Snap25ts mutants display a short term depression phenotype in response to train stimulation at 33[o]C.
At the restrictive temperature of 33[o]C, Snap25ts mutants exhibit a wild-type excitatory postsynaptic current (EPSC) in response to stimulus. However, subsequent stimulation produces a marked activity-dependent reduction in EPSC amplitude relative to wild-type.
At the restrictive temperature of 33[o]C, Snap25ts mutants exhibit disrupted first component of recovery in PPD, which is greatly diminished in weight and exhibits a slower time constant. Moreover, both the weight and time constant of the slow recovery component are markedly increased.
After 5Hz stimulation at 33[o]C, Snap25ts DLM neuromuscular synapses exhibit marked activity-dependent reduction in EPSC amplitude with respect to wild-type. Snap25ts synapses exhibit immediate enhancement of synaptic depression to a steady-state EPSC amplitude of 39.5 with respect to the first amplitude. Recovery in Snap25ts exhibits a similar time constant to the slow component in PP experiments.
Snap25ts does not alter basic calcium-dependent properties of neurotransmitter release such as synaptic facilitation and calcium sensitivity.
Snap25ts synapses stimulated at 33[o]C exhibit a wild-type first stimulation train but recover to only approximately 50% during the intertrain interval (compared to approximately 72% in wild-type).
The mean evoked excitatory junctional potential (EJP) amplitude at the neuromuscular junction is increased to 35.5mV in Snap25ts/Df(3L)1-16 animals (compared to 24.7 mV in control animals) at 22o. The frequency of miniature EJPs is increased from 2.3Hz in control animals to 13.5Hz in Snap25ts/Df(3L)1-16 animals at 22o. At 37o, the mean EJP amplitude of Snap25ts/Df(3L)1-16 animals is reduced about 50% compared to controls.
At 22oC evoked release of neurotransmitter is greatly increased as measured by excitatory junctional potentials. Quantal size is unaffected, though frequency of spontaneous release is 6 fold more frequent in mutants than wild type. There is no difference between mutants and wild type in the number of synaptic boutons. Flies can crawl, fly and mate. At 37oC release of neurotransmitter is reduced 60% compared with controls. Frequency of spontaneous release is not detectably different from controls. At 35oC and higher temperatures flies are paralyzed. Number, size and distribution of vesicles appears to be not significantly different from controls, though T-bars are more dense and filamentous than in wild type, particularly at 22oC. This may obscure docked vesicles close to the central beam of the T-bar.
Mutants show an increase in the number of morphologically docked vesicles at the permissive temperature in the synapse as compared to control synapses.