Association between intermale social aggression and cellular density within the central amygdaloid nucleus in rats with lithium/pilocarpine-induced seizures

Opportunities for improving animal welfare in rodent models of epilepsy and seizures

Animal models of epilepsy and seizures, mostly involving mice and rats, are used to understand the pathophysiology of the different forms of epilepsy and their comorbidities, to identify biomarkers, and to discover new antiepileptic drugs and treatments for comorbidities. Such models represent an important area for application of the 3Rs (replacement, reduction and refinement of animal use). This report provides background information and recommendations aimed at minimising pain, suffering and distress in rodent models of epilepsy and seizures in order to improve animal welfare and optimise the quality of studies in this area. The report includes practical guidance on principles of choosing a model, induction procedures, in vivo recordings, perioperative care, welfare assessment, humane endpoints, social housing, environmental enrichment, reporting of studies and data sharing. In addition, some model-specific welfare considerations are discussed, and data gaps and areas for further research are identified. The guidance is based upon a systematic review of the scientific literature, survey of the international epilepsy research community, consultation with veterinarians and animal care and welfare officers, and the expert opinion and practical experience of the members of a Working Group convened by the United Kingdom's National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs).

Rapamycin attenuates aggressive behavior in a rat model of pilocarpine-induced epilepsy

Psychiatric disorders are fairly common comorbidities of epilepsy in humans. Following pilocarpine-induced status epilepticus (SE), experimental animals not only developed spontaneous recurrent seizures, but also exhibited significantly elevated levels of aggressive behavior. The cellular and molecular mechanism triggering these behavioral alterations remains unclear. In the present study, we found that aggression is positively correlated with development of spontaneous seizures. Treatment with rapamycin, a potent mTOR (mammalian target of rapamycin pathway)-pathway inhibitor, markedly diminished aggressive behavior. Therefore, the mTOR pathway may have significance in the underlying molecular mechanism leading to aggression associated with epilepsy.

Normal and abnormal aggression: human disorders and novel laboratory models

We review here aggression-related human psychopathologies and propose that human aggressiveness is mainly due to three major factors: (i) brain dysfunction affecting aggression-controlling brain centers (e.g. in certain types of brain lesions, epilepsy, Alzheimer disease, etc.); (ii) hypoarousal associated with chronically low plasma glucocorticoids, which foster violence by diminishing emotional barriers that limit such behaviors (e.g. in conduct disorder and antisocial personality disorder); (iii) hyperarousal which leads to irritability and outbursts (e.g. in depression, intermittent explosive disorder, chronic fatigue, etc.). Different disorders are associated with different types of aggressiveness; e.g. hypoarousal is often associated with instrumental aggression, whereas hyperarousal is associated with uncontrollable outbursts. Many psychological disorders have been simulated in laboratory models, which were used to assess aggressiveness. Little effort was invested, however, in assessing the abnormal dimension of such aggressiveness. We present here three models that appear especially suitable to assess abnormal aspects of rodent aggression: (i) abnormal attack targeting (head, throat, and belly) that is induced by hypoarousal in rats and models violence in hypoarousal-driven human aggression (ii) 'escalated' aggression (increased aggressive response due to frustration or instigation), which models irritability and hyperarousal-driven aggressiveness; and (iii) context-independent attacks induced by hypothalamic stimulation or genetic manipulations. These three models address different aspects of abnormal aggressiveness, and can become extremely useful in three areas: in evaluating and assessing models of human psychopathologies, in studying transgenic animals, and in developing new treatment strategies. Research based on these or similar models do not address aggressiveness in quantitative terms, but follows the development of abnormal aspects, and the possibilities of their specific treatment.

Mechanisms differentiating normal from abnormal aggression: glucocorticoids and serotonin

Psychopathology-associated human aggression types are induced by a variety of conditions, are behaviorally variable, and show a differential pharmacological responsiveness. Thus, there are several types of abnormal human aggression. This diversity was not reflected by conventional laboratory approaches that focused on the quantitative aspects of aggressive behavior. Recently, several laboratory models of abnormal aggression were proposed, which mainly model hyperarousal-driven aggressiveness (characteristic to intermittent explosive disorder, post-traumatic stress disorder, depression, chronic burnout, etc.) and hypoarousal-driven aggressiveness (characteristic mainly to antisocial personality disorder and its childhood antecedent conduct disorder). Findings obtained with these models suggest that hyperarousal-driven aggressiveness has at its roots an excessive acute glucocorticoid stress response (and probably an exaggerated response of other stress-related systems), whereas chronic hypoarousal-associated aggressiveness is due to glucocorticoid deficits that affect brain function on the long term. In hypoarousal-driven aggressiveness, serotonergic neurotransmission appears to lose its impact on aggression (which it has in normal aggression), certain prefrontal neurons are weakly activated, whereas the central amygdala (no, or weakly involved in the control of normal aggression) acquires important roles. We suggest that the specific study of abnormal aspects of aggressive behavior would lead to important developments in understanding the specific mechanisms underlying different forms of aggression, and may ultimately lead to the development of better treatment approaches.

The neuromatrix and the epileptic brain: behavioral and learning preservation in limbic epileptic rats treated with ketamine but not acepromazine

Conceiving the organization of the brain as a "neuromatrix" could provide significant insights into how different injuries to the nervous system could result in very distinct changes in behavior. The use of different pharmacological treatments to combat the deleterious consequences of such injuries is common practice. However, such treatments may have the capacity to alter the configurations of various neuronal circuits that contribute to the "neuromatrix" by selectively preventing damage to some pathways while facilitating the spread of destruction along others. The choice of pharmacological treatment may have profound consequences on the recovery of normal functioning following injury. We examined the behavior of rats treated with one of two potentially neuroprotective agents, the N-methyl-D-aspartate antagonist ketamine and the atypical neuroleptic acepromazine, on seizures induced by lithium-pilocarpine. Rats treated with ketamine following seizure onset were virtually indistinguishable from nonepileptic controls on a variety of behavioral tasks that included tests on learning, memory, and anxiety. In contrast, acepromazine-treated rats showed marked deficits on all learning and behavioral measures tested. These results suggest that administration of ketamine relatively soon after the emergence of epilepsy can prevent many of the cognitive deficits that are commonly found in rats subjected to lithium-pilocarpine-induced seizures. Further clinical testing investigating ketamine as a potential adjunct treatment for epilepsy may be well warranted.

Synchronized feeding as a "conditioned stimulus" for overt seizures in chronically (limbic) epileptic rats: a model for "psychogenic seizures" with complex partial epilepsy

Chronic limbic epilepsy was induced in male albino rats by a single systemic injection of lithium (3 mEq/kg) and pilocarpine (30 mg/kg). During the subsequent months the numbers of spontaneous, paroxysmal stereotyped episodes (analogous to Racine stages 4 and 5) were monitored. The numbers of these "overt seizures" increased within 10 min of the daily presentation of a food stimulus even though food was available ad libitum. The majority of the paroxysmal, stereotyped behaviours occurred within 1 min of the stimulus presentation; they were attenuated by oral prednisolone. Three rats displayed evidence of "conditioned seizures" to specific stimuli. The results suggest that the display of these behaviours can be synchronized and learned in contexts that are associated with the release of CRF (corticotrophin releasing factor) and may involve the disinhibited activity within the central amygdaloid nucleus of these rats. Implications for the occurrence of psychogenic seizures in patients with complex partial (limbic) epilepsy are discussed.

Temporal changes in neuronal dropout following inductions of lithium/pilocarpine seizures in the rat

Estimates of neuronal dropout for approximately 100 structures as defined by Paxinos-Watson were completed for brains of male Wistar albino rats between 1 and 50 days after status epilepticus was evoked by a single systemic injection of lithium and pilocarpine. Sample estimates of neuronal loss were strongly correlated with direct measures of cell density. The most extensive immediate damage occurred within the substantia nigra reticulata, CA1 field of the hippocampus, the piriform cortex and the reuniens and paratenial nuclei of the thalamus. Neuronal dropout continued in many other structures over a 50-day period. Structures that showed the greatest 2-deoxyglucose (2-DG) uptake during discrete seizures and waxing and waning seizures within the early stages of status epilepticus but the least 2-DG uptake at the time of late continuous spiking and fast spiking with pauses [Neuroscience 64 (1995) 1057, 1075] exhibited the most neuronal dropout. Relationships between the delay of injection of acepromazine (which facilitated survival) and the amount of damage suggested that the source of the process that results in permanent brain damage may originate within the region of the piriform cortices and its subcortices.

Experimental induction of intermale aggressive behavior in limbic epileptic rats by weak, complex magnetic fields: implications for geomagnetic activity and the modern habitat?

In three separate experiments, groups (4/group) of male rats with limbic epilepsy were exposed for 80 min every 24 hr during the midscotophase for 24 successive days to sham-field conditions or to one of four complex patterns of magnetic fields whose average intensities ranged between 20 nT to 500 nT. The numbers of episodes of boxing, biting, mounting, eating, drinking and grooming were then recorded each night during the latter 20 min. Moderately strong statistically significant interactions occurred between the presence or absence of the field and the pattern of the field explained 25% and 50% of the variance in the numbers of biting and boxing responses, respectively. Other behaviors were not affected. The results suggest that group aggression can be increased or decreased as a function of the temporal characteristics and morphology (shape) of the applied magnetic field.

Role of the central amygdala in social communication in Syrian hamsters (Mesocricetus auratus)

In Syrian hamsters, vasopressin (AVP) controls a form of scent marking called flank marking. Microinjection and lesion studies have identified several components of the neural circuit controlling this behavior. Microinjection of AVP into the medial preoptic-anterior hypothalamus (MPOA-AH), lateral septal nucleus (LS), bed nucleus of stria terminalis (BNST), and periaqueductal gray (PAG) stimulates an intense bout of flank marking. Lesions of areas such as the MPOA-AH and the LS inhibit flank marking. Other studies employing Fos immunocytochemistry suggest that the central amygdala (Ce) might be a component of this neural circuit. The purpose of the present study was to assess the significance of the Ce in regulation of AVP-induced flank marking. In Expt. 1A, the Ce of hamsters were either lesioned with ibotenic acid or sham-lesioned. In Expt. 1B, the Ce of hamsters were either lesioned electrolytically or sham-lesioned. All lesions were made bilaterally. One week later, hamsters were microinjected with AVP into the MPOA-AH and immediately tested for flank marking. In Expt. 2, the hamsters were microinjected with AVP into the Ce and were immediately tested for flank marking. Ibotenic lesions of the Ce reduced flank marking and electrolytic lesions completely inhibited flank marking in response to AVP microinjected into the MPOA-AH. Sham-lesions or lesions placed in other areas of the amygdala resulted in intense bouts of AVP-induced flank marking and flank grooming. No flank marking or flank grooming was observed in response to AVP microinjected into the Ce. These data indicate that the Ce plays a critical role in AVP-induced flank marking, although flank marking is not induced by AVP within the Ce itself.