mAChRs functionalism in the skeletal muscle synapses, direct evidence of mAChRs in newborn and adult NMJs

immunohistochemistry, we studied the presynaptic muscarinic autoreceptor subtypes controlling ACh release in the neuromuscular junctions of the newborn (3-6 days postnatal) and adult (30-40 days) rat. In the Levator auris longus muscles of both newborn and adult rats, acetylcholine release was modified by the M1receptor selective antagonists pirenzepine (10 μM) and MT-7 (100 nM) and by the M2-receptor selective antagonists methoctramine (1 μM) and AF-DX 116 (10 μM). The M4-receptor selective antagonists tropicamide (1 μ M) and MT-3 (100 nM) can also modify the neurotransmitter release in certain synapses of the newborn muscles. The neurotransmitter release was not altered by the M3-receptor selective antagonist 4-DAMP (1 μM) in the adult or newborn rats. However, we directly demonstrate by immunocytochemistry the presence of these receptors in the motor endplates and conclude that M1-, M2-, M3and M4-type muscarinic receptors are present in all the neuromuscular junctions of the rat muscle both in newborn and adult animals. These receptors may be located in the perisynaptic glial cell as well as at the nerve terminals.