Effects of phosphodiesterase inhibition on the excitability of hippocampal pyramidal neurons in vitro.

Extracellular field potentials were evoked in the CA1 pyramidal cell layer of the isolated rat hippocampus by electrical stimulation of the stratum radiatum. Of the three phosphodiesterase (PDE) inhibitors, 3-isobutyl-1-methylxanthine (IBMX), zardaverine and rolipram, only the adenosine receptor antagonist, IBMX, increased the amplitudes of the extracellular excitatory postsynaptic potential (EPSP) and population spike (PS). The beta-adrenoceptor agonist, isoproterenol, also facilitated these potentials and became more potent in the presence of zardaverine or rolipram. The results suggest that PDE blockade increases the excitability of pyramidal neurones only after preceding stimulation of beta-adrenoceptors.