Reduced soma size of the M-neurons in the lateral geniculate nucleus following foetal alcohol exposure in non-human primates

Limbic brain subregions associated with mental health symptoms in youth with and without prenatal alcohol exposure

BACKGROUND

Prenatal alcohol exposure (PAE) can result in reduced brain volume and an increased risk of mental health challenges. Limbic brain structures such as the hippocampus, thalamus, and amygdala often exhibit smaller volumes in youth with PAE, and similar volume reductions are observed in unexposed youth with symptoms of depression, bipolar disorder, anxiety, and schizophrenia. However, the role of volume reductions in these brain regions in mental health challenges remains unclear for individuals with PAE.

METHODS

Thirty-four youth with PAE and 72 unexposed youth aged 7-16 years completed a T1-weighted magnetic resonance imaging scan. FreeSurfer was used to process and extract volumes for hippocampal subfields, thalamic subnuclei, and amygdalar subnuclei. Depression and anxiety symptoms were measured using the Behavioral Assessment System for Children (BASC-2/3-PRS), the Children's Depression Inventory, and the Multidimensional Anxiety Scale for Children. We tested whether limbic subregion volumes differed between youth with and those without PAE and whether volumes were associated with depression and/or anxiety symptoms, controlling for age and gender.

RESULTS

Multiple hippocampal and thalamic subregions, but not amygdalar subnuclei, were smaller in individuals with PAE. Multiple group-brain interactions were observed for depression symptoms and subregion volumes. Negative associations between anxiety and limbic subregions were observed across groups.

CONCLUSIONS

These findings show extensive volume reductions in the hippocampus and thalamus in youth with PAE. PAE also appears to disrupt the association between depression symptoms and limbic subregions in youth, which may have implications for interventions in these individuals. Anxiety symptoms in youth with and without PAE are similarly associated with limbic volumes.

Cell death in the lateral geniculate nucleus, and its possible relationship with nicotinic receptors and sudden infant death syndrome (SIDS)

The role of the lateral geniculate nucleus (LGN) in vision has been extensively studied, yet its extraretinal capacities are still being investigated, including its role in arousal from sleep. The β2 nicotinic acetylcholine receptor (nAChR) subunit is involved in the laminal organisation of the LGN with magnocellular (MC) and parvocellular (PC) neurons. Sudden infant death syndrome (SIDS) occurs during a sleep period and, neuropathologically, is associated with increased neuronal cell death and altered nAChRs. A recent qualitative pilot study from our group implicates the possibility of increased neuronal death/apoptosis in the SIDS LGN. The present study used quantitative analysis to report the baseline expression of apoptotic and nAChR subunits α7 and β2 in the PC and MC layers of the LGN, to determine correlations amongst these markers within layers and across layers, and to evaluate changes in the expression of these markers in the LGN of SIDS infants, along with associations with SIDS risk factors, such as age, sex, cigarette smoke exposure, bed-sharing, and presence of an upper respiratory tract infection (URTI). Tissue was immunohistochemically stained for cell death markers of active caspase-3 (Casp-3) and TUNEL, and for the α7 and β2 nAChR subunits. Amongst 43 cases of sudden and unexpected deaths in infancy (SUDI), classifications included explained deaths (eSUDI, n = 9), SIDS I (n = 5) and SIDS II (n = 29). Results indicated a strong correlation of the apoptotic markers and β2 nAChR subunit between the LGN layers, but not across the markers within the layers. Amongst the diagnostic groups, compared to eSUDI, the SIDS II cases had decreased Casp-3 expression while β2 nAChR expression was increased in both PC and MC layers. Amongst the SIDS risk factors, URTI and bed-sharing were associated with changes in neuronal death but not in the α7 and β2 markers. In conclusion, our findings do not support a role for the α7 and β2 nAChRs in apoptotic regulation of the LGN layers during infancy. However, for SIDS victims, an inverse correlation between the changes for markers of apoptosis and the β2 nAChR subunit expression suggests altered LGN function.

Retinal structure and function in monkeys with fetal alcohol exposure

Exposure to ethanol in utero leads to several brain development disorders including retinal abnormalities whose underlying cellular pathogenesis remains elusive. We recently reported that fetal alcohol exposure (FAE) in vervet monkeys induces anomalies of full-field electroretinogram (ERG) waveforms that suggest premature aging of the retina. The goal of this study is to characterize the anatomo-functional mechanisms underlying the retinal changes observed in fetal alcohol exposed (FAE) monkeys, and age- and sex-matched normals. First, we examined in vivo the fundus of the eyes, measured intraocular pressure (IOP) and assessed cone activity using flicker ERG. Second, we investigated ex vivo, protein expression and anatomical organization of the retina using Western blotting, classical histology and immunohistochemistry. Our results indicated that the fundus of the eyes showed both, increased vascularization (tessellated fundus) and IOP in FAE monkeys. Furthermore, light-adapted flicker responses above 15 Hz were also significantly higher in FAE monkeys. Although there were no obvious changes in the overall anatomy in the FAE retina, Glial Fibrillary Acidic Protein (GFAP, a potent marker of astrocytes) immunoreactivity was increased in the FAE retinal ganglion cell layer indicating a strong astrogliosis. These alterations were present in juvenile (2 years old) monkeys and persist in adults (8 years old). Moreover, using specific cell type markers, no significant modifications in the morphology of the photoreceptors, horizontal cells, bipolar cells, and amacrine cells were observed. Our data indicate that FAE does indeed induce anatomical changes within the retinal ganglion cell layer that are reflected in the increased photosensitivity of the cone photoreceptors.

Effects of Early Alcohol Exposure on Functional Organization and Microstructure of a Visual-Tactile Integrative Circuit

BACKGROUND

Children with fetal alcohol spectrum disorders (FASD) often have deficits associated with multisensory processing. Because ethanol (EtOH) disrupts activity-dependent neuronal plasticity, a process that is essential for refining connections during cortical development, we hypothesize that early alcohol exposure results in alterations in multisensory cortical networks, which could explain the multisensory processing deficits seen in FASD. Here, we use a gyrencephalic animal model to test the prediction that early alcohol exposure alters the functional connectivity and microstructural features of the rostral posterior parietal cortex (PPr), a visual-tactile integrative area.

METHODS

Ferrets were exposed to moderate doses of EtOH during the brain growth spurt period. Functional connectivity and microstructural features were assessed using resting-state functional magnetic resonance imaging and ex vivo diffusion kurtosis imaging (DKI), respectively, when the animals reached juvenile age and adulthood, respectively.

RESULTS

While the whole brain volume was smaller in alcohol-treated animals, the relative size of the frontal brain area was larger when compared to control animals. Altered functional connectivity was observed in alcohol-treated animals, where increased connectivity was observed between PPr and the region that provides its major visual inputs (the caudal portion of the parietal cortex), but not with the region that provides its major somatosensory inputs (tertiary somatosensory cortex). DKI revealed reduced microstructural tissue complexity in all investigated sensory areas of alcohol-treated animals.

CONCLUSIONS

In this study, we observed alterations in cortical functional connectivity and microstructural integrity in a cortical area involved in multisensory processing in a ferret FASD model. These findings indicate an alteration in cortical networks that may be related to the multisensory processing deficiencies observed in FASD.

Hematologic and biochemical RIs for an aged population of captive African Green monkeys (Chlorocebus aethiops sabaeus)

BACKGROUND

Established RIs for geriatric African Green monkeys (Chlorocebus aethiops sabaeus) are critical for clinical differentiation of normal aging from disease-related changes in this population.

OBJECTIVE

The aim of this study was to establish hematologic and serum biochemical RIs for a Caribbean captive population of geriatric (≥ 15 years of age) African Green monkeys, or Vervets.

METHODS

Inclusion and exclusion criteria were defined for a cohort of 109 healthy, aged (15- to 30-year-old, median 19-year-old) Vervets. Both male (34) and female (75) monkeys were included in RI generation. Complete manual and analyzer-generated blood counts and serum biochemistry profiles were performed at Ross University School of Veterinary Medicine, West Farm, St. Kitts, West Indies. All results were evaluated using Reference Value Advisor. Isolated outliers were identified using Dixon's outlier range statistic and not included in determination of RIs for individual analytes. Reference intervals were determined using parametric and nonparametric methods depending on the distribution. Data, including mean, median, maximum, and minimum values, were tabulated.

RESULTS

Of the 109 animals, 12 monkeys were excluded due to abnormal physical examination results (2 monkeys), and ≥ 2 confirmed outliers (9 monkeys), or evidence of disease based on laboratory data (one monkey).

CONCLUSIONS

This study provides useful RIs for assessment of hematology and serum biochemical variables in a geriatric population of African Green monkeys in the Caribbean.

Prenatal Alcohol Exposure Affects Progenitor Cell Numbers in Olfactory Bulbs and Dentate Gyrus of Vervet Monkeys

Fetal alcohol exposure (FAE) alters hippocampal cell numbers in rodents and primates, and this may be due, in part, to a reduction in the number or migration of neuronal progenitor cells. The olfactory bulb exhibits substantial postnatal cellular proliferation and a rapid turnover of newly formed cells in the rostral migratory pathway, while production and migration of postnatal neurons into the dentate gyrus may be more complex. The relatively small size of the olfactory bulb, compared to the hippocampus, potentially makes this structure ideal for a rapid analysis. This study used the St. Kitts vervet monkey (Chlorocebus sabeus) to (1) investigate the normal developmental sequence of post-natal proliferation in the olfactory bulb and dentate gyrus and (2) determine the effects of naturalistic prenatal ethanol exposure on proliferation at three different ages (neonate, five months and two years). Using design-based stereology, we found an age-related decrease of actively proliferating cells in the olfactory bulb and dentate gyrus for both control and FAE groups. Furthermore, at the neonatal time point, the FAE group had fewer actively proliferating cells as compared to the control group. These data are unique with respect to fetal ethanol effects on progenitor proliferation in the primate brain and suggest that the olfactory bulb may be a useful structure for studies of cellular proliferation.

Extracellular nucleotide regulation and signaling in cardiac fibrosis

Following myocardial infarction, purinergic nucleotides and nucleosides are released via non-specific and specific mechanisms in response to cellular activation, stress, or injury. These extracellular nucleotides are potent mediators of physiologic and pathologic responses, contributing to the inflammatory and fibrotic milieu within the injured myocardium. Via autocrine or paracrine signaling, cell-specific effects occur through differentially expressed purinergic receptors of the P2X, P2Y, and P1 families. Nucleotide activation of the ionotropic (ligand-gated) purine receptors (P2X) and several of the metabotropic (G-protein-coupled) purine receptors (P2Y) or adenosine activation of the P1 receptors can have profound effects on inflammatory cell function, fibroblast function, and cardiomyocyte function. Extracellular nucleotidases that hydrolyze released nucleotides regulate the magnitude and duration of purinergic signaling. While there are numerous studies on the role of the purinergic signaling pathway in cardiovascular disease, the extent to which the purinergic signaling pathway modulates cardiac fibrosis is incompletely understood. Here we provide an overview of the current understanding of how the purinergic signaling pathway modulates cardiac fibroblast function and myocardial fibrosis.

Hippocampal neuron populations are reduced in vervet monkeys with fetal alcohol exposure

Prenatal exposure to beverage alcohol is a major cause of mild mental retardation and developmental delay. In nonendangered alcohol-preferring vervet monkeys, we modeled the most common nondysmorphic form of fetal alcohol syndrome disorder with voluntary drinking during the third trimester of pregnancy. Here, we report significant numerical reductions in the principal hippocampal neurons of fetal alcohol-exposed (FAE) offspring, as compared to age-matched, similarly housed conspecifics with isocaloric sucrose exposure. These deficits, particularly marked in CA1 and CA3, are present neonatally and persist through infancy (5 months) and juvenile (2 years) stages. Although the volumes of hippocampal subdivisions in FAE animals are not atypical at birth, by age 2, they are only 65-70% of those estimated in age-matched controls. These data suggest that moderate, naturalistic alcohol consumption during late pregnancy results in a stable loss of hippocampal neurons and a progressive reduction of hippocampal volume.

Scaling the primate lateral geniculate nucleus: niche and neurodevelopment in the regulation of magnocellular and parvocellular cell number and nucleus volume

New stereological assessments of lateral geniculate nucleus (LGN) neuron numbers and volumes in five New World primates (Cebus apella, Saguinus midas niger, Alouatta caraya, Aotus azarae, and Callicebus moloch) and compiled LGN volumes for an additional 26 mammals were analyzed for a better understanding of visual system evolution. Both the magnocellular (M)- and the parvocellular (P)-cell populations scale allometrically with brain volume in primates, P cells with a significantly higher slope such that, for every increase in M neuron number, P neuron numbers more than double (ln scale; y = 0.89x + 2.42R(2) = 0.664). In diurnal primates, the ratio of P to M cells was slightly but significantly higher than in nocturnal primates. For all mammals, including primates, LGN volume was unrelated to nocturnal or diurnal niche but showed marked differences in slope and intercept depending on taxonomic group. The allometric scaling of M and P cells can be related to the order of neurogenesis, with late-generated P cells increasing with positive allometry compared with the earlier-generated M cells. This developmental regularity links relative foveal representation to relative isocortex enlargement, which is also generated late. The small increase in the P/M cell ratio in diurnal primates may result from increased developmental neuron loss in the M-cell population as it competes for limited termination zones in primary visual cortex.

Standardized full-field electroretinography in the Green Monkey (Chlorocebus sabaeus)

Full-field electroretinography is an objective measure of retinal function, serving as an important diagnostic clinical tool in ophthalmology for evaluating the integrity of the retina. Given the similarity between the anatomy and physiology of the human and Green Monkey eyes, this species has increasingly become a favorable non-human primate model for assessing ocular defects in humans. To test this model, we obtained full-field electroretinographic recordings (ERG) and normal values for standard responses required by the International Society for Clinical Electrophysiology of Vision (ISCEV). Photopic and scotopic ERG recordings were obtained by full-field stimulation over a range of 6 log units of intensity in dark-adapted or light-adapted eyes of adult Green Monkeys (Chlorocebus sabaeus). Intensity, duration, and interval of light stimuli were varied separately. Reproducible values of amplitude and latency were obtained for the a- and b-waves, under well-controlled adaptation and stimulus conditions; the i-wave was also easily identifiable and separated from the a-b-wave complex in the photopic ERG. The recordings obtained in the healthy Green Monkey matched very well with those in humans and other non-human primate species (Macaca mulatta and Macaca fascicularis). These results validate the Green Monkey as an excellent non-human primate model, with potential to serve for testing retinal function following various manipulations such as visual deprivation or drug evaluation.

Effects of early postnatal alcohol exposure on the developing retinogeniculate projections in C57BL/6 mice

Previous studies on the adverse effects of perinatal exposure to ethanol (EtOH) on the developing visual system mainly focused on retinal and optic nerve morphology. The aim of the present study was to investigate whether earlier reported retinal and optic nerve changes are accompanied by anomalies in eye-specific fiber segregation in the dorsal lateral geniculate nucleus (dLGN). C57BL/6 mice pups were exposed to ethanol by intragastric intubation at either 3 or 4 g/kg from postnatal days (PD) 3-10, the third trimester equivalent to human gestation. Control (C) and intubation control (IC) groups not exposed to ethanol were included. On PD9, retinogeniculate projections were labeled by intraocular microinjections of cholera toxin-β (CTB) either conjugated to Alexa 488 (green) or 594 (red) administrated to the left and right eye, respectively. Pups were sacrificed 24 h after the last CTB injection. The results showed that ethanol exposure decreased the total number of dLGN neurons and significantly reduced the total dLGN projection as well as the contralateral and ipsilateral projection areas.

Does moderate drinking harm the fetal brain? Insights from animal models

Although public health campaigns advise pregnant women to abstain from ethanol, drinking during pregnancy is pervasive. Here, we highlight recent studies that have clearly demonstrated long-lasting neurobehavioral deficits in the offspring of laboratory animals exposed to moderate levels of ethanol during development. Alterations in learning, memory, motor coordination, social behavior, and stress responses were identified in these animals. Increased vulnerability to substance abuse was also demonstrated. These behavioral alterations have been associated with impairments in neurotransmitter systems, neuromodulators, and/or synaptic plasticity in several brain regions. With this review we hope to contribute to a better appreciation of the potential effects of developmental exposure to moderate ethanol levels, leading to better interventions aimed at relieving fetal alcohol spectrum disorders.

Selective effects of perinatal ethanol exposure in medial prefrontal cortex and nucleus accumbens

Ethanol exposure during development is the leading known cause of mental retardation and can result in characteristic physiological and cognitive deficits, often termed Fetal Alcohol Spectrum Disorders (FASD). Previous behavioral findings using rat models of FASD have suggested that there are changes in the nucleus accumbens (NAC) and medial prefrontal cortex (mPFC) following ethanol exposure during development. This study used a rat model of FASD to evaluate dendritic morphology in both the NAC and mPFC and cell number in the NAC. Dendritic morphology in mPFC and NAC was assessed using a modified Golgi stain and analyzed via three dimensional reconstructions with Neurolucida (MBF Bioscience). Cell counts in the NAC (shell and core) were determined using an unbiased stereology procedure (Stereo Investigator (MBF Bioscience)). Perinatal ethanol exposure did not affect neuronal or glial cell population numbers in the NAC. Ethanol exposure produced a sexually dimorphic effect on dendritic branching at one point along the NAC dendrites but was without effect on all other measures of dendritic morphology in the NAC. In contrast, spine density was reduced and distribution was significantly altered in layer II/III neurons of the mPFC following ethanol exposure. Ethanol exposure during development was also associated with an increase in soma size in the mPFC. These findings suggest that previously observed sexually dimorphic changes in activation of the NAC in a rat model of FASD may be due to altered input from the mPFC.

Magnetic resonance-based imaging in animal models of fetal alcohol spectrum disorder

Magnetic resonance imaging (MRI) techniques, such as magnetic resonance microscopy (MRM), diffusion tensor imaging (DTI), and magnetic resonance spectroscopy (MRS), have recently been applied to the study of both normal and abnormal structure and neurochemistry in small animals. Herein, findings from studies in which these methods have been used for the examination of animal models of Fetal Alcohol Spectrum Disorder (FASD) are discussed. Emphasis is placed on results of imaging studies in fetal and postnatal mice that have highlighted the developmental stage dependency of prenatal ethanol exposure-induced CNS defects. Consideration is also given to the promise of methodological advances to allow in vivo studies of aberrant brain and behavior relationships in model animals and to the translational nature of this work.