Signalling routes and developmental regulation of group I metabotropic glutamate receptors in rat auditory midbrain neurons

Abstract Group I metabotropic glutamate receptors (mGluRs) are linked to intracellular Ca 2+ signalling and play important roles related to synaptic plasticity and development. In neurons from the central nucleus of the inferior colliculus (CIC), the activation of these receptors evokes large [Ca 2+ ] i responses. By using optical imaging of the fluorescent Ca 2+ ‐sensitive dye Fura‐2, we have explored which [Ca 2+ ] i routes are triggered by group I mGluR activation in young CIC neurons and whether mGluR‐induced [Ca 2+ ] i responses are regulated during postnatal development. In addition, real‐time quantitative RT‐PCR was used to study the developmental expression of both group I mGluR subtypes, mGluR1 and mGluR5. Application of DHPG, a specific agonist of group I mGluRs, was used on CIC slices from young rats to elicit [Ca 2+ ] i responses. A majority of responses consisted of an initial thapsigargin‐sensitive Ca 2+ peak, related to store depletion, followed by a plateau phase, sensitive to the store‐operated Ca 2+ entry blocker 2‐APB. During postnatal development, from P6 to P17, DHPG‐induced [Ca 2+ ] i responses changed. The largest Ca 2+ responses were reached at P6, whereas lower peak and plateau responses were found after hearing onset, at P13–P14 and P17. qRT‐PCR analysis also revealed important differences in the expression of both mGluR1 and mGluR5 subtypes during development, with the highest levels of both subtypes at P7 and a developmental decrease of both transcripts. Our results suggest both intra‐ and extracellular routes for [Ca 2+ ] i increases linked to group I mGluRs in CIC neurons and a regulation of group I mGluR activity and expression during auditory development. © 2012 Wiley Periodicals, Inc.