A.M. van der Poel

Hypothalamic substrates for brain stimulation-induced attack, teeth-chattering and social grooming in the rat.

In this paper the boundaries of the hypothalamic response areas for brain stimulation-induced attack, social grooming and teeth-chattering were delimited. A total of 641 hypothalamic sites in 71 male CPW/WU Wistar rats were electrically stimulated. Positive sites for any behavioural response cluster into restricted hypothalamic areas. Discriminant analysis of both positive and negative electrode localizations yields areas with high, intermediate and low probabilities of inducing the behavioural response concerned. Each response has its own response area where probabilities are high. Neuroanatomical correlates of these response areas are discussed. The response area of attack is suggested to be an integrative processing area, stimulation of which overrules some aspects of integration and directly activates the behavioural program of attack. Although some authors consider all three responses to be part of the behavioural repertoire of aggression, the response areas are not identical. Social grooming and attack are considered to be induced from different neural systems. Similarly, attack and teeth-chattering have been shown to derive from different neural mechanisms, despite substantial overlap of both response areas. It is suggested that teeth-chattering derives from the simultaneous activation of both attack and flight tendencies. No further distinctions with respect to threshold current intensities can be made within responses areas. However, the underlying neural substrates are not homogeneous, for thresholds vary along the course of individual electrodes.

Hypothalamic substrates for brain stimulation-induced patterns of locomotion and escape jumps in the rat

The hypothalamic response area for electrically induced locomotion was determined using moveable electrodes and discriminant analysis as an appropriate statistical technique. At 241 out of 641 stimulated sites locomotion was induced. The distribution of locomotion sites is relatively diffuse. Discriminant analysis of both positive and negative electrode localizations yields areas with high, intermediate or low probability of inducing the response. The response is considered to be mediated by fibres of the subpallido-pedunculopontine system, which includes the mesencephalic locomotor region. Different categories of exploratory and flight-directed locomotion were distinguished, and response areas for both categories were determined. In addition the response area for escape jumps was delimited. Exploratory locomotion is mainly induced from the lateral hypothalamus, while flight-directed locomotion and escape jumps are evoked from the medial hypothalamus. The response area for exploratory locomotion reflects the lateral hypothalamic distribution of the subpallidal projection to the mesencephalic locomotor region. A diffuse substrate for flight behavior seems to occupy almost the entire medial hypothalamus. It is concluded that a locomotor subroutine subserving different behavioural mechanisms can be activated at many hypothalamic sites.

Temporal patterning of ultrasonic distress calls in the adult rat: effects of morphine and benzodiazepines

Opioids and benzodiazepines modulate the ultrasounds that rats emit before being presented with aversive stimulation. Mild, intermittent 10 s electrical tail stimulation induces rats to emit 20–30 kHz ultrasounds before and after the stimulation. Analysis of the temporal parameters of the sounds via a customized computer system reveals them to be emitted in bouts of about five sounds, each sound being separated from the next by 0.2–0.35 s pauses. Morphine decreases the per cent time volalizing during the pre-stimulation period, with 6 mg/kg being fully suppressive. This effect is reversed by 1 mg/kg naloxone pre-treatment. Chlordiazepoxide and morphine have opposite effects on the temporal structure of the pre-stimulation calls; chlordiazepoxide induces longer bouts with more pulses, and morphine dissolves the bout structure into a series of single pulses. These differential and selective effects of morphine and benzodiazepines on the occurrence and temporal structure of ultrasounds may be relevant to characteristics of different affective expressions.

Comparison of Aggressive Behaviour Induced by Electrical Stimulation in the Hypothalamus of Male and Female Rats

Publisher Summary Sex differences in aggressive behavior are present in many species, and the genders often become aggressive in different ways or in different conditions. This chapter describes and attempts to induce aggression by stimulation in the hypothalamus of female as well as male rats and compares behavior, histology, and current intensity required to induce attacks in the two sexes. The chapter also discusses the effects of ovariectomy and subsequent oestradiol replacement on attack thresholds in female rats. The results show that electrical stimulation in the hypothalamus elicits aggression in both male and female rats, which seems to be derived from the same neural systems and no sex differences could be detected in the sensitivity of these neural systems to stimulation. Slight differences are observed in the forms of attack behavior induced by hypothalamic stimulation: males tend to show more intense, females weaker forms of attack. These differences may be due to hormonal differences of the animals, the males having normal levels of testosterone. Neither ovariectomy nor subsequent oestrogen replacement affects thresholds for hypothalamic attack in a convincing way, which is in contrast with the effects of castration and testosterone replacement in male rats. However, the precise neural mechanisms of this behavioral facilitation are not known.

A note on ‘stretched attention’, a behavioural element indicative of an approach-avoidance conflict in rats

Abstract The behaviour of rats in a passive-avoidance test is described. Following the administration of painful electric footshocks the animals avoid the grid box by displaying overt flight behaviour (walking backwards and walking away) and stretched attention. The latter behaviour is followed either by approach or retreat. During stretched attention auditory stimulation is especially effective in producing flight behaviour. It is concluded that stretched attention is an ambivalent behaviour, indicating a behavioural conflict between exploratory (approach) and flight (avoidance) tendencies. The tension of the body and the absence of locomotion in high intensity stretched attention are taken as indications that, during the conflict, competition for the effectors takes place. The reversal of the orientation of flight evoked by auditory stimuli during stretched attention is best explained by assuming that a competition for the mechanisms of selective attention is also involved.

Hypothalamic substrates for brain stimulation-induced grooming, digging and circling in the rat

Despite a great number of studies concerned with the induction of specific behavioural responses from the rat hypothalamus by electrical brain stimulation, hypothalamic response areas and underlying neural substrates have never been determined accurately. In this study the boundaries of the hypothalamic response areas for grooming, digging and circling were delimited using moveable electrodes, an enriched environment containing a variety of goal objects, and an appropriate statistical technique. A total of 641 hypothalamic sites in 71 male CPB/WU Wistar rats were electrically stimulated. Results are plotted on a detailed stereotaxic brain atlas of the rat hypothalamus. Positive sites for any behavioural response cluster into restricted hypothalamic areas. Discriminant analysis of both positive and negative electrode localizations yields areas with high, intermediate or low probabilities of inducing the behavioural response concerned. Each response has its own response area where probabilities are high, although there may be overlap. Even within response areas a distinction can be made between areas in which the response can be induced at relatively high or low threshold current intensities. Lowest threshold sites within electrode tracks are often clustered. In search of neuroanatomical correlates, grooming is related to the distribution of ACTH-immunoreactive neural elements, digging is related to the distribution of efferent fibres from the bed nucleus of the stria terminalis, and circling is related to the distribution of dopaminergic fibres of the nigrostriatal pathway. The results clearly point to the stimulation site being the most important determinant of the evoked behavioural response. Evidently behavioural specificity does exist within the hypothalamus.

Is There Evidence for a Neural Correlate of an Aggressive Behavioural System in the Hypothalamus of the Rat

Publisher Summary Ideally, the unraveling of the “wiring diagram” of the brain should go together with the testing of intelligent assumptions on the purpose and the functions of its subassemblies and their interactions if we are to clarify the functioning of the brain in behavior. Naturally, many of these assumptions will have to stem from theories derived from behavioral observations of intact animals. However, even very clear, well defined behavioral constructs may lack a specific correlate or a distinct localization in the brain. Such constructs may be the consequence of several brain mechanisms, none of which is specifically related to a behavioral phenomenon, each with its own localization and correlates. There can be little doubt that neural networks in the brain, somehow, integrate information concerning internal and external events involved in aggression. But “aggression” is hardly a suitable concept for testing assumptions on brain functions in behavior. One will have to provide more accurate behavioral constructs. Saying “bite, rage, and attack integrating networks” might be just another way of saying “brain” itself. The number of autonomic, endocrine, and physiological processes that can be influenced by the hypothalamus suggests that there is more to this structure than behavioral systems alone. Also, anatomical studies reveal many intricate neural networks even within well-defined parts of the hypothalamus. All these networks may eventually appear to serve a distinct function of their own.

Postpartum aggression in rats does not influence threshold currents for EBS-induced aggression

Female Wistar rats were tested for aggressive behaviour induced by electrical brain stimulation (EBS) in the lateral hypothalamus. Threshold currents for the induction of aggression were determined on several days before the females were paired with experienced breeder males. Beginning in the second week of pregnancy threshold current values were measured once or twice weekly. No change in thresholds was observed either during pregnancy, the early postpartum period or after weaning. Lactation was the only period during which the females were spontaneously aggressive towards male intruders in their home cage, but not in the EBS cage. Analysis of bite targets revealed no difference between the bite patterns in the postpartum maternal aggression test and the EBS-induced attacks. The results demonstrate that the change in physiological and hormonal status in pregnant and lactating females has no influence on the propensity to attack during EBS. The similarity in wound patterns does not advocate a major difference in the types of aggression studied. We speculate upon the nature of EBS-induced attacks as the activation of a rigid, final pathway of aggression which is rather insensitive to mild modulations.

Ethopharmacology of Hypothalamic Aggression in the Rat

An ethopharmacological study of hypothalamic aggression may seem a little paradoxical, as essentially an artificially-induced response is studied using ethological methods, which stress the importance of studying natural behaviour in a natural environment. An attempt will be made to show, however, that an ethopharmacological study of hypothalamic responses is worthwhile for both behavioural pharmacology and ethology.

Centrally Acting Cholinolytics and the Choice Behaviour of the Rat

Publisher Summary This chapter shows the spontaneous alternation behavior shown by rats during successive trials in a T-maze that is dependent on the intertrial interval. Lengthening the intertrial interval beyond one hour is attended by a decrease in the percentage of animals alternating. A procedure is described to train rats to alternate at a rate of about 70% at an intertrial interval of two hours. The short acting, centrally active cholinolytic drug N-methyLCpiperidyl cyclopentyl methylethynyl glycollate (PCMG) has been used to analyze the suppressing influence of cholinolytics on alternation behavior. With an intertrial interval of two hours, administration of PCMG 20 min prior to trial I or 20 min prior to trial II reduce the alternation percentage to about 50%, whereas administration immediately following trial I has less effect. Analysis of running speeds and behavior, shown in different parts of the maze, demonstrate that treated animals are as strongly motivated to run and to choose as untreated ones. It is concluded that cholinolytic drugs exert their effect by disrupting registration and may be retrieval, whereas they probably have no effect on consolidation and motivation.