Dixon M. Woodbury

Effects of Vagal Stimulation on Experimentally Induced Seizures in Rats

Summary: Repetitive stimulation of the vagus nerve inhibits chemically induced seizures in dogs. We report here the results and conclusions from studies designed to answer some of the immediate questions raised by this finding. (1) Maximal stimulation of vagal C fibers at frequencies greater than 4 Hz prevents or reduces chemically and electrically induced seizures in young male rats. (2) Antiepileptic potency is directly related to the fraction of vagal C fibers stimulated. (3) Vagal stimulation shortens but does not shut down a chemical seizure once it has begun. (4) In rats, optimal stimulus frequency is approximately 10–20 Hz; duration of stimulus, 0.5‐1 ms; and stimulus strength, 0.2‐0.5 mA/mm2 of nerve cross‐section. These results, when taken together with similar results obtained from dogs, monkeys, and humans, strongly suggest that periodic stimulation of the vagus nerve using appropriate stimulation parameters is a powerful method for preventing seizures. The data from the literature suggest that the antiepileptic actions of vagal stimulation are largely mediated by widespread release of GAB A and glycine in the brainstem and cerebral cortex. The probable pathway is via projections from the nucleus of the solitary tract to the reticular formation and thence by diffuse projections to the cortex and other areas. Intermittent vagal stimulation has the potentiality of reducing the number and/or the intensity of seizures in patients with intractable epilepsy. These results indicate that feasibility studies in humans should be continued and expanded.

The effects of prostaglandin E2 in growing rats: Increased metaphyseal hard tissue and cortico-endosteal bone formation

SummaryTo assess the efficacy of PGE2 in inducingin vivo bone formation, graded doses of prostaglandins E2 were administered to 255 g rats. Histomorphometric analyses of selected sequential fluorescent-labeled bones of rats treated with 0,0.3, 1.0, 3, or 6 mg PGE2/kg/d for 21 days showed that the doses of PGE2 depressed longitudinal bone growth, increased growth cartilage thickness slightly, decreased degenerative cartilage cell size and cartilage cell production slightly, and increased proximal tibial metaphyseal hard-tissue mass markedly. Periosteal bone formation was depressed at the higher doses, and an early, slight depression in endosteal bone formation was also observed, along with a striking late increase in endosteal bone formation and in the formation of trabecular bone in the marrow cavity of the tibial shaft. The characteristics and magnitude of these responses were quite similar to those observed in our previous study of the effects of PGE2 on weanling rats except for the delayed increase in cortico-endosteal bone formation.

Penetration of 14C-inulin and 14C-sucrose into brain, cerebrospinal fluid, and skeletal muscle of developing rats

Summary1.We studied the decrease in brain uptake of two substances, inulin and sucrose, during maturation of the brain. Concentration ratios of CSF/plasma and brain/plasma for 14C-labeled inulin and sucrose were calculated and time-uptake curves plotted for prenatal and postnatal rats. Comparisons of these ratios among the various ages showed a progressive decrease in the inulin ratios of both compartments with increasing age. Sucrose “spaces” were always larger than inulin “spaces,” suggesting possible sucrose penetration into cells. The brain/CSF concentration ratio for inulin, however, appears to reflect brain extracellular space in young rats, but not in older animals. Electrolyte concentration ratios of CSF and plasma suggested progressive maturation of transport mechanisms at the choroid plexus and increase of CSF flow. The degree of concentration of inulin in the developing brain and the CSF of the young rat probably reflects cellular maturation of both barrier and secretory mechanisms.2.We also measured the inulin and sucrose space of skeletal muscle in rats of different age. In contrast to brain, the spaces measured by the two substances were the same and decreased with maturation of the animals.

Vagal Stimulation Reduces the Severity of Maximal Electroshock Seizures in Intact Rats: Use of a Cuff Electrode for Stimulating and Recording

J. Zabaru showed thai repetitive vagal stimulation (VS) prevents or ameliorates convulsive seizures in dogs. We have studied the effects of VS on maximal electroshock seizures (MES) in intact rats: (1) A 5 wire cuff electrode was developed for stimulating and recording from the vagus. Compound action potentials (AP) were recorded and strength‐duration curves obtained for A and C fibers. There is a monotonic relationship with a negative slope between heart rate (HR) and AP amplitude. C fibers remain excitable for 25 days after cuff implant. (2) The anticonvulsant efficacy of VS is directly related to the fraction of vagal C fibers stimulated and the frequency of stimulation. (3) The anticonvulsant efficacy of VS has been established using two rat models of human epilepsy. VS abolishes the extensor component of the tonic phase of a MES and shortens or prevents tonic seizures induced by pentylenetetrazol (PTZ). (4) VS appears to act via release of large quantities of the inhibitory mediators GABA and glycine throughout large volumes of the brain. (5) It is rational to test VS in man as a treatment for intractable seizures.

The Developing Animal as a Model

Evidence is presented that some excitatory systems are mature at birth and that inhibitory systems develop rapidly during the first 3 weeks after birth.

Seizure Susceptibility in DBA and C57 Mice: The Effects of Various Convulsants

Summary: Convulsive dose 50s (CD50s) for various convulsive drugs and minimal and maximal electroshock seizure thresholds were determined in DBA and C57 mice. DBA mice had lower maximal electroshock seizure thresholds (MESTs, 15%) and CD50s for homocysteine thiolactone (HTL, 23%) and bicuculline (69%), and a higher CD50 for pentylenetetrazol (PTZ) at 3 weeks of age, the age of maximal audiogenic seizure (AGS) susceptibility. At 8 weeks, when DBA mice are not susceptible to AGSs, significant differences were a lower minimal electroshock seizure threshold (mEST, 37%) and maximal EST (MEST) (19%), lower CDsos for N‐methyl‐D‐aspartate (NMDA) (39%), kainic acid (KA, 50%), HTL (32%), strychnine (37%), and a higher CD50 for nicotine (55%) in DBA mice. Based on these data it is suggested that pathways involving NMDA and KA receptors are responsible for increased susceptibility to seizure initiation (mEST), and are opposed by glycine pathways, and that opposing GABA and cholinergic systems at higher CNS levels are involved in seizure spread (AGSs and MEST) in these mice. Latency patterns indicate that nicotine, strychnine, PTZ and bicuculline have high blood‐brain barrier (BBB) penetrability. Picrotoxin and the excitatory amino acid receptor agonists had longer latencies, suggesting low BBB penetrability. Age‐related changes in latency, however, give evidence that difficulty in drug penetration of the BBB is not responsible for differences observed in CD50s between strains.

Effects of Carbon Dioxide on Brain Excitability and Electrolytes

Effects of various concentrations of CO2 on brain excitability and electrolyte distribution in rats were studied, and also some properties of seizures induced by abrupt withdrawal from high concent...

Humoral and ionic regulation of osteoclast acidity

SummaryRegulation of the acidity of osteoclasts was determinedin situ on the endocranial surfaces of mouse calvaria using acridine orange, a fluorescent weak base. Osteoclasts could be identified by (1) large size, (2) multiple nuclei, (3) relatively small numbers of cells, and (4) the way and the extent to which they took up the dye. Nonosteoclastic cells were stained mainly in their nuclei and occasionally in a few lysosomes surrounding their nuclei, which were uniformly single in nonosteoclasts. Nuclei in osteoclasts were also stained, but the staining of the nuclei was partially masked by the intensity and completeness of the staining of the cytoplasm. In some cells the cytoplasmic staining appeared to be in discrete granules, giving the cytoplasm a bright, frothy appearance. This fluorescence was present in both treated and untreated cells and aided in identifying the osteoclasts. Acridine orange fluorescence at 624 nm intensity, and hence, osteoclast acidity, was increased by parathyroid hormone and prostaglandin E2. Parathyroid hormone-induced increases in acidity were inhibited by calcitonin, cortisol, sodium fluoride, and prostaglandin E2. Furthermore, osteoclast acidity was dependent largely or partially on (1) maintenance of K+ and Na+ gradients, (2) patent Na+ channels, (3) chloride-bicarbonate exchange, and (4) H+, K+-ATPase. These findings demonstrate that osteoclasts become acidified by mechanisms similar to those occurring in gastric parietal cells.

Effects of ouabain and diphenylhydantoin on transmembrane potentials, intracellular electrolytes and cell pH of rat muscle and liver in vivo

1. The effects of ouabain and diphenylhydantoin (DPH) to inhibit and stimulate, respectively, the Na+—K+ pump were used to correlate transmembrane resting potentials (RP), ionic gradients, and cell pH (DMO method) in rat muscle and liver in vivo.

Kinetic analysis of [36Cl]-, [22Na]- and [3H]mannitol uptake into the in vivo choroid plexus-cerebrospinal fluid brain system: ontogeny of the blood brain and blood-CSF barriers.

The kinetics of penetration of radioactive [36Cl]-, [22Na]- and [3H]mannitol into the choroid plexus-CSF brain system was investigated in 1-week, 2-week and adult Sprague-Dawley rats. For adult rats (5 weeks), 36Cl and 22Na uptake by the choroid plexus of lateral ventricle (LVCP) and fourth ventricle (4VCP) resolved into a fast component (t1/2 0.02 - 0.05 h) representing isotope distribution within the extracellular and residual erythrocyte compartments, and a slow component (t1/2 0.8 - 1.9 h) representing isotope movement into the epithelial cell compartment. From steady-state distribution data, choroid cell [Cl] in both LVCP and 4VCP was calculated to be 67 mmol/kg cell H2O, a level nearly 4 times greater than that predicted by the membrane potential for passive distribution. In 1-week immature rats cell [Cl] and [Na] in the choroid plexuses were even greater than the corresponding levels in adults, probably because ion transport across the basolateral membrane is not yet coupled with ion movement from cell to CSF. In mature rats the 36Cl and 22Na uptake into the CSF resolved into 2 components (t1/2 0.18 h, fractional volume 0.24 and t1/2 1.2 h, fractional volume 0.76); however, the fast component of CSF uptake, which likely represents isotope movement across the choroid plexuses, was negligible in the 1-week animals. Permeability-surface area products (PA) were determined for the blood-CSF barrier (i.e. the choroid plexuses) as well as the blood-brain barrier (cerebral cortex and cerebellum). The PA values for 36Cl and 22Na as determined by the fast component of CSF uptake (choroid plexus secretion?) were an order of magnitude less in the 1-week rats than in adults. In contrast, the effective permeability of the blood-CSF barrier as well as the blood-brain barrier, as evaluated by changes in PA of [3H]mannitol, decreased steadily with advancing age.