Remodeling of an identified motoneuron during metamorphosis: Hormonal influences on the growth of dendrites and axon terminals

Abstract

During metamorphosis of the tobacco hawkmoth Manduca sexta, the femoral depressor motoneuron (FeDe MN) undergoes remodeling of its dendrites and motor terminals. Previous studies have established that remodeling of MNs during metamorphosis is mediated by the same hormones that control metamorphosis: the ecdysteroids and juvenile hormone (JH). During the pupal stage, the ecdysteroids promote adult-specific growth of MNs in the absence of JH, but JH or its synthetic mimics can interfere with ecdysteroid-mediated growth if applied during early sensitive periods. Hence, the application of a JH mimic (JHM) either systemically or locally to a target muscle has been used to distinguish those aspects of motor-terminal remodeling that are controlled by ecdysteroid action on the CNS from those that are influenced by ecdysteroid action on the peripheral targets. Here, we have extended the analysis of central and peripheral hormonal influences on MN remodeling by injecting JHM locally into the CNS thus altering the hormonal environment of the FeDe MN soma without altering the hormonal environment of its target muscle. Our results demonstrate that adult dendritic growth and motor-terminal growth can be experimentally uncoupled, suggesting that each is regulated independently. JHM application to the CNS perturbed dendritic growth, but had no measurable impact on motor-terminal growth. Peripheral actions of ecdysteroids, therefore, appear sufficient to promote the development of adult-specific motor terminals but not the development of an adult-specific dendritic arbor.

Dendrite-specific remodeling of Drosophila sensory neurons requires matrix metalloproteases, ubiquitin-proteasome, and ecdysone signaling

“…It is possible that local environments may play a role. A recent study in Manduca found central versus peripheral hormonal differences affecting axon versus dendrite remodeling (38). However, it remains to be tested whether the ecdysone levels are different in the fly epidermis and the VNC during metamorphosis.…”

Features of structure of nerve motor endings in the tongue of normal and dehydrated rats

“…По имеющимся данным литературы, форма двигательных окончаний в мышцах языка у большинства млекопитающих довольно однообразна (Mu and Sanders, 2010). Например, Knittel and Kent (2005), исследовавшие двигательные окончания языка у представителей класса рыб, также отмечает удивительное сходство в их строении.…”

“…Активность мионеврального синапса зависит как от количества терминальных веточек и ядер бляшек, так и от ее размеров. Об этом свидетельствуют работы Knittel and Kent (2005), показавших, что характерной особенностью двигательных окончаний является высокая концентрация и активность локализованных в ней энзимов по сравнению с нервными и мышечными волокнами. При этом Mu et al (2013) подчеркивают, что ферменты, необходимые для специфической деятельности нервных элементов, распределяются преимущественно в производных шванновской глии.…”

Hormone‐dependent expression of fasciclin II during ganglionic migration and fusion in the ventral nerve cord of the moth Manduca sexta

“…The somata of the monopolar motoneurons in A1 and A2, for example, move anteriorly into the forming pterothoracic ganglion. The axon terminals of motoneurons, however, remain in persistent, close contact with their muscle targets, even if the muscle undergoes remodeling during metamorphosis (Weeks and Truman, 1986; for review see Consoulas et al, 2000; Knittel and Kent, 2002, 2005). These constraints present a puzzle: How does an axon grow over a long distance when its soma and axon are anchored at both ends?…”