Early Life Experience Alters Stress-related Brain Circuits: Effects of Repeated Brief Postnatal Maternal Separation on Central Autonomic Pathways

Early life experience has a powerful influence on later stress reactivity, which is demonstrated by the animal model, repeated brief postnatal maternal separation. In this classic paradigm, rat pups undergo a 15-minute daily separation (MS15) from their dam for approximately one to two postnatal weeks. A substantial literature has demonstrated that adult rats with a developmental history of MS15 are significantly less stress reactive compared to controls, as evidenced by decreased stress-induced hormone release. Conversely, the effects of early life experience on brain circuits that control stress responses are virtually unknown. Descending preautonomic circuits govern the output of the autonomic nervous system, which mediates physiological responses to stress (e.g., increased heart rate and decreased digestion). These circuits begin in the paraventricular nucleus of the hypothalamus (PVN) and limbic forebrain and synaptically innervate preganglionic neurons in the brainstem dorsal vagal complex (DVC) and spinal cord that ultimately innervate body organs. A previous study from our laboratory has demonstrated that MS15 alters the developmental assembly of gastric preautonomic circuits (Card et al., 2005). These findings led us to hypothesize that MS15 rats would display altered circuit strength of gastric preautonomic circuits later in development, as assessed in juvenile rats. Indeed, the study described in Chapter 2 demonstrated that MS15 enhances the circuit strength of gastric preautonomic circuits originating within the PVN in juvenile rats. This enhanced circuit strength suggests that the function of preautonomic PVN pathways might also be altered by MS15. Thus, we hypothesized that MS15 rats would display altered stress-induced activation of the PVN to DVC pathway. The study described in Chapter 3 revealed that MS15 rats display decreased stress-induced Fos activation within the PVN and within a specific population of DVC neurons. Therefore, studies within this dissertation revealed that M15 alters the circuit strength of PVN preautonomic pathways and alters stress-induced activation of brainstem preautonomic pathways. These findings suggest that MS15 rats would display attenuated autonomic responses to stress and may provide insights into how early life experience shapes later stress reactivity

Reduced gray matter volume in ventral prefrontal cortex but not amygdala in bipolar disorder:significant effects of gender and trait anxiety

Neuroimaging studies in bipolar disorder report gray matter volume (GMV) abnormalities in neural regions implicated in emotion regulation. This includes a reduction in ventral/orbital medial prefrontal cortex (OMPFC) GMV and, inconsistently, increases in amygdala GMV. We aimed to examine OMPFC and amygdala GMV in bipolar disorder type 1 patients (BPI) versus healthy control participants (HC), and the potential confounding effects of gender, clinical and illness history variables and psychotropic medication upon any group differences that were demonstrated in OMPFC and amygdala GMV. Images were acquired from 27 BPI (17 euthymic, 10 depressed) and 28 age- and gender-matched HC in a 3T Siemens scanner. Data were analyzed with SPM5 using voxel-based morphometry (VBM) to assess main effects of diagnostic group and gender upon whole brain (WB) GMV. Post-hoc analyses were subsequently performed using SPSS to examine the extent to which clinical and illness history variables and psychotropic medication contributed to GMV abnormalities in BPI in a priori and non-a priori regions has demonstrated by the above VBM analyses. BPI showed reduced GMV in bilateral posteromedial rectal gyrus (PMRG), but no abnormalities in amygdala GMV. BPI also showed reduced GMV in two non-a priori regions: left parahippocampal gyrus and left putamen. For left PMRG GMV, there was a significant group by gender by trait anxiety interaction. GMV was significantly reduced in male low-trait anxiety BPI versus male low-trait anxiety HC, and in high- versus low-trait anxiety male BPI. Our results show that in BPI there were significant effects of gender and trait-anxiety, with male BPI and those high in trait-anxiety showing reduced left PMRG GMV. PMRG is part of medial prefrontal network implicated in visceromotor and emotion regulation

NORADRENERGIC INPUTS TO THE BED NUCLEUS OF THE STRIA TERMINALIS CONTRIBUTE TO THE NEURAL AND BEHAVIORAL EFFECTS OF THE ANXIOGENIC DRUG YOHIMBINE

NA inputs to the BNST are implicated in stress and anxiety. The alpha-2 adrenoceptor antagonist YO increases transmitter release from NA terminals, activates the HPA axis, and is anxiogenic. We have shown that YO dose-dependently activates Fos in the BNST and PVN. We also have shown that YO inhibits food intake and supports conditioned flavor avoidance. Recruitment of NA inputs to the BNST may underlie these neural and behavioral effects of YO. In the present study, NA inputs to the ventrolateral BNST were lesioned bilaterally by microinjecting saporin toxin conjugated to DBH antibody (DSAP). Ten to 14 days after surgery, DSAP (n=9) and sham rats (n=7) were food-deprived for 24 hrs. Half of the rats in each group were injected i.p. with saline vehicle, and half were injected with YO (5.0 mg/kg). Food was returned 30 min later, and cumulative intake was recorded. The experiment was later repeated in a counterbalanced design. YO significantly inhibited food intake to a similar extent in sham and DSAP rats. The second experiment examined the ability of YO to support conditioned flavor avoidance. In a two-bottle choice test, water-deprived rats significantly avoided drinking water containing flavors previously paired with YO treatment. The magnitude of conditioned aversion was similar in DSAP and sham rats. The third experiment examined YO-induced anxiety-like behaviors on the elevated plus maze. DSAP and sham rats were acclimated to handling, transport and timecourse of the experiment for 3 days prior to the first test day. Rats were left undisturbed in a room adjacent to the testing room for 30 minutes. Then, each rat was injected i.p. with either YO or saline. Thirty minutes after injection rats were placed on the elevated plus maze for 5 minutes while being recorded. YO-induced increases in anxiety-like behavior were attenuated in DSAP rats. Finally, DSAP and sham rats were injected with YO or vehicle and perfused with fixative 90-120 minutes later. Brain sections were processed to reveal lesion extent and Fos activation patterns. YO activated significantly fewer BNST neurons and CRH-positive PVN neurons in DSAP rats compared to sham controls. DBH immunolabeling in the BNST and medial parvocellular PVN was depleted in DSAP rats, whereas the lateral magnocellular PVN was unaffected. The NST and VLM contained significantly fewer NA neurons in DSAP rats compared to sham controls; however, YO activated similar proportions of the NA neurons that remained. We conclude that NA neurons innervating the BNST collateralize to innervate the medial parvocellular PVN, and that these NA inputs are necessary for YO to activate Fos within the BNST and PVN. Additionally, these inputs contribute to the YO-induced anxiety-like behaviors on the elevated plus maze. However, the NA inputs to the BNST are unnecessary for YO to inhibit food intake or support conditioned flavor avoidance, suggesting that other neural pathways are sufficient for these responses

Reduced gray matter volume in ventral prefrontal cortex but not amygdala in bipolar disorder: significant effects of gender and trait anxiety

Neuroimaging studies in bipolar disorder report gray matter volume (GMV) abnormalities in neural regions implicated in emotion regulation. This includes a reduction in ventral/orbital medial prefrontal cortex (OMPFC) GMV and, inconsistently, increases in amygdala GMV. We aimed to examine OMPFC and amygdala GMV in bipolar disorder type 1 patients (BPI) versus healthy control participants (HC), and the potential confounding effects of gender, clinical and illness history variables and psychotropic medication upon any group differences that were demonstrated in OMPFC and amygdala GMV. Images were acquired from 27 BPI (17 euthymic, 10 depressed) and 28 age- and gender-matched HC in a 3T Siemens scanner. Data were analyzed with SPM5 using voxel-based morphometry (VBM) to assess main effects of diagnostic group and gender upon whole brain (WB) GMV. Post-hoc analyses were subsequently performed using SPSS to examine the extent to which clinical and illness history variables and psychotropic medication contributed to GMV abnormalities in BPI in a priori and non-a priori regions has demonstrated by the above VBM analyses. BPI showed reduced GMV in bilateral posteromedial rectal gyrus (PMRG), but no abnormalities in amygdala GMV. BPI also showed reduced GMV in two non-a priori regions: left parahippocampal gyrus and left putamen. For left PMRG GMV, there was a significant group by gender by trait anxiety interaction. GMV was significantly reduced in male low-trait anxiety BPI versus male low-trait anxiety HC, and in high- versus low-trait anxiety male BPI. Our results show that in BPI there were significant effects of gender and trait-anxiety, with male BPI and those high in trait-anxiety showing reduced left PMRG GMV. PMRG is part of medial prefrontal network implicated in visceromotor and emotion regulation

Early infant prefrontal gray matter volume is associated with concurrent and future infant emotionality

Abstract High levels of infant negative emotionality (NE) are associated with emotional and behavioral problems later in childhood. Identifying neural markers of high NE as well as low positive emotionality (PE) in infancy can provide neural markers to aid early identification of vulnerability, and inform interventions to help delay or even prevent psychiatric disorders before the manifestation of symptoms. Prefrontal cortical (PFC) subregions support the regulation of NE and PE, with each PFC subregion differentially specializing in distinct emotional regulation processes. Gray matter (GM) volume measures show good test-retest reliability, and thus have potential use as neural markers of NE and PE. Yet, while studies showed PFC GM structural abnormalities in adolescents and young adults with affective disorders, few studies examined how PFC subregional GM measures are associated with NE and PE in infancy. We aimed to identify relationships among GM in prefrontal cortical subregions at 3 months and caregiver report of infant NE and PE, covarying for infant age and gender and caregiver sociodemographic and clinical variables, in two independent samples at 3 months (Primary: n = 75; Replication sample: n = 40) and at 9 months (Primary: n = 44; Replication sample: n = 40). In the primary sample, greater 3-month medial superior frontal cortical volume was associated with higher infant 3-month NE (p < 0.05); greater 3-month ventrolateral prefrontal cortical volume predicted lower infant 9-month PE (p < 0.05), even after controlling for 3-month NE and PE. GM volume in other PFC subregions also predicted infant 3- and 9-month NE and PE, together with infant demographic factors, caregiver age, and/or caregiver affective instability and anxiety. These findings were replicated in the independent sample. To our knowledge, this is the first study to determine in primary and replication samples associations among infant PFC GM volumes and concurrent and prospective NE and PE, and identify promising, early markers of future psychopathology risk