Exogenous calcitonin gene-related peptide can induce the testis to cross the scrotal septum

Objectives To determine: (i) whether the pattern of gubernacular migration can be changed by local injections of calcitonin gene-related peptide (CGRP) in rats with a normal testicular position, (ii) the effects of both endogenous and exogenous CGRP on contralateral gubernacular migration and (iii) whether the scrotal septum acts as a barrier to prevent gubernacular migration. Materials and methods Four groups of neonatal rats were used, all of which underwent right orchidectomy with: group 1 (29 rats) division of the genitofemoral nerve (GFN) on both sides; group 2 (31 rats) division of the left GFN; group 3 (31 rats) division of the left GFN and injections of oil into the right hemiscrotum; and group 4 (34 rats) division of the left GFN and injections of CGRP into the right hemiscrotum. After 26-38 days, the rats were killed and the testicular positions determined. Results In rats receiving no injections (groups 1 and 2), the testes were oriented further to the right side where the right GFN was not divided (group 2). With the addition of oil into the right hemiscrotum where the right GFN was not divided (group 3), the testes were oriented further to the left compared with those in group 2. Injections of CGRP into the right hemiscrotum in the presence of an intact right GFN (group 4) resulted in more testes where the axis was orientated to the right side of the scrotum compared with the other groups with an intact right GFN (groups 1 and 3) but this was not reflected in the mean distance from the midline, which was similar among these groups. A significant number of testes in groups 1,2 and 4 crossed the midline. Conclusions The presence of an intact GFN on the right side where the left nerve was divided provides a directional signal influencing migration of the contralateral gubernaculum to the right side of the scrotum. Oil injected into the scrotum interferes with the normal concentration gradient of CGRP released from the right GFN, resulting in gubernacular migration further toward the left side. CGRP injections were poorly localized to the right hemiscrotum, resulting in gubernacular migration toward in some and away from the site of injection in others. The midline scrotal septum is not a barrier to gubernacular migration and most likely forms as a secondary event following descent of the testis.