Hippocampal noradrenergic neurotransmission in concurrent EEG desynchronization and inhibition of penile erection induced by cocaine in the rat

1 We previously reported that cocaine may induce activation of cortical (cEEG) and hippocampal (hEEG) electroencephalographic signals, concurrent with inhibition of penile erection, via an action on the hippocampal formation. The present study further evaluates the role of noradrenergic neurotransmission at the hippocampal formation in this process, using adult, male Sprague-Dawley rats anaesthetized and maintained by chloral hydrate. 2 Unilateral microinjection of cocaine (100 nmoles) into the hippocampal CA1 or CA3 subfield or dentate gyrus elicited significant activation of both cEEG and hEEG activity. At the same time, the intracavernous pressure (ICP), our experimental index for penile erection, underwent a discernible reduction. 3 Co-administration of equimolar doses (250 pmoles) of prazosin, naftopidil, yohimbine or rauwolscine significantly reversed those effects elicited by cocaine on cEEG, hEEG and ICP. 4 Microinjection unilaterally of equimolar doses (5 nmoles) of norepinephrine, phenylephrine or BHT 933 into the hippocampal formation, similar to cocaine, also induced appreciable cEEG and hEEG excitation, with a simultaneous decrease in ICP. 5 We conclude that cocaine may activate cEEG and hEEG and decrease ICP via noradrenergic neurotransmission, possibly engaging at least alpha(1A/D)-, alpha(2B)- and alpha(2C)-adrenoceptors at the hippocampal formation.