AbstractsBiology & Animal Science

Kainate-type glutamate receptors modulating network activity in developing hippocampus

by Juuso Juuri




Institution: University of Helsinki
Department: Department of Biosciences, Physiology and Neuroscience
Year: 2015
Keywords: neurobiologia
Record ID: 1139440
Full text PDF: http://hdl.handle.net/10138/154172


Abstract

Kainate-type of ionotropic glutamate (KA) receptors are associated with the modulation of neuronal excitability, synaptic transmission, and activity of neuronal networks. They are believed to have an important role in the development of neuronal connections. In this thesis, the role of KA receptors in the early brain development was assessed by conducting in vitro electrophysiological recordings from individual neurons at CA3 region in acute slices of neonatal rodent hippocampi. It was found that activation of separate KA receptor populations promoted action potential firing in both glutamatergic pyramidal neurons and GABAergic interneurons. The receptors in pyramidal neurons displayed a high affinity for agonist kainate, appeared to lack subunit GluK1, and promoted spontaneous firing of pyramidal neurons without depolarizing them. The receptors in interneurons contained subunit GluK1 and their activation suppressed afterhyperpolarizing current of medium duration (ImAHP). Receptors in both neuron types appeared to be activated tonically by ambient glutamate, suggesting that their physiological role may be to act as a modulatory mechanism sensitive to changes in extracellular glutamate concentration. Changes in activity of neurons at CA3 by activation of KA receptors were reflected on the network level. Promotion of pyramidal cell firing by pharmacological activation of high-affinity KA receptors lead to enhanced glutamatergic drive and generation of network bursts in the CA3 region. The ImAHP in interneurons was also suppressed by apamin, a blocker of SK potassium channels that mediate majority of this current, and apamin enhanced generation of network bursts. This suggests that also KA receptor mediated regulation of ImAHP may modulate network activity. It was also found that there was an interaction between KA receptors and ethanol in the modulation of hippocampal network: ethanol decreased the occurrence of the network bursts at postnatal days 1 (P1) and P10, whereas it increased bursting at P5. The network effects of ethanol were partially or completely counteracted by specific pharmacological block of GluK1 subunit-containing KA receptors. The findings disclose that via regulation of activity of individual neurons, KA receptors are capable of robust modulation of network activity in immature hippocampus. Additionally, exogenous agents affecting KA receptors may perturb activity dependent developmental processes that are central for the synaptic development. The results shed light on the mechanisms underlying development of hippocampal connectivity, and may help to understand early pathologies of the brain that have developmental origins. Kainaattityypin ionotrooppiset glutamaattireseptorit (KA-reseptorit) säätelevät hermosolujen ärtyvyyttä, synaptista viestintää sekä hermosoluverkkojen aktiivisuutta. Niiden uskotaan olevan tärkeitä aivojen varhaiskehitykselle. Tässä väitöskirjassa KA-reseptoreiden osuutta aivojen kehityksessä tutkittiin hyödyntämällä sähköfysiologisia mittauksia yksittäisistä…