Temporal Processing of Aortic Nerve Evoked Activity in the Nucleus of the
Scheuer, Deborah A., Jing Zhang, Glenn M. Toney and Steven W. Mifflin.
Department of Pharmacology, The University of Texas Health Science Center
at San Antonio, San Antonio, TX 78284-7764.
APStracts 3:0167N, 1996.
SUMMARY AND CONCLUSIONS
1. Temporal processing of heterogeneous afferent signals by nucleus of the
solitary tract (NTS) neurons has been previously characterized. Experiments
were performed in 26 pentobarbital anesthetized male Sprague-Dawley rats to
characterize the temporal processing of evoked activity in NTS neurons using
the aortic nerve, which contains exclusively arterial baroreceptor afferent
fibers. 2. Extracellular single-cell activity was examined in the NTS during
electrical stimulation of the aortic nerve using a conditioning-test paradigm.
3. Results were obtained from 49 neurons, 22 of which were characterized as
receiving monosynaptic input from aortic nerve afferents. The average number
of evoked potentials per aortic nerve stimulation was 1.1+/-0.1 for the
monosynaptic and 1.2+/-0.2 for the polysynaptic neurons. Spontaneous activity
averaged 3.7+/-0.7 Hz. No neuron exhibited an obvious pulse-rhythmic
discharge. The average peak onset latency for monosynaptic cells of 17+/-2
msec (range 3-31 msec) was significantly (P<0.05) shorter than the average of
26+/-1 msec (range 13-38 msec) for the polysynaptic cells. The average onset
latency variability was also less in monosynaptic compared with polysynaptic
cells (4+/-1 msec vs. 8+/-1 msec; P<0.05). 4. Neurons characterized as
receiving a monosynaptic input from the aortic afferents generally did not
exhibit time dependent inhibition. Significant inhibition was observed only at
a conditioning-test interval of 50 msec, when the average test response was
79+/-8% of control. In contrast, the average response following a 50 msec
conditioning-test interval for neurons receiving polysynaptic input from the
aortic nerve was only 32+/-8% of control. Significant inhibition was observed
at conditioning-test intervals of up to 200 msec. 5. At a conditioning-test
interval of 50 msec only 5 of 22 monosynaptic neurons were inhibited by more
than 50%. Mean arterial pressure during the conditioning-test procedure was
significantly lower for these neurons than for the 17 cells which were
inhibited less than 50%. This suggests that the level of activity in
convergent afferent input might influence the magnitude of time dependent
inhibition. 6. There was an essentially linear recovery from time dependent
inhibition evident in polysynaptic neurons which were tested at all
conditioning-test intervals, suggesting a single mechanism of variable
duration. Results reported here are consistent with current theory that time
dependent inhibition is mediated by disfacilitation. 7. The results
demonstrate that NTS neurons receiving monosynaptic input from the aortic
depressor nerve infrequently exhibit time dependent inhibition. This could
allow for the original, unmodified afferent information to be dispersed to
subsequent neurons. In contrast, neurons receiving polysynaptic input undergo
time dependent inhibition similar to that which has been reported for other
afferent inputs. This could allow for differential degrees of fidelity in the
transfer of the afferent information to specific efferent pathways. Therefore,
the temporal pattern of firing in individual baroreceptor afferents could play
a critical role in the function of the arterial baroreflex, and therefore, in
the regulation of blood pressure.
Received 17 April 1996; accepted in final form 5 August 1996.
APS Manuscript Number J323-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996