Exogenous calcitonin gene-related peptide causes gubernacular development in neonatal (Tfm) mice with complete androgen resistance

Exogenous calcitonin gene-related peptide perturbs the direction and length of gubernaculum in capsaicin-treated rats

Calcitonin gene-related peptide (CGRP) released from the genitofemoral nerve (GFN) is proposed to control gubernacular migration to the scrotum during inguinoscrotal descent. As previous studies suggested that both CGRP and androgens are necessary to stimulate gubernacular elongation and proliferation, this study aimed to test whether CGRP perturbed growth of the gubernaculum by exogenous injection in a rat model of GFN blockade with an intact androgen pathway. Sprague-Dawley rats (day 0, n = 34) were injected with capsaicin (sensory neurotixin) or vehicle. CGRP (25 microl of 2 x 10 5 molar concentration) Or castor oil was administered at the umbilicus 24 h later, then every other day thereafter for 10 days. Groups of rats were sacrified on days 8 and 28, and the tip of the gubernaculunx was identified in relation to the scrotum and umbilicus. The length of the processus vaginalis (PV) was measured. In group 1 (capsaicin and CGRP), at 8 days of age (n = 8) the testes were found in the intraabdominal or suprainguinal position in 87.5% (14 testes) and the tip of the gubernaculum was oriented more laterally than normal. However the mean PV length was 5.1 mm, which was shorter than control groups (9-10.8 mm) (P < 0.001, t-test). On the other hand, at day 28, the testes were located proximal to the internal inguinal ring in 66.7% (8 testes) with their gubernacular tip oriented in part towards the umbilicus. The mean of the PV length was 12.2 mm, which was significantly decreased compared to other groups (P < 0.001, t-test). In group 2 (capsaicin and castor oil) and group 3 (vehicle and CGRP) the testes of one rat in each group at 28 days of age were located in the abdomen at the internal inguinal ring with the distal gubernacular attachment lying free and directed caudally towards the scrotum, while the rest of the testes were found in the normal location. These findings suggest that chemical interruption of sensory nerves followed by CGRP injections in rats can perturb gubernacular growth and can change the direction of migration.

Calcitonin gene-related peptide immunoreactivity in the hippocampus and its relationship to cellular changes following exposure to trimethyltin

Calcitonin gene-related peptide (CGRP) is a neuropeptide that is regionally regulated following peripheral insult and in central nervous system (CNS) damage models targeting limbic structures. Functional studies have shown this neuropeptide to be involved in neuronal protection and remodeling, vasodilation, immunomodulation, and apoptosis, thus making it an important constituent of the acute phase response. In the present study, we characterized the anatomic expression and distribution of CGRP immunoreactivity (CGRP-IR) after exposure to the toxin, trimethyltin (TMT). We chose this model because TMT causes dramatic changes in the endocrine system, the limbic system, particularly the hippocampus, as well as in the immune response. We have specifically focused on comparing the changes in CGRP-IR with the pattern of apoptosis (via TUNEL staining), cell-cycle activation (Ki67-IR), and in alteration in microglia (OX-42-IR) and astrocyte (gGFAP-IR) immunocytochemistry in TMT-treated hippocampus. Our results show a marked change in CGRP-IR in regions of the hippocampus that are temporally and anatomically correlated with the induction of apoptosis and activation of microglia, astrocyte, and the cell-cycle marker. Given the known effects of CGRP on these cell types and on programmed cell death elsewhere, these findings are consistent with a regional immunoregulatory/injury response role for CGRP following organotin poisoning.

The effect of the excision of future scrotal skin on testicular descent in neonatal rats: a new experimental model of cryptorchidism

The ingunoscrotal skin of neonatal rats was widely excised on either the right or left side to examine the role of the scrotum in testicular descent. At the age of 10 days, gubernacular migration was observed to be significantly inhibited on the operated side in comparison with that on the nonoperated side. At the age of 60 to 90 days, 12 of 17 testes on the operated side were located in the superficial inguinal position, 2 were in the perineum, and another 3 had descended into the contralateral nonoperated scrotum. All the testes descended into the scrotum on the nonoperated side and in the normal control rats. Though the histological development was remarkably inhibited in the cryptorchid testis, the contralateral descended testis did show the same histological appearance as that of the control testes in 90-day-old rats. This new model of cryptorchidism is considered to provide a simple technique for investigating the mechanism of testicular descent and the impaired development of the testes in cryptorchidism.

Lack of feminization of the cremaster nucleus in cryptorchid androgen insensitive rats

Androgens may control rat testicular descent via effects on the genitofemoral nerve or cranial gonadal ligaments. Androgen-mediated release of calcitonin gene-related peptide from the genito-femoral nerve (whose motoneuron cell bodies reside in the sexually dimorphic cremaster nucleus) may stimulate cremaster sac formation and testicular descent. Alternatively, androgens may cause regression of cranial gonadal ligaments and thereby allow the testes to descend. To evaluate these theories testicular position, and the cremaster sac and nucleus were studied in Tfm (androgen insensitive) rats. Testes were abdominal, inguinal and scrotal in 20%, 67% and 13% of Tfm male rats, respectively, and cranial ligaments were present in all cases. Mean cremaster nucleus motoneuron number was lower in female rats (70 +/- 14) but not significantly different between normal male (256 +/- 44) and Tfm male (231 +/- 42) rats, and it correlated poorly with testicular position. Calcitonin gene-related peptide immunoreactivity was rarely observed in cremaster motoneurons. These data suggest that the cremaster nucleus is not androgen-dependent, calcitonin gene-related peptide release from cremaster motoneurons is not the likely mechanism of testicular descent and persistent cranial ligaments may cause cryptorchidism in the Tfm rat.