-activates the natural sleep homeostasis pathway via galanin neurons. Collectively, the results emphasize that NREM sleep and the concurrent reduction in body temperature are entwined at the circuit level. SignificanceCatching up on lost sleep (sleep homeostasis) is a common phenomenon in mammals, but there is no circuit explanation for how this occurs. We have discovered that galanin neurons in the hypothalamus are essential for sleep homeostasis as well as for the control of body temperature. This is the first time that a neuronal cell type has been identified that underlies sleep homeostasis. Moreover, we show that activation of these galanin neurons are also essential for the actions of the 2 adrenergic agonist dexmedetomidine, which induces both hypothermia together with powerful delta oscillations resembling NREM sleep. Thus, sleep homeostasis, temperature control and sedation by 2 adrenergic agonists can all be linked at the circuit level by hypothalamic galanin neurons.

neuroscience↗