Biomedical subjects

J K Rilling

Publications and source records attributed to J K Rilling.

11 recordsLinked to original sources

PubMed2001

Anatomy and three-dimensional reconstructions of the brain of a bottlenose dolphin (Tursiops truncatus) from magnetic resonance images.

Cetacean (dolphin, whale, and porpoise) brains are among the least studied mammalian brains because of the formidable challenge of collecting and histologically preparing such relatively rare and large specimens. Magnetic resonance imaging offers a means of observing the internal structure of the brain when traditional histological procedures are not practical. Furthermore, internal structures can be analyzed in their precise anatomic positions, which is difficult to accomplish after the spatial distortions often accompanying histological processing. In this study, images of the brain of an adult bottlenose dolphin, Tursiops truncatus, were scanned in the coronal plane at 148 antero-posterior levels. From these scans a computer-generated three-dimensional model was constructed using the programs VoxelView and VoxelMath (Vital Images, Inc.). This model, wherein details of internal and external morphology are represented in three-dimensional space, was then resectioned in orthogonal planes to produce corresponding series of virtual sections in the horizontal and sagittal planes. Sections in all three planes display the sizes and positions of major neuroanatomical features such as the arrangement of cortical lobes and subcortical structures such as the inferior and superior colliculi, and demonstrate the utility of MRI for neuroanatomical investigations of dolphin brains.

Anatomy, Cross-Sectional↗

PubMed2001

Neural correlates of maternal separation in rhesus monkeys.

BACKGROUND: The neurobiological basis of stress and anxiety in primates remains poorly understood. In this study, we examined the neural response to a naturalistic social stressor: maternal separation. We used rhesus monkeys as an animal model because of their close phylogenetic affinity with humans. METHODS: Six juvenile rhesus monkeys received [(18)F]-fluorodeoxyglucose positron emission tomography scans following 1) a period together with their mothers and again after separation from their mothers 2) with or 3) without visual contact. Image subtraction revealed brain regions that exhibited altered activity during separation. In addition, plasma cortisol concentrations obtained following each condition were tested for correlations with regional brain activity. RESULTS: Maternal separation activated the right dorsolateral prefrontal cortex and the right ventral temporal/occipital lobe. There was also decreased activity in left dorsolateral prefrontal cortex associated with separation stress. Correlational analyses demonstrated these activated and deactivated regions to be positively and negatively correlated with cortisol, respectively. Additionally, correlational analyses revealed cortisol-related activation in brainstem areas previously implicated in stress and anxiety. CONCLUSIONS: In juvenile rhesus monkeys, the stress of maternal separation is associated with activation in the right dorsolateral prefrontal cortex and ventral temporal/occipital lobes and decreased activity in the left dorsolateral prefrontal cortex.

Aggression↗

PubMed2000

A comparative MRI study of the relationship between neuroanatomical asymmetry and interhemispheric connectivity in primates: implication for the evolution of functional asymmetries.

The authors tested the theory that hemispheric specialization evolved as a consequence of reduced interhemispheric connectivity by examining whether neuroanatomical asymmetries were associated with variation in the ratio of corpus callosum size to brain volume (CC:VOL) and to neocortical surface area (CC:NEO) in human and nonhuman primates. Magnetic resonance images were collected in a sample of 45 primates including 8 New World monkeys, 10 Old World monkeys, 4 lesser apes, 17 great apes, and 6 humans. CC:VOL and CC:NEO were determined and correlated with measures of brain asymmetry. The results indicate that brain asymmetry significantly predicted CC:VOL and CC:NEO. Subsequent analyses revealed that species variation in functional asymmetries in the form of handedness are also inversely related to CC:NEO. Taken together, these results support the hypothesis that leftward brain asymmetries may have evolved as a consequence of reduced interhemispheric connectivity.

Adult↗

PubMed2000

Relative volume of the cerebellum in dolphins and comparison with anthropoid primates.

According to the 'developmental constraint hypothesis' of comparative mammalian neuroanatomy, brain growth follows predictable allometric trends. Therefore, brain structures should scale to the entire brain in the same way across mammals. Evidence for a departure from this pattern for cerebellum volume has recently been reported among the anthropoid primates. One of the mammalian groups that has been neglected in tests of the 'developmental constraint hypothesis' is the cetaceans (dolphins, whales, and porpoises). Because many cetaceans possess relative brain sizes in the range of primates comparative tests of the 'developmental constraint hypothesis' across these two groups could help to delineate the parameters of this hypothesis. In this paper, we compare relative cerebellum volumes in two cetacean species, the bottlenose dolphin (Tursiops truncatus) and the common dolphin (Delphinus delphis), with published data from anthropoid primates. We found that relative cerebellum size is significantly greater in the two dolphin species than in any of the primates, including humans. These results suggest that there is possibly expansion of brain structures independent of strictly allometric processes.

Animals↗

PubMed1999

Differential expansion of neural projection systems in primate brain evolution.

Whole brain MRI scans from 11 primate species (43 individuals) spanning more than a 50-fold range in brain volume were used to determine whether the corpus callosum keeps pace with the growth of the forebrain among living anthropoid primates. Interhemispheric connectivity via the corpus callosum and anterior commissure was reduced in larger primate brains, whereas intrahemispheric connectivity was augmented. We also show that the splenium constitutes an increasing proportion of callosal area with increasing brain size. This may function to maintain rapid integration of the left and right visual space as brain size increases. These results indicate that the evolution of larger brain size in primates results in increasingly independent hemispheres.

Animals↗

PubMed1999

The primate neocortex in comparative perspective using magnetic resonance imaging.

In this study we use neuroanatomic data from living anthropoid primate subjects to test the following three hypotheses: (1) that the human neocortex is significantly larger than expected for a primate of our brain size, (2) that the human prefrontal cortex is significantly more convoluted than expected for our brain size, and (3) that increases in cerebral white matter volume outpace increases in neocortical gray matter volume among anthropoid primates. Whole brain MRI scans were obtained from 44 living primate subjects from 11 different species. Image analysis software was used to calculate total brain volume, neocortical gray matter volume, cerebral white matter volume, and the cross sectional area of the spinal cord in each scan. Allometric regression analyses were used to compare the relative size of these brain structures across species, with an emphasis on determining whether human brain proportions correspond with predictions based on nonhuman primate allometric trajectories. All three hypotheses were supported by our analysis. The results of this study provide additional insights into human brain evolution beyond the important observation that brain volume approximately tripled in the hominid lineage by demonstrating that the neocortex was uniquely modified throughout hominid evolution. These modifications may constitute part of the neurobiological substrate that supports some of our species most distinctive cognitive abilities.

Animals↗

PubMed1998

Differential rearing affects corpus callosum size and cognitive function of rhesus monkeys.

This study investigated the effects of different rearing conditions on neural and cognitive development of male rhesus monkeys (Macaca mulatta). Infants raised individually in a nursery from 2 to 12 months of age (NURSERY, n=9) were compared to age-matched infants raised in a semi-naturalistic, social environment (CONTROL, n=11). Various brain regions were measured by MRI. Although overall brain volumes did not differ between NURSERY and CONTROL animals, corpus callosum (CC) size, measured in mid-sagittal sections, was significantly decreased in the NURSERY group. Group differences were most evident in the posterior aspects of the corpus callosum and appeared to result from changes in the number of cross-hemispheric projections rather than from a decrease in cortical gray matter volume. The decrease in corpus callosum size in the NURSERY animals persisted after 6 months of social housing in a peer-group. Rearing group differences were not found in other structures analyzed, including the hippocampus, cerebellum and anterior commissure. In cognitive testing, NURSERY animals had more difficulty acquiring the delayed non-matching to sample (DNMS) task, but showed no deficits in subsequent memory performance when a 2 or 10 min delay was imposed. The NURSERY infant monkeys were also impaired in object, but not in spatial, reversal learning, although there were no differences in a simple object discrimination task. The cognitive deficits exhibited by the NURSERY animals were significantly correlated with the alterations found in the CC. In summary, rearing environment was associated with sustained differences in cross-hemispheric projections, white matter volume and cognitive performance.

Animals↗

PubMed1998

Planum temporale asymmetries in great apes as revealed by magnetic resonance imaging (MRI).

The planum temporale (PT), a portion of Wernicke's area, is important for linguistic functions in humans and is larger in the left compared to the right hemisphere. In this study, we assessed the presence and size of the PT in a sample of non-human primates including 21 great apes, four lesser apes, 11 Old World monkeys and eight New World monkeys using magnetic resonance imaging. The PT was measured in both the sagittal and coronal planes by use of multiplanar reformatting software. The PT could only be identified in the sample of great apes and not in the remaining non-human primate species. Within the great ape sample, the PT was larger in the left hemisphere than in the right in a statistical majority of the subjects. These results are consistent with the notion that the PT evolved as a definable structure about 15 million years ago and may have arisen as a result for selection for greater cortical folding which in turn led to greater gyrification in larger brains.

Animals↗

PubMed1998

Evolution of the cerebellum in primates: differences in relative volume among monkeys, apes and humans.

According to the 'developmental constraint hypothesis' of comparative mammalian neuroanatomy, brain structures enlarge predictably as the entire brain grows both ontogenetically and phylogenetically. In this study, brain and cerebellum volumes are measured from in vivo magnetic resonance scans of 44 primates from 11 haplorhine species. After controlling for overall brain volume, the cerebellum in both pongid and hylobatid apes is, on average, 45% larger than in monkeys. These results demonstrate that all primate brains are not similarly organized and that developmental constraints are not tight enough to preclude selection for increased cerebellar volume independent of selection on overall brain size.

Animals↗

PubMed1996

Ratios of plasma and salivary testosterone throughout puberty: production versus bioavailability.

Because diffusion of testosterone (T) into the salivary gland is thought to be largely limited to the free, biologically active fraction, salivary testosterone is expected to provide a better measure of testosterone bioavailability in the body than is plasma testosterone. Matched saliva and blood spot samples were collected from 218 Zimbabwean males (age 11-23) who were at different stages of puberty, as assessed by self-reported Tanner genital stage ratings. Testosterone concentrations in these matched samples were highly correlated (r = 0.83). Both salivary and plasma testosterone (converted from blood spot value) showed expected significant increases across puberty. However, plasma testosterone distinguished among subjects at different stages of genital development more effectively than did salivary testosterone, suggesting the former to be a better marker of testosterone bioavailability. Sex hormone-binding globulin (SHBG) levels were also measured in a subgroup of 93 of these subjects. After controlling for plasma T concentrations, we found a small but significant inverse correlation between blood spot SHBG levels and the proportion of plasma testosterone recovered in salvia, supporting the hypothesis that SHBG-related changes in T bioavailability are detectable in saliva. We conclude that salivary testosterone accurately reflects testicular production of testosterone, but that neither salivary testosterone nor plasma testosterone is clearly superior to the other as a measure of testosterone bioavailability.

Adolescent↗

PubMed1992

Regulation of chorionic gonadotropin-alpha and chorionic somatomammotropin messenger ribonucleic acid expression by 8-bromo-adenosine 3',5'-monophosphate and dexamethasone in cultured rhesus monkey syncytiotrophoblasts.

We wished to establish an in vitro culture system to examine gene expression in the context of differentiated function with rhesus monkey syncytiotrophoblasts. Chorionic villous tissue from placentas obtained at cesarean section was dispersed with trypsin and DNase and fractionated on a 5-70% Percoll gradient. When placed in culture, cells from a mononuclear fraction demonstrated to be very highly enriched (95-97% pure) for cytotrophoblasts aggregated and began to form syncytia within 24 h in culture, reminiscent of placental syncytiotrophoblast formation. The migration and fusion of individual cytotrophoblasts to form multinuclear syncytia were documented with time-lapse video microscopy. Incorporation studies with tritiated thymidine supported the conclusion from videomicroscopy that syncytia form by the fusion of individual cells and the addition of mononuclear cells to existing syncytia, rather than by endomitosis. The syncytiotrophoblast marker pregnancy-specific beta 1-glycoprotein (SP1) was immunocytochemically identified in both intact placenta and cultured syncytiotrophoblast cells. With cells isolated from placentas obtained on day 28, 50, 70, or 140 of pregnancy, treatment with 8-bromo-cAMP increased both rhesus monkey CG alpha-subunit (mCG alpha) and chorionic somatomammotropin (mCS) mRNA levels by an average of 4-fold. Increases of up to 2.5-fold were seen with mCG alpha mRNA in as little as 2 h after treatment, with a statistically significant average response seen within 6 h. The response with mCS required at least 24 h before a significant effect was seen. Actin mRNA levels were generally unchanged or suppressed by this treatment, indicating that the effect of 8-bromo-cAMP is relatively specific for the hormone mRNAs. Treatment of syncytiotrophoblasts with dexamethasone, but not progesterone or androstenedione, resulted in an approximately 4-fold increase in mCG alpha mRNA levels within 6 h of treatment. Steroid treatment did not affect mCS mRNA levels. Treatment with 4.5-400 nM GnRH or 0.1 to 100 ng/ml basic fibroblast growth factor likewise had no effect on the level of either mRNA, suggesting that any actions of these factors on hormone secretion are not effected via changes in steady state mRNA. These results communicate that the expression of the mRNAs for rhesus monkey CG alpha and CS in syncytiotrophoblast are regulated by steroid hormone- and cAMP-mediated pathways.

8-Bromo Cyclic Adenosine Monophosphate↗