On transmitter accumulation in lobster neurons

A thorough understanding of neurotransmitter accumulation requires: first, the identification of the transmitter compound used by a neuron; next, a knowledge of the substrates, enzymes and other macromolecules involved in transmitter metabolism and compartmentalization; and finally, an understanding of the genetic regulation of the production of these components. These studies are aimed at such an understanding using the lobster nervous system, from which one can isolate single physiologically identified neurons. The transmitter compounds believed to be used by three distinct lobster neuron types are: efferent inhibitory (I), GABA; efferent excitatory, glutamate; sensory (S), acetylcholine (Ach). Measurements of levels of the transmitter candidates ACh, GABA and glutamate and of the enzymes choline acetyltransferase (ChAc), acetylcholinesterase (AChE), glutamic decarboxylase (GD) and GABA glutamic transaminase (GT) have been carried out in axons of all 3 neuron types. The results demonstrate that ACh and its synthetic enzyme (ChAc) are selectively localized in S axons (enzyme Δ = 500:1), GABA and its synthetic enzyme (GD) are concentrated in I axons (enzyme Δ = 300:1), while the degradative enzymes AChE and GT are found evenly distributed amongst all 3 neuron types.