Jl. Witten et Jw. Truman, DISTRIBUTION OF GABA-LIKE IMMUNOREACTIVE NEURONS IN INSECTS SUGGESTS LINEAGE HOMOLOGY, Journal of comparative neurology, 398(4), 1998, pp. 515-528
gamma-Aminobutyric acid (GABA) is an important inhibitory neurotransmi
tter in vertebrates and invertebrates (Sattelle [1990] Adv. Insect Phy
siol. 22:1-113). The GABA phenotype is lineally determined in postembr
yonic neurons in the tobacco hawkmoth, Manduca sexta (Witten and Truma
n, [1991] J. Neurosci. 11:1980-1989) and is restricted to six identifi
able postembryonic lineages in the moth's thoracic hemiganglia. We use
d a comparative approach to determine whether this distinct clustering
of GABAergic neurons is conserved in Insecta. In the nine orders of i
nsects surveyed (Thysanura, Odonata, Orthoptera, Isoptera, Hemiptera,
Coleoptera, Diptera, Lepidoptera, and Hymenoptera), GABA-like immunore
active neurons within a thoracic hemiganglion were clustered into six
distinct groups that occupied positions similar to the six postembryon
ic lineages in Manduca. On the basis of cell body position and axon tr
ajectories, we suggest that these are indeed homologous lineage groups
and that the lineal origins of the GABAergic cells have been very con
servative through insect evolution. The distinctive clustering of GABA
-positive cells is shared with crustaceans (Mulloney and Hall [1990] J
. Comp. Neurol. 291:383-394; Homberg et al. [1993] Cell Tissue Res. 27
1:279-288) but is not found in the centipede Lithobius forficulatus. T
here is a two- to threefold increase in numbers of thoracic neurons be
tween the-flightless Thysanura and the most advanced orders of insects
. Using the GABA clusters as indicators of specific lineages, we find
that only selected lineages have significantly contributed to this inc
rease in neuronal numbers. J. Comp. Neurol. 398:515-528, 1998. (C) 199
8 Wiley-Liss, Inc.