Peripheral projections of primary sensory neurons immunoreactive for brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) is synthesized in a subpopulation of primary sensory neurons and transported anterogradely to the spinal cord and peripheral targets. In the present study, the peripheral projection of sensory neurons immunoreactive (-ir) for BDNF was examined by a combined method of immunohistochemistry and retrograde tracing in rats. It was found that 36.3% of sensory neurons projecting to subcutaneous tissues, 9.8% to epidermis and 8.3% to muscle, contained BDNF immunoreactivity. In contrast, only 0.2% of sensory neurons projecting to adrenal gland and 0.9% to coeliac ganglia contained BDNF. A small proportion of sensory neurons projecting to muscles, mesenteric blood vessels and hair follicles was also BDNF immunoreactive. These results provide evidence that primary sensory neurons immunoreactive for BDNF project mainly to subcutaneous tissues but not to autonomic ganglia and their adjacent viscera.