1. Marked temperature dependence of impulse activity is a property of
mammalian neurons which are mainly localized in the hypothalamus and a
djoining brain regions. 2. Data is presented on the similarity of ther
mal behaviour of neurons in vivo and in vitro. It follows from the evi
dence on the synaptic blockade, postnatal development, and intracellul
ar recordings that inherent thermosensitivity is a property primarily
of warm-sensitive hypothalamic neurons. 3. The Na+/K+ pump does not un
derlie hypothalamic neuron thermosensitivity. Warm-sensitive units pos
sess highly thermosensitive non-inactivating inward sodium current. 4.
Data is presented on thermo-induced membrane structural rearrangement
s based on changes in the physical state of lipids, changes in protein
conformation and membrane skeleton activity. A hypothesis of the rela
tion of threshold temperature responses of warm sensitive hypothalamic
neurons with these membrane phenomena, as well as alternative hypothe
ses, are viewed.