Long-term in vitro turtle preparation for the study of spinal organization.

A method by which muscles, nerves, and a section of spinal cord from a turtle can be stably maintained in vitro for many days has been developed. Tests of the viability of central and neuromuscular synapses, and the histochemical properties of muscle fibers have indicated that the preparation is viable and shows little decrement in function over a period of 3-5 days. The system allows continuous access to the muscles, nerves, and the spinal cord, as well as a controlled external environment.

Investigation of sexual dimorphism in the rabbit masseter muscle showing different effects of androgen deprivation in adult and young adult animals.

To evaluate the role played by androgens in the development and maintenance of sex differences in the proportion of muscle fibres of different phenotypes, the effects of castration in adult (>6 months old) and in young adult (2-3 months old) male rabbits was examined. Immunohistochemical methods were used to evaluate the proportion of muscle fibres containing different myosin heavy-chain isoforms in 10 different neuromuscular compartments of the masseter. In young adult animals of both sexes, the proportion of fibres of different phenotypes in different compartments was not significantly different from that of normal adult females. In animals castrated as young adults, the development of adult male phenotype proportions was completely blocked in most compartments. In animals castrated as adults, proportions were not significantly different from those of the intact males. For most masseter compartments, androgens produced permanent changes in muscle fibre phenotype during a critical period of postnatal development. However, in the posterior deep compartment, androgen deprivation in young adults had no effect on phenotype proportions, but castration of adults resulted in a striking increase in the proportion of fibres containing the IIa myosin heavy-chain isoform.