Nematodes neurotransmitters

Fig. 6.1 Interrelationships of chemoreceptors internal (neurotransmitters) and external chemosignals. Phylogenetic connections for sequences in transmembrane (Fig. 6.2) domains Nos. = bootstrap values from 100 Megaline searches (based on majority consensus tree). Invertebrate — DrOR fruit-fly, CeOR nematode vertebrate — FOR fish, LOR (1 2) lamprey, MOR mouse VR (1 2) vomeronasal (from Dryer and Berghard, 1999).

The evolution of understanding of the roles of classical neurotransmitters versus those of neuropeptides is perhaps best displayed by research in nematodes. For many years, cutting-edge research on the physiology of nematodes focused on the actions of the classical... 

Muscle cell membranes of nematodes possess ion channel receptors that are opened by neurotransmitters and which are gated by selective therapeutic agents. This chapter is an introduction to the physiology and pharmacology of ligand-gated ion channels of nematode muscle. 

Nematodes and other invertebrates with relatively simple nervous systems have receptors for 5-HT and other neurotransmitters in their genomes (see Table 1). Interestingly, most of the invertebrate 5-HT receptors discovered to date resemble either the mammalian 5-HT1A receptors or the 5-HT7 receptors, although... 

Compounds of this class mimic the action of inhibitory neurotransmitters like GABA. These compounds increase the membrane potential causing hyperpolarisation of the muscle fibre membrane. This leads to flaccid paralysis of the worm. Piperazine is a potent muscle hyperpolariser of nematode muscles. 

The Range and Biological Activity of FMR Famide-related Peptides and Classical Neurotransmitters in Nematodes... 

The nervous system in helminths has important differences from that of humans and these differences form the basis of the selective toxicity of most drugs used to treat such infections. For example, nematode muscles have both excitatory and inhibitory neuromuscular junctions. The neurotransmitters are acetylcholine and gamma-aminobutyric acid (GABA), respectively. 

For the parasitic nematodes putative neurotransmitters and/or neuromodulators include ACh (excitatory), y-aminobutyric acid (inhibitory), and glutamate (excitatory). Though 5-FIT and the catecholamines are indicated by immuno-cytochemical, biochemical and anatomical techniques, their precise functions as neurosignals remains to be determined. The study of neuropeptides in nematodes has revealed the strong candidacy of the family of FMRFamide-like peptides and in particular the AF peptides which have been shown to have specific physiological effects. 

Mechanisms Ivermectin intensifies GABA-mediated neurotransmission in nematodes and causes immobilization of parasites, facilitating their removal by the reticuloendothelial system. Selective toxicity results because in humans GABA is a neurotransmitter only in the CNS, and ivermectin does not cross the blood-brain barrier. 

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