Pi granules and related intracytoplasmic inclusions in equine Schwann cells

Comparative Pathology of the Peripheral Nervous System

The peripheral nervous system (PNS) relays messages between the central nervous system (brain and spinal cord) and the body. Despite this critical role and widespread distribution, the PNS is often overlooked when investigating disease in diagnostic and experimental pathology. This review highlights key features of neuroanatomy and physiology of the somatic and autonomic PNS, and appropriate PNS sampling and processing techniques. The review considers major classes of PNS lesions including neuronopathy, axonopathy, and myelinopathy, and major categories of PNS disease including toxic, metabolic, and paraneoplastic neuropathies; infectious and inflammatory diseases; and neoplasms. This review describes a broad range of common PNS lesions and their diagnostic criteria and provides many useful references for pathologists who perform PNS evaluations as a regular or occasional task in their comparative pathology practice.

Novel mesostructured inclusions in the epidermal lining of Artemia franciscana ovisacs show optical activity

Background

Biomineralization, e.g., in sea urchins or mollusks, includes the assembly of mesoscopic superstructures from inorganic crystalline components and biopolymers. The resulting mesocrystals inspire biophysicists and material scientists alike, because of their extraordinary physical properties. Current efforts to replicate mesocrystal synthesis in vitro require understanding the principles of their self-assembly in vivo. One question, not addressed so far, is whether intracellular crystals of proteins can assemble with biopolymers into functional mesocrystal-like structures. During our electron microscopy studies into Artemia franciscana (Crustacea: Branchiopoda), we found initial evidence of such proteinaceous mesostructures.

Results

EM preparations with high-pressure freezing and accelerated freeze substitution revealed an extraordinary intracellular source of mesostructured inclusions in both the cyto-and nucleoplasm of the epidermal lining of ovisacs of A. franciscana. Confocal reflection microscopy not only confirmed our finding; it also revealed reflective, light dispersing activity of these flake-like structures, their positioning and orientation with respect to the ovisac inside. Both the striation of alternating electron dense and electron-lucent components and the sharp edges of the flakes indicate self-assembly of material of yet unknown origin under supposed participation of crystallization. However, selected area electron diffraction could not verify the status of crystallization. Energy dispersive X-ray analysis measured a marked increase in nitrogen within the flake-like inclusion, and the almost complete absence of elements that are typically involved in inorganic crystallization. This rise in nitrogen could possibility be related to higher package density of proteins, achieved by mesostructure assembly.

Conclusions

The ovisac lining of A. franciscana is endowed with numerous mesostructured inclusions that have not been previously reported. We hypothesize that their self-assembly was from proteinaceous polycrystalline units and carbohydrates. These mesostructured flakes displayed active optical properties, as an umbrella-like, reflective cover of the ovisac, which suggests a functional role in the reproduction of A. franciscana. In turn, studies into ovisac mesostructured inclusions could help to optimizing rearing Artemia as feed for fish farming. We propose Artemia ovisacs as an in vivo model system for studying mesostructure formation.

Light Microscopic Sciatic Nerve Changes in Control Beagle Dogs from Toxicity Studies

Although the dog is a common choice among nonrodent species in evaluation of compound safety for regulatory submission, information regarding the incidence of spontaneous or incidental microscopic changes in canine peripheral nerve is limited. A retrospective examination was performed of routine histologic preparations of sciatic nerve from eighty-one control dogs in toxicity studies ranging from ten days to three months in duration. Spontaneous background changes included digestion chambers, foci of vacuolation, nerve fibers circumscribed by proliferating Schwann cells (bands of Büngner), and small foci of myelin aggregation. The latter accounted for 91% of the microscopic changes and were noted in all sections examined. These changes were quantified, and the number per square millimeter of evaluable nerve tissue was determined for each slide. Densities of foci varied among the slides examined; no age- or sex-related trends were apparent. In addition, anatomic features of peripheral nerves including nodes of Ranvier, Schmidt-Lanterman incisures, Renaut bodies, and effects resulting from sectioning plane were noted. By demonstrating the range of effects observed within control animals, these observations provide a basis for recognition of possible compound-related effects in routine nerve preparations from dogs included in toxicity studies.

Light and electron microscopy studies of the ulnar, saphenous, and caudal cutaneous sural nerves of the dog

Transverse sections of the ulnar, saphenous, and sural nerves taken at specific levels in normal, young-adult beagle dogs were examined qualitatively and quantitatively at both the light and electron microscopic levels. The aim of this investigation was to provide baseline information for future studies of peripheral nerve disease in this species. A systematic sampling technique was used for the determination of nerve components (i.e., unmyelinated axons and Schwann cell and fibroblast nuclei). In all nerves sampled, the average size distribution for unmyelinated axons was unimodal, and most of the axons were 0.4-1.1 micron in diameter. Within this range, there were slight individual and nerve-to-nerve variations in the location of the largest diameter peak. The mean densities of Schwann cell nuclei (numbers/mm2) ranged from 841/mm2 in the palmar branch of the ulnar nerve, to 1,223/mm2 in the caudal cutaneous sural nerve, being nearly four times the average density or fibroblast nuclei. In every animal and in almost every nerve, a few abnormalities were found; and these should be kept in mind when assessing peripheral nerves in the dog.