Lesions of rat skeletal muscle after local block of acetylcholinesterase and neuromuscular stimulation

Abstract

In skeletal muscle, a local increase of acetylcholine (ACh) in a few end plates has been hypothesized to cause the formation of contraction knots that can be found in myofascial trigger points. To test this hypothesis in rats, small amounts of an acetylcholinesterase inhibitor [diisopropylfluorophosphate (DFP)] were injected into the proximal half of the gastrocnemius muscle, and the muscle nerve was electrically stimulated for 30-60 min for induction of muscle twitches. The distal half of the muscle, which performed the same contractions, served as a control to assess the effects of the twitches without DFP. Sections of the muscle were evaluated for morphological changes in relation to the location of blocked end plates. Compared with the distal half of the muscle, the DFP-injected proximal half exhibited significantly higher numbers of abnormally contracted fibers (local contractures), torn fibers, and longitudinal stripes. DFP-injected animals in which the muscle nerve was not stimulated and that were allowed to survive for 24 h exhibited the same lesions but in smaller numbers. The data indicate that an increased concentration of ACh in a few end plates causes damage to muscle fibers. The results support the assumption that a dysfunctional end plate exhibiting increased release of ACh may be the starting point for regional abnormal contractions, which are thought to be essential for the formation of myofascial trigger points.

Effect of the bendiocarb on the ultrastructure of rabbit skeletal muscle

“…This was confirmed also by studies of other authors who observed necrotic changes in muscle fibres at the site of the motor end plate (Dettbarn 1984;Patterson et al 1987). In parallel with inhibition of AChE, Ca 2+ is released from the endoplasmic reticulum (Mense et al 2003). The released Ca 2+ might also be responsible for muscle degeneration.…”

Muscle Pain and Muscle Spindles

“…These wave forms in EMG are a very common finding in quite normal muscles, without any taut bands or trigger points. The situation may be different in experimental studies, where the function of acetylcholinesterase was blocked [41]. The findings of microdialysis of trigger points [38] can be explained by intrafusal microdialysis: a twitch elicited by insertion of the capillary needle may show a myotatic reflex by the activation of intrafusal 1a-afferents of the given muscle spindle.…”

Diagnose und Therapie myofaszialer Triggerpunkte

“…Lokale Kontraktionsknoten wurden in TrPs von Hunden beobachtet [22].Kontraktionsscheiben sind in Rattenmuskeln nach Hemmung der Cholinesterase beschrieben worden [16]. Eine verstärkte Überlappung von Aktin und Myosin wurde in Untersuchungen von myogelotischen Knötchen beim Menschen festgestellt [19].…”