الفهرس 
Introduction and Aim of the workOnly 14 pages are availabe for public view
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Abstract
The present work was carried out to study the effect of T3 injection on the structure and enzymatic contents of extrafusal and intrafusal muscle fibres of the adult mice and also the therapeutic effect of melatonin after T3injection.
The animals were divided into three groups, each group include 18 animals.
Group I was designated as control, including animals which were injected intraperitoneally daily with saline for 20 days and then with 0.1 ml of 10% ethanol subcutaneously for 20 days.
Group II was designated as T3-injected group, including animals which were daily administrated intraperitoneal injection of triiodothyronine (T3) (10 ug/ 100 g body weight) in 2 ml saline for 20 days and then T3 + 0.1 ml of 10% ethanol subcutaneously for 20 days.
Group III was designated as T3/Melatonin injected group
including animals that were daily administrated intraperitoneal injection of T3 (10 ug/ 100 g body weight) in 2 ml saline for 20 days and then T3 (10 ug/ 100 g body weight) +
melatonin (6 mg/ kg) in 0.1 ml of 10% ethanol subcutaneously for 20 days.
The body weight and Calf muscle weight of mice of different groups were assessed before and after experimental period.
Calf muscles were selected because of their superficial position and easy dissection especially for histochemical visualisation of their enzymes.
The muscle sections were obtained and stained with hematoxylin and eosin and Van Gieson’s stains for histological study and stained with succinic dehydrogenase and acetylcholine estrase stains for histochimical study.
In group I, animals showed that, there was an increase of body weight and muscle weight that was proportionate to age change.
Histological study showed normal findings in the form of the extrafusal muscle fibres appeared polyhedral with oval nuclei under cell membrane. There were muscle spindles that contain three types of intrafusal muscle fibres; nuclear bag, intermediate and the nuclear chain fibres. The spindle capsule was well defined and composed of connective tissue layers with blood vessels and nerves within the capsular layer, it also showed that the skeletal muscle as a whole was surrounded by epimysium. Perimysium extended inward from the epimysium; enveloping each of the bundles of muscle fibres.
Histochemical study demonstrated that, the three types of extrafusal muscle fibres were recognized based on their cytochemical distribution of succinic dehydrogenase activity, type A fibre had the largest diameter and a low succinic dehydrogenase activity, type B was intermediate in size and enzymatic activity, while type C was the smallest fibre in size and the highest fibre in enzymatic activity. Also the true or specific acetylcholinestrase appeared to be localized at the motor end plate. The deposition of the specific acetylcholinesterase at the intrafusal motor end plates appeared to be similar to that of the extrafusal end plates.