Defensive behaviors in infant rhesus monkeys: environmental cues and neurochemical regulation

Allostasis, amygdala, and anticipatory angst

Regions of the amygdala are involved in anticipation of negative events. Chronic anticipation of negative events leads to what we call allostatic load, or arousal pathology. Two hormones appear to be involved in arousal pathology; corticotropin-releasing hormone in the brain and glucocorticoids. We suggest that increases in corticotropin-releasing hormone, by stress or glucocorticoids, in the amygdala may have functional consequences for allostatic load. Whereas, corticotropin-releasing hormone in the parvocellular region of the paraventricular nucleus of the hypothalamus is decreased by glucocorticoids thereby under negative feedback and homeostatic control, the central nucleus of the amygdala is to some extent under positive feedback and is increased by glucocorticoids, and perhaps under allostatic control. The human and animal literature suggest that a variety of psychopathologies (e.g., melancholia) may be tied to neurohormonal signals activating regions of the amygdala.

Effect of a preferred companion in modulating stress in adult female rhesus monkeys

Using a counterbalanced design, seven adult female rhesus monkeys were removed from their social group and housed in a novel environment both alone and with a companion chosen on the basis of quantitative affiliative behaviors. Blood samples (n = 2) were collected from all study animals before the exposure to the novel environment, then at 2, 24, and 96 h thereafter for cortisol and immunological analyses. During both conditions, subjects showed evidence of stress as indicated by elevated cortisol concentrations and decreases in absolute numbers of lymphocyte subsets. There was no significant interaction between condition (alone vs. companion) and time in cortisol percent change and further planned post hoc analyses showed no significant between-condition differences for any of the postseparation time points. Similarly, no significant interaction was found between conditions and time for the absolute number of CD4+CD8-T cells, CD8+CD4- T cells, or CD20+CD2- B cells. However, planned post hoc comparisons showed that subjects in the companion condition exhibited a significantly smaller percent change from baseline than in the alone condition at the 24 h and 96 h sample periods in absolute numbers of CD4+CD8- and CD8+CD4- T cells. Results showed that adult female rhesus monkeys exhibited a profound stress response when removed from their social group to a novel environment and that recovery time of T cell subsets was significantly enhanced by the presence of a preferred companion.

Effect of a preferred companion in modulating stress in adult female rhesus monkeys

Using a counterbalanced design, seven adult female rhesus monkeys were removed from their social group and housed in a novel environment both alone and with a companion chosen on the basis of quantitative affiliative behaviors. Blood samples (n = 2) were collected from all study animals before the exposure to the novel environment, then at 2, 24, and 96 h thereafter for cortisol and immunological analyses. During both conditions, subjects showed evidence of stress as indicated by elevated cortisol concentrations and decreases in absolute numbers of lymphocyte subsets. There was no significant interaction between condition (alone vs. companion) and time in cortisol percent change and further planned post hoc analyses showed no significant between-condition differences for any of the postseparation time points. Similarly, no significant interaction was found between conditions and time for the absolute number of CD4+CD8-T cells, CD8+CD4- T cells, or CD20+CD2- B cells. However, planned post hoc comparisons showed that subjects in the companion condition exhibited a significantly smaller percent change from baseline than in the alone condition at the 24 h and 96 h sample periods in absolute numbers of CD4+CD8- and CD8+CD4- T cells. Results showed that adult female rhesus monkeys exhibited a profound stress response when removed from their social group to a novel environment and that recovery time of T cell subsets was significantly enhanced by the presence of a preferred companion.

Lateralized effects of diazepam on frontal brain electrical asymmetries in rhesus monkeys

A growing body of literature has documented the differential role of the frontal regions of the two cerebral hemispheres in certain positive and negative affective processes. This corpus of evidence has led to the hypothesis of a possible differential effect of diazepam on asymmetry of frontal activation. To examine this question, nine infant rhesus monkeys were tested on two occasions during which brain electrical activity was recorded from left and right frontal and parietal scalp regions. During one session, recordings were obtained under a baseline restraint condition and then after an injection of diazepam (1 mg/kg). In the other session, following the same baseline restraint condition, a vehicle injection was given. In response to diazepam, the animals showed an asymmetrical decrease in power in the 4-8 Hz frequency band, which was most pronounced in the left frontal region. No change in electroencephalogram (EEG) activity was observed in response to vehicle. Asymmetry in parietal EEG activity was also unchanged by diazepam. Diazepam also produced overall reductions in power across different frequency bands in both frontal and parietal regions. Good test-retest stability of EEG measures of activation asymmetry was also found between the two testing sessions separated by three months. The possible proximal cause of the asymmetrical change in frontal brain electrical activity in response to diazepam, as well as the implications of these findings for understanding the mechanism of action of benzodiazepines are discussed.

Effects of beta-carboline on fear-related behavioral and neurohormonal responses in infant rhesus monkeys

We examined the effects of the inverse benzodiazepine agonist ethyl-beta-carboline-3-carboxylate (beta-CCE) on behavioral, hormonal, and neurochemical responses in infant rhesus monkeys exposed to fearful situations. Our paradigm elicits three distinct adaptive patterns of defensive behavior. From previous work, we hypothesized that behaviors induced by attachment bond disruption are predominantly mediated by opiate systems, whereas behaviors induced by the threat of attack are mediated by benzodiazepine systems. When beta-CCE (0, 125, 250, and 500 micrograms/kg) was administered immediately after maternal separation, the 500 micrograms/kg dose increased freezing and the 250 and 500 micrograms/kg doses reduced environmental exploration. Test conditions produced increased plasma ACTH and cortisol concentrations and increased cerebrospinal fluid (CSF) concentrations of MHPG and DOPAC; beta-CCE did not further affect these metabolites. A dose of 1000 micrograms/kg of beta-CCE increased CSF concentrations of DOPAC and MHPG in infants left with their mothers. During test conditions, it further increased CSF MHPG (but not DOPAC) concentrations, and reduced cooing while increasing freezing and barking and other hostile behaviors. Our results thus confirm that benzodiazepine systems mediate threat-related behaviors and suggest that coos, which were thought to predominantly reflect the degree of distress during separation, can be modulated by the infant's level of fear. beta-CCE also activated stress-related pituitary-adrenal hormonal systems and brain norepinephrine (NE) and dopamine (DA) systems. These effects occurred when animals remained undisturbed in their home cages with their mothers, suggesting that benzodiazepine receptors directly modulate brain NE and DA systems.

Opiate receptor blockade in juvenile macaques: effect on affiliative interactions with their mothers and group companions

The aim of this study was to test the hypothesis that, in non-human primates, the offspring-mother attachment and other social bonds within the group have in common neural mediating mechanisms involving brain opioids. The subjects were 10 juvenile macaques living in a stable social group with their mothers and other group companions. A within-subjects design, balanced for the order of drug administration (naloxone 1 mg/kg i.m. and saline), was used. In the naloxone condition, the juveniles increased their relative role in maintaining proximity with their mothers, made more grooming solicitations, and received more grooming. We found no evidence for differential effects of naloxone on the affiliative bonds the subjects had with their mothers and other group companions. The subjects' increased demands for social comfort were evenly addressed to, and responded to by, both their mothers and other group companions. This finding supports the hypothesis that, at a neural level, the endogenous opioid peptides form a common substrate for different types of social attachments in primates.

Morphine attenuates antipredator ultrasonic vocalizations in mixed-sex rat colonies

Mixed-sex groups of laboratory rats living in a visible burrow system (VBS) emit 18-27 kHz ultrasound and retreat to the burrow when a cat is placed in the open area of the VBS. The total duration of ultrasonic vocalizations was reliably reduced by pretreatment with 5 mg/kg morphine. In a subsequent study using male-female colony pairs, presentation of a cat to individual rats in the absence of their colony mate indicated significant gender differences in base frequency, degree of emission, and characteristics of pulses elicited. Specifically, females showed a greater number and duration of vocalizations, of higher frequency (kHz), and with shorter individual pulse durations than males. In the same study, morphine (5 mg/kg) produced a general decrease in the level of ultrasonic emissions in both sexes, reduced the mean base frequency (kHz), and increased the mean duration of individual pulses. These data suggest that endogenous opioid mechanisms may be involved in the mediation of ultrasonic vocalization in response to a predator, and are discussed with reference to known involvement of such systems in defensive responding.

"Paradoxical" effects of morphine on antipredator defense reactions in wild and laboratory rats

In a Fear/Defense Test Battery, measuring defensive reactions to a present, approaching and contacting predator, the highest dose of morphine tested (7.5 mg/kg) reliably reduced vocalization to dorsal contact, to vibrissae stimulation, and to an anesthetized conspecific in laboratory-bred wild R. norvegicus. Except for a dose-dependent reduction in flinch/jump reactions to dorsal contact (taps), other defensive behaviors (flight, freezing, etc.) were not reliably altered by morphine treatment (0, 1.0, 2.5, 7.5 mg/kg). Vocalization responses to vibrissae stimulation in wild-trapped R. rattus were reliably increased following naloxone (1.0 and 10.0 mg/kg) administration, lending support for opiate receptor involvement in the mediation of defensive vocalization. In the Anxiety/Defense Test Battery, measuring defensive reactions to situations associated with a predator (cat) or with cat odor, laboratory rats showed no decrease in defensive behavior with morphine (0, 1.0, 5.0 mg/kg). In direct contrast to the above findings, the effects of morphine treatment in this test battery suggested a generalized increase in defensiveness to noncontacting and nonpainful threat stimuli. These effects included a decrease in time spent near the cat compartment, with a complementary increase in time spent at maximum distance, a decrease in transits between these sections, an increase in crouching, and a decrease in grooming and rearing. This pattern of results suggests that morphine may have two opposing effects on defensive behavior, a generalized enhancement, together with a more specific reduction of responses to tactile or painful stimulation. A very widespread pattern of reliable sex or sex x drug effects in the Anxiety/Defense Test Battery was in good agreement with previous reports of sex differences in these tests, with females generally more defensive than males. Consonant with previous findings, no reliable sex differences were found with the Fear/Defense Test Battery, although several values approached an acceptable level of statistical significance.

Enkephalinergic involvement in periaqueductal gray control of hypothalamically elicited predatory attack in the cat

The effects of central infusion of naloxone into the midbrain periaqueductal gray (PAG) upon predatory attack behavior in the cat were studied in 12 cats. Initially, quiet biting attack was elicited by electrical stimulation of sites within the lateral hypothalamus using monopolar electrodes. Then cannula-electrodes were implanted into sites within the PAG from which electrical stimulation facilitated or suppressed the attack response. Following identification of modulatory sites within the PAG, naloxone (1.0 micrograms/0.5 microliter) was microinjected into those sites and the effects upon hypothalamically elicited attack were assessed. At nine of twelve sites in the PAG where suppression was obtained, administration of naloxone served to block those effects. Similarly, at six of eight facilitatory sites within the PAG, naloxone also blocked the modulatory effects of PAG stimulation. However, vehicle (isotonic saline) alone did not alter the modulatory effects of PAG stimulation. Administration of DAME (250 ng/0.3 microliter) into PAG modulatory sites in four cats, two which facilitated and two that suppressed the attack response, reversed the effects of naloxone at these sites. These results demonstrate that opioid peptides within the PAG play a complex role in the expression of predatory attack behavior in the cat.

Isolation-induced vocalization in Wistar rat pups is not increased by naltrexone

Rat pups, when removed from dam and littermates and isolated in an unfamiliar milieu, emit a characteristic ultrasonic vocalization that can be quieted by the administration of a nonsedating dose of morphine. Wistar pups, aged 7, 10, 12, 14, or 16 days, were tested after receiving intraperitoneal injections of the opiate antagonist naltrexone (0.0, 0.5, 1.0, or 5.0 mg/kg). The rate of isolation-induced ultrasonic vocalizations was unaffected by naltrexone at any dose, and there were no significant naltrexone-related changes on other behavioral measures. The complexity of the opioid system is discussed, as it may be involved in the vocal reaction to isolation.

Effects of alprazolam on fear-related behavioral, hormonal, and catecholamine responses in infant rhesus monkeys

We tested the effects of various doses of the triazolobenzodiazepine alprazolam on behavioral, hormonal, and neurochemical responses of infant rhesus monkeys under three conditions of separation from their mothers: alone, in the presence of a human who stared at them, and in the presence of a human who avoided eye contact. Alprazolam affected stress-induced responses in all three of these classes. Unrelated to its effects on the stress response, alprazolam appears to reduce the function of brain dopamine systems.

Day-night rhythms of shoaling behavior in goldfish: opioid and pineal involvement

Intracerebroventricular (ICV) administration of the opioid peptide, beta-endorphin (5.0 pg/g) to goldfish, Carassius auratus, significantly increased the cohesiveness and duration of shoaling ('bout' length) in shoals of five fish, as well as decreasing the latency of shoal formation in response to an external disturbance, while a higher dose of beta-endorphin (15 pg/g) decreased shoaling. There were day-night rhythms in shoaling and in the extent of the facilitatory effects of beta-endorphin (5.0 pg/g) on shoaling behavior, the fish displaying significantly greater shoaling responses in the day than during the night. The facilitatory effects of the low dose of beta-endorphin were blocked by systemic administration of naloxone (1.0 mg/kg), while ICV administrations of naloxone (1.0 pg/g) decreased daytime shoaling behavior. Removal of the pineal gland disrupted the day-night rhythm of shoaling, reducing daytime levels of shoaling. In addition, pinealectomy reduced the stimulatory effects of beta-endorphin (5.0 pg/g) on shoaling, and attenuated the day-night rhythms in the effects on beta-endorphin on shoaling. These results suggest that both opioid systems and the pineal gland influence shoaling behavior and the expression of its day-night rhythm in goldfish.