Topical Application Of Penicillin Research Articles

Acute effect of an extract of Ambrosia paniculata (Willd.) O. E. Schultz (mugwort) in several models of experimental epilepsy

The acute effect of Ambrosia paniculata was studied in several animal models of epilepsy. Intraperitoneal injections (0.01 mL/g body wt) of a decoction of the dry leaves significantly enhanced the latency to the first convulsion and survival time in mice injected with picrotoxin (7 mg/kg) or isoniazid (210 mg/kg). Epileptic spikes were induced by topical application of penicillin through a glass electrode filled with a penicillin–agar–saline mixture and recorded in sensorimotor and occipital cortices, in rats immobilized with d-tubocurarine. The plant decoction reduced significantly the spike amplitude in both sites. The mentioned effects were elicited at doses that also reduced general motor activity (Irwin test) and exploratory behavior. The decoctions were not effective against electroshock-induced convulsions in mice. The convulsions induced by isoniazid, picrotoxin, and penicillin differed from those induced by electroshock implicating selective disruption of GABAergic neurotransmission. The results suggest that A. paniculata, like several conventional antiepileptic drugs, might act by enhancing GABAergic neurotransmission, a hypothesis that requires further demonstration. These results explain and justify the traditional use of the plant in epilepsy.

The brainstem cardioarrhythmogenic triggers and their possible role in sudden epileptic death

The cardiovascular effects of simultaneous activation of hypothalamic and mesencephalic cardioarrhythmogenic triggers were studied in hemispherectomized rats. Paroxysmal activity of hypothalamic neurons (HEF), elicited by topical application of penicillin G on the thalamus, triggered short-lasting bradyarrhythmic episodes, up to a maximum of 6 s, and alterations in repolarization. In the hypothalamic neurons, an additional penicillin G epileptic focus at mesencephalic level (MEF) induced the enhancement of paroxysmal activity by a recruitment of new units and potentiation of their background activity. HEF + MEF triggered second-degree 2:1–8:1 atrioventricular (A-V) blocks, impairment of the A-V conduction, alterations in the recovery phase and bundle branch blocks. After HEF, the arterial blood pressure decreased by 4–6%. HEF + MEF induced a further reduction of 17% in systolic pressure only. It is possible that the enhancement of the HEF following MEF could depend on MEF spreading upward. The HEF, in turn, by spreading downward could influence the MEF and so activate, between HEF and MEF, a circuitry with reciprocal co-excitation that could explain the more serious cardiovascular alterations observed during HEF + MEF compared with those observed during HEF only or during MEF only. However, this cardiovascular impairment, which must be neurogenic in origin as it was observed in animals with normal acid-base and blood parameter values, did not induce heart death. Thus, additional concomitances must be considered, such as metabolic derangement which can occur during seizures, to explain sudden death in epileptic patients. Some aspects of metabolic complications in cardiac activity during epilepsy are also discussed.

Effects of corpus callosum stimulation on the morphology and frequency of epileptic bursts in the feline topical penicillin generalized model.

Twelve cats were stimulated at the rostrum of the corpus callosum while full epileptic activity was recorded after topical application of penicillin on the cortex bilaterally. Electrocorticography was performed bilaterally. In 6 animals the electrode position was checked by evoked potentials. Stimulation parameters ranged from 0.5 to 1,000 Hz, from 2 to 10 mA, and from 0.5 to 5.0 ms. No significant modification was found in frequency, synchrony, and morphology of the epileptic bursts and spikes, suggesting that callosal stimulation, at least using this model, is ineffective in reducing epileptic activity.

The effects of focal epileptic activity on the somatosensory evoked potentials in the rat.

The cortical somatosensory evoked potential (SEP) of the rat, evoked by contralateral forepaw stimulation, consisted of early (P 1 and N 1) and the late components (P 2 and N 2). Microelectrode recording yielded evoked unitary responses of short latencies in the range of the early components and responses of longer latencies in the range of P 2. During the development of focal epilepsy after topical application of penicillin, the late components of SEP were enhanced and the enhanced late negativity corresponded to a surface negative cortical spike. The prominent enlargement of later components was associated with prolonged, often recurrent discharges of long latency unitary responses and with enlarged local field potentials. Early components of SEP remained relatively unaffected and so did unitary responses with short latencies. Epileptic spike-conditioned SEPs in the cuneate nucleus, thalamic sensory relay nucleus and sensory cortex were depressed from 100 ns (cuneate nucleus) to about 300 ms (thalamus and cortex) subsequent to spike discharge. Transmission in the cuneate nucleus was least affected. Thalamic and cortical early components of SEP had similar time courses of recovery, which differed markedly from hat of cortical late components. Our findings suggest that two different neuronal activities generate different components of SEP and are differentially involved in the epileptic activities, which results in the different amplitude recovery following spontaneous epileptic spike discharges.

Simultaneous measurement of blood flow and glucose metabolism by autoradiographic techniques.

A double tracer autoradiographic technique using 131I-iodo-antipyrine and 14C-deoxyglucose is presented for the simultaneous measurement of blood flow and cerebral glucose utilization in the same animal. 131I is a gamma emitting isotope with a half life of 8.06 days and can be detected with adequate resolution on standard autoradiographic films. Autoradiograms are made before and after decay of 131I; the time interval between the 2 exposures and the concentration of the 2 tracers is adjusted to avoid significant cross-contamination. In this way, 2 film exposures are obtained which can be processed quantitatively like single tracer autoradiograms. The validity of the method for the investigation of local coupling of flow and metabolism was tested under various physiological and pathophysiological conditions. Coupling was tight in barbiturate-anesthetized healthy animals, but not under halothane anesthesia where uncoupling occurred in various subcortical structures. Focal seizures induced by topical application of penicillin on the cortical surface led to a coupled increase of metabolism and flow in thalamic relay nuclei but not at the site of penicillin administration where increased glucose utilization was not accompanied by similar increase in blood flow. Both coupled and uncoupled increases in local glucose utilization were observed in spreading depression and in circumscribed areas of experimental brain tumors. The results obtained demonstrate that double tracer autoradiography allows allows the very precise local assessment of cerebral blood flow and glucose utilization, and, therefore, is particularly suited to the study of regional coupling processes under various experimental conditions.

Changes in the rate of cortical epileptiform activity by increased intragastric pressure in cats

The purpose of this study was to evaluate what effects distension of the stomach would have on the discharge rate of cerebral cortical epileptogemic foci in cats. Epileptiform spiking was produced by focal freezing or topical application of penicillin. Intragastric pressure was increased by the inflation of an intraluminal latex balloon. Results showed that increases in intragastric pressure produced a decrease in epileptiform spike discharge rate in some preparations. Decreases in or the sudden release of intragastric pressure often produced an enhancement or “rebound” of epileptiform spiking. These findings agree with earlier reports from our laboratory in which passive distension of the urinary bladder or increased intracranial pressure produced similar results. We suggest that the decrease in spike rate may be due to the desynchronizing effect of afferent input produced by stomach distension. In this regard, sensory activity initiated by the gastric stretch receptors probably play a major role.

Effects of artificially induced increases in intracranial pressure on epileptic activity.

The effects of induced increases in intracranial pressure (ICP) on epileptic activity following topical application of penicillin on the cerebral cortex or dorsal hippocampus were investigated in rabbits. Enhanced basal epileptic activity was brought about by the rise in the ICP, obtained with repeated lumbar infusions of saline. In some animals, this increased activity was already evident during the test, while in others it became obvious only at the end of the procedure. When induced, the increased epileptic activity could persist even after the ICP had returned to within normal limits.

Topical application of penicillin into hippocampal in vitro slices: A methodological study using benzyl (14C) penicillin.

A gas pressure system is employed for topical application of pico/nanolitre volumes of 9 mmol/l benzyl (14C) penicillin into guinea-pig in vitro transverse hippocampal slices. Control of pressure pulse parameters enables ejectates, computed after liquid scintillation, from 10 micrometer, 5 micrometer and 2 micrometer pipettes with high reliability of ejection. A detailed study was done on the ejection performance of 5 micrometer and 2 micrometer pipettes. It shows that for the 5 micrometer tips, with the chosen ejection parameters, feeding pressure = 0.5 MPa, feeding pulse duration 50 ms, a 99% ejection incidence was obtained (n = 200). The mean volumes ejected were 0.12 and 0.5 nl (n = 50) for one and four pulses delivered respectively. The corresponding ejectate means obtained from five 2 micrometer pipettes given a feeding pressure of 1.5 MPa, and a feeding pulse duration of 70 ms, were 0.04 and 0.13 nl. Statistical evaluation of the individual pipette ejection performances gave characteristic regression slopes within each pipette group. A comparison between visually controlled injection into oil and injection into slice, showed a close correspondence. The applicability of the ejection method is discussed in relation to functional studies on the conversion of single neurones into "epileptic" ones.

Suppression of epileptiform activity by increased intracranial pressure in cat

This study investigated the relationships between changes in intracranial pressure and the activity of cortical epileptogenic foci in cats. Epileptiform spiking was produced by focal freezing and/or topical application of penicillin. Increases in intracranial pressure were produced by infusion of mock cerebrospinal fluid into the cisterna magna. We found that increases in intracranial pressure always produced decreases in epileptiform spike discharge rate. Some preparations also showed an enhancement or “rebound” of spike discharge rate soon after the intracranial pressure was returned to normal. We concluded that it is unlikely that compression or distortion of cerebral tissue play any role in these results. Decreases in cerebral blood flow may be a factor but only for the higher values of intracranial pressure in the less sensitive preparations. We suggest that the most important mechanism responsible for these findings is the desynchronizing effect of afferent input related to increased intracranial pressure. The source of this sensory activity may be from receptors in the cerebrospinal meninges and blood vessels.

Relation between extracellular potassium concentration and neuronal activities in cat thalamus (VPL) during projection of cortical epileptiform discharge

Neuronal and potassium activities (a k) were measured in the nucleus ventro-posterolateralis thalami (VPL) during propagated epileptiform activity from the somatosensory cortex of cats. Seizures were induced by repetitive electrical stimulation of the cortical surface or by topical application of penicillin. The recruitment of VPL into a seizure resulted in large increases of a k to levels of up to 11.6 mmoles/l, accompanied by increases in neuronal discharge rate to 300/sec. Sometimes the rise in a k preceded active participation of a given thalamo-cortical relay (TCR) neuron in the seizure. After reaching a peak level, a k and neuronal discharge rate slowly declined during an ictal episode. After cessation of seizures all TCR neurons were inhibited, while a k fell to subnormal levels. The duration of these postictal depressions increased with the amplitude of preceding increases and subsequent undershoots in a k and could last up to 120 sec. During decay and undershoot in a k, relay capability of TCR neurons was reduced. Also the probability that action potentials elicited in intracortical endings of TCR cells would antidromically invade their cell bodies was decreased. The duration of these periods varied with the amplitude of undershoot in a k. Seizure threshold was increased during undershoots. These observations are consistent with a long-lasting postical hyperpolarization of neuronal membranes. The hyperpolarization may be caused by the action of an electrogenic pump, which is probably involved in termination of seizure discharge.

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.

Focal penicillin epilepsy in an isolated cerebral hemisphere

The cortex of an entire cerebral hemisphere in the cat was chronically isolated to allow assessment of the role of intrinsic association pathways in the regulation of focal epileptic activity induced by topical application of penicillin. EEG recordings indicated that interictal spike activity in the normal hemisphere was maximal at the focus and markedly reduced in amplitude at distances of 5 to 7 mm. Activity in the isolated hemisphere was similar in morphology to that of the normal cortex, but there were largeamplitude epileptiform discharges 10 to 15 mm from the focus. These distant penicillin spikes appeared early in the development of the focus and were not attributable to diffusion of penicillin. Intracellular recordings at the center of the focus and at remote sites showed the characteristic paroxysmal depolarizing shifts (PDSs) previously described for intact cortex, i.e., large-amplitude membrane depolarizations with superimposed high-frequency spike activity and subsequent spike inactivation. Hyperpolarizing potentials followed termination of PDSs in most cells and were occasionally seen as the sole accompaniment of the focal penicillin discharges. We suggest that the similarity of intracellular findings in normal and isolated cortices could have resulted from a direct effect of penicillin on neurons, whereas the spread of interictal spikes in the isolated hemisphere apparently involved abnormal utilization of existing intracortical association pathways.

Effect of Magnesium on Epileptic Foci

Parenteral magnesium sulfate has been used to control acute convulsions of diverse etiologies and is currently a mainstay in controlling eclamptic convulsions. However, the site of this anticonvulsant action has remained controversial and not well studied in experimental epileptic models. Therefore we determined the effects of intravenously infused magnesium sulfate on the epileptic neural activity induced by topical application of penicillin G to motor cortex in anesthetized cats and dogs and in awake, undrugged primates. Magnesium sulfate was able to directly suppress neuronal burst firing and interictal EEG spike generation at serum levels below those producing paralysis. The degree of suppression corresponded to the serum magnesium concentration and was reversible. These results corroborate the clinical observations in patients that magnesium can produce an anticonvulsant effect apart from neuromuscular blockade and suggest it may have clinical applicability in treating a wider range of acute convulsions.

Effects of a focal penicillin lesion on responses of rabbit cortical neurones to putative neurotransmitters.

1. Epileptogenic foci were generated in rabbit cerebral cortex by the topical application of penicillin.2. Responses to iontophoretically applied putative neurotransmitters were compared in cortical neurones firing spontaneously with those driven by applied excitant substances, both before and after establishing the penicillin focus.3. In the presence of the spiking focus, currents of gamma-aminobutyric acid, which normally produced 100% depression of neuronal firing, were ineffective.4. In the same situation, currents of (+/-)-homocysteic acid, glutamate and acetylcholine produced predominantly depolarization block responses, and hence depression of firing.5. It is concluded that an epileptogenic focus can alter the responses of rabbit cortical neurones to microiontophoretically applied neurotransmitter substances. Possible mechanisms for the spread of seizure activity are discussed.

Penicillin as an epileptogenic agent: effect on an isolated synapse.

Penicillin enhances the excitatory postsynaptic potential of the squid stellate ganglion. This effect suggests the hypothesis that the epileptic focus created by the topical application of penicillin to the mammalian cerebral cortex is produced by the facilitation of excitatory synaptic coupling within the preexisting positive recurrent feedback system.

DC activity in the depth of an experimental epiletic focus

Experimental seizure foci were created in the cortex of cats by the topical application of penicillin. Glass micro-pipettes were used to record the DC field in the depth of the cortex underneath the focus. Vertically oriented dipoles of differing structure were found. In the area of intense surface negative ictal shifts, the maximum negativity was found in layer V of the cortex. No reversal of sign was found within the depths of the cortex. This was interpreted to mean that nearly the entire neuron was depolarized with the source of current flow located in the axons and/or the finest arborizations of the dendrites. In the periphery of the focus, where positive shifts can be recorded from the surface, the shifts reverse sign in the upper 300–500 μ of the cortex, and the maximum negativity also was located in layer V.

Penicillin as epileptogenic agent: its effect on an isolated neuron.

Penicillin induces partial depolarization and increased excitability of the neuronal membrane of crayfish stretch receptor. Such effects suggest that the epileptic focus created by the topical application of penicillin to the mammalian cerebral cortex may result from the lowering of the threshold for impluse initiation by excitatory synaptic action within the neuron population.

Intracellular recording from cortical pyramids and small interneurons as identified by subsequent staining with the recording microelectrode

In fifty-two albino rats under barbiturate anesthesia the cortical neurons were marked by staining with the intracellular recording micropipette filled with methyl or aniline blue, using the modified method of Thomas and Wilson destined originally for spinal motoneurons. In addition, two alternative histological procedures were tested. In twelve cases perfectly stained neurons were found. They were either large pyramidal cells at the depth of 1.0 to 1.3 mm whose sustained spontaneous intracellular activity increased in frequency following topical application of penicillin (convulsive drug) onto the cortical surface, or small neurons of round or stellate shape located in the depths of 0.2 to 1.7 mm whose sustained spontaneous intracellular activity (of different patterns) stopped in most cases following penicillin for a long time. These neurons are considered inhibitory intracortical interneurons. It is concluded that in rats large pyramidal cells as well as small intracortical interneurons can be recorded intracellularly (which was questioned in the latter case) and subsequently marked. The small intracortical interneurons were thus directly identified, and-if the depression of activity of inhibitory interneurons is accepted as a possible mechanism of convulsive action of locally applied penicillin in the cortex-identified as inhibitory cortical interneurons.

Convulsive effect elicited by topical application of penicillin on glutamate-glutamine system of brain.

PREVIOUS investigations in our laboratory1,2 have shown that the topical application of mescaline to the ectosylvian gyrus induces significant changes in the glutamine, glutamic acid and ammonia content of the whole neocortex. The experiments reported here were carried out in order to investigate the influence of the topical application of another convulsant drug—penicillin—on the same compounds.

Intracellular events during the activation of cortical epileptiform discharges

1. 1. The problem of reflex epilepsy has been investigated experimentally. Cortical epileptogenic foci were produced by topical application of penicillin in 33 cats (acute preparations). The characteristic electrographic manifestations within such foci were studied (by means of surface electrode and intracellular micro-pipettes) with specific reference to the effects elicited by various types and parameters of electrical stimulation. 2. 2. “Triggering” of epileptiform paroxysms and the modifications of this phenomenon observed in different conditions and with certain stimulation parameters have been described and analyzed at the cellular level. 3. 3. The findings suggest that the periodically recurring, paroxysmal depolarization shifts (PDS) which characterize the behavior of “epileptic” neurons are of a graded nature. Presence and duration of the hyperpolarizing shifts which commonly follow each PDS may determine, but do not seem to be the exclusive factor for the upper limit of stimulation frequency at which “triggering” is possible. 4. 4. The latency with which the PDSs are triggered is highly variable and can be modified by various factors. It might be excessively long and, in any case, it was always longer than that for isolated “normal” spikes activated by the same stimulus. Such latency could often be shown to correspond to the time required for a decrease of the membrane polarization to critical levels. It is suggested that this delay results from a progressive recruitment of a certain number of elements which would then act as a pacemaker for the entire epileptic neuronal population.