Previous research has demonstrated that ingesting fluid of different temperatures results in different whole-body sweat losses (WBSL) and transient changes in local sweat rate (LSR) without any parallel differences in core or skin temperatures. The purpose of this thesis was to determine the potential location and relative contribution of gastrointestinal thermoreceptors that modify sudomotor activity. Eight participants cycled for 75 min while cold (1.5°C) and warm (50°C) water was either swilled in the mouth, or delivered directly to the stomach bypassing the mouth using a nasogastric tube, after 15, 30 and 45-min of exercise. Mouth-swilling warm or cold water did not alter sudomotor output, however delivering warm or cold water directly into the stomach led to a temperature-dependent change in sudomotor output, despite similar core and skin temperatures. These data indicate that thermoreceptors independently modulating sudomotor output probably reside within the abdominal area, but not the mouth.

Previous research has demonstrated that ingesting fluid of different temperatures results in different whole-body sweat losses (WBSL) and transient changes in local sweat rate (LSR) without any parallel differences in core or skin temperatures. The purpose of this thesis was to determine the potential location and relative contribution of gastrointestinal thermoreceptors that modify sudomotor activity. Eight participants cycled for 75 min while cold (1.5°C) and warm (50°C) water was either swilled in the mouth, or delivered directly to the stomach bypassing the mouth using a nasogastric tube, after 15, 30 and 45-min of exercise. Mouth-swilling warm or cold water did not alter sudomotor output, however delivering warm or cold water directly into the stomach led to a temperature-dependent change in sudomotor output, despite similar core and skin temperatures. These data indicate that thermoreceptors independently modulating sudomotor output probably reside within the abdominal area, but not the mouth.

The ability to sense humidity and wetness is an important sensory attribute for many species across the animal kingdom, including humans. Although this sensory ability plays an important role in many human physiological and behavioural functions, as humans largest sensory organ i.e. the skin seems not to be provided with specific receptors for the sensation of wetness (i.e. hygroreceptors), the neurophysiological mechanisms underlying this complex sensory experience are still poorly understood. The aim of this Thesis was to investigate the neurophysiological mechanisms underpinning humans remarkable ability to sense skin wetness despite the lack of specific skin hygroreceptors. It was hypothesised that humans could learn to perceive the wetness experienced when the skin is in contact with a wet surface or when sweat is produced through a complex multisensory integration of thermal (i.e. heat transfer) and tactile (i.e. mechanical pressure and friction) inputs generated by the interaction between skin, moisture and (if donned) clothing. Hence, as both thermal and tactile skin afferents could contribute significantly to drive the perception of skin wetness, their role in the peripheral and central sensory integration of skin wetness perception was investigated, both under conditions of skin s contact with an external (dry or wet) stimulus as well as during the active production of sweat. A series of experimental studies were performed, aiming to isolate the contribution of each sensory cue (i.e. thermal and tactile) to the perception of skin wetness during rest and exercise, as well as under different environmental conditions. It was found that it is not the contact of the skin with moisture per se, but rather the integration of particular sensory inputs which drives the perception of skin wetness during both the contact with an external (dry or wet) surface, as well as during the active production of sweat. The role of thermal (cold) afferents appears to be of a primary importance in driving the perception of skin wetness during the contact with an external stimulus. However, when thermal cues (e.g. evaporative cooling) are limited, individuals seem to rely more on tactile cues (i.e. stickiness and skin friction) to characterise their perception of skin wetness. The central integration of conscious coldness and mechanosensation, as sub-served by peripheral cutaneous A-nerve fibers, seems therefore the primary neural process underpinning humans ability to sense wetness. Interestingly, these mechanisms (i.e. integration of thermal and tactile sensory cues) appear to be remarkably consistent regardless of the modality for which skin wetness is experienced, i.e. whether due to passive contact with a wet stimulus or due to active production of sweat. The novelty of the findings included in this Thesis is that, for the first time, mechanistic evidence has been provided for the neurophysiological processes which underpin humans ability to sense wetness on their skin. Based on these findings, the first neurophysiological sensory model for human skin wetness perception has been developed. This model helps explain humans remarkable ability to sense warm, neutral and cold skin wetness.

Opiliões (Arachnida, Opiliones) são especialmente dependentes da quimiorecepção de contato, além de serem muito dependentes de altos níveis de umidade e de temperaturas amenas. No entanto, o conhecimento acerca das estruturas que detectam esses estímulos é muito limitado em opiliões, quando comparado ao que se sabe sobre outros aracnídeos. Além disso, são raros os estudos investigando a morfologia interna dessas estruturas - um tipo de informação essencial para a determinação de suas funções- e o potencial das sensilla para a sistemática. Neste trabalho, nós investigamos as sensilla tarsais de todos os pares de perna do opilião Heteromitobates discolor (Laniatores, Gonyleptidae), buscando refinar o conhecimento das sensilla quimioreceptoras e investigar a localização dos receptores de temperatura e umidade, através de microscopia eletrônica de varredura (MEV) e transmissão. Para determinar a abrangência dos resultados obtidos com H. discolor e testar o uso de algumas estruturas para a sistemática do grupo, realizamos uma amostragem com MEV em espécies das quatro subordens de Opiliones (Cyphophthalmi, Eupnoi, Dyspnoi e Laniatores), com foco em Laniatores (subordem com 2/3 das espécies do grupo). Na primeira parte, fornecemos a primeira evidência morfológica de receptores olfativos em Laniatores (em H. discolor), mostrando que há abundância e diversidade de sensilla olfativas. Além disso, fornecemos evidência (com MEV) de cerdas olfativas em 17 famílias de Laniatores, o que sugere que a olfação é mais importante para os Laniatores do que previamente considerado. Na segunda parte, fornecemos a primeira evidência morfológica de detectores de umidade e temperatura em opiliões (em H. discolor), discutindo os mecanismos de funcionamento dessas estruturas e uma associação morfológica entre elas, localizada na parte mais distal das pernas I e II. Por fim, mostramos que essas sensilla candidatas a detectores de umidade e temperatura são extremamente conservadas em Laniatores (28 famílias), e que existem estruturas comparáveis em espécies de Cyphophtalmi, Eupnoi e Dyspnoi. Com uma análise de reconstrução de estado ancestral em uma filogenia de Opiliones compilada da literatura, mostramos que as variações na morfologia externa dessas estruturas fornecem informação filogenética em vários níveis de relacionamento em Opiliones. Esse estudo contribui para o conhecimento de aspectos básicos da anatomia celular de sensilla em Opiliones, refinando o conhecimento sobre a função das sensilla tarsais e forncendo uma base para fomentar o uso de sensilla para a sistemática do grupo / Harvestmen (Arachnida, Opiliones) are especially dependent on contact chemoreception and are dependent on high humidity levels and amenable temperatures. However, knowledge on the sensory structures (sensilla) that detect such stimuli is limited in harvestmen when compared with other arachnid orders. Besides, there are few studies investigating the internal morphology of these structures -which is important for inferring function - and the potential of sensilla for systematics. To refine the knowledge on chemoreceptive sensilla and investigate the identity of hygro- and thermoreceptors, we investigated the tarsal sensilla of all leg pairs of the species Heteromitobates discolor (Laniatores, Gonyleptidae), using scanning electron microscopy (SEM) and transmission electron microscopy. To determine scope of the results obtained with H. discolor and to test the use of some structures for systematics, we surveyed (with SEM) species in all four suborders of Opiliones (Cyphophthalmi, Eupnoi, Dyspnoi and Laniatores), with focus in Laniatores (suborder with 2/3 of harvestmen species). In the first part, we provide the first morphological evidence of olfactory receptors in a species of Laniatores (H. discolor), showing that olfactory sensilla are abundant and diverse. Also, we show evidence (with SEM) of olfactory sensilla on 17 families of Laniatores, which suggests that olfaction is more important for Laniatores than previously considered. In the second part, we provide the first morphological evidence of hygro- and thermoreceptors in harvestmen (in H. discolor) discussing the functioning mechanisms of these structures and their morphological inter-association on the distal-most part of leg pairs I and II. Finally, we show that these putative hygro- thermoreceptive sensilla are widespread in species of Laniatores (28 families) and that comparable structures occur on species of the suborders Cyphophthalmi, Eupnoi and Dyspnoi. With an ancestral state reconstruction on a compiled phylogeny of Opiliones, we show that morphological variations on these sensilla are informative on several levels of phylogenetic relationships in Opiliones. This study constributes for the basic knowledge on the cellular anatomy of Opiliones sensilla, refining the function of tarsal sensillar types and providing a base for their use in systematics

Opiliões (Arachnida, Opiliones) são especialmente dependentes da quimiorecepção de contato, além de serem muito dependentes de altos níveis de umidade e de temperaturas amenas. No entanto, o conhecimento acerca das estruturas que detectam esses estímulos é muito limitado em opiliões, quando comparado ao que se sabe sobre outros aracnídeos. Além disso, são raros os estudos investigando a morfologia interna dessas estruturas - um tipo de informação essencial para a determinação de suas funções- e o potencial das sensilla para a sistemática. Neste trabalho, nós investigamos as sensilla tarsais de todos os pares de perna do opilião Heteromitobates discolor (Laniatores, Gonyleptidae), buscando refinar o conhecimento das sensilla quimioreceptoras e investigar a localização dos receptores de temperatura e umidade, através de microscopia eletrônica de varredura (MEV) e transmissão. Para determinar a abrangência dos resultados obtidos com H. discolor e testar o uso de algumas estruturas para a sistemática do grupo, realizamos uma amostragem com MEV em espécies das quatro subordens de Opiliones (Cyphophthalmi, Eupnoi, Dyspnoi e Laniatores), com foco em Laniatores (subordem com 2/3 das espécies do grupo). Na primeira parte, fornecemos a primeira evidência morfológica de receptores olfativos em Laniatores (em H. discolor), mostrando que há abundância e diversidade de sensilla olfativas. Além disso, fornecemos evidência (com MEV) de cerdas olfativas em 17 famílias de Laniatores, o que sugere que a olfação é mais importante para os Laniatores do que previamente considerado. Na segunda parte, fornecemos a primeira evidência morfológica de detectores de umidade e temperatura em opiliões (em H. discolor), discutindo os mecanismos de funcionamento dessas estruturas e uma associação morfológica entre elas, localizada na parte mais distal das pernas I e II. Por fim, mostramos que essas sensilla candidatas a detectores de umidade e temperatura são extremamente conservadas em Laniatores (28 famílias), e que existem estruturas comparáveis em espécies de Cyphophtalmi, Eupnoi e Dyspnoi. Com uma análise de reconstrução de estado ancestral em uma filogenia de Opiliones compilada da literatura, mostramos que as variações na morfologia externa dessas estruturas fornecem informação filogenética em vários níveis de relacionamento em Opiliones. Esse estudo contribui para o conhecimento de aspectos básicos da anatomia celular de sensilla em Opiliones, refinando o conhecimento sobre a função das sensilla tarsais e forncendo uma base para fomentar o uso de sensilla para a sistemática do grupo / Harvestmen (Arachnida, Opiliones) are especially dependent on contact chemoreception and are dependent on high humidity levels and amenable temperatures. However, knowledge on the sensory structures (sensilla) that detect such stimuli is limited in harvestmen when compared with other arachnid orders. Besides, there are few studies investigating the internal morphology of these structures -which is important for inferring function - and the potential of sensilla for systematics. To refine the knowledge on chemoreceptive sensilla and investigate the identity of hygro- and thermoreceptors, we investigated the tarsal sensilla of all leg pairs of the species Heteromitobates discolor (Laniatores, Gonyleptidae), using scanning electron microscopy (SEM) and transmission electron microscopy. To determine scope of the results obtained with H. discolor and to test the use of some structures for systematics, we surveyed (with SEM) species in all four suborders of Opiliones (Cyphophthalmi, Eupnoi, Dyspnoi and Laniatores), with focus in Laniatores (suborder with 2/3 of harvestmen species). In the first part, we provide the first morphological evidence of olfactory receptors in a species of Laniatores (H. discolor), showing that olfactory sensilla are abundant and diverse. Also, we show evidence (with SEM) of olfactory sensilla on 17 families of Laniatores, which suggests that olfaction is more important for Laniatores than previously considered. In the second part, we provide the first morphological evidence of hygro- and thermoreceptors in harvestmen (in H. discolor) discussing the functioning mechanisms of these structures and their morphological inter-association on the distal-most part of leg pairs I and II. Finally, we show that these putative hygro- thermoreceptive sensilla are widespread in species of Laniatores (28 families) and that comparable structures occur on species of the suborders Cyphophthalmi, Eupnoi and Dyspnoi. With an ancestral state reconstruction on a compiled phylogeny of Opiliones, we show that morphological variations on these sensilla are informative on several levels of phylogenetic relationships in Opiliones. This study constributes for the basic knowledge on the cellular anatomy of Opiliones sensilla, refining the function of tarsal sensillar types and providing a base for their use in systematics