Lateral Giant
From NeuronBankWiki
The Lateral Giant interneurons (LG) are found in crayfish and many other decapod crustaceans.
Escape responses in crayfish are among the best known circuit pathways, exhibiting consistent, robust behavioral response to stimuli. Such robust response to stimuli allows researchers to reveal connection patterns in circuit pathways (Antonson & Edwards, 2003). In the case of decapod crustaceans behaviors can be instituted with command neurons, giant fibers that fire to produce meaningful behavior (Edwards, 1999). The Lateral Giant (LG) is one such command neuron.
The name Lateral Giant is also used in reference to large axons in annelids.
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Identification
Making up a pair of giant axons at the dorsal surface of the ventral nerve cord (Johnson, 1924 in Wine, 1972) the lateral giant is a giant axon spanning the entire nerve cord in partially fused segments (Krasne, 2002, Payton, 1969 in Wine, 1972).
Anatomy
The lateral giants are a segmental chain of neurons that are joined by gap junctions, so they function much like a single pair of neurons. Each lateral giant consists of a giant axon, an ipsilateral dendrite, and a contralateral soma (Remler et al. 1968). They make synaptic connections with fast flexor motor giant neurons in the first three anterior segments of the abdomen, but not the posterior three (Wine 1984).
Physiology
Lateral giant neurons are responsible for escape responses (Wine 1984).
Escape Reflex
Escape response was first studied utilizing electrophysiological techniques by Wiersma (1947). Lateral Giants receive stimuli from the posterior region of the animal which is summed resulting in an upward movement away from the stimuli (Krasne & Edwards, 2002). The pathway begins at primary afferents to sensory interneurons of the abdomen and synapses with giant motoneurons that innervate phasic flexor muscles, bending the rostral abdominal segments (Edwards, 1999). In crayfish, the stimulus creates mechanosensory input to the LG interneuron requiring a single LG spike, both necessary and sufficient, to produce this tail flip (Herberholz, et al 2002). LG tail flips are initiated by a synaptic connection from LG to giant motor neurons in the first three segments of the abdomen (Wine and Krasne, 1972). The result is a “jack-knife” tail-flip produced by curvature around the thoracic-abdominal junction (Heitler, Fraser, 1993).
References
Antonsen, BL; Edwards, DH (2003) Differential dye coupling reveals lateral giant escape circuit in crayfish. The Journal of Comparative Neurology, 466:1-13.
Edwards, DH, Heitler, WJ; Krasne, FB (1999) Fifty years of a command neuron: the neurobiology of escape behavior in the crayfish. Trends in Neuroscience, 22:153-161.
Heitler, WJ; Fraser, K (1993) Thoracic connections between crayfish giant fibres and motor giant neurons reverse abdominal patter. Journal of Experimental Biology, 181:329-333.
Herberholz, J; Antonsen, B; Edwards, DH (2002) A lateral excitatory network in the escape circuit of crayfish. The Journal of Neuroscience, 22:9078-9085.
Krasne, FB; Edwards, DH (2002) Modulation of the crayfish escape reflex-physiology and neuroethology. Integrative and Comparative Biology, 42:705 -715.
Remler MP, Selverston AI, Kennedy D. 1968. Lateral giant fibers of crayfish: location of somata by dye injection. Science 162(3850): 281-283. http://dx.doi.org/10.1126/science.162.3850.281
Wiersma, C.A.G. (1947) Journal of Neurophysiology, 10:23–38.
Wine, JJ; Krasne, FB (1972) Journal of Experimental Biology, 56:1–18.
Wine JJ. 1984. The structural basis of an innate behavioural pattern. The Journal of Experimental Biology 112: 283-319.
