David M. Robertson

Quantitative estimate of pinocytosis in experimental acute hypertension

SummaryCerebral cortical arterioles in focal neocortical areas develop increased permeability to plasma proteins and protein tracers in experimental hypertensive encephalopathy. The mechanism underlying this increased permeability has been the subject of several studies. In our previous studies of angiotensin-induced acute hypertension, pinocytosis appeared to be the pricipal mechanism for the increased blood-brain barrier (BBB) permeability observed. In the present study pinocytotic activity was assessed quantitatively to determine whether enhanced pinocytosis was confined to the permeable arteriolar segments of hypertensive animals. In addition, the effect of horseradish peroxidase (HRP) itself on the pinocytotic activity of normal cerebral cortical arteriolar endothelium was determined.In 12 rats following administration of HRP, hypertension was induced by an infusion of angiotensin. The animals were perfusion-fixed 90s after the onset of the infusion. Control animals received saline only or HRP only. The area of arteriolar endothelium in cross section was determined by a planimeter from overlapping electron micrographs taken at a constant magnification around the circumference of the vessel wall.Results indicate a significant (P<0.001) increase in the number of pinocytotic vesicles in the permeable arteriolar segments of hypertensive animals as compared with nonpermeable arteriolar segments of the same animals and comparable segments of normotensive rats. In addition, eight times as many vesicles appear to be transporting tracer in the permeable arteriolar segments of hypertensive animals as compared to the nonpermeable segments of the same animals and normotensive animals. HRP alone did not affect the pinocytotic index, there being no difference (P>0.05) in the number of vesicles in normotensive animals receiving saline only and those receiving HRP only. Our previous observation that disruption of endothelial cells or their tight junctions did not occur was confirmed.

Diabetic Neuropathy in the Mutant Mouse [C57BL/ks(db/db)]: A Morphometric Study

Detailed studies of peripheral nerves were undertaken in the mutant diabetic mouse of the [C57BL/ks(db/db)] strain using electrophysiologic and morphometric techniques. Electrophysiologic studies showed severely impaired motor nerve conduction velocity (MNCV), which developed promptly during the early phase of the diabetic syndrome. Morphometric changes occurred first after 20 wk of diabetes in both myelinated and unmyelinated fibers. There were both loss and shrinkage of myelinated fibers, most pronounced in the sural nerve and the ventral root. Changes appeared late in the dorsal root and in the peroneal and vagus nerves. Unmyelinated fibers showed both shrinkage and loss of axons, presumably involving sympathetic and afferent somatic fibers. Teased fiber studies and calculations of axon-myelin ratios confirmed our earlier suggestion18 that the neuropathy is primarily axonal in nature. The temporal discrepancy between functional and structural impairments in the present model strongly suggests a metabolic cause of the early neuropathy. This was further supported by the positive effect of insulin treatment on MNCV during the early phase of diabetes, whereas, during the late phase, treatment failed to show any effect.

A Syndrome of Acute Severe Muscle Necrosis in Intensive Care Unit Patients

Four septic patients and one asthmatic patient are described who developed a severe paralytic disorder in an intensive care unit (ICU), associated with a rise in serum creatine kinase and a severe necrotizing myopathy. All cases had received non-depolarizing muscle blocking agents and large intravenous doses of glucocorticoids. Three patients developed myoglobinuria. No improvement or very little improvement in muscle function was noted in the four fatal cases. The single survivor recovered his strength after 6 months. This syndrome (“necrotizing myopathy of intensive care”) provides one of the differential diagnoses for ICU-acquired weakness. The myopathy appears to have several interdependent causes and it is proposed that these should be classified as myonecrosis “priming” factors (glucocorticoids, myotropic infections, sepsis) and “triggering” factors (non-depolarizing muscle blocking agents).

Peripheral neuropathy in mutant diabetic mouse [C57BL/Ks (db/db)]

SummaryA new animal model for the study of diabetic neuropathy is presented. The homozygote (db/db) of the mouse strain C57BL/Ks shows severe diabetes with longstanding hyperglycemia. Electrophysiological studies showed severely decreased motor nerve conduction velocity. Morphometric examination of sensory and motor nerves at different levels revealed absence of large myelinated fibers, with morphological features indicative of axonal atrophy.

Pharmacological modification of bradykinin induced breakdown of the blood-brain barrier

Internal carotid artery infusion of bradykinin caused extensive breakdown of the blood-brain barrier to protein as demonstrated by the extravasation of the marker, horseradish peroxidase, into vessel walls and the adjacent parenchyma. Pretreatment of the animals with indomethacin, trifluoperazine, or imidazole significantly reduced the quantity of abnormally permeable vessels as determined by light microscopy. By electron microscopy, it was determined that bradykinin caused an intense increase in the number of pinocytotic vesicles in the permeable segments, but no change in the interendothelial junctions. After imidazole pretreatment, although the extent of the permeability change was markedly reduced, the intensity of pinocytotic activity in the involved areas was not altered.

Temporal relationships of neuropathologic conditions caused by perinatal asphyxia

The neuropathologic conditions in 120 perinatal deaths attributed to fetal or newborn asphyxia were examined. Central nervous system necrosis was present in 16 of these deaths. The approximate time of asphyxial insult was established by determining the duration of the process, based on the findings of neuronal necrosis, macrophage response, or an astrocyte response, in conjunction with clinical data. The time of the asphyxial insult for the 16 perinatal deaths was as follows: antepartum fetal asphyxia, two cases; antepartum-intrapartum fetal asphyxia, five cases; intrapartum fetal asphyxia, four cases; and neonatal asphyxia, five cases. These observations indicate that an asphyxial insult may occur in the antepartum period, in the prodromal period of preterm labor, in the intrapartum period, and in the neonatal period. Five to ten percent of the asphyxial insults in each reproductive time period were initially sublethal, allowing necrosis of the brain of the fetus or newborn to develop.

Morphological changes in spontaneously hypertensive rats.

SummaryOur previous studies of angiotension-induced acute hypertension showed increased intracerebral arteriolar permeability associated with markedly enhanced pinocytosis. This study was performed to determine whether similar findings occurred in spontaneous non-pharmacologically induced chronic hypertension.Cerebrovascular permeability to horseradish peroxidase (HRP) was studied over an 82-week period in spontaneously hypertensive rats (SHR) derived from a strain that originated from Japan. In a few animals increased cerebrovascular permeability to HRP was observed, associated with enhanced pinocytosis. Quantitatively, the number of pinocytotic vesicles in permeable arteriolar segments was significantly increased suggesting that enhanced pinocytosis is the principal mechanism of early cerebrovascular changes in SHR.Light microscopy of renal, ocular and cerebral vessels revealed medial hyperplasia affecting renal vessels at 16 weeks and occurring later in ocular and cerebral vessels. Deposition of fibrin in renal vessels was observed from 64 weeks onwards but was not associated with renal failure.

Primary neuroblastoma of the central nervous system with spontaneous extracranial metastases Case report

A case of spontaneous extracranial metastases from a cerebral neuroblastoma in the absence of prior surgery is reported. The tumor was discovered ineidently through biopsy of an enlarged retro-aurieular lymph node in an apparently well 7-year-old boy who had not previously received surgery or radiotherapy. The patient died 15 months later. Autopsy excluded neuroblastoma of the adrenal glands or the sympathetic chains.

The perineurial and blood-nerve barriers in experimental diabetes

SummaryThe permeabilities of the blood-nerve barrier and the perineurial barrier were investigated in alloxan and streptozotocin diabetic rats and in the mutant diabetic mouse [C57BL/Ks(db/db)]. In the mouse model both fluorescence and electron microscopic techniques were employed using Evans blue albumin (EBA) and horseradish peroxidase (HRP), respectively, as exogeneous tracers. In the rat models only HRP was used. Tracers were applied locally around the sciatic nerve in order to investigate the perineurial barrier, and systemically to detect changes in the blood nerve barrier.None of the models was found to show increased permeability across either of the barriers.

Tuberous sclerosis in an infant of 28 weeks gestational age.

A case of tuberous sclerosis diagnosed at autopsy in a neonate at 28 weeks gestation is described. This is believed to be the earliest case yet reported. The CNS lesions consist of cortical tuberosities, heterotopic white matter nodules and subependymal nodules. These nodules consist predominantly of giant astrocytes but a small undifferentiated cell component is present as well. Multiple cardiac rhabdomyomas are also present. An explanation for neuronal hypocellularity within the cortical tuberosities is suggested.