title: Transsynaptic activity-dependent regulation of axon branching and neurotrophin expression in vivo.
abstract: The two major classes of activity-dependent neuroplasticity predict different consequences of activity alteration on circuit response. Hebbian plasticity (positive feedback) posits that alteration of neuronal activity causes a parallel response within a circuit. In contrast, homeostatic plasticity (negative feedback) predicts that altering neuronal activity results in compensatory responses within a circuit. The relative roles of these modes of plasticity in vivo are unclear, since neuronal circuits are difficult to manipulate in the intact organism. In this study, we tested the in vivo effects of activity deprivation in the superior cervical ganglion-pineal circuit of adult rats, which can be noninvasively silenced by exposing animals to constant light. We demonstrated that total deprivation of sympathetic activity markedly decreased the presence of axonal proteins in the pineal and reduced the density and thickness of sympathetic axonal arbors. In addition, we demonstrated that sympathetic inactivity eliminated pineal function and markedly decreased pineal expression of neurotrophins. Administration of β-adrenergic agonist restored the expression of presynaptic and postsynaptic proteins. Furthermore, compensatory axonal growth through collateral sprouting, normally seen following unilateral denervation of the pineal, was profoundly impaired in the absence of neural activity. Thus, these data suggest that sympathetic axonal terminals are maintained by neural activity that induces neurotrophins, which may act through a retrograde mechanism to preserve the integrity of axonal arbors via a positive feedback loop. Conversely, by using Hebbian-like neuroplasticity, silent yet intact circuits enter a hibernation mode marked by reduction of presynaptic axonal structures and dramatically reduced postsynaptic expression of neurotrophins.
authors: Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan 48109-5622, USA.
authors: Anda-Alexandra
authors: AA
authors: Calinescu
authors: Tiecheng
authors: T
authors: Liu
authors: Michael M
authors: MM
authors: Wang
authors: Jimo
authors: J
authors: Borjigin
mesh_terms: D000322:Adrenergic Agonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001369:Axons / Q000502:physiology*; D015153:Blotting, Western; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D007150:Immunohistochemistry; D007545:Isoproterenol / Q000494:pharmacology; D009043:Motor Activity / Q000502:physiology; D020932:Nerve Growth Factor / Q000096:biosynthesis; D009414:Nerve Growth Factors / Q000096:biosynthesis*; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D009473:Neuronal Plasticity / Q000502:physiology; D010870:Pineal Gland / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017783:Superior Cervical Ganglion / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects; D013569:Synapses / Q000502:physiology*
chemical_list: D000322:Adrenergic Agonists; D000318:Adrenergic beta-Agonists; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D020932:Nerve Growth Factor; D007545:Isoproterenol