Endocrine and Neural Mediation of the Effects of Constant Light on Water Intake of Rats

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Abstract
Brattleboro rats with a genetic defectin antidiuretic hormone (ADH) synthesis are profoundly polydipsic and have a substantially at-tenuated light-dark distribution of drinking when compared to intact rats maintained on an alter-nating cycle of 12 h of light and 12 h of darkness. Twice daily injections of vasopressin tannate markedly reduced water consumption of Brattle-boro rats and also re-established nearly normal nocturnal drinking patterns. The depressive effects of constant light on water intake of albino rats were abolished by nephrectomy; this response may ordinarily depend on ADH-mediated renal water retention. The light-mediated decrease in fluid intake was attenuated by adrenalectomy although nocturnal drinking patterns and phase-shifting of drinking rhythms were normal in these rats. Intact Long-Evans rats were far less responsive than albino rats in that they did not decrease their daily water intake when placed in constant light; responsiveness to continuous illumination was increased in Long-Evans rats by lesions that bilaterally interrupted the superior accessory and primary optic tracts. These components of the central visual projections may inhibit responsiveness to constant light, possibly by modulating activity of the inferior accessory optic tracts.

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