Changes in substance P content at the hypothalamic-pituitary axis during the Wallerian degeneration of peripheral sympathetic neurons after superior cervical ganglionectomy in male rats: Effect of hyperprolactinemia

The effects of Wallerian degeneration of the peripheral sympathetic neurons projecting to the hypothalamus on the mechanism of interaction between pro lactin and substance P (SP) were examined. The effects of superior cervical ganglionectomy (SCGx) on SP content in various hypothalamic regions and in the hypophysis were evaluated in control and hyperprolactinemic rats. Male rats that received pituitary transplants at the age of 5 days and age-matc hed sham-operated controls were used. Pituitary grafting significantly incr eased circulating values of prolactin, as did SCGx. In hyperprolactinemic r ats, SCGx partially decreased plasma prolactin levels. Neonatal hyperprolac tinemia decreased SP content in the anterior (AH) and posterior (PH) hypoth alamus and in the median eminence (ME), but increased it in the mediobasal hypothalamus (MBH). Acute SCGx significantly increased SP in the MBH, PH, a nd ME. SCGx in hyperprolactinemic animals further increased SP content in M BH. In the ME and Ah, SCGx in pituitary grafted rats decreased SP content a s compared with the controls. In the pituitary gland (PG), SCGx only decrea sed SP content in hyperprolactinemic, but not in control rats. An interacti on between peripheral noradrenergic neurons and prolactin to, regulate SP w ithin the hypothalamus was positive in the MBH, AH, ME, and PG, but not in the PH. These data indicate the existence of interactive mechanisms between prolactin and the peripheral sympathetic neurons to regulate SP content at the hypothalamic-pituitary axis. Interrelationships between prolactin and SP were also observed.