Journal of Neurophysiology, Vol 66, Issue 2 623-634, Copyright © 1991 by APS
Temperature neurons in the crotaline trigeminal ganglia
S. Terashima and Y. F. Liang
Department of Physiology, University of the Ryukyus School of Medicine, Okinawa, Japan.
1. Intrasomal recordings were made with microelectrodes from 153 warm
(infrared) neurons in the trigeminal ganglia of 36 crotaline snakes,
Trimeresurus flavoviridis. Background discharges were observed at room
temperature. The 153 warm neurons were classified into two groups: 81 were
sensitive to less than or equal to 10 mg of von Frey hair mechanical
stimulation (warm T + M neuron), and 72 were insensitive to up to 100 mg or
more of mechanical stimulation (warm T neuron). For T + M and T neurons the
receptive fields were all located in the pit organ. The mechanically
sensitive field of warm T + M neurons located within the infrared receptive
field on the pit membrane was less than 1 mm in diameter, and there was
only one field per neuron. 2. Electrophysiological parameters were
measured. These measurements included membrane potential, action potential
amplitude, time of peaking, time duration at the resting membrane potential
level, afterhyperpotential (AHP) height and AHP time to half-decay, and
maximum rates of depolarization and repolarization. No difference in action
potential parameters between the means of these two submodality groups was
observed. 3. Intracellular horseradish peroxidase (HRP) labeling was used
for defining the warm neuron profile. The somata of warm T and warm T + M
neurons and T- or Y-shaped bifurcations of the axon were observed in the
ganglion. At the bifurcation point, nodes of Ranvier were observed, but
without broad triangular expansion. Diameters of the central axons were
thinner than those of the peripheral or stem axons. There were no
differences between the mean diameters of the two submodalities. 4. The
central axons of warm T and T + M neurons projected to the lateral
descending nucleus of the trigeminal nerve (LTTD). Their synaptic boutons
were found in the LTTD. No branching of the axons to the principal sensory
nucleus or the descending nucleus of the trigeminal nerve was found. These
results were the same for six warm T and eight warm T + M neurons. 5.
Conduction velocities of the peripheral fibers were measured by stimulating
superficial branches of the maxillary nerve electrically. Three groups of
conduction velocity were identified in the compound potentials. The
conduction velocity of the peak action potential of the warm T fibers was
6.9 +/- 1.2 (SD) m/s (n = 18), that of the T + M fibers 6.7 +/- 0.9 m/s (n
= 23). These fell into the second group of the compound
potentials.(ABSTRACT TRUNCATED AT 400 WORDS)
