Drinking by rats after irritative lesions in the hypothalamus

The deposition of metallic ions in or near the lateral hypothalamus with a stainless-steel anode causes primary polydipsia lasting about six hours. During this time rats are hyperactive and drink as much as two to three times their normal daily intake. This irritative effect accounts for the polydipsia which sometimes follows lesions in the median eminence of the tuber cinereum of nephrectomized rats. Non-irritative lesions there do not cause primary polydipsia. After six hours rats with chronic diabetes insipidus produced by lesions in the median eminence do not show any effects of irritative lesions on water intake. In addition, when their urine output is suppressed these diabetic rats drink almost exactly the amount of water needed to dilute a cellular thirst stimulus (hypertonic saline) to isotonicity and drink the same amount as controls after equivalent extracellular thirst stimuli (polyethylene glycol) suggesting that important drinking mechanisms are not located in the median eminence.