Post-conflict affiliation in common marmosets (Callithrix jacchus jacchus).

Post-conflict (PC) affiliation has been demonstrated in a number of Old World monkeys and apes, but very little is known about the occurrence of the phenomenon in New World monkeys. This study examined 282 PC interactions after spontaneous conflicts around feeding time in two family groups (N = 12) of captive common marmosets, Callithrix jacchus jacchus. We found an overall corrected conciliatory tendency of 31%. Selective attraction was seen: former opponents met significantly more often in PCs than in matched controls (MCs) (27% and 16%, respectively). There was no difference in the occurrence of PC affiliation between dyads consisting of parent-offspring constellations compared to offspring-offspring constellations. PC affiliative behaviors were seen in the first three minutes following conflict termination, and consisted mainly of proximity, play invitations, and food transfer. Notably, former opponents remained within arm's reach after 17% of conflicts. Affiliation was more likely to follow after conflicts involving play issues. The functional importance of the PC affiliation in marmosets remains to be examined.

Conflict resolution in 5-year-old boys: does postconflict affiliative behaviour have a reconciliatory role?

In nonhuman primates, affiliative behaviours, such as social grooming and various forms of body contact, become more frequent after an aggressive interaction. Since such behaviours lead to a decrease in postconflict aggressive behaviour and displacement activities and to increased social tolerance, they have been labelled reconciliatory. We videofilmed sessions of free play in daycare centres in Stockholm and investigated whether affiliative behaviours used by 5-year-old boys in the postconflict period had a similar reconciliatory function. For 219 conflicts in 21 h 40 min of observation we recorded postconflict affiliative/prosocial, aggressive and displacement behaviours. When affiliative behaviours were shown and accepted by the opponent, aggressive and displacement behaviours decreased and play was promoted. These behaviours thus serve a function similar to reconciliatory behaviour in nonhuman primates and we think it is applicable to call accepted affiliative behaviours in postconflict periods of preschool children reconciliatory. However, conflicts were often polyadic and nonconflict periods consisted of intense play with a rich exchange of affiliative behaviours. These factors were limitations to the postconflict/matched-control method traditionally used in primatological research to document reconciliatory behaviour. We suggest that for preschool children, video recordings and an analysis and description of postconflict affiliative, aggressive and displacement behaviours can be used instead. Copyright 1999 The Association for the Study of Animal Behaviour.

Responses of monkey dopamine neurons to reward and conditioned stimuli during successive steps of learning a delayed response task.

The present investigation had two aims: (1) to study responses of dopamine neurons to stimuli with attentional and motivational significance during several steps of learning a behavioral task, and (2) to study the activity of dopamine neurons during the performance of cognitive tasks known to be impaired after lesions of these neurons. Monkeys that had previously learned a simple reaction time task were trained to perform a spatial delayed response task via two intermediate tasks. During the learning of each new task, a total of 25% of 76 dopamine neurons showed phasic responses to the delivery of primary liquid reward, whereas only 9% of 163 neurons responded to this event once task performance was established. This produced an average population response during but not after learning of each task. Reward responses during learning were significantly more numerous and pronounced in area A10, as compared to areas A8 and A9. Dopamine neurons also showed phasic responses to the two conditioned stimuli. These were the instruction cue, which was the first stimulus in each trial and indicated the target of the upcoming arm movement (58% of 76 neurons during and 44% of 163 neurons after learning), and the trigger stimulus, which was a conditioned incentive stimulus predicting reward and eliciting a saccadic eye movement and an arm reaching movement (38% of neurons during and 40% after learning). None of the dopamine neurons showed sustained activity in the delay between the instruction and trigger stimuli that would resemble the activity of neurons in dopamine terminal areas, such as the striatum and frontal cortex. Thus, dopamine neurons respond phasically to alerting external stimuli with behavioral significance whose detection is crucial for learning and performing delayed response tasks. The lack of sustained activity suggests that dopamine neurons do not encode representational processes, such as working memory, expectation of external stimuli or reward, or preparation of movement. Rather, dopamine neurons are involved with transient changes of impulse activity in basic attentional and motivational processes underlying learning and cognitive behavior.

Neuronal activity in monkey ventral striatum related to the expectation of reward.

Projections from cortical and subcortical limbic structures to the basal ganglia are predominantly directed to the ventral striatum. The present study investigated how the expectation of external events with behavioral significance is reflected in the activity of ventral striatal neurons. A total of 420 neurons were studied in macaque monkeys performing in a delayed go-no-go task. Lights of different colors instructed the animal to do an arm-reaching movement or refrain from moving, respectively, when a trigger light was illuminated a few seconds later. Task performance was reinforced by liquid reward in both situations. A total of 60 ventral striatal neurons showed sustained increases of activity before the occurrence of individual task events. In 43 of these neurons, activations specifically preceded the delivery of reward, independent of the movement or no-movement reaction. In a series of additional tests, these activations were time locked to the subsequent reward, disappeared within a few trials when reward was omitted, and were temporally unrelated to mouth movements. Changes in the appetitive value of the reward liquid modified the magnitude of activations, suggesting a possible relationship to the hedonic properties of the expected event. Activations also occurred when reward was delivered in a predictable manner outside of any behavioral task. These data suggest that neurons in the ventral striatum are activated during states of expectation of individual environmental events that are predictable to the subject through its past experience. The prevalence of activations related to the expectation of reward suggests that ventral striatal neurons have access to central representations of reward and thereby participate in the processing of information underlying the motivational control of goal-directed behavior.

Neuronal activity in monkey striatum related to the expectation of predictable environmental events.

1. This study investigated neuronal activity in the striatum preceding predictable environmental events and behavioral reactions. Monkeys performed in a delayed go-nogo task that included separate time periods during which animals expected signals of behavioral significance, prepared for execution or inhibition of arm reaching movements, and expected the delivery of reward. In the task, animals were instructed by a green light cue to perform an arm reaching movement when a trigger stimulus came on approximately 3 s later (go situation). Movement was withheld after the same trigger light when the instruction cue had been red (nogo situation). Liquid reward was delivered on correct performance in both situations. 2. A total of 1,173 neurons were studied in the striatum (caudate nucleus and putamen) of 3 animals, of which 615 (52%) showed some change in activity during task performance. This report describes how the activity of 193 task-related neurons increased in advance of at least 1 component of the task, namely the instruction cue, the trigger stimulus, or the delivery of liquid reward. These neurons were found in dorsal and anterior parts of caudate and putamen and were slightly more frequent in the proximity of the internal capsule. 3. The activity of 16 neurons increased in both go and nogo trials before the onset of the instruction and subsided shortly after this signal. These activations may be related to the expectation of the instruction as the first signal in each trial. 4. The activity of 15 neurons increased between the instruction and the trigger stimulus in both go and nogo trials. These activations may be related to the expectation of the trigger stimulus independent of an arm movement. Further 56 neurons showed sustained activations only when the instruction requested a movement reaction. Activations were absent in trials in which the movement was withheld. Twenty-one of these neurons were tested with 2 different movement targets, 5 of which showed activity related to the direction of movement. These activations may be related to the preparation of movement or expectation of the specific movement triggering signal. The activity of an additional 20 neurons was unmodulated before the trigger stimulus in movement trials but increased in the interval between the no-movement instruction and the trigger stimulus for withholding the movement. These activations may be related to the preparation of movement inhibition as specific nogo reaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses of monkey dopamine neurons during learning of behavioral reactions.

1. Previous studies have shown that dopamine (DA) neurons respond to stimuli of behavioral significance, such as primary reward and conditioned stimuli predicting reward and eliciting behavioral reactions. The present study investigated how these responses develop and vary when the behavioral significance of stimuli changes during different stages of learning. Impulses from DA neurons were recorded with movable microelectrodes from areas A8, A9, and A10 in two awake monkeys during the successive acquisition of two behavioral tasks. Impulses of DA neurons were distinguished from other neurons by their long duration (1.8-5.0 ms) and low spontaneous frequency (0.5-7.0 imp/s). 2. In the first task, animals learned to reach in a small box in front of them when it opened visibly and audibly. Before conditioning, DA neurons were activated the first few times that the empty box opened and animals reacted with saccadic eye movements. Neuronal and behavioral responses disappeared on repeated stimulus presentation. Thus neuronal responses were related to the novelty of an unexpected stimulus eliciting orienting behavior. 3. Subsequently, the box contained a small morsel of apple in one out of six trials. Animals reacted with ocular saccades to nearly every box opening and reached out when the morsel was present. One-third of 49 neurons were phasically activated by every door opening. The response was stronger when food was present. Thus DA neurons responded simultaneously to the sight of primary food reward and to the conditioned stimulus associated with reward. 4. When the box contained a morsel of apple on every trial, animals regularly reacted with target-directed eye and arm movements, and the majority of 76 DA neurons responded to door opening. The same neurons lacked responses to a light not associated with task performance that was illuminated at the position of the food box in alternate sessions, thus demonstrating specificity for the behavioral significance of stimuli. 5. The second task employed the operant conditioning of a reaction time situation in which animals reached from a resting key toward a lever when a small light was illuminated. DA neurons lacked responses to the unconditioned light. During task acquisition lasting 2-3 days, one-half of 25 DA neurons were phasically activated when a drop of liquid reward was delivered for reinforcing the reaching movement. In contrast, neurons were not activated when reward was delivered at regular intervals (2.5-3.5 s) but a task was not performed.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses of monkey midbrain dopamine neurons during delayed alternation performance.

Cognitive deficits are important components of the parkinsonian syndrome. In order to investigate the role of dopamine (DA) neurons in cognitive functions, we recorded the electrical activity of midbrain DA neurons in a monkey performing in a spatial delayed alternation task. Triggered by a light, the animal reached toward one of two levers to receive a drop of liquid reward. The lever associated with reward was alternated after each correct movement. Of 88 DA neurons, 65% and 52% showed phasic responses to the trigger light and reward, respectively. By contrast, sustained delay-related activity described for striatum and frontal cortex was not observed, suggesting that the activity of DA neurons does not reflect mnemonic or preparatory representational task components. Rather, DA neurons respond to the salient attentional and motivating stimuli guiding task performance.

Long-term effects of toluene inhalation on rat behavior.

The effect of inhalation exposure to toluene (3700 mg/m3, 1000 ppm, 21 h/day, 5 days/week, during 4 weeks) on male Sprague-Dawley rats was tested. A wide range of test situations was used, including an operant test with baseline performance and extinction, motor coordination, and exploratory activity. All tests were made 11 to 35 days after the end of the exposure. The results indicate that toluene exposure causes a long-lasting impairment on the extinction process and reduction in the variability of the baseline response in the operant behavior situation. Toluene also had an effect on the water regulation.

Responses to reward in monkey dorsal and ventral striatum.

The sources of input and the behavioral effects of lesions and drug administration suggest that the striatum participates in motivational processes. We investigated the activity of single striatal neurons of monkeys in response to reward delivered for performing in a go-nogo task. A drop of liquid was given each time the animal correctly executed or withheld an arm movement in reaction to a visual stimulus. Of 1593 neurons, 115 showed increased activity in response to delivery of liquid reward in both go and nogo trials. Responding neurons were predominantly located in dorsal and ventromedial parts of anterior putamen, in dorsal and ventral caudate, and in nucleus accumbens. They were twice as frequent in ventral as compared to dorsal striatal areas. Responses occurred at a median latency of 337 ms and lasted for 525 ms, with insignificant differences between dorsal and ventral striatum. Reward responses differed from activity recorded in the face area of posterior putamen which varied synchronously with individual mouth movements. Responses were directly related to delivery of primary liquid reward and not to auditory stimuli associated with it. Most of them also occurred when reward was delivered outside of the task. These results demonstrate that neurons of dorsal and particularly ventral striatum are involved in processing information concerning the attribution of primary reward.

Is the behavioural effect of diazepam in rats unique to negative secondary stimuli?

Studies of the behavioural effects of benzodiazepines have focused in particular on situations with negative secondary stimuli, i.e., stimuli signalling negative primary events such as punishment or non-reward. The general result is that benzodiazepines attenuate behavioural reactions to this type of stimuli. The aim of the present study was to investigate if there are any differences between positive and negative secondary stimuli in this respect. Rats were treated with diazepam in a modified Skinner box with two levers. One of the levers always gave a small reward. A lamp being ON or OFF was used as a secondary stimulus indicating if the other lever would give a large or no reward. Pretreatment with diazepam (1.0 mg/kg) did not act differently on the response to the positive or negative secondary stimulus. The main effect was a general attenuation of optimal responding with a concomitant decrease in water intake. An alternative hypothesis stating that benzodiazepines alter the reactivity to secondary stimuli more in general is supported.

Diazepam and decision making in the rat: negative evidence for reduced tolerance to reward delay.

A laboratory decision-making paradigm was developed in which changes in behavioural planning in response to delays in reward delivery could be studied in the rat. The problem given was to choose between three behavioural options, lever-pressing or running into one of two arms fitted to the experimental chamber, in order to obtain rewards (water). Basically, the animal received rewards with a certain probability when pressing the lever. At certain random intervals, reward delivery by lever-presses was stopped. To restart the system, the animal had to abandon lever-pressing and run out into one of the arms. The arm lengths could be varied, and a time-delay for restarting the system could be introduced into one of the arms. These manipulations changed the arm preference so that a long arm, or an arm with a time delay, was avoided. It was specifically investigated whether the benzodiazepine diazepam selectively lowered the tolerance to accept reward delay. Such an effect of benzodiazepines has previously been proposed. After diazepam 1 mg/kg, the number of lever-presses before running into an arm and number of behavioural interruptions were increased, and interpreted to show a deficit in information processing and/or decision making. No evidence for a selective effect of diazepam to reduce tolerance to reward delays could be detected.

Effects of dopamine D-1 and D-2 antagonists on decision making by rats: no reversal of neuroleptic-induced attenuation by scopolamine.

The effects of the dopamine (DA) D-1 antagonist SCH 23390 and the D-2 antagonists haloperidol and sulpiride on decision making in thirsty rats were investigated. The problem given to the rats was to choose between two behaviours, locomoting or lever-pressing, in order to obtain rewards (water). SCH23390 and haloperidol dose-dependently reduced the number of rewards obtained. However, only minor effects were seen on the decision making parameters. DA is thus important for initiation and/or performance of learned behavioural acts, not for information sampling and processing leading to the decision of which behaviour to perform. There were no differences between D-1 and D-2 antagonism in this respect. After sulpiride, no significant effects were observed. A specific behavioural prolife obtained by extinction was not mimicked by any of the doses of neuroleptics tested. It has previously been shown that performance per se of the two behavioural options used in the task can be reinstated by scopolamine after haloperidol attenuation. However, when these options had to be organized into functional sequences to reach a goal, haloperidol-induced attenuation could not be counteracted by scopolamine.

Differential attenuation of water intake and water-rewarded operant responding by repeated administration of haloperidol and SCH 23390 in the rat.

It has previously been described that water intake in thirsty rats require higher doses of dopamine (DA) D-1 and D-2 antagonists to be attenuated than operant lever-pressing with water as reward. In the present study, effects of repeated administration of the DA D-1 antagonist SCH 23390 and the DA D-2 antagonist haloperidol were investigated in the same experimental paradigm. In agreement with previous reports, attenuation of operant responding increased progressively by haloperidol (0.05 mg/kg) given for four consecutive days. However, this attenuation was not accompanied by decreased water intake, tested for in parallel experiments. After haloperidol (0.2 mg/kg), in contrast, a progressively decreasing attenuation of water intake was found. After SCH 23390, both the initial attenuation of lever-pressing (0.02 mg/kg) and consummatory water intake (0.1 mg/kg) became less pronounced over time. The results thus show that: 1) the previously reported progressively increasing attenuation of operant responding caused by repeated administration of D-2 antagonists is not mimicked by the D-1 antagonist SCH 23390, and 2) attenuation of water intake caused by higher doses of neuroleptics is, in direct opposition, less pronounced after repeated administrations. The results also show that attenuation of operant responding by neuroleptics cannot solely be dependent upon a blunting of the impact of the reward.

Effects of the dopamine D-1 antagonist SCH 23390 on water intake, water-rewarded operant responding and apomorphine-induced decrease of water intake in rats.

The specific dopamine (DA) D-1 receptor antagonist SCH 23390 was found to attenuate operant lever-pressing with water as reward in a dose-dependent manner and more potently than drinking itself. This effect occurred in the same fashion as previously reported for DA D-2 antagonists. In contrast to the DA D-2 antagonist haloperidol, the attenuated operant lever-pressing induced by the DA D-1 antagonist SCH 23390 was not counteracted by the anticholinergic drug scopolamine. The decreased water intake in thirsty animals caused by a low dose of apomorphine was not antagonised by SCH 23390. This has previously been found with DA D-2 antagonists, such as haloperidol and sulpiride. The results show that in spite of some similarities in the behavioural effects of DA D-1 and D-2 antagonists, a closer pharmacological analysis is able to reveal pronounced differences.

Attenuation of water intake and operant responding by dopamine D2 antagonists: raclopride provides important cues for understanding the functional mechanism of action.

The selective dopamine (DA) D2 receptor antagonist raclopride was found to attenuate operant lever-pressing with water as reward in a dose dependent manner and more potently than the corresponding consummatory act, i.e. the unconditioned water intake. This is the same way as previously reported for other DA D2 antagonists. In screening experiments raclopride has been selected on the basis of great separation between antagonism of DA-agonist induced hyperactivity, stereotypies and production of catalepsy. We found that attenuation of lever-pressing and water intake by raclopride were not more separated in dose than after, for example, haloperidol. We further found that attenuation of lever-pressing and water intake occurred in doses relatively lower than those producing catalepsy, thus excluding catalepsy as a cause for the attenuation. Decreased water intake in thirsty animals caused by a low dose of apomorphine (APO) was counteracted by raclopride. This has previously been found with DA D2, but not with D1, antagonists, which further supports that this apomorphine-effect is mediated via D2 receptors. However, raclopride only showed this antagonism in a narrow dose-range, like haloperidol. The selective profile previously found for sulpiride, proposed to be related to low incidence of extrapyramidal side-effects in the clinic, was thus not replicated.

Dopamine D-2 antagonists reverse apomorphine-induced decreased water intake in the rat: prediction of antipsychotic drugs with few extrapyramidal side-effects?

Water intake in water deprived rats was decreased by administration of a low dose of apomorphine (0.1 mg/kg s.c.). This dose is too low to induce hyperactivity and stereotypies. Four different dopamine (DA) D-2 antagonists were used to counteract this effect of apomorphine; haloperidol [an antipsychotic inducing extrapyramidal side-effects (EPS)], sulpiride (an antipsychotic inducing less EPS than haloperidol), metoclopramide (not used as an antipsychotic but inducing EPS) and domperidone (not passing through the blood brain barrier). Domperidone did not counteract the apomorphine effect, indicating a central mechanism of action for apomorphine. Metoclopramide did not counteract the apomorphine effect and, in higher doses, water intake was even further reduced. Sulpiride completely counteracted the apomorphine effect but, in higher doses, did not by itself reduce water intake. Haloperidol counteracted the apomorphine effect in a small dose-range and caused a further reduction in the water intake when given in high doses. The results can be explained by the existence of two subpopulations of D-2 receptors related to different functions. The model described may be used in screening experiments aimed at finding new antipsychotic drugs with a low incidence of EPS.

The reduction of water intake in rats caused by a low dose of apomorphine is unaltered by alpha-methyl-p-tyrosine: are autoreceptors not involved?

Low doses of the dopamine (DA) agonist apomorphine (APO) induces a behavioural syndrome characterized by reduced spontaneous activity, reduced food and water intake and induction of yawning and penile erections. Traditionally these effects of APO have been considered to be caused by a preferential stimulation of DA autoreceptors, causing a decreased amount of transmitter at the postsynaptic receptors. If this is so, it could be hypothesized that 1) the same behavioural effects should be obtained if DA transmission is decreased by some other means, for example by synthesis inhibition, and that 2) the response to APO should be altered if DA transmission is already lowered. It was found that high doses of alpha-methyl-p-tyrosine (alpha-MPT; 50-200 mg/kg) did not reduce water intake in thirsty rats, which low doses of APO do. It was further found that pretreatment with alpha-MPT did not alter the response to APO. These results are difficult to reconcile with the DA autoreceptor hypothesis claiming that behavioural effects of low doses of APO are caused by a decreased release of DA. An alternative interpretation is that low doses of APO stimulates a certain population of sensitive postsynaptic D-2 receptors.

Effects of repeated administration of low doses of apomorphine in three behavioural models in the rat.

A low dose of the dopamine (DA) receptor agonist apomorphine (APO 0.05 mg/kg) was given repetitively and the effects were tested in three different behavioural models: reduction of spontaneous locomotion, induction of yawning and decrease in water intake in water-deprived animals. The APO-induced suppression of exploration and decrease in water intake were not affected by a previous injection of APO given 1 or 3 hours before the test dose of APO. There was a small, but significant, decrease in the induction of yawning by a previous dose of APO given 1 hour or 30 min before the test dose. However, pretreatment with APO 3 hours before the test dose did not diminish the yawning response. It is suggested that the dopaminergic mechanisms mediating APO induced yawning are different from those mediating decrease in water intake and suppression of exploration. The results are also discussed in relation to the proposed efficiency of low doses of DA agonists in the treatment of various neurological and psychiatric disorders.

Scopolamine reverses haloperidol-attenuated lever-pressing for water but not haloperidol-attenuated water intake in the rat.

The operant lever-pressing response has previously (Ljungberg, Pharmacol Biochem Behav 27: 341-350, 1987) been found to be inhibited by lower doses of haloperidol than the corresponding consummatory act, i.e., water intake. In the present study it was found that the attenuation of the lever-pressing response caused by the neuroleptic, but not the attenuation of the water intake, could be counteracted by scopolamine. The results support the notion that blockade of operant responding by low doses of neuroleptics are probably related to the extra-pyramidal side-effects of neuroleptics seen in the clinic, as both phenomena can be counteracted by anticholinergics. These results therefore conflict with the anhedonia hypothesis put forward as an explanation of the attenuating effects of neuroleptics in operant settings. The findings also have a clear bearing on the role of dopamine in feeding and drinking behavior, as the results implies that different aspects of the control of water intake (i.e., the operant vs. the consummatory phase) are governed by different mechanisms in the CNS.