A researcher destroys the suprachiasmatic nucleus (SCN) bilaterally in experimental animals. The most consistent endocrine consequence is:

• A Selective loss of the preovulatory LH surge with retained basal gonadotropin secretion
• B Loss of circadian rhythmicity of ACTH, cortisol and melatonin secretion ✓
• C Permanent abolition of all pulsatile hormone secretion including GnRH pulses
• D Loss of ADH responses to osmotic stimuli with preserved circadian rhythms

Explanation

The SCN is the master circadian pacemaker, receiving direct retinal input via the retinohypothalamic tract and driving rhythmic output that times the HPA axis, pineal melatonin synthesis and sleep-wake coupled hormonal cycles. Lesioning it abolishes these rhythms without eliminating ultradian GnRH pulses, which arise from arcuate kisspeptin neurons, nor osmotically driven ADH release, which depends on the organum vasculosum and magnocellular nuclei.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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