Evaluation of the Toxicity of Eugenol at Anesthetic Doses in African Clawed Frogs (Xenopus laevis)

Eugenol has been shown to induce anesthesia in African clawed frogs ( Xenopus laevis). The toxicity of eugenol, administered at anesthetic doses, was evaluated in Xenopus frogs with an average body weight of 28.2 ± 13.7 g. Frogs were immersed in 250 mL of an aqueous solution containing 350 µl/L of eugenol for ten minutes and received a single administration (group 1, twelve animals) or three consecutive daily administrations (group 2, twelve animals). In each group, six frogs were scheduled to be euthanized the following day (subgroup A) and the other six were scheduled to be euthanized after a one-week recovery period (subgroup B). Morphologic changes consistent with renal tubular apoptosis affecting distal tubules in the medulla were observed in all subgroup A animals, ranging from mild to moderate in group 1, and from mild to severe in group 2. In subgroup B, renal tubular regeneration was present in all but one animal examined. These findings suggest that eugenol toxicity in amphibians is first manifested by renal tubular apoptosis. Other eugenol-related lesions were massive hepatic necrosis in group 2 ( n = 6), hyaline membranes in the lung ( n = 5), and adipose tissue hemorrhages in group/subgroup 2B ( n = 4).

Joint inflammation increases glucosamine levels attained in synovial fluid following oral administration of glucosamine hydrochloride

OBJECTIVE

To compare synovial glucosamine levels in normal and inflamed equine joints following oral glucosamine administration and to determine whether single dose administration alters standard synovial parameters of inflammation.

METHODS

Eight adult horses were studied. On weeks 1 and 2, all horses received 20mg/kg glucosamine hydrochloride by nasogastric (NG) intubation or intravenous injection. On weeks 3 and 4, 12h after injection of both radiocarpal joints with 0.25 ng Escherichia coli lipopolysaccharide (LPS) to induce inflammation, glucosamine hydrochloride or a placebo was administered by NG intubation. Plasma samples were collected at baseline and 5, 15, 30, 60, 120, 360, 480 and 720 min after dosing. Synovial fluid (SF) samples were collected within 48 h before dosing and 1, 6 and 12h post-dosing. Glucosamine was analyzed by Liquid Chromatography Electrospray Tandem Mass Spectrometry (LC-ESI/MS/MS). Clinicopathological evaluation of SF parameters included white blood cell (WBC) count and total protein (TP) analyses.

RESULTS

No significant differences between groups were observed in SF baseline levels of WBC and TP at any stage of the study. SF WBC and TP significantly increased following IA LPS. The mean (+/-SD) maximal SF glucosamine levels (422.3+/-244.8 ng/mL) were significantly higher (>fourfold) in inflamed joints when compared to healthy joints (92.7+/-34.9 ng/mL). Glucosamine did not have any effect on standard SF parameters of inflammation.

CONCLUSION

Synovial inflammation leads to significantly higher synovial glucosamine concentrations compared to levels attained in healthy joints following oral administration of glucosamine hydrochloride. Whether these higher levels are translated into a therapeutic effect on the joint tissues remains to be elucidated.

Comparison of pharmacokinetics of glucosamine and synovial fluid levels following administration of glucosamine sulphate or glucosamine hydrochloride

OBJECTIVE

To compare the pharmacokinetics of glucosamine and the synovial fluid levels attained following treatment with glucosamine sulphate or glucosamine hydrochloride in a large animal model at clinically relevant doses.

METHODS

Eight adult female horses were used. Crystalline glucosamine sulphate (Dona) or glucosamine hydrochloride was administered at a dose of 20 mg/kg by either intravenous (i.v.) injection or nasogastric (n.g.) intubation. Plasma samples were collected before dosing and at 5, 15, 30, 60, 120, 360, 480 and 720 min after dosing. Synovial fluid samples were collected from the radiocarpal joints within 48 h before dosing and at 1, 6 and 12 h post-dosing. Glucosamine was assayed by Liquid Chromatography Electrospray Tandem Mass Spectrometry (LC-ESI/MS/MS).

RESULTS

Plasma concentrations reached approximately 50 microg/mL after i.v. injection and approximately 1 microg/mL after n.g. administration of both types of glucosamine. The median oral bioavailability was 9.4% for glucosamine sulphate and 6.1% for glucosamine hydrochloride. Synovial fluid concentrations were significantly higher at 1 and 6 h following oral treatment with glucosamine sulphate compared to glucosamine hydrochloride. Twelve hours following oral administration, glucosamine levels in the plasma and the synovial fluid were still significantly higher than baseline for the glucosamine sulphate preparation, but not for the hydrochloride preparation.

CONCLUSION

Following oral administration of a clinically recommended dose of glucosamine sulphate (Dona), significantly higher synovial fluid concentrations of glucosamine are attained, when compared to an equivalent dose of glucosamine hydrochloride. Whether this difference is translated into a therapeutic effect on the joint tissues remains to be elucidated.

Optimization and validation of a simple method using P22::luxAB bacteriophage for rapid detection of Salmonella enterica serotypes A, B, and D in poultry samples

A simple method was developed for the fast and inexpensive detection of Salmonella Typhimurium using a recombinant P22::luxAB phage. All the steps from phage production to detection were considered. A strain of Salmonella Typhimurium harboring the prophage P22::luxAB was grown in batch culture to produce spontaneously the recombinant bacteriophage. Batch production to stationary phase was better for propagation of the phage and led to a total population of 4.3 x 10(9) (+/-4.3 x 10(9)) PFU/ml of P22, including only 1.4 x 10(6) (+/-1 x 10(6)) PFU/ml harboring the luxAB genes. After preenrichment, a simple four-step bioassay was tested and optimized for several parameters. The detection limit of the luminometer was only 5 x 10(2) (+/-1.75 x 10(2)) CFU Salmonella Typhimurium per ml, but increased to 1.5 x 10(4) (+/-1.17 x 10(4)) CFU Salmonella Typhimurium per ml when the cells were in a complex matrix. The detection limit after the preenrichment was 6.5 x 10(3) (+/-1.5 x 10(3)) CFU Salmonella Typhimurium per ml, but the detection limit after the preenrichment also increased markedly to 1.65 x 10(5) (+/-0.15 x 10(5)) CFU Salmonella Typhimurium per ml when Salmonella Typhimurium was in a complex matrix. Finally, the bioassay was applied to the detection of Salmonella Typhimurium LT2 in 14 different feed and environmental samples (including duck feed, litters, and feces) spiked either before or after the preenrichment process. It was possible to detect Salmonella Typhimurium LT2 in all samples within 16 h.

Pharmacokinetics and anesthetic activity of eugenol in male Sprague-Dawley rats

Eugenol, the principle chemical constituent of clove oil, has recently been evaluated for its anesthetic and analgesic properties in fish and amphibians. The objective of this study was to determine the pharmacokinetic (PK) and anesthetic activity of eugenol in rats. Male Sprague-Dawley rats received single i.v. doses of eugenol (0, 5, 10, 20, 40 and 60 mg/kg) and anesthetic level was evaluated with the withdrawal reflex. For the 20 mg/kg dose level, blood and urinary samples were collected over 1 h for the PK assessment. Plasma and blood concentrations of eugenol, as well as metabolite identification in urine, were determined using a novel dansyl chloride derivatization method with liquid chromatography mass spectrometry (LC/MS/MS). PK parameters were calculated using noncompartmental methods. Eugenol-induced loss of consciousness in a dose-dependent manner, with mean (+/-SEM) recovery in reflex time of 167 +/- 42 sec observed at the highest dose level. Mean systemic clearance (Cl) in plasma and blood were 157 and 204 mL/min/kg, respectively. Glucuronide and sulfate conjugates were identified in urine. Overall, eugenol produced a reversible, dose-dependent anesthesia in male Sprague-Dawley rats.

Impact of peripheral elimination on the concentration-effect relationship of remifentanil in anaesthetized dogs

BACKGROUND

This study elucidates the impact of sampling site when estimating pharmacokinetic-pharmacodynamic (PK-PD) parameters of drugs such as remifentanil that undergo tissue extraction in the biophase. The interrelationship between the concentrations of remifentanil predicted for the effect compartment and those measured in arterial, venous, and cerebrospinal fluid were investigated under steady-state conditions.

METHODS

Following induction of anaesthesia with pentobarbital, an arterial cannula (femoral) and two venous catheters (jugular and femoral) were inserted. Electrodes were placed for EEG recording of theta wave activity. Each dog received two consecutive 5-min infusions for the PK-PD study and a bolus followed by a 60-min infusion was started for the steady-state study. Cerebrospinal fluid, arterial and venous blood samples were drawn simultaneously after 30, 40, and 50 min. At the end of the infusion, arterial blood samples were collected for pharmacokinetic analysis.

RESULTS

Remifentanil PK-PD parameters based on theta wave activity were as follows: apparent volume of distribution at steady-state (V(ss)) (231+/-37 ml kg(-1)), total body clearance (Cl) (63+/-16 ml min(-1) kg(-1)), terminal elimination half-life (t(1/2 beta)) (7.71 min), effect compartment concentration at 50% of maximal observed effect (EC(50)) (21+/-13 ng ml(-1)), and equilibration rate constant between plasma and effect compartment (k(e0)) (0.48+/-0.24 min). The mean steady-state cerebrospinal fluid concentration of 236 ng ml(-1) represented 52 and 74% of that in arterial and venous blood, respectively.

CONCLUSIONS

Our study re-emphasizes the importance of a sampling site when performing PK-PD modelling for drugs undergoing elimination from the effect compartment. For a drug undergoing tissue elimination such as remifentanil, venous rather than arterial concentrations will reflect more exactly the effect compartment concentrations, under steady-state conditions.

Evaluation of dexamethasone for the treatment of intracerebral hemorrhage using a collagenase-induced intracerebral hematoma model in rats

Dexamethasone was evaluated for the treatment of intracerebral hemorrhage using a rat model of cerebral hematoma induced by intracerebral injection of collagenase. The treatment group consisted of hematoma rats receiving dexamethasone 1 mg/kg intraperitoneal (i.p.) at 1 and 24 h following surgery. Controls included hematoma rats receiving saline i.p. and sham-operated animals receiving saline i.p. Each animal was evaluated neurologically prior to, as well as 24 and 48 h following surgery. After the last neurological evaluation, animals were deeply anesthetized and the brain was removed following perfusion for microscopic examination and glial fibrillary acidic protein immunohistochemistry. Behavioral scores were significantly improved in the treated group (P < 0.0001). The hematoma volume was significantly smaller (P < 0.02). Neutrophils and astrocytes were less numerous in the hematoma of dexamethasone-treated animals (P < 0.001), however the number of necrotic neurons in the penumbra was not changed by the treatment. The number of necrotic neurons in the cerebral cortex was less in treated than in nontreated animals (P < 0.01). Controls had many vascular changes including necrotic endothelium and fibrin deposits compared with treated animals. In conclusion, dexamethasone administered shortly after an intracerebral hematoma appears beneficial for the treatment of this condition.

Influence of concomitant quinidine administration on dextromethorphan disposition in rats

High doses of dextromethorphan (DM) have been clinically investigated for the treatment of multiple neuronal disorders including neuropathic pain. Several authors have suggested the concomitant administration of DM and a CYP2D6 reversible inhibitor in order to enhance the exposure of DM and limit the exposure to total dextrorphan (DX). The present study proposes to determine whether or not a single dose of quinidine is sufficient to enhance the plasma concentrations of DM in rats and keep those of DX at a minimal level. Oral doses of DM (50 mg/kg) were administered with increasing dose levels of quinidine (0, 2, 20, and 50 mg/kg) to male Sprague-Dawley rats and blood samples were collected over 24 h. Plasma concentrations of DM and total DX were determined using ESI-LC/MS/MS. Quinidine coadministration resulted in a more than twofold increase in the area under the curve of DM with an ED(50) of approximately 2 mg/kg whereas those of total DX were only increased by 21%. These results support the working hypothesis that a single dose of quinidine may enhance the plasma concentrations of DM relative to those of total DX and may therefore improve the treatment of neuropathic pain.

A pharmacokinetic study of amoxycillin in febrile beagle dogs following repeated administrations of endotoxin

The pharmacokinetics of amoxycillin was studied in nine male beagle dogs under healthy and febrile conditions. In Period 1, dogs received 20 mg/kg of an oral suspension of amoxycillin. Intravenous doses of saline, 2 and 20 microg/kg of endotoxin (LPS from Escherichia coli serotype) were administered to dogs (three per group) prior to administration of 20 mg/kg of amoxycillin in Period 2. Rectal temperature and behavioral changes were recorded and blood samples were collected over 12 h for pharmacokinetic analysis. Amoxycillin was assessed in plasma using liquid chromatography coupled with mass spectrometry. Plasma concentrations were analysed using a one-compartment model with lag-time for absorption using an iterative two-stage method. As compared with control groups, amoxycillin clearance decreased significantly with preliminary treatments of 2 microg/kg endotoxin (0.209 vs. 0.140 L/h kg, P < 0.05) and 20 microg/kg endotoxin (0.214 vs. 0.075 L/h kg, P < 0.05). As a result of this, the area under curve for the 2 and 20 microg/kg endotoxin groups increased significantly 100.4 vs. 149.4 microg h/mL (P < 0.05) and 99.2 vs. 277.7 microg h/mL (P < 0.05), respectively. Other drugs currently used for the treatment of fever and septic shock should be re-evaluated using a febrile animal model to avoid improper dose administration.

Erectile dysfunction occurs following substantia nigra lesions in the rat

Erectile function was assessed 6 weeks following uni- and bilateral injections of 6-hydroxydopamine in the substantia nigra nucleus of the brain. Behavioral apomorphine-induced penile erections were reduced (5/8) and increased (3/8) in uni- and bilateral lesioned animals. Intracavernous pressures, following electrical stimulation of the cavernous nerve, decreased in lesioned animals. Lesions of the substantia nigra were confirmed by histology. Concentration of dopamine and its metabolites were decreased in the striatum of substantia nigra lesioned rats. Lesions of the substantia nigra are therefore associated with erectile dysfunction in rats and may serve as a model to study erectile dysfunction in Parkinson's disease.

Serum corticosterone and blood glucose in rats after two jugular vein blood sampling methods: comparison of the stress response

The purpose of this study was to evaluate stress by comparing blood glucose and serum corticosterone levels after repeated blood sampling over 2 h (five time points) in anesthetized noncannulated rats to those of nonanesthetized jugular-cannulated animals. Noncannulated rats underwent isofluorane anesthesia for the duration of the blood sampling at each time point. For both sampling methods, blood glucose concentrations increased after the initiation of blood sampling, peaked at significantly increased (noncannulated rats, P < 0.01; cannulated rats, P < 0.01) concentrations at 0.5 h, and decreased thereafter until the end of the assessment period. Despite the observed fluctuations, blood glucose concentrations remained within normal ranges. Similarly, corticosterone concentrations increased significantly (noncannulated rats, P < 0.01; cannulated rats, P < 0.001) to peak values at 0.5 h. However, corticosterone was significantly lower at the 1- (P < 0.01) and 2-h (P < 0.05) time points in cannulated rats compared with anesthetized rats. Therefore, although both sampling methods are similar regarding blood glucose and corticosterone peak concentrations and time-to-peak, stress was slightly less in the cannulated rats than the rats that underwent repeated anesthesia.

Postnatal development of penile NADPH diaphorase in male rats (Rattus norvegicus): an indicator of erectile function

The aim of this study was to determine the contribution of nitric oxide (NO) to the development of penile erection in rats and was accomplished by evaluating the nicotinamide adenine dinucleotide phosphate diaphorase (NADPH) content of juvenile penile tissues. NADPH is an enzyme involved in the synthesis of NO, a mediator of smooth muscle relaxation in penile tissues. We euthanized 36 rats (age, 1 to 65 days) and obtained penile midshaft specimens for NADPH staining. The number of NADPH-positive granules in the corpus cavernosum and dorsal penile nerve increased significantly (P < 0.001) until animals were 50 days of age. Penile erections in young rats are known to occur around 30-40 days, and penile tissues showed a very significant (P < 0.001) increase of NADPH-positive granules in the corpus cavernosum and the dorsal penile nerve during this period. Therefore, NO seems important for the development of penile erection in juvenile rats.

[Anesthesia of the New Zealand rabbit using the the combination of tiletamine-zolazepam and ketamine-midazolam with or without xylazine]

In this study, anesthesia levels obtained with tiletamine-zolazepam (TZ) and ketamine-midazolam (KM) with or without xylazine (X) were compared in rabbits. Reflexes (corneal, palpebral and withdrawal), blood parameters (PaO2, PaCO2, pH and ions HCO3-), cardiovascular function (heart rate and mean arterial blood pressure) and body temperature were evaluated before and after the injections of the anesthetic combination in the same rabbits (n = 10). With KM and TZ, no suppression of reflexes occurred. The body temperature and pH decreased and HCO3- increased similarly to KMX et TZX. Some physiological and blood parameters were less (PAM, PaCO2) and not (PaO2) affected comparatively to KMX et TZX. These protocols were of short duration of action and did not offer any anesthesia or analgesia. Therefore, their utilization should be restricted to short procedures where no painful manipulations are performed. Ketamine-midazolam-xylazine and tiletamine-zolazepam-xylazine on the other hand are indicated for interventions that require anesthesia. With these combinations, all reflexes were absent for 30-45 and 60-90 min following injections of KMX et TZX, respectively. However, these combinations induce cardiac depression, as well as a decrease of all measured blood parameters and body temperature and a reduction of PaO2. Supplementation with oxygen is recommended with the introduction of xylazine in the protocol.

Increases in intracavernous penile pressure following injections of excitatory amino acid receptor agonists in the hypothalamic paraventricular nucleus of anesthetized rats

PURPOSE

We examined whether N-methyl-D-aspartate (NMDA), amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) or trans-1-amino-1,3-cyclo-pentadicarboxylic acid (ACPD) increase intracavernous pressures when injected in the paraventricular nucleus of the hypothalamus.

MATERIALS AND METHODS

Sprague-Dawley rats weighing 250 to 300 gm. were anesthetized with pentobarbital and placed in a stereotaxic apparatus after catheterization of the carotid artery and insertion of a 25 gauge needle in the corpus cavernosum. Both catheters were coupled to pressure transducer systems. Electrical stimulations with glass tungsten microelectrodes and chemical injections with a 0.5 microl. syringe were done in the paraventricular nucleus. At the end of each experiment rats were perfused with saline and 10% formalin solutions. Brains slices 16 microm. thick were mounted and stained with cresyl violet to identify chemical and electrical stimulation sites.

RESULTS

Electrical stimulations of the paraventricular nucleus increased intracavernous pressure from 15.5 +/- 5.7 to 50.02 +/- 20.4 cm. H2O in 10 rats (p <0.001) and decreased central pressure in 10 (p <0. 001). Intracavernous pressure increased from 17.2 +/- 5.26 to 60.6 +/- 14.36 cm. H2O with NMDA, 26.0 +/- 8.9 to 49.6 +/- 12.2 cm. H2O with AMPA and 18.0 +/- 2.3 to 41.0 +/- 22.68 cm. H2O with ACPD when injected in the paraventricular nucleus of 5 rats (analysis of variance 12.18, df 3, p <0.007). Mean delays and durations varied between 3.6 to 4.0 and 5.6 to 7.0, respectively, and were similar for all agonists (analysis of variance not significant).

CONCLUSIONS

Glutamate receptor subtypes NMDA, ACPD and AMPA cause an increase in intracavernous pressure when injected in the paraventricular nucleus. Therefore, increases in intracavernous pressure following injection of glutamate must be initiated by the synergistic or additive effects of all of these receptor subtypes.

Hydroxyl radical production in the cortex and striatum in a rat model of focal cerebral ischemia

BACKGROUND

Increases in hydroxyl radical production have been used as evidence of oxidative stress in cerebral ischemia/ reperfusion. Ischemia can also induce increased dopamine release from the striatum that may contribute to hydroxyl radical formation. We have compared hydroxyl radical production in the cortex and striatum as an index of oxidative stress in a rat model of focal cerebral ischemia with cortical infarction.

METHODS

Using a three vessel occlusion model of focal cerebral ischemia combined with bilateral microdialysis, hydroxylation of 4-hydroxybenzoate (4HB) was continuously monitored in both hemispheres in either the lateral striatum or frontoparietal cortex. The ischemia protocol consisted of one hour equilibration, 30 min of three vessel occlusion, then release of the contralateral common carotid artery (CCA) for 2.5 h.

RESULTS

Induction of ischemia resulted in a 30-fold increase in dopamine release in the lateral striatum. Compared to the nonischemic striatum, the ratio of the hydroxylation product 3,4-dihydroxybenzoate (34DHB) to 4HB (trapping agent) in the ipsilateral striatum increased significantly 30 min after ischemia induction. In contrast, during the 30 min of three vessel occlusion there was no increase in the ratio in the cortex. Following the release of the contralateral CCA, the ratio from the ischemic cortex increased significantly compared to sham-operated animals. However, under all circumstances, the 34DHB/4HB ratio was greater in the striatum than in the cortex.

CONCLUSION

The increase in the 34DHB/4HB ratio in the lateral striatum coincides with the increased dopamine release suggesting a role for dopamine oxidation in the increased production of hydroxyl radicals. The significant increase in the ratio from the ischemic cortex compared to that from the sham-operated animals is consistent with increased oxidative stress induced by ischemia. However, the lower 34DHB/4HB ratio in the cortex which does not receive dopaminergic innervation compared to the striatum suggests a different mechanism for hydroxyl radical production. Such an alternate mechanism may represent a more toxic oxidative insult that contributes to infarction.

Increases in clitoral and vaginal blood flow following clitoral and pelvic plexus nerve stimulations in the female rat

The objective of this present study is to establish a model in the rat for the study of female clitoral and vaginal vascular changes during sexual excitation. A laser Doppler was used to measure blood flow changes following clitoral and pelvic plexus nerve stimulations. Results show an increase in clitoral blood flow following clitoral nerve (df1 = 12, df2 = 108, F = 21.4, P < 0.001) and pelvic plexus nerve stimulations (n = 3). A vaginal blood flow increase is also observed following pelvic plexus nerve stimulations (df1 = 12, df2 = 108, F = 4.75, P < 0.001). The female rat can therefore be used as a model for the study of the physiology, pharmacology and sexual dysfunction relating to blood flow in clitoral and vaginal tissue.

A pathophysiological study of abdominal organs following intraperitoneal injections of chloral hydrate in rats: comparison between two anaesthesia protocols

Chloral hydrate (CH) is used as an anaesthetic agent in laboratory rats. Side effects occurring with high concentrations have mainly occurred in abdominal organs. The objective of the present study was to minimize these side effects following intraperitoneal administration of CH using lower concentrations. Animals were evaluated using different procedures including a general necropsy, intraperitoneal white cell counts, histology and duodenal peristalsis and acetylcholine-induced contractions. Results clearly show that lower concentrations of CH while keeping the same anaesthetic dose (400 mg/kg) will minimize the irritancy of CH on abdominal organs while providing the same level of anaesthesia.

Self-mutilation in rabbits following intramuscular ketamine-xylazine-acepromazine injections

Following hind leg intramuscular injections of ketamine, xylazine, and acepromazine, 4 of 6 rabbits exhibited self-mutilation of the digits. At necropsy, the affected sciatic nerve appeared enlarged. Lymphohistiocytic perineural inflammation and fibrosis were observed, together with nerve degeneration. Neuronal regeneration as the reason for self-mutilation is discussed.

Anatomical and histological observations of fore- and hind limb toes in adult mice after amputations performed at the age of two weeks

Amputation of fore- and hind limb toes in order to numerically identify mice, although an effective and conditionally accepted method, is an ethical issue because of the pain involved and because of the detrimental long term side effects that may be encountered. In transgenic mice sacrificed between the ages of 1 and 1-1/2 y, and in which toe amputations were performed at the age of 2 wk, we observed anatomical (n = 60) and histological (n = 10) changes in bones and soft tissues. In stumps, meduallary cavities of sectioned phalanges became sealed and, therefore, some regrowth must have occurred distal to the amputation plane. However, an important increase in width is seen in the diaphysis of transected bones (P < 0.001) when compared to normal phalanges. Normal epidermis-dermis reorganisation occurred in the stumps. Therefore, when considering solely detrimental long-term side effects related to bone growth and tissue reorganization, toe amputations to numerically identify mice seems an acceptable procedure.

Monosynaptic GABA-mediated inhibitory postsynaptic potentials in CA1 pyramidal cells of hyperexcitable hippocampal slices from kainic acid-treated rats

To examine the mechanisms underlying chronic epileptiform activity, field potentials were first recorded to identify hyperexcitable hippocampal slices from kainic acid-treated rats. Intracellular recordings were then obtained from CA1 pyramidal cells in the hyperexcitable areas. Twenty-two of the 47 cells responded to electrical stimulation of the stratum radiatum with a burst of two or more action potentials and reduced early inhibitory postsynaptic potentials, and were considered hyperexcitable. The remaining 25 cells were not hyperexcitable, displaying a single action potential and biphasic inhibitory postsynaptic potentials after stimulation, like control cells (n = 20). A long duration, voltage-sensitive component was associated with subthreshold excitatory postsynaptic potentials in the majority of hyperexcitable (12/15) and non-hyperexcitable (3/5) cells examined from kainic acid-treated animals, but not from cells (1/10) of control animals. Stimulation of stratum radiatum during pharmacological blockade of ionotropic excitatory amino acid synaptic transmission elicited biphasic monosynaptic inhibitory postsynaptic potentials in all hyperexcitable (n = 9) and non-hyperexcitable (n = 9) cells tested from kainate-treated animals, as well as in control cells (n = 8). The mean amplitude, latency to peak, equilibrium potential, and conductance changes of early and late monosynaptic inhibitory postsynaptic potentials were not different between cells of kainic acid-treated and control animals. In seven hyperexcitable cells tested, the early component of monosynaptic inhibitory postsynaptic potentials was significantly reduced by the GABAA receptor antagonist bicuculline (100-200 microM). The late component was significantly decreased by the GABAB receptor antagonist 2-hydroxysaclofen (1-2 mM; n = 3). Comparable effects were observed on early and late monosynaptic inhibitory postsynaptic potentials in non-hyperexcitable cells (n = 4) from kainic acid-treated animals and control cells (n = 5). These results suggest that GABAergic synapses on hyperexcitable hippocampal pyramidal cells of kainate-treated rats are intact and functional. Therefore, epileptiform activity in the kainate-lesioned hippocampus may not arise from a disconnection of GABAergic synapses made by inhibitory interneurons on pyramidal cells. The hyperexcitability may be due to underactivation of inhibitory interneurons and/or reorganization of excitatory inputs to pyramidal cells since, in kainate-treated animals, pyramidal cells appear to express additional excitatory mechanisms.

[Pathologic study of Morton's neuroma]

The clinical syndrome of Morton's neuroma [correction of nephroma] was described over a century ago, but its etiopathology remains unknown. Recent studies suggest that it may be induced by compression neuropathy. Histologic changes in digital nerves resected for therapeutic purposes were compared with histologic findings of digital nerves sampled at autopsy of asymptomatic subjects. Results show that approximately one-third of resected "diseased" digital nerves were histologically normal. The authors question the therapeutic approach, which consists of resecting the nerves.