The skin crawls, the stomach turns: ectoparasites and pathogens elicit distinct defensive responses in humans

Disgust has long been viewed as a primary motivator of defensive responses to threats posed by both microscopic pathogens and macroscopic ectoparasites. Although disgust can defend effectively against pathogens encountered through ingestion or incidental contact, it offers limited protection against ectoparasites, which actively pursue a host and attach to its surface. Humans might, therefore, possess a distinct ectoparasite defence system—including cutaneous sensory mechanisms and grooming behaviours—functionally suited to guard the body's surface. In two US studies and one in China, participants (N = 1079) viewed a range of ectoparasite- and pathogen-relevant video stimuli and reported their feelings, physiological sensations, and behavioural motivations. Participants reported more surface-guarding responses towards ectoparasite stimuli than towards pathogen stimuli, and more ingestion/contamination-reduction responses towards pathogen stimuli than towards ectoparasite stimuli. Like other species, humans appear to possess evolved psychobehavioural ectoparasite defence mechanisms that are distinct from pathogen defence mechanisms.

The skin crawls, the stomach turns: ectoparasites and pathogens elicit distinct defensive responses in humans

Disgust has long been viewed as a primary motivator of defensive responses to threats posed by both microscopic pathogens and macroscopic ectoparasites. Although disgust can defend effectively against pathogens encountered through ingestion or incidental contact, it offers limited protection against ectoparasites, which actively pursue a host and attach to its surface. Humans might, therefore, possess a distinct ectoparasite defence system—including cutaneous sensory mechanisms and grooming behaviours—functionally suited to guard the body's surface. In two US studies and one in China, participants ( N = 1079) viewed a range of ectoparasite- and pathogen-relevant video stimuli and reported their feelings, physiological sensations, and behavioural motivations. Participants reported more surface-guarding responses towards ectoparasite stimuli than towards pathogen stimuli, and more ingestion/contamination-reduction responses towards pathogen stimuli than towards ectoparasite stimuli. Like other species, humans appear to possess evolved psychobehavioural ectoparasite defence mechanisms that are distinct from pathogen defence mechanisms.

The execution of movement - a spinal affair

In this tribute to Reggie Edgerton, I briefly review the spinal mechanisms that coordinate locomotion and the interaction between the different sensory mechanisms that help coordinate the locomotor movements and the central locomotor network. The step cycle has four distinct parts, the support phase, the lift off, the flexion phase and the most complex, the touch down, when the limb makes a smooth contact with ground again. Each of these phases is affected by different sensory mechanisms, which interact with the central network (CPG) generating the basic movements with its four components. Conversely, the CPG also gates the sensory reflex pathways, so that they are active only in a given phase of the step cycle, or even produces opposite effects in different parts of the step cycle. These different examples from mammals are most likely important also to consider for human locomotion, and in particular in patients with spinal cord injury, partial or complete.

TONIC ACTIVITY AND GRAVITATIONAL CONTROL OF THE POSTURAL MUSCLE

The review is an attempt to describe and give a meaning to the accumulated data about the mechanisms controlling the structure and functionality of the postural muscle the almost continuous work of which makes it possible for the humans and animals to exist actively on Earth's surface. A great bulk of these data was obtained, described and systematized by professor I.B. Kozlovskaya and her pupils. A body of the most interesting facts and regularities was documented in other laboratories and research centers, quite often under the influence of ideas suggested by I.B. Kozlovskaya. The concept of the tonic system, that is, an integral physiological apparatus comprising not only slow and fast muscular fibers and small controlling motoneurons but also a complex of the brain (up to and including the striatum and motor cortex) and sensory mechanisms, constitutes the most important parts of her theoretical legacy. The fundamental conclusion of this review is that the gravity-dependent tonic contracting activity of the postural muscle controlled by the nervous system and afferent mechanisms is key to maintaining its structure, signal pathways and mechanic properties crucial for its constant anti-gravity activity.

The subterranean catfish Phreatobius cisternarum provides insights into visual adaptations to the phreatic environment

Vertebrate eyes share the same general organization, though species have evolved morphological and functional adaptations to diverse environments. Cave-adapted animals are characterized by a variety of features including eye reduction, loss of body pigmentation, and enhanced non-visual sensory systems. Species that live in perpetual darkness have also evolved sensory mechanisms that are independent of light stimuli. The subterranean catfish Phreatobius cisternarum lives in the Amazonian phreatic zone and displays a diversity of morphological features that are similar to those observed in cavefish and appear to be adaptations to life in the dark. Here we combine histological and transcriptome analyses to characterize sensory adaptations of P. cisternarum to the subterranean environment. Histological analysis showed that the vestigial eyes of P. cisternarum contain a rudimentary lens. Transcriptome analysis revealed a repertoire of eleven visual and non-visual opsins and the expression of 36 genes involved in lens development and maintenance. In contrast to other cavefish species, such as Astyanax mexicanus, Phreatichthys andruzzii, Sinocyclocheilus anophthalmus and Sinocyclocheilus microphthalmus, DASPEI neuromast staining patterns did not show an increase in the number of sensory hair cells. Our work reveals unique adaptations in the visual system of P. cisternarum to underground habitats and helps to shed light into troglomorphic attributes of subterranean animals.