CELL RECOGNITION DURING SYNAPTOGENESIS IS REVEALED AFTER TEMPERATURE-SHOCK-INDUCED PERTURBATIONS IN THE DEVELOPING FLYS OPTIC LAMINA

Houseflies (Musca domestica) were exposed to pulses of heat (1 h) or c old (several hours) during early pupal life, and the effects were inve stigated on the development of the first optic neuropile, or lamina, o f the visual system. The treatments were designed to perturb the cellu lar organization of the cartridges, the unit synaptic structures of th e lamina, so as to provide novel synaptic opportunities amongst the no rmally fixed composition of these modules, thereby testing the prefere nces of their component cells during synaptogenesis. Various abnormali ties were identified, but these were not always consistent between fli es: retinal abnormalities included the loss ad fusion of rhabdomeres, especially of the central cells of the ommatidium, whereas in the lami na low frequencies of abnormal cartridges were found. These included s even that were studied with serial sections, which instead of the norm al pair of L1 and L2 monopolar interneurons had supernumerary cells of this type. The normal pairing of L1 and L2 at postsynaptic sites of r eceptor terminal tetrad synapses was preserved in these cases, the cel ls eschewing pairings of homologous L1/L1 or L2/L2 partners. This mean t that more than one L1 could pair with a single L2 and vice versa, ev en at the same terminal, and appeared to do so opportunistically on th e basis of proximity, with cells closer to each other pairing more fre quently. Thus the cells behave during synaptogenesis as if they recogn ize other cells only as cell types (receptor, L1 or L2) and not as ind ividual cells. (C) 1993 John Wiley & Sons, Inc.