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Journal of Neuroscience, Vol 15, 1484-1495, Copyright © 1995 by Society for Neuroscience

ARTICLE

Decreased monosynaptic sensory input to an identified motoneuron is associated with steroid-mediated dendritic regression during metamorphosis in Manduca sexta

LC Streichert and JC Weeks
Institute of Neuroscience, University of Oregon, Eugene 97403-1254.

The proleg withdrawal reflex of Manduca sexta larvae is mediated by mono- and polysynaptic connections from afferents innervating mechanosensory planta hairs (PHs) to ipsilateral proleg retractor motoneurons. During the larval-pupal transformation, a rise in ecdysteroids causes the dendrites of proleg motoneurons to regress and, concurrently, the proleg withdrawal reflex is lost. The objective of this study was to identify synaptic correlates of dendritic regression that contributed to this behavioral change. The accessory planta retractor (APR) motoneuron regresses during the larval-pupal transformation and dies in a segment-specific pattern after pupation. The compound excitatory postsynaptic potential (cEPSP) evoked in APR by electrically stimulating the proleg sensory nerve decreased in amplitude during the larval-pupal transformation. The developmental decrease in cEPSP amplitude, the extent of APR's regression, and several of APR's intrinsic electrical properties were similar in segments in which the motoneuron was fated to live or die. In heterochronic mosaic pupae bearing retained larval PH afferents, APR's dendritic regression was associated with decreases in both the mean amplitude of monosynaptic EPSPs produced by PH afferents and the proportion of PH afferents that produced detectable EPSPs. These changes appeared due to a developmental decrease in the size of the synaptic currents produced by PH afferents. Evidence was also obtained suggesting that PH afferents do not regress at pupation. These findings support the hypothesis that the ecdysteroid-mediated regression of proleg motoneuron dendrites disconnects them from sensory inputs and, thereby, contributes to the elimination of the proleg withdrawal reflex.

This article has been cited by other articles:

				C. Duch and T. Mentel Activity Affects Dendritic Shape and Synapse Elimination during Steroid Controlled Dendritic Retraction in Manduca sexta J. Neurosci., November 3, 2004; 24(44): 9826 - 9837. [Abstract] [Full Text] [PDF]

				J. R. Gray and J. C. Weeks Steroid-Induced Dendritic Regression Reduces Anatomical Contacts between Neurons during Synaptic Weakening and the Developmental Loss of a Behavior J. Neurosci., February 15, 2003; 23(4): 1406 - 1415. [Abstract] [Full Text] [PDF]

				C. Consoulas, L. L. Restifo, and R. B. Levine Dendritic Remodeling and Growth of Motoneurons during Metamorphosis of Drosophila melanogaster J. Neurosci., June 15, 2002; 22(12): 4906 - 4917. [Abstract] [Full Text] [PDF]

				J. Lubischer, L. Verhegge, and J. Weeks Respecified larval proleg and body wall muscles circulate hemolymph in developing wings of Manduca sexta pupae J. Exp. Biol., January 4, 1999; 202(7): 787 - 796. [Abstract] [PDF]

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