Late developmental changes in the ability of adenosine A1 receptors to regulate synaptic transmission in the hippocampus

Paired-pulse facilitation (PPF) of CA3-CA1 excitatory postsynaptic potentials (EPSP) was compared in hippocampal slices from juvenile (postnatal day (P) 15-21) and young adult rats (P28-P35) following application of adenosine. Relative to juveniles, young adults expressed an increase in baseline synaptic strength that was accompanied by a decrease in PPF suggesting a developmental increase in transmitter release. While adenosine depressed the EPSP slope to a similar extent in juveniles and young adults, PPF increased during adenosine application only for young adults. The differential effect of adenosine on PPF was not due to differences in receptor function or in extracellular ligand levels, since the A1 antagonist cyclopentyltheophylline (CPT) did not differentially affect PPF across age. Adenosine could increase PPF in juvenile slices under conditions of enhanced transmitter release, through an increase in the bath Ca2+ concentration, or addition of forskolin to the bath. These data indicate that the ability to modify synaptic transmission through presynaptic adenosine A1 receptors increases across postnatal development with the maturation of release mechanisms.