The emetic reflex in a reptile (Crocodylus porosus)

Microraptor with Ingested Lizard Suggests Non-specialized Digestive Function

Direct indicators of diet and predator-prey relationships are exceedingly rare in the fossil record [1, 2]. However, it is through such traces that we can best understand trophic interactions in ancient ecosystems [3], confirm dietary inferences derived from skeletal morphologies [4], and clarify behavioral and ecological interpretations [5]. Here, we identify a previously unrecognized lizard species in the abdomen of a specimen of Microraptor zhaoianus, a small, volant dromaeosaurid (Paraves) with asymmetrical flight feathers on both its forelimbs and hindlimbs from the Early Cretaceous Jehol Biota [6-8]. The lizard is largely complete and articulated, confirming the current perception of Microraptor as an agile opportunistic predator that, like extant reptiles, including raptorial birds, ingested small prey whole and head first [9]. The lizard can be readily distinguished from previously recognized Early Cretaceous species based on its unusual widely spaced and brachydont dentition. Phylogenetic analysis suggests Indrasaurus wangi gen. et sp. nov. is a basal scleroglossan closely related to the slightly older Liushusaurus [10]. Comparison of ingested remains preserved across Paraves suggests that dromaeosaurids retained the plesiomorphic condition in which ingested prey were fully digested, rather than egested, as has been demonstrated was the case in the probable troodontid Anchiornis [11]. This supports a closer relationship between Aves and Anchiornis [12, 13] and suggests that flight did not precipitate the evolution of pellet egestion in Paraves and that the evolution of the "modern avian" digestive system in paravians was highly homoplastic [14]. A preliminary Jehol food web is reconstructed from current data.

Evolution and Functional Differentiation of the Diaphragm Muscle of Mammals

Symmorphosis is a concept of economy of biological design, whereby structural properties are matched to functional demands. According to symmorphosis, biological structures are never over designed to exceed functional demands. Based on this concept, the evolution of the diaphragm muscle (DIAm) in mammals is a tale of two structures, a membrane that separates and partitions the primitive coelomic cavity into separate abdominal and thoracic cavities and a muscle that serves as a pump to generate intra-abdominal (Pab ) and intrathoracic (Pth ) pressures. The DIAm partition evolved in reptiles from folds of the pleural and peritoneal membranes that was driven by the biological advantage of separating organs in the larger coelomic cavity into separate thoracic and abdominal cavities, especially with the evolution of aspiration breathing. The DIAm pump evolved from the advantage afforded by more effective generation of both a negative Pth for ventilation of the lungs and a positive Pab for venous return of blood to the heart and expulsive behaviors such as airway clearance, defecation, micturition, and child birth. © 2019 American Physiological Society. Compr Physiol 9:715-766, 2019.

Why is the neurobiology of nausea and vomiting so important?

Nausea and vomiting are important as biological systems for drug side effects, disease co-morbidities, and defenses against food poisoning. Vomiting can serve the function of emptying a noxious chemical from the gut, and nausea appears to play a role in a conditioned response to avoid ingestion of offending substances. The sensory pathways for nausea and vomiting, such as gut and vestibular inputs, are generally defined but the problem of determining the brain's final common pathway and central pattern generator for nausea and vomiting is largely unsolved. A neurophysiological analysis of brain pathways provides an opportunity to more closely determine the neurobiology of nausea and vomiting and its prodromal signs (e.g., cold sweating, salivation).

Serotonin--a link between disgust and immunity?

Immune systems maintain the integrity of organisms by recognising and attacking foreign substances and/or pathogens. However, immune defences can only take place following direct contact with threats. Disgust can prevent infection before contact with potential pathogens: we propose that disgust is an evolved nervous response to a signal reliably co-occurring with infectious environmental disease threats, which motivates behaviour leading to the avoidance of infection. We hypothesize that disgust and immunity form a defensive continuum with overlaps: disgust acts prior to contact with the infectious agent and prevents it from getting into the body; emesis (vomiting) gets it out once inside the gastrointestinal tract, before penetration of the body boundaries; and immunity expels or kills infectious threats following penetration of the body proper. We further propose that serotonin (5-hydroxytryptamine, 5-HT) might be the link between disgust and immunity. 5-HT plays a central role in the induction of the emetic reflex and is possibly involved in the development of learned aversion; it is also a signal used by immune cells and modulates both innate and acquired immunity. We therefore propose 5-HT might mediate the interaction between these two defensive mechanisms.

Signals for nausea and emesis: Implications for models of upper gastrointestinal diseases

Nausea and vomiting are amongst the most common symptoms encountered in medicine as either symptoms of diseases or side effects of treatments. In a more biological setting they are also important components of an organism's defences against ingested toxins. Identification of treatments for nausea and vomiting and reduction of emetic liability of new therapies has largely relied on the use of animal models, and although such models have proven invaluable in identification of the anti-emetic effects of both 5-hydroxytryptamine(3) and neurokinin(1) receptor antagonists selection of appropriate models is still a matter of debate. The present paper focuses on a number of controversial issues and gaps in our knowledge in the study of the physiology of nausea and vomiting including: The choice of species for the study of emesis and the underlying behavioural (e.g. neophobia), anatomical (e.g. elongated, narrow abdominal oesophagus with reduced ability to shorten) and physiological (e.g. brainstem circuitry) mechanisms that explain the lack of a vomiting reflex in certain species (e.g. rats); The choice of response to measure (emesis[retching and vomiting], conditioned flavour avoidance or aversion, ingestion of clay[pica], plasma hormone levels[e.g. vasopressin], gastric dysrhythmias) and the relationship of these responses to those observed in humans and especially to the sensation of nausea; The stimulus coding of nausea and emesis by abdominal visceral afferents and especially the vagus-how do the afferents encode information for normal postprandial sensations, nausea and finally vomiting?; Understanding the central processing of signals for nausea and vomiting is particularly problematic in the light of observations that vomiting is more readily amenable to pharmacological treatment than is nausea, despite the assumption that nausea represents "low" intensity activation of pathways that can evoke vomiting when stimulated more intensely.

How snakes eat snakes: the biomechanical challenges of ophiophagy for the California kingsnake, Lampropeltis getula californiae (Serpentes: Colubridae)

In this study we investigated how ophiophagous snakes are able to ingest prey snakes that equal or exceed their own length. We used X-ray video, standard video, dissection, and still X-rays to document the process of ophiophagy in kingsnakes (Lampropeltis getula) feeding on corn snakes (Elaphe guttata). Most kingsnakes readily accepted the prey snakes, subdued them by constriction, and swallowed them head first. In agreement with previous observations of ophiophagy, we found that the predator snake forces the vertebral column of the prey snake to bend into waves. These waves shorten the prey's body axis and allow it to fit inside the gastrointestinal (GI) tract and body cavity of the predator. Dissection of a kingsnake immediately following ingestion revealed extensive longitudinal stretching of the anterior portion of the GI tract (oesophagus and stomach), and no visible incursion of the prey into the intestine. X-ray video of ingestion showed that the primary mechanism of prey transport was the pterygoid walk, with some contribution from concertina-like compression and extension cycles of the predator's vertebral column in two out of three observations. Complete digestion was observed in only one individual, as others regurgitated before digestion was finished. X-ray stills taken every 4 days following ingestion revealed that the corn snakes were about half digested within the first 4 days, and digestion was complete within 15 days.