Glutamatergic cells in the periaqueductal gray matter mediate sensory inputs after bladder stimulation in freely moving rats

Objectives To determine the phenotype of the ventrolateral part of the periaqueductal gray matter neurons after bladder stimulation. Methods In the experimental group, electrical stimulation of the bladder was carried out under freely moving condition by a bipolar stimulation electrode implanted in the bladder wall. Thereafter, the brain sections were processed for immunohistochemical analysis using antibodies against c-Fos (neuronal activation marker) together with one of the following: tyrosine hydroxylase (dopaminergic cell marker), vesicular glutamate transporter (glutamatergic cell marker), serotonin, glutamate decarboxylase (glutamate decarboxylase 67, gamma-aminobutyric acid cell marker) and neuronal nitric oxide synthase. We used design-based confocal stereological analysis to quantify the immunohistochemically stained sections. Results A significant increase in the number of c-Fos-positive cells in the ventrolateral part of the periaqueductal gray matter after stimulation was found. Furthermore, the ratio of c-Fos cells double labeled with vesicular glutamate transporter was significantly higher in the ventrolateral part of the periaqueductal gray matter region in the stimulated compared with the sham group. Quantitative analysis of the other four cell types did not show any significant difference. Conclusion These findings suggest that glutamatergic neurotransmission in the ventrolateral part of the periaqueductal gray matter is seemingly the main pathway to be activated after receiving sensory signals from the bladder.