Developmental changes in the electrophysiological properties of brainstem
trigeminal neurons during pattern (barrelette) formation.
William Guido, Emine Gnhan-Agar, & Reha S. Erzurumlu.
Department of Cell Biology and Anatomy and Neuroscience Center of
Excellence, LSU Medical Center New Orleans, LA 70112.
APStracts 4:326N, 1997.
ABSTRACT
Developmental changes in the electrophysiological properties of brainstem
trigeminal neurons during pattern (barrelette) formation. In the brainstem
trigeminal nuclei of rodents there is a patterned representation of whiskers
and sinus hairs. The subnucleus interpolaris (SPI) contains the largest and
the most conspicuous whisker patterns (barrelettes). Although neural activity
plays a role in pattern formation, little is known about the
electrophysiological properties of developing barrelette neurons. Here we
examined the functional state of early postnatal SPI neurons during and after
the consolidation of patterns by using in vitro intracellular recording
techniques. _After the consolidation of barrelettes (>P4), responses to
intracellular current injection consistently reflected the activation of a
number voltage-dependent conductances. Most notable was _a mixed cation
conductance (IH) that prevented strong hyperpolarization, and _a large low
threshold Ca2+ conductance which led to Ca2+ spikes and burst firing. At the
oldest ages tested (P11-P14) some cells also exhibited an outward
K+conductance (IA) which led to significant delays in action potential firing.
Between P0-3 a time when the formation of barrelettes in the brainstem is
still susceptible to damage of the sensory periphery, cells responded linearly
to intracellular current injection, indicating they either lacked such
voltage-gated properties or weakly expressed them. At all ages tested (P0-14),
SPI cells were capable of generating trains of action potentials in response
to intracellular injection of depolarizing current pulses. However, during the
first few days of postnatal life, spikes were shorter and longer.
Additionally, spike trains rose more linearly with stimulus intensity and
showed frequency accommodation at early ages. Taken together, these results
indicate that the electrophysiological properties of SPI neurons change
markedly during the period of barrelette consolidation. Moreover, the
properties of developing SPI neurons may play a significant role in pattern
formation by minimizing signal distortion and ensuring that excitatory
responses from sensory periphery are accurately received and transmitted
according to stimulus strength.
Received 28 August 1997; accepted in final form 17 November 1997.
APS Manuscript Number J718-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997