The effect of temperature on electrical interactions between antidromically stimulated frog motoneurons and dorsal...

The effect of temperature on electrical interactions between antidromically stimulated motoneurons and dorsal root afferents was studied in the isolated and hemisected spinal cord of the frog, superfused with Ringer in which Ca2+ was equimolarly replaced by Co2+ or Mn2+ to suppress chemical synaptic transmission. Suction electrodes were used for stimulating and/or recording from dorsal and ventral roots from segments IX or X. Intrafibre recordings from sensory fibres were made at their point of entry into the spinal cord. Supramaximal ventral root stimuli elicited two distinct responses in the segmental dorsal root. First a brief short-latency depolarizing potential. Second, at temperatures below 11 degrees C, a second depolarizing root potential appeared following the short-latency depolarizing potential-I. Amplitude and duration of short-latency depolarizing potential-II reversibly increased as the bath temperature was decreased, reaching a maximum at 3 degrees C. Between 8 and 3 degrees C, short-latency depolarizing potential-II increased in amplitude by 20%/degrees C. In contrast short-latency depolarizing potential-I did not show substantial changes with temperature. The short-latency depolarizing potential-II, unlike short-latency depolarizing potential-I showed stepped fluctuations in amplitude, and appeared to be composed of unitary events. Intrafibre records revealed that the unitary events corresponded to action potentials on individual dorsal root fibres. Double shocks applied to the ventral root, at constant bath temperatures (below 11 degrees C), revealed facilitation of the short-latency depolarizing potential-II, which was maximal between 50 and 80 ms and lasted about 200 ms. Neither the antidromic motoneurone field potential nor the short-latency depolarizing potential-I were facilitated.(ABSTRACT TRUNCATED AT 250 WORDS)