John L. Falk

The nature and determinants of adjunctive behavior

Abstract A review of the various behaviors induced as adjuncts to the behaviors under direct schedule control is given. The similarities among these adjunctive behaviors are described in terms of their intensities, temporal loci, and the variables which produce them. The relation of adjunctive behavior to displacement activities, adjustive, and toxic behavior is discussed. The general nature of adjunctive behavior is described in terms of a formal definition.

CONDITIONS PRODUCING PSYCHOGENIC POLYDIPSIA IN ANIMALS

A brief summary of the first report (Falk, 1961a) on schedule-induced polydipsia will suffice to introduce this phenomenon. Fourteen normal rats were maintained at 70-80 percent of their free-feeding body weight by limiting their intake of food. The animals earned most of their daily food ration by bar-pressing on a variable-interval one-minute (VI 1 min) schedule for 45-mg Noyes food pellets during 3.17-hour daily experimental sessions. On this schedule, a barpress is reinforced by a food pellet at varying times from a previous reinforcement (from a few seconds to two minutes), the average interreinforcement time being one minute. Each animal performed in a sound-attenuated box, with the automatic control and recording equipment in an adjoining room. No external environmental cue informed the animal exactly when a bar-press would yield a pellet. At the end of each daily session, the animal was returned to its home cage and given any food supplement necessary to maintain body weight at the value selected. Water was always available. During the session licks from a calibrated water reservoir were recorded electronically. In the home cage, any water drunk from a calibrated animal drinking tube between sessions was measured. On this schedule a typical behavior pattern rapidly developed. After earning a food pellet, the rat would consume it and drink about 0.5 ml of water. During the 3.17-hour session, intake averaged 92.5 ml, or 3.43 times the preexperimental, 24-hour water intake level. Between sessions, although water was available, intake averaged less than 1 ml. Such a phenomenon is strange and unprecedented, for the animals are drinking approximately one-half their body weight in a few hours. Water deprivation, heat stress, or osmotic-loading techniques do not approach comparable stimulation of water intake. Under normal laboratory maintenance conditions, daily water intake levels remain rather constant, and even strong facilitating stimuli induce only moderate increases. The evidence will be examined to determine whether this polydipsic phenomenon can be explained either on physiological grounds or with respect to simple behavioral considerations. The variables of which the polydipsia is a function will be summarized as far as these are known at present. A theoretical explanation in terms of adjunctive behavior will be given, and methodological implications and cautions for thirst research attempted.

Behavioral Maintenance of High Concentrations of Blood Ethanol and Physical Dependence in the Rat

Rats maintained on an intermittent food schedule with an available ethanol solution drink to excess (13.1 grams of ethanol per kilogram of body weight, daily). Removal of ethanol produces symptoms of physical dependence including death from tonic-clonic seizures. Overindulgence in oral self-administration of an aqueous ethanol solution, resulting in unequivocal physical dependence, approximates a model of human alcoholism.

The origin and functions of adjunctive behavior

The major determinants of schedule-induced or adjunctive behavior are reviewed briefly. Adjunctive behavior and its ethological equivalent, displacement activity, has a stabilizing function on agonistic, mating, parental, and intermittent-feeding behavior when any of these activities are in unstable equilibrium with an escape vector. This buffering action of adjunctive behavior is analogous to the diversity-stability rule of ecology in which an increase in the diversity of species stabilizes the populations of the component species, thereby preventing extinction. Opposing behavioral vectors in unstable equilibrium can function to exaggerate certain behavioral adjuncts that preexist in a situation. The resulting increase in diversification (information) augments the overall stability of the opposing-vector circumstance, conserving the context. This strengthening process is discussed in relation to ritualization and the preadaptation of exaggerated behavior to new functions.

Drug dependence: myth or motive?

The acceptability of nonmedical use for a particular drug is a function of diverse social needs. Drug dependence is due less to intrinsic effects than to the situation in which drug taking occurs. An addictive level of drug self-administration is a symptom of behavioral troubles rather than a definition of the trouble itself. The intrinsic effects of drugs do not in themselves produce either misuse or evoke specific kinds of behavior such as sexual or aggressive activities. Drugs can, however, come to function as discriminative stimuli for socially sanctioned behavior that would not under other circumstances be tolerated. The intrinsic reinforcing potential of an agent evolves in and dominates situations in which other reinforcing opportunities are either absent or remain unavailable to an individual who is unprepared to exploit them. While certain intrinsic properties of a drug contribute to its potential as a reinforcer (e.g., rapid onset and brief duration of action), reinforcing efficacy is notoriously malleable. It is a function of historic and currently-acting factors, particularly social reinforcers. The importance of physical dependence in the maintenance of drug seeking and taking is mainly unproven and probably overrated. Situations under which important reinforcers are available only in small portions intermittently can induce various excessive activities, including an untoward concern with obtaining and using drugs. Drug dependence prevention as a species of environmental dependence can be best effected by either alterations in the intermittent reinforcement situations inducing excessive behavior or by providing opportunities and training with respect to reinforcing alternatives other than drugs.

Serial sodium depletion and NaCl solution intake

Abstract Rapid sodium depletion was produced by intraperitoneal dialysis (IPD) in rats. This produced an increased intake of 3% NaCl solution during the following overnight fluid test period. Although more sodium was ingested than had been removed by IPD, a second dialysis (IPD 2 ) produced a much larger increase in NaCl solution ingestion. If the greater intake response to IPD 2 were a function of an intake adjustment learned after IPD 1 , then stomach loading the NaCl solution after IPD 1 , rather than making it available for ingestion, should eliminate the larger ingestion effect found after IPD 2 . This did not occur. IPD 2 produced the larger ingestion effect whether or not the opportunity for post-IPD 1 ingestion was given.

Agonistic action of a benzodiazepine antagonist: Effects of Ro 15-1788 and midazolam on hypertonic NaCl intake

Rats adapted to a 23-hr water deprivation regimen were allowed a daily 1-hr water rehydration session. On test days the session drinking fluid was 1.5% NaCl solution rather than water. One group was injected (SC) with the benzodiazepine antagonist Ro 15-1788 (2.5-10 mg/kg) and another group with the agonist agent midazolam (0.13-2.0 mg/kg) every 5-6 days at 10 and 15 min before a test session, respectively. Both Ro 15-1788 and midazolam increased 1.5% NaCl solution intake in a dose-related manner. In this study and in previous research, benzodiazepines and barbiturates were shown to increase the intake of hypertonic NaCl solutions. The present results reveal a similar effect for Ro 15-1788, indicating an agonistic dimension to the spectrum of action of this specific receptor antagonist.

Schedule-induced ethanol polydipsia: Enhancement by saccharin

Abstract The effect of adding sodium saccharin to a 5% ethanol solution on intake was examined. One set of animals were maintained at 80% of their free-feeding weight, in their home-cages with either 5% ethanol, or 5% ethanol-0.25% sodium saccharin as the only fluid available for three months (home-cage condition). A second set of animals were maintained in cages with automatic food dispensers that provided a 24 hr feeding regimen known to produce ethanol overdrinking (schedule-induced condition). These animals had 5% ethanol as their only available fluid for one month, followed by the 5% ethanol-0.25% sodium saccharin mixture for two months. No significant differences in ethanol intake were found between the 2 home-cage conditions (5% ethanol = 11.6 g ethanol/kg/day; 5% ethanol in 0.25% sodium saccharin = 11.7 g ethanol/kg/day. However, the addition of saccharin in the schedule-induced condition produced a marked increase in ethanol intake (5% ethanol = 13.1 g ethanol/kg/day; 5% ethanol in 0.25% sodium saccharin = 15.1 g ethanol/kg/day). The home-cage animals showed no sign of an abstinence syndrome upon substitution of water for ethanol. In the schedule-induced group, severe tonic-clonic seizures occured as a result of ethanol withdrawal.

Pattern of daily blood ethanol elevation and the development of physical dependence

Schedule-induced ethanol polydipsia regimens were used which produced either one or two daily peaks in blood ethanol levels. After 3 months on these regimens, rats were withdrawn from ethanol and tested for the presence of abstinence signs. No evidence of physical dependence was found, a result which contrasted with the previous finding of a severe withdrawal syndrome when blood ethanol was maintained at a more continuously elevated level prior to withdrawal. It was concluded that, as in the case of barbiturates, the development of physical dependence on ethanol requires more than an episodic peaking of the blood ethanol level once or twice per day.

Cocaine pharmacodynamics after intravenous and oral administration in rats: relation to pharmacokinetics

Abstract  Rationale: To design optimal dose regimes for oral cocaine, it is essential to characterize pharmacokinetics (PK) of cocaine after IV and PO administration. Objectives: To investigate the absolute bioavailability of oral cocaine, its effectiveness and the relation between PK and PD in a within-subject design. Methods: We used the effects of IV and PO cocaine on a contingency-controlled timing behavior, the differential reinforcement of low rate schedule (DRL 45-s) in 3-h sessions, as the PD measures [i.e., the shorter-response rate (srr) and the reinforcement rate (rr)]. Cocaine PK parameters were determined by simultaneous modeling of the concentration-time profiles (CTPs) after IV 2 mg/kg and PO 20 mg/kg cocaine administration. The absolute oral cocaine bioavailability was determined pharmacokinetically (F) and pharmacodynamically (Fsrr and Frr). Results: IV and PO cocaine increased the shorter response rate and decreased the reinforcement rate in a dose- and time-related fashion, which mirrored the respective prototypical serum cocaine CTPs. After the absorption phase, the serum cocaine CTP of PO cocaine paralleled that of IV cocaine. The duration of action for PO cocaine was longer than that for IV cocaine owing to its larger mean residence time. The active metabolite, norcocaine, was not detected after IV but after PO cocaine administration. The value of F was 4.66% which was significantly lower than the values of Fsrr (13.67%) and Frr (32.63%). Furthermore, the concentration-effect relations for the reinforcement rate revealed that PO cocaine was more potent than IV cocaine. Conclusions: Oral cocaine is more effective behaviorally than from predictions made in terms of its PK. The differences in active metabolite profiles as well as the rate and extent of acute tolerance for IV versus PO cocaine may account for the greater potency observed for oral cocaine.