Associations Between Midlife Menopausal Hormone Therapy Use, Incident Diabetes, and Late Life Memory in the Wisconsin Longitudinal Study

BACKGROUND

Prior research suggests a link between menopausal hormone therapy (MHT) use, memory function, and diabetes risk. The menopausal transition is a modifiable period to enhance long-term health and cognitive outcomes, although studies have been limited by short follow-up periods precluding a solid understanding of the lasting effects of MHT use on cognition.

OBJECTIVE

We examined the effects of midlife MHT use on subsequent diabetes incidence and late life memory performance in a large, same-aged, population-based cohort. We hypothesized that the beneficial effects of MHT use on late life cognition would be partially mediated by reduced diabetes risk.

METHODS

1,792 women from the Wisconsin Longitudinal Study (WLS) were included in analysis. We employed hierarchical linear regression, Cox regression, and causal mediation models to test the associations between MHT history, diabetes incidence, and late life cognitive performance.

RESULTS

1,088/1,792 women (60.7%) reported a history of midlife MHT use and 220/1,792 (12.3%) reported a history of diabetes. MHT use history was associated with better late life immediate recall (but not delayed recall), as well as a reduced risk of diabetes with protracted time to onset. Causal mediation models suggest that the beneficial effect of midlife MHT use on late life immediate recall were at least partially mediated by diabetes risk.

CONCLUSION

Our data support a beneficial effect of MHT use on late life immediate recall (learning) that was partially mediated by protection against diabetes risk, supporting MHT use in midlife as protective against late life cognitive decline and adverse health outcomes.

Associations of the Lifestyle for Brain Health index with longitudinal cognition and brain amyloid beta in clinically unimpaired older adults: Findings from the Wisconsin Registry for Alzheimer's Prevention

Introduction

Modifiable health and lifestyle factors increase risk of dementia, but whether modifiable factors, when measured in late-midlife, impact the emergence or progression of Alzheimer's disease (AD) pathophysiologic or cognitive changes remains unresolved.

Methods

In initially cognitively unimpaired, late middle-aged participants (N = 1215; baseline age, M [standard deviation] = 59.3 [6.7] years) from the Wisconsin Registry for Alzheimer's Prevention (WRAP), we investigated the influence of the Lifestyle for Brain Health (LIBRA) index, a lifestyle-based dementia risk score, on AD-related cognitive trajectories and amyloid beta (Aβ) plaque accumulation.

Results

Overall, lower baseline LIBRA, denoting healthier lifestyle and lower dementia risk, was related to better overall cognitive performance, but did not moderate apolipoprotein E ε4 or Aβ-related longitudinal cognitive trajectories. LIBRA was not significantly associated with Aβ accumulation or estimated age of Aβ onset.

Discussion

In WRAP, late-midlife LIBRA scores were related to overall cognitive performance, but not AD-related cognitive decline or Aβ accumulation in the preclinical timeframe.

Highlights

The Lifestyle for Brain Health (LIBRA) index was associated with cognitive performance in late-midlife.LIBRA did not moderate apolipoprotein E ε4 or amyloid-related cognitive decline.LIBRA was not associated with the onset or accumulation of amyloid plaques.

Assessing Dementia Prevalence in the Wisconsin Longitudinal Study: Cohort Profile, Protocol, and Preliminary Findings

BACKGROUND

There is growing consensus that non-genetic determinants of dementia can be linked to various risk- and resiliency-enhancing factors accumulating throughout the lifespan, including socioeconomic conditions, early life experiences, educational attainment, lifestyle behaviors, and physical/mental health. Yet, the causal impact of these diverse factors on dementia risk remain poorly understood due to few longitudinal studies prospectively characterizing these influences across the lifespan.

OBJECTIVE

The Initial Lifespan's Impact on Alzheimer's Disease and Related Dementia (ILIAD) study aims to characterize dementia prevalence in the Wisconsin Longitudinal Study (WLS), a 60-year longitudinal study documenting life course trajectories of educational, family, occupational, psychological, cognitive, and health measures.

METHODS

Participants are surveyed using the modified Telephone Interview for Cognitive Status (TICS-m) to identify dementia risk. Those scoring below cutoff undergo home-based neuropsychological, physical/neurological, and functional assessments. Dementia diagnosis is determined by consensus panel and merged with existing WLS data for combined analysis.

RESULTS

Preliminary findings demonstrate the initial success of the ILIAD protocol in detecting dementia prevalence in the WLS. Increasing age, hearing issues, lower IQ, male sex, APOE4 positivity, and a steeper annualized rate of memory decline assessed in the prior two study waves, all increased likelihood of falling below the TICS-m cutoff for dementia risk. TICS-m scores significantly correlated with standard neuropsychological performance and functional outcomes.

CONCLUSION

We provide an overview of the WLS study, describe existing key lifespan variables relevant to studies of dementia and cognitive aging, detail the current WLS-ILIAD study protocol, and provide a first glimpse of preliminary study findings.

A pilot protocol to assess the feasibility of a virtual multiple crossover, randomized controlled trial design using methylphenidate in mild cognitive impairment

BACKGROUND

The conventional clinical trial design in Alzheimer's disease (AD) and AD-related disorders (ADRDs) is the parallel-group randomized controlled trial. However, in heterogeneous disorders like AD/ADRDs, this design requires large sample sizes to detect meaningful effects in an "average" patient. They are very costly and, despite many attempts, have not yielded new treatments for many years. An alternative, the multi-crossover, randomized control trial (MCRCT) is a design in which each patient serves as their own control across successive, randomized blocks of active treatment and placebo. This design overcomes many limitations of parallel-group trials, yielding an unbiased assessment of treatment effect at the individual level ("N-of-1") regardless of unique patient characteristics. The goal of the present study is to pilot a MCRCT of a potential symptomatic treatment, methylphenidate, for mild-stage AD/ADRDs, testing feasibility and compliance of participants in this design and efficacy of the drug using both standard and novel outcome measures suited for this design.

METHODS

Ten participants with mild cognitive impairment or mild-stage dementia due to AD/ADRDs will undergo a 4-week lead-in period followed by three, month-long treatment blocks (2 weeks of treatment with methylphenidate, 2 weeks placebo in random order). This trial will be conducted entirely virtually with an optional in-person screening visit. The primary outcome of interest is feasibility as measured by compliance and retention, with secondary and exploratory outcomes including cognition as measured by neuropsychological assessment at the end of each treatment period and daily brain games played throughout the study, actigraphy, and neuropsychiatric and functional assessments.

DISCUSSION

This pilot study will gauge the feasibility of conducting a virtual MCRCT for symptomatic treatment in early AD/ADRD. It will also compare home-based daily brain games with standard neuropsychological measures within a clinical trial for AD/ADRD. Particular attention will be paid to compliance, tolerability of drug and participation, learning effects, trends and stability of daily measures across blocks, medication carryover effects, and correlations between standard and brief daily assessments. These data will provide guidance for more efficient trial design and the use of potentially more robust, ecological outcome measures in AD/ADRD research.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03811847 . Registered on 21 January 2019.

Cerebrospinal fluid and plasma biomarkers in individuals at risk for genetic prion disease

BACKGROUND

Prion disease is neurodegenerative disease that is typically fatal within months of first symptoms. Clinical trials in this rapidly declining symptomatic patient population have proven challenging. Individuals at high lifetime risk for genetic prion disease can be identified decades before symptom onset and provide an opportunity for early therapeutic intervention. However, randomizing pre-symptomatic carriers to a clinical endpoint is not numerically feasible. We therefore launched a cohort study in pre-symptomatic genetic prion disease mutation carriers and controls with the goal of evaluating biomarker endpoints that may enable informative trials in this population.

METHODS

We collected cerebrospinal fluid (CSF) and blood from pre-symptomatic individuals with prion protein gene (PRNP) mutations (N = 27) and matched controls (N = 16), in a cohort study at Massachusetts General Hospital. We quantified total prion protein (PrP) and real-time quaking-induced conversion (RT-QuIC) prion seeding activity in CSF and neuronal damage markers total tau (T-tau) and neurofilament light chain (NfL) in CSF and plasma. We compared these markers cross-sectionally, evaluated short-term test-retest reliability over 2-4 months, and conducted a pilot longitudinal study over 10-20 months.

RESULTS

CSF PrP levels were stable on test-retest with a mean coefficient of variation of 7% for both over 2-4 months in N = 29 participants and over 10-20 months in N = 10 participants. RT-QuIC was negative in 22/23 mutation carriers. The sole individual with positive RT-QuIC seeding activity at two study visits had steady CSF PrP levels and slightly increased tau and NfL concentrations compared with the others, though still within the normal range, and remained asymptomatic 1 year later. T-tau and NfL showed no significant differences between mutation carriers and controls in either CSF or plasma.

CONCLUSIONS

CSF PrP will be interpretable as a pharmacodynamic readout for PrP-lowering therapeutics in pre-symptomatic individuals and may serve as an informative surrogate biomarker in this population. In contrast, markers of prion seeding activity and neuronal damage do not reliably cross-sectionally distinguish mutation carriers from controls. Thus, as PrP-lowering therapeutics for prion disease advance, "secondary prevention" based on prodromal pathology may prove challenging; instead, "primary prevention" trials appear to offer a tractable paradigm for trials in pre-symptomatic individuals.

The effect of white matter signal abnormalities on default mode network connectivity in mild cognitive impairment

Regions within the default mode network (DMN) are particularly vulnerable to Alzheimer's disease pathology and mechanisms of DMN disruption in mild cognitive impairment (MCI) are still unclear. White matter lesions are presumed to be mechanistically linked to vascular dysfunction whereas cortical atrophy may be related to neurodegeneration. We examined associations between DMN seed‐based connectivity, white matter lesion load, and cortical atrophy in MCI and cognitively healthy controls. MCI showed decreased functional connectivity (FC) between the precuneus‐seed and bilateral lateral temporal cortex (LTC), medial prefrontal cortex (mPFC), posterior cingulate cortex, and inferior parietal lobe compared to those with controls. When controlling for white matter lesion volume, DMN connectivity differences between groups were diminished within bilateral LTC, although were significantly increased in the mPFC explained by significant regional associations between white matter lesion volume and DMN connectivity only in the MCI group. When controlling for cortical thickness, DMN FC was similarly decreased across both groups. These findings suggest that white matter lesions and cortical atrophy are differentially associated with alterations in FC patterns in MCI. Associations between white matter lesions and DMN connectivity in MCI further support at least a partial but important vascular contribution to age‐associated neural and cognitive impairment.

Are primary and secondary types of brain anomalies exclusive factors affecting the attention networks in individuals with spina bifida?

OBJECTIVE

Individuals with spina bifida myelomeningocele (SBM) frequently exhibit cognitive impairments on tasks mediated by brain regions involved in the posterior attention network. Although such deficits have been historically assumed to result from primary and secondary brain insults, there is a dearth of literature regarding whether sequential versus simultaneous surgical closure of neural folds and surgical shunt placement affect neuropsychological function and brain structure of attention networks that have been widely studied in individuals with SBM. The current study addressed these gaps in a large cohort of children and adults with SBM.

METHOD

White matter pathways and regional brain volumes of anterior and posterior attention networks were quantified through probabilistic tractography and automated segmentation, respectively. The Child Attention Network Test measured behavioral components of posterior and anterior attention networks.

RESULTS

Sequential operations were associated with reduced orienting accuracy and smaller left superior parietal and dorsolateral prefrontal cortex volumes compared to simultaneous operations, controlling for a number of shunt revisions and age. Greater number of shunt revisions was associated with higher radial diffusivity values in the parietal tectocortical pathway. Older participants had greater accuracy and faster conflict resolution performance compared to younger participants, across operation type and number of shunt revisions.

CONCLUSIONS

Shunt treatment and revision history related to brain structure and functions associated with the posterior attention network. Neurosurgical history also differentiated the harmful effects of early hydrocephalus on brain structure of the posterior from the anterior attention networks in SBM. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Task-related fMRI BOLD response to hyperinsulinemia in healthy older adults

BACKGROUND

There is growing evidence to suggest that the brain is an important target for insulin action, and that states of insulin resistance may extend to the CNS with detrimental effects on cognitive functioning. Although the effect of systemic insulin resistance on peripheral organs is well-studied, the degree to which insulin impacts brain function in vivo remains unclear.

METHODS

This randomized, single-blinded, 2-way-crossover, sham-controlled, pilot study determined the effects of hyperinsulinemia on fMRI brain activation during a 2-back working memory task in 9 healthy older adults (aged 57-79 years). Each participant underwent two clamp procedures (an insulin infusion and a saline placebo infusion, with normoglycemia maintained during both conditions), to examine the effects of hyperinsulinemia on task performance and associated blood-oxygen-level dependent (BOLD) signal using fMRI.

RESULTS

Hyperinsulinemia (compared to saline control) was associated with an increase in both the spatial extent and relative strength of task-related BOLD signal during the 2-back task. Further, the degree of increased task-related activation in select brain regions correlated with greater systemic insulin sensitivity, as well as decreased reaction times and performance accuracy between experimental conditions.

CONCLUSION

Together, these findings provide evidence of insulin action in the CNS among older adults during periods of sustained cognitive demand, with the greatest effects noted for individuals with highest systemic insulin sensitivity.

FUNDING

This work was funded by the National Institutes of Health (5R21AG051958, 2016).

Cortical Thickness and Local Gyrification in Children with Developmental Dyslexia

Developmental dyslexia is frequently associated with atypical brain structure and function within regions of the left hemisphere reading network. To date, few studies have employed surface-based techniques to evaluate cortical thickness and local gyrification in dyslexia. Of the existing cortical thickness studies in children, many are limited by small sample size, variability in dyslexia identification, and the recruitment of prereaders who may or may not develop reading impairment. Further, no known study has assessed local gyrification index (LGI) in dyslexia, which may serve as a sensitive indicator of atypical neurodevelopment. In this study, children with dyslexia (n = 31) and typically decoding peers (n = 45) underwent structural magnetic resonance imaging to assess whole-brain vertex-wise cortical thickness and LGI. Children with dyslexia demonstrated reduced cortical thickness compared with controls within previously identified reading areas including bilateral occipitotemporal and occipitoparietal regions. Compared with controls, children with dyslexia also showed increased gyrification in left occipitotemporal and right superior frontal cortices. The convergence of thinner and more gyrified cortex within the left occipitotemporal region among children with dyslexia may reflect its early temporal role in processing word forms, and highlights the importance of the ventral stream for successful word reading.

Biomarkers in Alzheimer's, Frontotemporal, Lewy Body, and Vascular Dementias

This article reviews the current evidence base for biomarkers of the most common causes of dementia in later life: Alzheimer's disease (AD), frontotemporal lobar degenerations, Lewy body dementias, and vascular cognitive impairment and dementia. Biomarkers are objectively measurable indicators of normal physiology, pathological processes, or response to an intervention. Ideally, they are sensitive, specific, easy to obtain, and closely reflect the underlying biological processes of interest. While such markers are well established and in broad clinical use for common disorders in general medicine (e.g., thallium stress tests for coronary artery disease or serum blood urea nitrogen and creatinine for renal failure), analogous, validated markers for AD or other common dementias are limited, although biomarkers in research settings and specialty dementia clinics are progressing toward clinical use. By way of introducing current and future biomarkers for dementias of later life, this article will benefit the practicing clinician by increasing awareness of the availability and utility of current and emerging biomarkers in dementia diagnosis and prognosis and for monitoring new disease-modifying therapeutics that arrive in the clinic over the coming decade.

FMRI activity during associative encoding is correlated with cardiorespiratory fitness and source memory performance in older adults

Older adults (OA), relative to young adults (YA), exhibit age-related alterations in functional Magnetic Resonance Imaging (fMRI) activity during associative encoding, which contributes to deficits in source memory. Yet, there are remarkable individual differences in brain health and memory performance among OA. Cardiorespiratory fitness (CRF) is one individual difference factor that may attenuate brain aging, and thereby contribute to enhanced source memory in OA. To examine this possibility, 26 OA and 31 YA completed a treadmill-based exercise test to evaluate CRF (peak VO₂) and fMRI to examine brain activation during a face-name associative encoding task. Our results indicated that in OA, peak VO₂ was positively associated with fMRI activity during associative encoding in multiple regions including bilateral prefrontal cortex, medial frontal cortex, bilateral thalamus and left hippocampus. Next, a conjunction analysis was conducted to assess whether CRF influenced age-related differences in fMRI activation. We classified OA as high or low CRF and compared their activation to YA. High fit OA (HFOA) showed fMRI activation more similar to YA than low fit OA (LFOA) (i.e., reduced age-related differences) in multiple regions including thalamus, posterior and prefrontal cortex. Conversely, in other regions, primarily in prefrontal cortex, HFOA, but not LFOA, demonstrated greater activation than YA (i.e., increased age-related differences). Further, fMRI activity in these brain regions was positively associated with source memory among OA, with a mediation model demonstrating that associative encoding activation in medial frontal cortex indirectly influenced the relationship between peak VO₂ and subsequent source memory performance. These results indicate that CRF may contribute to neuroplasticity among OA, reducing age-related differences in some brain regions, consistent with the brain maintenance hypothesis, but accentuating age-differences in other regions, consistent with the brain compensation hypothesis.

Cardiorespiratory fitness is differentially associated with cortical thickness in young and older adults

Aging is associated with reductions in gray matter volume and cortical thickness. One factor that may play a role in mitigating age-associated brain decline is cardiorespiratory fitness (CRF). Although previous work has identified a positive association between CRF and gray matter volume, the relationship between CRF and cortical thickness, which serves as a more sensitive indicator of gray matter integrity, has yet to be assessed in healthy young and older adults. To address this gap in the literature, 32 young and 29 older adults completed treadmill-based progressive maximal exercise testing to assess CRF (peak VO₂), and structural magnetic resonance imaging (MRI) to determine vertex-wise surface-based cortical thickness metrics. Results indicated a significant CRF by age group interaction such that Peak VO₂ was associated with thicker cortex in older adults but with thinner cortex in young adults. Notably, the majority of regions demonstrating a positive association between peak VO₂ and cortical thickness in older adults overlapped with brain regions showing significant age-related cortical thinning. Further, when older adults were categorized as high or low fit based on normative data, we observed a stepwise pattern whereby cortex was thickest in young adults, intermediate in high fit older adults and thinnest in low fit older adults. Overall, these results support the notion that CRF-related neuroplasticity may reduce although not eliminate age-related cortical atrophy.

White matter integrity of cerebellar-cortical tracts in reading impaired children: A probabilistic tractography study

Little is known about the white matter integrity of cerebellar-cortical pathways in individuals with dyslexia. Building on previous findings of decreased volume in the anterior lobe of the cerebellum, we utilized novel cerebellar segmentation procedures and probabilistic tractography to examine tracts that connect the anterior lobe of the cerebellum and cortical regions typically associated with reading: the temporoparietal (TP), occipitotemporal (OT), and inferior frontal (IF) regions. The sample included 29 reading impaired children and 27 typical readers. We found greater fractional anisotropy (FA) for the poor readers in tracts connecting the cerebellum with TP and IF regions relative to typical readers. In the OT region, FA was greater for the older poor readers, but smaller for the younger ones. This study provides evidence for discrete, regionally-bound functions of the cerebellum and suggests that projections from the anterior cerebellum appear to have a regulatory effect on cortical pathways important for reading.

Gray matter integrity within regions of the dorsolateral prefrontal cortical-subcortical network predicts executive function and fine motor dexterity in spina bifida

OBJECTIVES

This study examined microstructural properties of cortical and subcortical gray matter components of the dorsolateral prefrontal (DLPFC) cortical-subcortical circuit in relation to parent-rated executive function and fine motor dexterity performance in youth with spina bifida myelomeningocele (SBM). Aberrant gray matter integrity of the DLPFC, basal ganglia nuclei, and thalamus were hypothesized to differentially relate to neurobehavioral outcomes.

METHODS

Forty-nine youth between 8 and 18 years (M = 12.34) old with SBM underwent a 3T MRI including diffusion tensor imaging. Neurobehavioral measures of parent-rated executive function and fine motor dexterity were obtained from a standardized neuropsychological evaluation. Relations among indices of gray matter microstructural integrity (mean diffusivity [MD], fractional anisotropy [FA], cortical thickness) and neurobehavior were examined using 3 correlational methods to enhance reliability of brain-behavior relations.

RESULTS

In SBM, higher FA values in the caudate were associated with poorer behavioral regulation. Higher FA values in the putamen and greater DLPFC thickness were both associated with poorer fine motor dexterity.

CONCLUSION

Behavioral regulation and FA in the caudate related to behavioral inhibition in SBM. Similarly, associations between fine motor dexterity and indices of gray matter integrity in the putamen and DLPFC support fronto-striatal involvement in motor control in SBM. Examination of these neurobehavioral correlates revealed a pattern of attenuated behavioral impairments when gray matter structure was more similar to that of typically developing youth. (PsycINFO Database Record

Postshunt lateral ventricular volume, white matter integrity, and intellectual outcomes in spina bifida and hydrocephalus

OBJECT

No previous reports exist that have evaluated the relationships of white matter (WM) integrity with the number of shunt revisions, ventricular volume after shunting, and cognition in medically stable children who have spina bifida and hydrocephalus (SBH). The authors hypothesized that enlarged ventricles and a greater number of shunt revisions decrease WM integrity in children.

METHODS

In total, 80 children (mean age 13.7 years) who had SBH underwent MRI and IQ testing. Probabilistic diffusion tractography was performed to determine mean diffusion tensor imaging (DTI) metrics along the frontal and parietal tectocortical pathways. The DTI metrics were evaluated for significant correlation with a composite IQ measure and with the total number of shunt revisions and the total lateral ventricular volume obtained through semiautomated parcellation of T1-weighted MRI scans.

RESULTS

An enlargement in total lateral ventricle volume and an increase in the number of shunt revisions were both associated with higher fractional anisotropy (FA) and with lower radial diffusivity (RD) along both frontal and parietal tectocortical pathways. Children who had not undergone a shunt revision had on average a greater lateral ventricle volume and higher FA and lower RD along frontal and parietal pathways than those who had undergone multiple shunt revisions. The mean DTI metrics along parietal pathways predicted IQ scores, but intellectual ability was not significantly correlated with ventricular volume or with the number of lifetime shunt revisions.

CONCLUSIONS

Significant changes in DTI metrics were observed as a function of ventricular volume. An increased lateral ventricle volume was associated with elevated FA and decreased RD. Given that the participants were medically stable at the time of the MRI examination, the results suggested that those who have enlarged ventricles show a DTI pattern consistent with axonal compression due to increased intracranial pressure (ICP) in attenuated hydrocephalus. Although limited by a cross-sectional design, the study's findings suggest that DTI metrics may serve as sensitive indicators for chronic, mild hydrocephalus in the absence of overt clinical symptoms due to increased ICP. Having enlarged ventricles and undergoing multiple shunt revisions did not affect intellectual ability in children with SBH.

Attention in spina bifida myelomeningocele: Relations with brain volume and integrity

This study investigated the relations of tectal volume and superior parietal cortex, as well as alterations in tectocortical white matter connectivity, with the orienting and executive control attention networks in individuals with spina bifida myelomeningocele (SBM). Probabilistic diffusion tractography and quantification of tectal and superior parietal cortical volume were performed on 74 individuals aged 8–29 with SBM and a history of hydrocephalus. Behavioral assessments measured posterior (covert orienting) and anterior (conflict resolution, attentional control) attention network functions. Reduced tectal volume was associated with slower covert orienting; reduced superior parietal cortical volume was associated with slower conflict resolution; and increased axial diffusivity and radial diffusivity along both frontal and parietal tectocortical pathways were associated with reduced attentional control. Results suggest that components of both the orienting and executive control attention networks are impaired in SBM. Neuroanatomical disruption to the orienting network appears more robust and a direct consequence of characteristic midbrain dysmorphology; whereas, executive control difficulties may emerge from parietal cortical anomalies and reduced frontal and parietal cortical–subcortical white matter pathways susceptible to the pathophysiological effects of congenital hydrocephalus.

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We use robust correlations to model structure–function relations.

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We use a large sample of individuals with spina bifida myelomeningocele.

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Reduced tectal volume is associated with slower covert orienting.

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Reduced superior parietal cortical volume is associated with slower conflict resolution.

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Tectocortical pathways are associated with reduced attentional control.

Anatomical and diffusion MRI of deep gray matter in pediatric spina bifida

Individuals with spina bifida myelomeningocele (SBM) exhibit brain abnormalities in cortical thickness, white matter integrity, and cerebellar structure. Little is known about deep gray matter macro- and microstructure in this population. The current study utilized volumetric and diffusion-weighted MRI techniques to examine gray matter volume and microstructure in several subcortical structures: basal ganglia nuclei, thalamus, hippocampus, and amygdala. Sixty-six children and adolescents (ages 8–18; M = 12.0, SD = 2.73) with SBM and typically developing (TD) controls underwent T₁- and diffusion-weighted neuroimaging. Microstructural results indicated that hippocampal volume was disproportionately reduced, whereas the putamen volume was enlarged in the group with SBM. Microstructural analyses indicated increased mean diffusivity (MD) and fractional anisotropy (FA) in the gray matter of most examined structures (i.e., thalamus, caudate, hippocampus), with the putamen exhibiting a unique pattern of decreased MD and increased FA. These results provide further support that SBM differentially disrupts brain regions whereby some structures are volumetrically normal whereas others are reduced or enlarged. In the hippocampus, volumetric reduction coupled with increased MD may imply reduced cellular density and aberrant organization. Alternatively, the enlarged volume and significantly reduced MD in the putamen suggest increased density.

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Spina bifida resulted in reduced hippocampal and enlarged putamen volumes.

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Spina bifida resulted in reduced MD and increased FA in the putamen.

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Periventricular regions were differentiated by increased MD and FA in spina bifida.

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Spina bifida resulted in greater FA for all regions, except the hippocampus.

Examination of frontal and parietal tectocortical attention pathways in spina bifida meningomyelocele using probabilistic diffusion tractography

Abnormalities of the midbrain tectum are common but variable malformations in spina bifida meningomyelocele (SBM) and have been linked to neuropsychological deficits in attention orienting. The degree to which variations in tectum structure influence white matter (WM) connectivity to cortical regions is unknown. To assess the relationship of tectal structure and connectivity to frontal and parietal cortical regions, probabilistic diffusion tractography was performed on 106 individuals (80 SBM, 26 typically developing [TD]) to isolate anterior versus posterior tectocortical WM pathways. Results showed that those with SBM exhibited significantly reduced tectal volume, along with decreased fractional anisotropy (FA) in posterior but not anterior tectocortical WM pathways when compared with TD individuals. The group with SBM also showed greater within-subject discrepancies between frontal and parietal WM integrity compared with the TD group. Of those with SBM, qualitative classification of tectal beaking based on radiological review was associated with increased axial diffusivity across both anterior and posterior tectocortical pathways, relative to individuals with SBM and a normal appearing tectum. These results support previous volumetric findings of greater impairment to posterior versus anterior brain regions in SBM, and quantifiably relate tectal volume, tectocortical WM integrity, and tectal malformations in this population.

Associations between T1 white matter lesion volume and regional white matter microstructure in aging

White matter lesions, typically manifesting as regions of signal intensity abnormality (WMSA) on MRI, increase in frequency with age. However, the role of this damage in cognitive decline and disease is still not clear, as lesion volume has only loosely been associated with clinical status. Diffusion tensor imaging (DTI) has been used to examine the quantitative microstructural integrity of white matter, and has applications in the examination of subtle changes to tissue that appear visually normal on conventional imaging. The primary goal of this study was to determine whether major macrostructural white matter damage, (total WMSA volume), is associated with microstructural integrity of normal appearing white matter, and if these macrostructural changes fully account for microstructural changes. Imaging was performed in 126 nondemented individuals, ages 43-85 years, with no history of cerebrovascular disease. Controlling for age, greater WMSA volume was associated with decreased fractional anisotropy (FA) in widespread brain regions. Patterns were similar for FA and radial diffusivity but in contrast, WMSA was associated with axial diffusivity in fewer areas. Age was associated with FA in several regions, and many of these effects remained even when controlling for WMSA volume, suggesting the etiology of WMSAs does not fully account for all age-associated white matter deterioration. These results provide evidence that WMSA volume is associated with the integrity of normal-appearing white matter. In addition, our results suggest that overt lesions may not account for the association of increasing age with decreased white matter tissue integrity.

Interindividual variation in serum cholesterol is associated with regional white matter tissue integrity in older adults

Prior research has demonstrated links among vascular health and the occurrence of stroke, mild cognitive decline, and dementia in older adults. However, little is known about whether normal variation in vascular indicators may be related to changes in neural tissue integrity. Even less is known about how the brain is affected by cholesterol levels in the normal to moderate risk range, leading up to overt disease pathology. This study examined associations between serum lipid levels and DTI indicators of white matter (WM) structural integrity in a sample of 125 generally healthy older adults aged 43-87 years. Whole-brain voxelwise analysis, controlling for age and gender, revealed low density lipoprotein levels (LDL) as the most robust correlate of regional WM structural integrity of the measured lipids. Higher LDL was associated with decreased WM integrity in right frontal and temporal regions, the superior longitudinal fasciculus and internal/external capsules. Increasing LDL was associated with increased radial and axial diffusivity; however, more widespread statistical effects were found for radial diffusivity. These findings suggest that normal interindividual variation in lipid levels is associated with compromised regional WM integrity, even in individuals below clinical thresholds for hyperlipidemia. Given the prevalence of cholesterol-associated sequelae in older adults, and mounting evidence suggesting a vascular role in the etiology of dementia, the current data suggest that understanding the relationship between cholesterol and brain tissue microstructure may have important clinical implications for early detection of vascular-related cognitive disorders and optimal regulation of serum lipids to maintain neural health in older adults.

Association between white matter microstructure, executive functions, and processing speed in older adults: the impact of vascular health

Cerebral white matter damage is not only a commonly reported consequence of healthy aging, but is also associated with cognitive decline and dementia. The aetiology of this damage is unclear; however, individuals with hypertension have a greater burden of white matter signal abnormalities (WMSA) on MR imaging than those without hypertension. It is therefore possible that elevated blood pressure (BP) impacts white matter tissue structure which in turn has a negative impact on cognition. However, little information exists about whether vascular health indexed by BP mediates the relationship between cognition and white matter tissue structure. We used diffusion tensor imaging to examine the impact of vascular health on regional associations between white matter integrity and cognition in healthy older adults spanning the normotensive to moderate-severe hypertensive BP range (43-87 years; N = 128). We examined how white matter structure was associated with performance on tests of two cognitive domains, executive functioning (EF) and processing speed (PS), and how patterns of regional associations were modified by BP and WMSA. Multiple linear regression and structural equation models demonstrated associations between tissue structure, EF and PS in frontal, temporal, parietal, and occipital white matter regions. Radial diffusivity was more prominently associated with performance than axial diffusivity. BP only minimally influenced the relationship between white matter integrity, EF and PS. However, WMSA volume had a major impact on neurocognitive associations. This suggests that, although BP and WMSA are causally related, these differential metrics of vascular health may act via independent pathways to influence brain structure, EF and PS.

Inter-individual variation in blood pressure is associated with regional white matter integrity in generally healthy older adults

Prior studies have documented a range of brain changes that occur as a result of healthy aging as well as neural alterations due to profound dysregulation in vascular health such as extreme hypertension, cerebrovascular disease and stroke. In contrast, little information exists about the more transitionary state between the normal and abnormal physiology that contributes to vascular disease and cognitive decline. Specifically, little information exists with regard to the influence of systemic vascular physiology on brain tissue structure in older individuals with low risk for cerebrovascular disease and with no evidence of cognitive impairment. We examined the association between resting blood pressure and diffusion tensor imaging (DTI) indices of white matter microstructure in 128 healthy older adults (43-87 years) spanning the normotensive to moderate-severe hypertensive range. Mean arterial blood pressure (MABP) was related to diffusion measures in several regions of the brain with greatest associations in the anterior corpus callosum and lateral frontal, precentral, superior frontal, lateral parietal and precuneus white matter. Associations between white matter integrity and blood pressure remained when controlling for age, when controlling for white matter lesions, and when limiting the analyses to only normotensive, pharmacologically controlled and pre-hypertensive individuals. Of the diffusion measures examined, associations were strongest between MABP and radial diffusivity which may indicate that blood pressure has an influence on myelin structure. Associations between MABP and white matter integrity followed spatial patterns resembling those often attributed to the effects of chronological age, suggesting that systemic cerebrovascular health may play a role in neural tissue degeneration classically ascribed to aging. These results demonstrate the importance of the consideration of vascular physiology in studies of cognitive and neural aging, and that this significance extends to even the normotensive and medically controlled population. These data additionally suggest that optimal management of blood pressure may require consideration of the more subtle influence of vascular health on neural health in addition to the primary goal of prevention of a major cerebrovascular event.

Thickness of the human cerebral cortex is associated with metrics of cerebrovascular health in a normative sample of community dwelling older adults

We examined how wide ranges in levels of risk factors for cerebrovascular disease are associated with thickness of the human cerebral cortex in 115 individuals ages 43-83 with no cerebrovascular or neurologic history. Cerebrovascular risk factors included blood pressure, cholesterol, body mass index, creatinine, and diabetes-related factors. Variables were submitted into a principal components analysis that confirmed four orthogonal factors (blood pressure, cholesterol, cholesterol/metabolic and glucose). T1-weighted MRI was used to create models of the cortex for calculation of regional cortical thickness. Increasing blood pressure factor scores were associated with numerous regions of reduced thickness. Increasing glucose scores were modestly associated with areas of regionally decreased thickness. Increasing cholesterol scores, in contrast, were associated with thicker cortex across the whole brain. All findings were primarily independent of age. These results provide evidence that normal and moderately abnormal levels of parameters used to assess cerebrovascular health may impact brain structure, even in the absence of cerebrovascular disease. Our data have important implications for the clinical management of vascular health, as well as for what is currently conceptualized as "normal aging" as they suggest that subclinical levels of risk may impact cortical gray matter before a disease process is evident.

Variation in blood pressure is associated with white matter microstructure but not cognition in African Americans

Although hypertension is a major risk factor for cerebrovascular disease (CVD) and is highly prevalent in African Americans, little is known about how blood pressure (BP) affects brain-behavior relationships in this population. In predominantly Caucasian populations, high BP is associated with alterations in frontal-subcortical white matter and in executive functioning aspects of cognition. We investigated associations among BP, brain structure, and neuropsychological functioning in 52 middle-older-age African Americans without diagnosed history of CVD. All participants underwent diffusion tensor imaging for examination of white matter integrity, indexed by fractional anisotropy (FA). Three regions of interest were derived in the anterior (genu) and posterior (splenium) corpus callosum and across the whole brain. A brief neuropsychological battery was administered from which composite scores of executive function and memory were derived. Blood pressure was characterized by mean arterial blood pressure (MABP). When controlling for age, higher MABP was associated with lower FA in the genu, and there was a trend for this same relationship with regard to whole-brain FA. When the sample was broken into groups on the basis of treatment for BP regulation (medicated vs. nonmedicated), MABP was related to genu and whole-brain FA only in the nonmedicated group. Neither MABP nor FA was significantly related to either neuropsychological composite score regardless of medication use. These data provide important evidence that variation in BP may contribute to significant alterations in specific neural regions of white matter in nonmedicated individuals without symptoms of overt CVD.

Perioperative bladder management after primary total hip arthroplasty

A retrospective review of 95 consecutive primary total hip arthroplasty patients was performed to assess the clinical outcome of two postoperative bladder management protocols. The first 49 patients (group 1) were treated with a pro re nata straight catheterization protocol. The next 46 patients (group 2) were treated with an indwelling catheterization protocol. There were no differences between the groups with respect to sex or age. The patients in group 2 had significantly lower incidences of urinary retention (P < .0005) and bladder distention (P < .0005) than those in group 1. Preoperative systemic diseases and urologic symptoms did not correlate with the occurrence of postoperative urinary retention or bladder distention. There were no infections in group 1. In group 2, one patient (2%) had bacteriuria and one patient (2%) had a urinary tract infection (P > .1). This trend of increased contamination in the catheterization group may be related to a mean catheterization duration of 72 hours.

Calorimetric measurements made on rats during repeated periods of weight gain and weight loss

1. Rats in respiration chambers were grown for 32 days and their weight reduced by 27-40% on three occasions and realimentated. After the first cycle rats lost body weight more rapidly and regained that weight more quickly than previously. 2. The initial growth phase took 32 days compared with only 8 days in the final period. Each gram of weight gain was associated with 13-14 kJ of dietary net energy during the last two periods of realimentation compared with 19-20 kJ during the first period. 3. Calorimetric measurements showed that although maintenance energy requirement increased during the periods of growth, mean net availability of metabolizable energy was 0.91 compared to 0.60 during weight loss. 4. During the final period much of the weight gain was in the form of lean (67%) but the majority of energy retained was as fat (67-70%).

The efficiency of growth during body weight recovery in young adult female rats

1. Six young adult female rats were subjected to 40% body weight loss in 84 days by food restriction followed by recovery of body weight in 36.2 +/- 4.28 days by ad libitum food intake. The regimen was then repeated, with 40% body weight loss in 105 days followed by recovery of body weight in 22.8 +/- 2.00 days. 2. Food intakes were measured continuously. 3. These rats used digestible energy more efficiently during the second recovery (49.1 +/- 3.11 v. 77.3 +/- 7.91 kJ digestible energy intake per g body wt gain). 4. Seven rats were subjected to one body weight loss and recovery. Five of them had an efficiency of 44.1 +/- 3.34 kJ/g live wt gain which was not significantly different from that of the first group during their second recovery; they may not have been capable of improvement after a second deprivation. 5. It is concluded that some rats can adapt after a period of severe body weight loss and recovery to utilize food more efficiently during body weight recovery after a second episode.

Effects of intraruminal sodium chloride infusion on rumen and renal nitrogen and electrolyte dynamics in sheep

1. Sheep were given 800 g low-protein roughage/d at 2 h intervals and infused intraruminally with 0,500, 750, 1000, 1250, 1500 or 2000 mmol sodium chloride/d in 436 ml water. The digestibility of various food fractions and rumen ammonia, volatile fatty acids (VFA) and liquid turnover rate were measured, along with renal haemodynamics and the renal excretory patterns of nitrogen and electrolytes. Ad lib. food intake was determined during the infusion of 0 and 2000 mmol NaCl/d. 2. Infusion of NaCl up to 750 mmol/d had virtually no effect on the indices measured, except water intake and water excretion. Infusion of greater amounts caused a step-wise decrease in the digestibility of organic matter (OM) and N. Rumen liquid turnover rate was increased substantially and rumen NH3 and VFA concentrations were decreased. Ad lib. food intake was not different when either 0 or 2000 mmol NaCl/d were infused into the rumen. 3. The glomerular filtration rate and effective renal plasma flow (ERPF) were substantially increased after the infusion of 1250 mmol or more NaCl/d. Extracellular fluid volume was also increased. The renal excretion of urea and uric acid + allantoin (URAL) were decreased at the higher infusion rates but the fractional excretions of both these substances were enhanced. The excretion of sodium, chloride, calcium and magnesium were markedly increased with increasing salt infusion. 4. The results suggest that high NaCl inputs into the rumen increase the rumen turnover rate, which in turn decreases the digestibility of OM, particularly N. This causes lower rumen NH3 and VFA concentrations. Plasma urea and URAL concentrations are also decreased and this causes lower renal excretion of these substances despite a much higher fractional excretion resulting from the greatly enhanced urine flow rate. 5. When roughages low in N are given, NaCl intake should be kept below 20 mmol/kg body-weight per d to prevent a decline in the digestibility of the food and any consequent reduction in protein available to the sheep.

The effects of coprophagy in the adult rat on rate of passage of digesta and on digestibility of food fed ad libitum and in restricted amounts

The rate of passage of digesta and the digestibility of a nonpurified diet were studied in adult female rats prevented from coprophagy on alternate weeks by confinement to their normal feeding tunnels in metabolism cages. In food-restricted rats a decrease in the time for the first appearance in the feces of a digesta marker was noted when prevention of coprophagy was followed by permitting rats to feed on their feces while being maintained on a restricted food intake, as compared to control rats permitted coprophagy throughout. The prevention of coprophagy had no effect on the rate of passage of digesta along the small intestine. The prevention of coprophagy had no effect on the apparent digestibility of dry matter, organic matter, energy or protein when the rats were fed ad libitum. However, when rats had lost 20% or more of their body weight by restricted feeding, digestibility of the measured constituents of the food offered in restricted amounts increased, but this effect was abolished when coprophagy was prevented.

Renal control of plasma urea level in sheep: the diuretic effect of urea, potassium and sodium chloride

Two merino ewes were fed 800 and then 1000 g of lucerne chaff per day and renal responses and extracellular fluid volume (E.C.F.) were determined. Urine urea nitrogen, glomerular filtration rate (G.F.R.), urine volume, effective renal plasma flow (E.R.P.F.) and E.C.F. increased in both animals with the greater nitrogen intake. In a second experiment, five merino wethers and four merino ewes were infused intraruminally with increasing quantities of urea, whilst being fed a mainly roughage ration, and the above parameters were determined. No significant changes in G.F.R., E.R.P.F. or E.C.F. were noted. Urinary excretion maintained a linear response to nitrogen input until 20.6 g of urea nitrogen per day were infused. At this level of infusion, an increased fractional reabsorption of urea resulted in a large increase in plasma urea concentration, but when 500 mmol of NaCl or KCl were added to the infusate, urine urea nitrogen excretion increased from 10.4 to 11.4 and 11.9 g/d respectively and plasma urea concentration decreased from 68.0 to 35.2 and 37.3 mg nitrogen/100 ml. Urea clearance virtually trebled with both electrolyte infusions and E.C.F. and G.F.R. increased by approximately 10 and 25% respectively. It is concluded that urea alone has limited diuretic ability and that the increased electrolyte content of higher protein dry roughage diets aids urine urea excretion by increasing G.F.R., and the urine flow rate by an osmotic diuretic effect.

Effects of Caecectomy on the Digestibility of Food and Rate of Passage of Digesta in the Rat

Minimum transit time through the alimentary tract of young adult female rats fed a stock diet adlibitum was reduced from 6� 6 � 0�4 h for sham-operated rats to 5�0 � 0�3 h for caecectomized rats, but there was no effect on transit time of digesta along the small intestine. Caecectomy decreased the apparent digestibility of crude protein, soluble carbohydrate, cellulose and hemicellulose. Digestibility of lipid was not affected. However, caecectomized rats did not increase their dry matter intakes to compensate for the reduced digestible energy intakes.

Effects of food restriction and body weight loss on metabolic fecal nitrogen excretion in the rat

Metabolic fecal nitrogen was measured in young adult female rats fed synthetic diets before and after weight losses had been caused by restricted food intake. When food intake was decreased from 5.5 to 2.4 g or from 6.7 to 2.3 g per 100 g body weight per day, metabolic fecal nitrogen per gram food intake increased by 48 and 59%, respectively. However, weight losses did not affect metabolic fecal nitrogen excretion significantly until some 40% loss of weight had been obtained. At this point metabolic fetal nitrogen excretion was observed to increase by 11%. These results indicate that the 6% increase in apparent digestibility of crude protein in a stock diet which occurs during food restriction is due to a genuine increase in absorption of dietary nitrogen.

Effects of caecectomy in the young adult female rat on digestibility of food offered ad libitum and in restricted amounts

Caecectomized and sham-operated rats were fed a laboratory chow ad libitum and the effects of caecectomy on the digestibility of the food were studied. Compared with sham-operated controls, caecectomized rats showed a decrease in apparent digestibiltiy of organic matter from 77.8 to 73.0%, of crude protein from 83.0 to 79.4%, and of 'carbohydrate' from 74.6 to 69.0%. However, faecal water content increased from 41.6 to 54.8%. 51Cr-labelled EDTA was excreted faster in the faeces after caecectomy. The colon partly adapted to the loss of caecal mucosa by increased length and thus mucosal surface area. In a second concurrent experiment the effect of caecectomy on the apparent digestibility of food during food restriction was studied. Six caecectomized rats, comparable in all respects to those used in the first study, were fed the laboratory chow ad libitum for 3 weeks. They were then fed submaintenance amounts of food to achieve body weight losses of 40--50% and to maintain these low weights for 4 weeks. Finally, they were again fed ad libitum for 3 weeks. During the period of restriction the apparent digestibility of organic matter increased from 72.7 to 75.4%. This was largely due to the increased apparent digestibility of crude protein which rose from 78.4 to 81.9%. Digestibility coefficients returned to control values immediately upon refeeding ad libitum.

Changes in body composition and efficiency of food utilization for growth in young adult female rats before, during and after a period of food restriction

Changes in body composition were studied in three groups of young adult female rats; the treatments were (1) ad libitum food intake to obtain normal growth, (2) restricted food intake to cause body weight loss, and (3) restricted followed by ad libitum food intake to obtain recovery of lost body weight. In each of the three groups of rats the percentage body water was linearly and negatively correlated with the percentage body fat, the weight of body water was linearly and positively correlated with the weight of body protein, and the ratio of the weight of body protein to water was relatively constant at 1:3.20 +/- 0.02 (mean +/- standard error). The percentage body water in the fat-free body was linearly and negatively correlated with fat-free body weight during normal growth between 109 and 334 g body weight but positively correlated during body weight loss and recovery. During recovery of body weight rats laid down more fat and less protein than during normal growth through the same body weight range and the percentage of digestible energy retained as body tissue was increased.

Changes in Body Composition and Efficiency of Food Utilization for Growth in Young Adult Female Rats Before, During and After a Period of Food Restriction

Changes in body composition were studied in three groups of young adult female rats; the treatments were (1) ad libitum food intake to obtain normal growth, (2) restricted food intake to cause body weight loss, and (3) restricted followed by ad libitum food intake to obtain recovery of lost body weight.

The effect of semi-starvation on the digestibility of food in young adult female rats

The apparent digestibilities of organic matter, protein, lipid and carbohydrate of a laboratory chow were determined in young adult female rats fed ad libitum, after losing 40-50% body weight and prolonging the loss for up to 15 weeks, and while recovering the lost body weight during a second period of ad libitum food intake. During deprivation the animals increased the apparent digestibility of crude protein but there was no significant change in digestibility coefficients of lipid or carbohydrate in relation to treatments. When food was again offered ad libitum to the deprived animals they ate large amounts compared with their body weights but normal amounts when compared with their age peers. Apparent crude protein digestibility immediately returned to pre-deprivation values. No impairment of ability to ingest and digest quantities of food relative to age was detected.

Rate of passage of digesta in sheep. 6. The effect of level of food intake on mathematical predictions of the kinetics of digesta in the reticulorumen and intestines

1.Five sheep were given 400, 625, 850, 1075 and 1300 g lucerne chaff/d according to a 5 × 5 Latin square design to perturbate a mathematical model describing the rate of passage of digesta in terms of rate constants for the reticulo-rumen (k1) and caecum and proximal

2.colon (k2), and a transit time (TT) for the intestines. These values were obtained from the concentration curves of51Cr EDTA and144Ce-144Pr (144Pr) excretion in faeces for comparison with similar measurements obtained directly.

3.The retention times of markers in the reticulo-rumen, caecum and proximal colon and intestines all decreased by approximately 50% as intakes were increased from 400 to 1300 g/d. For both markers, the direct and indirect measures of half-time in the reticulo-rumen were essentially identical. The predicted (indirect) values for half times in the caecum and proximal colon were smaller than the direct values (P< 0.005) but the correlations between them were significant (P< 0.01) for51Cr EDTA (r0.66) and144Pr (r0.78). The direct measures of transit time were smaller (P< 0.025) by 5–10% than the predicted values but correlations between them were significant (P< 0.01) for51Cr EDTA (r0.91) and for144Pr (r0.93). Thus the model predicted the changes produced in the rate of passage of digesta and its usefulness and limitations are discussed.

3.With144Pr1/2k1for the reticulo-rumen andT1/2k2for the caecum and proximal colon were both positively correlated (P< 0.025) with the organic matter digestibilities.T1/2k2decreased at half the rate ofT1/2k1with increasing intakes. This would have favoured compensatory digestion in the large intestine.

Changes in plasma volume and haematocrit in intact and splenectomized sheep during feeding

Changes in jugular haematocrit during daily 2-h feeding periods in trained sheep with and without spleens were compared with changes in the concentration of the plasma tracer radio-iodinated human serum albumin. Jugular haematocrit was increased by 16% in intact sheep and 9% in splenectomized sheep 20 min after they started to eat dry rations. The dilution of tracer in plasma, studied after mixing in the vascular system had been completed, showed four phases. Phase 1 was the rate of removal of tracer in the period before eating began. Phase 2 was the sudden increase in plasma radioactivity that occurred in the first 20 min of eating, indicating a loss of plasma from the circulation. Phase 3 was the decrease in tracer concentration during the remaining feeding period and phase 4 was a post-feeding phase, characterized by a slower rate of decrease of tracer than during phase 3, implying that there was significant recycling of tracer during this phase. The sudden increase in plasma radioactivity, initiated by the onset of feeding, represented a reduction in plasma volume of 10-12%. Minimum plasma volume coincided with peak haematocrit values. The reduced plasma volume accounted for the increased haematocrit in splenectomized sheep, but only accounted for about half of the increase in intact sheep. The residual increase in haematocrit in intact sheep was most likely the result of splenic contraction.

Milk-substitute diet composition and abomasal secretion in the calf

1. The effect of different protein sources in milk-substitute diets on abomasal acidity and proteolytic activity was studied in Friesian calves, aged 20-58 d (Expt 1). The diets contained 'mildly' preheated, spray-dried skim-milk powder (MHM), severely preheated, spray-dried skim-milk powder (SHM), fish-protein concentrate (FPC) or solvent-extracted soya-bean flour (SF) as the main protein source. 2. Gastric juice was collected from abomasal pouches before feeding and at 15 min intervals for 8 h after the morning feed. Samples of digesta were obtained from the abomasum at 1 h intervals during the same period. 3. Digesta pH was lower and titratable acidity higher 0-3 after giving the diet containing MHM than when any of the other three diets was given. 3. Acid secretion from the pouches for the different diets was in the order: FPC greater than MHM greater than SHM greater than or equal to SF. 5. Protease secretion from the pouches, assayed at pH 2-1, was in the order: MHM greater than SHM = FPC greater than SF. 6. The effect of dry matter (DM) intake and concentration on abomasal acidity was also studied in calves given diets which contained MHM (Expt 2). This diet was reconstituted at either 100 or 149 g DM/kg liquid diet and fed at either 32-5 or 49-0 g DM/kg live weight 0-75 per d. Samples of abomasal digesta were collected as in Expt 1. 7. A high intake of DM at a low DM concentration resulted in low acidity of the digesta in the first 3 h after feeding, which suggested a dilution effect. Comparison of two diets of different DM concentration, which were fed in the same volume of liquid, indicated that the greater the DM intake, the greater was the amount of acid secreted. 8. It is concluded that the protein sources varied in their ability to stimulate abomasal acid and protease secretion and it is suggested that this may relate to calf performance.

Effects of semi-starvation on the total body composition and absorptive function of the small intestine of the young adult female rat

Sixteen female rats aged about 80 days and with a mean body weight of 175 g were fed 40% of their ad libitum intake of a laboratory chow. They were killed and analysed for water, protein, lipid and ash after 9, 21-5, 30-2 and 38-8% of body weight had been lost. Compared to a control group of four animals, the 38-8% group lost 13 g or 34% of their protein. The animals in the 21-5, 30-2 and 38-8% groups lost 7-5 g or 87% of their lipid leaving only 1-1 g of lipid. The percentage protein in the body was little affected by body weight loss but lipid decreased from 5 to 1%. In another experiment with 26 rats of 205 g mean body weight and aged about 115 days, absorption rates by the small intestine were measured in vivo after variable weight losses between 0 and 39%. D(+)-Glucose uptake was increased by about 70% in those animals which had lost only 5% of body weight and this increased uptake was retained in those rats which had lost up to 39% of body weight. The absorption of L-leucine was not affected by the decline in body weight compared to the controls but relative to body weight, the ability of the intestine to absorb increased. In the same animals, the wet and dry weights of the small intestine declined slightly faster than body weight and the length of the small intestine tended to decrease slightly with increasing loss of body weight.

Growth of the Parts of the Alimentary Tract of the Rat, and the Small Intestine of the Sheep, Relative to Growth in Live Weight

The dry weight of stomach, small intestine, caecum and colon was obtained from male and female rats from 8 to 184 days old weighing from 18 to 400 g. The length of the colon and small intestine was also measured. The length and dry weight of the small intestine of 35 merino sheep from birth to aged or 3 to 40 kg liveweight were also measured. Regressions between the logarithms of gut measurements and logarithms of the liveweights were calculated. The gut measurements were length, length/kg liveweight, DM, DM/kg liveweight and DM/m for the tubular small intestine and colon, and DM and DM/kg liveweight for the saccular stomach and caecum. For the rat, 2 relations were required to describe the data from all organs. A change in percentage increase or decrease relative to percentage liveweight increase occurred at about 70 to 80 g liveweight or 37 to 44 days old. This is the age range at which increase in metabolic rate relative to liveweight declines to about one-quarter of its previous rate. It is unlikely that there is a causal relation between the maturation of sex hormone output and gut growth and metabolic rate. One allometric regression coefficient adequately described growth of the small intestine of the sheep relative to weight gain.

Effects of insulin hypoglycaemia in the sheep on jugular haematocrit and plasma corticosteroid concentrations

Insulin hypoglycaemia, by acting as a stressor, caused an increase in plasma corticosteroid concentration in sheep. It did not increase jugular haematocrit in splenectomized sheep, but caused an increase, presumably by splenic contraction, in the following sheep: two control, one with one adrenal cortex as its only adrenal tissue, two with denervated spleens, and two splanchnicotomized animals. These preparations showed that insulin hypoglycaemia can cause a splenic contraction in the absence of an increase in plasma adrenaline and after splenic extrinsic denervation.