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Title: Cellular mechanisms of presynaptic nAChR-mediated excitatory amino acid release from rat prefrontal cortex
Author: Dickinson, Jane A.
ISNI:       0000 0001 3423 9990
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2007
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Nicotine-mediated activation of nicotinic acetylcholine receptors (nAChRs) located in the prefrontal cortex (PFC) has been associated with the augmentation of attention and working memory. Whilst studies have implicated a.7 and p2* nAChRs in nicotine-elicited cognitive enhancement, the cellular mechanisms underlying these effects have yet to be elucidated. The aim of this project was to characterise the cellular mechanisms bywhich presynaptic a.7 and p2* ~ChRs mediate excitatory amino acid (EAA) release from rat PFC. The first part of this project established the suitability of PFC P2 synaptoso~es and [3H]D-aspartate for measuring presynaptic mechanisms of EAA release, as well as confirming the presence of a.7 and p2* nAChRs in the PFC. Initial experiments showed that nicotine could evoke EAA release via both a.7 and p2* nAChRs, this was confirmed following the characterisation of selective nAChR subtype agonists, (R)-N-(1-azabicyclo[2.2.Z]oct-3-yl)(5-(Zpyridyl) thiophene-2-c~rboxamide) (compound A) and 5-iodo-A-85380. Having established that compound A and 5-iodo-A-85380 evoke EAA release via a.7 and pZ* nAChRs, respectively; investigations into the cellular mechanisms mediating this release were carried out. Whilst higher concentrations of KCI application revealed that EAA release can be mediated by EAA transporter reversal and a Ca2+-dependent mechanism, EAA release mediated by a.7 or p2* nAChRs was entirely Ca2+-dependent. The use of voltage-operated Ca2+ channel (VOCC) inhibitors and modulators of intracellular Ca2+storesdetermined that a.7 and p2* nAChR-mediated EAA release was elicited via distinct pathways. Whilst p2* nAChR-mediated responses were dependent upon VOCC activation, a.7 nAChR-mediated responses required Ca2+-induced Ca2+release (CICR) with no VOCC involvement. To establish whether this distinct coupling of a.7 and pZ* nAChRs was a widespread phenomenon, a.7 and pZ* 0 nAChR subtype selective tools were used to alter Ca2+ levels in PCIZ cells. As seen at the presynaptic terminal, a.7 and pZ* nAChRs were coupled to VOCCs and CICR, respectively. The segregation of these two nAChR subtypes to separate Ca2+pathways may constitute a method by which they regulate different neuronal events. Intracellular Ca2+ stores have recently been implicated in synaptic plasticity, and may provide a mechanism by which a.7 nAChRs mediate their effects on cognition. One possible pathway that can translate presynaptic Ca2+ release into synaptic plasticity is the extracellular regulated kinase cascade. The use of inhibitors and western blotting revealed that this pathway was activated in PFC synaptosomes following a.7 nAChR activation and was essential for a.7 nAChR-mediated EAA release, consistent with a,possible role for this receptor in nicotine-evoked synaptic plasticity in the PFC.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available