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fbtwitterlinkedinvimeoflicker grey 14rssslideshare1
Languages: English
Types: Doctoral thesis
Subjects: QP
The release and clearance of adenosine are reasonably well-documented in the\ud mature CNS but relatively little is known about how adenosine signalling changes\ud during postnatal development. The activation of presynaptic A1 receptors (A1R) at\ud cerebellar parallel fibre terminals is known to inhibit synaptic transmission and the\ud expression of A1R has been observed in mature rat cerebellar slices. However its\ud distribution during development or in relation to parallel fibre–Purkinje cell (PF-PC)\ud synapses has not previously been described. In the mature cerebellum blockade of\ud presynaptic A1R at PF-PC synapses enhances synaptic transmission suggesting an\ud inhibitory adenosine tone and an extracellular purine tone is detectable with\ud microelectrode biosensors under basal conditions. The active release of adenosine\ud can be stimulated with trains of activity in the molecular layer of mature slices\ud although this does not appear to be a source of the basal extracellular adenosine tone.\ud This study used immunohistochemistry to determine the distribution of A1R at PFPC\ud synapses in cerebellar slices at postnatal day 3 prior to PF-PC synapse formation,\ud postnatal days 8-14 and postnatal days 21-28. This study also used cerebellar slices\ud from rats at postnatal days 9-14 to investigate the pharmacological profile of the\ud immature rat PF-PC synapse with electrophysiology and microelectrode biosensors.\ud The immunohistochemistry suggests that A1R are widely distributed across Purkinje\ud cell bodies and their dendrites and within the granule layer of the cerebellum and that\ud its expression does not change during development. The same staining patterns were\ud also observed prior to PF-PC synapse formation.\ud Application of adenosine resulted in a variable A1R-mediated inhibition at immature\ud PF-PC synapses. This did not appear to be gender-specific or correlated with age of\ud rat and the synapses otherwise appeared identical in their properties. The\ud comparison of log concentration-response curves generated for an A1R agonist\ud suggested that some A1R may have a lower efficacy at this stage of development.\ud Blockade of presynaptic A1R at immature PF-PC synapses suggested that an\ud inhibitory adenosine tone is low or absent at this stage of development and is not the\ud result of a low A1R expression or developmental differences in A1R efficacy.\ud Inhibition of adenosine clearance via adenosine deaminase, adenosine kinase and\ud equilibrative transporters had little effect on synaptic transmission suggesting that\ud little adenosine is moving between the intracellular and extracellular spaces under\ud basal conditions in immature slices. Active adenosine release measured by\ud electrophysiology and microelectrode biosensors could be stimulated with hypoxia in\ud immature slices but this was delayed and slower in comparison to the release\ud observed in mature slices. Adenosine could not be actively released at immature PFPC\ud synapses in response to electrical stimulation in the molecular layer.
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