Journal of Neuroscience, Vol 2, 1538-1553, Copyright © 1982 by Society for Neuroscience
Effects of temperature on identified central neurons that control jumping in the grasshopper
TW Abrams and KG Pearson
Grasshoppers, like many poikilotherms, are generally more active at warmer
body temperatures. In particular, they jump more frequently when warm. To
determine the neuronal basis of this increase in jumping activity, we
investigated the effects of temperature on the properties of identified
central neurons known to be involved in the control of the jump; these
included the fast extensor tibiae (FETi) motoneuron and the C, G, and M
interneurons. Heating did not result in a reduction in the current or
voltage threshold for action potentials; in most cases, there was an
increase in the current threshold with heating. At higher temperatures, the
frequency-current relations of interneurons and motoneurons had steeper
slopes. With strong current pulses, increasing the temperature resulted in
an increase in the initial peak firing frequencies of central neurons and
usually also in their steady state firing frequencies. A second temperature
effect favoring increased CNS activity in warm grasshoppers was increased
afferent input from the periphery. In a broad variety of sensory receptors,
there was a dramatic increase in their sensitivity to sensory stimuli at
both threshold and suprathreshold intensities. Various identified central
neurons differed in the way in which some of their properties were
influenced by temperature. The C and G interneurons showed a striking
similarity in the unusual way in which their repetitive firing properties
were influenced by heating. Since these neurons are sibling progeny of a
single neuroblast, this shared physiological property is correlated with
their developmental history.
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