The Spinal Ejaculatory Generator
Lumbar interneurons integrate genital afferents into the reflex arc.
- L3–L5: Spinal level (lumbar spinothalamic cells)
- Somato-autonomic: Reflex type (sensory to motor arc)
- LSt cells: Key structure (ejaculation generator)
- Descending 5-HT: Modulation (from brainstem raphe)
Circuit overview
Placeholder: pudendal afferents drive spinal generator output.
5-HT1A Receptors Lower the Threshold
5-HT1A activation is pro-ejaculatory, shortening latency.
- Gi-coupled: Receptor class (inhibits adenylate cyclase)
- Threshold ↓: Net effect (facilitates ejaculation)
- 8-OH-DPAT: Agonist example (preclinical probe)
- Lifelong PE: Clinical link (proposed hypersensitivity)
Mechanism
Placeholder: 1A signaling disinhibits spinal output neurons.
5-HT2C Receptors Raise the Threshold
5-HT2C activation is anti-ejaculatory, prolonging latency.
- Gq-coupled: Receptor class (activates PLC pathway)
- Threshold ↑: Net effect (delays ejaculation)
- SSRIs: Drug class link (chronic dosing upregulates 2C)
- Delayed-onset therapy: Clinical use (dapoxetine mechanism)
Mechanism
Placeholder: 2C signaling enhances inhibitory tone centrally.
Raphe Serotonergic Tone Balance
Raphe output sets the relative 1A versus 2C drive.
- Dorsal raphe: Source nucleus (main forebrain 5-HT source)
- 1A:2C ratio: Balance metric (net excitatory/inhibitory)
- Tone shift: SSRI effect (toward 2C dominance)
- Weeks: Time course (receptor adaptation delay)
Integration
Placeholder: descending tone integrates both receptor drives.
Final Reflex Threshold Determination
Combined receptor balance yields observed ejaculatory latency.
- IELT: Outcome measure (intravaginal latency time)
- Premature: Low threshold (1A-dominant state)
- Delayed: High threshold (2C-dominant state)
- Normal: Balanced state (euthreshold range)
Outcome
Placeholder: threshold gauge reflects net receptor balance.
Placeholder: balance of 1A and 2C tone determines clinical phenotype.