Activity of neurons in the lateral preoptic area during drinking behavior by the rat

Rats were trained to drink water, sucrose solution, and saline while their heads were painlessly held in a stereotaxic apparatus with an attachment fixed to the skull. A total of 286 neurons in the lateral preoptic area (LPO) were recorded during the drinking behavior. During water intake, 40% of the neurons tested were either excited or inhibited. Sucrose elicited responses in 25% of the neurons, and saline in 34%. Of the 52 neurons recorded while rats drank all test solutions, 8 specifically responded to water, 3 were sucrose specific, 4 were saline specific, 12 responded to all solutions, and the remaining 25 did not respond to any solutions. Artificial cerebrospinal fluids (ACSFs) with physiologically hypertonic (+30 mOsm/kg, by NaCl or mannitol) and hypotonic (-30 mOsm/kg) osmotic pressure were applied to 88 neurons through a multibarrel micropipette. Of these neurons, 15 (17%) were hypotonic-sensitive; they were excited by hypotonic ACSF and/or inhibited by hypertonic ACSFs. There were 4 (5%) that were hypertonic-sensitive; they were excited by hypertonic ACSFs and/or inhibited by hypotonic ACSF. Of six hypotonic-sensitive neurons examined, three were water specific, and none were sucrose nor saline specific. Of four hypertonic-sensitive neurons, one was water specific, and another was saline specific. These results showed activity of some LPO neurons specifically related to water intake. Osmosensitive neurons in the LPO may regulate water intake.