Walter Tornatzky

Long-term impairment of autonomic circadian rhythms after brief intermittent social stress

This experiment was designed to examine the short- and long-term behavioral, cardiovascular, and thermoregulatory responses to brief intermittent agonistic confrontation in rats. The experimental procedure involves resident-intruder confrontations consisting of a 10-min period during which both animals are separated in the home cage of the resident, followed by a brief physical encounter leading to defeat of the intruder and a 10-min period, when the intruder was alone in the home cage of the resident. These 30-min-long confrontations were repeated on 5 consecutive days. Before the first confrontation with a resident, an intruder rats telemetered heart rate and core temperature show a stable circadian rhythm that is entrained by the light cycle. Acutely, the confrontations produce immediate and large tachycardia and hyperthermia in intruders. A decrease in amplitude of the circadian rhythms for heart rate and core temperature, as detected by cosinor analysis, persists for at least 10 days after the last of five daily brief confrontations with the resident. The defensive upright posture is nearly absent during the first exploration of the residents home cage, but is displayed by the intruder for one-third of the available time before and after the fifth defeat. Intermittent brief social stress is sufficient to induce profound changes in defensive behavior and long-lasting depression of circadian rhythmicity that persist for weeks.

Accumbal dopamine and serotonin in anticipation of the next aggressive episode in rats

Autonomic and limbic neural activities are linked to aggressive behavior, and it is hypothesized that activities in the cardiovascular and monoaminergic systems play a role in preparing for an aggressive challenge. The objective was to learn about the emergence of monoamine activity in nucleus accumbens before an aggressive confrontation that was omitted at the regular time of occurrence, dissociating the motoric from the aminergic activity. Dopamine, serotonin, heart rate and behavioral activity were monitored before, during and after a single 10‐min confrontation in resident male Long‐Evans rats fitted with a microdialysis probe in the n. accumbens and with a telemetry sender (experiment 1). DA, but not 5‐HT efflux, was confirmed to increase in n. accumbens during and after a single aggressive episode. In aggressive males that confronted an opponent daily for 10 days (experiment 2) heart rate rose 1 h before the regularly scheduled encounter relative to control rats, as measured on day 11 in the absence of any aggression. Concurrently, DA levels increased by 60–70% over baseline levels and 5‐HT levels decreased by 30–35% compared to baseline levels. These changes were sustained over 1 h, and contrasted with no significant changes in DA, 5‐HT, heart rate or behavioral activity in control rats. The rise in mesolimbic DA appears to be significant in anticipating the physiological and behavioral demands of an aggressive episode, and the fall in 5‐HT in its termination, dissociated from the actual execution of the behavior.

Behavioral and autonomic responses to intermittent social stress: differential protection by clonidine and metoprolol

The present study investigated physiological and pharmacological characteristics of socially “stressed” animals. Specifically, we examined (1) to what degree autonomic and behavioral “stress” reactions during intermittent confrontations between an intruder male adult Long-Evans rat with an aggressive resident undergo habituation, and (2) to what extent the defeat-experienced animal can be protected against these “stress” reactions with clonidine or metoprolol, two adrenergic agents with clinical anxiolytic effects. We developed an acute social stress situation that consisted of initially placing an experimental rat as an intruder into the homecage of a resident while the resident was not present, thereafter permitting brief physical agonistic interactions with the reintroduced resident until the intruder was forced into a submissive supine posture and emitted ultrasonic vocalizations (USV), and eventually exposing the intruder to the residents threats for one hour, while being shielded from potentially injurious attacks (“threat encounter”). Over the course of the initial 4-weekly threat encounters the acute tachycardia but not the hyperthermic stress responses decreased in magnitude. Following the first three threat encounters core temperature (Tc) was significantly elevated for at least 3 h. The Tc was already elevated when the repeatedly defeated intruder was confronted with the olfactory cues of the residents cage. This conditioned “anticipatory” hyperthermia developed in the course of the first three confrontations and was paralleled by a decrease in exploratory and motor behavior and by an increase in defensive behaviors and in both types of USV emitted in the “low” (20–30 kHz) and the “high” (31–70 kHz) frequency range. Clonidine (0.01–0.1 mg/kg, IP), anα2-adrenergic agonist and metoprolol, a β-adrenergic blocker (1.0–10.0 mg/kg, IP), dose-dependently prevented the tachycardic response to stress. Only clonidine, but not metoprolol, also attenuated the rise in T0 during the 1-h agonistic interaction. Clonidine decreased those aspects of motor behavior (e.g. rearing, walking) that are of lesser “cost” for the individual but maintained high levels of defensive reactions and increased the duration of “low” USV. The high doses of clonidine (0.06, 0.1 mg/kg) attenuated the homeostatic regulation and sedated the intruder while exposed to threats during a social confrontation. The absence of attenuation of the high level of defensive behavior and the prolonged “low” USV suggest a stress intensification by the higher doses of clonidine. In conclusion, after the fourth encounter, the autonomic, behavioral and vocal response pattern prior to and during repeated weekly confrontations show no evidence for habituation for the following 6 weeks. Moreover, adrenergic therapeutic agents that are applied to treat symptoms of anxiety block the tachycardic response but may actually intensify defensive behavior and certain “stress” vocalizations.

Cocaine self-administration binges : transition from behavioral and autonomic regulation toward homeostatic dysregulation in rats

Abstract Background: An essential feature of cocaine addiction is the breakdown to control or regulate drug intake. Objective: The present studies aimed to examine the transition from regulated intravenous cocaine reinforcement to a more unpredictable, chaotic pattern of cocaine self-administration in rats that were given continuous access to the drug. Autonomic activity was continuously monitored via biotelemetry senders for heart-rate and core temperature before, during and after the cocaine ”binges”, in an attempt to characterize the breakdown of homeostatic regulation. Methods: After Long-Evans rats were fitted with intravenous catheters and intraperitoneal telemetry senders, they acquired cocaine self-administration with each fifth lever press being reinforced by a 0.25 mg cocaine infusion. Rats self-administered 15 cocaine infusions daily at stable rates for ca. 2–3 weeks, when continuous access periods (”binges”) of 26 and 72 h were scheduled, with a 3-week cocaine-free period between and following the two ”binges”. Results: A distinctive pattern of cocaine self-administration emerged during the ”binges” that consisted of (1) an initial loading phase, (2) stable, predictable inter-infusion intervals for up to 8–10 h, termed ”regulatory phase”, (3) increased variability in inter-fusion intervals, mostly beginning at 22–24 h of continuous access. During the first half of the 72-h ”binge”, the autonomic activities remained elevated, showed a greatly constrained variability, and the characteristic circadian rhythmicity was substantially decreased. The average cocaine intake (6.8±0.5 mg/kg per hour) during the ”regulatory” phase did not change during the subsequent phases. Following the 72-h ”binge”, the amplitude of autonomic circadian rhythms remained attenuated for more than 2 weeks. In a separate set of animals, the dose effect of inter-infusion intervals following the self-administered infusion was similar during a variable dose protocol, scheduled in an early and a late phase of a 30-h long ”binge”. Conclusions: The homeostatic dysregulation during the ”binge” as evidenced by the diminished capacity of autonomic functions to vary is accompanied by emerging irregularities in the pattern of cocaine self-administration.

Ethology and Neuropharmacology: Rodent Ultrasounds

One of the most fascinating and instructive illustrations of how neural networks mediate complex communication comes from the neuroethological studies with zebra finches and canaries that sing to court mates and defend their territories (e.g., Nottebohm, 1985, 1981). The results from oscine songbirds inform importantly on the plasticity of the neural network, its seasonal androgen-dependent expression, and the behavioural significance in reproductive and agonistic contexts. However, less is known about the neurochemical characteristics of these communication-specific networks and how potential neural receptors in these networks may be targeted by substances with known effects of affective expression in mammals. Nonetheless these investigations point to multisynaptic networks involving aminergic and steroid-sensitive cells that mediate the initiation and production of important communicative signals.

Stress induced disorganization of circadian and ultradian rhythms: Comparisons of effects of surgery and social stress

Persistent autonomic disturbances following stressful events suggest that the rhythmical nature of homeostatic functioning may be disrupted by these experiences. We assessed the effects of two different stressors on circadian and ultradian rhythms of Long-Evans rats by using nonlinear multi-oscillator cosinor analysis. Heart rate and intraperitoneal temperature were monitored continuously in 5-min intervals in two groups of animals via radio-telemetry for 15 days after surgery (n = 9) and 15 days following social defeat (n = 6). Circadian amplitude of heart rate and temperature increased significantly for the first nine days of the recovery from surgery but only circadian temperature amplitude increased following social defeat. Circadian acrophase of temperature but not heart rate changed significantly for a similar period following the surgery but not after the social defeat. A mathematical model incorporating the first five harmonics of the circadian rhythm was found to fit the data significantly better than a circadian model alone with rhythms of 3 and 5 cycles/day in temperature and heart rate entraining significantly to the light-dark schedule. Full recovery of the circadian and ultradian rhythms did not occur until a minimum of nine to twelve days after surgery or social defeat. The results suggest that rhythms with multiple periodicities are involved in homeostatic functioning and that models incorporating these rhythms may aid in understanding an organisms adaptive response to surgical intervention and social defeat, long after the challenges have terminated.

Alcohol and “bursts” of aggressive behavior: ethological analysis of individual differences in rats

A quantitative ethological analysis of rodent aggression was performed in order to characterize the aggression-heightening effects of alcohol in certain individuals. In dyadic confrontations, a resident rat pursues, threatens and attacks an intruder, who reacts with defensive, flight and submissive behaviors. The behavioral data from five series of experiments conducted from 1984 through 1989 were subjected to a lag sequential analysis that identified highly predictable sequences of aggressive behavior, and to interval analysis that delineated a burst pattern of aggressive behavior. These analyses revealed a distinct behavioral sequence of pursuit → sideways threat → attack bite → aggressive posture that occurs in bursts with an inter-event interval of less than 6.6 s. In the total population, alcohol heightened attack behavior at low acute doses (0.1, 0.3, 1.0 g/kg) in 47% of the animals (n=44), suppressed reliably attack behavior in another 25% (0.1–3.0 g/kg;n=23) and had unreliable effects in the remaining 28% (n=24). The peak enhancement of aggressive behavior was seen over more than a log cycle of alcohol doses (0.1, 0.3 or 1.0 g/kg) in different individuals. In an additional group of rats (n=20), individuals were identified according to whether or not acute low alcohol doses enhanced or suppressed the frequency of attack bites. In the subgroup of five rats who doubled their attack frequency upon acute alcohol challenge, this aggression-heightening effect was confirmed on repeated occasions. The aggression-heightening effects of alcohol were seen during the high-rate interactions in the initial phase of the confrontation and particularly during the lower level of fighting later on. Regardless of alcohol dose and subgroup, the highly predictable sequence of pursuit → sideways threat → attack bite → aggressive posture remained intact as long as the individual was able to fight. The present analysis identifies those individuals in whom low alcohol doses increase the frequency of attack behavior, the number of aggressive elements in bursts and particularly the “time in burst”. Alcohol produces these changes without altering the latency to initiate aggressive behavior, the rate of aggressive behavior within a burst or the number of bursts in an encounter. Alcohol may lengthen aggressive bursts by preventing termination of longer aggressive sequences rather than by altering the initiation of this behavior.

Alcohol, anxiolytics and social stress in rats

The main objective was to compare the anxiolytic-like profiles of alcohol, diazepam and gepirone along the stress intensity gradient which characterizes consecutive phases of a social confrontation. The acute social stress situation consisted of initially placing the experimental rat as an intruder into the homecage of a resident while the resident was not present, termed the “anticipatory” phase, thereafter permitting brief physical agonistic interactions with the re-introduced resident until the intruder was forced into a submissive supine posture and emitted ultrasonic vocalizations (USV), and eventually exposing the intruder to the residents threats for 1 h, while being shielded from potential injurious attacks. The hyperthermia, measured via telemetry, in the “anticipatory” phase prior to defeat and in reaction to threats, was decreased by alcohol, gepirone and diazepam; alcohol and gepirone were also effective in attenuating “anticipatory” tachycardia. Alcohol, like gepirone and diazepam, also decreased defensive responses and ultrasonic vocalizations in the “anticipatory” phase of the confrontation, but none of these drugs affected defensive reactions to threats which immediately followed defeat. Gepirone had no systematic sedative effects throughout the confrontation; infact, it dose-dependently reduced the stress-induced suppression of locomotor activity during the “anticipatory” phase. In contrast, at higher doses, alcohol as well as diazepam had marked sedative effects as evidenced by several behavioral parameters (i.e. lie, crouch, walk). The anxiolytic-like profile of hyperthermia, tachycardia, USV and defensive behavior in the “anticipatory” phase of the confrontation by alcohol, gepirone and diazepam contrasted with the lack thereof during the more intense reactive phase. This differential pattern of effects appears to be relevant to the clinical distinctions between anticipatory anxiety and other affective disturbances.

Prevention of the pro-aggressive effects of alcohol in rats and squirrel monkeys by benzodiazepine receptor antagonists

Pharmacological manipulations at the benzodiazepine-GABAA-chloride ionophore receptor complex modify some of the behavioral and physiological actions of alcohol (ethanol). The interactions between alcohol, benzodiazepines and aggression were examined in similar ethopharmacological studies in squirrel monkeys and in rats in confrontations with conspecifics. Dominant male squirrel monkeys were tested (1) within their social groups, and (2) in dyadic confrontations with “rival” males from a different social group, and resident male rats were tested in their home cage in confrontations with an inexperienced male intruder. Low doses of alcohol (0.1–0.3 g/kg) increased aggressive behaviors in dominant squirrel monkeys and a subgroup of resident rats, whereas high doses of alcohol (1–3 g/kg) decreased aggression and produced marked motor incoordination. Individuals that showed alcohol-enhanced aggression were selected, and pretreated with benzodiazepine antagonists (flumazenil, ZK 93426) prior to alcohol administration. Both ZK 93426 (3 mg/kg) and flumazenil (10 mg/kg) blocked the aggression-enhancing effects of alcohol in dominant squirrel monkeys and resident rats in confrontations with conspecifics. Neither compound altered the reductions in aggression and increases in inactivity produced by high doses of alcohol. Interestingly, agonist-like increased feeding and inverse agonist-like reductions in social behaviors were observed simultaneously at the same dose of flumazenil, in the same individual and testing situation. ZK 93426 did not alter feeding but also reduced social behaviors. The two antagonists were also not equipotent in their interactions with alcohol. ZK 93426 reduced alcohol-induced motor incoordination in squirrel monkeys, whereas flumazenil did not. In fact, flumazenil potentiated the effects of low doses of alcohol. Locomotion was reduced, while staggering and time spent sitting were increased in squirrel monkeys pretreated with flumazenil plus low to moderate alcohol doses that previously did not produce these effects when administered alone. The blockade of the motor-incoordinating effects of alcohol may depend on inverse agonist activities of the antagonist acting at the GABAA-benzodiazepine receptor coupled chloride channel.

“Anxiolytic” and “anxiogenic” benzodiazepines and β-carbolines: effects on aggressive and social behavior in rats and squirrel monkeys

Ethopharmacological studies on the behavior of socially housed rats and squirrel monkeys were conducted to explore the role of the benzodiazepine GABAA-coupled ionophore receptor complex in aggressive and social interactions. Benzodiazepine receptor (BZR) antagonists, ZK 93426 (1–10 mg/kg) and flumazenil (3–10 mg/kg), the partial agonist, ZK 91296 (1–10 mg/kg) and the partial inverse agonists RO 15-4513 (0.3–10 mg/kg), were administered to (1) squirrel monkeys prior to 1 h focal observations within established social groups or to (2) resident male rats before confrontations with a naive male intruder in their home cage for 5 min. Aggression was modified in a similar manner in both species, although squirrel monkeys were more sensitive to BZR challenges. Specifically, resident male rats showed dose dependent reductions in attack bites directed at intruder males that were significant at the highest dose of ZK 93426 (10 mg/kg). In squirrel monkeys, ZK 93426 (3 and 10 mg/kg) reduced aggressive grasps, threats and displays, as well as reducing the duration of being the target of aggression from untreated group members (1–10 mg/kg). The BZR partial agonist, ZK 91296 and the antagonist, flumazenil produced few effects on social behavior, low and high intensity aggression and motor activity in both species. Flumazenil (10–30 mg/kg) and ZK 91296 (10 mg/kg), but not ZK 93426, produced significant increases in foraging and feeding behaviors in squirrel monkeys. The hyperphagic effects of ZK 91296 and flumazenil, that are typical of BZR agonists compounds, were not observed in rats. Similarly, the inverse agonist-like reductions in social interactions produced by ZK 93426 (3–10 mg/kg) were observed only in squirrel monkeys. The partial inverse agonist Ro 15-4513 reduced aggression in rats, but low doses (1 mg/kg) produced tremors or seizures in 80% of the monkeys tested. Decreases in aggressive and social behaviors are often interpreted to reflect “anxiogenic” drug properties, whereas increased feeding has been associated with “anxiolytic” actions. The concurrent emergence of these apparent opposites suggests independent actions on social and alimentary functions.