Increased shock-induced fighting with supersensitive beta-adrenergic receptors

Adrenergic and glucocorticoid receptor antagonists reduce ozone-induced lung injury and inflammation

Recent studies showed that the circulating stress hormones, epinephrine and corticosterone/cortisol, are involved in mediating ozone-induced pulmonary effects through the activation of the sympathetic-adrenal-medullary (SAM) and hypothalamus-pituitary-adrenal (HPA) axes. Hence, we examined the role of adrenergic and glucocorticoid receptor inhibition in ozone-induced pulmonary injury and inflammation. Male 12-week old Wistar-Kyoto rats were pretreated daily for 7days with propranolol (PROP; a non-selective β adrenergic receptor [AR] antagonist, 10mg/kg, i.p.), mifepristone (MIFE; a glucocorticoid receptor [GR] antagonist, 30mg/kg, s.c.), both drugs (PROP+MIFE), or respective vehicles, and then exposed to air or ozone (0.8ppm), 4h/d for 1 or 2 consecutive days while continuing drug treatment. Ozone exposure alone led to increased peak expiratory flow rates and enhanced pause (Penh); with greater increases by day 2. Receptors blockade minimally affected ventilation in either air- or ozone-exposed rats. Ozone exposure alone was also associated with marked increases in pulmonary vascular leakage, macrophage activation, neutrophilic inflammation and lymphopenia. Notably, PROP, MIFE and PROP+MIFE pretreatments significantly reduced ozone-induced pulmonary vascular leakage; whereas PROP or PROP+MIFE reduced neutrophilic inflammation. PROP also reduced ozone-induced increases in bronchoalveolar lavage fluid (BALF) IL-6 and TNF-α proteins and/or lung Il6 and Tnfα mRNA. MIFE and PROP+MIFE pretreatments reduced ozone-induced increases in BALF N-acetyl glucosaminidase activity, and lymphopenia. We conclude that stress hormones released after ozone exposure modulate pulmonary injury and inflammatory effects through AR and GR in a receptor-specific manner. Individuals with pulmonary diseases receiving AR and GR-related therapy might experience changed sensitivity to air pollution.

Considerations on nonclinical approaches to modeling risk factors of suicidal ideation and behavior

Given the serious nature of suicidal ideation and behavior (SIB) and the possibility of treatment-emergent SIB, pharmaceutical companies are now applying more proactive approaches in clinical trials and are considering the value of nonclinical models to predict SIB. The current review summarizes nonclinical approaches to modeling three common risk factors associated with SIB: aggression, impulsivity, and anhedonia. For each risk factor, a general description, advantages and disadvantages, species considerations, nonclinical to clinical translation, and pharmacological validation with respect to treatments associated with SIB are summarized. From this review, several gaps were identified that need to be addressed before use of these nonclinical models can be considered a viable option to predict the relative risk for SIB. Other future directions that may compliment these nonclinical approaches, including the use of selectively-bred or genetically-modified rodent models, transgenic models, gene expression profiling, and biomarker analysis, are discussed. This article was developed with the support of the DruSafe Leadership Group of the International Consortium for Innovation and Quality in Pharmaceutical Development (IQ, www.iqconsortium.org).

Maternal defense is modulated by beta adrenergic receptors in lateral septum in mice

Maternal defense (offspring protection) is a critical and highly conserved component of maternal care in mammalian systems that involves dramatic shifts in a female's behavioral response to social cues. Numerous changes occur in neuronal signaling and connectivity in the postpartum female, including decreases in norepinephrine (NE) signaling in subregions of the CNS. In this study using a strain of mice selected for maternal defense, we examined whether possible changes in NE signaling in the lateral septum (LS) could facilitate expression of maternal aggression. In separate studies that utilized a repeated measures design, mice were tested for maternal defense following intra-LS injections of either the β-adrenergic receptor agonist isoproterenol (10 μg or 30 μg) or vehicle (Experiment 1), the β-adrenergic receptor antagonist propranolol (2 μg) or vehicle (Experiment 2), or the β1-receptor antagonist, atenolol (Experiment 3). Mice were also evaluated for light-dark performance and pup retrieval. Thirty micrograms of the agonist isoproterenol significantly decreased number of attacks and time aggressive relative to vehicle without affecting pup retrieval or light-dark box performance. In contrast, the antagonist propranolol significantly increased maternal aggression (lowered latency to attack and increased total attack time) without altering light-dark box test. The β1-specific antagonist, atenolol, significantly decreased latency to attack (1 μg vs. vehicle) without altering other measures. Although the findings were identified in a unique strain of mice, the results of these studies support the hypothesis that changes in NE signaling in LS during the postpartum period contribute to the expression of offspring protection.

Catecholaminergic involvement in the control of aggression: hormones, the peripheral sympathetic, and central noradrenergic systems

Noradrenaline is involved in many different functions, which all are known to affect behaviour profoundly. In the present review we argue that noradrenaline affects aggression on three different levels: the hormonal level, the sympathetic autonomous nervous system, and the central nervous system (CNS), in different, but functionally synergistic ways. Part of these effects may arise in indirect ways that are by no means specific to aggressive behaviour, however, they are functionally relevant to it. Other effects may affect brain mechanisms specifically involved in aggression. Hormonal catecholamines (adrenaline and noradrenaline) appear to be involved in metabolic preparations for the prospective fight; the sympathetic system ensures appropriate cardiovascular reaction, while the CNS noradrenergic system prepares the animal for the prospective fight. Indirect CNS effects include: the shift of attention towards socially relevant stimuli; the enhancement of olfaction (a major source of information in rodents); the decrease in pain sensitivity; and the enhancement of memory (an aggressive encounter is very relevant for the future of the animal). Concerning more aggression-specific effects one may notice that a slight activation of the central noradrenergic system stimulates aggression, while a strong activation decreases fight readiness. This biphasic effect may allow the animal to engage or to avoid the conflict, depending on the strength of social challenge. A hypothesis is presented regarding the relevance of different adrenoceptors in controlling aggression. It appears that neurons bearing postsynaptic alpha2-adrenoceptors are responsible for the start and maintenance of aggression, while a situation-dependent fine-tuning is realised through neurons equipped with beta-adrenoceptors. The latter phenomenon may be dependent on a noradrenaline-induced corticosterone secretion. It appears that by activating very different mechanisms the systems working with adrenaline and/or noradrenaline prepare the animal in a very complex way to answer the demands imposed by, and to endure the effects caused by, fights. It is a challenge for future research to elucidate how precisely these mechanisms interact to contribute to functionally relevant and adaptive aggressive behaviour.

Chronic treatment with eltoprazine does not lead to tolerance in its anti-aggressive action, in contrast to haloperidol

The behavioral effects of eltoprazine and haloperidol during a 4 week treatment period were studied in the resident-intruder model of aggression in male rats. Eltoprazine, a serotonergic (5-HT1A/1B) agonist with specific anti-aggressive actions in animals, was compared to haloperidol, a neuroleptic often used to control behavioral disorders. Eltoprazine (1 or 3 mg/kg p.o.) and haloperidol (2 mg/kg p.o.) were given 60 min before a 10 min aggression test. Acutely, eltoprazine reduced aggression, without adversely affecting other behaviors. Eltoprazine (1 or 3 mg/kg p.o.) was subsequently given daily for 4 weeks and aggression tests were performed each week. The anti-aggressive effects of eltoprazine remained stable over the period of 4 weeks whereas exploration was increased. After a wash-out period of 1 week aggression had returned to baseline levels. Acutely given, haloperidol (2 mg/kg p.o.) completely reduced aggression concomitant with massive sedation. Significant tolerance developed to the sedatory actions of haloperidol over the 4 week treatment period. Aggression returned slowly, but remained below baseline values. One week after wash-out a new challenge with haloperidol (2 mg/kg p.o.) revealed significant tolerance. After 2 weeks wash-out aggression had returned to baseline. The data demonstrate persistent and specific anti-aggressive effects after eltoprazine showing no tolerance. In contrast, haloperidol showed tolerance and rebound effects for aggression. The development of tolerance after haloperidol has a different course for sedation than for the anti-aggressive action.

Propranolol-induced increases in target-biting attack

The effect of a beta-adrenoreceptor blocking agent on defensive aggression in mice was evaluated. Acute doses of d,l-propranolol (0.2, 0.4, 0.8, 1.6, 3.2, 6.4, and 12.8 mg/kg) were administered to male Rockland-Swiss mice prior to testing in a target-biting paradigm. Baseline conditions established a high target-biting rate low biting rate during a 15-s tone stimulus preceding the next shock. Every dose of propranolol increased target-biting rates above baseline during each interval with one exception: 0.4 mg/kg decreased the biting rate immediately after delivery of the tail shock. The overall increase in aggression observed following dosing with propranolol was not expected from a review of the clinical literature. These results are discussed in reference to propranolol's known effects on the brain serotoninergic systems and the use of an animal model of defensive aggression.

Antiaggressive and motor effects of haloperidol show different temporal patterns in the development of tolerance

The study of the temporal course of tolerance development was used as a means to separate different aspects of the action of haloperidol on social behavior. Agonistic behavior was studied in isolated male mice that confronted standard opponents (anosmic and grouped conspecifics) in a neutral area. The aggressive and motor behaviors of the experimental animals were evaluated 30 min or 24 h either after a single injection of haloperidol (0.4 mg/kg) or following the last of a series of 15 or 30 injections. When animals were evaluated 30 min after the haloperidol injection, no tolerance to the antiaggressive effects was evident. The action on immobility, on the contrary, showed a clear tolerance development with repeated drug administration, both with 15 and 30 injections. When evaluated 24 h after the last injection, tolerance to the antiaggressive effects developed with repeated injections. Increased immobility was never found in the tests carried out after 24 h, not even in the single injection group. The clear divergence found in the temporal courses of tolerance to haloperidol in its antiaggressive and motor effects suggests that these actions are mediated through different neurophysiological mechanisms. A parallel with extrapyramidal and therapeutic effects is discussed.

Effects of alcohol dependence on shock-induced fighting: action of muscimol and homotaurine

We have applied the electroshock-induced fighting behavior to the study of experimental alcohol dependence. Adult Wistar rats were intoxicated chronically with ethanol (10 g/kg/24 h) for 13 days. Electroshock-induced fighting behavior was studied during chronic intoxication and withdrawal in comparison with normal rats receiving a water-carbohydrate solution isocaloric to ethanol. Rats were divided into groups receiving respectively muscimol (0.25 mg/kg), a GABAA agonist; homotaurine (140 mg/kg) a GABA mimetic; and physiological saline (10 ml/kg), intraperitoneally. During chronic intoxication, rats showed an increase in defensive-fighting behavior. Withdrawal accentuated the aggressive behavior and muscimol and homotaurine inhibited it. These results confirm the relevance of the electroshock-induced defensive fighting behavior test in chronic intoxication with alcohol, but to show the involvement of GABAergic transmission in the behavioral effects of alcohol withdrawal, additional experiments with other GABA mimetics and with GABA antagonists should be considered.

Biochemical and pharmacological evidence for central cholinergic regulation of shock-induced aggression in rats

Acetylcholinesterase (AChE) activity was estimated in brain and heart homogenates and plasma of 'aggressive' and 'nonaggressive' rats. Brain homogenates of 'nonaggressive' rats hydrolyzed significantly more substrate when compared to the 'aggressive' rats. Such differences were not seen in the heart homogenates or plasma of these two groups of rats. Acute DFP (0.1, 0.3 and 1.0 mg/kg) attenuated shock-induced aggression (SIA) 2 hr after treatment but facilitated SIA 24 hr and 48 hr after drug administration. Long-term DFP (0.3 mg/kg x 10 days), on the other hand, induced a significant enhancement in the SIA score, whereas atropine (1.0 and 5.0 mg/kg) produced a dose-related attenuation of the same. Pretreatment of rats with atropine (5 mg/kg) antagonized the long-term DFP-induced facilitation of SIA. These results are discussed in the light of an inhibitory central cholinergic mechanism in the regulation of SIA.

Involvement of brain transmitters in the modulation of shock-induced aggression in rats by propranolol and related drugs

(+/-)Propranolol (1, 3, 10 and 30 mg/kg) exhibited a differential effect on footshock aggression (FSA) in rats. Lower doses (1 and 3 mg/kg) of the drug facilitated FSA, whereas an inhibitory effect was observed with higher doses (10 and 30 mg/kg) of the same. (+)Propranolol (30 mg/kg) and UM-272 (1 and 10 mg/kg) as well as physostigmine (0.1 and 0.5 mg/kg) all produced inhibition of FSA. Similar FSA inhibitory effects were also observed with salbutamol (1 and 5 mg/kg). Pretreatment with atropine and not methylatropine attenuated the anti-aggressive effect of (+/-)propranolol (10 mg/kg) without appreciably altering the facilitatory effect (1 mg/kg) of the drug on FSA. In addition, at the anti-aggressive doses, (+/-)propranolol (10 mg/kg) and UM-272 (10 mg/kg), significantly inhibited brain cholinesterase enzyme activity when compared to saline controls. (+/-)Propranolol (10 mg/kg) also inhibited significantly the aggression induced by reserpine-apomorphine treatment. It is inferred that a central cholinergic and dopaminergic mechanism is involved in the anti-aggressive effect of (+/-)propranolol, whereas the low dose induced facilitation of affective aggression could be attributed to central beta-adrenoceptor blockade.

Catecholamines and aggression in animals

This paper assesses the evidence for the role of catecholamines in the aggressive behaviour of animals. The effects of manipulating dopamine and noradrenaline function, either alone or in combination, are considered with respect to two categories of aggression, predatory and affective. Affective aggression is further subdivided into shock-induced defensive fighting, isolation-induced aggression and irritable aggression. The results indicate that catecholamines may not have a specific role in aggressive behaviour. Rather, they may act more to excite or inhibit general behavioural systems, although certain treatments do have a specific influence on aggressive behaviour. The review also highlights certain problems concerning the psychopharmacology of aggression; different species may make varying responses to the same treatment, whilst treatments exerting a similar pharmacological action may result in diverse behavioural effects.