Exp Neurobiol 8:93-98, 1999

The Effects of Capsaicin on the Ultrastructure of the Hypothalamic Neurosecretory Cell in the Adult Rat.

Jong Eun Lee, Won Taek Lee, Seung Hwa Park, Sung Ho Lee, Kyung Ah Park

Department of Anatomy, Yonsei University College of Medicine, Seoul, Korea.

Capsaicin, the pungent algesic substance of the red pepper is known to be a neurotoxic substance, interrupting the pain conducting pathway. To investigate the effects on the adult animals, immunohistochemical and electron microscopical observations were made after capsaicin treatment. Capsaicin (50 mg/kg) was injected subcutaneously to adult rats, and vasopressin and oxytocin-immunoreactive neurons in supraoptic and paraventricular nuclei of the hypothalamic area were observed after 1 week, 1 month and 2 months later. In electron microscopical findings, vasopressin- and oxytocin-immunoreactive cells showed high density immunopositive materials in the axoplasm of unmyelinated fibers and also in the small diameter myelinated fiber. In the capsaicin treated group, immunopositive profiles were hardly observed. In addition, swelling axons, and destruction of cell organelles and microtubules were observed in capsaicin treate rats. The substance P- and somatostatin-immunoreactive fibers in the hypothalamus did not chang. These results indicate that capsaicin treatment in adult rats have profound effect on the substance P- and oxytocin-immunoreactive neurons, but have little effect on the substance P- and somatostatin-immunoreactivity of the hypothalamus. Therefore it was concluded that the effects of capsaicin in the thalamus varies depending on the cell types and location.

Key Words: capsaicin, hypothalamus, neurosecretory cell, vasopressin, oxytocin, substance P, somatostatin, immunocytochemistry