enkephalin--leucine-2-alanine and Seizures

The antinociception of opiates is mediated through the activation of opioid receptors in several mid brain and brain stem areas. This paper reports that the forebrain area termed area tempestas (AT), first identified as a convulsant trigger area, is also a component of the endogenous pain suppression system. Unilateral AT application of DAMGO, morphine and U-50,488H in rats at doses in the nanogram range produced marked and dose-dependent increases in the latency to respond to nociceptive stimuli. A lower effect is found after application of DPDPE and DADLE. Antinociception is more evident in the hot plate than in the tail flick test. In the former test, the effect was restricted to the paws contralateral to the hemisphere of injection. Unilateral AT application of naltrexone (4 ng) reduced in the contralateral paws the antinociceptive effect that the bilateral AT application of morphine (20 ng/hemisphere) had induced in both body sides. Unilateral application of naltrexone, (20 ng) ICI 154, 129 (20 ng) and Win 44,441-3 (8 ng) antagonized the antinociceptive effect elicited by the systemic injection of morphine (2.5 mg/kg s), DPDPE (20 mg/kg s) and U-50,488H (20 mg/kg s), respectively. In the hot plate test, the antagonism was found in the paws ipsilateral and contralateral to the hemisphere of injection of the antagonists.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Anticonvulsants; Azocines; Bicuculline; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine-2-Alanine; Enkephalins; Escape Reaction; Foot; Hot Temperature; Male; Morphine; Naltrexone; Narcotic Antagonists; Olfactory Pathways; Pain; Phenazocine; Pressure; Pyrrolidines; Rats; Rats, Sprague-Dawley; Reaction Time; Receptors, Opioid; Seizures; Tail

Opioid agonists were used to investigate the modulation of seizures in the seizure-susceptible El mouse. Morphine and D-Ala2-D-Leu5-enkephalin (DADLE) were injected subcutaneously or intracisternally as prototypic agonists for mu and delta opioid receptors. Systemic or intracisternal injection of both morphine and DADLE decreased the incidence of seizures and the seizure score in El mice in a dose-dependent manner. The anticonvulsant effects of morphine and DADLE were reversed by naloxone (2 mg/kg, s.c.). This implies that opioid agonists have anticonvulsant properties which are mediated by mu and delta opioid receptors. In conclusion, a deficit in endogenous opioid peptides, which act as anticonvulsants may play a significant role in the etiology or pathophysiology of seizures in the El mouse.

Topics: Animals; Anticonvulsants; Enkephalin, Leucine-2-Alanine; Mice; Mice, Mutant Strains; Morphine; Naloxone; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

The distribution density of opioid receptors in the brain of El mice (seizure-susceptible strain) was examined to determine the relation between seizures and the opioid system. Saturation curves and Scatchard plots of [3H]2-D-alanine-5-D-leucine enkephalin binding revealed that the opioid delta receptor density in adult El mice during interictal periods was significantly increased in the cerebral cortex, hippocampus, and septal area. It was further shown that the concentration of such receptors in 25-day-old El mice that had no seizures was also significantly increased in the hippocampus and septal area, with no changes in apparent affinities, as compared with in the corresponding regions in ddY mice (seizure-nonsusceptible strain; the mother strain of El). Such up-regulation of opioid receptors in the El mouse brain could result from deficits in endogenous opioid peptides, which could be associated with the pathogenesis of seizure diathesis in the El mouse.

Topics: Animals; Brain; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Kinetics; Mice; Receptors, Opioid; Seizures; Subcellular Fractions

The opioid receptor types involved in the mediation of enkephalin-induced electroencephalographic (EEG) seizures were studied in unanesthetized, freely moving rats. Four receptor-selective peptide ligands were evaluated for effectiveness in producing nonconvulsive EEG seizures after i.c.v. administration; these included the mu agonist, [D-Ala2-N-methyl-Phe4-Gly5-ol]enkephalin (DAGO), the mixed mu-delta agonist, [D-Ala2-D-Leu5]enkephalin (DADLE), and the selective delta agonists, [D-Pen2-D-Pen5]enkephalin and [D-Pen2-L-Pen5]enkephalin. Only DAGO and DADLE were found to produce EEG seizures, with DAGO being 9 times more potent than DADLE. DAGO produced a greater number of seizure episodes with a greater overall incidence compared with DADLE, reflecting its potent effect to elicit EEG seizure activity in these rats. Injections of [D-Pen2-D-Pen5]enkephalin or [D-Pen2-L-Pen5]enkephalin, even at the highest doses tested, failed to produce seizure activity. Behaviorally, the DAGO and DADLE EEG seizures were nonconvulsive but were temporally associated with episodic bursts of wet-dog shakes. The enkephalin-induced responses were extremely sensitive to antagonism by naloxone and completely blocked by pretreatment with the irreversible mu antagonist beta-funaltrexamine. The selective delta opioid receptor antagonist ICI 174,864 (N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH) was ineffective. The use of the most selective agonists and antagonists for mu and delta opioid receptors suggests that, in rats, enkephalin-induced EEG seizures are mediated exclusively by mu opioid receptors and not by delta opioid systems.

Topics: Animals; Electroencephalography; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Male; Naloxone; Naltrexone; Rats; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

Two groups of experiments were conducted to determine if morphine- and enkephalin-induced seizures are specifically mediated by the mu and delta receptor, respectively. In the first experiments, designed to assess the ontogeny of mu- or delta-seizures, rats from 6 h to 85 days of age received implanted cortical and depth electrodes as well as an indwelling cannula in the lateral ventricle. Various amounts of the mu-receptor agonists, morphine and morphiceptin, and the delta agonists, D-Ala2-D-Leu5-enkephalin (DADL) and Tyr-D-Ser-Gly-Phe-Leu-Thr (DSLET), were then administered intracerebroventricularly (icv) with continuous EEG monitoring. The second experiments entailed use of the nonspecific opiate antagonist, naloxone, as well as the specific delta antagonist, ICI 154,129, against seizures induced by icv-administered morphine, morphiceptin, DADL, or DSLET. Both morphine and morphiceptin produced electrical seizure activity in rats as young as 5 days after birth. The drugs produced similar seizure activity in terms of electrical morphology, observed behavior, ontogeny, threshold dose, and reversibility with small doses of naloxone. In the pharmacologic experiments, icv naloxone blocked all opiate-induced seizures. ICI 154,129 blocked DSLET seizure, had little effect on enkephalin or DADL seizures, and no effect on morphine or morphiceptin seizures. These data indicate that DSLET seizures are delta-specific but that all other opiate-induced seizures studied may involve multiple opiate receptor-mediated mechanisms.

Topics: Animals; Electroencephalography; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Morphine; Narcotics; Oligopeptides; Rats; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

Bilateral microinjections of DADL (D-Ala2-D-Leu5-enkephalin) and morphine were carried out in rats in a systematic fashion at histologically identified medial and lateral thalamic sites. DADL produced a dose-dependent (1.5-15.0 nmol), naloxone-reversible (1 mg/kg, i.p.) increase in the hot-plate (HP), tail-flick (TF) and catalepsy (CAT) response latencies with a predominance of activity occurring at lateral as opposed to medial thalamic sites. These effects were seen within 5 min of microinjection. At a significant number of sites, DADL precipitated convulsive seizure activity. Equimolar doses of morphine had a negligible effect on nociceptive indices and were not productive of seizures even at sites where DADL was found to be active. To further examine seizure activity, rats were prepared with bilateral frontal cortical electrodes and microinjected also at medial and lateral thalamic sites with equimolar doses of DADL and morphine (15 nmol). DADL was found to produce electrographically defined seizures unaccompanied by convulsive motor behavior (cataleptic seizures), as well as convulsive seizures. All animals in this group exhibiting analgesia and catalepsy had electrographic evidence of a seizure with markedly abnormal EEG tracings showing postictal spiking and changes in baseline frequency and amplitude. These seizures appeared to be naloxone-reversible. Morphine on the other hand was not productive of seizures, but did produce changes in electroencephalographic activity including spindle bursting, high-voltage slow-frequency activity as well as spiking. As noted, these changes were not associated with any effects on nociceptive measures.

Topics: Animals; Electroencephalography; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Male; Morphine; Pain; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Seizures; Sensory Thresholds; Thalamus

In rats the influence of the delta opioid agonists [Leu]enkephalin, [D-Ala2-D-Leu5]enkephalin, [D-Ala2]methionine enkephalinamide and synthetic analogue of [Met]enkephalin: Tyr-D-Ala-Gly-Phe-D-Leu-OMe on audiogenic seizures was tested during ethanol abstinence. All investigated drugs significantly inhibited this ethanol withdrawal symptom. The results are compatible with the hypothesis of opioid involvement in the ethanol abstinence syndrome.

Topics: Acoustic Stimulation; Animals; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalin, Methionine; Ethanol; Female; Naloxone; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Seizures; Substance Withdrawal Syndrome

Dose-response comparisons of the ability of the selective delta antagonist ICI 154,129 (12.5-50 nmol), the nonselective antagonist naloxone (29-290 nmol), and the irreversible selective mu antagonist beta-fNA (1.3-21 nmol) to alter the threshold response to DADLE or etorphine was studied in the rat flurothyl seizure test. DADLE (35 nmol, i.c.v.) and etorphine (122 nmol/kg, s.c.) both caused increases in seizure threshold which were differentially antagonized by pretreatment (i.c.v.) with the respective antagonists. For DADLE, only ICI 154,129 and naloxone produced a dose-related blockade of the increase in seizure threshold, with ICI 154,129 being more potent than naloxone. In contrast, the anticonvulsant action of etorphine was not antagonized by ICI 154,129 (50 nmol), but was blocked by a low dose of naloxone (29 nmol) or beta-fNA (21 nmol). In addition, prior occupancy of mu-sites with beta-fNA (21 nmol) significantly diminished the abilities of either ICI 154, 129 (50 nmol) or naloxone (290 nmol) to antagonize the anticonvulsant action of DADLE. The results of this study demonstrated that the effects of DADLE to increase seizure threshold in the rat were primarily mediated by activation of a delta-opioid receptor system. Furthermore, evidence has been provided for a functional interaction between delta and mu receptors in the opioid regulation of seizure threshold.

Topics: Animals; Anticonvulsants; Cerebral Ventricles; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Etorphine; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

A peptide analogue of Leu-enkephalin was synthesized in which the amide linkages between Tyr-Gly and Gly-Gly were replaced by ketomethylene groups. The resulting analogue, 12, had 1/4000th and 1/2400th the opiate receptor binding activity of Leu-enkephalin when (3H) [D-Ala2,D-Leu5]enkephalin and (3H)naloxone, respectively, were used as tritiated ligands. When tested for analgesia in mice by the tail-flick assay, 12 produced analgesia in 50% of the mice tested at a dose of 24.3 micrograms/mouse (icv), while the ED50 of Leu-enkephalin is 240 micrograms/mouse (icv). At a dose of 40 micrograms/mouse (icv) or higher, 12 caused convulsions in a dose-dependent manner. No analgesia was observed after intravenous (iv) administration of 240 micrograms/mouse of 12.

Topics: Analgesia; Animals; Biological Assay; Chemical Phenomena; Chemistry; Dose-Response Relationship, Drug; Enkephalin, Leucine; Glycine; Mice; Receptors, Opioid; Seizures; Structure-Activity Relationship; Tyrosine

Topics: Animals; Disease Models, Animal; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, mu; Seizures

DPDPE ([D-Pen2, D-Pen5]-Enkephalin) and DPLPE ([D-Pen2, L-Pen5]-Enkephalin) are conformationally-constrained cyclic analogs of enkephalin with high selectivity for delta opioid receptors. Intracerebroventricular (i.c.v.) administration of each analog acutely produces a complex EEG response in rats characterized by a dose-related increase in spectral power and HVSA (peak frequency of 5.0 Hz) during behavioral stupor, and a theta driving (5.25-8.0 Hz) associated with intense behavioral arousal. These effects were antagonized by high (10 mg/kg), but not low (1.0 mg/kg), doses of naloxone. Both analogs failed to cause EEG or convulsive seizures. In contrast, i.c.v. administration of DADLE ([D-Ala2, D-Leu5]-Enkephalin), an enkephalin analog with activity at both mu and delta binding sites, caused initial nonconvulsive EEG seizures followed by HVSA (3.0 Hz); theta driving was not evident. The incidence of the seizures was dose-related and antagonized by very low doses of naloxone (0.01-1.0 mg/kg). Collectively, the inability of DPDPE and DPLPE to cause seizure activity, and the marked sensitivity of DADLE-induced EEG seizures to naloxone, suggest that delta receptors are not directly responsible for DADLE-induced EEG seizure activity. Furthermore, these data implicate mu opioid receptors as the primary sites responsible for enkephalin-induced seizures.

Topics: Animals; Electroencephalography; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalins; Male; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Seizures

Acute i.c.v. administration of ICI 154,129 (100-600 micrograms), a delta-opioid receptor antagonist, raised the seizure threshold in a dose-related manner in rats exposed to flurothyl, a volatile convulsant. Pretreatment with naloxone or beta-funaltrexamine (beta-FNA) antagonized this effect. Lower doses of ICI 154,129 (12.5-50 micrograms), which did not influence seizure threshold, selectively antagonized the anticonvulsant action of [D-Ala2,D-Leu5]enkephalin (DADLE) in the same procedure. Consequently, it may be inferred that ICI 154,129 at high doses has mu-agonist and at low doses delta-antagonist properties in the rat flurothyl test.

Topics: Animals; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Male; Naloxone; Naltrexone; Narcotic Antagonists; Rats; Rats, Inbred Strains; Receptors, Opioid; Seizures

Morphine, beta-endorphin and [D-Ala2, D-Leu5] enkephalin administered intracerebroventricularly exerted a protective effect on electroconvulsive shock (ECS)-induced seizures in mice. This effect was reversed by intraperitoneal injections of naltrexone. The role of mu and delta receptors in ECS-induced convulsions is discussed.

Topics: Animals; beta-Endorphin; Electroshock; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Male; Mice; Mice, Inbred C57BL; Morphine; Naltrexone; Narcotics; Seizures; Time Factors

In an effort to identify delta-receptor-specific properties for opioid modulation of seizure activity, studies were conducted with ICI 154,129, a putative delta-receptor antagonist, in the rat flurothyl test. Rats were pretreated i.c.v. with ICI 154,129 (50 micrograms) which, at this dose, does not alter normal seizure thresholds. Mean seizure thresholds for control groups (i.c.v. saline) ranged between 323-349 sec. In this test, D-Ala2-D-Leu5 enkephalin (20 micrograms, i.c.v.), metkephamid (40 mg/kg, s.c.), and etorphine (20 micrograms/kg, s.c.) raised seizure thresholds by 117, 128, and 140% of control, respectively. Meperidine (25 mg/kg, s.c.) lowered seizure thresholds by 14% less than control. Pretreatment with ICI 154,129 failed to antagonize the proconvulsant action of meperidine or the anticonvulsant and behavioral depressant actions of etorphine. The increases in seizure threshold produced by DADL and metkephamid (two delta-directed ligands) were significantly attenuated by ICI 154,129. However, the DADL-induced wet-shakes, rigid immobility, and behavioral depression were insensitive to ICI 154,129. These data indicate that ICI 154,129 possesses delta-receptor antagonistic properties in this in vivo model of seizure activity. Furthermore, since only the changes in seizure threshold were antagonized, it may be inferred that opioid-induced behavioral depression and DADLE wet-shakes are not a function of delta-receptor activity.

Topics: Animals; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Etorphine; Male; Meperidine; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, Opioid, delta; Seizures; Sensory Thresholds

The correlation between the distribution of the intraventricularly (i.v.t.) administered delta agonist [3H](D-ala2,D-leu5)-enkephalin ([3H]DADL) and the anatomical regions involved in enkephalin-induced seizures has been studied in rat by using an autoradiographic method and recording of the electromyogram (EMG) and the electroencephalogram (EEG). The results indicate that within 10 min, the radioactivity of the intraventricularly administered drug reached all parts of the ventricular system, including the central canal of the spinal cord. However, within 2.5 min after the intraventricular administration of [3H]DADL, which corresponds to the onset of DADL-induced seizures, the substance appeared mainly in the left lateral ventricle and occasionally in the third ventricle. During the first 2.5 min the substance penetrated regularly into the surrounding periventricular tissue of the striatum, septum and hippocampus to a depth of about 100 microns. The most intensive and long-lasting epileptic discharges, exceeding 30 min were observed in the hippocampus, in contrast to the mild and short-lasting electrophysiological responses of the septum and corpus striatum. The experiments suggest that the short onset of enkephalin-induced excitatory phenomena is due to the rapid distribution and penetration of the substance in the surrounding periventricular tissue. According to these data, it is proposed that activation of delta opiate receptors, localized within the first 100 microns of the periventricular tissue, mainly in the hippocampus, is essential for the triggering of endorphin-induced seizure activity.

Topics: Animals; Autoradiography; Brain; Diffusion; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Evoked Potentials; Injections, Intraventricular; Male; Rats; Rats, Inbred Strains; Seizures