Evidence that preimmunization with a heat-killed preparation of Mycobacterium vaccae reduces corticotropin-releasing hormone mRNA expression in the extended amygdala in a fear-potentiated startle paradigm

Posttraumatic stress disorder (PTSD) is a trauma and stressor-related disorder that is characterized by dysregulation of glucocorticoid signaling, chronic low-grade inflammation, and impairment in the ability to extinguish learned fear. Corticotropin-releasing hormone (Crh) is a stress- and immune-responsive neuropeptide secreted from the paraventricular nucleus of the hypothalamus (PVN) to stimulate the hypothalamic-pituitary-adrenal (HPA) axis; however, extra-hypothalamic sources of Crh from the central nucleus of the amygdala (CeA) and bed nucleus of the stria terminalis (BNST) govern specific fear- and anxiety-related defensive behavioral responses. We previously reported that preimmunization with a heat-killed preparation of the immunoregulatory environmental bacterium Mycobacterium vaccae NCTC 11659 enhances fear extinction in a fear-potentiated startle (FPS) paradigm. In this follow-up study, we utilized an in situ hybridization histochemistry technique to investigate Crh, Crhr1, and Crhr2 mRNA expression in the CeA, BNST, and PVN of the same rats from the original study [Fox et al., 2017, Brain, Behavior, and Immunity, 66: 70–84]. Here, we demonstrate that preimmunization with M. vaccae NCTC 11659 decreases Crh mRNA expression in the CeA and BNST of rats exposed to the FPS paradigm, and, further, that Crh mRNA expression in these regions is correlated with fear behavior during extinction training. These data are consistent with the hypothesis that M. vaccae promotes stress-resilience by attenuating Crh production in fear- and anxiety-related circuits. These data suggest that immunization with M. vaccae may be an effective strategy for prevention of fear- and anxiety-related disorders.     

Photoperiod-induced neurotransmitter plasticity declines with aging: An epigenetic regulation?

Neuroplasticity has classically been understood to arise through changes in synaptic strength or synaptic connectivity. A newly discovered form of neuroplasticity, neurotransmitter switching, involves changes in neurotransmitter identity. Chronic exposure to different photoperiods alters the number of dopamine (tyrosine hydroxylase, TH+) and somatostatin (SST+) neurons in the paraventricular nucleus (PaVN) of the hypothalamus of adult rats and results in discrete behavioral changes. Here, we investigate whether photoperiod-induced neurotransmitter switching persists during aging and whether epigenetic mechanisms of histone acetylation and DNA methylation may contribute to this neurotransmitter plasticity. We show that this plasticity in rats is robust at 1 and at 3 months but reduced in TH+ neurons at 12 months and completely abolished in both TH+ and SST+ neurons by 18 months. De novo expression of DNMT3a catalyzing DNA methylation and anti-AcetylH3 assessing histone 3 acetylation were observed following short-day photoperiod exposure in both TH+ and SST+ neurons at 1 and 3 months while an overall increase in DNMT3a in SST+ neurons paralleled neuroplasticity reduction at 12 and 18 months. Histone acetylation increased in TH+ neurons and decreased in SST+ neurons following short-day exposure at 3 months while the total number of anti-AcetylH3+ PaVN neurons remained constant. Reciprocal histone acetylation in TH+ and SST+ neurons indicates the importance of studying epigenetic regulation at the circuit level for identified cell phenotypes. The findings may be useful for developing approaches for noninvasive treatment of disorders characterized by neurotransmitter dysfunction.     

Achieving CLARITY on bisphenol A,brain and behaviour

There is perhaps no endocrine disrupting chemical more controversial than bisphenol A (BPA). Comprising a high‐volume production chemical used in a variety of applications, BPA has been linked to a litany of adverse health‐related outcomes, including effects on brain sexual differentiation and behaviour. Risk assessors preferentially rely on classical guideline‐compliant toxicity studies over studies published by academic scientists, and have generally downplayed concerns about the potential risks that BPA poses to human health. It has been argued, however, that, because traditional toxicity studies rarely contain neural endpoints, and only a paucity of endocrine‐sensitive endpoints, they are incapable of fully evaluating harm. To address current controversies on the safety of BPA, the United States National Institute of Environmental Health Sciences, the National Toxicology Program (NTP), and the US Food and Drug Administration established the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY‐BPA). CLARITY‐BPA performed a classical regulatory‐style toxicology study (Core study) in conjunction with multiple behavioural, molecular and cellular studies conducted by academic laboratories (grantee studies) using a collaboratively devised experimental framework and the same animals and tissues. This review summarises the results from the grantee studies that focused on brain and behaviour. Evidence of altered neuroendocrine development, including age‐ and sex‐specific expression of oestrogen receptor (ER)α and ERβ, and the abrogation of brain and behavioural sexual dimorphisms, supports the conclusion that developmental BPA exposure, even at doses below what regulatory agencies regard as “safe” for humans, contribute to brain and behavioural change. The consistency and the reproducibility of the effects across CLARITY‐BPA and prior studies using the same animal strain and almost identical experimental conditions are compelling. Combined analysis of all of the data from the CLARITY‐BPA project is underway at the NTP and a final report expected in late 2019.     

Complex negative emotions induced by electrical stimulation of the human hypothalamus

BackgroundStimulation of the ventromedial hypothalamic region in animals has been reported to cause attack behavior labeled as sham-rage without offering information about the internal affective state of the animal being stimulated.ObjectiveTo examine the causal effect of electrical stimulation near the ventromedial region of the human hypothalamus on the human subjective experience and map the electrophysiological connectivity of the hypothalamus with other brain regions.MethodsWe examined a patient (Subject S20_150) with intracranial electrodes implanted across 170 brain regions, including the hypothalamus. We combined direct electrical stimulation with tractography, cortico-cortical evoked potentials (CCEP), and functional connectivity using resting state intracranial electroencephalography (EEG).ResultsRecordings in the hypothalamus did not reveal any epileptic abnormalities. Electrical stimulations near the ventromedial hypothalamus induced profound shame, sadness, and fear but not rage or anger. When repeated single-pulse stimulations were delivered to the hypothalamus, significant responses were evoked in the amygdala, hippocampus, ventromedial-prefrontal and orbitofrontal cortices, anterior cingulate, as well as ventral-anterior and dorsal-posterior insula. The time to first peak of these evoked responses varied and earliest propagations correlated best with the measures of resting-state EEG connectivity and structural connectivity.ConclusionThis patient's case offers details about the affective state induced by the stimulation of the human hypothalamus and provides causal evidence relevant to current theories of emotion. The complexity of affective state induced by the stimulation of the hypothalamus and the profile of hypothalamic electrophysiological connectivity suggest that the hypothalamus and its connected structures ought to be seen as causally important for human affective experience.     

Isolation and identification of endogenous RFamide‐related peptides 1 and 3 in the mouse hypothalamus

Although the RFamide‐related peptide (RFRP) preproprotein sequence is known in mice, until now, the molecular structure of the mature, functional peptides processed from the target precursor molecule has not been determined. In the present study, we purified endogenous RFRP1 and RFRP3 peptides from mouse hypothalamic tissue extracts using an immunoaffinity column conjugated with specific antibodies against the mouse C‐terminus of RFRP‐1 and RFRP‐3. Employing liquid chromatography coupled with mass spectrometry, we demonstrated that RFRP1 consists of 15 amino acid residues and RFRP3 consists of 10 amino acid residues (ANKVPHSAANLPLRF‐NH2 and SHFPSLPQRF‐NH2, respectively). To investigate the distribution of RFRPs in the mouse central nervous system, we performed immunohistochemical staining of the brain sections collected from wild‐type and Rfrp knockout animals. These data, together with gene expression in multiple tissues, provide strong confidence that RFRP‐immunoreactive neuronal cells are localised in the dorsomedial hypothalamic nucleus (DMH) and between the DMH and the ventromedial hypothalamic nuclei. The identification of RFRP1 and RFRP3 peptides and immunohistochemical visualisation of targeting RFRPs neurones in the mice brain provide the basis for further investigations of the functional biology of RFRPs.     

Characterisation of endogenous players in fibroblast growth factor‐regulated functions of hypothalamic tanycytes and energy‐balance nuclei

The mammalian hypothalamus regulates key homeostatic and neuroendocrine functions ranging from circadian rhythm and energy balance to growth and reproductive cycles via the hypothalamic‐pituitary and hypothalamic‐thyroid axes. In addition to its neurones, tanycytes are taking centre stage in the short‐ and long‐term augmentation and integration of diverse hypothalamic functions, although the genetic regulators and mediators of their involvement are poorly understood. Exogenous interventions have implicated fibroblast growth factor (FGF) signalling, although the focal point of the action of FGF and any role for putative endogenous players also remains elusive. We carried out a comprehensive high‐resolution screen of FGF signalling pathway mediators and modifiers using a combination of in situ hybridisation, immunolabelling and transgenic reporter mice, aiming to map their spatial distribution in the adult hypothalamus. Our findings suggest that β‐tanycytes are the likely focal point of exogenous and endogenous action of FGF in the third ventricular wall, utilising FGF receptor (FGFR)1 and FGFR2 IIIc isoforms, but not FGFR3. Key IIIc‐activating endogenous ligands include FGF1, 2, 9 and 18, which are expressed by a subset of ependymal and parenchymal cells. In the parenchymal compartment, FGFR1‐3 show divergent patterns, with FGFR1 being predominant in neuronal nuclei and expression of FGFR3 being associated with glial cell function. Intracrine FGFs are also present, suggestive of multiple modes of FGF function. Our findings provide a testable framework for understanding the complex role of FGFs with respect to regulating the metabolic endocrine and neurogenic functions of hypothalamus in vivo.     

颅脑损伤大鼠下丘脑前部、延髓内脏带突触膨体素和突触蛋白Ⅰ的表达变化

目的探讨颅脑损伤大鼠伤后不同时间下丘脑前部和延髓内脏带脑组织突触膨体素（SYN）和突触蛋白I（SYN-I）表达的变化,以及致应激性胃溃疡的变化。方法将40只成年SD大鼠按随机数字表法随机分为四组：对照组（C组,n=10）、颅脑损伤后1 h组（T1组,n=10）、颅脑损伤后6 h组（T1组,n=10）、颅脑损伤后12 h组（T1组,n=10）。利用液压装置以1.8个标准大气压的压力打击致大鼠颅脑损伤。应用胃溃疡指数评估应激性胃溃疡,利用免疫印迹法观察各组下丘脑前部和延髓内脏带脑组织SYN和SYN-I的表达变化。结果 C组、T1组、T6组、T12组胃溃疡指数分别为0、7.2±0.6、13.8±1.4、29.1±3.0,两两比较均有统计学差异（P〈0.05）。与C组相比,下丘脑前部脑组织SYN和SYN-Ia伤后6 h内无明显变化（P〉0.05）,伤后12 h SYN和SYN-Ia明显升高（P〈0.05）;SYN-Ib伤后1 h即明显升高（P〈0.05）。与C组相比,延髓内脏带脑组织SYN伤后1 h即明显升高（P〈0.05）,而SYN-Ⅰb明显降低（P〈0.05）;SYN-Ⅰa伤后1 h显著增高（P〈0.05）,伤后6 h达高峰,伤后12 h逐渐降低,但仍显著高于C组（P〈0.05）。结论颅脑损伤导致的应激性胃溃疡随时间延长逐渐加重;还可导致下丘脑前部和延髓内脏中枢发生突触可塑性的改变,其引起的突触传递效率的改变可能与应激性胃溃疡有关。