Nitric oxide mediates activity-dependent change to synaptic excitation during a critical period in Drosophila

Abstract

The emergence of coordinated network function during nervous system development is often associated with critical periods. These phases are sensitive to activity perturbations during, but not outside, of the critical period, that can lead to permanently altered network function for reasons that are not well understood. In particular, the mechanisms that transduce neuronal activity to regulating changes in neuronal physiology or structure are not known. Here, we take advantage of a recently identified invertebrate model for studying critical periods, the Drosophila larval locomotor system. Manipulation of neuronal activity during this critical period is sufficient to increase synaptic excitation and to permanently leave the locomotor network prone to induced seizures. Using genetics and pharmacological manipulations, we identify nitric oxide (NO)-signaling as a key mediator of activity. Transiently increasing or decreasing NO-signaling during the critical period mimics the effects of activity manipulations, causing the same lasting changes in synaptic transmission and susceptibility to seizure induction. Moreover, the effects of increased activity on the developing network are suppressed by concomitant reduction in NO-signaling and enhanced by additional NO-signaling. These data identify NO signaling as a downstream effector, providing new mechanistic insight into how activity during a critical period tunes a developing network.

Critical periods in Drosophila neural network development: Importance to network tuning and therapeutic potential

“…Our analysis showed that activity perturbation during the CP (achieved by exposing embryos to the proconvulsant PTX or use of the genetic seizure mutation, para bss ) results in increased excitatory synaptic drive not only during this period, but also throughout the larval life course, consistent with permanent change being locked-in (Marley and Baines, 2011). This change in excitatory synaptic drive was accompanied by increased action potential firing in aCC (Giachello et al, 2021) (Figure 4). Thus, our observations in Drosophila mirror, to some extent, those in mammals in that activity perturbation, during an embryonic CP, alters synaptic balance, both during the CP and, in this instance, beyond.…”

“…By contrast, reducing neural activity during the CP is overcome by increasing NO-signaling. These, and additional manipulations, again indicate that it is the level of activity, rather than activity per se, that determines network function via, at least in part, changes in NO production (Giachello et al, 2021). This seemingly duplicitous activity of NO has been highlighted before, in different systems, from cell survival (Calabrese et al, 2009) to nociceptive transmission (Jin et al, 2011) and, particularly, epileptogenesis where its role is highly contradictory with significant evidence supporting both proconvulsive, and anticonvulsive activity (Hrncic et al, 2012).…”

“…A recent study identified nitric-oxide (NO) to mediate, at least in part, the effects of activity manipulation during the CP in the larval Drosophila motor network (Giachello et al, 2021). Thus, the effect of activity-perturbation, during this CP, is potentiated or blocked by simultaneous manipulation of this signaling pathway.…”

Presynaptic contact and activity opposingly regulate postsynaptic dendrite outgrowth

“…Critical periods are developmental windows of heightened neural plasticity that are present from vertebrates ( Kalb, 1994 ; Keck et al, 2017 ; Takesian and Hensch, 2013 ; Walton et al, 1992 ) to insects ( Caglayan and Gilbert, 1987 ; Elekonich et al, 2003 ; Hartfelder et al, 1995 ; Levine et al, 1986 ; Morgan et al, 1998 ). In Drosophila , critical periods have been identified in the late embryo/early larva ( Ackerman et al, 2021 ; Crisp et al, 2011 ; Fushiki et al, 2013 ; Giachello et al, 2021 ; Giachello and Baines, 2015 ; Hartwig et al, 2008 ; Jarecki and Keshishian, 1995 ; Tripodi et al, 2008 ) and in the newly eclosed adult ( Doll et al, 2017 ; Doll and Broadie, 2016 ; Doll and Broadie, 2015 ; Golovin et al, 2021 ; Golovin et al, 2019 ). Altered activity during the critical period can lead to long-lasting defects in neuronal morphology and behavior ( Ackerman et al, 2021 ; Crisp et al, 2011 ; Fushiki et al, 2013 ; Giachello et al, 2021 ; Giachello and Baines, 2015 ; Hartwig et al, 2008 ; Jarecki and Keshishian, 1995 ; Tripodi et al, 2008 ).…”

“…In Drosophila , critical periods have been identified in the late embryo/early larva ( Ackerman et al, 2021 ; Crisp et al, 2011 ; Fushiki et al, 2013 ; Giachello et al, 2021 ; Giachello and Baines, 2015 ; Hartwig et al, 2008 ; Jarecki and Keshishian, 1995 ; Tripodi et al, 2008 ) and in the newly eclosed adult ( Doll et al, 2017 ; Doll and Broadie, 2016 ; Doll and Broadie, 2015 ; Golovin et al, 2021 ; Golovin et al, 2019 ). Altered activity during the critical period can lead to long-lasting defects in neuronal morphology and behavior ( Ackerman et al, 2021 ; Crisp et al, 2011 ; Fushiki et al, 2013 ; Giachello et al, 2021 ; Giachello and Baines, 2015 ; Hartwig et al, 2008 ; Jarecki and Keshishian, 1995 ; Tripodi et al, 2008 ). In the Drosophila embryonic motor system, dendrite length can be homeostatically modified by levels of activity ( Tripodi et al, 2008 ).…”