Regulation of axonal and dendritic growth by the extracellular calcium-sensing receptor (CaSR)

Thomas Vizard1, Gerard O'Keeffe1, Humberto Gutierrez1, Claudine Kos2, Daniela Riccardi1, Alun Davies1
1School of Biosciences, Biomedical Building, Museum Avenue, Cardiff, UK, 2Vitamins and Carcinogenesis Laboratory, HNRCA at Tufts University, Boston, Massachusetts , USA

The extracellular calcium-sensing receptor (CaSR) monitors the systemic extracellular free ionized calcium level ([Ca2+]o) in organs involved in systemic [Ca2+]o homeostasis. However, the CaSR is also expressed in the nervous system where its role is unknown. We studied the CaSR in the mouse superior cervical ganglion (SCG), an experimentally tractable population of neurons from the peripheral nervous system and a well established model of neuronal development. The morphology of individual neurons was analysed after a range of manipulations by quantification of total neurite length, and neuritic arbors by Sholl analysis. Comparison of the sympathetic innervation of CaSR mice was by quantification of tyrosine hydroxylase staining of the iris. Statistical analyses were carried out using either Student's t-test or one-way ANOVA with Tukey's post hoc test. We found high levels of the CaSR in perinatal (embryonic day 18 - postnatal day 0) mouse sympathetic neurons when their axons are innervating and branching extensively in their targets. Manipulating CaSR function in these neurons by varying [Ca2+]o, using CaSR agonists (NPS R-467) and antagonists (NPS-89636) or expressing a dominant-negative CaSR (R185Q) markedly affects neurite growth in vitro (n>3; P<0.001). Sympathetic neurons lacking the CaSR have smaller neurite arbors in vitro (n>3; P<0.001), and sympathetic innervation density is reduced in CaSR-deficient mice in vivo (postnatal day 1; n=3; P<0.001). Hippocampal pyramidal neurons, which also express the CaSR, have smaller dendrites when transfected with dominant-negative CaSR in postnatal organotypic cultures (n=5; P<0.001). Our findings reveal a crucial role for the CaSR in regulating the growth of neural processes in the developing peripheral and central nervous systems.