Possible peripheral adrenergic and cholinergic mechanisms in pseudoconditioning

Amnesia induced by stimulation of the amygdala is attenuated by hexamethonium

Bilateral subseizure stimulation of the amygdala given immediately following training in an inhibitory avoidance task produced retrograde amnesia. Hexamethonium (3.0 and 10.0 mg/kg), a peripherally acting nicotinic cholinergic antagonist, attenuated the retention deficits induced by amygdala stimulation if the drug was given 30 min prior to, but not immediately following training. Hexamethonium had no effect in normal unoperated animals, but did produce a retention deficit in operated control (nonstimulated) animals if it was given immediately following training (3.0 and 10.0 mg/kg). The results suggest that memory deficits induced by electrical stimulation of the amygdala are associated with, or perhaps mediated in some way by peripheral autonomic function.

The effect of atropine or atropine methylnitrate on salt-induced hypertension in the inbred S/JR and R/JR Dahl rat

The cholinergic antagonists atropine (ATR) and atropine methylnitrate (ATRMN) were chronically administered to inbred Dahl hypertension-sensitive (S/JR) and -resistant (R/JR) rats maintained on an 8.0% NaCl-containing diet. The effects on blood pressure (BP), heart rate (HR), and mortality were then examined during and after a four week period of treatment. Administration of ATR (7.2 mg/day) or ATRMN (2.4 mg/day) attenuated the development of salt-induced hypertension (HT) in the S/JR strain but had relatively little effect on BP in the R/JR strain. HR during the treatment period was significantly greater in S/JR and R/JR rats that received ATR or ATRMN than vehicle-treated controls. Each drug also reduced HT-related mortality in S/JR rats. In general, the effects of ATR on BP and mortality were greater than those of ATRMN. However, the results suggest that the central and peripheral cholinergic systems participate in the development of salt-induced HT in the S/JR rat.

Amphetamine, conditioned stimulus, and nondebilitating preshock effects on activity and avoidance: further evidence for interactions between associative and nonassociative changes

A literature survey and preliminary experiments with rats on the consequences of shock preexposure on subsequent activity and escape or avoidance showed the need for further work on the interactions between nondebilitating preshock and various test and treatment factors. The two main experiments used 16 preexposure conditions, namely, presence or absence of unavoidable punishment (36 shocks of 2.5 mA and 5 sec subdivided in three daily sessions), a light CS, a central partition in the shuttle-box, and dl-amphetamine sulfate (1 mg/kg ip 15 min before each session). In both experiments the four factors studied exerted more than additive effects on activity in preexposure sessions, leading to a very high frequency of crossing in the CS-shock-no-partition-drug condition. Upon retesting for activity (Experiment 1) suppression of locomotion by prior shock was less marked in animals preexposed to CS-US pairings in the absence of partition, while proactive amphetamine effects consisted mainly of a progressive increase of activity over successive retest sessions in the groups not preshocked. Upon retesting for light-cued, two-way avoidance acquisition (Experiment 2) the groups preexposed to US only were mostly retarded, while those preexposed to paired CS and US were mostly facilitated. Other changes, including drug pretreatment consequences, were negligible or unsystematic, but in general the data showed that the effects of various preexposure conditions on activity could not account for those on avoidance. Overall, it appears that the interactions between nondebilitating preshock and other test and treatment factors can be further exploited to clarify the respective roles of various associative and nonassociative mechanisms in modulation of activity and adaptive responding in aversive situations.

Effect of brain lesions on rat shuttle behavior in four different tests

Rats were trained to perform shuttle responses to a buzzer in four different situations: pseudoconditioning or D test (buzzers and footshocks presented at random), classical conditioning or DP test (buzzers and footshocks paired on every trial), avoidance without stimulus pairing or DC test (buzzer-shock intervals varied at random, shocks contingent upon non-emission of a shuttle response to the preceding buzzer), and standard two-way avoidance or DPC test (buzzers paired to shocks, but the latter omitted every time there was shuttling to the buzzer). The letters in each test disignate the factors involved in the emission of responses in each one, which were shown in previous papers to be: a non-associative factor or "drive" (D), the Pavlovian or stimulus-stimulus relation ("pairing", P), and the shuttle-no shock or main avoidance contingency (C). The effects of various brain lesions on these behaviors were studied. Ventral caudate and amygdala lesions depress both the Pavlovian (P) and the avoidance (C) component. Dorsal caudate lesions have an opposite influence on these two factors. Septal (n.medialis + lateralis, and n.accumbens) and tuberculum olfactorium lesions enhance the non-associative component (D); accumbens lesions, in addition, impair operation of the C factor. The effect of the diverse lesions on jumping responses to the buzzer or on performance of intertrial crossings does not correlate with the effect on shuttle responses.

Brain dopamine and noradrenaline levels in rats submitted to four different aversive behavioral tests

Rats were trained to perform shuttle responses to a buzzer in four different situations: Pseudoconditioning (buzzers and footshocks presented at random), classical conditioning (buzzers and footshocks paired on every trial), avoidance without stimulus pairing (buzzer--shock intervals varied at random, shocks contingent upon the nonemission of a shuttle response to the preceding buzzer), and standard two-way avoidance (buzzers paired to shocks, but the latter omitted every time there was a shuttle to the buzzer). Animals were killed immediately after the last trials and the noradrenaline and dopamine content of their hypothalamus, amygdala, caudate nucleus, and nucleus accumbens was determined. There were falls of dopamine content in the caudate and accumbens and falls of noradrenaline levels in all structures except the caudate after the pseudoconditioning test. Noradrenaline levels were normal, and dopamine levels were partially recovered, in the animals submitted to the other training situations. Thus learning factors (stimulus pairing and/or the avoidance contingency) offset the depleting influence of footshocks per se on both catecholamines in at least the structures studied.

Enhancement of pseudoconditioning and retardation of escape by low doses of ethanol

Independent groups of mature Wistar rats were injected intraperitoneally with 0.9% NaCl solution or 0.5 g/kg, 1 g/kg or 2 g/kg ethanol prepared from a 30% ethanol solution in 0.9% NaCl. Thirty min later each animal was placed in a two compartment shuttlebox and given 25 trials during which footshock was presented every 60 sec and tones of 8 sec duration were randomly programed. Shock-escape latencies and frequencies of intercompartmental (pseudoconditioned) responses to the tone were measured. The results showed that 1 g/kg and 2 g/kg ethanol significantly retarded escape performance but 2 g/kg ethanol significantly enhanced pseudoconditioning. These findings have implications for the design of experiments concerned with the effects of drugs on learning processes, and for theories of the effects of ethanol on behavior.

Three main factors in rat shuttle behavior: their pharmacology and sequential entry in operation during a two-way avoidance session

The effects of eserine (0.1 mg/kg), nicotine (0.2 mg/kg), atropine (2 mg/kg), methylatropine (5 mg/kg), clonidine (0.2 mg/kg), phenoxybenzamine (10 mg/kg), apomorphine (0.5 mg/kg), and haloperidol (0.5 mg/kg), i.p., on shuttle responses to a buzzer (SBs) were studied on four different behavioral paradigms in rats: (a) D test: 50 buzzers and 25 shocks at random intervals and in random order; (b) DP test: 50 buzzers paired on all trials with shocks irrespective of the performance of SBs (Pavlovian conditioning); (c) DC test: 50 buzzers followed at a randomly variable interval by shocks unless there was an SB; (d) DPC test: 50 buzzer-shock trials omitting shocks every time there was an SB (two-way avoidance). Shock-induced drive was assumed to equally pervade all four situations; stimulus contiguity ('pairing') was present only in the DP and DPC tests; and the avoidance 'contingency' was present only in the DC and DPC paradigms. An analysis of the distribution of SB performance in control animals over the 10 successive blocks of 5 buzzers of each session revealed that the response level was similar for all tests during the first 2 blocks; that of the DC and DPC groups increased above the level of the other two from the third block on; and from the fifth block on, SB performance was higher in the DPC than in the DC group and in the DP over the D group. At all blocks the sum of SBs obtained in the D test, plus DP-D, plus DC-D, gave a value quite close to that experimentally determined in the DPC group. This was interpreted as showing that during the first 10 buzzers drive was the main (or the only) factor influencing SB performance in all groups; after the third block of 5 buzzers 'contingency' became a factor on its own; and 'pairing' assumed some control over SB behavior only from the fifth block on. Eserine depressed SBs in the D test, starting from the first block of buzzers; its effect was antagonized by atropine and by methylatropine. Clonidine depressed responding in the DP and DPC paradigms, and its effect was blocked by phenoxybenzamine. Nicotine, eserine, and apomorphine increased, and atropine, methylatropine, and haloperidol decreased SB performance in both the DC and the DPC test; the effect of the two former substances could be antagonized by any of the two anticholinergic agents, and haloperidol antagonized that of apomorphine. The possibilities are discussed of: (a) a peripheral cholinergic mechanism which inhibits drive; (b) a similar mechanism which favors operation of the 'contingency' factor; (c) a dopaminergic mechanism in 'contingency'; (d) a central adrenergic inhibitory mechanism in 'pairing'.

Interaction between cholinergic and catecholaminergic agents in a spontaneous alternation task

Spontaneous alternation was examined in a free running Y-maze task after various pharmacological manipulations. Whereas scopolamine reduced alternation to chance levels, d-amphetamine in some doses resulted in alternation significantly below chance (perservation). Physostigmine treatment increased levels of alternation whereas reserpine was without effect. Concurrent administration of drugs revealed that reserpine effectively reversed the effects of scopolamine, while the perseveration induced by d-amphetamine was antagonized by physostigmine. When animals were pre-exposed to the Y-maze the effects of d-amphetamine were enhanced, but effects of scopolamine were not modified. Finally, scopolamine treatment augmented the perseverative effects of d-amphetamine. It was suggested that cholinergic agents modify alternation by effects on habituation. On the other hand d-amphetamine produces genuine perseveration without effects on habituation per se. Alternation performance and perseveration were suggested to be mediated by the interaction between the distinct behavioral effects of cholinergic and catecholaminergic activity.

The effect of adrenaline, tyramine and guanethidine on two-way avoidance conditioning and on pseudoconditioning

Adrenaline (0.5 mg/kg) or guanethidine (10 mg/kg) given i.p. depressed performance of pseudoconditioned shuttle responses by rats. In a previous paper it had been shown that tyramine (5 mg/kg) had an opposite effect (Izquierdo, 1974a). Pre-trial administration of any of the three drugs also depressed two-way avoidance conditioning. Following posttrial administration, only guanethidine had a deleterious effect on retention. Since none of these drugs is believed to reach the brain in significant amounts following systemic injection, the present results suggest that peripheral factors may influence both conditioned and pseudoconditioned shuttle behavior.