Natural cytotoxicity toward K562 cells by macaque lymphocytes from infancy through puberty: effects of early social challenge

Calcium Channel Antagonists for Mood Disorders

PURPOSE

Development of new thymoleptic medications has primarily centered on anticonvulsants and antipsychotic drugs. Based on our studies of intracellular calcium ion signaling in mood disorders, we were interested in the use of novel medications that act on this mechanism of neuronal activation as potential mood stabilizers.

METHOD

We reviewed the dynamics of the calcium second messenger system and the international body of data demonstrating increased baseline and stimulated intracellular calcium levels in peripheral cells of patients with bipolar mood disorders. We then examined studies of the effect of established mood stabilizers on intracellular calcium ion levels and on mechanisms of mobilization of this second messenger. After summarizing studies of calcium channel blocking agents, whose primary action is to attenuate hyperactive intracellular calcium signaling, we considered clinical experience with this class of medications and the potential for further research.

FINDINGS

Established mood stabilizers normalize increased intracellular calcium ion levels in bipolar disorder patients. Most case series and controlled studies suggest an antimanic and possibly mood stabilizing effect of the calcium channel blocking medications verapamil and nimodipine, with fewer data on isradipine. A relatively low risk of teratogenicity and lack of cognitive adverse effects or weight gain suggest possible applications in pregnancy and in patients for whom these are considerations.

IMPLICATIONS

Medications that antagonize hyperactive intracellular signaling warrant more interest than they have received in psychiatry. Further experience will clarify the applications of these medications alone and in combination with more established mood stabilizers.

Nonhuman primate models of depression: effects of early experience and stress

Depression causes significant morbidity in the human population. The Diathesis-Stress/Two-Hit model of depression hypothesizes that stress interacts with underlying (probably genetic) predispositions to produce a central nervous system that is primed to express psychopathology when confronted with stressful experiences later in life. Nonhuman primate (NHP) studies have been extensively utilized to test this model. NHPs are especially useful for studying effects of early experience, because many aspects of NHP infancy are similar to humans, whereas development occurs at an accelerated rate and therefore allows for more rapid assessment of experimental variables. In addition, the ability to manipulate putative risk factors, including introducing experimental stress during development, allows inference of causality not possible with human studies. This manuscript reviews experimental paradigms that have been utilized to model early adverse experience in NHPs, including peer-rearing, maternal separation, and variable foraging. It also provides examples of how this model has been used to investigate the effects of early experience on later neurobiology, physiology, and behavior associated with depression. We conclude that the NHP offers an excellent model to research mechanisms contributing to the Diathesis-Stress/Two-Hit model of depression.

The influences of perinatal challenge persist into the adolescent period in socially housed bonnet macaques (Macaca radiata)

Social challenges during the perinatal period influence the mother-infant relationship in nonhuman primates and may affect the offspring's response to later social challenge(s). Relocation of a breeding colony of monkeys (Macaca radiata) created two groups of infants: one group experienced social group relocation to a new housing facility during the perinatal period (ATYPICAL) and the second group developed within a constant environment (TYPICAL). At a mean age of 25 months, all animals were removed from their natal group and placed in same sex adolescent social groups. Behavioral observations were collected after group formation or introduction to a new group. ATYPICAL subjects showed increased aggression and reduced affiliation compared to TYPICAL subjects. Hair cortisol in male subjects collected 6 months after introduction was elevated in the ATYPICAL subjects compared to TYPICAL subjects. These findings demonstrate that early life challenges affect behavior as well as stress hormone responses to social challenge in adolescence.

Challenges to bonnet monkey (Macaca radiata) social groups: Mother-infant dyad and infant social interactions

The mother-infant dyad is crucial to early development in a variety of species. The complexity of social groupings in nonhuman primates makes this relationship resilient as well as susceptible to early challenges associated with environmental chaos. Quantitative behavior observations of bonnet monkey mother-infant interactions were collected from 28 mother-infant dyads between one and twelve months of age. Social groups were subjected to several prenatal and/or postnatal housing relocations within a single year resulting in two study groups. One group experienced relocations (ATYPICAL, n = 14) and the second group (TYPICAL, n = 14) was conceived and reared in the same location. Behaviors in the ethogram included mother-infant interactions and infant social interactions with other members of the group. Observations between ages of two to four months were analyzed by a mixed model analysis of variance including fixed effects of per and postnatal history (TYPICAL, ATYPICAL), age, and history by age interaction and random effects of mother and infant nested within mother. A significant effect of relocation history was noted on a number of infant behaviors. ATYPICAL infants were out of direct contact with their mother at an earlier age but remained in her proximity. Control of proximity shifted to offsrping in the ATYPICAL group compared to the TYPICAL group. Furthermore, greater social interactions between two and four months of age with other members of the social group as well as the ir mother were observed in the ATYPICAL group. It is suggested that continuous challenge associated with relocation may affect the infant at later developmental ages due to these early differences in ways that are yet unclear.

When is enough measurement, enough? Generalizability of primate immunity over time

A statistical generalizability analysis gauges the degree to which a single assessment of a parameter successfully estimates that measure over repeated assessments for that individual. The generalizability of enumerative and functional immune parameters was estimated for two species of macaque monkeys assessed every 3 months between 18 and 42 months of age. Subjects were cross-balanced by species (bonnet, Macaca radiata, n=22; pigtail, Macaca nemestrina, n=21), sex (male, n=21; female, n=22), and brief early maternal separation with reunion (control, n=21; separated, n=22). Cell subset analysis showed the best generalizability (35-69%). Natural cytotoxicity also performed well (44-70%), but when computed on a lysis per cell basis, removing the effect of cell phenotype, it was less stable (15-48%). For most immune parameters, at least 5 assessments would be necessary to establish conventionally reliable (0.80) characterizations of long-term, stable individual differences in immunity, and three for minimally reliable (0.60) characterizations. More reactive parameters, as well as more behaviorally reactive species, yielded more generalizable results. Cell subsets that are typically most sensitive to acute stress (CD8, CD16) were more stable than other subsets (CD4, CD20). Behaviorally reactive species (pigtail) yielded more stable natural cytotoxicity results than the less reactive species (bonnet). Sex and rearing condition (early, brief maternal separation) did not substantially affect generalizability, although females tended to generate more stable results than did males.

Risk and resilience: early manipulation of macaque social experience and persistent behavioral and neurophysiological outcomes

OBJECTIVE

To review the contributions of research on nonhuman primates, specifically macaque monkeys, to the understanding of early social stress and its effects on behavior and neurophysiology.

METHOD

Review and synthesis of two bodies of work on macaque monkeys and early social manipulation: peer rearing and variable foraging demands. The literature was searched with Medline using key terms macaque, variable foraging, and peer rearing. The reference lists of these articles were also used to generate potential studies for review.

RESULTS

Nonhuman primate macaques show similarities to humans in their social development and functioning. Peer rearing of young macaques and rearing of young macaques with mothers experiencing variable foraging conditions both result in increased anxious, impulsive, and aggressive temperament and behavior; more reactive stress physiology; altered neurotransmitter functioning; and immune and metabolic changes. Functional variants of specific genes that code for neuromodulators are mediators of these effects.

CONCLUSIONS

Disrupted social relations during macaque rearing contribute to the risk for developing emotional and neurophysiological disturbance. In the face of such disruption, certain genotypes contribute to resilience. This can be alternately stated that, for animals of high-risk genotypes, resilience is conferred by quality relationships during rearing. This interaction of genetics with early social environment also applies to child mental health, implicating biological mediators identified in macaques as contributing to more complex outcomes in humans.

Characterization of rhesus macaque natural killer activity against a rhesus-derived target cell line at the single-cell level

Natural killer (NK) cells and NK cell activities in the rhesus macaque have been incompletely characterized. Using a recently developed rhesus NK target cell line with down-regulated MHC-I (B116Lo) as stimulators and FACS-sorted cells as effectors in a 4-h [51Cr]-release assay we showed that the CD3-CD8lo subpopulation is the primary effector population for NK cell-mediated cytolysis. The majority of these cells co-express CD16, CD11b, NKG2D, and NKp46. To evaluate functional activity at the individual cell level, we employed intracellular cytokine staining and a flow cytometric assay for degranulation, based on cell surface CD107a expression. Flow cytometric analysis revealed that a greater proportion of NK cells degranulated than produced cytokines in response to B116Lo stimulation; the frequency of CD107a-expressing cells within the total NK cell population ranging from 5 to 39%. Somewhat surprisingly, we did not find a significant correlation between lysis, measured by [51Cr]-release assay, and the size of the degranulating NK cell population, implying that additional mechanisms may regulate lytic activity. Use of these approaches should facilitate an improved understanding of NK activity in the rhesus macaque.

Response to social challenge in young bonnet (Macaca radiata) and pigtail (Macaca nemestrina) macaques is related to early maternal experiences

Previous experience affects how young primates respond to challenging social situations. The present retrospective study looked at one aspect of early experience, the quality of the mother-infant relationship, to determine its relationship to young bonnet and pigtail macaques' responses to two social challenges: temporary maternal separation at 5-6 months and permanent transfer to an unfamiliar peer group at 16-17 months. Relationship quality was measured quantitatively on 30 macaque mother-infant pairs with the Relationship Quality Index (RQI), the ratio of relative affiliation to relative agonism as previously applied to capuchin monkeys. Infants with high RQI values had amicable mother-infant relationships and infants with low RQI values had agonistic mother-infant relationships. Young monkeys with amicable and agonistic relationships showed consistent differences in behavior before, during, and after each social challenge, supporting the hypothesis that juveniles from amicable mother-infant relationships based on the RQI coped more effectively with social challenges than did juveniles from agonistic mother-infant relationships. Results suggest 1) characteristic amicability or agonism in early mother-offspring macaque relationships has the potential to influence offspring behavior in tense social contexts and 2) the RQI is useful as one of a coordinated suite of methods for studying the development of social skills.

Individual differences in peripheral blood immunological and hormonal measures in adult male rhesus macaques (Macaca mulatta): evidence for temporal and situational consistency

A growing body of research has indicated that consistent individual differences exist in physiological systems with which the immune system interacts. Few data have been reported that demonstrate stable individual differences in immunological measures, however. In the present study, enumerative measures of immune system activity were examined in 36 adult male rhesus macaques over a 13 month period under baseline conditions as well as under conditions of pharmacological and physical challenge. Blood samples were assayed for plasma concentrations of ACTH and cortisol, as well as neutrophil, total lymphocyte, CD4+ and CD8+ lymphocyte numbers, and the CD4/CD8 ratio. Analyses revealed that individual differences in the CD4/CD8 ratio and, to a lesser extent, plasma ACTH and cortisol concentrations, and neutrophil and CD4+ lymphocyte numbers were consistent across situations and times, despite changes in mean values during the various blood sampling sessions. The results suggest that the CD4/CD8 ratio might be considered trait-like and a useful immunological measure of biobehavioral organization.

Antidepressant treatment during social challenge prior to 1 year of age affects immune and endocrine responses in adult macaques

Antidepressants are widely used in treating depression and other behavioral problems in children and adolescents. Little is known about the long-term effects of these agents, particularly on physiological systems. The effects of previous antidepressant treatment during a social challenge in 9-month-old rhesus monkeys (Macaca mulatta) on their adult immune and endocrine responses were studied. Prior to the social challenge, the monkeys were reared either by their mother or in a peer group. Monkeys were treated with either a serotonergic agonist (fluoxetine), a noradrenergic agonist (desipramine), or saline during social separation. Non-separated, saline-treated monkeys served as control monkeys. In order to evaluate immune effects of early antidepressant treatment, adult monkeys were immunized with a novel antigen, tetanus toxoid. Blood samples were collected prior to and at 4-5-day intervals for 28 days after immunization. Plasma total immunoglobulins (IgG and IgM), complement levels (C3 and C4), tetanus antibody titers, and cortisol were assessed. Antibody levels were lowest in monkeys treated with antidepressants regardless of specific drug treatment or early rearing condition. Drug-treated subjects had elevated plasma immunoglobulins and complement protein levels. Cortisol was also highest in drug-treated subjects. These results should be considered when prescribing commonly used antidepressants for treatment of childhood disorders.

A comparison of cell-mediated immune responses in rhesus macaques housed singly, in pairs, or in groups

A variety of psychosocial factors have been shown to influence immunological responses in laboratory primates. The present investigation examined the effects of social housing condition on cell-mediated immune responses, comparing rhesus macaques (Macaca mulatta) in three housing conditions (single, pair, and group). Subjects included 12 adults of both sexes in each housing condition (N=36). Multiple blood samples (0, 4, 8, and 12 months) were collected for immunological analyses, including lymphocyte subsets, lymphocyte proliferation to pathogens and nonspecific mitogens, natural killer cell activity, and cytokine production. CD4(+) to CD8(+) ratios differed significantly across housing conditions and singly caged subjects had significantly lower CD4(+)/CD8(+) after the 4-month timepoint than did socially housed (pair and group) subjects. CD4(+) to CD8(+) ratios were positively correlated within subjects, suggesting a trait-like aspect to this parameter. Lymphocyte proliferation responses to all four gastrointestinal pathogens differed across housing conditions (at least at the 0.08 level), as did proliferation responses to StaphA, and the production of cytokines (IFN-gamma, IL-2, and IL-10). Proliferation responses of singly caged monkeys did not differ from socially housed monkeys and the highest levels of both IFN-gamma and IL-10 were produced by group housed subjects. The data demonstrate that social housing condition affects immune responses. While not unidirectional, these effects generally suggest enhanced immune responses for socially housed animals. Since rhesus monkeys live socially in nature, and the immune responses of singly housed animals differed from those housed socially, there is considerable motivation and justification for suggesting that the use of singly housed rhesus macaques may complicate interpretations of normal immunological responses. This may have important implications for the management, treatment, and selection of primate subjects for immunological studies.

A preliminary description of responses of free-ranging rhesus monkeys to brief capture experiences: behavior, endocrine, immune, and health relationships

A cohort of free-ranging rhesus monkeys has been followed since birth in 1994 on the island of Cayo Santiago, Puerto Rico. At 3 years of age, subjects were trapped and blood samples were collected after capture and prior to release the following day. Blood samples were processed for natural cytotoxicity toward xenogeneic tumors, phenotyping, and plasma hormones. Intestinal parasites were determined from fresh stool samples collected during trapping. Data were also available from the previous year for antibody titers to latent viruses prevalent in this population. Behavioral traits of each monkey were characterized using a previously developed trait scale for rhesus monkeys. Natural cytotoxicity toward both K562 and Raji targets declined from capture until release the following day. Plasma cortisol rose and plasma prolactin and growth hormone fell during the period of captivity; a rise in insulin was significant. It was expected that individual differences in behavioral traits might predict immune and hormone levels at the time of capture or changes in these parameters during the capture period. Although behavioral adjectives tended to cluster along three orthogonal dimensions (Insecurity, Irritability, and Sociability), they bore no relationship to the physiological parameters collected acutely (in vitro immune and endocrine parameters). The individual difference markers of gender and maternal rank were not related to the magnitude of the observed changes in these in vitro parameters, either. However, an in vivo measure (CMV titer) was related to individual differences in Irritability. It was concluded that the magnitude of the stress associated with capture overwhelmed the individual difference effects.

Elevated cytotoxicity in combat veterans with long-term post-traumatic stress disorder: preliminary observations

Resting immune [WBC and differential cell counts lymphocyte phenotyping (CD2, CD4, CD8, CD16, CD20, and CD56), and NK activity] and endocrine (cortisol, prolactin, growth hormone, and DHEA-SO4) parameters were measured in 10 male, Vietnam combat veterans diagnosed with long-term post-traumatic stress disorder (PTSD) and 9 control Vietnam combat veterans without a PTSD diagnosis but with a comparable history of alcohol abuse. Subjects completed a battery of psychological questionnaires. We report on preliminary observations of the relationship between PTSD and physiological and psychological parameters. With some important exceptions, PTSD patients did not differ from the age-matched control group with regard to hormone levels or lymphocyte phenotypes. However, NK activity was higher in the PTSD population than in the controls. Beck, Mississippi, and Combat Exposure scores were significantly elevated in the PTSD population. In contrast to previous observations in depressed populations, depression (indicated by elevated Beck scores), comorbid with PTSD, was associated with increased natural cytotoxicity.