Controversy remains about the contribution of hypoglycemia to brain damage in the newborn. Therefore, the objective of this study was to determine the effects of isolated hypoglycemia on damage to the immature rat brain. Seven-day-old rats, equivalent to a late preterm human newborn, were placed in either Sham or hypoglycemic groups. Hypoglycemia was induced by insulin infusion for variable periods of time. Outcomes were assessed by behavioral, neurochemical and neuropathologic determination. Rats were categorized as having mild, moderate, or severe hypoglycemia. Behavioral tests revealed no abnormality in hypoglycemic animals. Floro-JadeB showed significant damage in the thalamic reticular nucleus (TRN) of the severe hypoglycemic animals at PD9. However, neuronal (Neu-N), astrocytic (GFAP), and myelin (MBP) staining at PD21 showed no brain injury. There was a significant rise in aspartate and arginine, and drop in glutamine and alanine of hypoglycemic brains. Oxidative stress markers were also increased in hypoglycemic brains. We conclude that isolated prolonged severe hypoglycemia caused a transient, region specific increase in neuronal cell death within the TRN. Though transient in nature, the associated neurochemical alterations warrant further research to determine if more subtle long-term effects may result.

Thesis (Ph. D.)--Michigan State University. Dept. of Neuroscience, 2008. / Title from PDF t.p. (viewed July 31, 2009). Includes bibliographical references (p. 135-152). Also issued in print.

Issued also as Schulte's thesis, Leiden. / Text in Latin and Dutch, with summary in English and Russian.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

No description available.

Epilepsy affects over 450,000 people in the UK and there are over 50 epilepsy phenotypes; genetic generalised epilepsy (GGE) account for up to 30% of seizure types. It is established that GGE and other neurological disorders are, in some cases, caused by channelopathies within post-synaptic inhibitory neurotransmitter systems such as GAB A (epilepsy) and Glycine (hyperekplexia). GAB A is the primary inhibitory neurotransmitter in the brain and is synthesised from glutamate by GAD65 and 67, and is released from the pre-synaptic nerve terminal into the synaptic cleft, where it binds to post-synaptic GABA receptors and initiate neuroinhibition. This inhibition is removed by post-synaptic GABA transporters (GAT1 and GAT3) that uptake GABA back into the cell for re-packaging in presynaptic vesicles or breakdown by transamination. Abnormalities in this system have been linked to diseases including anxiety, psychosis, Parkinsons’s Disease and epilepsy. GABAergic animal models have demonstrated a tendency to seizure, including GABA transporter and enzyme models in relation to epilepsy. Given the above, the aim of this study was to identify GGE causing variants in four GABAergic genes. GGE patient samples (n=101) were recruited from 3 global centres and screened for variations in GAT1, GAT3, GAD65, GAD67 using high-throughput LightScanner analysis and bi-directional Sanger sequencing. Control population studies («=480) were carried out and analysis of online databases to determine the frequency of variants. Twenty novel or very rare variants were identified in 48 patient samples representing a detection rate of 6.8%, where a clustering of phenotypes included a predisposition towards absence seizures. The biological consequences of these variants were predicted using three online predictive programmes, multiple phylogenetic alignments and 3D structural modelling. Mutation expression constructs were prepared and expression levels were validated by immunocytochemistry. Functional characterisation of these variants will hopefully improve genetic diagnosis in GGE and determine causality of GABAergic absence seizures.

The organization of retinal ganglion cell (RGC) axons within the optic nerve (ON), chiasm (OCh), and tract of the frog, Rana pipiens, was examined using both light and electron microscopy. In one group of experiments, anterograde and retrograde transport of horseradish peroxidase (HRP) revealed the spatial reorganizations of RGC axons between the retina and central retinorecipient targets. Optic axons form a concentric representation or map of the retinal surface across the distal ON cross-section. Within this map, the distal ON contains two representations of the temporal and nasal retinal quadrants. Fiber reorganizations within the proximal ON result in axons from central RGCs becoming positioned within the dorsal region of the nerve and in axons of more peripheral RGC becoming localized to the ventral, anterior, and posterior margins of the nerve. As a result of this proximal ON fiber reorganization, age-related RGC axons become grouped in laminae that are aligned perpendicular to the posterodorsal-anteroventral axis of the optic projection. Axons occupying complementary positions in different retinal representations converge in a dorsal-to-ventral sequence as the projection passes through the perichiasm. Within the prechiasm, axons separate from the laminated optic projection to form four fascicles; the projection to corpus geniculatum, the projection to the neuropil of Bellonci, the basal optic root, and the marginal optic tract (MOT). In addition, electron microscopic examination of the optic fiber spectrum revealed the morphological organization of the retinofugal projection within the ON and the lateral division of the marginal optic tract (lMOT). Within the ON, myelinated and unmyelinated axons of various sizes are homogeneously distributed. Optic axons are reorganized within the MOT such that within the lMOT large myelinated optic axons become concentrated within ventromedial regions and small myelinated axons become concentrated within the dorsolateral regions. In rostral lMOT larger unmyelinated axons are also concentrated along the ventromedial regions. The morphological organization of the optic axons within lMOT, established by the reorganization of the retinofugal projection within MOT, anticipates the innervation pattern of the optic axons within the laminated, superficial layers of the optic tectum.

The neuromuscular junction is the site where signals are transmitted from a nerve to a target muscle fiber. The mechanisms responsible for the maintenance of motor nerve terminals at synaptic sites are not understood. Here, I investigated the role of target-muscle fibers in the maintenance of frog motor nerve terminals. Cutaneous pectoris muscle fibers were selectively removed and prevented from regenerating while leaving the motor innervation intact. The role of target muscle fibers in nerve terminal structure and function was examined. First, the maintenance of presynaptic activity in the absence of target was assayed with the activity-dependent dye FM1-43. I found that target-deprived nerve terminals maintain their presynaptic function of synaptic vesicle recycling for up to 5 months of target deprivation. These results indicated that the molecular machinery required for vesicular release is maintained in a functional state for long periods of target deprivation. Second, I quantified the stability of target-deprived nerve terminals using in vivo repeated imaging. I found that most target-deprived nerve terminals were remarkably well maintained for several months after muscle fiber removal. These data indicate that the cues that confer stability to frog motor nerve terminals reside outside the muscle fibers such as in the synaptic basal lamina or terminal Schwann cells. Destabilization observed at some nerve terminals after extended target-deprivation, could result from the turning over of the stabilizing cues. Finally, the molecular organization of target-deprived nerve terminals was analyzed. I found that the levels of two synaptic vesicle proteins, SV-2 and synaptotagmin were reduced in target-deprived nerve terminals when compared to intact neuromuscular junctions. Analysis of cytoskeletal proteins revealed that F-actin was located at discrete bands along synaptic sites that do not colocalize with synaptic vesicle clusters. F-actin is suggested to be located at either the Schwann cell processes and/or the nerve terminal immediately above them. A possible adhesion between nerve terminals and Schwann cell processes, could contribute to the maintenance of the frog nerve terminal at the synaptic site. Finally, all target-deprived synaptic sites were found to be associated with variable levels of agrin immunoreactivity, implicating agrin as a possible maintenance molecule.

This research involved systematic investigation of mechanisms which underlie neural adaptations to training. Observations were made of human motor unit control properties. Considerable evidence suggests impairment of neural, neuromuscular, and musculoskeletal function with aging, thus the process of adaptation to training was compared between healthy young and older adults. Experiment I examined whether early strength gains result from changes in central drive, defined as maximal motor unit discharge rate (MUDR). MUDR was obtained at four points over a six week strength training program. Both young and older adults demonstrated significantly increased maximal MUDR on Day 2 which returned to baseline by the end of the training period. Despite significantly lower maximal MUDR at baseline, older adults produced central drive comparable to young individuals on Days 2 and 14. Experiment II addressed the role of variability of sustained motor unit discharge (MUV) and its effect on the generation of muscular force. MUV was significantly redistributed with aging, punctuating the frequency content between 0-4 Hz. With training, only young individuals demonstrated significant adaptation, reducing the 0-4 Hz contribution and increasing the 5-8 Hz and 9-12 Hz contributions to MUV. These training-related adaptations suggest the role of supraspinal influences in damping oscillatory activity of musculoskeletal dynamics. Experiment III examined the range over which motor unit discharge is modulated for adaptation with strength training. MUDR range was similar between young and older individuals when examined with respect to absolute force differences but was significantly lower in older adults when examined with respect to relative effort. Importantly, significant adaptations to training were not evidenced in MUDR range by young adults, while a transient increase, paralleling the pattern of change in maximal MUDR, was demonstrated by elders. Experiment IV examined adaptation and modulation of antagonist motoneuron excitability. Hoffman reflex (H-reflex) responses were obtained from the soleus muscle while a concurrent force modulation task was performed with tibialis anterior. Over six weeks subjects trained to improve control of dorsiflexion force. H-reflex amplitudes were significantly smaller in older adults suggesting alteration in motoneuron pool activation due, potentially, to remodeling of spinal pathways in favor of antagonist muscle co-contraction.

Animals exhibit physiological and behavioral changes in anticipation of and response to changing environmental conditions. One example of this is the influence of photoperiod on the reproductive cycle of temperate zone seasonal breeders, such as Syrian hamsters. In addition to physiological changes which prevent ovulation and reduce gonadal steroid secretion, photoperiod can influence behavioral responses to gonadal steroid replacement, suggesting that photoperiods which inhibit reproduction alter neural responsiveness to estradiol and progesterone. The experiments described here were designed to address possible mechanisms by which photoperiod might produce these changes. In Experiment 1, immunocytochemistry was used as a semi-quantitative and anatomically specific technique to explore the hypothesis that reduced neural responsiveness to gonadal steroids was due to changes in the number of estrogen and progestin receptors in nuclei mediating hormonal effects on reproductive behavior and physiology. Exposure to a short photoperiod was associated with decreased progestin receptor immunoreactivity (Experiment 1B) but not with changes in estrogen receptor immunoreactivity (Experiments 1A, 1D), suggesting that neural responsiveness to estradiol is reduced in short photoperiods but that this effect is not due to changes in estrogen receptor number. Changes in responsiveness to estradiol are not dependent on peripheral effects of photoperiod on estradiol metabolism, as progestin receptor-immunoreactivity was reduced in short days even when estradiol was implanted directly into the mediobasal hypothalamus (Experiment 1C). Experiment 2 utilized Fos as a marker of neuronal activity to identify specific neural sites where photoperiod might act to influence neural responsiveness to steroid hormones and sociosexual cues responsible for induction of lordosis. Effects of photoperiod on lordosis and Fos were highly variable among experiments, but exposure to a short photoperiod was associated in three of the four experiments (Experiment 2A, 2B, and 2D) with increased Fos immunoreactivity in the ventromedial hypothalamus. Exposure to a short photoperiod may increase the responsiveness of the ventromedial hypothalamus to one or more hormonal or sociosexual cues to which hamsters were exposed.