Ipsilateral subcortical atrophy associated with temporal lobectomy

Stereologic methods for determining the volume of cerebral structures in vivo via magnetic resonance imaging have identified unilateral hippocampal atrophy among patients with complex partial epilepsy of temporal lobe origin. Metabolic imaging has also identified altered metabolism in temporal as well as extratemporal regions among these patients. As the temporal cortex and subcortical nuclei of the limbic system are reciprocally connected with striatal projection fields, we examined the putamen nuclei for evidence of associated extratemporal volume asymmetry in patients before and after temporal lobectomy. There was no evidence of preoperative putamen volume asymmetry, but a significant postoperative decrement in ipsilateral putamen volume was observed. The magnitude of postsurgical putamen volume asymmetry was correlated with the duration of time since resection. Progressive degeneration of extratemporal projections of the temporal lobe may occur in association with temporal lobectomy.

Role of neutrophils in breakdown of the blood-retinal barrier following intravitreal injection of platelet-activating factor

Breakdown of the blood-retinal barrier occurs in inflammatory conditions and in ischemic retinal diseases such as diabetic retinopathy. Platelet-activating factor (PAF) is a potent inflammatory mediator which increases vascular permeability. The purpose of this study was to determine if intravitreally-injected PAF would cause breakdown of the blood-retinal barrier and, if so, by what mechanism. Fluorescein angiography was performed before and at 0.5, 1, 2, 3 and 4 hr after PAF injection into the vitreous cavity of rabbit eyes and the eyes were enucleated immediately for light and electron microscopy. Slow flowing thrombi were observed in all PAF-injected eyes. Complete vascular occlusion was observed in 10 of 16 eyes after 3 and 4 hr. There was no fluorescein leakage in any of eyes before or at 0.5 or 1 hr after PAF injection. Fourteen of 20 eyes had fluorescein leakage at 2, 3 and 4 hr after PAF injection. The extent of fluorescein leakage correlated with the degree of polymorphonuclear leukocyte (PMN) margination, disruption of the endothelial cell layer, infiltration into vascular walls and migration into the vitreous cavity. PMNs appeared to migrate by both intercellular and transcellular routes across the endothelium. Pretreatment of rabbits with a PAF inhibitor, BN52021, prevented most of the abnormal findings.

MR and positron emission tomography in the diagnosis of surgically correctable temporal lobe epilepsy

PURPOSE

To determine the association of an MR abnormality and a positron emission tomography (PET) abnormality with a good outcome in patients with temporal lobe epilepsy after lobectomy, the association of combined PET and MR findings with good outcomes after lobectomy, and MR and PET pathologic correlation.

METHODS

MR and PET were performed on 27 patients in a blinded study. Histologic studies were correlated with foci of increased T2 signal.

RESULTS

Increased signal or decreased volume of the hippocampus was noted in 13 of 15 patients with mesial temporal sclerosis. Twelve of 15 had positive PET findings. MR identified 20 (83%) of the 24 patients with good outcomes. PET identified 71%. When MR and PET were combined, they detected 95% of the patients with good outcome. Region of interest measurements of the hippocampus in 11 study patients and 7 control subjects documented a significant increase in signal in the patients with seizures. Histologic correlative studies demonstrated that increased T2 signals related to astrocytosis in the hippocampus and adjacent white matter.

CONCLUSIONS

MR (increased signal and decreased volume of the hippocampus) significantly improved the capability to identify those persons who would be helped by lobectomy. MR sensitivity exceeded that of PET.

Effects of anticonvulsant drugs on substantia nigra pars reticulata neurons

Enhancement of gamma-aminobutyric acid transmission within the substantia nigra has been shown to prevent the motor manifestations of chemically induced and kindled seizures. These findings raise the possibility that the substantia nigra might constitute a site of anticonvulsant drug action if these drugs share an ability to suppress propagation of seizure activity from the nigra to motor effector sites. The current studies monitored effects of a diverse group of anticonvulsant drugs on the extracellular, single unit activity of nondopaminergic neurons of the substantia nigra pars reticulata in awake, paralyzed and locally anesthetized male rats. Intravenous phenytoin (1.25-160 mg/kg) and carbamazepine (1.25-40 mg/kg) did not alter neuronal firing at any dose. Conversely, both diazepam (31.25-8,000 micrograms/kg) and clonazepam (2-500 micrograms/kg) partially inhibited firing (to 46 +/- 11% and 59 +/- 6% of base-line rates, respectively), although clonazepam was approximately 16 times more potent in eliciting equivalent degrees of inhibition. Valproic acid (5-640 mg/kg) and phenobarbital (1.25-80 mg/kg) also slowed firing to 65 to 70% of base-line rates, but did so only at the highest doses administered. However, the anesthetic barbiturate pentobarbital (0.3125-80 mg/kg) completely suppressed firing by the highest dose tested. Of those drugs used exclusively for treatment of absence seizures, trimethadione (12.5-800 mg/kg) caused dose-related inhibitions to 37.6 +/- 9.8% of base-line, whereas ethosuximide (12.5-800 mg/kg) markedly stimulated firing, nearly doubling firing rates after the 200 mg/kg dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dopamine system activation on substantia nigra pars reticulata output neurons: variable single-unit responses in normal rats and inhibition in 6-hydroxydopamine-lesioned rats

Previous single-unit recording studies have revealed that randomly selected pars reticulata neurons respond in a highly variable and complex fashion to intravenous administration of the dopamine agonist, apomorphine. The current studies were undertaken (1) to assess whether the variable pattern of responses of reticulata neurons to intravenous apomorphine correlates with their sites of projection and (2) to determine how reticulata responses to apomorphine might be altered by the presence of striatal dopaminergic supersensitivity. Extracellular, single-unit recording studies were conducted in anesthetized, paralyzed rats. Pars reticulata neurons were identified by antidromic activation from either the ventromedial nucleus of the thalamus or superior colliculus. Neurons of both subpopulations exhibited similar, highly variable changes in firing rate during the 10-min period immediately following intravenous injection of 320 micrograms/kg of apomorphine, a dose of the drug considered sufficient to stimulate striatal postsynaptic dopamine receptors. These responses, which were not qualitatively different from those previously observed among reticulata cells not distinguished on the basis of projection site, could be reversed by subsequent administration of dopamine antagonist drugs. In contrast to the variable responses in normal animals, the same dose of apomorphine caused a rapid and usually total inhibition of pars reticulata cell firing in rats which received 6-hydroxydopamine lesions of the nigrostriatal dopamine pathway 6 to 8 weeks prior to recording experiments. These inhibitions of firing could also be reversed by administration of dopamine antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Single unit responses of substantia nigra pars reticulata neurons to apomorphine: effects of striatal lesions and anesthesia

Many of the behavioral consequences of dopamine system activation are thought to be mediated by substantia nigra pars reticulata output pathways. Extracellular, single unit recording studies were conducted to determine how i.v. administration of the dopamine agonist, apomorphine, affects the activity of these pars reticulata neurons. Results revealed that a 320 micrograms/kg dose of the drug, considered sufficient to stimulate striatal postsynaptic dopamine receptors, caused highly variable changes in reticulata cell firing. Cells exhibited increases, decreases, or no changes in firing. Many cells also displayed marked minute to minute changes in firing. This non-uniform pattern of responses was not related to state of consciousness since similar responses were observed in both chloral hydrate-anesthetized as well as conscious, paralyzed rats. Both the increases and decreases could be reversed by subsequent administration of haloperidol. The variable responses to apomorphine were reduced but not totally prevented by striatal kainic acid lesions, suggesting that changes in striatonigral transmission may account for some but not all of the firing changes which were observed. A lower dose of apomorphine (20 micrograms/kg), thought to act primarily at dopamine cell autoreceptors, had little effect on reticulata cell firing and did not modify the variable responses normally observed after the higher dose. These results contrast strikingly with the consistent excitatory responses to apomorphine which have previously been observed in the globus pallidus and suggest that complex or multiple indirect effects of the drug may contribute to the varied reticulata responses.

Evaluating health planning: empirical evidence on HSA regulation of prepaid group practices

The regulation of HMOs by health planning agencies serves as a "tracer" to aid in evaluating HSAs, and as a source of empirical evidence for the heretofore largely theoretical health policy debate between market reformers and regulators. Two complementary studies (the authors' 1979 survey investigating the hospitalization policies of prepaid group practices, and AMPI 's study of all HMO applications submitted to HSAs from 1975 through mid-1978) provide information about the extent of HMO applications to planning agencies, the rate of rejections, the burden of the planning process of HMOs, and the possibility that negative perceptions of regulation may have led HMOs to refrain from activities requiring planning approval. Both studies reveal that health planning review was detrimental to 20 to 30 percent of HMOs. Thus data collected during the period of extensive HSA regulation of HMOs seem to justify the current policy that gives HSAs only very limited authority over HMOs.

Effects of benzodiazepines on single unit activity in the substantia nigra pars reticulata

Intravenous administration of two benzodiazepines, flurazepam and diazepam, had an inhibitory effect on the firing rates of neurons of the substantia nigra pars reticulata, a brain region with an identified GABAergic innervation. Diazepam was more potent than flurazepam. Bicuculline and picrotoxin, two drugs which block GABAergic transmission, and caffeine and theophylline, two methylxanthines which inhibit benzodiazepine binding, all reversed the inhibition produced by diazepam. The action of theophylline was less consistent than that of caffeine. Similarly, Ro 15-1788, an imidazodiazepine which putatively functions as a specific benzodiazepine antagonist, reversed the diazepam-induced inhibition. These findings are consistent with previous reports which suggest that the benzodiazepines may act through a GABAergic mechanism. In a separate group of experiments, caffeine or Ro 15-1788 was administered alone. While caffeine excited all reticulata, generally had little excitatory effect. These results suggest: 1) that cells of the substantia nigra pars reticulata may not receive a substantial, tonic inhibition mediated by an endogenous benzodiazepine-like substance; and 2) that the methylxanthines may increase reticulata cell firing, at least in part, through mechanisms unrelated to the blockade of benzodiazepine receptors.

Novel electrode adaptation for N2 lasers

A novel electrode design is described and its performance is indicated.

Isotopic Molecules: Separation by Recycle Gas Chromatography

Gas chromatographic columns, greatly extended in length by the use of paired columns in a recycling apparatus, have been used to separate butane (n-C4H10) from deuterated butane (n-C4D10) and methane (CH4) from deuterated methane (CD4). The separation of monotritiated cyclobutane (C4H7T) from cyclobutane (C4H8) is nearly complete. This procedure is generally applicable to a wide variety of separations of isotopic molucules.