Excitatory actions of orexins in rat paraventricular nucleus of thalamus

Abstract

The midline thalamic paraventricular nucleus (PVT) receives a unique orexinergic innervation. To address possible function, this investigation used patch clamp recordings in rat brain slice preparations to evaluate intrinsic properties of PVT neurons and neuronal responses to bath-applied orexin peptides (A and/or B). PVT neurons displayed distinct state-dependent burst or tonic firing patterns, time dependent and time-independent inward rectification, T-type currents and low threshold spikes, action potential after-hyperpolarizations, spike frequency adaptation and spike broadening. A majority responded to both orexin peptides with slowly rising and prolonged membrane depolarizations, and inward currents that involved closure of potassium channels and/or opening of nonselective cationic channels. These data imply that endogenously released orexins likely act at both types of orexin receptors that can engage two conductances to modulate and increase neuronal excitability in PVT, a role that may be important for 'arousal' and neurotransmission within this midline thalamic nucleus.