Naloxone reverses retrograde amnesia induced by electroconvulsive shock

Augmentation strategies in electroconvulsive therapy

Electroconvulsive therapy (ECT) is a highly effective treatment, but strategies to enhance therapeutic outcomes are occasionally needed. This review examines the evidence for approaches used for enhancing seizure production: hyperventilation, pretreatment with xanthines, and use of remifentanil or ketamine in ECT anesthesia. Hyperventilation may be a useful strategy to enhance seizure production, but its effects on ECT outcomes have not been systematically studied and require further research. Pretreatment with caffeine, theophylline or aminophylline (xanthines) prolongs the duration of ECT seizures but has not been clearly shown in controlled trials to increase efficacy. Caution is also warranted because their use may be associated with significant adverse effects. There are case reports of the usefulness of remifentanil in assisting seizure induction by reducing the dose of barbiturate anesthetic required, but there are no controlled data on whether it independently enhances efficacy outcomes. Preliminary evidence suggests that ketamine and ECT may have synergistic antidepressant effects, although this needs to be further examined in randomized controlled trials.

Pharmacological attenuation of electroconvulsive therapy--induced cognitive deficits: theoretical background and clinical findings

Electroconvulsive therapy (ECT) is an effective treatment for depression and other psychiatric disorders. However, the practice of ECT is limited by memory and nonmemory cognitive adverse effects. Technical strategies such as a preference for unilateralover bilateral ECT and low-dose over high-dose stimulation reduce these cognitive adverse effects but may also be associated with lesser treatment efficacy or slower treatment response. This article therefore reviews the use of psychopharmacological agents in the attenuation of ECT-induced cognitive deficits with 2 objectives: the identification of implicated mechanisms and the identification of putative efficacy in both animal and human studies. Drugs examined include N-methyl-d-aspartate receptor antagonists, cyclooxygenase inhibitors, calcium channel blockers, cholinesterase inhibitors, glucocorticoid receptor antagonists, thyroid hormones, opioid antagonists, NO donors, nootropic agents, and other medications. Although the clinical data at present are sparse and inconsistent, many recently opened lines of research improve our understanding of the mechanisms involved as well as suggest possible avenues for the testing of new treatments with the potential to attenuate the cognitive adverse effects of ECT.

Temporally graded, context-specific retrograde amnesia and its alleviation by context preexposure: effects of postconditioning exposures to morphine in the rat

Five experiments studied retrograde impairments in Pavlovian fear conditioning following prolonged exposure to the opioid receptor agonist morphine. Injections of morphine commencing 1-7 days but not 14 days after conditioning produced amnesia for that conditioning episode. This amnesia was (a) selective such that morphine impaired freezing to the conditioning context but not to the auditory conditioned stimulus, (b) independent of the interval between the last injection of morphine and test, and (c) accompanied by a failure of contextual discrimination. Context preexposure protected context conditioning and discrimination from the amnestic effects of morphine. These results show that retrograde deficits in contextual fear conditioning are mediated by failures to consolidate a contextual representation.

Opioid Receptors Regulate the Extinction of Pavlovian Fear Conditioning

Rats received a single pairing of an auditory conditioned stimulus (CS) with a footshock unconditioned stimulus (US). The fear (freezing) that had accrued to the CS was then extinguished. Injection of naloxone prior to this extinction significantly impaired the development of extinction. This impairment was mediated by opioid receptors in the brain and was not observed when naloxone was injected after extinction training. Finally, an injection of naloxone on test failed to reinstate extinguished responding that had already accrued to the CS. These experiments show that opioid receptors regulate the development, but not the expression, of fear extinction and are discussed with reference to the roles of opioid receptors in US processing, memory, and appetitive motivation.

Electroconvulsive shock blocks the opioid-mediated inhibition of dopamine release in rat striatal slices

The fractional release technique was applied to investigate the effects of single electroshock (ECS) on the opioid-mediated inhibition of dopamine release in rat striatal slices. Animals were submitted to ECS 24h before the experiments. The results demonstrate that pre-treatment with ECS suppresses the inhibition of dopamine release mediated by kappa opioid receptors. These data suggest that single ECS treatment modifies the sensitivity of the kappa opioid receptors located on the presynatic dopamine terminals in the rat striatum.

Retrieval effects of beta-endorphin and naloxone, and the novelty-induced antinociception in the developing rat

Three experiments were conducted to assess the retrieval effects of a single dose of beta-endorphin and of naloxone, and of the novelty-induced antinociception response in the developing rat. Wistar rats 30, 45, 60, and 90 days old from our breeding stock were used. Animals were trained and tested, with a 24-h interval between sessions, in a two-way active avoidance task (using 20 presentations of a 5-s, 1-kHz tone and a 0.4-mA footshock) or in a step-down inhibitory avoidance task (using a 60-Hz, 0.2-mA footshock). Saline (1.0 ml/kg), beta-endorphin (2.0 microgram/Kg), or naloxone (0.8 mg/kg), was administered ip immediately after training, and saline or beta-endorphin was administered 6 min before testing. The retrieval enhancing effects of post-training naloxone and pretest beta-endorphin, and the retrieval impairing effect of post-training beta-endorphin, were consistently observed only in 60- and 90-day-old rats, on both tasks. In a third experiment, another group of naive rats was placed for 2 min in a novel environment (the shuttlebox) and nociception was assessed by the tail-flick method. Novelty-induced antinociception was observed only for 60- and 90-day-old rats, and this response was cancelled by naloxone given 6 min before exposure to novelty. These results suggest that both the retrieval effects of naloxone and beta-endorphin, in the doses used, and the novelty-induced antinociception response, which are possibly dependent on the activity of hypothalamic beta-endorphin system, become established between 45 and 60 days postnatal in the rat.

Retrieval effects of both post- and presession beta-endorphin administration in a three-session paradigm

Rats were submitted to three sessions, with a 24-hr interval between, of step-down inhibitory avoidance task using a 60-Hz, 0.3-mA footshock, or of two-way active avoidance task using 25 presentations of a 5-sec. 1-kHz tone and a 0.4-mA footshock. Animals received intraperitoneal injections of either saline or beta-endorphin (2.0 microgram/kg) after the first session, and before the second or the third sessions, in a 2 x 2 x 2 design. beta-Endorphin given before the second or the third sessions improved retention for both tasks, but when administered after the first session, it impaired retention for the second session. The administration of beta-endorphin after the first session prevented the retrieval enhancement by the opioid given before the third session. Rats receiving beta-endorphin both after the first and before the second sessions, whilst showing no retrieval impairment on the second session, also did not show the pre-third session beta-endorphin retrieval enhancing effect. These data suggest that the post-first session exaggeration of the endogenous opioid state by beta-endorphin administered after the first session causes a long-lasting change in retrievability for the active and inhibitory avoidance tasks, as shown by the lack of the retrieval enhancing effect of beta-endorphin given before the third session.

Beta-endorphin enhancement of retrieval in a three-session paradigm

Rats were submitted to three consecutive sessions, one session per day, of step-down inhibitory avoidance task (60-Hz, 0.3-mA footshock) or of two-way active avoidance task (25 trials of a 5-s, 1-kHz tone and a 0.4-mA footshock). Animals received intraperitoneal (ip) injections of saline or beta-endorphin (2.0 micrograms/kg) before or after the second session and before the third session. beta-Endorphin given before either the second or the third session improved retention of both tasks, while its administration after the second session had no effect upon performance on both tasks. In Experiment 2, it was shown that rats receiving naloxone (0.2 mg/kg) ip after the first session did not exhibit the enhancement of retrieval by beta-endorphin administration before the second session, so a non-state-dependent improvement of retrieval by the opioid seems to be unlikely. In view of these results we can propose that the presession retrieval enhancing effect of beta-endorphin is due to an endogenous state dependency on the opioid that can be expressed either in the second or in the third session of aversive tasks.

Distinct mechanisms underlying memory modulation after the first and the second session of two avoidance tasks

Rats were subjected to three consecutive sessions, one session per day, of either a step-down inhibitory avoidance task using a 60-Hz. 0.3-mA footshock, or a two-way active avoidance task using 20 presentations of a 5-s, 1-kHz tone and a 0.3-mA footshock. After either the first or the second training session animals received an intraperitoneal injection of ACTH (0.2 microgram/kg), epinephrine-HCl (5.0 micrograms/kg), or naloxone-HCl (0.8 mg/kg). All these treatments caused memory facilitation on both tasks when administered after the first training session. When administered after the second training session only ACTH and adrenaline were effective, on both tasks. As previous physiological and pharmacological reports point to the activation of the brain beta-endorphin system after the first, but not the second, session of a task, we propose that (a) memory facilitation by naloxone depends on the previous activation of the brain beta-endorphin system; and (b) memory facilitation due to ACTH or epinephrine does not depend on the opioid activity, so their effects are expressed after both the first and the second training sessions. It was also observed that the enhancement of performance in the second training session due to post-training facilitatory treatments carried over to the test session. These results suggest that some form of consolidation occurs both after the first and after the second training session.

Different forms of post-training memory processing

Memories are not acquired in their definitive form, but can be considerably modified in the period that follows after acquisition, both quali- and quantitatively. This may happen either by a process of consolidation or strengthening of each memory trace or by the incorporation of further information to each experience. This further information may be provided by the action of drugs, including that of endogenous substances released by each training experience, and by the addition of information provided by other tasks or events. Evidence in favor of the existence of these various post-training processes, and of their importance for memory formation, is discussed. All of these processes are time dependent, all may depend on stimulus aftereffects, each is differently affected by drugs given in the post-training period, and all may interact with each other.

The impairment of retention induced by pentylenetetrazol in mice may be mediated by a release of opioid peptides in the brain

Pentylenetetrazol (PTZ, 45 mg/kg, ip) impaired retention of a one-trial step-through inhibitory avoidance task when injected into male Swiss mice 10 min after training, as indicated by retention performance 48 h later. The amnestic effect of PTZ was prevented by naltrexone (0.01 or 0.10 mg/kg, ip) administered after training, but prior to PTZ-treatment. On the contrary, neither naltrexone methyl bromide (0.01, 0.10, or 10.0 mg/kg, ip), a quaternarium analog of naltrexone, nor MR2266 (0.01 or 0.10 mg/kg, ip), a putative kappa opiate receptor antagonist, modified the behavioral effects of PTZ. On the other hand, the body seizures produced by PTZ were unaffected by any of the three opiate receptor antagonists that were given before the convulsant. Taken together, these results suggest that the effects of PTZ on retention are mediated, at least in part, by opioid peptides of central origin, and rules out a possible participation of opioid peptides derived from prodynorphin-precursor molecule. Administration of beta-endorphin (0.01 or 0.10 microgram/kg, ip) 10 min prior to testing attenuate the retrograde amnesia caused by PTZ. The effect of beta-endorphin was prevented by the simultaneous administration of naltrexone (0.10 mg/kg, ip) prior to testing. Naltrexone has no effect of its own upon retrieval. These results suggest that the impairment of retention induced by PTZ is probably due, at least in part, to a release of opioid peptides in the brain during the post-training period. PTZ given after training do not affect consolidation or memory storage, as mice thus treated may retrieve the learned information when they are submitted to an appropriate neurohumoral and/or hormonal state in the test session, that is, beta-endorphin injection. Therefore, the action of PTZ would be primarily at the level of the mechanism that make stored information available for late retrieval.

Pre-test administration of beta-endorphin, or of electroconvulsive shock reverses the memory disruptive effect of posttraining electroconvulsive shock

Memory disruption by posttraining electroconvulsive shock was studied in adult Wistar rats using three different tasks: step-down inhibitory avoidance, two-way active avoidance, and habituation of rearing to an open field. The animals were given training and test sessions 24 hours apart in each of these tasks. Immediate posttraining transcorneal, 15 mA, 60 Hz, 2 sec electroconvulsive shock disrupted memory of the three tasks. The effect was completely reversed by the IP administration of beta-endorphin (2.0 micrograms/kg), 6 min prior to testing, or of another electroconvulsive shock, 30 min prior to testing. These findings indicate that the posttraining electroconvulsive shock did not affect memory storage. In view of the fact that electroconvulsive shock has been previously shown to cause a pronounced decrease of brain beta-endorphin immunoreactivity, attributable to a release of the peptide, the present findings can be interpreted as showing that memory disruption by posttraining electroconvulsive shock results from the induction of state dependency on beta-endorphin.

Influence of electroconvulsive shock and naloxone on acquisition and retention of a spatial navigation task in rats

The effects of electroconvulsive shock (ECS) on learning and memory were examined in rats using the Morris navigation task. Rats were trained to escape from a large pool of water onto an invisible underwater platform. Application of ECS at various intervals before training (15 to 120 min) induced a significant time-dependent impairment of the acquisition of escape behavior; naloxone (1 mg/kg IP 15 min before ECS) did not prevent the ECS-induced impairment. One single active escape trial preceding ECS prevented ECS-interference with the subsequent acquisition of the task. Spatial navigation in well trained animals was significantly impaired 30 and 60 min after ECS. It is concluded that ECS disturbs the disturbs the formation of a spatial memory trace more than the retrieval of a previously formed spatial trace. Release of opioid peptides do not seem to contribute substantially to the amnesic effects of ECS in the spatial navigation task.

The antagonistic effects of naloxone on cycloheximide and anisomycin-induced amnesia

The amnesia induced by cycloheximide (CXM) injected SC and by CXM or anisomycin injected ICV immediately after the training test was antagonized in combination with an opiate antagonist, naloxone (NLX). This antagonism occurred on both the passive avoidance- and escape-learning responses in a dose-dependent manner in mice. NLX alone (0.3-10.0 mg/kg) did not alter the performances of these tasks. Furthermore, the decrease in retention performance on shuttle avoidance in rats induced by CXM was also antagonized by NLX. Treatment with CXM and/or NLX did not affect spontaneous locomotor activity. The interaction of these drugs on the performance of the passive avoidance- and escape-learning and the shuttle avoidance tasks may be related to neurochemical memory processes. These results suggest that an opioid system may participate in the amnesic actions induced by protein synthesis inhibitors in these models.

Differential effect of posttraining naloxone, beta-endorphin, leu-enkephalin and electroconvulsive shock administration upon memory of an open-field habituation and of a water-finding task

Rats were trained and tested in an open field for habituation of rearing responses, for a water-finding task, or for both tasks simultaneously. Training-test interval was 24 hr. The water-finding task consisted of locating a metal tube in one of the walls of the box, which was attached to a water bottle on the outside; animals were water deprived between training and testing. Retention was estimated by measuring the latency to lick from the tube on the test session. Rats learned this task either with or without water deprivation, also prior to training. Habituation learning (reduction of the number of rearings between the training and test session) occurred either simultaneously with the water-finding task or in animals trained without the water tube, so that they could not learn the water-finding task. As happens with many other tasks, training in the open field was followed by a large decrease of hypothalamic beta-endorphin immunoreactivity, attributable to a release of this substance. Posttraining IP naloxone (1.6 mg/kg) administration facilitated, and posttraining beta-endorphin (2.0 micrograms/kg), leu-enkephalin (5.0 micrograms/kg), or electroconvulsive shock (15 mA, 60 Hz, 2 sec) depressed the retention of habituation; this occurred regardless of whether the animals were trained and/or tested with or without water deprivation, and whether the task was acquired alone or simultaneously with the water-finding task. By contrast, none of these treatments had any effect on retention of the water finding task, acquired either with or without prior water deprivation. Thus, habituation was, and water-finding was not, sensitive to posttraining treatments known to affect endogenous opioids: the opioids themselves, their antagonist, naloxone, and electroconvulsive shock which releases brain opioids and causes naloxone-reversible retrograde amnesia. Learning of the water-finding task was merely incidental to exploration of the open field; it took place even when the animals were trained without the water tube. This suggests that the posttraining treatments that affect endogenous opioid function affect memory only of the task(s) that actually cause the release of brain beta-endorphin (in this case, probably habituation), and not of others that may occur simultaneously but are merely incidental (water-finding). A feature apparently common to the former is that they must directly involve either the recognition of novelty, or the initiation of an interaction with a new environment, or perhaps the habituation of such interaction.

Effect of naltrexone on senile dementia of the Alzheimer type

Some reports have suggested that naloxone, a short-acting opiate receptor blocker given intravenously, has a beneficial effect on the symptoms of senile dementia of the Alzheimer type. We have performed a double-blind, crossover trial of naltrexone, an orally active, long acting opiate antagonist, in 17 Alzheimer-type dementia patients. None showed any improvement in assessments of day-to-day living skills or on a battery of neuropsychological tests. No side effects were noted. In the dosage used, naltrexone appears not to be useful in Alzheimer-type dementia.

Repeated electroconvulsive shock downregulates the opioid receptors in rat brain

Ten consecutive daily electroconvulsive shocks (ECSs), which produce maximal tonic and clonic convulsions, caused reductions of mu- and delta-opioid receptor binding in the hypothalamus, hippocampus and caudate nucleus, but not in the frontal cortex and brainstem. These changes of opioid receptor binding were not observed in rats receiving a single ECS. Scatchard analysis revealed that ECS-induced reduction of mu- and delta-receptor binding was due to a decrease in the binding sites but not to a change in the binding affinity. Time course studies showed that 7 days after the end of 10 consecutive daily ECSs, both mu- and delta-receptor binding remained lower than those of sham controls. However, the effects of ECS on the opioid receptor binding disappeared in 2-3 weeks. These observations are consistent with the hypothesis that ECS treatments increase the release of opioid peptides in certain brain regions which in turn down-regulate the opioid receptors.

Delayed onset of the amnestic effect of posttraining beta-endorphin: effects of propranolol administered prior to retention testing

Mice were trained in a 1-trial inhibitory avoidance task (0.7 mA FS) and tested for retention at 1, 3, or 6 h following training. Posttraining beta-endorphin (0.1 micrograms/mouse i.p.) administration impaired retention at 6 h, but not 1 or 3 h after training. Propranolol (0.3 mg/mouse i.p.), but not naloxone (0.1 mg/mouse i.p.) administered prior to retention testing at 1 or 3 h accelerated the onset of amnesia in mice given posttraining beta-endorphin. Neither propranolol nor naloxone affected retention when given alone. These findings suggest that the delayed onset of the amnesia produced by posttraining beta-endorphin is due to the activation of a beta-adrenergic system.

Unlike beta-endorphin, dynorphin 1-13 does not cause retrograde amnesia for shuttle avoidance or inhibitory avoidance learning in rats

Posttraining administration of the opioid peptides, beta-endorphin or the enkephalins, is known to cause retrograde amnesia for a variety of tasks in rats. The present paper studies the effect of the posttraining administration of dynorphin 1-13 on retention of a step-down inhibitory avoidance task and of a shuttle avoidance task. For the purpose of comparison, the effect of human beta-endorphin was also studied. In confirmation of previous results, beta-endorphin (1.0 or 10.0 micrograms/kg, IP) caused retrograde amnesia for the two tasks. Dynorphin 1-13 had no effect at doses between 0.008-125.0 micrograms/kg IP or 1.25-125.0 ng/rat ICV in the inhibitory avoidance task, or at doses of 5.0, 25.0, or 125.0 micrograms/kg in the shuttle avoidance paradigm. These findings suggest that, in contrast to beta-endorphin, dynorphin 1-13 may not be involved in memory regulation at the posttraining period in rats.

Electroconvulsive shock increases preproenkephalin messenger RNA abundance in rat hypothalamus

Daily administration of electroconvulsive shock (ECS) to rats for 10 days increased the content of [Met5]enkephalin in the hypothalamus and the striatum by 64% and 45%, respectively. The effect of ECS on the relative abundance of mRNA coding for the enkephalin precursor preproenkephalin was investigated. Analysis by cell-free translation of polyadenylylated RNA and immunoprecipitation of preproenkephalin revealed ECS-elicited increases of 79% and 14% in preproenkephalin mRNA activity in the hypothalamus and striatum, respectively. ECS treatment did not affect the general translational activity of total polyadenylylated RNA from these brain regions. A 32P-labeled probe prepared from a rat preproenkephalin cDNA clone hybridized with an apparently single species of polyadenylylated RNA of approximately equal to 1450 nucleotides from both hypothalamus and striatum. Dot-blot hybridization of polyadenylylated RNA with the rat probe indicated that ECS elicits a 76% increase in the preproenkephalin mRNA abundance in the hypothalamus and no significant change in the striatum. These results suggest that ECS treatment leads to enhanced biosynthesis of the enkephalin precursor in hypothalamic neurons.

Posterior hypothalamic deafferentation abolishes the amnestic effect of electroconvulsive shock in rats

The amnestic effect of immediate post-training transcorneal electroconvulsive shock ECS (15.0 mA, 60 Hz, 2 sec) on step-down inhibitory avoidance learning (0.5 mA, 60 Hz training footshock) was studied in intact rats and in rats submitted to bilateral surgical transection of the dorsal fornix, to anterior or posterior hypothalamic deafferentation, and in sham-operated animals. Animals were tested for retention 24 hr after training. The amnestic effect of ECS was observed in all groups except in the one with the posterior hypothalamic lesion. Fornix-lesioned animals showed a moderate retention deficit which was considerably worsened by the ECS treatment. The results indicate that the amnestic effect of ECS requires integrity of posterior hypothalamic pathways. One possibility is that the amnestic effect of ECS may be mediated by posterior afferent fibers to the hypothalamus acting on hypothalamic opioid systems such as have been previously proposed to play a role in ECS-induced amnesia.

Naloxone attenuates amnesia caused by amygdaloid stimulation: the involvement of a central opioid system

This study investigated the effect of naloxone on amnesia produced by subseizure amygdaloid stimulation. Animals were trained in an inhibitory avoidance task, and given amygdaloid stimulation following training. Immediately after training, prior to stimulation, naloxone was injected either peripherally (i.p.) or into the bed nucleus of the stria terminalis (BNST) where the Met-enkephalin-containing fibers from the amygdala terminate. Amygdaloid stimulation caused retention deficits. The deficits were attenuated by 3.0 mg/kg naloxone given peripherally or by 1.0 microgram or 0.3 microgram naloxone injected bilaterally into the BNST. The attenuative effect was anatomically and receptor specific: 0.3 microgram of naloxone injected into the caudate nucleus was ineffective; the attenuative effect of naloxone was antagonized by simultaneous injection of 1.5 or 4.5 micrograms levorphanol into the BNST. These results suggest that endogenous opioids, possibly the enkephalins of the stria terminalis released into the BNST following amygdaloid stimulation, are at least partially involved in mediating the effect of amygdaloid stimulation on memory.