Temperature-sensitive properties of rat suprachiasmatic nucleus neurons

The hypothalamic suprachiasmatic, nucleus (SCN) contains a heterogeneous po pulation of neurons, some of which are temperature sensitive in their Bring rate activity. Neuronal thermosensitivity may provide cues that synchroniz e the circadian clock. In addition, through synaptic inhibition on nearby c ells, thermosensitive neurons may provide temperature compensation to other SCN neurons, enabling postsynaptic neurons to maintain a constant firing r ate despite changes in temperature. To identify mechanisms of neuronal ther mosensitivity, whole cell patch recordings monitored resting and transient potentials of SCN neurons in rat hypothalamic tissue slices during changes in temperature. Firing rate temperature sensitivity is not due to thermally dependent changes in the resting membrane potential, action potential thre shold, or amplitude of the fast afterhyperpolarizing potential (AHP). The p rimary mechanism of neuronal thermosensitivity resides in the depolarizing prepotential, which is the slow depolarization that occurs prior to the mem brane potential reaching threshold. In thermosensitive neurons, warming inc reases the prepotential's rate of depolarization, such that threshold is re ached sooner. This shortens the interspike interval and increases the firin g rate. In some SCN neurons, the slow component of the AHP provides an addi tional mechanism for thermosensitivity. In these neurons, warming causes th e slow AHP to begin at a more depolarized level, and this, in turn, shorten s the interspike interval to increase firing rate.