Effects of hormones and gonadal status on the midventral gland of the grasshopper mouse Onychomys leucogaster.

A midventrally located fusiform sebaceous gland is found in the northern grasshopper mouse Onychomys leucogaster. Microscopically, the gland consists of numerous multilobular units. Copious secretory material collects in the central duct of each unit and is extruded to the outside. The gland is larger in the male than in the female. Castration causes an involution of the gland in both sexes. Testosterone propionate (1.0 mg/0.1 cc olive oil, subcutaneously every other day for 4 weeks) restores the gland to full activity in castrates of both sexes. Estradiol benzoate (0.1 mg/0.1 cc olive oil, subcutaneously every other day for 4 weeks) has no effect on the midventral gland of ovariectomized females. A long photoperiod (18 L/6 D) leads to the development of testes, ovaries, and uteri that are significantly heavier than those of animals from a short photoperiod (6 L/18 D) regime. Midventral glands in animals of both sexes from the long photoperiod are larger and more active than glands from animals from the short photoperiod. The secretions of the midventral gland of Onychomys are probably used for communications such as territorial marking, advertisement of gonadal status, or pup identification.