RESUMEN

Food-deprived rats were given intermittent access or, in a replication, continuous access to a 20% sucrose solution. Both drinking and nondrinking behaviors were recorded. During the ensuing drinking bout, latency of lapping after snout apposition, and duration of lapping bouts, did not change. Approaches to the sipper tube usually eventuated in lapping, though aborted approaches increased in frequency late in the session. Drinking was interrupted by nondrinking behaviors which appeared in a characteristic rostro-caudal sequence: partial head withdrawal from the drinking aperture, then full head withdrawal, then movements of the front paws, then movement of the hind paws with full-body locomotion. All these behavioral changes occurred before there was any appreciable reduction in rate of lapping.

Asunto(s)

RESUMEN

Esophagostomized rats were permitted to "real-feed" a glucose solution (Experiment 1) or milk (Experiment 2), by receiving intragastric (IG) infusions concurrent with sham feeding. This was done for the first part of the feeding session; then the IG infusions were discontinued so that subsequent ingestion was sham. When such infusions stopped after 80% of real-meal volume had been delivered, they had no measurable effect on subsequent oral ingestion: sham feeding persisted as if nothing had been delivered IG. Therefore, the onset of postingestive satiety, at least in experienced sham-feeding rats, is all-or-none or close to it: if the IG loads are even slightly short of what is required to abolish sham feeding, then they do not affect sham feeding at all. This is so even if the postingestive events occur within their normal behavioral context.

Asunto(s)

RESUMEN

In rats on a stringent deprivation schedule and at reduced body weight, an intragastric load of liquid diet that equals or exceeds normal meal size has no effect at all on subsequent sham feeding of milk diet or of glucose. Removing the acute deprivation period and reversing, or preventing, severe weight reduction has no effect on this "persistence" of sham feeding: a full intragastric meal may leave sham feeding quite unaffected, even if that meal follows the previous meal at a physiological interval, in rats at normal weight. These data contrast with graded, dose-dependent effects of other manipulations by other investigators. Perhaps such effects depend on conditioned or anticipatory controls of feeding, whereas our findings apply to unconditioned controls.

Asunto(s)

RESUMEN

Rats with chronic esophageal fistulas were permitted to sham-feed a carbohydrate solution (a simplified model food) for a 40-min session each day. Body weight was elevated, then reduced again, by varying the caloric density of the liquid diet by which the rats were maintained. With 1M glucose as tastant, induction of mild obesity caused an abrupt reduction in sham meal size. Sucrose concentration-intake functions were lowered at all concentrations by mild obesity, but without change in slope. Both changes were reversed by weight reduction to around normal body weight; further weight reduction produced no further change. Therefore, some correlate of body weight biases the oral control of bout size. The bias seems to change rather abruptly between one value and another at a weight level slightly above normal.

Asunto(s)

RESUMEN

College students (N = 64, 50, and 36 in three replications) were asked to complete the statement, "I usually stop eating a meal when ...". A number of alternatives were offered, together with an open (write-in) option. By far the most common completion was "... I feel full". The hedonic alternatives, "... the food stops tasting good" (first study) or "the food tastes less good" (first replication) were chosen by very few of the subjects, though explicitly presented as alternatives. In a second replication, subjects rank-ordered in importance the various reasons for ending a meal; not all subjects ranked the hedonic alternative at all, and most of those who did ranked it low in importance. Though hedonic shifts during a meal have been repeatedly shown to occur, these data suggest that they are of little salience, and perhaps of little importance, as factors in meal termination.

Asunto(s)

Asunto(s)

RESUMEN

We report significant improvements in our procedures for preparing and maintaining rats with esophageal fistulas and gastric cannulas. The most important of these are 1) a new cannula assembly, 2) a two-stage surgical procedure, 3) a modified diet, and 4) a less stringent maintenance regimen.

Asunto(s)

RESUMEN

Rats were permitted to sham feed a 1 M glucose solution after varying delays (0-40 min) following the intragastric (IG) infusion of a large, nutritionally adequate meal. (a) The meal affected sham feeding in an all-or-none way. After such a meal, sham feeding was either suppressed almost entirely, or it was not suppressed at all as compared with a no-meal control condition. (b) When it occurred, the suppression was short-lived: As little as a 20-min delay after the meal could suffice to change its suppressant effect from "all" to "none." This implies in turn that the much longer suppression found under other conditions is not a product of systemic inhibition on readiness to ingest. (c) The duration of the suppression appeared to decrease with successive exposures to the experimental conditions. After several such exposures, some rats showed no postprandial suppression at all, even immediately after the IG meal.

Asunto(s)

RESUMEN

Restriction of maternal dietary sodium beginning on or before embryonic day 8 and continued thereafter results in reduced taste responses of the chorda tympani nerve to NaCl in the offspring. The effects of deprivation, however, are reversible. A single ingestive bout of 30 ml isotonic NaCl was sufficient to restore normal sodium taste, and the restorative effects of the single exposure apparently persisted throughout multiple generations of taste receptor cells. Furthermore, the recovery apparently did not depend on direct receptor cell-stimulus interactions. Rats permitted to drink 30 ml of isotonic NaCl, but not allowed to retain it, did not recover normal sodium taste responses, suggesting that factors other than taste stimulation are important in the restorative effects of sodium.

Asunto(s)

RESUMEN

Hungry rats drink saccharin solutions with avidity, but the ingestion is self-limited: rate of lapping slows down progressively. Since postingestive changes do not produce this suppression, it must depend on a feedback signal generated by lapping the fluid. We show that the suppression depends on the number of laps emitted, not on the taste of the fluid; a given number of laps early in the session produces the same suppression later in the session, whether those early laps are accompanied by a moderate saccharin taste, a weak taste, or no sweet taste at all. Therefore, the feedback signal is provided by the act of lapping; taste does not contribute to it. Yet taste does influence amount ingested. Perhaps it provides a feed-forward signal, that in turn sets the amount of feedback required to end the bout.

Asunto(s)

RESUMEN

Hungary rats were permitted to drink saccharin under conditions in which (a) the drinking spout was available continuously, or (b) it was withdrawn during alternate 30-sec periods. Rats adjust to such constraint by increasing their integrated lap rate (laps/min). We show that one way in which they do this is to lap at a higher rate within bursts of lapping. This faster lapping is not an artifact of forced interruptions and resumptions. It cannot only be maintained over a drinking session, but also initiated midway through the session if restricted access is imposed then. Therefore, the period of the lapping cycle can be adjusted, within limits, in response to situational constraints on access to the fluid.

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

RESUMEN

Sham-drinking patterns were observed in rats with oesophageal fistulae and gastric cannulae. In rats both food- and water-deprived at test, first-session sham intake was an inverted U-shaped function of glucose concentration (the preference-aversion pattern). Sham intake at low and high extremes rose with repeated exposure, so that the function flattened. When the rats were hydrated by a gastric water preload, sham intake of glucose at low concentrations was much reduced, whereas sham intake at high concentrations was little affected, so that the function became monotonic increasing. This time sham intake rose with repeated testing at high concentrations, but not low ones, so that the function steepenned. At low concentrations, the low sham intakes reflected a rapid termination of the sham-drinking bout. This does not reflect a delayed effect of the gastric water load, for introducing a further delay between load and drinking test did not enhance the effect. Finally, an intragastric load of isotonic NaCl was less effective than water in suppressing sham drinking, just as it is less effective in inhibiting thirst. We conclude: (1) sham drinking is terminated by an accumulation of orosensory feedback; and (2) the taste presented to the mouth, and the animal's hydrational status, jointly determine the amount of such feedback that is necessary to end the ingestive bout.

Asunto(s)

RESUMEN

In rats sham drinking through oesophageal fistulae, sham intake of a dilute glucose solution (0.25 M) is greatly reduced, but not abolished, by an intragastric water preload. Since no further fluid enters the body, the early cessation of sham drinking must reflect a purely oral control, set by hydrational status. We show that lapping after the water load is abolished if the rat has sham-drunk appreciable quantities before the load is delivered. This is true even if the initial sham drinking is of plain water, with no sweet taste. Therefore, (1) the effect of the preload is to set the total quantity of oral feedback required to end the sham drinking bout; and (2) the necessary oral feedback is provided by the lapping response itself. It does not depend upon gustation.

Asunto(s)

RESUMEN

Hungry rats drink saccharin solutions avidly. When access to the cylinder is restricted, so that it is available during alternate 30-sec periods rather than continuously, rats adjust to this constraint so that total amount of lapping, over each period of a few minutes each, is defended. We show that the rats achieve this defense, in part, by pausing less often and for briefer periods between bursts. Log-survivorship analysis of the pauses in drinking suggests (a) that they are generated by two processes with different time constants, (b) that early in the session, both processes are suppressed when access is restricted; and (c) that later in the session, pauses reflecting the shorter-term process begin to appear, even if access is restricted. Therefore, adjustment to constraints on access is achieved in part by suppression or inhibition of two processes that generate pauses, and the suppression is relaxed earlier for the one with shorter time constant.

Asunto(s)

RESUMEN

In rats that are food- but not water-deprived, a saccharin "meal" is characterized by a progressive decrease in lap rate as the bout progresses. However, saccharin does not trigger a fixed rate of lapping at any point in the sequence. When rats have only intermittent access to saccharin early in the session, they increase their rates of lapping so that, within each few minutes, the amount of lapping (or some correlate such as volume drunk) is held constant. This happens over a wide range of restriction conditions. And if compensation cannot occur during a period of constraint, then it occurs afterward, promptly and precisely. When constraint is withdrawn, rats drink amounts such that the total amount of drinking (or its correlate), through that point in the ingestive bout, is defended. These findings imply that the controlling system includes (1) an integrator that keeps track of the amount of drinking that has occurred, even across interruptions; and (2) a short-term feedback loop that operates minute by minute within the bout. This loop regulates, not the rate of lapping to be emitted, but the amount of lapping to be done (or its correlate); Thus the decline in responsiveness to saccharin as drinking progresses reflects a depression of this regulated value, not of lap rate per se.

Asunto(s)

RESUMEN

We describe surgical and maintenance procedures for the "double-fistula" preparation in rat. Rats are prepared with esophageal fistulas, so that material swallowed escapes from an opening in the throat; and with gastric cannulas that permit both nutritional and hydrational maintenance, and the experimental intubation of fluids directly into the stomach.

Asunto(s)

RESUMEN

In food-deprived rats, rate of lapping at a saccharin cylinder declines progressively over a session. The decline is unaffected, within limits, by restricted access: Whether the cylinder is available continuously, or only during alternate 30-sec intervals, the rat adjusts its momentary lap rate so that the amount of lapping within each 5-min period remains the same. It is as if the rat specifies over each brief period how much ingestive behavior is to occur, and then adjusts its lap rate so that actual ingestive behavior matches the specification. The specification in turn moves down as the drinking bout progresses.

Asunto(s)