Distribution and effects of 5-HT(1A) receptors in distal cerebral spinal fluid-contacting neurons in rat brain parenchyma in neuropathic pain / 生理学报

ABSTRACT

The present study aimed to explore the effects of 5-HT(1A) receptors in the distal cerebral spinal fluid-contacting neurons (CSF-CNs) in rat brain parenchyma in neuropathic pain. The model of neuropathic pain with chronic constriction injury (CCI) of the sciatic nerve was made in Sprague-Dawley rats. The behavioral studies of animal were scored and the paw withdrawal latency (PWL) and paw withdrawal threshold (PWT) were measured. The distribution and expression of 5-HT(1A) receptors were observed in the distal CSF-CNs in brain parenchyma with double labeling of cholera toxin subunit B with horseradish peroxidase (CB-HRP) and 5-HT(1A) receptors with immunhistochemistry. The relationship between 5-HT(1A) receptors in distal CSF-CNs and neuropathic pain was analyzed. The results were as follows. On days 1, 3, 7, 14 of neuropathic pain, the PWL was 19.37±2.74, 12.04±1.77, 8.74±1.15 and 12.31±1.94, respectively; the PWT was 18.58±3.62, 13.05±1.81, 6.66±1.43 and 11.55±2.01, respectively. CB-HRP-labeled neurons of two clusters were always found in definite region but not in other area in brain parenchyma. The number of neurons double-labeled with CB-HRP/5-HT(1A) receptors in each group was 276.14±36.00, 161.72±28.41, 108.64±6.81, and 139.76±44.64, which was about 95%, 60%, 40% and 55% of all CB-HRP-labeled neurons in the four courses of neuropathic pain, respectively. It is suggested that the distal CSF-CNs are always located in a special region in rat brain parenchyma and most of them have 5-HT(1A) receptors. A negative correlation is found between the expression of 5-HT(1A) receptors and neuropathic pain.