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W M Burnham

Publications and source records attributed to W M Burnham.

82 records · Page 5Linked to original sources
PubMed1977

Afterdischarge thresholds and kindling rates in dorsal and ventral hippocampus and dentate gyrus.

Electrodes were implanted to dorsal hippocampus (CA1), ventral CA1, DOrsal dentate gyrus or ventral dentate gyrus. Epileptiform afterdischarge (AD) thresholds were lower in dorsal areas than in ventral areas. Dorsal areas, however, required a greater number of stimulations to develop ("kindle") a fully generalized convulsion than did ventral areas. Thresholds and kindling rates in the dentate gyrus were intermediate between dorsal and ventral CA1, except for the ventral dentate which had higher AD thresholds than ventral CA1. Secondary sites within the hippocampus subsequently kindled within a few stimulations following completion of kindling in the primary site, regardless of which hippocampal area served as the primary site.

Animals↗
PubMed1976

A microelectrode study of amygdaloid afferents: temporal neocortical inputs.

Acute experiments were performed on anesthetized cats using standard techniques of electrical stimulation and single unit recording in order to study the responses of amygdaloid neurons to neocortical inputs. Satisfactory records were obtained from 272 amygdaloid neurons. The majority of those fired spontaneously, at low rates, with single, randomly occurring spikes. The lateral neocortex, particularly the portion which is homologous to temporo-insular cortex in man, is capable of influencing the discharges of many amygdaloid neurons. The typical response pattern consisted of an excitatory-inhibitory sequence with the median onset latency of 12.0 msec, which is consistent with monosynaptic excitation of the output-type nerve cells in the affected regions of the amygdala (Al, Ac, Ab). There was an absence of clear topographical arrangement: all of the effective neocortical areas influenced the neuronal discharges in Al, Ac and Ab fairly equally. These results correlate well with neuroanatomical studies of amygdaloid structure and connectivity. Our finding of diffuse non-topographic excitatory influence upon the lateral, central and basal amygdaloid nuclei exerted by insular-temporal regions known to be involved with higher order sensory analysis and pattern recognition is quite consistent with a view of this system serving as a link between neocortical information stores and the fundamental motivational drive mechanisms of the hypothalamus.

Amygdala↗
PubMed1975

Post-activation potentiation and the kindling phenomenon.

Potentials evoked in the hippocampus and preoptic region of rats by single biphasic pulses applied to the amygdala were compared during recruiting, after post-tetanic potentiation (PTP) and after amygdaloid kindling. The same components were enhanced temporarily by recruiting and PTP as were enhanced permanently by kindling. Trains of tetanic stimulation with parameters which partially mimicked the cellular discharge parameters during an amygdaloid afterdischarge (AD) were applied to the amygdala at a frequency of 1 per 5 sec continuously for 2.5 h or for 15 min a day for 10 days to produce a total of 1800 trains. Amygdaloid kindling rates were then measured and compared with control groups. Animals pretreated with tetanic stimulation required significantly fewer ADs to develop maximal seizures. Further experiments showed that tetanic stimulation, but not recruiting stimulation (10 c/sec), low frequency stimulation (1 c/sec), or handling, would produce a permanent change in potentials evoked in secondary sites by single pulses applied to the amygdala. This change in evoked potential amplitude was significant but smaller than that produced by kindling. Also tetanic stimulation, but not recruiting or single pulses, facilitated subsequent kindling.

Amygdala↗
PubMed1975

Primary and "transfer" seizure development in the kindled rat.

An investigation was made of both primary and "transfer" kindling as they occur in ipsilateral limbic sites. Primary kindling was found to involve progressive growth of afterdischarge (AD), propagation and convulsive behavior. It was noted that AD growth did not take place gradually but occurred in sudden, large increments. "Transfer" (a significant acceleration of secondary kindling) was found at every secondary limbic site. It was associated with the early appearance of full-blown AD's, super-normal propagation, and well-developed seizures. The post-transfer interference of primary site function previously reported by Goddard et al was also found, but it occurred in significant amounts only after transfer kindling of the amygdala. It is believed that the data offer some support for both of the hypothetical mechanisms of transfer which have been proposed.

Amygdala↗
PubMedDate not supplied

Unchanged regional norepinephrine glycol metabolite levels in rat brain two months after amygdala kindling.

Concentrations of the norepinephrine (NE) glycol metabolites MHPG (3-methoxy-4-hydroxyphenylethyleneglycol) and DHPG (3,4-dihydroxyphenylethyleneglycol) were examined in 13 brain regions of amygdala-kindled and yoked control rats. The subjects were killed 2 months after the kindled rats had exhibited their sixth 'stage 4-5' generalized seizure. In experiment 1, small but statistically significant decreases in total MHPG levels were found in the right hippocampus (91.6% of control) and hypothalamus (90.7% of control). When the study was repeated with 2 additional control groups, non-kindled, electrically stimulated controls and maximal electroshock convulsion controls, however, these small changes were not seen. The data suggest that since amygdala kindling does not produce any consistent, long-lasting alterations in brain regional NE glycol metabolite levels, there are no consistent, long-term changes in central NE neuronal activity.

Amygdala↗
PubMedDate not supplied

An evaluation of the anticonvulsant effects of vitamin E.

The anticonvulsant effects of D-alpha-tocopherol (vitamin E) were studied in 4 animal seizure models: the Metrazol threshold model (MET), the maximal electroshock model (MES), the kindling model (well-established seizures), and the ferrous chloride model. Vitamin E failed to antagonize seizures in the MES, MET, or the kindling models. It was, however, able to significantly delay the onset of electrographic seizures in the intracerebral ferrous chloride model. Thus, vitamin E shows activity in the ferrous chloride model, but not in the animal models commonly used to screen for anticonvulsant drug actions.

Animals↗
PubMedDate not supplied

Reduced GABA-mediated chloride flux in entorhinal cortex-kindled rat brains.

Gamma-aminobutyric acid (GABA)-mediated chloride uptake was determined in synaptoneurosomes prepared from the brains of entorhinal cortex-kindled and paired control rats. Subjects were sacrificed either 24 h or 28 days after the experimental animals had exhibited their sixth stage 5 convulsion. In the cortex and cerebellum, no difference was observed between kindled and control animals at either time period. In the brain-stem, however, a significant reduction (approximately 50%) in chloride uptake was observed in kindled subjects both 24 h and 28 days after the last seizure. These findings are consistent with the hypothesis that the 'kindled state' results from a long-lasting decrease in GABA-mediated inhibitory activity.

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