Behavioural studies described embryonic motility as random and lacking coordination whereas electrophysiological studies found orderly, reliable patterns of motor neuron recruitment suggesting the potential for coordinated movement exists early in development. To address this apparent paradox, the study measured and described patterns of joint excursions in the ipsilateral wing and leg of the chick embryo at embryonic day 9, in ovo, during spontaneous motility. Methods were developed to obtain kinematic measures, corrected for movement out-of-plane, from video recordings of continuous activity. Within a limb, synchronous movement of joints into flexion and extension was the prevailing pattern in all embryos. Between limbs, synchronous movements were present but less common, however, there were distinct, orderly spatiotemporal patterns of ankle and elbow excursions suggesting that movements of ipsilateral limbs are nonrandom and partially interdependent. Results suggest that organized, coordinated movements are a reliable feature of embryonic motility.

The purpose of our study was to examine if there is an ERG component (a-wave, b-wave, or OPs) that could be used as an estimate of the intraretinal time of visual processing. To investigate that matter, we proceeded to simultaneous recordings of the ERG and of single cell unit activity at the geniculate level in paralyzed and anesthetized rabbits. Our results show that 86.4% of the geniculate cells (n = 162) responded to the flash before the peak of the b-wave. One of the oscillatory potentials, the OP2, was preceding the geniculate activity in 77.8% of the cases. Furthermore, the shifts in latency of the geniculate cells induced by varying the intensity of the flash were better correlated to the peak time of OP2 than to the peak time of the b-wave. The mean correlation coefficient between the peak time of OP2 and the latency of the LGN unit response is 0.91 $ pm$ 0.13, against 0.70 $ pm$ 0.29 for the b-wave, and 0.63 $ pm$ 0.27 for the a-wave. Our results suggest that OP2 better reflects the primary visual processes at the retinal level and provides a better estimate of the intraretinal time taken for visual processing.

<p> The early visual system is a widely-studied model of parallel processing and neural coding in the brain. In this system, neural populations composed from several distinct cell types perform computations and carry relevant sensory information into other brain areas. While the early visual system, including the retina, shares basic organizational features with other sensory systems, it has several advantages that make it particularly well-suited to studying questions related to population coding. The first of these is the ability to capture the output of ganglion cells in experiments, which form a complete representation of the visual world due to the bottleneck of the optic nerve. The second is the development of models which accurately describe the input/output relationships between stimuli and the cells' spiking output. Here, using the modeling and experimental advantages afforded in this system, we investigate several open questions related to parallel processing: the role of correlated activity, and the role of canonical cell class divisions in representing stimulus information. We find that the information carried by neural populations in the retina is largely done so by the independent responses, and we identify novel asymmetries in the information carried by the responses cells on either side of a canonical cell division &ndash; ON vs. OFF &ndash; that is explained by an interaction between their linear and nonlinear response components.</p>

Autonomic circuits depend critically on cholinergic synaptic transmission to develop and function normally, and severe dysautonomias emerge if cholinergic transmission is disrupted. Yet, we do not fully understand how synaptic activity helps cholinergic synapses develop on autonomic neurons nor do we understand whether or not disrupted postsynaptic nAChRs render cholinergic synapses non-functional, resulting in dysautonomias. To study these two issues, I investigated sympathetic neurons from mice with a disruption in the 3 nAChR subunit gene (3 KO). I hypothesized that (1) the loss of 3 subunits would remove functional nAChRs from cholinergic synapses and abolish synaptic transmission; (2) the loss of postsynaptic activity would prevent cholinergic nerve terminals from developing normally; and (3) functional 3 nAChRs are inactivated by diabetes-induced reactive oxygen species (ROS) to render cholinergic synapses non-functional and cause dysautonomias. To test these hypotheses I combined electrophysiological, molecular biology and imaging techniques to examine cholinergic synapses on sympathetic neurons in 3 KO mice. I found that the loss of 3 prevents the appearance of functional nAChRs on sympathetic neurons and abolishes synaptic transmission through sympathetic ganglia. In spite of this, morphologically normal cholinergic synapses form and persist for months on sympathetic neurons from 3 KO mice. Surprisingly, in the absence of postsynaptic activity the presynaptic terminals are immature and lack high-affinity choline transporters (CHTs). As a result, they cannot sustain ACh release and become quickly depleted. Moreover, using in vivo gene transfer strategies I demonstrate that CHT expression in nerve terminals is induced and maintained by signals downstream of postsynaptic activity; converting these immature terminals that deplete rapidly to mature terminals capable of sustaining / Les circuits autonomes nécessitent la transmission synaptique cholinergique pour un développement et une fonction normale. Le résultat d'une perturbation de cette transmission cholinergique est l'apparition de dysautonomies sévères. Hors, nous ne comprenons pas complètement comment l'activité synaptique aide au développement des synapses cholinergiques sur les neurones autonomes, ni si les dysautonomies sont la conséquence d'une perturbation des nAChRs post-synaptiques ayant comme résultat des synapses cholinergiques non-fonctionnelles. Pour en savoir plus sur ces deux sujets, j'ai étudié des neurones sympatiques provenant de souris qui possèdent une perturbation du gène sous-unité a3 nAChR (a3KO). J'ai formulé l'hypothèse que (1) l'absence d'activité post-synaptique empêcherait le développement normal des terminaisons nerveuses cholinergiques ; et (2) les dérivés réactifs de l'oxygène (DRO) provoqués par le diabète causent l'inactivation des nAChRs fonctionnels produisant des synapses cholinergiques non-fonctionnelles et les dysautonomies qui les accompagnent. J'ai combiné plusieurs méthodes pour tester ces hypothèses en examinant les synapses cholinergiques sur des neurones sympatiques dans des souries a3KO. J'ai trouvé que la perte de a3 empêche l'apparition de nAChRs fonctionnels dans les neurones sympathiques et supprime la transmission synaptique à travers les ganglions sympathiques. Malgré cela, des synapses cholinergiques morphologiquement normales se forment et persistent pendant plusieurs mois dans les neurones de souries a3KO. Étonnement, en l'absence d'activité post-synaptique, les terminaisons pre-synaptiques sont immatures et ne possèdent pas de transporteurs à haute affinité de choline (CHT). L'absence de CHTs à comme résultat l'inhabilité de soutenir le relâchement d'ACh causant son épuisement rapide. De plus, en utilisant des techniques de trans

Neurotensin (NT) is a putative neurotransmitter, the central actions of which appear to be mediated by specific high affinity binding sites. Radioautographic studies using emulsion-coated sections have selectively localized a major proportion of NT binding sites over nerve cell bodies in the rat midbrain tegmentum and basal forebrain. In the present studies, it was shown that the vast majority of $ sp{125}$I-NT-labeled neurons in the rat midbrain tegmentum were dopaminergic, while those in the magnocellular basal forebrain of both rats and humans were predominantly cholinergic using adjacent-section light microscopic $ sp{125}$I-NT radioautography combined with either tyrosine hydroxylase (TH) immunohistochemistry or acetylcholinesterase (AChE) pharmacohistochemistry. In specific, cell counts demonstrated that 95-100% of TH-immunoreactive neurons in the rat substantia nigra (SN) and 80-90% in the ventral tegmental area (VTA) exhibited dense $ sp{125}$I-NT labeling. In the rat basal forebrain, 65-80% of AChE-positive perikarya in the vertical limb of the diagonal band, 45-60% in the horizontal limb of the diagonal band, and 75-90% in the nucleus basalis magnocellularis demonstrated selective $ sp{125}$I-NT binding sites. Moreover, competition studies using levocabastine, a selective blocker of the low affinity NT binding component, revealed that the vast majority of $ sp{125}$I-NT binding sites labeled in the SN, VTA, and NBM were of the levocabastine insensitive, high affinity type, previously documented to correspond to the physiologically active NT receptor. These data provide an anatomical substrate for NT-dopaminergic interactions in the rat midbrain tegmentum and for NT-cholinergic interactions in the rat and human basal forebrain. / Ibotenic acid-induced lesions of the NBM produced a marked reduction in both AChE reactivity and cellular $ sp{125}$I-NT binding suggesting that most of the labeled binding sites detected in this region were indeed associated with cholinergic neurons themselves rather than with impinging afferent terminals. In fact, electron microscopic examination of the distribution of $ sp{125}$I-NT binding sites in the NBM revealed that 84% of labeled sites were inside AChE-positive perikarya and proximal dendrites and presumably represented intracellular receptors undergoing synthesis, transport, and/or degradation. The remainder were evenly dispersed along the plasma membrane of AChE-reactive neurons, but were only rarely concentrated opposite synapsing axon terminals. These latter results are consistent with a paracrine mode of action of NT in influencing the NBM cholinergic system.

This work describes the neuromodulatory effects of norepinephrine (NE) on single neurons isolated in the somatosensory cortex of halothane-anaesthetized cats. In 46 animals, a sample of 465 isolated neurons were characterized according to the presence or absence of peripheral input, of spontaneous activity and sensitivity to glutamate. The effects of NE were examined in 117 cases using two different paradigms; either the receptive fields of neurons displaying peripheral inputs were stimulated mechanically during NE administration or the effects of NE were studied on the response to iontophoretically-administered glutamate on neurons lacking a receptive field. / In the presence of NE, 54% (63/117) of the neurons were inhibited. 36% (42/117) displayed some increase in neuronal activity and 10% (12/117) were unaffected. Often, the inhibitory effects of NE were more important on the spontaneous activity than on the induced activity producing an increase in the signal-to-noise ratio in 74% (28/38) of neurons. In contrast, when NE produced some excitation, the signal-to-noise ratio was increased in only 38% (11/29) of those cases. Inhibited neurons were located predominantly in the middle layers of the cortex while excited neurons were found in upper and lower layers. These results suggest that NE has different functions in different layers of the somatosensory cortex. / After the cessation of NE administration, the response to a peripheral stimulus was increased for more than 5 min in 22% (2/9) of neurons. In contrast, long-lasting increases in the response to glutamate followed NE administration in 70% (31/44) of cases. In this latter group, NE also produced long-lasting decreases in the ongoing activity in 39% (9/23) of neurons and long-lasting increases in the signal-to-noise ratio in 59% (13/23). / Pharmacological evidence suggests that the inhibitions were mediated by $ alpha sb{2}$- and $ beta$-receptors while the excitations and the long-lasting increases in neuronal activity were mediated by $ alpha sb1$-receptors.

The Trk family of receptor tyrosine kinases is involved in synaptic plasticity and behavioral memory in mammals. Here, we report the discovery of a Trk-like receptor, termed ApTrkl, in Aplysia. We show that it is expressed in the sensory neurons, the locus for synaptic facilitation, a cellular model for memory formation. Serotonin, the facilitatory neurotransmitter, activates ApTrkl. Activation of ApTrkl leads to activation of ERK. Finally, inhibiting activation of ApTrkl with the Trk inhibitor K252a blocks serotonin-mediated activation of ERK, and a form of cell-wide long-term facilitation. Thus, transactivation of the receptor tyrosine kinase ApTrkl by serotonin is an essential step in the biochemical events leading to long-term facilitation in Aplysia .

The Groucho/Transducin-like Enhancer of split (Gro/TLE) proteins are a family of transcriptional corepressors involved in a variety of cell differentiation mechanisms in both invertebrates and vertebrates. In particular, they act as negative regulators of neuronal development. Gro/TLEs can be recruited to DNA by forming complexes with a number of DNA-binding transcription factors and are thus involved in the regulation of numerous genes. The aim of this study was to characterize a new member of the Gro/TLE family named Groucho-related gene 6 (Grg6). It is reported here that Grg6 is expressed in selected regions of the murine embryonic nervous system in both mitotic progenitor cells and postmitotic neurons. Exogenous expression of Grg6 in cortical neural progenitor cells does not significantly affect neuronal differentiation. However, when co-expressed with Gro/TLE1 and the anti-neurogenic Gro/TLE-binding protein brain factor 1 (BF-1; also called Foxg1), Grg6 causes an increase in the number of differentiated neurons. In agreement with these findings, Grg6 interacts with BF-1 and decreases transcriptional repression mediated by BF1:Gro/TLE complexes. In addition, Grg6 disrupts the interaction between BF-1 and Gro/TLE1. Together, these results suggest that Grg6 acts as a negative regulator of BF1 activity and as a positive regulator of cortical neuronal differentiation.

From the association of the epsilon4 allele of apolipoprotein (apo) E with Alzheimer's disease (AD) to the more recent reports of reduced risks of developing the disease when taking cholesterol lowering agents, links seem to point for a central role for lipoprotein metabolism in the AD brain. While the association with apoE4 is the strongest and most reproduced risk factor for AD, roles for other proteins involved in lipoprotein metabolism in the periphery have not been thoroughly investigated. / Using the entorhinal cortex lesion (ECL) paradigm in human apoE-targeted replacement mice we examine whether apoE4 has effects on reactive synaptogenesis in the absence of the concentration bias observed in human and how these effects are mediated. In a second study, again using the ECL model, we investigate the role of lipoprotein lipase (LPL) in the brain in response to injury. Finally, we study the effect of intronic polymorphisms of the LPL on the risk and severity of AD. / The results show that mice expressing apoE4 have impaired astroglial organization resulting from an exacerbated inflammatory state and culminating into reactive synaptogenesis impairment. We also observe isoform-specific tau phosphorylation and beta-amyloid (Abeta) accumulation. Furthermore, we report that LPL plays a role in the degeneration phase following ECL. We propose that it is involved in the recycling of lipids together with the glial-specific proteoglycan syndecan-4. Finally we report associations between LPL polymorphisms and AD risk and severity. Since the polymorphisms associate with increased expression of LPL in AD brain as well as with increased senile plaque number, we propose that LPL may be involved in amyloid clearance and deposition. / Taken together these results confirm the importance of lipoprotein metabolism in AD as apoE and LPL are both involved in maintaining cholesterol homeostasis in the brain and also both participate in Abeta metabolism.

O6-Methylguanine DNA methyltransferase (MGMT) is an inducible DNA repair protein that acts to repair damage by DNA alkylating agents currently used in chemotherapy, such as temozolomide. MGMT removes the alkyl group placed at the O6-position of guanine by these alkylating agents, decreasing their efficacy. It has been shown that epigenetic methylation of the O6-MGMT DNA promoter region in tumour tissue from glioblastoma multiforme (GBM) is associated with improved survival from patients treated with temozolomide and concomitant radiotherapy. We wanted to assess the levels of MGMT promoter methylation, RNA and protein expression of cell lines to determine if there is a correlation between these three variables. We also hypothesized that MGMT promoter methylation mosaicism exists in glial tumours and would affect response to temozolomide. To assess this mosaicism we sampled multiple regions of each tumour intra-operatively and analyzed them using methylation specific PCR. Blood was drawn from these patients and the aforementioned MGMT assays were assessed in the peripheral blood mononuclear cells (PBMCs) to determine its usefulness as a prognostic tool. Our results show that MGMT promoter methylation is not a binary event, as currently calculated, but that an intermediate levels of promoter methylation percentage can be assessed. Promoter methylation also does not correlate with RNA or protein expression, but they do trend together. MGMT promoter methylation and RNA expression also vary intratumourally. MGMT promoter methylation can also be assayed in the PBMC fraction of blood in certain patients with high grade gliomas. These methylation levels appear to be associated with recurrence of the tumour and were altered after resection. Our study shows that promoter methylation may need to be looked at as a percentage-based variable and not as a binary system. Furthermore, due to intratumoural heterogeneity more areas of a tumour may need to be assessed for promoter me / O6-Methylguanine DNA methyltransferase (MGMT) est une protéine qui répare l'ADN à la suite de dommages génétiques causées par des traitements de chimiothérapiques tel que Temozolomide (TMZ). MGMT corrige l'addition alkyle à la position O6 de guanine et par conséquence, diminue l'efficacité des agents alkylateurs. La méthylation épigénétique de la région promoteure de MGMT dans les tissues de glioblastomes corrèle avec l'augmentation de la survie des patients traités avec le TMZ et la radiothérapie. Le but de notre recherche était d'évaluer le niveau de méthylation du promoteur de MGMT, de l'ARN, et de l'expression de la protéine dans des lignées cellulaires afain de déterminer si une corrélation existe entre ces trois facteurs. De plus, nous avons prédit que le niveau de méthylation du promoteur de MGMT varierait entre chaque échantillon de tumeur cérébrale. Nous avons testé plusieurs régions d'une tumeur par <methylation-specific PCR> (MSP). Ce teste a été performé sur les cellules périphérales mononucléaires sanguines (CPMS). Nos résultats suggèrent que le niveau de la méthylation varie énormément. De plus le niveau d'expression de l'ARN et de la protéine de MGMT ne corrèle pas avec le niveau de méthylation du promoteur de MGMT. Ces niveaux sont souvent différents chez des échantillons qui proviennent de la même tumeur. Chez certains patients diagnostiqués avec un glioblastome, le niveau de méthylation dans les CPMS semble indiquer la récidive de la tumeur. Nous suggérons que la méthylation du promoteur de MGMT n'est pas binaire, et qu'elle doit être évaluée en terme de spectre variant de zero à cent pour cent. En plus, plusieurs spécimens d'une même tumeur doit être évalué par MSP. Finallement, l'analyse des CPMS peut servir d'outil pour prédire la réponse des patients traités avec des agents alkylateurs tel que TMZ.