Histopathological changes of neuronal tissue following the use of hydrogen peroxide in neurosurgical procedures

Background: Hydrogen peroxide (HP) is routinely used in neurosurgical procedures to achieve surgical hemostasis. However, its safety profile is still debatable with various reports depicting range of adverse effects on neuronal tissue. The objective of this paper is to evaluate the safety and efficacy of HP as a hemostatic agent in normal neuronal tissue during neurosurgical procedures conducted on rats. Methods: One hundred rats were divided into three groups. The first and third group underwent cortical irrigation with HP and the second group underwent spinal irrigation with HP. All groups were irrigated with different concentrations of HP (1%, 3%, or 6%) for 3 min and tissue biopsies were obtained immediately afterwards (Groups A and B) or 1 week after HP irrigation (Group C). Study specimens were examined histologically and compared to control tissue. Results: All rats showed normal behavioral, functional, and motor neurological activity following the procedures. Histopathologically, dark neurons were observed in all HP exposed tissue. The cytoplasm revealed condensed and dark Nissl substance and the neurites and axons exhibited a corkscrew morphology. No ischemic changes or inflammatory infiltrates were detected. The majority of dark neurons were observed at the periphery of tissue fragments. These findings were present and consistent in both the short- and long-term groups. Conclusion: HP irrigation showed no significant short- or long-term clinical and histopathological changes in comparison to normal saline when used on rats’ neuronal tissue. This may confirm the safety of intraoperative HP usage as hemostatic agent during neurosurgical procedures.

Chromatolysis: Do Injured Axons Regenerate Poorly when Ribonucleases Fragment or Degranulate Rough Endoplasmic Reticulum, Disaggregate Polyribosomes, Degrade Monoribosomes and Lyse RNA?

After axonal injury, chromatolysis (fragmentation of Nissl substance) occurs in both intrinsic neurons (whose processes are within the CNS) and extrinsic neurons (whose axons extend outside the CNS). Electron microscopy shows that chromatolysis involves fission of the rough endoplasmic reticulum. In intrinsic neurons (which do not regenerate axons) or in extrinsic neurons denied axon regeneration, chromatolysis is often accompanied by degranulation (loss of ribosomes from rough endoplasmic reticulum), disaggregation of polyribosomes and degradation of monoribosomes into dust-like particles. Ribosomes and rough endoplasmic reticulum may also be degraded in autophagic vacuoles by Ribophagy and Reticulophagy, respectively. In other words, chromatolysis is disruption of parts of the protein synthesis infrastructure. Whereas some neurons may show transient or no chromatolysis, severely injured neurons can remain chromatolytic and never again synthesise normal levels of protein; some may atrophy or die. What molecule(s) cause fragmentation or degranulation of rough endoplasmic reticulum, disaggregation of polyribosomes and degradation of monoribosomes? Ribonucleases can modify (and perhaps fragment) rough endoplasmic reticulum; various endoribonucleases can degrade mRNA causing polyribosomes to unchain and disperse; they can disassemble monoribosomes; Ribonuclease 5 can control rRNA synthesis and degrade tRNA; Ribonuclease T2 can degrade ribosomes, rough endoplasmic reticulum and RNA within autophagic vacuoles; and Ribonuclease IRE1α acts as a stress sensor within the endoplasmic reticulum. Regeneration might be improved after axonal injury by protecting the protein synthesis machinery from catabolism; targeting ribonucleases could be a profitable strategy.

THREE-DIMENSIONAL RECONSTRUCTION OF THE ANTERIOR OLFACTORY NUCLEUS IN THE HUMAN OLFACTORY BULB AND PEDUNCLE. Reconstrucción tridimiensional del núcleo olfatorio anterior en el bulbo y pedúnculo olfatorio humano

El bulbo y pedúnculo olfatorio humano contienen muchos grupos celulares más o menos separados que habitualmente son considerados como parte del núcleo olfatorio anterior retro-bulbar (AON). La presunción que estos grupos celulares sean considerados como extensión rostral del AON en el hemisferio rostral retrocede a la descripción de un único caso por Crosby y Humphrey (1941). Para mejorar nuestra comprensión de la anatomía del AON bulbar y peduncular humano investigamos la morfología, forma y tamaño de estas partes en este núcleo en tejido post-mortem de individuos de edades conocidas. Se obtuvieron seis bulbos y pedúnculos olfatorios, incluyendo la sustancia perforada anterior (SPA), de cerebros donados; se realizaron cortes seriales horizontales a 40µm y se tiñó con substancia de Nissl. Las neuronas de tamaño mediano a grande de esta parte del AON se tiñeron intensamente y tenían un diámetro promedio de 16µm. La reconstruc-ción tridimensional demostró que en todos los casos, excepto uno, el AON bulbar y peduncular consistieron en una cadena discontinua de grupos celulares conectados por puentes de neuropilas pobres o libres de células. El número de grupos celulares y de puentes conectores difiere en cada individuo. Concluimos que las porciones bulbar y peduncular del AON humano debería ser considerado como una especialización humana más que como una extensión rostral del área AON retro-bulbar. Esto es acorde con las propiedades neuro-clínicas previamente publicadas y la degeneración temprana selectiva, pre-clínica, de estos nichos celulares en la enfermedad neuro-degenerativa. The human olfactory bulb and peduncle contain several more or less separated cell groups that are usually regarded to be part of the retrobulbar anterior olfactory nucleus (AON). The assumption that these cell groups are to be considered as the rostral extension of the AON in the rostral hemisphere goes back to the description of one single case by Crosby and Humphrey (1941). To improve our understanding of the anatomy of the human bulbar and peduncular AON, we investigated the morphology, size and shape of these parts of this nucleus in postmortem tissue of aged individuals. Six olfactory bulbs and peduncles including the substantia perforata anterior (SPA) were obtained from donor brains and 40µm horizontal serial sections were cut and stained with Nissl substance. The medium to large sized neurons of these parts of the AON were intensely stained and had an average diameter of 16µm. Three dimensional reconstruction demonstrated that in all but one of the cases the bulbar and peduncular AON consisted on a discontinuous chain of cell groups connected by cell poor to cell free bridges of neuropile. The number of cell groups and the connecting bridges differ in every individual. We arrived at the conclusion that the bulbar and peduncular parts of the human AON should be regarded a human specialization rather than just being rostral extensions of the retrobulbar AON area. This is in line with previously published neurochemical properties and the selective early, preclinical degener-ation of these cell clusters in neurodegenerative diseases.

Morphometric Comparative Study of the Striatum and Globus Pallidus of the Common Shrew, Bank Vole, Rabbit, and Fox

The morphology of the striatum (St, caudoputamen complex) and globus pallidus (GP) was studied by stereological methods in representatives of four mammalian orders (Insectivora, Rodentia, Lagomorpha, Carnivora). The aim of our study was to give the first detailed morphometric characteristics of the St and GP in the animals. The paraffin-embedded brain tissue blocks were cut in the coronal plane into 50 μm sections, which were stained for Nissl substance. The morphometric analysis of the St and GP has included such parameters as the volume, numerical density, and total number of neurons. The increase in the volume of the St and GP was accompanied by an increase in the total number of neurons and a decrease in their numerical density. The percentage contribution of the GP volume in the corpus striatum shows progressive traits in the common shrew and fox.

Architectonic subdivisions of the inferior pulvinar in New World and Old World monkeys

Architectonic subdivisions of the inferior pulvinar (PI) complex were delineated in New World owl and squirrel monkeys and Old World macaque monkeys. Brain sections were processed for Nissl substance, myelin, cytochrome oxidase (CO), acetylcholinesterase (AChE), calbindin-D28K (Cb), or with the monoclonal antibody Cat-301. In all three primates, we identified the posterior nucleus (PIp) and the medial nucleus (PIm) of previous reports, and divided the previously recognized central nucleus (PIc) into two subdivisions, medial (PIcm) and lateral (PIcl). Each nucleus had several features that allowed it to be readily distinguished. (1) PIp was dark in Cb, and moderately dark in AChE and CO preparations. (2) PIm was Cb light, and AChE and CO dark. (3) PIcm was Cb dark, and AChE and CO light. (4) PIcl was Cb moderate with a scattering of dark neurons, and moderately dark for AChE and CO. (5) In sections processed for Cat-301, PIm in macaque monkeys and PIcm and PIp in squirrel monkeys stained darkly, while little staining was apparent in owl monkeys. The results allowed subdivisions of the inferior pulvinar to be more clearly defined, homologized, and compared across taxa. All monkeys appear to have the same four subdivisions of the PI, although properties vary.