Social dominance in female monkeys: dopamine receptor function and cocaine reinforcement.

BACKGROUND: Brain imaging and behavioral studies suggest an inverse relationship between dopamine (DA) D2/D3 receptors and vulnerability to cocaine abuse, although most research has used males. For example, male monkeys that become dominant in a social group have significant elevations in D2/D3 receptor availability and are less vulnerable to cocaine reinforcement. METHODS: DA D2/D3 receptor availability was assessed in female cynomolgus monkeys (n = 16) with positron emission tomography (PET) while they were individually housed, 3 months after stable social hierarchies had formed, and again when individually housed. In addition, PET was used to examine changes in dopamine transporter (DAT) availability after social hierarchy formation. After imaging studies were complete, monkeys received implantation with indwelling intravenous catheters and self-administered cocaine (.001-.1 mg/kg/injection) under a fixed-ratio 30 schedule of reinforcement. Acquisition of cocaine reinforcement occurred when response rates were significantly higher than when saline was self-administered. RESULTS: Neither DAT nor D2/D3 receptor availability in the caudate nucleus and putamen was predictive of social rank, but both significantly changed after formation of social hierarchies. DA D2/D3 receptor availability significantly increased in females that became dominant, whereas DAT availability decreased in subordinate females. Dominant female monkeys acquired cocaine reinforcement at significantly lower doses than subordinate monkeys. CONCLUSIONS: The relationship between D2/D3 receptor availability and vulnerability to cocaine reinforcement seems, on the basis of these findings, opposite in females and males. These data indicate that the social environment profoundly affects the DA system but does so in ways that have different functional consequences for females than for males.

Changes in brain size during the menstrual cycle.

BACKGROUND: There is increasing evidence for hormone-dependent modification of function and behavior during the menstrual cycle, but little is known about associated short-term structural alterations of the brain. Preliminary studies suggest that a hormone-dependent decline in brain volume occurs in postmenopausal, or women receiving antiestrogens, long term. Advances in serial MR-volumetry have allowed for the accurate detection of small volume changes of the brain. Recently, activity-induced short-term structural plasticity of the brain was demonstrated, challenging the view that the brain is as rigid as formerly believed. METHODOLOGY/PRINCIPAL FINDINGS: We used MR-volumetry to investigate short-term brain volume changes across the menstrual cycle in women or a parallel 4 week period in men, respectively. We found a significant grey matter volume peak and CSF loss at the time of ovulation in females. This volume peak did not correlate with estradiol or progesterone hormone levels. Men did not show any significant brain volume alterations. CONCLUSIONS/SIGNIFICANCE: These data give evidence of short-term hormone-dependent structural brain changes during the menstrual cycle, which need to be correlated with functional states and have to be considered in structure-associated functional brain research.

Decreased cerebrospinal fluid allopregnanolone levels in women with posttraumatic stress disorder.

BACKGROUND: Alterations in the gamma-amino-butyric acid (GABA) neurotransmitter system have been identified in some populations with posttraumatic stress disorder (PTSD). METHODS: To further investigate factors of relevance to GABAergic neurotransmission in PTSD, we measured cerebrospinal fluid (CSF) levels of allopregnanolone and pregnanolone combined (ALLO: congeners that potently and positively modulate effects of GABA at the GABA(A) receptor), 5alpha-dihydroprogesterone (5alpha-DHP: the immediate precursor for allopregnanolone), dehydroepiandrosterone (DHEA: a negative modulator of GABA(A) receptor function), and progesterone with gas chromatography, mass spectrometry in premenopausal women with (n = 9) and without (n = 10) PTSD. Subjects were free of psychotropic medications, alcohol, and illicit drugs; all were in the follicular phase of the menstrual cycle except three healthy and four PTSD subjects receiving oral contraceptives. RESULTS: There were no group differences in progesterone, 5alpha-DHP, or DHEA levels. The PTSD group ALLO levels were < 39% of healthy group levels. The ALLO/DHEA ratio correlated negatively with PTSD re-experiencing symptoms (n = -.82, p < 008; trend) and with Profile of Mood State depression/dejection scores (n = -0.70, p < 0008). CONCLUSION: Low CSF ALLO levels in premenopausal women with PTSD might contribute to an imbalance in inhibitory versus excitatory neurotransmission, resulting in increased PTSD re-experiencing and depressive symptoms.

Cerebrospinal fluid levels of monoamine metabolites. A preliminary study of their relation to menstrual cycle phase, sex steroids, and pituitary hormones in healthy women and in women with premenstrual syndrome.

The cerebrospinal fluid (CSF) levels of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), the noradrenaline metabolite 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), and the dopamine metabolite homovanillic acid (HVA) were measured in a group of drug-free non-depressed women with premenstrual syndrome (PMS) (late luteal phase dysphoric disorder) (n = 13) and in controls with no premenstrual complaints (n = 13). In six patients and eight controls, CSF samples from both the luteal and the follicular phase were obtained, whereas in the remainder of the subjects, samples from either the follicular phase (patients: 4, controls: 2) or the luteal phase (patients: 3, controls: 3) were taken. The following observations were made: (1) Neither in the follicular phase nor in the luteal phase did the mean concentrations of CSF monoamine metabolites in the PMS group differ from the corresponding values in the control group. (2) Neither in the PMS group nor in the control group did the mean concentrations of monoamine metabolites in CSF samples obtained in the luteal phase differ from the corresponding values obtained in the follicular phase. (3) The intraindividual, intersample variations of CSF HVA and 5-HIAA concentrations were significantly smaller in the PMS group than in the control group. (4) CSF HVA correlated strongly to CSF 5-HIAA in the luteal phase of both patients and controls whereas in the follicular phase, particularly in controls, this correlation was much weaker. (5) In the luteal phase, the CSF HVA/5-HIAA ratio correlated negatively to serum levels of estradiol, progesterone, and testosterone. (6) The CSF HVA/5-HIAA ratio was significantly lower in PMS patients than in controls. (7) A positive correlation between CSF MHPG and serum luteinizing hormone was observed in the follicular phase. (8) A positive correlation between CSF HVA and serum prolactin was observed in the luteal phase. Because the study was comprised of a small number of subjects, the reported findings until replicated should be interpreted with caution.