Sue Wagner

Orosensory suppression of saccharin drinking in rat: The response, not the taste ☆

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.

Sham drinking of glucose solutions in rats: Some effects of hydration☆

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 animals hydrational status, jointly determine the amount of such feedback that is necessary to end the ingestive bout.

Preparation and maintenance of chronic esophagostomized rats: An update

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.

Glucose sham drinking in the rat: Satiety for the sweet taste without the sweet taste ☆

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.

Adjustment to intermittent access in rats drinking saccharin: I. Pauses in drinking

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.

Adjustment to intermittent access in rats drinking saccharin: II. Adjustment of lapping rate

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.

Effect of body weight manipulations on sham feeding in the rat

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.

Persistence of sham feeding after intragastric meals in the rat: Concentration-intake relations

In rats sham fed through esophageal fistulas, responsiveness to sucrose over a range of concentrations was assessed under two conditions: immediately following a large intragastric (IG) preload of liquid diet, and after 10 h of deprivation with no preload. The preload had no reliable effect on sucrose sham feeding at any sucrose concentration. Therefore, the insensitivity of sham feeding to IG loads is not confined to intense or highly palatable oral stimuli, but extends even to minimally effective ones.