Submitted on June 19, 2007
Accepted on October 8, 2007
Differential effects of estradiol on encoding properties of TMJ units in laminae I and V at the spinomedullary junction in female rats
Akimasa Tashiro1, Keiichiro Okamoto1, Stephan B Milam2, and David A Bereiter3*
1 Diagnostic and Biological Sciences, Univ. Minnesota, Minneapolis, Minnesota, United States
2 Oral and Maxillofacial Surgery, Univ. Texas Health Science Center, San Antonio, Texas, United States
3 Dept Diagnostic and Biological Sciences, U. of Minnesota, Minneapolis, Minnesota, United States
* To whom correspondence should be addressed. E-mail: bereiter{at}umn.edu.
To determine if estrogen status modulated dorsal horn neural activity relevant to temporomandibular joint (TMJ) processing single units were recorded in superficial and deep laminae at the trigeminal subnucleus caudalis/upper cervical cord (Vc/C1-2) junction of ovariectomized (OvX) female rats under barbiturate anesthesia after 17?-estradiol (E2) treatment for two days. E2 dose-dependently enhanced the response to intra-TMJ stimulation by ATP of neurons classified as nociceptive specific (NS), but not wide dynamic range (WDR), in superficial laminae. ATP caused similar responses among NS and WDR neurons from deep laminae in all groups. By contrast, the cutaneous receptive field areas of WDR, but not NS, units in superficial and deep laminae were enlarged in high E2- (HE2) compared to low E2-treated (LE2) females. Units from untreated or vehicle-treated male rats displayed responses similar to LE2 females. TMJ units in superficial laminae from females were more likely to receive convergent cutaneous input and respond to jaw movement than males, independent of E2 treatment. Western blot analysis revealed similar levels of P2X2 and P2X3 receptor protein in Vc/C1-2 or trigeminal ganglion samples in all groups. Immunohistochemistry revealed dense terminal labeling for P2X3 receptors in superficial laminae and moderate labeling in deep laminae at the Vc/C1-2 junction. These data indicated a significant linkage between estrogen status and the magnitude of articular input evoked by ATP from TMJ neurons in the superficial laminae at the Vc/C1-2 junction, while estrogenic modulation of TMJ neurons in deep laminae affected only the convergent input from overlying facial skin.
