Brain area Neural network Afferent or efferent neurons Circadian rhythm center of the brainstem Noradrenergic neurons from the locus coeruleus and serotonergic neurons from the medial raphe nucleus have alternating levels during the course of the day. Alpha1 noradrenergic neurons activate glutaminergic neurons which, via NMDA receptors, inhibit 5-HT1A serotonergic neurons. The latter neurons activate GABAergic neurons which, via GABAA receptors, inhibit alpha1 noradrenergic neurons. • GABAergic neurons from the “mood center” in the brainstem inhibit GABAergic neurons via GABAB receptors. •Glutaminergic neurons from the “mood center” in the brainstem inhibit glutaminergic neurons via m5Glu receptors. “Mood center” of the brainstem Alpha1 noradrenergic neurons activate glutaminergic neurons which, via m5Glu receptors, inhibit 5-HT1A serotonergic neurons. The latter neurons activate GABAergic neurons which, via GABAB receptors, inhibit alpha1 noradrenergic neurons. •Glutaminergic neurons from the hypothalamus which are activated by CRH neurons inhibit 5-HT1A serotonergic neurons via m5Glu receptors. Hypothalamus Neurons containing corticotropin-releasing hormone activate GABAergic and glutaminergic neurons via CRH1 receptors. •GABAergic neurons inhibit D2 dopaminergic neurons in the hippocampus. •Glutaminergic neurons inhibit 5-HT1A serotonergic neurons in the “mood center” of the brainstem. Hippocampus D2 dopaminergic neurons activate glutaminergic neurons, which via NMDA receptors inhibit 5-HT2A serotonergic neurons. The latter neurons activate GABAergic neurons which, via GABAA receptors, inhibit D2 dopaminergic neurons. •Nicotinic cholinergic neurons activate D2 dopaminergic neurons via alpha4beta2 nAch receptors. •Neuropeptide Y neurons from the dentate gyrus inhibit GABAergic neurons via NPY1 receptors. •Substance P neurons activate GABAergic neurons via NK1 receptors.

Table 1: Neural networks in the brainstem, hypothalamus and hippocampus in bipolar disorder.