Functional neuroanatomy of tachykinins in brainstem autonomic regulation

Little is known about the role that tachykinins, such as substance P and its receptor, the neurokinin-1 receptor, play in the generation of sympathetic nerve activity and the integration within the ventrolateral medulla (VLM) of many vital autonomic reflexes such as the baroreflex, chemoreflex, somato-sympathetic reflex, and the regulation of cerebral blood flow. The studies described in this thesis investigate these autonomic functions and the role of tachykinins through physiological (response to hypercapnoea, chapter 3), anatomical (neurokinin-1 receptor immunohistochemistry, chapter 4) and microinjection (neurokinin-1 receptor activation and blockade, chapters 5 and 6) experiments. In the first series of experiments (chapter 3) the effects of chemoreceptor activation with hyperoxic hypercapnoea (5%, 10% or 15% CO2 in O2) on splanchnic sympathetic nerve activity and sympathetic reflexes such as the baroreflex and somato-sympathetic reflex were examined in anaesthetized rats. Hypercapnoea resulted in sympatho-excitation in all groups and a small increase in arterial blood pressure in the 10 % CO2 group. Phrenic nerve amplitude and phrenic frequency were also increased, with the frequency adapting back to baseline during the CO2 exposure. Hypercapnoea selectively attenuated (5% CO2) or abolished (10% and 15% CO2) the somato-sympathetic reflex while leaving the baroreflex unaffected. This selective inhibition of the somato-sympathetic reflex while leaving the baroreflex unaffected was also seen following neurokinin-1 receptor activation in the rostral ventrolateral medulla (RVLM) (see below). Microinjection of substance P analogues into the RVLM results in a pressor response, however the anatomical basis for this response is unknown. In the second series of experiments (chapter 4), the distribution of the neurokinin-1 receptor in the RVLM was investigated in relation to catecholaminergic (putative sympatho-excitatory “C1”) and bulbospinal neurons. The neurokinin-1 receptor was demonstrated on a small percentage (5.3%) of C1 neurons, and a small percentage (4.7%) of RVLM C1 neurons also receive close appositions from neurokinin-1 receptor immunoreactive terminals. This provides a mechanism for the pressor response seen with RVLM microinjection of substance P analogues. Neurokinin-1 receptor immunoreactivity was also seen a region overlapping the preBötzinger complex (the putative respiratory rhythm generation region), however at this level a large percentage of these neurons are bulbospinal, contradicting previous work suggesting that the neurokinin-1 receptor is an exclusive anatomical marker for the propriobulbar rhythm generating neurons of the preBötzinger complex. The third series of experiments (chapter 5) investigated the effects of neurokinin-1 receptor activation and blockade in the RVLM on splanchnic sympathetic nerve activity, arterial blood pressure, and autonomic reflexes such as the baroreflex, somato-sympathetic reflex, and sympathetic chemoreflex. Activation of RVLM neurokinin-1 receptors resulted in sympatho-excitation, a pressor response, and abolition of phrenic nerve activity, all of which were blocked by RVLM pre-treatment with a neurokinin-1 receptor antagonist. As seen with hypercapnoea, RVLM neurokinin-1 receptor activation significantly attenuated the somato-sympathetic reflex but did not affect the sympathetic baroreflex. Further, blockade of RVLM neurokinin-1 receptors significantly attenuated the sympathetic chemoreflex, suggesting a role for RVLM substance P release in this pathway. The fourth series of experiments (chapter 6) investigated the role of neurokinin-1 receptors in the RVLM, caudal ventrolateral medulla (CVLM), and nucleus tractus solitarius (NTS) on regional cerebral blood flow (rCBF) and tail blood flow (TBF). Activation of RVLM neurokinin-1 receptors increased rCBF associated with a decrease in cerebral vascular resistance (CVR). Activation of CVLM neurokinin-1 receptors decreased rCBF, however no change in CVR was seen. In the NTS, activation of neurokinin-1 receptors resulted in a biphasic response in both arterial blood pressure and rCBF, but no significant change in CVR. These findings suggest that in the RVLM substance P and the neurokinin-1 receptor play a role in the regulation of cerebral blood flow, and that changes in rCBF evoked in the CVLM and NTS are most likely secondary to changes in arterial blood pressure. Substance P and neurokinin-1 receptors in the RVLM, CVLM and NTS do not appear to play a role in the brainstem regulation of tail blood flow. In the final chapter (chapter 7), a model is proposed for the role of tachykinins in the brainstem integration of the sympathetic baroreflex, sympathetic chemoreflex, cerebral vascular tone, and the sympatho-excitation seen following hypercapnoea. A further model for the somato-sympathetic reflex is proposed, providing a mechanism for the selective inhibition of this reflex seen with hypercapnoea (chapter 3) and RVLM neurokinin-1 receptor activation (chapter 5). In summary, the ventral medulla is essential for the generation of basal sympathetic tone and the integration of many vital autonomic reflexes such as the baroreflex, chemoreflex, somato-sympathetic reflex, and the regulation of cerebral blood flow. The tachykinin substance P, and its receptor, the neurokinin-1 receptor, have a role to play in many of these vital autonomic functions. This role is predominantly neuromodulatory

Lipid-protein and protein-protein interactions in the mechanisms of photosynthetic reaction centre and the Na+,K+-ATPase

Lipid-protein and protein-protein interactions are likely to play important roles in the function and regulation of charge-transporting membrane proteins. This thesis focuses on two different membrane proteins, the photosynthetic reaction centre (RC) from purple bacteria and the Na+,K+-ATPase. The influence of the lipid surroundings and cholesterol derivatives on the kinetics of electron transfer of the RC were investigated by reconstituting the protein in phosphatidylcholine vesicles containing cholesterol and derivatives known to modulate the membrane dipole potential. The experiments performed on the Na+,K+-ATPase were designed to contribute to a better understanding of the role that oligomeric protein-protein interactions have in the enzyme’s mechanism. Our results show that the cholesterol derivatives significantly modify the electron transfer kinetics within the RCs and their multiphasic behavior. These effects seem to be associated with the extent of the dipole potential change experienced by the RC within the phospholipid membrane. Indeed, the largest effects on the rates are observed when 6-ketocholestanol and cholesterol are present, consistent by with their previously demonstrated significant increase of the dipole potential. We interpret this data as indicating an increased free energy barrier for protons to enter the protein. The consequences of the increased dipole potential seem to be experienced across the entire protein, since the rates of the P+QA- charge recombination in the presence of AQ- acting as QA are also modified by the same effectors. Also interesting is the effect of the dipole potential on the two conformational states of the RCs (previously reported) as revealed by the biphasic decays of the electron transfer kinetics. In particular, we report for the first time a biphasicity of the P+QA- charge recombination in the WT RCs. This non exponential behaviour, absent in the phospholipid membrane or isolated RCs, is induced by the presence of the cholesterol derivatives, suggesting that the equilibration time between the two RC conformations is slowed down significantly by these molecules. According to this work, the dipole potential seems to be an important parameter that has to be taken into account for a fine understanding of the charge transfer function of the RCs. Reported literature values of the dissociation constant, Kd, of ATP with the E1 conformation of the Na+,K+-ATPase based on equilibrium titrations and kinetic methods disagree. Using isothermal titration calorimetry (ITC) and simulations of the expected equilibrium behaviour for different binding models, this thesis presents an explanation for this apparent discrepancy based on protein-protein interactions. Because of the importance of Mg2+ in ATP hydrolysis, kinetic studies of Mg2+ binding to the protein were also carried out. These studies showed that ATP alone is responsible for Mg2+ complexation, with no significant contribution from the enzyme environment

A Specific Role of the Human Hippocampus in Recall of Temporal Sequences

There is a growing interest in how temporal order of episodic memories is represented within the medial temporal lobe (MTL). Animal studies suggest that the hippocampal formation (HF) is critical for retrieving the temporal order of past experiences. However, human imaging studies that have tested recency discrimination between pairs of previously encoded items have generally failed to report HF activation. We hypothesized that recalling a naturalistic sequence of past events would be particularly sensitive to HF function, attributable to greater involvement of associative processes. To test this prediction, we let subjects watch a novel movie and later, during functional magnetic resonance imaging, asked them to rearrange and "replay" scenes from the movie in correct order. To identify areas specifically involved in retrieval of temporal order, we used a control condition where subjects logically inferred the order of scenes from the same movie. Extensive MTL activation was observed during sequence recall. Activation within the right HF was specifically related to retrieval of temporal order and correlated positively with accuracy of sequence recall. Also, the bilateral parahippocampal cortex responded to retrieval of temporal order, but the activation here was not related to performance. Our study is the first to unequivocally demonstrate that correct sequence recall depends on H

The kinetics of the gas-phase reactions of selected monoterpenes and cyclo-alkenes with ozone and the NO3 radical

The relative rate method has been used to measure the room-temperature rate constants for the gasphase reactions of ozone and NO3 with selected monoterpenes and cyclo-alkenes with structural similarities to monoterpenes. Measurements were carried out at 298 ! 2 K and 760 ! 10 Torr. The following rate constants (in units of 10"18 cm3 molecule"1 s"1) were obtained for the reaction with ozone: methyl cyclohexene (132 ! 17), terpinolene (1290 ! 360), ethylidene cyclohexane (223 ! 57), norbornene (860 ! 240), t-butyl isopropylidene cyclohexane (1500 ! 460), cyclopentene (543 ! 94), cyclohexene (81 ! 18), cyclooctene (451 ! 66), dicyclopentadiene (1460 ! 170) and a-pinene (107 ! 13). For the reaction with NO3 the rate constants obtained (in units of 10"12 cm3 molecule"1 s"1) were: methyl cyclohexene (7.92 ! 0.95), terpinolene (47.9 ! 4.0), ethylidene cyclohexane (4.30 ! 0.24), norbornene (0.266 ! 0.029), cyclohexene (0.540 ! 0.017), cyclooctene (0.513 ! 0.029), dicyclopentadiene (1.20 ! 0.10) and a-pinene (5.17 ! 0.62). Errors are quoted as the root mean square of the statistical error (95% con!dence) and the quoted error in the rate constant for the reference compound. Combining these results with previous studies, new recommendations for the rate constants are presented. Molecular orbital energies were calculated for each alkene and the kinetic data are discussed in terms of the deviation from the structureeactivity relationship obtained from the rate constants for a series of simple alkenes. Lifetimes with respect to key initiators of atmospheric oxidation have been calculated suggesting that the studied reactions play dominant roles in the night-time removal of these compounds from the atmosphere

[Conventional retaining of removable partial dentures],[Conventional retaining of removable partial dentures]

Contains fulltext : 79781.pdf (publisher's version ) (Open Access)Mechanical and biological criteria have to be met in retaining the metal frame of a removable partial denture. Additionally, a removable partial denture is part of the occlusal interface by the clasps and the denture teeth. With respect to mechanical aspects, all rigid parts of the removable partial denture are of importance. However, as clasp arms tend to loose retention during long-term function, it is primarily the minor connectors and rigid clasp arms that provide stability and retention by friction with the guiding planes of the abutment teeth. With respect to biological aspects, comfort and cleansing ability are most important. Their functioning is enhanced by a low number of components crossing the marginal gingiva, such as minor connectors and infrabulge clasps. In the occlusal interface, occlusal interferences both in occlusion and during articular excursions should not be introduced by retainers or denture teeth

A 6-year follow-up study of the oral function in shortened dental arches

Contains fulltext : mmubn000001_167201212.pdf (publisher's version ) (Open Access)Promotores : A. Käyser en G. van Rossum133 p

On the interface of occlusion.

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Dental laboratory production of prosthetic restorations in a population in sofia, bulgaria: a descriptive study.

Contains fulltext : 88297.pdf (publisher's version ) (Open Access)Objective. To describe prosthodontic production related to mutilated dentitions in Sofia, Bulgaria. Methods. Prosthodontic production from 5 dental laboratories was recorded during a 14-day period. Production was related to dentitions as noted from casts. Dentitions were classified as edentulous, interrupted/reduced, slightly interrupted, shortened, and complete. The representativeness of the laboratory sample was verified trough comparison with a Sofia population sample using proportions of crowned or replaced teeth per dental region. Results. The total production consisted of 243 crowns, 16 post and cores, 82 fixed dental prostheses, and 41 removable dentures. Proportions of crowned teeth were significantly different between the samples; proportions of replaced teeth were not. Of the 58 incomplete dentitions analyzed, 19 were restored to the level of completeness, 15 resulted in slightly interrupted, and 24 in shortened dentitions. Conclusions. Predominantly fixed restorations were provided to restore mutilated dentitions to a functional level and not necessarily to complete dentitions