AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 2 440-R448, Copyright © 1993 by American Physiological Society
Temperature sensitivity of neurons in slices of the rat PO/AH hypothalamic area: effect of calcium
H. A. Schmid and F. K. Pierau
Max-Planck-Institut fur Physiologische, W. G. Kerckhoff-Institut, Bad Nauheim, Germany.
The temperature sensitivity of spontaneously active neurons in slices of
the preoptic and anterior hypothalamic areas (PO/AH) of rats was assessed
by extracellular recording during sinoidal temperature displacements.
Classifying cells according to their temperature coefficients (TC,
impulses.s-1.degree C-1) revealed that 48% of the 177 cells tested were
warm sensitive, 5% were cold sensitive, and 47% were temperature
insensitive. Increasing the calcium concentration ([Ca2+]) of the
artificial cerebrospinal fluid (aCSF) from 0.9 to 1.5 mM Ca2+ decreased the
firing rate (FR) and TC of PO/AH neurons. Decreasing extracellular [Ca2+],
however, elicited concentration-dependent increases in both parameters.
This means in physiological terms that the number and temperature
sensitivity of PO/AH neurons is strongly dependent on the extracellular
[Ca2+]. Furthermore, these results suggest that caution is warranted when
comparing numbers and temperature sensitivities of PO/AH neurons. After
blocking synaptic transmission by superfusing the slice with aCSF
containing reduced [Ca2+] and elevated [Mg2+], 8 out of 35 neurons ceased
their spontaneous activity within 6 min, and 27 remained spontaneously
active in low [Ca2+]-high [Mg2+] solution, but displayed unstable
spontaneous activity and temperature sensitivity. It is concluded that aCSF
with reduced [Ca2+] and elevated [Mg2+] is not a suitable tool to
discriminate between inherent and synaptically mediated thermosensitivity.
