Differential regulation of a homologous peptidergic neuron in grasshoppers: evolution of a neural circuit

The vasopressin-like immunoreactive (VPLI) neurons of grasshoppers have paired cell bodies in the suboesophageal ganglion and both anterior and posterior running axons. In non-oedipodine grasshopper species (e.g. Schistocerca gregaria), most of their arborisations are distributed in dorsal and later...

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Bibliographic Details
Published in:Journal of Comparative Physiology 1998-06, Vol.182 (6), p.755-765
Main Authors: Lundquist, C.T, Baines, R.A, Thompson, K.S.J, Bacon, J.P
Format: Article
Language:English
Subjects:
acetylcholine
antagonists
Axons
Biological evolution
Brain
cholinergic mechanisms
Chorthippus parallelus
Circuits
Correlation analysis
electrophysiology
evolution
gamma-aminobutyric acid
Grasshoppers
Histamine
Homology
interneurons
Lobes
Locusta migratoria
Neural networks
Neurons
neurophysiology
Neuropil
Oedaleus senegalensis
Orthoptera
Peripheral nerves
Photoreceptors
Protocerebrum
regulation
Schistocerca gregaria
scopolamine
Species
species differences
Synapses
Vasopressin
vasopressin like immunoreactive neurons
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Summary:The vasopressin-like immunoreactive (VPLI) neurons of grasshoppers have paired cell bodies in the suboesophageal ganglion and both anterior and posterior running axons. In non-oedipodine grasshopper species (e.g. Schistocerca gregaria), most of their arborisations are distributed in dorsal and lateral neuropil, while in oedipodine species (e.g. Locusta migratoria), the neurons have additional extensive axonal projections in both the optic lobes and proximal portions of the ganglionic peripheral nerves. This study demonstrates that these morphological differences correlate with their physiology. In L. migratoria, VPLI neuron activity is regulated primarily via a spontaneously active inter-neuron which descends from the brain. This descending interneuron is inhibited by a light-activated brain extraocular photoreceptor. Regulation of VPLI neuron activity by an extraocular photoreceptor is also seen in the other oedipodine grasshopper investigated. In the four non-oedipodines examined (from two subfamilies), we find no extraocular photoreceptor regulation of VPLI neuron activity. Despite this, VPLI neuron in S. gregaria does appear to be driven by a descending interneuron homologous to that in L. migratoria. The descending interneuron in both species receives similar mechanosensory input and excites the VPLI neuron via cholinergic synapses. Histamine injection into the medial protocerebrum of both species causes strong inhibition of the descending interneuron. The evolution of the neural circuitry, by which an extraocular photoreceptor comes to regulate the descending interneuron in oedipodine species, is discussed.
ISSN:0340-7594
1432-1351
DOI:10.1007/s003590050220