PHYSIOLOGICAL AND PHARMACOLOGICAL STUDIES ON ANNELID AND NEMATODE BODY-WALL MUSCLE

1. This review covers the pharmacology and physiology of the body wall muscle systems of nematodes and annelids. 2. Both acetylcholine and g amma-aminobutyric acid (GABA) play important roles in the control of b ody wall muscle in both phyla. In annelids and nematodes, acetylcholin e is the excitatory neuromuscular transmitter while GABA is the inhibi tory neuromuscular transmitter. In addition, 5-hydroxytryptamine (5-HT ) has a modulatory role at annelid body wall muscle but little if any effect on nematode body wall muscle. 3. The acetylcholine receptor of the body wall muscle can be classified as nicotinic-like in both phyla though the annelid receptor has not been analysed in detail. In nemat odes, vertebrate ganglionic nicotinic agonists were the most effective of those so far examined while mecamylamine and benzoquinonium were t he most effective antagonists. Both neuronal bungarotoxin and neosurug atoxin were potent antagonists of acetylcholine excitation at the nema tode receptor. 4. The GABA receptor of the body wall muscle exhibits s imilarities with the vertebrate GABA-A receptor in both phyla. Picroto xin is a very weak or inactive antagonist at leech and nematode GABA r eceptors, while bicuculline methiodide blocks leech GABA receptors but is inactive on nematode GABA receptors. Picrotoxin does block GABA re sponses of earthworm body wall muscle. All these GABA responses are ch loride mediated. 5. Neuroactive peptides of the RFamide family occur i n both phyla and FMRFamide has been identified in leeches. RFamides pr obably have an important role in heart regulation in leeches and in mo dulation of their body wall muscles. RFamides also modulate nematode b ody wall muscle activity with KNEFIRFamide raising muscle tone while S DPNFLRFamide relaxes the muscle. It is likely that this family and oth er neuroactive peptides play an important role in the physiology of bo dy wall muscle throughout both phyla.