Assessment of reproductive status in male echidnas.

This study reports the development and application of techniques to assess the reproductive status of male echidnas. The pattern of testosterone secretion over a 24-h period in five echidnas was documented. Testosterone secretion after injection i.m. of either 1000 IU hCG (n=4) or 4 microg GnRH agonist (n=6) was determined to establish whether this could be used as a practical index of the prevailing steroidogenic capacity of the testes. hCG (1000 IU) was also used to assess seasonal changes in testosterone secretion in six echidnas over a 13-month period. Seasonal changes in testicular volume were examined by transabdominal ultrasonography. Electroejaculation was attempted to monitor seasonal changes in sperm production, which was also determined by spermatorrhea. There was no apparent diurnal pattern of testosterone secretion in echidnas and circulating concentrations of testosterone remained relatively low (maximum 1.2 ng/mL) and stable over 24h. Injection of hCG resulted in an increase (P<0.01; n=4) in testosterone concentration with a peak (2.9+/-0.3 ng/mL) approximately 4h after injection. GnRH also induced an increase (P<0.01; n=6) in circulating testosterone that was apparent after 1h (2.6+/-0.3 ng/mL) and concentrations remained elevated (3.4+/-0.3 ng/mL) for up to 8h after injection. Seasonal changes in testosterone secretion determined after injection of hCG, increased (P=0.03; n=6) from late-autumn, peaked in late-winter, and decreased by early-spring. Testicular volume followed a similar seasonal pattern (P<0.01; n=6) with an increase from late-autumn, peak in winter and a decline in mid-spring. There was no seasonal change in live weight. Electroejaculation was attempted throughout two breeding seasons but no semen was obtained. Spermatorrhoea in the echidna was described for the first time and was subsequently used to assess seasonal sperm production. Spermatozoa were found in the urine from June to September. This study has demonstrated that exogenous hormones can be used to obtain an index of the prevailing steroidogenic capacity of the testes in echidnas, which is not apparent with repetitive non-stimulated samples over 24 h. The assessment of testosterone secretion after injection of trophic hormones provides a valuable and practical procedure for the assessment of reproductive status. Testicular ultrasonography and spermatorrhea are useful in assessing reproductive status and in this study were successfully used to determine seasonal reproduction in captive echidnas.

Source dipole analysis of the early components of the RREP.

Occlusion of the inspiratory airway produces a series of early RREP components. The predominant early positive and negative peaks are seen over the parietal and frontal scalp respectively and have been hypothesised to represent parallel activation of somatosensory and motor cortices in a manner similar to electrically produced SEP components. An alternative hypothesis is that both components are produced by somatosensory cortex, with the frontally maximal negativity reflecting the activity of a tangential dipole source. Respiratory-related evoked potentials (RREPs) elicited by brief occlusion of the inspiratory airway, were recorded using 29 scalp electrodes from six subjects. Early latency components were analysed using the Electromagnetic Source Estimation (EMSE) program for modelling equivalent electrical dipoles, in order to suggest likely generator sources. Two hypotheses were tested: first, that radial dipoles generated by both pre- (motor cortex) and post-centrally (somatosensory cortex) produce the early components; and second, that generator sources are limited to the somatosensory cortex, with activity recorded as frontally maximal reflecting volume conduction from tangential dipoles. Results were highly consistent between subjects and suggested that Nf-P1 was best accounted for by two post-central and two pre-central radial dipoles supporting the first hypothesis. Locations of generator sources are discussed in relation to anatomical correlates.