Background:The aim of this review was to identify the mechanisms by which serotonin receptors involved at the central level are able to modulate the nociceptive response. Pain is a defense mechanism of the body that entails physio-logical, anatomical, neurochemical, and psychological changes, and is defined as an unpleasant sensory and emotional expe-rience with potential risk of tissue damage, comprising the leading cause of appointments with Physicians worldwide. Treatment for this symptom has generated several neuropharmacological lines of research, due to the different types of pain and the various drugs employed to treat this condition. Serotonin [5-HydroxyTryptamine (5-HT)] is a neurotransmitter with seven families (5-HT1–5-HT7) and approximately 15 receptor subtypes. Serotonin modulates neuronal activity; however, this neurotransmitter is related with a number of physiological processes, such as cardiovascular function, gastric motility, renal function, etc. On the other hand, several researches reported that serotonin modulates nociceptive response through 5-HT1, 5-HT2, 5-HT3, and 5-HT7 receptors in the Central Nervous System (CNS).Method:In this review, a search was conducted on PubMed, ProQuest, EBSCO, and the Science Citation Index for studies evaluating the effects of 5-HT1, 5-HT2, 5-HT3, and 5-HT7 receptors in the CNS on the modulation of different types of pain.ConclusionWe concluded that 5-HT1, 5-HT2, 5-HT3, and 5-HT7 receptors in the CNS modulate the pain, but this depends on the distribution of the receptors, dose of agonists or antagonists, administration route, pain type and duration in order to inhibit, excite, or even maintain the nociceptive response.

In many animal species, facial expressions are key elements for recognizing emotions and numerous types of social interaction. Emotions are complex reactions that allow individuals to cope with full events that have either positive or negative meaning and involve certain neurophysiological responses proper to each emotion and species. Regulation of emotional states requires integrating a whole series of responses - peripheral, autonomous, endocrine and muscular - that entail activating various sub-cortical structures, including the amygdale, hypothalamus and brainstem. In recent decades, interest in the emotions expressed by animals has grown, and researchers have come to understand that some problems of animal welfare can be detected by examining and comprehending the emotional experiences that animals may suffer, and identifying how they demonstrate their reactions through facial expressions and corporal postures. The objective of this review is to examine recent literature on aspects related to the function of the emotions and facial expressions in certain domestic species (cats, dogs, rats, sheep, horses and pigs) and propose that understanding facial expressions can be useful as a complement to existing tools in assessing welfare and working with, or doing research on, these species.

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The recent pandemic of the coronavirus infectious disease 2019 (COVID-19) has affected around 192 countries, and projections have shown that around 40% to 70% of world population could be infected in the next months. COVID-19 is caused by the virus SARS-CoV-2, it enters the cells through the ACE2 receptor (angiotensin converting enzyme 2). It is well known that SARS-CoV-2 could develop mild, moderate, and severe respiratory symptoms that could lead to death. The virus receptor is expressed in different organs such as the lungs, kidney, intestine, and brain, among others. In the lung could cause pneumonia and severe acute respiratory syndrome (SARS). The brain can be directly affected by cellular damage due to viral invasion, which can lead to an inflammatory response, by the decrease in the enzymatic activity of ACE2 that regulates neuroprotective, neuro-immunomodulatory and neutralizing functions of oxidative stress. Another severe damage is hypoxemia in patients that do not receive adequate respiratory support. The neurological symptoms that the patient presents, will depend on factors that condition the expression of ACE2 in the brain such as age and sex, as well as the mechanism of neuronal invasion, the immune response and the general state of the patient. Clinical and histopathological studies have described neurological alterations in human patients with COVID-19. These conditions could have a possible contribution to the morbidity and mortality caused by this disease and may even represent the onset of neurodegenerative activity in recovered patients.