Morphine inhibits dopaminergic and cholinergic induced ejaculation in rats

Area of Science:

• Neuropharmacology
• Reproductive Endocrinology

Background:

• Ejaculation is a complex physiological process influenced by various neurotransmitter systems.
• Dopaminergic and cholinergic pathways are implicated in sexual behavior, but their specific roles in ejaculation require further elucidation.

Purpose of the Study:

• To investigate the roles of dopaminergic and cholinergic systems in male rat ejaculation.
• To examine the modulatory effects of opioid agonists and antagonists on drug-induced ejaculation.

Main Methods:

• Administration of dopaminergic agents (apomorphine, quinpirole), cholinergic agents (physostigmine, pilocarpine), opioid agents (morphine, naloxone), and receptor antagonists (sulpiride, domperidone, atropine) in male rats.
• Observation and quantification of drug-induced ejaculatory responses.
• Assessment of the effects of pre-treatment with various pharmacological agents on ejaculation.

Main Results:

• Apomorphine, quinpirole, physostigmine, and pilocarpine induced ejaculation, while neostigmine did not.
• Morphine pretreatment reduced drug-induced ejaculation, an effect reversed by naloxone.
• Naloxone alone induced slight ejaculation.
• Sulpiride reduced ejaculation induced by apomorphine and quinpirole but not physostigmine and pilocarpine.
• Atropine decreased the frequency of ejaculation induced by all tested agents.

Conclusions:

• D-2 receptor activation appears to induce ejaculation through modulation of cholinergic mechanisms.
• Morphine inhibits ejaculation via opiate receptors, affecting both cholinergic and dopaminergic pathways.
• Cholinergic systems play a crucial role in mediating ejaculation induced by dopaminergic and cholinergic stimulation.