Sperm release evoked by electrical stimulation of the fish brain: a functional-anatomical study

Area of Science:

• Neuroscience
• Ichthyology
• Reproductive Biology

Background:

• Understanding the neural control of reproduction is crucial for fish aquaculture and conservation.
• The specific brain regions and pathways regulating semen discharge in teleosts remain incompletely understood.

Purpose of the Study:

• To identify the brain areas involved in controlling semen discharge in male green sunfish (Lepomis cyanellus) through electrical stimulation.
• To elucidate the neural pathway mediating reproductive reflexes in this species.

Main Methods:

• Acute experiments involving anesthetized male green sunfish.
• Low-level electrical stimulation (≤100 μA) applied to discrete brain regions.
• Observation of semen discharge as the primary response indicator.
• Surgical interventions including optic tectum/cerebellum removal and spinal cord transection.

Main Results:

• Semen discharge was consistently evoked by stimulation of the preoptic region, dorsal hypothalamus, thalamus, midbrain tegmentum, and basolateral midbrain/medulla.
• Stimulation of other brain areas (telencephalon, optic tectum, cerebellum, etc.) did not induce sperm release.
• Responses from the preoptic area persisted after optic tectum/cerebellum removal but were abolished by rostral spinal cord transection.
• Electrical stimulation of an isolated spinal cord segment induced sperm release.

Conclusions:

• A neural pathway for semen release in green sunfish originates in the preoptic area and extends to the spinal cord.
• The pathway involves the hypothalamus, midbrain tegmentum, and basal midbrain/medulla.
• The spinal cord possesses intrinsic mechanisms for regulating semen discharge.