Compartment‐specific regulation of plasma membrane calcium ATPase type 2 in the chick auditory brainstem

Abstract

Calcium signaling plays a role in synaptic regulation of dendritic structure, usually on the time scale of hours or days. Here we use immunocytochemistry to examine changes in expression of the plasma membrane calcium ATPase type 2 (PMCA2), a high-affinity calcium efflux protein, in the chick nucleus laminaris (NL) following manipulations of synaptic inputs. Dendrites of NL neurons segregate into dorsal and ventral domains, receiving excitatory input from the ipsilateral and contralateral ears, respectively, via nucleus magnocellularis (NM). Deprivation of the contralateral projection from NM to NL leads to rapid retraction of ventral, but not the dorsal, dendrites of NL neurons. Immunocytochemistry revealed symmetric distribution of PMCA2 in two neuropil regions of normally innervated NL. Electron microscopy confirmed that PMCA2 localizes in both NM terminals and NL dendrites. As early as 30 minutes following transection of the contralateral projection from NM to NL or unilateral cochlea removal, significant decreases in PMCA2 immunoreactivity were seen in the deprived neuropil of NL compared to the other neuropil which continued to receive normal input. The rapid decrease correlated with reductions in the immunoreactivity for the microtubule-associated protein 2, which affects cytoskeleton stabilization. These results suggest that PMCA2 is regulated independently in ventral and dorsal NL dendrites and/or their inputs from NM in a way that is correlated with presynaptic activity. This provides a potential mechanism by which deprivation can change calcium transport that, in turn, may be important for rapid, compartment-specific dendritic remodeling.

Relative input strength rapidly regulates dendritic structure of chick auditory brainstem neurons

“…Locally regulated calcium signaling has also been observed in vivo in other developing sensory systems in response to physiological stimuli (Bollman and Engert, 2009). Local changes in calcium signaling can alter the activation of kinases and transcriptional regulators (Wong and Ghosh, 2002), influence gene expression (Flavell and Greenberg, 2008; Redmond and Ghosh, 2005), as well as the expression and localization of glutamate receptors (Martin and Henley, 2004; Wang et al, 2009) and cytoskeletal elements (Ciani and Salinas; Luo, 2002; Okamoto et al, 2004; Zheng and Poo, 2007), all of which can shape dendritic form. In NL cytoskeletal changes are known to accompany deafferentationand deprivation-induced losses in dendrite structure (Deitch and Rubel, 1989; Wang and Rubel, 2008), and rapid changes in calcium regulatory proteins have also been observed (Wang et al, 2009).…”

“…In this scenario unstimulated NL dendrites may lose TDBL in response to degeneration or complete inactivation of their unstimulated presynaptic terminals, while stimulated terminals and their postsynaptic dendrites either grow or are maintained. Indeed, in this system input-dependent changes in calcium regulation within presynaptic terminals have been suggested (Wang et al, 2009). Simultaneous imaging of pre and postsynaptic structures will shed light on whether presynaptic changes facilitate and/or accompany changes in postsynaptic structure in NL.…”

In VivoReversible Regulation of Dendritic Patterning by Afferent Input in Bipolar Auditory Neurons

“…Briefly, animals were anesthetized with a mixture of 40 mg/kg ketamine and 12 mg/kg xylazine. For transection of the crossed dorsal cochlear tract (XDCT), an ophthalmic knife was inserted through the fourth ventricle and into the brainstem to transect the XDCT at the midline (Deitch and Rubel, 1984; Wang et al, 2009). The XDCT contains the decussating NM axons that project to the ventral NL on both sides of the brain.…”

“…The XDCT contains the decussating NM axons that project to the ventral NL on both sides of the brain. For cochlea removal, the basilar papilla, including the lagena macula, was removed via the oval window following removal of the tympanic membrane and columella (Born and Rubel, 1985; Wang et al, 2009). The membranous cochlear duct was floated on water in a petri dish and inspected under an operating microscope to insure complete removal.…”

“…Although not sensitive enough to detect changes in dendritic length at early time points following the manipulations, MAP2 staining provides a reliable way to evaluate later changes when dendritic retraction accumulates and leads to substantial changes in the extension of the dendritic filed at several days following afferent deprivation. This analysis has been used to study dynamics of a number of cellular events following the same manipulations (Durham and Rubel, 1985; Wang and Rubel, 2008; Wang et al, 2009). …”