Similarities in development of substance P and somatostatin in peripheral sensory neurons: effects of capsaicin and nerve growth factor.

Abstract

Development of the 2 putative peptide neurotransmitters, substance P (SP) and somatostatin (SS), were compared in rat dorsal root ganglion (DRG) and spinal cord in vivo. The content of SS in the 6th cervical DRG increased 5-fold during the first 5 wk of life, rising from 24 pg/ganglion at birth. SP content increased 4.5-fold during the first 5 wk, from 56 pg/ganglion at birth. The developmental profiles for these 2 peptides were virtually parallel, suggesting that their respective neuronal populations developed in synchrony. Treatment with nerve growth factor (NGF) significantly increased the content of both SP and SS in the DRG and dorsal spinal cord. Treatment with capsaicin significantly decreased both SP and SS in the DRG and dorsal spinal cord. Experiments involving NGF or capsaicin treatment of sensory neurons must be interpreted with extreme care, because specificity is not limited to a single peptide phenotype. Although the mechanisms of action of NGF and capsaicin on SP and SS are not defined, the similarity of the responses of the 2 peptides suggests that their development may be regulated by similar processes.