Neurotransmitters regulating defensive rage behavior in the cat

This review summarizes recent findings of our laboratory that have been directed at: (1) identifying the neural circuits underlying the expression and modulation of defensive rage behavior in the cat and the neurotransmitters associated with these pathways; and (2) determining which components of the circuitry are affected by alcohol administration and which significantly alter the rage mechanism. The experiments described herein incorporated a number of converging methods, which include brain stimulation, behavioral pharmacology, immunocytochemistry, retrograde tract tracing and receptor binding. For behavioral pharmacological studies, monopolar electrodes and cannula-electrodes were implanted into selected regions along the limbic-midbrain axis for electrical stimulation and local microinfusion of drugs. The findings demonstrated: (1) a direct pathway from the anterior medial hypothalamus to the dorsal periaqueductal gray (PAG) over which this response is mediated. This pathway utilizes excitatory amino acids that act upon NMDA receptors within the midbrain PAG; (2) that the region of the dorsal PAG, from which defensive rage could be elicited, receives other inputs from the basal amygdala that facilitate this response by acting upon NMDA receptors; (3) a pathway from the medial amygdala to the medial hypothalamus that also facilitates defensive rage and whose functions are mediated by substance P receptors within the medial hypothalamus; (4) that the PAG also receives enkephalinergic inputs from the central nucleus of amygdala, which act upon mu receptors, and which powerfully suppress defensive rage; and (5) that recent findings reveal that ethanol administration facilitates defensive rage by virtue of its interactions with the medial hypothalamus, its descending projection to the PAG, and possibly with NMDA receptors within this pathway.

Brain SPECT findings and aggressiveness

Forty adolescents and adults who exhibited aggressive behavior within the six months prior to evaluation by physically attacking another person or destroying property were evaluated with brain SPECT imaging. A control group of 40 psychiatric patients who had never been reported to exhibit aggressive behavior were also studied. The brain SPECT studies were read blind to aggressiveness by nuclear physician on two separate occasions. The interreading reliability was very high. The brain SPECT patterns of the group with aggressive behavior showed significant differences from the control group in several areas of brain. These findings were most often seen in the following combination: decreased activity in the prefrontal cortex, increased activity in the anteromedial portions of the frontal lobes, leftsided increased activity in the basal ganglia and/or limbic system in comparison to the whole brain and focal abnormalities in the left temporal lobe. These findings indicate a possible cerebral perfusion profile for those who exhibit violent or aggressive behavior. Several case studies and the implications for treatment are discussed.

Differential effects of ethanol on feline rage and predatory attack behavior: an underlying neural mechanism

Previous studies have shown that, at certain dose levels, ethanol can exert a powerful, facilitatory effect on aggressive behavior in both animals and humans. In the cat, however, it was discovered that ethanol differentially alters two forms of aggression that are common to this species. Defensive rage behavior is significantly enhanced, whereas predatory attack behavior is suppressed by ethanol administration. One possible mechanism governing alcohol's potentiation of defensive rage behavior is that it acts on the descending pathway from the medial hypothalamus to the midbrain periaqueductal gray (PAG)-an essential pathway for the expression of defensive rage behavior that uses excitatory amino acids as a neurotransmitter. This hypothesis is supported by the finding that the excitatory effects of alcohol on defensive rage behavior are blocked by administration of the N-methyl-D-aspartate antagonist alpha-2-amino-7-phosphoheptanoic acid (AP-7) when microinjected into the periaqueductal gray, a primary neuronal target of descending fibers from the medial hypothalamus that mediate the expression of defensive rage behavior. Thus, the present study establishes for the first time a specific component of the neural circuit for defensive rage behavior over which the potentiating effects of ethanol are mediated.

NMDA receptors in the midbrain periaqueductal gray mediate hypothalamically evoked hissing behavior in the cat

The present study was designed to test the hypothesis that the descending pathway from the medial hypothalamus to the dorsal periaqueductal gray (PAG) is critical for the expression of defensive rage behavior in the cat and utilizes excitatory amino acids as a neurotransmitter. In the first phase of the study, monopolar stimulating electrodes were implanted into the medial hypothalamus from which defensive rage behavior could be elicited by electrical stimulation. For the entire study, the hissing response was used as a measure of defensive rage behavior. Cannula electrodes were implanted into the PAG from which defensive rage sites could be identified and were later used for microinfusion of the NMDA receptor antagonist, DL-2-amino-7-phosphoheptanoic acid (AP-7), into behaviorally identified sites within the PAG. Initially, intracerbral microinjections of the NMDA receptor antagonist, AP-7 (0.2, 2.0 nmol), which were placed directly into sites within the PAG from which defensive rage had been elicited, blocked the occurrence of hypothalamic hissing. Microinjections of similar doses of AP-7 into the PAG also blocked the facilitatory effects of medial hypothalamic stimulation upon hissing behavior elicited from the PAG. However, microinjections of 2 nmol into the PAG had no effect upon hissing that was also elicited from the region of the injection site. This finding indicates that AP-7 selectively blocks hissing elicited from the medial hypothalamus and that the suppressive effects of AP-7 cannot be the result of anesthetic or other nonselective properties of the drug. The next phase of the study, which employed immunohistochemical, receptor autoradiographic techniques, identified NMDA receptors to be present in highest concentrations in the dorsolateral aspect of the PAG where defensive rage is typically elicited. The final phase of the study, which employed a combination of retrograde labeling procedures following microinjections of Fluoro-Gold into defensive rage sites in the dorsal PAG and the immunocytochemical labeling of glutamatergic neurons, identified large numbers of neurons in the medial hypothalamus that were labeled positively for both Fluoro-Gold and glutamate. The overall findings of this study support the hypothesis that descending fibers of the medial hypothalamus that supply the dorsal aspect of the PAG mediate defensive rage behavior and utilize excitatory amino acids that act upon NMDA receptors within the dorsal PAG.

Acute frontal lobe syndrome and dyscontrol associated with bilateral caudate nucleus infarctions

BACKGROUND

A 67-year-old man presented with acute onset of spatial and temporal disorientation, memory loss and associated episodic dyscontrol. Investigations showed infarctions of both caudate nuclei. This patient presented a unique opportunity to study the relationship between the lesions, his behaviour, and neuropsychological testing.

METHOD

Single case report. Investigations included interviews to determine cognitive impairment, i.e. WAIS-R, MMSE, and neurological examination.

RESULTS

Extensive neuropsychological testing revealed severe impairment on tasks requiring planning, memory or abstract thought. These findings are very similar to those seen in Huntington's disease.

CONCLUSIONS

A neurobiological hypothesis is proposed to account for his symptoms, and recent discoveries in the basic sciences used to inform his management.

Neurobiological factors in aggressive behavior

OBJECTIVE

The author's aim was to review literature in the neurosciences and psychiatric clinical research reports about biological factors in aggression and the pathophysiological mechanisms that accompany aggression in neuropsychiatric syndromes.

METHOD

Studies were located through computer searches of relevant experimental reports and review articles mainly from the last 25 years.

RESULTS

Several studies using neuroimaging and neurophysiological and neuropathological research techniques have identified lesions in the limbic structures, temporal lobes, and frontal lobes of the brain in abnormally aggressive individuals. Several reports have associated deficiency or dysregulation of serotonin with homicidal, suicidal, and impulsive behavior. However, few studies have focused on polypeptides or second messenger systems, although abnormalities in these systems have been reported in patients with neuropsychiatric syndromes who have shown aggressive behavior. Even fewer studies focus on the correlation of brain structures and metabolic markers.

CONCLUSIONS

The understanding of aggressive behavior in psychiatric patients is fragmented. Some explanations are speculative and extrapolated to clinical psychiatric syndromes from experimental data on the neurophysiology of cats, rats, and other mammals. Identification of biochemical markers that can be used in predicting patients' response to pharmacological interventions may be the next step in developing more rational treatment of violent patients.

Neuroanatomy and neurotransmitter regulation of defensive behaviors and related emotions in mammals

1. There is suggestive evidence that the septo-hippocampal system and the amygdala are involved in risk assessment behavior, a response to potential threat possibly related to anxiety. In addition, experimental results have been reported implicating the medial hypothalamus in coordinated escape, while the periaqueductal gray matter (PAG) and the median raphe nucleus serotonergic projection to the hippocampus seem to mediate freezing. The latter defensive behaviors are evoked by distal danger stimuli and may be viewed as manifestations of fear. Finally, there is a sound body of evidence indicating that the PAG commands primitive fight or flight reactions elicited by proximal threat, acute pain or asphyxia. These defense reactions may be related to rage and panic, respectively. In contrast, the lateral septal area and the bed nucleus of the stria terminalis have been shown to exert tonic inhibitory influence on defense. 2. Experimental evidence indicates that gamma-aminobutyric acid (GABA) tonically inhibits defensive behavior in the amygdala, hypothalamus and the PAG, an effect opposed by excitatory amino acids. Among monoamines, serotonin (5-HT) has been suggested to facilitate anxiety in the amygdala while inhibiting panic in the PAG. The role of noradrenaline in defense is less clear, although hypotheses implicating the locus coeruleus in anxiety and panic have been suggested. Among peptides, corticotropin-releasing factor (CRF) acting as a central neurotransmitter is thought to mediate behavioral and physiological effects of acute stress, while opioid peptides have been shown to inhibit defense in the amygdala and in the dorsal PAG. Finally, acetylcholine seems to facilitate defensive behavior in the hypothalamus and the PAG.

Basal amygdaloid facilitation of midbrain periaqueductal gray elicited defensive rage behavior in the cat is mediated through NMDA receptors

The present study tested the hypotheses that: (1) defensive rage behavior elicited from the midbrain periaqueductal gray (PAG) in the cat is facilitated from the basal complex of amygdala; and (2) such facilitation from this region of amygdala is mediated via a pathway in which excitatory amino acids acting upon NMDA receptors within the PAG are utilized as a neurotransmitter. In the first phase of this study, cannula electrodes were implanted into PAG sites for the elicitation of defensive rage behavior as well as for drug delivery. Then, a second monopolar electrode was implanted into the basal nucleus of amygdala from which facilitation of defensive rage could be obtained. As a result of dual stimulation of the basal amygdala and PAG, response latencies for defensive rage were significantly lowered relative to PAG stimulation alone (P < 0.01). In the second phase of this experiment, 3 doses of a selective NMDA receptor antagonist, AP-7 (0.1, 0.5, 1.0 mg/kg), were peripherally (i.p.) administered in 5 animals. The results indicated a significant decrease in the facilitatory effects of amygdaloid stimulation in a dose and time dependent manner (P < 0.001). In the third phase, AP-7 was administered intracerebrally into PAG defensive rage sites in doses of 0.2 and 2.0 nmol. It was noted that intracerebral microinjections of AP-7 at the higher dose (2.0 nmol) also significantly suppressed the facilitatory effects of amygdaloid stimulation (P < 0.01); however, these effects were somewhat less potent then those observed following peripheral drug administration. A fourth phase of the study was conducted at the completion of the pharmacological experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that substance P is utilized in medial amygdaloid facilitation of defensive rage behavior in the cat

The present study was designed to test the hypothesis that a major excitatory mechanism for the expression of feline defensive rage behavior involves the medial nucleus of the amygdala which utilizes substance P as a neurotransmitter in a direct output pathway that supplies the medial hypothalamus. In phase I of the experiment, stimulating electrodes were implanted into the medial amygdala and cannula electrodes were implanted into the medial and lateral hypothalamus from which defensive rage and predatory attack behavior could be elicited by electrical stimulation, respectively. Response latencies for defensive rage were significantly lowered after dual stimulation of the medial amygdala and medial hypothalamus relative to single stimulation of the medial hypothalamus alone. In phase II, dose- and time-dependent decreases in medial amygdaloid-induced facilitation of defensive rage were observed after the i.p. administration of the NK1 antagonist, CP-96,345 (0.05, 2 and 4 mg/kg). In phase III of the study, the effects of microinjections of CP-96,345 placed directly into defensive rage sites within the medial hypothalamus (0.05, 0.5 and 2.5 nmol) upon medial amygdaloid modulation of this response were assessed. Again, intracerebral administration of this antagonist blocked the facilitatory effects of medial amygdaloid-induced facilitation of defensive rage in a manner parallel to that observed with peripheral administration of the NK1 antagonist. The results suggest that the medial amygdala facilitates defensive rage by acting through a substance P mechanism at the level of the medial hypothalamus. Other experiments revealed that peripheral administration of the NK1 antagonist: (1) had little upon the latency or threshold for elicitation of defensive rage, suggesting that the medial amygdaloid-substance P facilitatory mechanism acts in a phasic rather than tonic manner; and (2) also blocks the suppressive effects of medial amygdaloid stimulation upon predatory attack behavior elicited from the lateral hypothalamus. The latter finding suggest that similar neurochemical mechanisms regulate medial amygdaloid modulation of both forms of hypothalamically elicited aggression. The final aspect of this study utilized the combination of retrograde-tracing of amygdaloid neurons into the medial hypothalamus after microinjections of Fluoro-Gold into defensive rage sites, and the immunocytochemical analysis of substance P neurons within the amygdala. The data indicated that large numbers of retrogradely and immunocytochemically positive labeled cells were identified in the medial nucleus, including many that were double-labeled.(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdalo-hippocampectomy for pathological aggression

Two patients are reported, one with severe brain damage and epilepsy, and the other with limbic epilepsy, who were treated with unilateral microsurgical amygdalo-hippocampectomy for the control of rage and aggression. Both had significant improvement in their aggressiveness, and the second patient also improved in the frequency of his seizures and psychotic episodes. The significance of these observations for our understanding of the morphophysiological basis of rage and aggression is discussed.

Role of NMDA receptors in hypothalamic facilitation of feline defensive rage elicited from the midbrain periaqueductal gray

The present study tested the hypothesis that the pathway from the medial hypothalamus to the midbrain periaqueductal gray (PAG) subserving defensive rage behavior in the cat facilitates the occurrence of this response when elicited from the PAG by utilizing excitatory amino acids as a neurotransmitter or neuromodulator. Cannula electrodes were implanted into the PAG for the elicitation of defensive rage behavior as well as for microinjections of excitatory amino acid antagonists and N-methyl-D-aspartic acid (NMDA). Monopolar stimulating electrodes were also implanted into the medial hypothalamus from which this response could also be elicited and, when stimulated at subthreshold levels for elicitation of behavior, could also facilitate the occurrence of PAG elicited defensive rage. Initially, dual stimulation of the PAG and medial hypothalamus facilitated the occurrence of defensive rage elicited from the PAG. Then, the identical dual stimulation paradigm was repeated with the same current parameters following the infusion of various antagonists for different receptors into the PAG defensive rage sites. The results indicate that infusion of either kynurenic acid [(0.1-2.0 nmol), a non-selective excitatory amino acid receptor antagonist] or D-2-amino-7-phosphonoheptanoic acid (AP7) [(0.1-2.0 nmol), a specific NMDA receptor antagonist], produced a dose and time dependent blockade of the facilitatory effects of medial hypothalamic stimulation. In contrast, microinjections of relatively larger doses of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) [(4 nmol), a non-NMDA receptor (quisqualate and kainate) antagonist] or atropine [(4.4 nmol), a muscarinic receptor antagonist] had little effect upon medial hypothalamically elicited facilitation of the PAG response. In a second experiment, NMDA [0.1-1.0 nmol] was microinjected directly into PAG defensive rage sites in the absence of medial hypothalamic stimulation. In these animals, drug infusion mimicked the effects of dual stimulation by producing a dose and time dependent decrease in response latencies. A third experiment was designed to further test the hypothesis by neuroanatomical methods. Here, the retrograde label, Fluoro-Gold, was microinjected into defensive rage sites within the PAG and following a survival time of 5-6 days, the animals were sacrificed. The brains were then processed for immunocytochemical analysis of cells that immunoreact positively for aspartate and glutamate. The results indicated the presence of many retrogradely labelled and immunocytochemically positive cells within the rostro-caudal extent of the medial hypothalamus as well as others that were double labelled.(ABSTRACT TRUNCATED AT 400 WORDS)

Posteromedial hypothalamotomy in the treatment of violent, aggressive behaviour

Although emotion in the human is largely modified by the frontal association areas (software) and may better be called affect, it is still very much influenced by the balance of the ergotropic and the trophotropic circuits in the prosencephalon (hardware) especially in patients with organic brain lesions. Violent, aggressive, restless behaviours or rage can be regarded as an unbalanced state of these two circuits with dominance of the ergotropic circuit. In order to restore the balance of these two circuits, small stereotactic lesions were made in the ergotropic portion of the posterior hypothalamus (posteromedial hypothalamotomy) with good results in the follow-up of 10-25 years. Postoperatively there was no disturbance in endocrine activities and growth.

EEG and brainstem auditory evoked potentials in brain-injured patients with rage attacks and self-injurious behavior

Attacks of rage and self-injurious behavior are often encountered in brain-injured individuals. Clinical and experimental evidence suggests that brainstem centers may be involved in such behavior. We compared brainstem auditory evoked potentials in 10 normal controls, 10 patients with rage attacks, and 10 individuals with self-injurious behavior. The two patient groups had significantly longer group means for I-V and III-V interpeak latencies than controls. EEGs showed no specific features within or between the two groups. The findings suggest that the EEG may add little to the evaluation of such patients, except of course evidence of epilepsy or encephalopathy, while BAEPs may be a useful tool in the study of rage or self-injurious behaviors, in which brainstem centers may play an important role, possibly through abnormal or diminished reticular formation output.

Aggression

Pathologic aggression can be evaluated in terms of its psychosocial provocations, but it also must be recognized as a physiologically generated behavior and that disruptions of those controlling physiologic mechanisms can lead to pathologic states of aggression. Laboratory and clinical evidence indicates that the phylogenetically older limbic system is the anatomic core and that serotonin is the major neurotransmitter linked to that behavior. Hormonal factors influence aggression but are, to a large extent, altered by the aggressive acts themselves. There are a number of recognizable clinical syndromes which, by producing abnormal activity in limbic structures, by interfering with higher cortical control, or by causing neuroendocrine dysfunction, lead to states of pathologic aggression.

Effects of substantia nigra stimulation on hypothalamic rage reaction in cats

The effects of substantia nigra (SN) (pars compacta) stimulation on the rage reaction elicited by ventromedial hypothalamic nucleus (VMH) were investigated in the cat. The studied parameters of the rage reaction were: the current and the frequency threshold for the appearance of the hissing and the hissing latency. A facilitatory effect induced by the SN on the hypothalamic rage reaction was observed in the form of a decrease in the hypothalamic stimulus threshold for the hissing appearance and a decrease in the hissing latency. Moreover, when the VMH was stimulated with parameters below the threshold for the hissing display, simultaneous nigral activation determined its appearance. The excitatory influence exerted by the SN on the affective component of the aggressive behavior is discussed.

The role of the substantia nigra on the rage reaction elicited by hypothalamic stimulation, in the cat

The effects of substantia nigra stimulation on the rage reaction evoked by hypothalamic activation were studied. The reference value of the rage reaction was the latency of the hissing, which was constant in all animals when hypothalamic stimulation was performed with the same parameters. Simultaneous activation of substantia nigra and hypothalamus determined a significant decrease in hissing latency. The influence of the substantia nigra on the affective components of the aggressive behavior is underlined.

[Effects of stimulation of the substantia nigra on the rage reaction evoked in the cat by hypothalamic stimulation]

The effects of substantia nigra stimulation on the rage reaction evoked by hypothalamic activation were studied. The reference value of the rage reaction was the latency of the hissing, which was constant in all animals when hypothalamic stimulation was performed with the same parameters. Simultaneous activation of substantia nigra and hypothalamus determined a significant decrease of the hissing latency. The influence of the substantia nigra on the affective components of the aggressive behaviour in underlined.

Influence of environmental rearing history and postsurgical environmental change on the septal rage syndrome in mice

Reactivity to handling was examined in Binghamton Heterogeneous (HET) mice given septal lesions or control surgery following 5 weeks of postweaning rearing in enriched or restricted environments. Three housing conditions were employed: continuous enrichment, continuous restriction (both pre- and postsurgically), and a group switched from environmental enrichment to restriction 24 hours after surgery. The restricted mice were more reactive to handling than the enriched mice presurgically (60 days old), and interactions of housing conditions and surgery were found over the seven day postsurgical handling and testing period. The restricted mice given septal lesions greatly increased in reactivity postsurgically, while the intact controls declined in reactivity over the postsurgical week. The enriched septals were only moderately increased over the low presurgical reactivity baseline, and were much less reactive than the restricted septals. Perhaps the most remarkable finding was the dramatic and immediate increase in reactivity in the septals switched from enrichment to restriction, while intact controls showed no effect of the switch. These results emphasize the importance of experience in determining the effects of septal damage, and may be useful in examining other correlates of septal rage.