A. Basil Harris

Ultrastructure of exogenous peroxidase in cerebral cortex

Abstract Protein uptake and transport and the intercellular spaces were studied electron microscopically in normal rabbit, cat and monkey cerebral cortex using horseradish peroxidase (HRP) as a cytochemical tracer. Extensive endocytosis and accumulation of tracer were seen as a result of delivering high concentrations of HRP into the intercellular space followed by long observation experiments, up to 120 h. Incorporation of HRP into neurons and their processes after a single application was studied by following the progress of neuron organelle labeling; the disappearance of tracer from these structures gave new information on the optimal times when HRP could be seen as a cellular tracer in cortical neurons. Neurons and their processes demonstrated a remarkable facility to take up peroxidase in coated invaginations and vesicles and accumulate it in multivesicular and other lysosomal bodies. The first structures labeled were coated vesicles, synaptic vesicles, sacs and tubules. HRP disappeared from the intercellular space after 24 h, and coated vesicles and synaptic vesicles no longer contained it at this time. Sacs and tubules were free of tracer by 48 h. Multivesicular bodies contained HRP after 30 min and lost all label between 72–96 h. Dense bodies became labeled after 1.5 h, and remained labeled until 96–120 h. Evidence of axon transport of the tracer was added to that extant on this pathway.

Neurotransmitter, receptor and biochemical changes in monkey cortical epileptic foci

Epileptic and normal Macaca mulatta monkey cortex was investigated using ligand binding techniques. Subpial injections of aluminum hydroxide gel into the left sensorimotor cortex produced stable seizure frequencies over a two year period and resulted in specific biochemical and receptor abnormalities. Pair matched CSF samples comparing epileptic and non-epileptic hemispheres showed a significant decreased GABA concentration over the epileptic side. The epileptic cortex demonstrated markedly reduced GABA receptor binding and diminished tissue GABA concentration and GAD activity. Two patterns of receptor loss were observed: nonspecific local cellular drop out involving multiple neurotransmitter receptors; and distal receptor loss which was specific for the neurotransmitter intervention pattern of the cortex. GABAergic receptor loss was more marked than receptor losses for the other neurotransmitter and was more widespread. Scatchard plot analysis demonstrated that the diminished GABAergic receptors within the focus were due to receptor loss and not affinity changes. Spearman rank correlations showed a significant correlation only between the degree of GABAergic receptor loss or decrease in GAD activity and the seizure frequency. Epilepsy appears to be a multifactoral disorder with multiple neuroreceptor abnormalities, the most notable of which are the destruction of GABAergic neurons and GABA receptors.

Time course of the reduction of GABA terminals in a model of focal epilepsy: a glutamic acid decar☐ylase immunocytochemical study

Immunocytochemical localization of glutamic acid decarboxylase (GAD), the synthesizing enzyme for the neurotransmitter gamma-aminobutyric acid (GABA), has been used to study the time course of the decrease in putative GABAergic synaptic terminals that occurs in an alumina gel-induced model of focal epilepsy. Monkeys were studied at progressive intervals following unilateral application of alumina gel to sensorimotor cerebral cortex, and were categorized into 3 different experimental groups depending upon their clinical status. These groups respectively exhibited: (1) no abnormal bioelectrical (EEG and ECoG) activity; (2) abnormal bioelectrical activity, but no clinical seizures; and (3) both abnormal bioelectrical activity and clinical seizures. Normal and sham-operated monkeys were also studied. The amounts of GAD-positive terminal-like structures were determined on control and experimental sides of motor cortex (layer V) of all specimens with an image analysis system. This quantitative study revealed that monkeys from the 3 experimental groups showed reductions of GAD-positive terminals on the experimental cortical side, with greater losses occurring at progressively longer times following alumina gel implants. Statistical tests showed that there were no significant cortical side differences for the normal and sham groups, but that cortical side variations were significantly different for each of the 3 experimental groups. Conventional electron microscopy of an early experimental stage revealed degenerating axon terminals in layer V of motor cortex, as well as phagocytosis of degenerating material and astrogliosis. Similar findings were obtained from a chronically epileptic specimen, except that degenerating terminals were observed less often and fibrous astrocytic scarring was more prevalent, especially surrounding the somata of pyramidal neurons. The main conclusion drawn from the results of this investigation is that significant decreases of GAD-positive terminals occur prior to the onset of clinical seizures, and this is consistent with a causal role for a loss of GABAergic innervation in the development of seizure activity in this primate model of focal epilepsy.

Left thalamic hemorrhage with dysphasia: A report of five cases

Abstract A specific type of “thalamic speech” is being recognized with increasing frequency. Paucity of spontaneous speech, fading vocal volume, anomia, perseveration, and neologisms, with intact comprehension and word repetition, characterize the speech disorder associated with thalamic lesions. Nine cases of left thalamic hemorrhage and speech disturbance have been reported previously. This report details the speech, neurological, and neuroradiological findings in five additional cases of thalamic hemorrhage with dysphasia.

Cortical neuroglia in experimental epilepsy

Three different sites of aluminum hydroxide (alumina) application to sensorimotor cortex of monkey are compared: subdural, subarachnoid, and intracortical. The thin arachnoid membrane excludes subdural alumina from brain to prevent clinical or electrical seizures and histological changes. Subarachnoid alumina results in late onset of epilepsy (4–6 months), and seizures are often severe. This epileptic lesion spreads over the outermost cortex like an umbrella. Astrocyte reaction in the border zones results in thick pia-glial membranes, hypertrophied cells with increased filaments and microfilaments, greater number of processes, and increased numbers of cellular connections. The hypertrophic reaction is general in superficial cortex, but in deeper layers organized stripes or bands of giant hypertrophied astrocytes occur at depths where potassium electrode studies have shown increased potassium ions in extracellular spaces with seizures. Neuronal depopulation and neurofibrillary degeneration are not features of the subarachnoid model. Intracortical injections cause seizures in 6–8 weeks, but the lesions are an anatomical disarrangement. In addition to gliosis about the lesion, there are associated asymmetrically located stripes of reactive astrocytes far distant from the injection site. Astrocytes are thought to contribute to or cause the epileptic lesion. They appear to respond to the resulting hyperactivity in neurons, associated ion flux or transmitter release, by hypertrophic reaction in the epileptic focus.

Absence of Seizures or Mirror Foci in Experimental Epilepsy After Excision of Alumina and Astrogliotic Scar

Summary: In 15 rhesus monkeys (Macaca mulatto) made epileptic by the sensorimotor cortical injection of alumina, the roles of alumina and of “mirror foci” were investigated by serial surgical excisions of the granuloma, surrounding epileptic focus, and contralateral homotopic sensorimotor cortex. Electroencephalographic and electrocorticographic recordings documented foci and transmitted contralateral epileptic activity. After the granuloma was re‐moved, seizures continued but without alumina. After the epileptic cortex was removed, no seizure activity remained and no contralateral independent foci occurred. These findings indicate that the epilepsy incident to alumina injection into the sensorimotor cortex in monkey is not dependent on the continual presence of alumina and is not associated with independent or “mirror foci.”

Ultrastructure and histochemistry of alumina in cortex

Abstract After intracortical injection of the epileptogenic compound alumina, positive histochemical reactions occur in the lesion border immediately and later in macrophages of the granuloma, blood vessels, and cortex. Perivascular alumina deposits may appear intraneuronal but are overlying instead. Moderately electronopaque alumina crystals ∼15 A wide by 500 A long increase their densities by adhering osmiophilic serum and cell products. Endocytosed crystals are seen in monocytes, fibroblasts, and astrocytes, but not in polymorphonuclear leukocytes or neurons. Macrophage secondary lysosomes, complex cytosegresomes, and dense and light vacuoles contain crystals at all stages from 1 day to 5 1 2 years after injection. Some crystals appear entangled in filaments and microtubules without definite limiting membranes. Intracellular alumina is assciated with increased cytoplasmic filaments, multivesicular bodies, lysosomes, free ribosomes, autophagosomes, and multiple vacuoles. Intracellular digestive processes may slowly degrade crystals into soluble compounds reflected by increased filaments in astrocytes and macrophages. These changes may indicate the sites of importance in the genesis of this type of epilepsy.

Lipomatous meningioma: an uncommon tumor with distinct radiographic findings

A case of lipomatous (lipoblastic) meningioma is described. Atypical radiographic features of low density on computed tomography scanning and high intensity on T1-weighted magnetic resonance imaging corresponded to the presence of adipose tissue within the tumor. A review of the literature indicates few similar reported cases.

Epileptogenic agents applied to trigeminal ganglia: absence of neuronal hyperexcitability.

Chronic application of alumina cream to the trigeminal ganglion in 10 cats failed to produce a long‐lasting behavioral syndrome of facial dysesthesia. Histologic and electron microscopic analysis demonstrated morphologic similarities between these ganglia and primate neocortical alumina cream epileptic foci. None of 87 ganglia neurons recorded extracellularly exhibited evidence of intrinsic hyperexcitability, i.e., abnormal spontaneous or physiologically evoked activity or any significant differences in threshold of responses to antidromic or orthodromic electrical stimulation, compared to 67 normal ganglion cells. Furthermore, topical application of penicillin to normal ganglia failed to produce abnormal activity in 42 neurons tested. These data suggest that neuronal somata lacking either dendrites or postsynaptic membranes, or both, do not develop abnormal firing behavior when challenged with these two epileptogenic agents.

Macaca fascicularis: alternative epileptic model.

Abstract In view of the relatively recent Indian embargo on rhesus monkeys ( Macaca mulatta ), our data indicate that the iris (or crab-eating) macaque ( M. fascicularis ) is a suitable substitute species as a model for experimental epilepsy. Sensorimotor intracortical aluminum-hydroxide injections in the iris monkey result in chronic recurring seizures as readily as in rhesus. Comparable drug plasma levels and seizure frequency patterns show the former is a reliable alternative epileptic animal model for the latter. Differences between these two species in diet and body size do not require extensive readjustment of housing and maintenance facilities. The histochemical findings suggest that the iris monkey might also become an alternative to other experimental animal models for which the rhesus has been used in the health sciences.