J Neurophysiol (March 1, 2003). 10.1152/jn.00834.2002
Submitted on Submitted 19 September 2002; accepted in final form 1 November 2002

Corticosterone Acts Directly at the Amygdala to Alter Spinal Neuronal Activity in Response to Colorectal Distension

 ¹Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73190; and  ²Oklahoma Foundation for Digestive Research, Basic Science Laboratories, V. A. Medical Center, Oklahoma City, Oklahoma 73104

Qin, Chao, Beverley Greenwood-Van Meerveld, Dean A. Myers, and Robert D. Foreman. Corticosterone Acts Directly at the Amygdala to Alter Spinal Neuronal Activity in Response to Colorectal Distension. J. Neurophysiol. 89: 1343-1352, 2003. Administration of glucocorticoids to the amygdaloid nucleus facilitates visceromotor responses to colorectal distension in rats. The aim of this study was to determine if colorectal hypersensitivity develops through central modulation of spinal neuronal activity. Stereotaxic delivery of corticosterone (n = 10) or cholesterol (control, n = 10) onto the dorsal margin of the amygdala was performed on male Fischer-344 rats. Seven days later, extracellular potentials of single L₆-S₁ spinal neurons were examined for responses to colorectal distension (CRD, 20-80 mmHg, 20 s) in sodium pentobarbital anesthetized and paralyzed animals. The proportions of neurons that responded to noxious CRD in corticosterone-implanted (62/186, 33%) and cholesterol-implanted (55/163, 34%) animals were virtually identical. However, the mean excitatory response of spinal neurons to CRD in corticosterone-treated rats was significantly greater (26.7 ± 2.2 vs. 16.4 ± 1.8 imp/s, P < 0.01) and the duration was longer (37.0 ± 3.9 vs. 25.8 ± 1.5 s, P < 0.05) than in the control group. No significant differences were found in neural responses to nonnoxious and noxious mechanical stimulation of somatic fields between corticosterone-implanted and control groups. In conclusion, our data support the hypothesis that central stimulation of the amygdala by corticosterone sensitizes the lumbosacral spinal neurons that mediate visceromotor reflexes to CRD.