Specific appetite for NaCl without postingestional repletion.

Abstract

A series of experiments (Falk, unpublished paper; Falk, in press) has shown that the depletion of extracellular fluid electrolyte by the method of transperitoneal dialysis not only increases water intake, but also produces a large increase in the consumption of hypertonic NaCl solution. The measure of NaCl appetite used was the total amount of solution drunk in a 13-hr, period following a 4-hr, rest period after dialysis. During such a session of voluntary repletion, the animal has a protracted opportunity to sample the test fluids available and to learn, on the basis of postingestional effects, to compensate the induced deficiency by adjusting intake. However, the increased acceptability of a highly hypertonic NaCl solution following dialysis may result from a more immediate adjustive mechanism, e.g., a centrally mediated change in hedonic tone (Young, 1952). In order to test this notion, the animal may be given a series of fluid preference tests of brief over-all duration wherein it ingests minimal amounts of test solution. When testing time is short and intake very small, factors attributable to the actual electrolyte repletion value of the test fluid can be eliminated. Therefore, evidence for increased NaCl acceptance obtained under these conditions would argue that at least some aspect of compensatory intake is based on an immediately altered behavioral response to the test fluids. METHOD SubjectsTwenty-three male albino rats (Charles River Breeding Laboratories) were used. They were 90 to 100 clays old and obtained in three groups as they were needed. The weights of the first and third groups were between 300 and 400 gm., while the weights of the second group lay between 500 and 550 gm. They were caged in a constantly illuminated, temperaturecontrolled room.

The neural substrates of enhanced salt appetite after repeated sodium depletions

“…Previous research has established that repeated sodium depletions produce a significant increase in sodium appetite as indicated by incremental increases in hypertonic saline solution intake over the first three or four episodes of sodium depletion (Falk, 1966;Falk and Herman, 1961;Leshem et al, 2004;Roitman et al, 2002;Sakai et al, 1987;Sakai et al, 1989). The purpose of the present experiment was to investigate possible neural mechanisms underlying this behavioral plasticity.…”

Salt craving: The psychobiology of pathogenic sodium intake

“…Falk and Herman [59] were the first to report sodium appetite sensitization, which they induced via intraperitoneal dialysis (IPD).A 5% glucose solution injected into the peritoneal cavity sequesters isotonic extracellular fluid which can be withdrawn after several hours to produce an absolute sodium deficiency and robust sodium appetite. Rats given another identical IPDinduced intake test display enhanced 3% saline ingestion on the second depletion as compared to the first.…”

“…Sodium depletion can be achieved through the administration of diuretic agents (e.g., furosemide), intraperitoneal dialysis, or injections of inert colloids (e.g., polyethylene glycol) into the peritoneal cavity or subcutaneously which provoke sodium appetite by directly depleting extracellular volume or functionally by sequestering extracellular fluid in localized edematous depots [17,59,60]. A disruption in body fluid homeostasis leads to activation of the renin-angiotensin-aldosterone system (RAAS) which is also important in cardiovascular regulation [61,62].…”

Anion Size Does Not Compromise Sodium Recognition by Rats After Acute Sodium Depletion.

“…When rats are in a sodium-depleted state, the apparent perception of a "sodium-like" taste quality will promote ingestion of the stimulus (e.g., Falk & Herman, 1961;Handal, 1965;Nachman, 1962;Richter & Eckert, 1938). This depletion-induced elevation of intake, termed sodium appetite, is specific for sodium and lithium salts (Nachman, 1962) and has been described in a number of mammals (see Denton, 1982;Schulkin, 1991).…”

“…This depletion-induced elevation of intake, termed sodium appetite, is specific for sodium and lithium salts (Nachman, 1962) and has been described in a number of mammals (see Denton, 1982;Schulkin, 1991). Researchers have used this phenomenon for several decades to test hypotheses about salt taste perception, most notably through the use of brief-access taste tests which substantially reduce the contribution of postingestive receptors (e.g., Breslin, Spector, & Grill, 1993;Falk & Herman, 1961;Handal, 1965;Nachman, 1962).…”