Item – Theses Canada

​
OCLC number
299222635
Link(s) to full text
LAC copy
LAC copy
Author
Speechley, William J.(William Jonathan),1978-
Title
Continuous white noise exposure during and after the auditory critical period alters in vivo bi-directional auditory cortex plasticity in rats.
Degree
M.A. -- Queen's University, 2006
Publisher
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, [2007]
Description
1 microfiche
Notes
Includes bibliographical references.
Abstract
Long-term potentiation (LTP) and long-term depression (LTD) are processes thought to mediate developmental and experience-dependent plasticity in the brain. Both have been demonstrated 'in vitro' in the primary auditory cortex (A1) of adult rats, but 'in vivo' evidence is lacking. We examined these processes 'in vivo' by applying high and low frequency stimulating protocols to the medial geniculate nucleus of urethane anaesthetized rats. Higher frequency theta burst stimulation produced robust LTP (to ~140% of baseline amplitude) of field postsynaptic evoked potentials (fPSP) recorded in the superficial layers of the primary auditory cortex (A1). Low frequency (1 Hz) stimulation resulted in a transient depression (to ~60% of baseline amplitude) of fPSPs recorded in A1. Local, intracortical application of D-(-)-2-amino-5-phosphonopentanoic acid (APV) abolished LTP and reduced synaptic depression, verifying the involvement of cortical N-methyl-D-aspartate receptors in these effects. Thalamocortical plasticity mechanisms were also assessed after continuous white noise exposure, known to arrest auditory cortex maturation, during and after the postnatal critical period of A1 development. Rats housed in continuous white noise during the first 50 days of life exhibited greater LTP (~180%) than controls reared in normal sound environments. More stunningly, the protocol used to elicit depression also resulted in substantial LTP in white noise reared animals (~150%). Adults housed in white noise for the same length of time appeared to exhibit normal LTP, but displayed greater and persistent levels of synaptic depression (to ~30% of baseline amplitude). These results suggest that, in the absence of patterned auditory stimulation during early postnatal life, thalamocortical auditory synapses exhibit a preferential readiness for synaptic potentiation over depression. In adults, however, prolonged deprivation of patterned sound input results in synapses favouring depression over synaptic enhancement. Together, these data confirm the great potential for plasticity in the mature central auditory system and demonstrate the age-dependent impact of experiential factors on plasticity properties of the thalamocortical auditory system.
ISBN
9780494188156
0494188154