Morphological and functional maturation of a skeletal muscle regulated by juvenile hormone.

Reproductive behaviour of animals requires a well-adapted muscular system. This study examines the structural and functional development of ovipositor muscle properties in female locusts during reproductive development. A possible regulation by juvenile hormone (JH) was assessed by comparing muscle properties in immature and mature females and with those whose JH production was inhibited by allatectomy early in adult life. The results are related to the reproductive behaviour of locusts. Histological and ultrastructural comparison of muscle fibres and their associated cuticular structures (apodemes) revealed dramatic growth during the first 2 weeks of reproductive development. The cross-sectional area of muscle fibres increased sevenfold, and their mass-per-length 5.3-fold. Ultrastructural examination showed growth of mitochondria, development of sarcoplasmic reticulum and increasing levels of structural organisation of myofibrils. Muscles of mature females displayed pronounced fatigue resistance, contracted more powerfully (twitch, 33.22+/-10.8 mN; 50 Hz, 623.66+/-115.77 mN) and had almost two times faster kinetics than those of immature females (twitch, 6.5+/-2.6 mN; 50 Hz, 14.19+/-2.58 mN). Together with muscular maturation, cuticular apodemes, which serve as attachment sides for ovipositor muscles, grow considerably in length and width and assume a complex surface structure. Most of the described changes were suppressed in females deprived of JH (allatectomised). The results demonstrate an adaptation of muscle properties to the requirements of reproductive behaviour that is largely regulated by juvenile hormone.