Morphological, histological and immunohistochemical study of the area postrema in the dog

Aquaporin-4 protein expression in normal canine brains

BACKGROUND

Aquaporin-4 (AQP4) is in growing recognition as potential marker for cancer progression, differentiation and therapeutic intervention. No information is available about AQP4 expression in the normal canine brain. The aim of this histopathological study is to confirm the presence of AQP4 by immunohistochemistry technique in a group of non-pathological canine brains and to describe its expression and distribution across the brain.

RESULTS

Twelve non-pathological canine brains of various ages (ranging from 21 days to 17 years) and breeds were included in the study. Immunohistochemical expression of AQP4 was analyzed using formalin-fixed paraffin-embedded brain tissue sections. The findings were correlated between AQP4 expressing cells and astrocytes using glial fibrillary acidic protein (GFAP). AQP4 expression was more marked in the astrocyte foot processes of subpial, perivascular and periventricular surfaces in all specimens. The majority of the canine brain sections (9/12) presented with an AQP4 predilection for white matter tracts. Interestingly, the two youngest dogs (21 days and 3 months old) were characterized by diffuse AQP4 labelling in both grey and white matter tracts. This result may suggest that brain development and ageing may play a role in the AQP4 distribution throughout the canine brain.

CONCLUSIONS

This is the first study to describe immunohistochemical distribution of AQP4 in normal canine brains. The AQP4 expression and distribution in non-pathological canine brains was comparable to other species. Larger studies are needed to substantiate the influence of breed and ageing on AQP4 expression in the normal canine brain.

Area Postrema: Fetal Maturation, Tumors, Vomiting Center, Growth, Role in Neuromyelitis Optica

INTRODUCTION

The area postrema in the caudal fourth ventricular floor is highly vascular without blood-brain or blood-cerebrospinal fluid barrier. In addition to its function as vomiting center, several others are part of the circumventricular organs for vasomotor/angiotensin II regulation, role in neuromyelitis optica related to aquaporin-4, and somatic growth and appetite regulation. Functions are immature at birth. The purpose was to demonstrate neuronal, synaptic, glial, or ependymal maturation in the area postrema of normal fetuses. We describe three area postrema tumors.

METHODS

Sections of caudal fourth ventricle of 12 normal human fetal brains at autopsy aged six to 40 weeks and three infants aged three to 18 months were examined. Immunocytochemical neuronal and glial markers were applied to paraffin sections. Two infants with area postrema tumors and another with neurocutaneous melanocytosis and pernicious vomiting also studied.

RESULTS

Area postrema neurons exhibited cytologic maturity and synaptic circuitry by 14 weeks'. Astrocytes coexpressed vimentin, glial fibrillary acidic protein, and S-100β protein. The ependyma is thin over area postrema, with fetal ependymocytic basal processes. A glial layer separates area postrema from medullary tegmentum. Melanocytes infiltrated area postrema in the toddler with pernicious vomiting; two children had primary area postrema pilocytic astrocytomas.

CONCLUSIONS

Although area postrema is cytologically mature by 14 weeks, growth increases and functions mature during postnatal months. We recommend neuroimaging for patients with unexplained vomiting and that area postrema neuropathology includes synaptophysin and microtubule-associated protein-2 in patients with suspected dysfunction.