Spinal dorsal horn neurons responding to noxious distention of the ureter
in anaesthetized rats.
Laird, Jennifer M.A., carolina Roza and Fernando cERVERO.
Department of Physiology & Pharmacology, Faculty of Medicine, University of
Alcal[acute]a, Alcal[acute]a de Henares, E-28871 Madrid, Spain.
APStracts 3:0150N, 1996.
SUMMARY AND CONCLUSIONS
1. Stimulation of the ureter in man evokes only painful sensations. A large
proportion of ureteric afferents show high activation thresholds to ureter
pressure increases, and encode stimuli within the noxious range. However,
little is known about how these properties are reflected in the central
processing of ureteric information. In this study, dorsal horn neurons
recorded in the left side of T12 - L1 spinal cord of anaesthetized rats have
been tested for responses to innocuous and noxious pressure stimuli applied to
the ipsilateral ureter. 2. Single unit recordings were made from 76 neurons
with somatic receptive fields on the left flank, of which 57 were fully
characterized and tested by raising the ureter pressure to 80 mmHg for 30s. Of
these 57 neurons, 24 (42%) were influenced by the ureter stimulus, as follows:
18 were excited, 2 were inhibited, and 4 neurons showed changes in background
activity and/or in the area of their somatic receptive field, without a time-
locked change in firing rate. The remaining 33 cells (58%) showed no changes
in firing rate, background activity, somatic receptive field area or input
properties as a result of ureter stimulation. 3. Neurons responding to the 80
mmHg stimulus were further tested with a range of ureter pressures (5 - 100
mmHg). No responses were evoked by stimuli of less than 20 mmHg, and responses
observed were proportional to stimulus intensity. Excitatory responses showed
a long onset latency (median = 23s), and long afterdischarges (median = 145s).
4. All neurons with ureter input had nociceptive somatic inputs. When compared
to neurons without ureter input, cells with ureter input were more likely to
show background activity (80% vs. 27%), and more likely to have bilateral
somatic receptive fields (30% vs. 6%). Neurons with ureter input had higher
rates of background activity, and larger somatic receptive fields. Ureter
stimulation also produced changes in the somatic receptive field area of
neurons excited or inhibited by the stimulus, indicating a high degree of
plasticity in the ureteric nociceptive pathway. 5. We conclude that the
characteristics of the responses of dorsal horn neurons with ureter input to
noxious and innocuous ureter stimulation indicate that they receive ureteric
input mainly from high threshold afferents, and that their response properties
correlate well with ureteric pain sensation in man.
Received 22 March 1996; accepted in final form 24 June 1996.
APS Manuscript Number J241-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996