RESUMEN
Glutamate acts as the main excitatory neurotransmitter in the brain and plays a vital role in physiological and pathological neuronal functions. In mammals, glutamate can cause detrimental excitotoxic effects under anoxic conditions. In contrast, Trachemys scripta, a freshwater turtle, is one of the most anoxia-tolerant animals, being able to survive up to months without oxygen. Therefore, turtles have been investigated to assess the molecular mechanisms of neuroprotective strategies used by them in anoxic conditions, such as maintaining low levels of glutamate, increasing adenosine and GABA, upregulating heat shock proteins, and downregulating K ATP channels. These mechanisms of anoxia tolerance of the turtle brain may be applied to finding therapeutics for human glutamatergic neurological disorders such as brain injury or cerebral stroke due to ischemia. Despite the importance of glutamate as a neurotransmitter and of the turtle as an ideal research model, the glutamatergic circuits in the turtle brain remain less described whereas they have been well studied in mammalian and avian brains. In reptiles, particularly in the turtle brain, glutamatergic neurons have been identified by examining the expression of vesicular glutamate transporters (VGLUTs). In certain areas of the brain, some ionotropic glutamate receptors (GluRs) have been immunohistochemically studied, implying that there are glutamatergic target areas. Based on the expression patterns of these glutamate-related molecules and fiber connection data of the turtle brain that is available in the literature, many candidate glutamatergic circuits could be clarified, such as the olfactory circuit, hippocampal-septal pathway, corticostriatal pathway, visual pathway, auditory pathway, and granule cell-Purkinje cell pathway. This review summarizes the probable glutamatergic pathways and the distribution of glutamatergic neurons in the pallium of the turtle brain and compares them with those of avian and mammalian brains. The integrated knowledge of glutamatergic pathways serves as the fundamental basis for further functional studies in the turtle brain, which would provide insights on physiological and pathological mechanisms of glutamate regulation as well as neural circuits in different species.
RESUMEN
SUMMARY: Fixation is a crucial step in processing of tissue specimen for preservation of cellular architecture and composition of cells. Alcohol-based fixatives are considered some of the most promising alternatives to formalin. We evaluated the performance of alcohol-based fixatives (EthMeth and methacarn) and formalin as a comparator fixative in the research laboratory. Following 24 hours of fixation, tissue morphology and cellular details of the liver, spleen and brain (cerebral cortex) were evaluated. Morphological characteristics were evaluated by gross observations and analyzing cellular details, tissue architecture and overall staining characteristics (Hematoxylin and Eosin). EthMeth and methacarn fixation gave generally comparable and satisfactory results on the tissue morphology and subsequent identification of tissue characteristics. Particularly, tissues were well preserved and all nuclear as well as cytoplasmic details were clearly visible. However, formalin fixed tissues showed some peculiarity such as improper fixation, mild shrinkage, and alterations of tissue components. These results confirm that alcohol-based fixation is the superior alternative to formalin for preservation of tissue morphology. However, it is required to standardize the formalin-free methods and harmonize diagnosis in the laboratory worldwide.
RESUMEN: La fijación es un paso crucial en el procesamiento de muestras de tejido para preservar la arquitectura celular y la composición de las células. Los fijadores a base de alcohol se consideran algunas de las alternativas más prometedoras a la formalina. Evaluamos el rendimiento de los fijadores a base de alcohol (EthMeth y metacarn) y formalina como fijador comparativo en el laboratorio de investigación. Después de 24 horas de fijación, se observó la morfología del tejido y los detalles celulares del hígado, bazo y corteza cerebral. Se evaluaron las características morfológicas mediante observaciones generales y analizando detalles celulares, arquitectura de tejidos y características generales de tinción (hematoxilina y eosina). La fijación de EthMeth y metacarn dio resultados generalmente comparables y satisfactorios en la morfología del tejido y la posterior identificación de las características del mismo. Particularmente, los tejidos estaban bien conservados y todos los detalles nucleares y citoplasmáticos eran claramente visibles. Sin embargo, los tejidos fijados con formalina mostraron cierta peculiaridad, tal como una fijación inadecuada, la contracción leve y alteraciones de los componentes del tejido. Estos resultados confirman que la fijación a base de alcohol es la mejor alternativa a la formalina, para preservar la morfología del tejido. Sin embargo, es necesario estandarizar los métodos sin formalina y armonizar el diagnóstico en los laboratorios.
