Development of chemosensitivity of an identified insect interneurone

Abstract

Characteristic features of cockroach embryos (Periplaneta americana) are determined for different stages in development. Morphological changes in giant interneurone 2 (GI 2) in the terminal abdominal ganglion during embryogenesis are described based on cobalt injections. A sequential proliferation of branches preceded by filopodial extension is observed between 45 and 80% embryogenesis, by which time the characteristic arborization of the first instar cell is established. The cholinergic agonist carbamylcholine was ionophoretically applied to the cell body and dendritic region of GI 2 at various stages in development, and the responses were recorded intracellularly. Chemosensitivity of GI 2 appears at 40 to 45% embryogenesis, to a similar degree in both cell body and dendrites. The sensitivity of these areas subsequently diverges, and after the 60 to 65% stage, the dendrites are approximately 1000 times more sensitive than the cell body. At 80 to 85% embryogenesis, there is a temporary peak in dendritic sensitivity, and cell body sensitivity increases during postembryonic development. The changes in sensitivity take place before synaptogenesis, and the decline in dendritic sensitivity after the 80% stage may be related to synaptic maturation.

Sexually dimorphic patterns of neural organization in the feeding appendages of fiddler crabs

“…This suggests a close coupling of increased behavioral sensitivity to number of sensory elements. A similar correlation between sensory number and behavioral sensitivity has been observed in grasshoppers, where animals reared in less dense populations express more olfactory receptors, apparently resulting from the diminution of conspecific odor cues (Blagburn et al 1985).…”

Cholinergic Nerve Terminals in the Central Nervous System of Insects

“…2 shows cobalt staining of the pre-and postsynaptic neurons and an electron micrograph of the cockroach first instar terminal ganglion in which a GI has been stained with peroxidase. Electron microscopy has enabled confirmation that there are morphological synapses between LFHSN and GI3, and between MFHSN and GI2 (12,13). ACh ionophoreticially applied to GIs in the neuropile mimics the effects of cercal afferent inputs to GIs and the pharmacology of both types of response exhibit nicotinic properties.…”

A preparation of the blowfly (Calliphora erythrocephala) brain for in vitro electrophysiological and pharmacological studies

“…Cells can be stained and identified even during recording and the ionotophoretic electrode can be positioned with precision close to the dendritic tree of the stained cell. This is a major advantage of our preparation compared to other explants of the adult insect central nervous system like the abdominal ganglion of the cockroach (Callec and Sattelle, 1973;Callec, 1985) or the thoracic ganglion of the locust (Laurent, 1990) which cannot be observed in transillumination in the microscope although this is possible for first instar and embryonic preparations (Blagbum et al, 1985).…”