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

Abstract

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 sub®eld or dentate gyrus elicited signi®cant 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 signi®cantly reversed those e ects 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 a 1A/D -, a 2B -and a 2C -adrenoceptors at the hippocampal formation.

Involvement of noradrenergic innervation from locus coeruleus to hippocampal formation in negative feedback regulation of penile erection in the rat

“…Thus, it is conceivable that ascending sensory afferents initiated by tumescence of the penis may activate those hippocampal neurons that subserve the negative feedback mechanism via chemical mediators other than glutamate or oxytocin. That this chemical mediator may be norepinephrine was suggested in a recent study (Chang et al, 2000). We observed that cocaine may inhibit penile erection by triggering the descending limb of the feedback inhibitory mechanism via noradrenergic neurotransmission in the HF.…”

“…These included norepinephrine (Sigma, St. Louis, MO), phenylephrine (Sigma), BHT 933 (RBI, Natick, MA), prazosin (Sigma), naftopidil (RBI), yohimbine (Sigma), rauwolscine (RBI), and papaverine (U-Liang Pharmaceuticals, Taiwan, Republic of China). The doses used were exactly the same as in our previous study (Chang et al, 2000), in which these test agents were used for the same purpose as in the present study. With the exception of naftopidil and papaverine, which used, respectively, 20% methanol and saline as the solvent, all test agents were dissolved in artificial cerebrospinal fluid (aCSF).…”

Differential contributions of nitric oxide synthase isoforms at hippocampal formation to negative feedback regulation of penile erection in the rat

“…This included cannulation of the left femoral artery and vein for the measurement of systemic arterial pressure (SAP) and maintenance of anaesthetic level by intravenous infusion of chloral hydrate (40 mg kg h −1 ). Previous studies (Chang et al ., 1998a, 1998b; 2000; 2001) indicated that this management scheme provided satisfactory anaesthetic level while preserving the capacity of central cardiovascular regulation. SAP was recorded through a pressure transducer (Gould P23XL, Valley View, OH, U.S.A.) and a universal amplifier (Gould 20‐4615‐58).…”

“…The increase in ICP was used as our experimental index for penile erection (Chen et al ., 1992a, 1992b; 1997; Chang et al ., 1998a, 1998b; 2000; 2001). In brief, a 26‐gauge needle filled with saline and connected to a pressure transducer (Gould 23ID) was inserted into the corpus cavernosum on one side.…”

“…Microinjection bilaterally of test agents into the HF was carried out with a stereotaxically positioned 27‐gauge stainless steel needle connected to a 0.5‐μl Hamilton microsyringe (Reno, NV, U.S.A.). The stereotaxic co‐ordinates were 2.3 – 3.2 mm posterior to the bregma, 3.6 – 4.4 mm from the cortical surface, and 1.5 – 2.4 mm lateral to the midline (Chang et al ., 1998a, 1998b; 2000; 2001). A total of 50 nL was delivered over 1 – 2 min to allow for full diffusion of the injection solution.…”