Prolactin responses to haloperidol in normal young women

Review of serum prolactin levels as an antipsychotic-response biomarker

Antipsychotics acting as antagonists at dopamine D2 receptors concentrated in the striatum are the cornerstone of effective treatment of psychosis. Substantial progress in treating persons with schizophrenia could be achieved by the identification of biomarkers which reliably determine the lowest efficacious dose of antipsychotics. Prolactin levels have been considered a promising treatment-response biomarker due to dopamine’s regulation of serum prolactin levels through D2 receptors in the hypothalamic-pituitary pathway. Prolactin secretion in response antipsychotic administration is associated with the antipsychotics affinity for D2 receptors. This review assesses the available literature on the use of serum prolactin levels as an antipsychotic-response biomarker. Articles were identified through PubMed as well as the reference lists of full text articles available online. Relevant publications were summarized briefly to define the limitations and utility of serum prolactin levels as a tool for improving antipsychotic dosing. Serum prolactin levels in combination with prolactin-inducing potencies for each antipsychotic may help identify the lowest effective dose of antipsychotic medications. , In addition to the fact that prolactin secretion is dependent on serum antipsychotic levels and not brain levels, recent findings show that prolactin release is independent of the β-arrestin-2 pathway and GSK3β regulation, one branch of the pathway that has been implicated in antipsychotic efficacy. Therefore, serum prolactin is an indirect biomarker for treatment response. Further investigations are warranted to characterize prolactin-antipsychotic dose-response curves and systematically test the utility of measuring prolactin levels in patients to identify a person’s lowest efficacious dose.

Stress responses and the mesolimbic dopamine system: social contexts and sex differences

Organisms react to threats with a variety of behavioral, hormonal, and neurobiological responses. The study of biological responses to stress has historically focused on the hypothalamic-pituitary-adrenal axis, but other systems such as the mesolimbic dopamine system are involved. Behavioral neuroendocrinologists have long recognized the importance of the mesolimbic dopamine system in mediating the effects of hormones on species specific behavior, especially aspects of reproductive behavior. There has been less focus on the role of this system in the context of stress, perhaps due to extensive data outlining its importance in reward or approach-based contexts. However, there is steadily growing evidence that the mesolimbic dopamine neurons have critical effects on behavioral responses to stress. Most of these data have been collected from experiments using a small number of animal model species under a limited set of contexts. This approach has led to important discoveries, but evidence is accumulating that mesolimbic dopamine responses are context dependent. Thus, focusing on a limited number of species under a narrow set of controlled conditions constrains our understanding of how the mesolimbic dopamine system regulates behavior in response to stress. Both affiliative and antagonistic social interactions have important effects on mesolimbic dopamine function, and there is preliminary evidence for sex differences as well. This review will highlight the benefits of expanding this approach, and focus on how social contexts and sex differences can impact mesolimbic dopamine stress responses.

Triphasic oral contraceptive treatment alters the behavior and neurobiology of female cynomolgus monkeys

Oral contraceptives (OCs) are the most widely prescribed and effective of the reversible contraceptive methods. In addition to inhibiting ovulation, OCs alter central nervous system function in women; however, methodological problems have prevented clear human studies. Thus, in this experiment we investigated the effects of OC treatment on behavior, hypothalamic- pituitary-adrenal axis function and the central nervous system in 75 adult female cynomolgus monkeys (Macaca fascicularis) housed in social groups of four to five monkeys per pen. Monkey social groups were randomly divided into either a control or an OC treatment group which was administered a clinically prescribed OC (Triphasil(R), levonorgestrel and ethinyl estradiol tablets) for 2 years. OC treatment increased the frequency of contact aggression received, time spent in locomotion, and sitting close to another animal, and decreased time spent fearfully scanning. OC treatment decreased heart rate, increased activity levels, and increased baseline cortisol concentrations and the cortisol response to adrenocorticotropin compared to control animals. OC treatment decreased the prolactin response to fenfluramine suggesting decreased serotonergic activity. These results suggest that this triphasic OC disrupts social behavior, hypothalamic-pituitary-adrenal axis regulation and the underlying central nervous system function.

Social subordination stress, behavior, and central monoaminergic function in female cynomolgus monkeys

BACKGROUND

Social subordination in female cynomolgus monkeys is stressful and activates the hypothalamic-pituitary-adrenal axis. In a previous experiment behavioral depression was observed in a subset of subordinates.

METHODS

In the experiment reported here behavioral and physiological indicators of stress were evaluated in dominant and subordinate female cynomolgus monkeys, and brain dopaminergic activity was assessed, as reflected in the prolactin response to haloperidol, a dopamine2 (D2) receptor antagonist.

RESULTS

Subordinates were aggressed more, spent more time in fearful scanning of the social environment, spent less time as the recipients of the active affiliative behavior of being groomed, had more variable heart rates in response to a novel environment, and were hypercortisolemic compared to dominants. Prolactin responses to haloperidol challenge were lower in subordinates than dominants, an observation consistent with the hypothesis that subordinate females have decreased D2 receptor function.

CONCLUSIONS

These observations suggest that social subordination is stressful and may alter brain dopaminergic function in primates. The neurophysiological characteristics of social subordinates may contribute to their susceptibility to depression.

Behavioral and neurobiological effects of estrogen replacement therapy and a history of triphasic oral contraceptive exposure

The effects of contraceptive steroids and estrogen replacement therapy on behavior and neuroendocrine function were evaluated in adult female cynomolgus monkeys. During the 'premenopausal' phase of the experiment, the animals were assigned to either treatment with a triphasic oral contraceptive (OC) for 24 months or the untreated control group. The monkeys were then ovariectomized and half of each of the premenopausal groups were randomly assigned to either treatment with conjugated equine estrogens (ERT) or the untreated control group for 12 months (the 'postmenopausal' phase). All evaluations were completed during the postmenopausal phase of the experiment. Both types of exogenous steroid treatments appeared to increase cardiovascular and hypothalamic-pituitary-adrenal responses to stress in socially dominant but not socially subordinate females. A history of triphasic OC administration increased contact aggression received, and reduced the prolactin response to fenfluramine, suggesting reduced serotonergic activity, for at least a year following the cessation of triphasic OC treatment.

Cortisol response to intramuscular desipramine in patients with major depression and normal control subjects: a replication study

The authors conducted a double-blind study evaluating the cortisol response to 75 mg of desipramine (DMI), administered intramuscularly to 20 patients with major depressive disorder (MDD) and 20 age- and sex-matched normal control subjects. A blunted placebo-corrected cortisol response to DMI was found in MDD patients in comparison with the normal control subjects. Since the behavioral/side effect and pharmacokinetic profiles of DMI were similar for patients with MDD and normal control subjects, these findings suggest that patients with MDD have an underlying biological insensitivity of the hypothalamic-pituitary-adrenal axis to DMI. It is hypothesized that these findings are consistent with a norepinephrine deficit, an alpha 1-adrenergic receptor insensitivity, or both. Further use of DMI as a neuroendocrine probe for the noradrenergic system is indicated.