W.D. Winters

The anticonvulsant properties of melatonin on kindled seizures in rats.

Abstract The literature suggesting that the pineal gland and the indolamine, melatonin, have a significant role in regulating and modulating brain electrical activity is reviewed. The anticonvulsant properties of melatonin were investigated by testing acute doses of melatonin against two types of kindled Scizures in the rat. Against the electrically kindled amygdaloid Scizure, melatonin significantly reduced afterdischarge length at a non-sedative dose, but failed to modify Scizure rank scores. With larger doses of melatonin, which were associated with some sedation and ataxia, the Scizure rank score was reduced, but there was no additional reduction of afterdischarge length. Naloxone treatment (20 mg/kg, i.p.) did not reverse the sedation, ataxia, nor the anticonvulsant effects seen with the large dose of melatonin (200 mg/kg, i.p.). Additional animals were kindled with pentylenetetrazol injections (30 mg/kg, i.p.) given at 2–3 day intervals. Melatonin significantly reduced Scizure rank scores in these kindled animals at one dose (150 mg/kg, i.p.). A larger dose, associated with sedation and ataxia, did not result in any further reduction of Scizure rank scores. For comparison, large and small doses of both phenobarbital and diazepam were also tested against the pentylenetetrazol kindled Scizures. Neither phenobarbital (30 mg/kg) nor diazepam (2.5 mg/kg) induced a neurological deficit; however, both agents reduced Scizure rank to approximately the same score as did melatonin (150 mg/kg). This is the first report of a substantial anticonvulsant property of parenteral melatonin in two animal models of epilepsy. It would appear tha melatonin is most effective against the kindled pentylenetetrazol Scizure, and somewhat less effective against the electrically kindled amygdaloid Scizure. Further testing in other Scizure models and species is needed to define better the anticonvulsant profile of melatonin.

A modified rotating frame experiment based on a fourier series window function. Application to in vivo spatially localized NMR spectroscopy

A fourier series window approach to the rotating frame experiment is employed in conjunction with surface coils to accomplish one-dimensional spatial localization of phosphorus-containing metabolites in phantoms and the in vivo rat brain. The rotating frame experiment delineates sample regions on the basis of a B1 field gradient across the sample which for the experiments described in this paper are provided by a surface coil. In the usual rotating frame experiment, a suite of spectra (termed a metabolite map) is obtained by incrementing the evolution pulse duration with the spectra displayed as a function of the nutational frequency about the B1 field. The total time of the experiment depends on the desired degree of spatial resolution, and substantial time savings can be obtained when the desired result is spectral information from a single or a few selected regions (slices). The approach taken here is to utilize a Fourier series window function representation of the nutational frequencies over the region of interest. This procedure allows convenient selection of the localized region, thus avoiding Fourier transformation in the second (mapping) dimension. For the case of a single region of interest, the spectral parameters can be adjusted to maximize the number of data files in which the evolution pulse nutates the magnetizations at the center of the slice through a multiple of 180°. Data files not contributing significant signal to a selected slice can be omitted to further minimize the experimental accumulation time.

Ketamine-induced changes in kindled amygdaloid seizures

Abstract The effects of ketamine on seizures kindled by repetitive electrical stimulation of the amygdala were determined in the rat. The response of fully developed kindled amygdaloid seizures (KAS) to 20, 40, 80 and 120 mg/kg (i.p.) ketamine, administered from 5 to 60 min prior to elicitation of seizures was examined. Ketamine reduced the afterdischarge duration (AD) and behavioral response (BR) in a dose-dependent fashion. However, the effect of ketamine on the afterdischarge duration and behavioral response was not clearly time-dependent for each dose (20–120 mg/kg). A dose-dependent increase in the seizure spiking frequencies in the amygdala and cortex during kindled amygdaloid seizures was also induced by ketamine. Blood plasma and brain levels of ketamine and its metabolites were determined 15 min after 20, 40, 80 and 120 mg/kg ketamine as well as 60 min after 80 mg/kg ketamine. Brain and plasma levels of ketamine and nor-ketamine were similar to those previously reported. Low plasma levels of dehydro-nor-ketamine were seen only at 60 min after 80 mg/kg ketamine. The decrease in afterdischarge duration and behavioral response and the increase in afterdischarge duration spiking frequency seen at 15 min correlated with elevated levels of ketamine and nor-ketamine in brain and plasma. However, by 60 min plasma levels of ketamine remained high, yet the brain levels of both ketamine and nor-ketamine had decreased. This is despite the fact that afterdishcarge duration and behavioral response were still attenuated and afterdischarge duration spiking frequency was still increased. Thus, the exact contribution by ketamine and nor-ketamine to the alteration of afterdischarge duration, behavioral response and afterdischarge spiking frequency cannot be made at this time. It was apparent that inhibition of the afterdischarge duration and behavioral response along with an increase in spiking frequency was not dependent on dehydro-nor-ketamine. The possibility that an unidentified metabolite may contribute to the modification of kindled amygdaloid seizures by ketamine is discussed.

The effects of various anesthetics on amygdaloid kindled seizures

Abstract The effects of various doses of cataleptic anesthetics, gamma-butyrolactone (GBL), phencyclidine (PCP), and ketamine (KET), and the depressant anesthetics, pentobarbital (PB) and chloral hydrate (CH), on amygdaloid kindled seizures were tested in the rat. The seizure activity was monitored by behavioral observation and EEG recording. Anesthetic doses of the cataleptic anesthetics with the exception of KET had minimal effects on the afterdischarge duration (AD) and behavioral ranking (BR) of the elicited seizures. On the other hand, they were more inhibitory to the AD and BR than was the convulsant pentylenetetrazol (PTZ). The only cataleptic that induced spontaneous seizure activity at anesthetic doses was PCP, although KET induced epileptoid activity at supranesthetic doses. Ketamine, PB, and CH completely inhibited elicited seizure activity at anesthetic doses. In addition, rats were kindled by repetitive electrical stimulation during GBL-induced anesthesia or catalepsy. Although both these GBL groups averaged more stimulations to reach generalized seizures than the saline controls, GBL did not block the kindling process.

Seasonal and sex influences on ketamine-induced analgesia and catalepsy in the rat; a possible role for melatonin

Data from this laboratory on ketamine-induced analgesia and catalepsy in rats revealed that factors other than dose modified the difference in the latency of the tail flick response (TFLD), a measure of analgesia, and the duration of the loss of the righting reflex (DLRR), a measure of catalepsy. Untreated female rats showed a longer latency than males in their response to a noxious stimulus at midnight, but not at noon. Females also showed a longer loss of righting reflex response to ketamine than did males, whether at noon or midnight; the loss of righting reflex at night was augmented in both. Although females showed analgesia with administration of ketamine at doses smaller than those which induced catatonia, males showed no analgesia without catatonia and comparable loss of the righting reflex occurred at doses much larger than for females. There was a 3-fold increase in the latency of the tail flick response and loss of righting reflex during the winter, as compared with summer, for females treated with ketamine; males showed a similar variation in the loss of righting reflex. Since analgesia is produced by both melatonin and ketamine, and since ketamine appears to share opiate receptors with an endogenous ligand, beta-endorphin, a role was sought for the pineal and melatonin in the variation of responsiveness to ketamine. Pinealectomized rats failed to show augmentation of the loss of righting reflex induced by ketamine at night and mice showed a seasonal variation in the analgesia induced by melatonin.(ABSTRACT TRUNCATED AT 250 WORDS)

Catalepsy induced by combinations of ketamine and morphine: potentiation, antagonism, tolerance and cross-tolerance in the rat

Previous studies demonstrated that both ketamine and morphine induced analgesia and catalepsy in the rat. Pre-treatment with ketamine produced cross-tolerance to morphine, whereas pretreatment with morphine did not induce cross-tolerance to ketamine but rather augmented the cataleptic response; this augmentation was attributed to residual morphine in the brain. The present studies explored the duration of the loss of righting reflex induced by sub-effective doses of ketamine and morphine, administered simultaneously. There was mutual potentiation between sub-effective doses of ketamine and morphine, but sub-effective doses of ketamine partly antagonized fully-effective doses of morphine. Latency to the loss of righting reflex, rigidity and behavior on recovery, reflected the relative predominance of ketamine or morphine in each combination. Naloxone inhibited the induced cataleptic effects. The degree and time course of development of tolerance to daily administration of sub-effective dose combinations of ketamine and morphine were similar. Rats, tolerant to ketamine-dominant combinations, were cross-tolerant to both drugs, while those tolerant to morphine-dominant combinations were cross-tolerant to morphine but showed either no cross-tolerance or an augmented response to ketamine. While the mutual potentiation, antagonism and tolerance suggest common mechanisms for the induced catalepsy, differences in latency, rigidity and behavior, asymmetry of cross-tolerance and a widely-different ID50 for naloxone would argue against an action at a single opioid site.

Comparison of isomers of ketamine on catalepsy in the rat and electrical activity of the brain and behavior in the cat

The present study compared the relative potency and efficacy of the two isomers of ketamine on the duration of catalepsy (loss of righting reflex) in female rats and on the behavior and electroencephalogram of cats. In the rat, at small doses, the S(+) isomer was more potent than the R(-) isomer or racemic ketamine, while at larger doses, the S(+) isomer and the racemate were equipotent and the R(-) isomer was significantly less potent. Tolerance developed rapidly to the effects of either isomer and both were equally cross-tolerant to racemic ketamine. Sub-effective doses of morphine significantly increased the potency of S(+), R(-) and racemic ketamine on the duration of catalepsy. Sub-effective doses of either isomer augmented the duration of catalepsy, induced by small doses of morphine, but reduced that of large doses. In cats, there was a parallel time course and progression of behavioral and electroencephalographic states in response to equal total doses of either racemic ketamine, an artificial 50:50 mixture of S(+) and R(-) isomers, or the S(+) isomer alone; approximately equivalent effects required twice the dose of the R(-) isomer. It is concluded that there is a common site of action for the two isomers, but there is also a stereospecific difference in potency, as regards the induction of catalepsy in the rat and behavioral and electroencephalographic effects in the cat. Stereospecificity was not apparent in the development of tolerance, cross-tolerance or the augmentation of the response to morphine.

Cortical Kindled Seizures: Modification by Excitant and Depressant Drugs

Summary: The effects of several excitant‐convulsants, cataleptic anesthetics, and γ‐acetylenic γ ‐aminobutyric acid (GABA) were tested on seizures kindled by repetitive electrical stimulation of the motor cortex in the rat. A dose response was determined for each drug. For most of the drugs, the doses tested ranged from those causing some signs of behavioral excitation to those inducing epileptoid activity. None of the excitant‐convulsants, including strychnine, physostigmine, amphetamine, bicuculline, or pentylenetetrazol, increased the afterdischarge duration (AD) or behavioral response (BR) of the partially developed (PD‐KCS) or generalized fully developed (KCS) kindled cortical seizures. Whereas pentylenetetrazol had no effect on the PD‐KCS, it has been previously shown to increase significantly the AD and BR of the developing or partially developed amygdaloid kindled seizures. Lidocaine, 7‐butyrolactone, 7‐acetylenic GABA, phencyclidine, and ketamine inhibited the AD of the KCS by ≫ 80%. Lidocaine, phencyclidine, and ketamine decreased whereas γ ‐butyrolactone and γ ‐acetylenic GABA increased the AD of the PD‐KCS. The ability of γ ‐butyrolactone and γ ‐acetylenic GABA to potentiate the PD‐KCS while inhibiting the KCS presents a paradox not readily explained. Our results combined with previous reports of the effects of γ ‐butyrolactone and γ ‐acetylenic GABA on amygdaloid kindled seizures indicate that the KCS is more susceptible to GABAnergic and cataleptic inhibition than is the fully developed amygdaloid kindled seizures. The differences between the response of cortical kindled and that of amygdaloid kindled seizures to some of the drugs tested may indicate differences in the physiological and biochemical mechanisms involved in producing these seizures.

Synthetic opioids compared with morphine and ketamine: Catalepsy, cross-tolerance and interactions in the rat

Previously it has been shown in rats that both ketamine and morphine induced analgesia and, at larger doses, catalepsy and loss of the righting reflex, all of which were reversed by naloxone at widely different doses. Tolerance developed rapidly to either ketamine or morphine and there was cross-tolerance from ketamine to morphine. However, morphine potentiated the cataleptic effect of ketamine, whether fully-effective doses of morphine were given before ketamine or subeffective doses of both were given concurrently. The present study extends these observations to three specific mu-receptor agonists (sufentanil, fentanyl and alfentanil) and two mu- and kappa-agonist, mu-antagonist opioids (nalbuphine and butorphanol). All five of these opioids potentiated the cataleptic effect of ketamine. Each of the three specific mu agonists showed rapid development of tolerance. Fentanyl and alfentanil showed mutual cross-tolerance with ketamine, but sufentanil did not. This lack of sufentanil-ketamine cross-tolerance may reflect separation of the sites of agonist action and the sites of development of tolerance for the opioids and for ketamine. The potentiating effects of nalbuphine and butorphanol suggest that they potentiate ketamine-induced catalepsy, either by kappa-receptor interactions or by a mu agonist effect. It is suggested that the cataleptic effect of a combination of individually-subeffective doses of ketamine and morphine, rather than ketamine and one of the synthetic opioids, might be of more potential clinical usefulness.

Pentylenetetrazol augmentation of developing kindled amygdaloid seizures

Abstract The effects of daily administration of pentylenetetrazol (PTZ) on the rate of the development of kindled amygdaloid seizures (KAS) were tested in the rat. Rats were pretreated for 6 days with 25 mg/kg PTZ or normal saline 15 min. prior to each daily amygdaloid stimulation. The PTZ group exhibited fully developed KAS, including a maximal behavioral ranking (BR) and an afterdischarge duration (AD) of over 90 sec, in 3.8 ± 0.3 stimulations compared to 8.0 ± 0.6 stimulations (ave. ± SEM) for the saline controls. Within 10 min after dosing, PTZ consistently induced intermittent spiking of 5 sec or less in the EEG and behaviorally induced head nodding and sniffing. However, chemical kindling due to the 6 repetitive doses of PTZ was not observed. When the PTZ pretreatment was stopped on the 7th day, the BR and AD of the PTZ pretreatment group decreased from 187% and 161% of control values, respectively, to 118% and 100% of control. It appears that PTZ augments both the AD and BR of the developing KAS but does not accelerate the actual rate of the development of the KAS.