title: Development of functional thalamocortical synapses studied with current source-density analysis in whole forebrain slices in the rat.
abstract: We analysed the laminar distribution of transmembrane currents from embryonic (E) day 17 until adulthood after selective thalamic stimulation in slices of rat forebrain to study the development of functional thalamocortical and cortico-cortical connections. At E18 to birth a short-latency current sink was observed in the subplate and layer 6, which was decreased, but not fully abolished in a cobalt containing solution or after the application of glutamate receptor blockers (APV and DNQX). This indicated that embryonic thalamic axons were capable of conducting action potentials to the cortex and some of them had already formed functional synapses there. Between birth and P3, when thalamic axons were completing their upward growth, a sink gradually appeared more superficially in the dense cortical plate and synchronously, a current source aroused in layer 5. Both sinks and sources completely disappeared after blocking synaptic transmission. The adult-like distribution of CSDs became apparent after P7. The component in layer 6 cannot be blocked completely after this age suggesting antidromic activation. This study demonstrated that cells of the lowest layers of the cortex received functional thalamic input before birth and that thalamocortical axons formed synapses with more superficial cells as they grew into the cortical plate.
authors.affiliation: Department of Human Anatomy and Genetics, University of Oxford, South Parks Road, OX1 3QX, Oxford, UK. zoltan.molnar@anat.ox.ac.uk
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Molnár
authors.forename: Tohru
authors.initials: T
authors.lastname: Kurotani
authors.forename: Shuji
authors.initials: S
authors.lastname: Higashi
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Yamamoto
authors.forename: Keisuke
authors.initials: K
authors.lastname: Toyama
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000196:embryology* / Q000254:growth & development*; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D011247:Pregnancy; D016548:Prosencephalon / Q000196:embryology / Q000254:growth & development; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D013788:Thalamus / Q000196:embryology* / Q000254:growth & development*