ABSTRACT
Gap junctions consisting of connexin 43 subunits provide intercellular communication between astrocytes, contributing to their function of maintaining the central nervous system (CNS) microenvironment. Magnetic resonance imaging (MRI) studies demonstrate prolonged astrocyte swelling related to seizures, while in vitro studies show the disruption of intercellular coupling and the cytotoxic swelling of astrocytes in seizure-equivalent environments. We examined the relation between astrocyte swelling and connexin 43 regulation using an in vivo seizure model. Generalised tonic-clonic convulsions were induced in adult rats using intraperitoneally (i.p.)-administered 4-aminopyridine (4-AP). The expression of connexin 43 mRNA and protein at 1, 3 and 24 h after seizure induction was measured. Astrocytic swelling was assessed at the same time points using transmission electron microscopy. mRNA and protein levels remained unaltered at all time periods. However, a significant (≈50%) reduction was found in the amount of phosphorylated (P1, P2) to unphosphorylated (NP) forms of connexin 43 at 3 h. The amount increased thereafter, but was still significantly lower than in the controls at 24 h post-seizure. Simultaneously, marked astrocytic swelling was measured in the neocortex. Pre-treatment with N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801) resulted in the amelioration of seizure symptoms and the prevention of connexin 43 dephosphorylation, as well as significantly reduced astrocytic swelling. Dephosphorylation of connexin 43 was shown to reduce astrocytic gap junction (GJ) permeability. Our results therefore suggest that, during acute seizures, a prolonged inhibition of intercellular coupling develops in the astrocyte network. This accounts for the long-lasting astrocyte swelling observed, and potentially impairs buffering function. The results also imply that this uncoupling is regulated through neuronal and/or glial NMDA-type glutamate receptors.
ABSTRACT
An arteriovenous fistula (AVF) is an abnormal connection between an artery and a vein, whereby the interconnecting capillary network is missing. Such a malformation frequently occurs in the deep midline regions of the brain, and the subsequent increased flow into the draining vein of Galen substantially dilates in an aneurysmal manner. Congenital forms of the aneurysmal dilatation of the vein of Galen (AVG) often lead to death in the neonatal period, predominantly due to cardiac failure caused by the increased venous inflow as a consequence of the intracerebral arteriovenous shunting. In the presented case a male baby suffered from a rare combination of a cerebral AVF and an atrial septal defect (ASD). He was born at week 38 of pregnancy and subsequently developed tachydyspnoe. Ultrasound (US) and CT scans revealed a large bilateral AVF with dilated basal venous sinuses, hydrocephalus and brain atrophy. In the heart, severe right ventricular hypertrophy, patent ductus arteriosus and an ASD were detectable by US. Neurosurgical consultation rejected the possibility of an operative treatment due to size and localization of the lesion and the existing irreversible brain damage. The child died because of cardiac failure 6 days after birth. Autopsy examination in the brain demonstrated a large conglomerate of dilated blood vessels predominantly in the midline and left occipital lobe, edema and hydrocephalus. In the heart, the ASD detected by US proved to be an ostium secundum-type lesion. Histologically, the conglomerate of vessels revealed features of an AVF and matched the characteristics of AVG. Consequences of chronic ischemic brain injury were also present, with ferruginated neurons suggesting intrauterine damage caused by a congenital AVF. Based on data in the literature, we assume that the left-to-right shunt due to increased venous influx into the heart caused not only cardiomegaly, but may have also interfered with the normal development of the atrial septum leading to an ASD, contributing to the rapid progression of the cardiac failure.
