Synaptic ultrastructure in nerve terminals ofdrosophila larvae overexpressing the learning genedunce

Abstract

We investigated synaptic ultrastructure of individual nerve ending varicosities at the Drosophila larval neuromuscular junction in transgenic larvae overexpressing the learning gene dunce (dnc) in the nervous system. It was previously shown that cAMP is reduced to one‐third normal in these larvae and that they have fewer nerve terminal varicosities and smaller junction potentials, although transmitter release from individual nerve ending varicosities is not significantly altered. We tested the hypothesis that synaptic ultrastructure is modified to compensate for possible reduced efficacy of synaptic transmission resulting from lower than normal cAMP. Synaptic size and number of presynaptic dense bodies (active zone structures) per synapse are modestly enhanced in transgenic larvae overexpressing the dnc gene product and in rutabaga (rut1 ) mutant larvae, which have reduced adenylyl cyclase activity and reduced neural cAMP. The incidence of complex synapses (possessing 2 or more presynaptic dense bodies) was not consistently different in experimental larvae compared to controls. The observations suggest that chronic reduction of cAMP levels in the nervous system of Drosophila larvae, although leading to a modest compensatory change in synaptic structure, does not markedly alter several synaptic ultrastructural parameters which are thought to influence the strength of transmitter release; thus, homeostatic mechanisms do not act to maintain normal‐sized junction potentials by altering synaptic structure. © 2000 John Wiley & Sons, Inc. J Neurobiol 43: 89–97, 2000

Bruchpilot, a Protein with Homology to ELKS/CAST, Is Required for Structural Integrity and Function of Synaptic Active Zones in Drosophila

“…The fact that we see similar frequencies of T bars in wild-type photoreceptor terminals (16.8%) and of conspicuous membrane densities in brp-RNAi C8 -expressing terminals (19.5%) supports the proposition that these membrane thickenings may in fact represent presynaptic sites without typical T bars. However, we think it is unlikely that BRP is restricted to T bars because about 13%-37% of the active zones of type Ib boutons at NMJs of larval muscles 6/7 have no T bar (Atwood et al, 1993;Shayan and Atwood, 2000), whereas in our light microscopical preparations, only 3% of the active zones identified by their postsynaptic receptor fields contained no BRP label. Unfortunately, in our experiments the epitope recognized by MAB nc82 did not tolerate tissue fixation conditions required for immunoelectron microscopical analysis of T bars.…”

Drosophila RSK negatively regulates bouton number at the neuromuscular junction

“…A change in the number of boutons may be accompanied by a compensatory change in the number of synapses, as previously shown for mutations of the cAMP pathway. In larvae over-expressing the dnc phosphodiesterase or in the rut 1 mutant, both of which have a reduced numbers of boutons, the amount of dense bodies per synapse and the area of synapses in individual boutons were increased (Shayan and Atwood, 2000). To see if RSK has an impact on the number or size of individual synapses we measured the mean fluorescence intensity of nc82 staining which should be proportional to the number and size of active zones.…”

Gliocyte and synapse analyses in cerebral ganglia of the Chinese mitten crab, Eriocheir sinensis: ultrastructural study

“…In Drosophila , the complex synapses (containing two or more presynaptic profiles) also exist in the nerve terminals. 24 In this study, the dense projections (also referred to as T-bars, presynaptic density bars, or dense bars) were not observed in the presynaptic membranes of the synapses. The differences in the structures of dense projections imply a diversification of the central structure/function theme in various niches.…”