Electrophysiological properties of neurons and synapses in the lateral habenular complex (LHb).

Animal including human behavior is highly sophisticated. Besides reflective actions it is largely based on the desire for magnificent internal feelings, which are provided by the reward system. Its counterpart an "anti-reward" system is mainly composed of the lateral habenular complex (LHb) and its extensive interconnections with the monoaminergic cell groups in the mid- and hindbrain. The present review focuses on the neuronal composition and the internal signaling in the LHb. Morphologically six distinct types of neurons (spherical, fusiform-1, fusiform-2, polymorphic, vertical, neurogliaform) can be identified. In contrast, setting aside neurogliaform cells, only three broad categories (silent, tonic firing, bursting) can be identified using electrophysiological criteria. Functionally, LHb neurons express HCN channels and therefore in an "indifferent" situation LHb appears to be tonically active. When the situation takes a turn for the better habenular cells become inhibited, releasing dopaminergic VTA neurons from continuous damping. In contrast, when the situation takes a turn for the worse, LHb neurons are stimulated, completely shutting down the activity of dopaminergic cells in the VTA.