[Abstract Title]. - Society for Neuroscience

Title: Responses of T3 spinal neurons to cardiosomatic stimulation in proestrous female vs. male
rats
Authors: *J. M. LITTLE, J. P. FARBER, R. W. BLAIR, R. D. FOREMAN;
Physiol., Univ. Oklahoma HSC, Oklahoma City, OK
Abstract: Gender differences in cardiac pain have been reported from clinical studies: compared
to men, women experience chest pain from angina that is longer in duration, more severe, and
more frequent. Referred pain areas associated with cardiac pathophysiology are also different,
suggesting differences in processing of cardiosomatic input. The mechanisms underlying gender
differences in cardiac pain are unknown. One possible mechanism for the observed differences
could be related to the circulating levels of estradiol. The present study was done to test the
hypothesis that there were gender differences related to estradiol levels in the responses of T3
spinal neurons to cardiosomatic information in an animal model that has been shown to exhibit
cardiac pain. Estradiol levels peak between 50 and 150 pg/ml in female rats during proestrus. In
male rats, estradiol levels range from 10 to 15 pg/ml. In this study, adult Sprague-Dawley male
(n=10) and proestrous female rats (n=11) were anesthetized with sodium pentobarbital and
paralyzed. Extracellular potentials of T3 spinal neurons were recorded in response to mechanical
somatic stimulation and chemical cardiac stimulation. A volume of 0.2 ml saline (control) was
injected into the pericardial sac and removed after 60 seconds. This was followed by an injection
of 0.2 ml algesic chemicals (noxious stimuli) into the pericardial sac. Somatic fields were located
by applying brush, pressure, and pinch to the upper body. Sizes of the somatic fields were
evaluated before and after intrapericardial injection of chemicals to determine if the chemicals
sensitized the neurons. Thirty eight percent and 57% of neurons responded to noxious chemical
cardiac stimuli in female and male rats, respectively. Of those neurons receiving input from the
heart, 62% in female and 56% in male rats also received input from somatic structures. In female
rats, 76% of neurons responding to somatic stimuli had somatic receptive fields located on the
side of the upper body, while 24% of neurons had somatic fields located on the chest. Most of
the somatic fields in male rats were also located on the side of the upper body (90%), with only a
few located on the chest (10%). The size of the receptive fields between female and male rats
was not significantly different. Somatic field sizes in 69% of neurons in females and 76% of
neurons in males did not change after intrapericardial injection of noxious chemicals. These
results indicate there are no significant differences (p>0.05) in the responses of T3 spinal
neurons to mechanical somatic stimulation and noxious chemical cardiac stimulation between
male and proestrous female rats, despite differences in estradiol levels.
Disclosures: J.M. Little, None; J.P. Farber, None; R.W. Blair, None; R.D. Foreman, None.
Poster
269. Pain: Visceral Pain II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm