Associations of waking cortisol with DHEA and testosterone across the pubertal transition: Effects of threat-related early life stress

Atypical regulation of the hypothalamic-pituitary-adrenal (HPA) axis is a putative mechanism underlying the association between exposure to early life stress (ELS) and the subsequent development of mental and physical health difficulties. Recent research indicates that puberty is a period of HPA-axis plasticity during which the effects of exposure to ELS on cortisol regulation may change. In particular, increases in the sex hormones that drive pubertal maturation, including dehydroepiandrosterone (DHEA) and testosterone, may be implicated in pubertal recalibration of cortisol regulation. In the current study, we examined the associations among levels of objectively-rated threat-related ELS and salivary waking cortisol, DHEA, and testosterone in a sample of 178 adolescents (55 % female) who were in early puberty at baseline (Tanner stages 1-3; mean Tanner stage[SD] = 1.93[0.64]; mean age[SD] = 11.42[1.04]) and were followed up approximately two years later (mean Tanner stage[SD] = 3.46[0.86]; mean age[SD] = 13.38[1.06]). Using multi-level modeling, we disaggregated the effects of between-individual levels and within-individual increases in pubertal stage and sex hormones on change in cortisol. Controlling for between-individual differences in average pubertal stage, the association between levels of cortisol and DHEA was more strongly positive among adolescents who evidenced greater within-individual increases in pubertal stage across time. Both higher average levels and greater within-individual increases in DHEA and testosterone were associated with increases in cortisol across time, indicating positive coupling of developmental changes in these hormones; however, coupling was attenuated in adolescents who were exposed to more severe threat-related ELS prior to puberty. These findings advance our understanding of the development of the HPA-axis and its association with childhood environmental risk during puberty.

Early Life Stress, Frontoamygdala Connectivity, and Biological Aging in Adolescence: A Longitudinal Investigation

Early life stress (ELS) may accelerate frontoamygdala development related to socioemotional processing, serving as a potential source of resilience. Whether this circuit is associated with other proposed measures of accelerated development is unknown. In a sample of young adolescents, we examined the relations among ELS, frontoamygdala circuitry during viewing of emotional faces, cellular aging as measured by telomere shortening, and pubertal tempo. We found that greater cumulative severity of ELS was associated with stronger negative coupling between bilateral centromedial amygdala and the ventromedial prefrontal cortex, a pattern that may reflect more mature connectivity. More negative frontoamygdala coupling (for distinct amygdala subdivisions) was associated with slower telomere shortening and pubertal tempo over 2 years. These potentially protective associations of negative frontoamygdala connectivity were most pronounced in adolescents who had been exposed to higher ELS. Our findings provide support for the formulation that ELS accelerates maturation of frontoamygdala connectivity and provide novel evidence that this neural circuitry confers protection against accelerated biological aging, particularly for adolescents who have experienced higher ELS. Although negative frontoamygdala connectivity may be an adaptation to ELS, frontoamygdala connectivity, cellular aging, and pubertal tempo do not appear to be measures of the same developmental process.

Early life stress, cortisol, frontolimbic connectivity, and depressive symptoms during puberty

Early life stress (ELS) is a risk factor for the development of depression in adolescence; the mediating neurobiological mechanisms, however, are unknown. In this study, we examined in early pubertal youth the associations among ELS, cortisol stress responsivity, and white matter microstructure of the uncinate fasciculus and the fornix, two key frontolimbic tracts; we also tested whether and how these variables predicted depressive symptoms in later puberty. A total of 208 participants (117 females; M age = 11.37 years; M Tanner stage = 2.03) provided data across two or more assessment modalities: ELS; salivary cortisol levels during a psychosocial stress task; diffusion magnetic resonance imaging; and depressive symptoms. In early puberty there were significant associations between higher ELS and decreased cortisol production, and between decreased cortisol production and increased fractional anisotropy in the uncinate fasciculus. Further, increased fractional anisotropy in the uncinate fasciculus predicted higher depressive symptoms in later puberty, above and beyond earlier symptoms. In post hoc analyses, we found that sex moderated several additional associations. We discuss these findings within a broader conceptual model linking ELS, emotion dysregulation, and depression across the transition through puberty, and contend that brain circuits implicated in the control of hypothalamic-pituitary-adrenal axis function should be a focus of continued research.

Irritability and brain volume in adolescents: cross-sectional and longitudinal associations

Irritability is garnering increasing attention in psychiatric research as a transdiagnostic marker of both internalizing and externalizing disorders. These disorders often emerge during adolescence, highlighting the need to examine changes in the brain and in psychological functioning during this developmental period. Adolescents were recruited for a longitudinal study examining the effects of early life stress on the development of psychopathology. The 151 adolescents (73 M/78 F, average age = 11.5 years, standard deviation = 1.1) were scanned with a T1-weighted MRI sequence and parents completed reports of adolescent irritability using the Affective Reactivity Index. Of these 151 adolescents, 94 (46 M/48 F) returned for a second session (average interval = 1.9 years, SD = 0.4). We used tensor-based morphometry to examine cross-sectional and longitudinal associations between irritability and regional brain volume. Irritability was associated with brain volume across a number of regions. More irritable individuals had larger hippocampi, insula, medial orbitofrontal cortex and cingulum/cingulate cortex and smaller putamen and internal capsule. Across the brain, more irritable individuals also had larger volume and less volume contraction in a number of areas that typically decrease in volume over the developmental period studied here, suggesting delayed maturation. These structural changes may increase adolescents' vulnerability for internalizing and externalizing disorders.

Mothers' postpartum sleep disturbance is associated with the ability to sustain sensitivity toward infants

BACKGROUND/OBJECTIVE

Infancy is a period of rapid development when the quality of caregiving behavior may be particularly consequential for children's long-term functioning. During this critical period for caregiving behavior, parents experience changes in their sleep that may affect their ability to provide sensitive care. The current study investigated the association of mothers' sleep disturbance with both levels and trajectories of maternal sensitivity during interactions with their infants.

METHODS

At 18 weeks postpartum, mothers and their infants were observed during a home-based 10-minute "free play" interaction. Mothers' nighttime sleep was objectively measured using actigraphy and subjectively measured using sleep diaries. Maternal sensitivity was coded in two-minute intervals in order to characterize changes in sensitivity across the free play interaction. We used exploratory factor analysis to reduce the dimensionality of the objective and subjective measures of mothers' sleep, identifying a subjective sleep disturbance and an objective sleep continuity factor.

RESULTS

Using multi-level modeling, we found that mothers with poorer objective sleep continuity evidenced decreasing sensitivity toward their infants across the interaction. Mothers' self-reports of sleep disturbance were not associated with maternal sensitivity.

CONCLUSIONS

Although future research is necessary to identify the mechanisms that may explain the observed association between poor sleep continuity and the inability to sustain sensitivity toward infants, mothers' postpartum sleep continuity may be one factor to consider when designing interventions to improve the quality of caregiving.

CLINICAL TRIAL REGISTRATION

Clinicaltrials.gov, NCT01846585.

A person-centered approach to the assessment of early life stress: Associations with the volume of stress-sensitive brain regions in early adolescence

Researchers are becoming increasingly interested in linking specific forms of early life stress (ELS) to specific neurobiological markers, including alterations in the morphology of stress-sensitive brain regions. We used a person-centered, multi-informant approach to investigate the associations of specific constellations of ELS with hippocampal and amygdala volume in a community sample of 211 9- to 13-year-old early adolescents. Further, we compared this approach to a cumulative risk model of ELS, in which ELS was quantified by the total number of stressors reported. Using latent class analysis, we identified three classes of ELS (labeled typical/low, family instability, and direct victimization) that were distinguished by experiences of family instability and victimization. Adolescents in the direct victimization class had significantly smaller hippocampal volume than did adolescents in the typical/low class; ELS classes were not significantly associated with amygdala volume. The cumulative risk model of ELS had a poorer fit than did the person-centered model; moreover, cumulative ELS was not significantly associated with hippocampal or amygdala volume. Our results underscore the utility of taking a person-centered approach to identify alterations in stress-sensitive brain regions based on constellations of ELS, and suggest victimization is specifically associated with hippocampal hypotrophy observed in early adolescence.

Stressful Life Events, ADHD Symptoms, and Brain Structure in Early Adolescence

Despite a growing understanding that early adversity in childhood broadly affects risk for psychopathology, the contribution of stressful life events to the development of symptoms of attention-deficit/hyperactivity disorder (ADHD) is not clear. In the present study, we examined the association between number of stressful life events experienced and ADHD symptoms, assessed using the Attention Problems subscale of the Child Behavior Checklist, in a sample of 214 children (43% male) ages 9.11-13.98 years (M = 11.38, SD = 1.05). In addition, we examined whether the timing of the events (i.e., onset through age 5 years or after age 6 years) was associated with ADHD symptoms. Finally, we examined variation in brain structure to determine whether stressful life events were associated with volume in brain regions that were found to vary as a function of symptoms of ADHD. We found a small to moderate association between number of stressful life events and ADHD symptoms. Although the strength of the associations between number of events and ADHD symptoms did not differ as a function of the age of occurrence of stressful experiences, different brain regions were implicated in the association between stressors and ADHD symptoms in the two age periods during which stressful life events occurred. These findings support the hypothesis that early adversity is associated with ADHD symptoms, and provide insight into possible brain-based mediators of this association.

Associations Among Early Life Stress, Rumination, Symptoms of Psychopathology, and Sex in Youth in the Early Stages of Puberty: a Moderated Mediation Analysis

Despite the high prevalence and substantial costs of early life stress (ELS), the mechanisms through which ELS confers risk for psychopathology are poorly understood, particularly among youth who are in an earlier stage of the transition through puberty. We sought to advance our understanding of the link between ELS and psychopathology by testing whether rumination mediates the relation between ELS and symptoms of psychopathology in youth in the early stages of puberty, and whether sex moderates this mediation. We assessed levels of ELS, both brooding and reflection subtypes of rumination, and internalizing and externalizing symptoms in 170 youth in the early stages of puberty (56% girls) ages 9-13 years. Brooding, but not reflection, mediated the relation between ELS and both internalizing and externalizing symptoms. Importantly, however, sex moderated the relation among ELS, brooding, and symptoms. Specifically, brooding mediated the relation between ELS and both internalizing and externalizing symptoms for girls, but not for boys. Findings support the formulation that brooding is a mechanism linking ELS to multiple forms of behavioral and emotional problems exclusively in girls in the early stages of puberty.

Evidence for a sensitive period in the effects of early life stress on hippocampal volume

Exposure to stress has been causally linked to changes in hippocampal volume (HV). Given that the hippocampus undergoes rapid changes in the first years of life, stressful experiences during this period may be particularly important in understanding individual differences in the development of the hippocampus. One hundred seventy-eight early adolescents (ages 9-13 years; 43% male) were interviewed regarding exposure to and age of onset of experiences of stress; the severity of each stressful event was rated by an objective panel. All participants underwent structural magnetic resonance imaging, from which HVs were automatically segmented. Without considering the age of onset for stressful experiences, there was a small but statistically significant negative association of stress severity with bilateral HV. When considering the age of onset, there was a moderate and significant negative association between stress severity during early childhood (through 5 years of age) and HV; there was no association between stress severity during later childhood (age 6 years and older) and HV. We provide evidence of a sensitive period through 5 years of age for the effects of life stress on HV in adolescence. It will be important in future research to elucidate how reduced HV stemming from early life stress may contribute to stress-related health outcomes.

Maternal depressive symptoms, self-focus, and caregiving behavior

BACKGROUND

Parent-child interactions set the stage for child mental health and development. Given that maternal depressive symptoms are associated with poorer observed caregiving behaviors, examining potential cognitive mediators is important for identifying mechanisms underlying the intergenerational transmission of risk and possible targets for intervention.

METHODS

We assessed depressive symptoms and levels of self-focus and psychological distancing from infant-centered verbal narratives obtained from 54 mothers, and examined caregiving behaviors in a structured interaction with their six-month-old infants.

RESULTS

Higher depressive symptoms were associated with pronoun use in narratives (i.e., greater "I" and reduced "we" use), reflecting increased self-focus and psychological distancing. Further, increased self-focus was associated with lower levels of caregiver warmth, and mediated the association between depressive symptoms and caregiving warmth.

LIMITATIONS

This observational study does not allow for causal interpretations.

CONCLUSION

These findings suggest that the cognitive styles associated with depression interfere with the caregiving relationship, affecting behavior in parent-child interactions that may increase the risk for the intergenerational transmission of depression.

Self-reported neglect, amygdala volume, and symptoms of anxiety in adolescent boys

Experiences of psychosocial neglect affect the developing brain and may place individuals at increased risk for anxiety. The majority of research in this area has focused on children who have experienced severe psychosocial deprivation; it is not clear whether typical variation in neglect experienced in community samples would have the same neurobiological consequences as those documented in extreme samples. The present study examined the associations among self-reported childhood neglect, amygdala volume, and anxiety symptoms in a community sample of 138 adolescents ages 9-15 years (43% male). Linear mixed modeling yielded a three-way interaction of neglect, sex, and brain hemisphere, reflecting a significant positive association between neglect and right amygdala volume in boys. Additional analyses indicated that right amygdala volume significantly mediated the association between neglect and anxiety symptoms in boys. These findings are consistent with previous reports of larger amygdala volumes in previously institutionalized children, and with documented associations between caregiving deprivation and anxiety symptoms. The results suggest that the effects of childhood neglect on limbic structures are sex-specific and lateralized, and provide support for a neural mechanism relating childhood neglect to later difficulties in emotional functioning.

Effects of sensitivity to life stress on uncinate fasciculus segments in early adolescence

Previous research suggests that exposure to early life stress (ELS) affects the structural integrity of the uncinate fasciculus (UF), a frontolimbic white matter tract that undergoes protracted development throughout adolescence. Adolescence is an important transitional period characterized by the emergence of internalizing psychopathology such as anxiety, particularly in individuals with high levels of stress sensitivity. We examined the relations among sensitivity to ELS, structural integrity of the UF, and anxiety symptoms in 104 early adolescents. We conducted structured interviews to assess exposure to ELS and obtained subjective and objective ratings of stress severity, from which we derived an index of ELS sensitivity. We also acquired diffusion MRI and conducted deterministic tractography to visualize UF trajectories and to compute measures of structural integrity from three distinct segments of the UF: frontal, insular, temporal. We found that higher sensitivity to ELS predicted both reduced fractional anisotropy in right frontal UF and higher levels of anxiety symptoms. These findings suggest that fibers in frontal UF, which are still developing throughout adolescence, are most vulnerable to the effects of heightened sensitivity to ELS, and that reduced structural integrity of frontal UF may underlie the relation between early stress and subsequent internalizing psychopathology.

The impact of the severity of early life stress on diurnal cortisol: The role of puberty

Researchers have documented dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis in children and adolescents who experienced early life stress (ELS). The precise nature of this dysregulation, however, has been difficult to discern. In fact, both elevated and blunted patterns of diurnal cortisol regulation have been reported in children and adolescents exposed to greater ELS, including both reduced and heightened cortisol levels and change in cortisol across the day. These divergent findings may be due to developmental changes in the relation between ELS and HPA-axis functioning. The present study was designed to examine the role of puberty in the impact of the severity of ELS on the regulation of diurnal cortisol. Boys and girls (N=145) ages 9-13 years recruited from lower-risk communities completed an interview about their ELS experiences and at-home collection of diurnal cortisol. ELS experiences were objectively coded for severity, and children's level of pubertal development was measured using Tanner Staging. Multi-level piecewise mixed-effects models tested the effects of ELS severity and pubertal stage on cortisol levels at waking, the cortisol awakening response (CAR), and the daytime cortisol slope. While we found no significant interactive effects of pubertal stage and ELS severity on cortisol levels at waking or the daytime cortisol slope, findings indicated that pubertal stage interacted with ELS severity to predict the cortisol awakening response (CAR). Specifically, in earlier puberty, higher ELS was associated with a blunted CAR compared to lower ELS; in contrast, in later puberty, higher ELS was associated with a heightened CAR compared to lower ELS. Differences in the relation between ELS severity and the CAR were uniquely determined by puberty, and not by age. By considering and examining the role of puberty, the current study provides a developmental explanation for previous divergent findings of both blunted and heightened patterns of diurnal cortisol following ELS. These results indicate that careful attention should be given to children's pubertal status before drawing conclusions concerning the nature of diurnal cortisol dysregulation.

Enhanced resolution of experimental ARDS through IL-4-mediated lung macrophage reprogramming

Despite intense investigation, acute respiratory distress syndrome (ARDS) remains an enormous clinical problem for which no specific therapies currently exist. In this study, we used intratracheal lipopolysaccharide or Pseudomonas bacteria administration to model experimental acute lung injury (ALI) and to further understand mediators of the resolution phase of ARDS. Recent work demonstrates macrophages transition from a predominant proinflammatory M1 phenotype during acute inflammation to an anti-inflammatory M2 phenotype with ALI resolution. We tested the hypothesis that IL-4, a potent inducer of M2-specific protein expression, would accelerate ALI resolution and lung repair through reprogramming of endogenous inflammatory macrophages. In fact, IL-4 treatment was found to offer dramatic benefits following delayed administration to mice subjected to experimental ALI, including increased survival, accelerated resolution of lung injury, and improved lung function. Expression of the M2 proteins Arg1, FIZZ1, and Ym1 was increased in lung tissues following IL-4 treatment, and among macrophages, FIZZ1 was most prominently upregulated in the interstitial subpopulation. A similar trend was observed for the expression of macrophage mannose receptor (MMR) and Dectin-1 on the surface of alveolar macrophages following IL-4 administration. Macrophage depletion or STAT6 deficiency abrogated the therapeutic effect of IL-4. Collectively, these data demonstrate that IL-4-mediated therapeutic macrophage reprogramming can accelerate resolution and lung repair despite delayed use following experimental ALI. IL-4 or other therapies that target late-phase, proresolution pathways may hold promise for the treatment of human ARDS.

Trajectories of post-traumatic stress disorder symptoms among youth exposed to both natural and technological disasters

BACKGROUND

Theorists and researchers have demonstrated multiple trajectories of symptoms following disasters (Ecology and Society, 13, 2008, 9), highlighting the importance of obtaining more knowledge about exposed youth who demonstrate resilience as well as those who suffer chronic difficulties. This paper examines trajectories of post-traumatic stress disorder (PTSD) symptoms following exposure to hurricanes and the Deepwater Horizon Oil Spill to increase understanding of resilience and chronic reactions to both natural and technological disasters.

METHODS

A multiwave longitudinal design was used to follow N = 4,619 youth who were evaluated for PTSD symptoms, hurricane exposure, and oil spill exposure/stress at four time points over a period of 4 years. Trajectories were identified with cluster analyses and multilevel modeling.

RESULTS

Individual trajectories were statistically identified consistent with theory. The largest group exhibited stable-low symptoms (52%), a second group showed steep declines following initial symptoms (21%), a third group exhibited increasing symptoms (18%), and a fourth group showed stable-high symptoms (9%). Both hurricane exposure and oil spill stress predicted trajectories and overall levels of PTSD symptoms.

CONCLUSIONS

Results identified an effect of oil spill stress and hurricane exposure on symptom levels and trajectories of exposed youth. Results provide prospective data to support theories of multiple symptom trajectories following disasters and reinforce the importance of research that utilizes a developmental perspective to consider the long-term effects of disasters in youth. Findings highlight the importance of identifying symptoms and predictors of resilience as well as factors that contribute to resilience.

STUDIES ON EASTERN EQUINE ENCEPHALOMYELITIS : VI. FACILITATION OF INFECTION IN THE MOUSE

50 per cent glycerine injected intraperitoneally, intramuscularly, or intravenously, greatly enhances the activity of equine encephalomyelitis virus injected intramuscularly, increasing its virulence up to 100-fold. The same effect is produced by very concentrated sodium chloride. The result appears due to dehydration of the nervous system, suddenly produced. Gradual withdrawal of body fluids, produced by depriving animals of drinking water, results in sharp concentration of the blood, equal to that produced by glycerine or salt. But such deprivation of water alone does not result in significant dehydration of the brain, nor does it have any effect on virus action. The facilitation effect is not produced by drastic procedures involving shifts of electrolytes without loss of total water from the brain. Glycerine has no facilitating action when the virus is administered intranasally or intraocularly, suggesting a fundamental difference in pathogenesis between these routes and the intramuscular.

STUDIES ON EASTERN EQUINE ENCEPHALOMYELITIS : III. INTRAOCULAR INFECTION WITH FIXED VIRUS IN THE GUINEA PIG

The behavior of a fixed strain of Eastern equine encephalomyelitis virus was studied in guinea pigs after intraocular inoculation. Such inoculation concerns the central and not the peripheral nervous system. The susceptibility to intraocular injection lies midway between the highly virulent intracerebral and the quite avirulent peripheral routes. The virus must act for 10 to 13 hours in order to induce a fatal infection. Removal of the inoculated eyeball before this interval almost always prevents fatality although it may allow immunity to develop. The virus, at suitable intervals after injection into the eye, may be recovered from successive and appropriate optic centers before it is demonstrable in non-optic portions. Approximately 24 hours are required for the virus to reach a significant concentration in the contralateral geniculate body, 36 hours in the contralateral visual cortex. Significant amounts of virus may be present in the optic chiasm and tract prior to involvement of the higher centers. Virus placed in contact with the retina produces an insignificant, essentially non-specific reaction comparable to that produced at the site of direct intracerebral inoculation. In the retina there is no ganglion cell necrosis unless there is a complicating intraocular infection. In the cerebral visual centers the first reaction is inflammatory and interstitial, and may appear in the lateral geniculate body as early as 24 hours after injection. Neuronal necrosis is not the primary action of the virus on the nervous system in these experiments. The distribution of lesions in the brain is in excellent agreement with the method of direct testing for virus content, and is far more accurate than the latter. The virus in its primary distribution through the nervous system follows the nerve pathways of the optic system. This occurs within the central nervous system, where presumably there is first an involvement of the nerve cell body and then a spread along the cell process or axone.

ENCEPHALOPATHY FOLLOWING INJECTIONS OF BONE MARROW EXTRACT

Monkey bone marrow extract when injected intracerebrally into guinea pigs or rabbits produces a distinctive encephalopathy. The Purkinje cells are severely affected, especially those at the periphery of the cerebellum. Nuclear alterations first appear, with well marked intranuclear acidophilic inclusion bodies. Similar inclusions appear at a little later stage in the ectodermal glia. The affected cells later become necrotic and usually disappear. The reaction is essentially glial and non-inflammatory, and hence is called encephalopathy rather than encephalitis. A hyaline necrosis of cerebral blood vessels, especially at the base of the brain, is described. Small areas of softening may appear in the cerebellum as a result, but this is considered a secondary process, independent of the Purkinje cell loss. There may also inconstantly be found a loss of cerebellar granule cells and a selective necrosis of the hippocampal pyramidal cells. Secondary and reparative reactions are described. Similar changes are produced by extracts of lymph nodes from Hodgkin's disease, and by leucocytic cream of human blood. A tentative explanation of the pathogenesis is suggested, and similarities to certain virus diseases are pointed out.

EXPERIMENTAL ENCEPHALITIS : SOME FACTORS AFFECTING INFECTION WITH CERTAIN NEUROTROPIC VIRUSES

The action on mice of several neurotropic viruses was studied with reference to factors which influence infection. With pseudorabies virus, section of the sciatic nerve with inoculation into the ipsilateral foot pad significantly retarded the speed of infection. The virus ascended other nerves of the leg, but at a slower rate. It would appear that the number of nerve fibers available for passage may play a rôle in the speed with which infection occurs with this virus. When pseudorabies virus was inoculated into an area of inflammation its effects were markedly lessened. Similar experiments with unmodified equine encephalomyelitis virus which, unlike pseudorabies, does not ascend along local nerves, showed no impedance of infection. Brain trauma did not change the rate of infection with the viruses of St. Louis encephalitis, herpes, or pseudorabies. But intraperitoneal injection of glycerine, followed by intramuscular inoculation of St. Louis virus, resulted in marked facilitation of infection, as already remarked of fixed equine encephalomyelitis virus. This phenomenon did not occur with pseudorabies or herpes. In contrast to certain other viruses, pseudorabies and herpes viruses were only slightly more effective in young mice than in adults. With St. Louis virus, as with fixed equine encephalomyelitis viruses, inoculation into the eye or nose was far more effective than other peripheral routes. This was not the case with pseudorabies. Herpes, however, also showed greater sensitivity of the intraocular route. After injection into the eye, St. Louis and fixed equine encephalomyelitis viruses invaded the optic pathway, while herpes and pseudorabies avoided the optic fibers and attacked the trigeminal nerve. These phenomena are discussed in the light of cellufugal and cellupetal progression of viruses. The similarities in the action of fixed equine encephalomyelitis and St. Louis encephalitis viruses are discussed and contrasted with herpes and pseudorabies.

STUDIES ON EASTERN EQUINE ENCEPHALOMYELITIS : I. HISTOPATHOLOGY OF THE NERVOUS SYSTEM IN THE GUINEA PIG

The action of the virus of equine encephalomyelitis in the guinea pig brain has been studied, and various histological changes have been described in detail. After peripheral inoculation (as in the pad) the earliest detectable pathologic change in the nervous system is the accumulation of leucocytes within the lumen of blood vessels, and the proliferation of the vascular adventitia. This precedes the appearance of any significant perivascular cuffing, and may or may not be accompanied by a few polymorphonuclear leucocytes in the tissue. The typical lesion is a fairly well circumscribed focus of polymorphonuclear leucocytes accompanying the blood vessel changes described above. The leucocytes may be numerous or sparse, and may or may not be accompanied by neuronal destruction. In early cases, before the onset of symptoms, such circumscribed lesions appear in small number irregularly scattered through the gray matter. The neo- and olfactory cortices are the principal sites of predilection, although basal ganglia, thalamus, cerebellum, and lower olfactory centers may also be involved. The hippocampus is much less affected than other parts of the brain. A rough distinction is made between inflammatory and degenerative lesions, a distinction which depends on the relationship between the neuronal destruction and the exudative changes in any given site. These two types are described, and their significance is discussed. After intracerebral inoculation, the inflammatory changes are much less marked than after peripheral inoculation. This is due not to insufficient time for the development of lesions but to a different type of pathological process. Following intracerebral inoculation, there is primary destruction of neurones, involving especially the hippocampus, and also large areas of the neo-cortex. This change, similar to ischemic necrosis, is regarded in part as a non-specific reaction of especially vulnerable tissue.

STUDIES ON EASTERN EQUINE ENCEPHALOMYELITIS : II. PATHOGENESIS OF THE DISEASE IN THE GUINEA PIG

After inoculation with equine encephalomyelitis virus by various routes, guinea pigs were sacrificed at early stages, before symptoms were apparent. The brains were studied histologically, with serial sections; all lesions were noted, and subjected to topographical analysis. Nine cases are presented in detail. With any given mode of inoculation the distribution of lesions varied very widely from one instance to another. In some cases, affected regions bore a striking and definite anatomical relationship to each other. These distributions can be explained only by the assumption that the anatomical pathways played some rôle in the spread of the virus. In other instances lesions were present in areas, the anatomical connections of which were entirely normal. Attention is called to the frequency of lesions in the neocortex, with intact subcortical centers. Such distribution is held to render nerve spread extremely improbable. The only satisfactory explanation of such random distributions is by direct passage of virus from the blood stream into the brain tissue. There is no histological difference between lesions which result from blood spread and those resulting from nerve spread.

STUDIES ON EASTERN EQUINE ENCEPHALOMYELITIS : V. HISTOPATHOLOGY IN THE MOUSE

In mice affected with equine encephalomyelitis, the first pathological disturbance in infant animals is an inflammatory reaction, which is usually less pronounced in adult animals. A characteristic type of parenchymal damage appears to be independent of the inflammation. In such foci of injury there is initially a vacuolation of intercellular tissue. Neurones in such areas are at first intact, later show cytoplasmic changes, and finally nuclear alterations. Complete disintegration of tissue and all its elements may be the end result.