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Synapse formation is tightly associated with neuronal excitability. We found striking synaptic overgrowth caused by Drosophila K+- channel mutations of the seizure and slowpoke genes, encoding Erg and Ca2+-activated large-conductance (BK) channels, respectively. These mutants display two distinct patterns of "satellite" budding from larval motor terminus synaptic boutons. Double-mutant analysis indicates thatBKand ErgK+ channels interact with separate sets of synaptic proteins to affect distinct growth steps. Post-synaptic L-type Ca2+ channels, Dmca1D, and PSD-95-like scaffold protein, Discs large, are required for satellite budding induced by slowpoke and seizure mutations. Pre-synaptic cacophony Ca2+ channels and the NCAM-like adhesion molecule, Fasciclin II, take part in a maturation step that is partially arrested by seizure mutations. Importantly, slowpoke and seizure satellites were both suppressed by rutabaga mutations that disrupt Ca2+/CaM-dependent adenylyl cyclase, demonstrating a convergence of K+ channels of different functional categories in regulation of excitability-dependent Ca2+ influx for triggering cAMP-mediated growth plasticity. [ABSTRACT FROM AUTHOR]

Environmental temperature is an important factor exerting pervasive influence on neuronal morphology and synaptic physiology. In the Drosophila brain, axonal arborization of mushroom body Kenyon cells was enhanced when flies were raised at high temperature (30°C rather than 22°C) for several days. Isolated embryonic neurons in culture that lacked cell- cell contacts also displayed a robust temperature-induced neurite outgrowth. This cell-autonomous effect was reflected by significantly increased high-order branching and enlarged growth cones. The temperature-induced morphological alterations were blocked by the Na+ channel blocker tetrodotoxin and a Ca2+ channel mutation but could be mimicked by raising cultures at room temperature with suppressed K+ channel activity. Physiological analyses revealed increased inward Ca2+ currents and decreased outward K+ currents, in conjunction with a distal shift in the site of action potential initiation and increased prevalence of TTX-sensitive spontaneous Ca2+ transients. Importantly, the overgrowth caused by both temperature and hyperexcitability K+ channel mutations were sensitive to genetic perturbations of cAMP metabolism. Thus, temperature acts in a cell-autonomous manner to regulate neuronal excitability and spontaneous activity. Presumably, activity-dependent Ca2+accumulation triggers the cAMP cascade to confer the activity-dependent plasticity of neuronal excitability and growth. [ABSTRACT FROM AUTHOR]

The cacophony (cac) locus in Drosophila encodes a Ca2+ channel α subunit, but little is known about properties of cac-mediated currents and functional consequences of cac mutations in central neurons. We found that, in Drosophila cultured neurons, Ca2+ currents were mediated predominantly by the cac channels. The cac channels contribute to low- and high-threshold, fast- and slow-inactivating types of Ca2+ currents, take part in membrane depolarization, and strongly activate Ca2+-activated K+ current [IK(Ca)]. In cac neurons, unexpectedly, voltage-activated transient K+ current IA is upregulated to a level that matches IK(Ca) reduction, implicating a homeostatic regulation that was mimicked by chronic pharmacological blockade of Ca2+ currents in wild-type neurons. Among K+ channel transcripts, Shaker mRNA levels were preferentially increased in cac flies. However, Ca2+ current expression levels remained unaltered in several K+ channel mutants, illustrating a key role of cac in developmental regulation of Drosophila neuronal excitability. [ABSTRACT FROM AUTHOR]

Regulation of synaptic efficacy by nerve terminal excitability has not been extensively studied. We performed genetic and pharmacological dissections for presynaptic actions of K+ channels in Drosophila neuromuscular transmission by using electrophysiological and optical imaging techniques. Current understanding of the roles of the Shab IK channel and its mammalian Kv2 counterparts is relatively poor, as compared with that for Shaker IA channels and their Kv1 homologues. Our results revealed the striking effect of Shab mutations during high-frequency synaptic activity, as well as a functional division in synaptic regulation between the Shaker and Shab channels. Shaker channels control the basal level of release, indicated by a response to single nerve stimulation, whereas Shab channels regulate repetitive synaptic activities. These observations highlight the crucial control of nerve terminal excitability by Shaker and Shab channels to confer temporal patterns of synaptic transmission and suggest the potential participation of these channels, along with the transmitter release machinery, in activity-dependent synaptic plasticity. [ABSTRACT FROM AUTHOR]

Forward locomotion of Drosophila melanogaster larvae is composed of rhythmic waves of contractions that are thought to be produced by segmentally organized central pattern generators. We present a systematic description of spike activity patterns during locomotive contraction waves in semi-intact wild-type and mutant larval preparations. We have shown previously that TβhnM18 mutants, with altered levels of octopamine and tyramine, have a locomotion deficit. By recording en passant from the segmental nerves, we investigated the coordination of the neuronal activity driving contraction waves of the abdominal body-wall muscles. Rhythmic bursts of activity that occurred concurrently with locomotive waves were frequently observed in wild-type larvae but were rarely seen in TβhnM18 mutants. These centrally generated patterned activities were eliminated in the distal stumps of both wild-type and TβhnM18 larvae after severing the segmental nerve from the CNS. Patterned activities persisted in the proximal stumps deprived of sensory feedback from the periphery. Simultaneous recordings demonstrated a delay in the bursting activity between different segments, with greater delay for segments that were farther apart. In contrast, bilateral recordings within a single segment revealed a well synchronized activity pattern in nerves innervating each hemisegment in both wild-type and TβhnM18 larvae. Significantly, rhythmic patterns of bursts and waves could be evoked in TβhnM18 mutants by head or tail stimulation despite their highly irregular spontaneous activities. These observations suggest a role of the biogenic amines in the initiation and modulation of motor pattern generation. The technique presented here can be readily extended to examine the locomotion motor program of other mutants. [ABSTRACT FROM AUTHOR]

The development of the nervous system is influenced by environmental factors. Among all environmental factors, temperature belongs to a unique category. Besides activating some specific sensory pathways, it exerts nonspecific, pervasive effects directly on the entire nervous system, especially in exothermic species. This study uses mutants to genetically discover how temperature affects nerve terminal arborization at larval neuromuscular junctions of Drosophila. It is known that hyperexcitabilityin K+ channel mutants leads to enhanced ramification of larval nerve terminals. Elevated cAMP levels in dunce mutants with reduced phosphodiesterase activity also cause enhanced arborization. These genetic alterations are thought to perturb mechanisms relevant to activity-dependent neural plasticity, in which neuronal activity activates the cAMP pathway, and consequently affect nerve terminal arborization by regulating expression of adhesion molecules. Here we demonstrate the robust influence of rearing temperature on motor nerve terminal arborization. Analysis of ion channel and cAMP pathway mutants indicates that this temperature-dependent plasticity is mediated via neuronal activity changes linked to mechanisms controlled by the rutabaga-encoded adenylyl cyclase. [ABSTRACT FROM AUTHOR]