by Senok, Silas Solomon. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 194-217). / ACKNOWLEDGEMENT --- p.ii / ABSTRACT --- p.v / Chapter 1 --- INTRODUCTION AND OBJECTIVES --- p.1 / Chapter 2 --- LITERATURE REVIEW --- p.8 / Chapter 2.1 --- Classification of Cutaneous Mechanoreceptors --- p.8 / Chapter 2.2 --- Characteristics of Some Mammalian Cutaneous Mechanoreceptors --- p.21 / Chapter 2.3 --- Vibrissae --- p.30 / Chapter 2.4 --- Mechanosensory Transduction --- p.40 / Chapter 2.5 --- The Merkel Cell Controversy --- p.44 / Chapter 2.6 --- Intracellular Calcium Mobilisation --- p.53 / Chapter 3 --- METHODS --- p.59 / Chapter 3.1 --- The Isolated Vibrissal Preparation --- p.59 / Chapter 3.2 --- Experimental Protocol --- p.77 / Chapter 3.3 --- Data Analysis --- p.79 / Chapter 4 --- RESULTS --- p.82 / Chapter 4.1 --- Characterisation of The Receptors --- p.82 / Chapter 4.2 --- Stability And Viability of The Preparation --- p.94 / Chapter 4.3 --- Pharmacologic Studies --- p.103 / Chapter 5 --- DISCUSSION --- p.160 / Chapter 5.1 --- Outcome of Project --- p.160 / Chapter 5 2 --- The Isolated Vibrissal Preparation --- p.162 / Chapter 5.3 --- The Vibrissal Slowly Adapting Mechanoreceptors --- p.165 / Chapter 5 4 --- Mechanism of Chloroquine Inhibtion of Merkel Cell Receptors --- p.170 / Chapter 5.5 --- Evidence For CICR In Merkel Cell Endings --- p.175 / Chapter 5.6 --- Mechano-Electric Transduction In Merkel Cell Receptors --- p.182 / Chapter 5.7 --- Transduction in St II Nerve Terminals --- p.190 / Chapter 5.8 --- What Next? --- p.192 / Chapter 5.9 --- Conclusion --- p.193 / REFERENCES --- p.194

The vibrissal system of pinnipeds relies on sturdy, specialized vibrissae and supporting neural architecture apparently designed for the reception of waterborne disturbances. Although it is known that pinnipeds can use their vibrissae for fine-scale tactile discrimination and hydrodynamic detection, many aspects of vibrissal function remain poorly understood. The present work examined the adaptive significance of vibrissal structure, the sensitivity of the vibrissal system, and the signals received by this system. All of these points were considered with respect to their function in hydrodynamic reception. Four methods of study: laser vibrometry, computed tomography (CT) scanning, psychophysical testing and animal-borne tagging were used to investigate the functioning of this sensory system. Laser vibrometer recordings were used to investigate the effect of vibrissal surface structure and orientation on flow-induced vibrations in excised vibrissae. Vibrations were recorded from the shaft of excised vibrissae exposed to laminar water flow in a flume tank. Samples from three pinniped species were tested: the harbor seal (Phoca vitulina), northern elephant seal (Mirounga angustirostris) and California sea lion (Zalophus californianus). The vibrissae of the seals had an undulated surface structure, while the vibrissae of the sea lion had a smooth surface. No significant difference between species, and therefore surface structure, was observed. However, when vibrissae were tested at three angles of orientation to the water flow, a strong effect of orientation on vibration frequency and velocity was observed across species. CT scanning data revealed that the vibrissae of all the species tested had flattened cross-sectional profiles. This cross-sectional flattening could account for the observed orientation effects. Furthermore, this morphological characteristic may represent an adaptation for improved functioning in the aquatic environment by reducing self-induced-noise from swimming and potentially enhancing detection of signals from other planes. Psychophysical testing was conducted with a trained harbor seal in order to investigate the sensitivity of the vibrissal system of this species. A behavioral procedure was used to measure absolute detection thresholds for sinusoidal stimuli delivered to the vibrissae by a vibrating plate. Thresholds were measured at 9 discrete frequencies from 10 to 1000 Hz. The seal's performance in this stimulus detection task showed that the vibrissal array was sensitive to directly coupled vibrations across the range of frequencies tested, with best sensitivity of 0.09 mm/s at 80 Hz. The velocity thresholds as a function of frequency showed a characteristic U-shaped curve with a gradual low-frequency roll-off below 80 Hz and a steeper high-frequency roll-off above 250 Hz. The thresholds measured for the harbor seal in this study were about 100 times more sensitive than previous in-air measures of vibrissal sensitivity for this species. The results were similar to those reported by others for the detection of waterborne vibrations, but show an extended range of frequency sensitivity. Animal-borne tagging methods were used to investigate the signals received by the vibrissae and better understand the relevant signal components involved in hydrodynamic detection. A novel tagging system, wLogger, was developed to record vibrations directly from a vibrissa by means of an accelerometer coupled to the vibrissal shaft. Laboratory testing using excised whiskers in a water flume confirmed that the tag is capable of recording vibrational signals without hampering the natural movement of the vibrissa. In addition, the tag successfully measured vibrations from the vibrissae of a harbor seal during active swimming and hydrodynamic detection. Live animal testing, along with the supplemental recordings from excised vibrissae, revealed that interaction with hydrodynamic disturbances disrupted the vibrational signal received by the whisker. When exposed to a hydrodynamic signal, whisker vibrations increased in bandwidth, spreading energy across a wider range of frequencies. This finding suggests that modulation of the vibrational signal may play a key role in the detection of hydrodynamic stimuli by the seal. The results of this dissertation research provide insight into the functioning of the vibrissal system in pinnipeds and establishes the groundwork for future pathways of investigation. By investigating the vibrissal system from the focal points of structure, sensitivity and received signals, a more comprehensive understanding of this refined sensory modality is emerging.

by Chan Eliza. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1994. / Includes bibliographical references (leaves 183-196). / ACKNOWLEDGEMENTS / ABSTRACT --- p.i / Chapter CHAPTER ONE: --- INTRODUCTION --- p.1 / Chapter CHAPTER TWO: --- LITERATURE REVIEW / Chapter Section 1: --- History of Merkel cells --- p.3 / Chapter Section 2: --- Morphology and characteristic response of Merkel cell receptors in the skin --- p.5 / Chapter Section 3: --- Merkel cells and other mechanoreceptors in the mammalian sinus hair --- p.16 / Chapter Section 4: --- Functions of Merkel cells --- p.29 / Chapter Section 5: --- Review of technical approaches in the study of Merkel cell physiology --- p.39 / Chapter Section 6: --- Monitoring intracellular Ca2+ with the microfluorimetric technique --- p.42 / Chapter Section 7: --- Properties of voltage-gated and ligand-operated Ca2+ channels --- p.52 / Chapter CHAPTER THREE: --- METHODS / Chapter Section 1: --- Isolation of the rat vibrissal follicles --- p.60 / Chapter Section 2: --- Procedures for fluorimetric studies --- p.63 / Chapter Section 3: --- Procedures for electrophysiological study --- p.72 / Chapter Section 4: --- Chemicals --- p.82 / Chapter CHAPTER FOUR: --- RESULTS / Chapter Section 1: --- Electrophysiological studies in an isolated sinus hair preparation --- p.89 / Chapter Section 2: --- Electrophysiological studies on slowly adapting type I (SA I) mechanoreceptors in an isolated skin-nervein vitro preparation --- p.109 / Chapter Section 3: --- Microfluorimetric studies of Merkel cells in the isolated sinus hair preparation --- p.117

O comportamento exploratório do rato é caraterizado pela preferência por ambientes escuros e pela tendência a permanecer na proximidade de paredes verticais (tigmotatismo). Quando permitida a exploração espontânea de um labirinto em cruz elevado o rato exibe um menor número de visitas aos braços abertos e um menor tempo de permanência nos mesmos. Contudo, essa situação pode ser revertida pela administração de fármacos ansiolíticos. Embora utilizado amplamente no estudo do medo e da ansiedade, ainda não está muito claro qual ou quais são os estímulos aversivos que induzem a esquiva dos braços abertos. O presente trabalho estudou o papel da luminosidade e do tigmotatismo(mediado pelas vibrissas mistaciais) no comportamento exploratório do rato no labirinto em cruz elevado. Para tal fim, essas vibrissas foram removidas de forma aguda (5 minutos antes dos testes) ou crônica: dias (8, 14 e 25; corte diário) antes do teste ou no dia do nascimento e os ratos foram submetidos ao teste do labirinto em cruz elevado sob condições de claridade (150 Lux) e de obscuridade (2 Lux). Os resultados mostraram que na obscuridade os ratos com remoção das vibrissas entram mais e permanecem por mais tempo nos braços abertos, quando comparados tanto com os ratos com vibrissas intactas quanto com ratos com remoções equivalentes das vibrissas mas testados na claridade. Esses resultados sugerem um possível efeito de tipo ansiolítico causado pela remoção das vibrissas somada à falta de luz. O aumento da exploração dos braços abertos poderia dever-se à ausência conjunta de informações provenientes dos dois sistemas sensoriais (visual e tátil das vibrissas). Porém, a ausência de apenas a informação tátil das vibrissas ou de apenas a visual não aumentam a exploração. Estudos posteriores devem ser realizados com o objetivo de conhecer os mecanismos neuroniais envolvidos. / Exploratory behavior in the rat is characterized by a preference for dark environments and by a trend to remain close to vertical surfaces(thigmotaxis). When allowed to freely explore an elevated plus-maze a rat will exhibit a smaller number of entries into the open arms and a smaller time spent in them. This characteristic pattern of behavior can be reverted by the administration of anxiolytic drugs. Although broadly used in the study of fear and anxiety, it still remains unclear what or which are the aversive stimuli that induce the avoidance from the open arms. The present study investigated the role of environmental illumination and thigmotaxis (mediated by mistacial vibrissae) in the exploratory behavior of rats submitted to the elevated plus-maze test. To this end, the vibrissae were removed acutely (5 min before testing) or chronically: days (8, 14 or 25; daily cutting) or in the day of birth and the rats were tested in the plus-maze under two environmental conditions, brightness (150 Lux) or darkness (2 Lux). Results showed that in the darkness rats with vibrissae removed entered more and stayed longer in the open arms than rats with intact vibrissae or rats with removed vibrissae tested under brightness. These results suggest a possible anxiolytic-like effect cause by vibrissa removal added to the absence of light. The increase in exploration of the open arms could be due to the effect of the joint absence of information from both sensorial systems (visual and tactile from the vibrissae) an effect that did not happen when information was lacking from just any one system. Further studies should be performed in order to unravel the neuronal mechanisms involved in the phenomenon.

O comportamento exploratório do rato é caraterizado pela preferência por ambientes escuros e pela tendência a permanecer na proximidade de paredes verticais (tigmotatismo). Quando permitida a exploração espontânea de um labirinto em cruz elevado o rato exibe um menor número de visitas aos braços abertos e um menor tempo de permanência nos mesmos. Contudo, essa situação pode ser revertida pela administração de fármacos ansiolíticos. Embora utilizado amplamente no estudo do medo e da ansiedade, ainda não está muito claro qual ou quais são os estímulos aversivos que induzem a esquiva dos braços abertos. O presente trabalho estudou o papel da luminosidade e do tigmotatismo(mediado pelas vibrissas mistaciais) no comportamento exploratório do rato no labirinto em cruz elevado. Para tal fim, essas vibrissas foram removidas de forma aguda (5 minutos antes dos testes) ou crônica: dias (8, 14 e 25; corte diário) antes do teste ou no dia do nascimento e os ratos foram submetidos ao teste do labirinto em cruz elevado sob condições de claridade (150 Lux) e de obscuridade (2 Lux). Os resultados mostraram que na obscuridade os ratos com remoção das vibrissas entram mais e permanecem por mais tempo nos braços abertos, quando comparados tanto com os ratos com vibrissas intactas quanto com ratos com remoções equivalentes das vibrissas mas testados na claridade. Esses resultados sugerem um possível efeito de tipo ansiolítico causado pela remoção das vibrissas somada à falta de luz. O aumento da exploração dos braços abertos poderia dever-se à ausência conjunta de informações provenientes dos dois sistemas sensoriais (visual e tátil das vibrissas). Porém, a ausência de apenas a informação tátil das vibrissas ou de apenas a visual não aumentam a exploração. Estudos posteriores devem ser realizados com o objetivo de conhecer os mecanismos neuroniais envolvidos. / Exploratory behavior in the rat is characterized by a preference for dark environments and by a trend to remain close to vertical surfaces(thigmotaxis). When allowed to freely explore an elevated plus-maze a rat will exhibit a smaller number of entries into the open arms and a smaller time spent in them. This characteristic pattern of behavior can be reverted by the administration of anxiolytic drugs. Although broadly used in the study of fear and anxiety, it still remains unclear what or which are the aversive stimuli that induce the avoidance from the open arms. The present study investigated the role of environmental illumination and thigmotaxis (mediated by mistacial vibrissae) in the exploratory behavior of rats submitted to the elevated plus-maze test. To this end, the vibrissae were removed acutely (5 min before testing) or chronically: days (8, 14 or 25; daily cutting) or in the day of birth and the rats were tested in the plus-maze under two environmental conditions, brightness (150 Lux) or darkness (2 Lux). Results showed that in the darkness rats with vibrissae removed entered more and stayed longer in the open arms than rats with intact vibrissae or rats with removed vibrissae tested under brightness. These results suggest a possible anxiolytic-like effect cause by vibrissa removal added to the absence of light. The increase in exploration of the open arms could be due to the effect of the joint absence of information from both sensorial systems (visual and tactile from the vibrissae) an effect that did not happen when information was lacking from just any one system. Further studies should be performed in order to unravel the neuronal mechanisms involved in the phenomenon.

No description available.

Lorsque les rongeurs explorent leur environnement, ils contactent activement les objets environnants avec leurs vibrisses qui sont ainsi défléchies selon des séquences spatiotemporelles complexes. Le système vibrissal est néanmoins capable d'extraire des informations pertinentes de ces stimulations pour générer un comportement tactile-dépendant. Une question se pose alors: Comment l’information multivibrissale globale est-elle encodée? La représentation corticale des vibrisses au sein du cortex somatosensoriel primaire (S1) du rongeur est dotée de structures anatomiquement remarquables, nommées "tonneaux", au niveau de la couche IV, qui sont organisées de la même manière que les vibrisses sur le museau de l’animal. A chaque "tonneau" correspond une colonne corticale, unité de traitement de l’information, qui reçoit en priorité les informations provenant la vibrisse principale (VP) correspondante. Des enregistrements extracellulaires réalisés dans notre équipe chez le rat ont révélé que les réponses des neurones du cortex S1 et du thalamus sont non seulement sensibles à la direction de déflection locale de leur VP, mais aussi à la direction d'un mouvement global de l’ensemble de leurs vibrisses. Afin de mieux comprendre la manière dont le réseau cortical traite ces scènes tactiles globales, nous avons construit un poste expérimental permettant d’enregistrer en temps réel l’activité du cortex S1 chez la souris par imagerie sensible au potentiel, tout en appliquant des stimuli tactiles complexes à l'aide d'une matrice de 24-stimulateurs vibrissaux. Nous avons de plus développé une méthode permettant d’aligner les données fonctionnelles ainsi obtenues par rapport la carte cytoarchitecturale du réseau cortical sous-jacent. Nous avons ainsi étudié premièrement la distribution spatiale de la sélectivité à la direction de déflection locale d’une vibrisse au niveau d’une colonne corticale. Les réponses aux différentes directions étaient localisées de manière légèrement distincte, autour du centre de la colonne, mais selon une organisation différente de celle précédemment décrite chez le rat. Nous avons montré par la suite que la sélectivité à la direction globale est spatialement organisée dans le cortex "en tonneaux" à l’échelle supra-colonnaire. Les colonnes correspondant aux vibrisses rostrales étant plus sélectives à la direction globale que les colonnes associées aux vibrisses caudales. En outre, les colonnes correspondant aux vibrisses dorsales répondent préférentiellement aux directions globales ventrales, tandis que les colonnes associées aux vibrisses ventrales répondent préférentiellement aux directions globales caudales. Enfin, les réponses induites par des directions globales caudo-ventrales étaient en moyenne les plus fortes pour toutes les colonnes. Nous avons montré que la répartition spatiale de la sélectivité à la direction globale peut être expliquée ni par la saillance prédominante de la position de départ de la séquence de stimulation multivibrissale (effet de bord), ni par la sommation linéaire des réponses aux déflections de quelques vibrisses. Les réponses aux stimulations globales de l'ensemble des vibrisses sont en effet fortement sous-linéaires, indépendamment de la direction de la stimulation. Brièvement, nous montrons ici que sortir de la vision classique du système vibrissal permet une meilleure compréhension de la façon dont les différentes caractéristiques des stimuli complexes sont traitées et de la manière dont les propriétés émergentes du cortex, comme la sélectivité à la direction globale, sont construites. / While rodents explore their environment they actively contact surrounding objects with their array of whiskers, resulting in a complex pattern of multiwhisker deflections. Despite this complexity, the whisker system is able to extract relevant information from the spatiotemporal sequence of deflections to generate touch-dependent behavior. The question that arises is: How is global multiwhisker information encoded? Whiskers are mapped onto layer 4 of the primary somatosensory cortex (S1) as discrete units named “barrels”. Each barrel-related vertical column processes information coming primarily from its corresponding principal whisker (PW). Previous experiments in our lab done with extracellular recordings have revealed that neurons in the rat S1 and thalamus not only show a preferred direction for the local deflection of the PW but also for the direction of a global motion across the whisker pad. To further understand how the cortical network processes global tactile scenes, we built a set-up that enables to perform voltage sensitive dye imaging of the mouse barrel cortex while applying precise tactile stimuli using a 24-multi-whisker stimulator. We further developed a technical method to map the recorded functional data onto the cortical structure. We first studied whether local direction selectivity is spatially distributed within the barrel-related column. Responses to different directions were slightly segregated on space close to the barrel center, but the distribution differed from the one previously described in rat S1, namely a pinwheel-like structure. We then showed that global direction selectivity is spatially organized in the barrel cortex. Columns related to rostral whiskers were more selective to the global direction than columns related to caudal whiskers. Moreover, the columns related to dorsal whiskers preferred ventral global directions, while the columns related to ventral whiskers preferred caudal global directions. Overall the responses to the caudo-ventral global directions were the strongest in average for all the columns. We showed that the spatial distribution of the global direction selectivity can be explained neither by the high salience of the starting position of the deflections on the whiskerpad (a border effect), nor by the linear summation of the responses to deflections of several whiskers. Responses to the global motion of the whisker array are indeed highly sublinear independently of the direction of stimulation. In conclusion, we show here that stepping aside from the classical view of the whisker-to-barrel cortex system allows a better understanding of how different features of complex stimuli are processed and how the emergent properties of the cortex, like the global direction selectivity, are built-up.