Journal of Neuroscience, Vol 5, 1167-1175, Copyright © 1985 by Society for Neuroscience
Development of chemosensitivity of an identified insect interneurone
JM Blagburn, DJ Beadle and DB Sattelle
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.