Tracing studies have revealed LHA interconnections with the dorsomedial hypothalamic nucleus (DMH). These connections display subnuclear topography and are partially concentrated around a reciprocal innervation of medial parts of the LHA and the DMH.74,94,150-151 The DMH has been implicated in several homeostatic functions, in particular the stress response; see ref 152. Intriguingly, destruction of the DMH results in the disruption of circadian rhythms.153 In this context, a prominent GABAergic projection from the SCh to the DMH143 has generated much interest. Signals from the SCh to the DMH may be further transmitted to the LHA Hcrt neurons by way of glutamatergic neurons which also contain TRH, as demonstrated recently by Chou et al.153 Thus, in addition to the direct SCh-LHA pathway described above, signals from the circadian pacemaker may also regulate Hcrt neurons by inhibiting excitation deriving from the DMH. Adding to the complexity is the existence of a GABAergic projection from the DMH to the VLPO, which could serve to promote arousal drive by disinhibition of Hcrt neurons.148153
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