kappa-Opioid receptor agonists improve pirenzepine-induced disturbance of spontaneous alternation performance in the mouse

We investigated the effects of kappa-opioid receptor agonists such as dynorphin A-(1-13) and U-50,488H on the muscarinic M1-selective receptor antagonist pirenzepine (3 micrograms, i.c.v.)-induced impairment of spontaneous alternation performance in the mouse. Although dynorphin A-(1-13)(1-5.6 micrograms, i.c.v.) or U-50,488H ((+/-)trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]- benzeneacetamide, methanesulfonate hydrate) (0.1-1 mg/kg, i.p.) alone did not influence either spontaneous alternation performance or total arm entries, pirenzepine (3 micrograms, i.c.v.) impaired spontaneous alternation performance without producing any significant change in total arm entries. In contrast, dynorphin A-(1-13) (3 and 5.6 micrograms, i.c.v.) and U-50,488H (0.3 and 1 mg/kg, i.p.) ameliorated the pirenzepine (3 micrograms, i.c.v.)-induced impairment of spontaneous alternation performance. The ameliorating effects of dynorphin A-(1-13)(3 micrograms, i.c.v.) and U-50,488H (0.3 mg/kg, i.p.) were almost completely reversed by pretreatment with nor-binaltorphimine (4 micrograms, i.c.v.), a kappa-opioid receptor antagonist. These results suggest that the stimulation of kappa-opioid receptors improves memory dysfunctions resulting from the blockade of muscarinic M1 receptors.

Effects of centrally administered neuropeptides on discriminative stimulus properties of cocaine in the rat

The present study was designed to investigate the effects of centrally administered neuropeptides on the discriminative stimulus properties of cocaine in the rat. Rats were trained to discriminate 10.0 mg/kg of cocaine from vehicle in a shock avoidance paradigm. The mu-selective opioid agonist [D-Ala2,NMePhe4,Gly-ol]enkephalin (DAMGO) (0.03-0.3 microgram, ICV) or the kappa-selective opioid agonist dynorphin A-(1-13) (1.0-10.0 micrograms, ICV) did not generalize to cocaine cue, although the delta-selective opioid agonist [D-Pen2,L-Pen5]enkephalin (DPLPE) (10.0 micrograms, ICV) reportedly generalizes to it through the mediation of delta-opioid receptors. Thyrotropin-releasing hormone (10.0-56.0 micrograms, ICV), somatostatin (0.3-3.0 micrograms, ICV), substance P (3.0-17.5 micrograms, ICV), or neurotensin (3.0-17.5 micrograms, ICV) did not produce any stimulus effects in common with cocaine. It appears that neuropeptides other than the delta-selective opioid do not play a major role in the discriminative stimulus properties of cocaine.

Substance P markedly ameliorates scopolamine-induced impairment of spontaneous alternation performance in the mouse

We investigated the effects of intracerebroventricular injection of substance P (SP) on the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance in the mouse. SP (0.001-3 micrograms) alone did not influence either spontaneous alternation performance or total arm entries. Scopolamine (1 mg/kg) impaired spontaneous alternation performance accompanied by an increment in total arm entries. In contrast, SP (0.01-1 micrograms) significantly improved the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance without influencing the scopolamine (1 mg/kg)-induced increase in total arm entries. The effects of SP (0.1 micrograms) on the scopolamine (1 mg/kg)-induced impairment of spontaneous alternation performance were almost completely reversed by pretreatment with WIN 62577 (1 mg/kg), a tachykinin NK-1 receptor antagonist. These results suggest that SP improves the scopolamine-induced impairment of spontaneous alternation performance through the mediation of tachykinin NK-1 receptors.

Improvement in exercise-induced left ventricular dysfunction by infusion of alpha-human atrial natriuretic peptide in coronary artery disease

The effects of recombinant alpha-human atrial natriuretic peptide (alpha-hANP) infusion an acute left ventricular dysfunction provoked by exercise were examined in 14 men with coronary artery disease. Patients performed symptom-limited, graded exercise on a supine bicycle ergometer. Plasma alpha-hANP and guanosine 3',5'-monophosphate (cyclic GMP) concentrations as well as hemodynamic variables were measured at rest, during and after exercise. In 14 patients whose pulmonary artery wedge pressure was > 20 mm Hg at peak exercise, the same exercise protocol was repeated at 30 minutes after starting intravenous alpha-hANP infusion (0.05 microgram.kg-1.min-1). In 8 of these patients, a Webster thermodilution catheter was advanced into the coronary sinus for measurement of coronary sinus blood flow. From the control exercise test, plasma alpha-hANP concentration increased from 86 +/- 20 pg/ml at rest to 188 +/- 32 pg/ml at peak exercise (p < 0.001), and plasma cyclic GMP concentration increased from 4.8 +/- 1.9 pmol/ml at rest to 7.2 +/- 2.9 pmol/ml at peak exercise (p < 0.001). Both plasma alpha-hANP and cyclic GMP concentrations showed a significant positive correlation with pulmonary artery wedge pressure during control exercise. With alpha-hANP infusion, systolic and diastolic pulmonary artery pressures and pulmonary artery wedge pressure were significantly decreased at all time points during exercise testing. Heart rate was increased and systolic blood pressure was significantly decreased at rest and at 3 minutes of exercise. Diastolic blood pressure, systemic vascular resistance, and pulmonary vascular resistance were significantly decreased at rest.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynorphin A-(1-13) potently improves scopolamine-induced impairment of passive avoidance response in mice

The effects of intracerebroventricular administration of dynorphin A-(1-13) on scopolamine-induced amnesia were investigated in mice by using a step-down type passive avoidance task. The pre- or post-training, or pre-retention administration of dynorphin A-(1-13)(0.3-10 micrograms) alone failed to affect step-down latency of the passive avoidance response, while scopolamine (1 mg/kg) significantly shortened step-down latency. Dynorphin A-(1-13)(1 microgram) given 15 min before training and retention tests but not immediately after training significantly improved the scopolamine (1 mg/kg)-induced shortening of step-down latency of the passive avoidance response, indicating antiamnesic effects of dynorphin A-(1-13) (1 microgram). A lower dose (1 mg/kg) of the kappa-opioid receptor antagonist, (-)-(1R,5R,9R)-5,9-diethyl-2-(3-furyl-methyl)- 2'-hydroxy-6,7-benzomorphan, reversed the anti-amnesic effects of dynorphin A-(1-13) (1 microgram). These results suggest that the antiamnesic effects of dynorphin A-(1-13) depend on the timing of drug treatments.

Effects of galanin on passive avoidance response, elevated plus-maze learning, and spontaneous alternation performance in mice

The present study was done to characterize the effects of intracerebroventricular injection of galanin (GAL) on memory processes by observing passive avoidance response, elevated plus-maze learning, and spontaneous alternation performance in mice. An intermediate dose (3 micrograms) of GAL (3 micrograms) significantly decreased step-down latency of passive avoidance response when given 15 min before training, whereas in particular the middle doses (0.3 and 1 microgram) of GAL significantly decreased it when given 15 min before retention tests. However, GAL (0.3-10 micrograms) was ineffective when given immediately after training. Physostigmine (0.2 mg/kg), a cholinesterase inhibitor, and oxotremorine (0.01 and 0.03 mg/kg), a cholinergic agonist, significantly inhibited the shortening of step-down latency induced by GAL (0.3 microgram) administered 15 min before retention tests, indicating the involvement of cholinergic dysfunction in the GAL (0.3 microgram)-induced shortening of step-down latency. In contrast, GAL (0.3-3 micrograms) failed to influence transfer latency in elevated plus-maze learning or percent alternation in spontaneous alternation performance. These results suggest that the activation of cholinergic neurons improves memory dysfunctions induced by GAL, which primarily impairs retrieval processes of memory. The lack of effects of GAL on the elevated plus-maze learning and spontaneous alternation performance may result from the selective effects of GAL in different learning paradigms.

Binding and aggregation of human gamma-globulin by cis-diamminedichloroplatinum(II) through disulfide bond

The incubation of gamma-globulin with cis-diamminedichloroplatinum (II) (cis-DDP) resulted in gradual formation of insoluble aggregates. Since the precipitates, composed of polymerized gamma-globulin and cis-DDP, were completely solubilized with urea, the reaction mixture containing precipitate was examined in terms of the binding of cis-DDP and the effect on disulfide (S-S) bonds in the gamma-globulin. When gamma-globulin was incubated with 30 molar excess cis-DDP at pH 7.4 and 37 degrees C, cis-DDP gradually bound to as much as 12 mol per mol of gamma-globulin in 14 d. Concurrently, about four disulfide bonds were cleaved without reaching a certain plateau. An sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the aggregated gamma-globulin induced by cis-DDP was significantly different from that of the heat-denaturated aggregate form or the reduced form by sulfitolysis. The aquated complexes of cis-DDP also produced an insoluble precipitate and affected the S-S bond to a greater extent than the parent drug.

Effects of human epidermal growth factor on passive avoidance and habituation learning in mice

1. Human epidermal growth factor (hEGF:0.02-2.0 micrograms) did not affect passive avoidance response or habituation learning when given before or immediately after training, or before retention. 2. hEGF (0.02-2.0 micrograms) failed to influence the scopolamine- or electroconvulsive shock-induced shortening of step-down latency in passive avoidance response when given before or immediately after training, or before retention. 3. These results suggest that the acute administration of hEGF does not affect memory processes as indexed by passive avoidance or habituation learning in normal or amnesic mice.

Hemodynamic effects of the calcium channel blocker pranidipine on exercise-induced angina

Hemodynamic effects of a newly developed calcium channel blocker, pranidipine, on dynamic exercise-induced angina were investigated. Ten patients with stable effort angina pectoris underwent symptom-limited bicycle ergometer exercise testings before and after a single oral administration of pranidipine, and effects of pranidipine on systemic, cardiac and coronary hemo-dynamics induced by dynamic exercise were evaluated invasively. Pranidipine administration reduced systemic vascular resistance (from 1,764 +/- 109 to 1,115 +/- 60 dynes.sec/cm5; p < 0.01 at test, and from 1,120 +/- 102 to 795 +/- 62 dynes.sec/cm5; p < 0.05 at peak exercise) and mean arterial pressure (from 93 +/- 5 to 76 +/- 3 mmHg; p < 0.01 at test, and from 85 +/- 7 to 72 +/- 6 mmHg; p < 0.05 at peak exercise) with the increase in heart rate and cardiac index throughout exercise. Pranidipine also decreased coronary vascular resistance from 1.29 +/- 0.21 to 0.89 +/- 0.17 mmHg/ml/min (p < 0.05) at resting condition. At peak exercise, rate-pressure product and myocardial oxygen consumption decreased (from 237 +/- 21 to 215 +/- 18 x 10(2); p < 0.05, and from 31.3 +/- 7.5 to 21.7 +/- 3.9 ml/min; p < 0.05, respectively), while coronary vascular resistance did not change significantly. Furthermore, pranidipine mitigated ST-segment depression and elevation of pulmonary artery wedge pressure at peak exercise (from 0.20 +/- 0.03 to 0.13 +/- 0.02 mV; p < 0.01, and from 25 +/- 3 to 11 +/- 2 mmHg; p < 0.01, respectively). These results suggest that the major therapeutic effects of pranidipine for dynamic exercise-induced angina would be to reduce myocardial oxygen demand by improving peripheral circulation and reducing preload and afterload.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynorphin A-(1-13) potently improves galanin-induced impairment of memory processes in mice

The present study examined the effects of intracerebroventricular injection of dynorphin A-(1-13) on memory processes by using the passive avoidance task in mice. Galanin (0.3 microgram) significantly shortened the step-down latency when given 15 min before retention tests. Although dynorphin A-(1-13) (1 or 3 micrograms) did not prolong the step-down latency induced by weaker electroshocks, it inhibited the galanin (0.3 micrograms)-induced shortening of step-down latency. The effects of dynorphin A-(1-13) (3 micrograms) on the galanin-induced shortening of step-down latency were almost completely reversed by pretreatment with nor-binaltorphimine (4 micrograms), a kappa-selective opioid antagonist. These results strongly suggest that dynorphin A-(1-13) attenuates galanin-induced impairment of memory processes through the mediation of kappa-opioid receptors.

Differential modulation of behavioral responses by [D-Ala2, NMePhe4, Gly-ol]enkephalin, [D-Ala2] deltorphin II and [D-Pen2, L-Pen5]enkephalin in the mouse

The effects of [D-Ala2, NMePhe4, Gly-ol]enkephalin (DAMGO), a mu-selective opioid receptor agonist, [D-Ala2]deltorphin II (DELT) and [D-Pen2, L-Pen5]enkephalin (DPLPE), delta-selective opioid receptor agonists, on different behavioral responses were investigated in mice by multidimensional behavioral analyses. DAMGO (0.1 and/or 0.3 microgram) produced a marked increase in circling, rearing and grooming within 15-30 min after the start of behavioral measurements. DELT (0.3, 1.0 and/or 3.0 micrograms) produced a significant increase in linear locomotion and circling within 15-30 min after the start of behavioral measurements, whereas DPLPE (10.0 micrograms) increased only circling. The behavioral effects of DAMGO, DELT or DPLPE were almost completely antagonized by beta-funaltrexamine (2.5 and 5.0 micrograms) or naltrindole (3.0 and 10.0 mg/kg). These results suggest that opioid peptides selective for receptor types elicit different behavioral responses in mice. Moreover, the different behavioral effects between DPLPE and DELT may be due to the delta opioid receptor subtypes such as delta-1 and delta-2.

Opioid peptides selective for receptor types modulate cocaine-induced behavioral responses in mice

The effects of intracerebroventricular injection of mu-, kappa- and delta-selective opioid agonists on cocaine-induced behavior were investigated in mice using multidimensional behavioral analysis. Cocaine (3.0 mg/kg) produced a marked increase in linear locomotion, circling, rearing and/or grooming, although the mu-opioid agonist [D-Ala2, NMePhe4, Gly-ol] enkephalin (DAMGO) (0.003 and 0.01 microgram), the kappa-opioid agonist dynorphin A- (1-13) (3.0 and 12.5 micrograms) or the delta-opioid agonist [D-Pen2, L-Pen5]enkephalin (DPLPE) (0.3 and 1.0 micrograms) did not significantly affect behavioral responses. DAMGO (0.003 and 0.01 microgram) and dynorphin A- (1-13) (12.5 micrograms) inhibited the cocaine (3.0 mg/kg)-induced increase in linear locomotion, circling and/or rearing. In contrast, DPLPE (1.0 micrograms) enhanced the cocaine (3.0 mg/kg)-induced increase in circling. The effects of DAMGO (0.003 microgram), dynorphin A- (1-13) (12.5 micrograms) and DPLPE (1.0 micrograms) were fully reversed by receptor-selective opioid antagonists, such as beta-funaltrexamine (5.0 micrograms), Mr2266 (5.6 mg/kg) and naltrindole (10.0 mg/kg), respectively. These results suggest that the activation of mu- and kappa-opioid receptors inhibits cocaine-induced behavior, while that of delta-opioid receptors enhances the behavior.

Characterization of the effects of scopolamine on the habituation of exploratory activity: differential effects of oxotremorine and physostigmine

1. Habituation was regarded as a difference between exploratory activity measured first (session 1) and that measured second (session 2) in a novel environment. 2. Scopolamine (1.0 mg/kg) significantly increased the horizontal activity in sessions 1 and 2 when administered prior to session 1, resulting in the impairment of habituation. 3. Haloperidol (0.2 mg/kg) inhibited scopolamine-induced hypermotility in session 1, but it did not inhibit the scopolamine-induced impairment of habituation in session 2. 4. The direct cholinergic agonist oxotremorine (0.03 mg/kg), unlike the cholinesterase inhibitor physostigmine, significantly inhibited the scopolamine-induced impairment of habituation in the horizontal and vertical activities. 5. These results suggest that the direct stimulation of cholinergic receptors is more effective for scopolamine-induced amnesia than the indirect stimulation of cholinergic receptors by cholinesterase inhibitors in the habituation task.

Dynorphin A-(1-13) potently improves the impairment of spontaneous alternation performance induced by the mu-selective opioid receptor agonist DAMGO in mice

The effects of i.c.v. injection of the mu-selective opioid receptor agonist DAMGO and the effects of its combination with the endogenous kappa-opioid receptor agonist dynorphin A-(1-13) on memory processes were examined in mice, using spontaneous alternation performance associated with working memory in a Y-maze. DAMGO (10 and/or 30 ng) impaired spontaneous alternation performance and increased total arm entries, which are considered to reflect locomotor activity. beta-Funaltrexamine (5 micrograms, i.c.v.), a mu-selective opioid receptor antagonist, almost completely antagonized the impairment of alternation performance induced by DAMGO (10 ng). Physostigmine (0.1 mg/kg, i.p.), a cholinesterase inhibitor, improved the DAMGO (10 ng)-induced impairment of alternation performance. Dynorphin A-(1-13) (1, 3 and 10 micrograms, i.c.v.) alone was without significant effects on alternation performance. On the other hand, dynorphin A-(1-13) (3 and 10 micrograms) significantly improved the impairment of spontaneous alternation performance induced by DAMGO (10 ng). The effects of dynorphin A-(1-13) (3 micrograms) on the DAMGO-induced impairment of spontaneous alternation were almost completely reversed by pretreatment with nor-binaltorphimine (4 micrograms, i.c.v.), a kappa-selective opioid receptor antagonist. The present results demonstrate that DAMGO impairs alternation performance by activating mu-opioid receptors, whereas dynorphin A-(1-13) attenuates the DAMGO-induced impairment of alternation performance through the mediation of kappa-opioid receptors. These findings suggest that mu- and kappa-opioid systems are fully involved in memory function and have opposite effects on spontaneous alternation performance as it is reflected by working memory in mice.

Effects of several amnesic drugs on the habituation of exploratory activity in mice as indexed by horizontal and vertical activities

1. The effects of several drugs on the habituation of exploratory activity in mice were investigated by using animal movement analyzing systems which could detect horizontal and vertical activities. 2. Habituation was regarded as the difference between exploratory activity measured first (session 1) and that measured second (session 2). 3. Scopolamine (1, 3 and/or 6 mg/kg), pirenzepine (20 and 40 micrograms) injected immediately after session 1, cycloheximide (30 mg/kg), diazepam (1, 2 and/or 4 mg/kg) and dizocilpine (0.05, 0.1 and/or 0.2 mg/kg), unlike butylscopolamine (1, 3 and 6 mg/kg) or haloperidol (0.2 and 0.4 mg/kg), significantly increased horizontal activity but not always vertical activity in session 2. 4. From the results obtained, it appears that the increase in horizontal activity in session 2 is more appropriate as an indicator of the impairments of memory processes than that in vertical activity.

Receptor-selective opioid peptides fail to affect behavioral responses induced by a low dose of apomorphine in the mouse

The effects of intracerebroventricular injections of the mu-selective opioid agonist DAMGO ([D-Ala2,NMePhe4,Gly-ol]enkephalin), the kappa-selective opioid agonist dynorphin A-(1-13), and the delta-selective opioid agonist DPLPE ([D-Pen2,L-Pen5]enkephalin) on the decrease in different behavioral responses induced by a low dose of apomorphine (0.03 mg/kg) were investigated in the mouse. A low dose (0.03 mg/kg) of apomorphine produced a marked decrease in behavioral responses such as circling and rearing. Although the dopamine D1 antagonist SCH 23390 (0.01 and 0.03 mg/kg) did not influence behavior induced by apomorphine (0.03 mg/kg), the dopamine D2 antagonist sulpiride (3.0 mg/kg) reversed the decrease in circling and rearing behavior induced by apomorphine, suggesting that the effects of apomorphine on circling and rearing are mediated through dopamine D2 autoreceptors. DAMGO (0.003 or 0.01 microgram), dynorphin A-(1-13) (3.0 or 10.0 micrograms), or DPLPE (0.3 and 1.0 microgram) had no significant effects on the apomorphine-induced decrease in circling and rearing behavior. These in vivo results suggest that opioid peptides selective for receptor types fail to influence drug effects mediated by dopamine D2 autoreceptors.

Dynorphin A-(1-13) attenuates basal forebrain-lesion-induced amnesia in rats

The effects of dynorphin A-(1-13), an endogenous kappa opioid agonist, on basal forebrain (BF)-lesion-induced amnesia in rats were investigated using step-through-type passive avoidance task. The BF was lesioned by injecting the cholinergic neurotoxin ibotenic acid (6 micrograms/side). The number of rats achieving the cut-off time (600 s) of step-through latency (STL) in BF-lesioned group significantly decreased as compared with that in sham-operated group. Dynorphin A-(1-13) (0.3 micrograms) significantly increased the number of rats achieving the cut-off time of STL in BF-lesioned rats. These results suggest that dynorphins play an improving role in the impairment of memory processes in BF-lesioned rats.

DAMGO ([D-Ala2,NMePhe4,Gly-ol]enkephalin), but not DPLPE ([D-Pen2,L- Pen5]enkephalin), specifically inhibits methamphetamine-induced behavioral responses in the mouse

The effects of intracerebroventricular (i.c.v.) injections of mu- and delta-selective opioid agonists on the methamphetamine-induced behavioral alterations in the mouse were determined by using multi-dimensional behavioral analyses. Methamphetamine (1.0 mg/kg) produced a marked increase in linear locomotion, circling, rearing and grooming behavior. Although the mu-selective opioid agonist [D-Ala2,NMePhe4,Gly-ol]enkephalin (DAMGO) (0.003 and 0.01 microgram) itself did not significantly affect different behavioral responses, DAMGO (0.003 and/or 0.01 microgram) antagonized the methamphetamine (1.0 mg/kg)-induced increase in behavioral responses such as linear locomotion, circling, rearing and grooming. Additionally, the effects of DAMGO (0.01 microgram) on the methamphetamine (1.0 mg/kg)-induced behavioral responses were fully reversed by pretreatment with the mu-selective alkylating agent beta-funaltrexamine (beta-FNA) (5.0 micrograms). In contrast, the delta-selective opioid agonist [D-Pen2,L-Pen5]enkephalin (DPLPE) (0.3 or 1.0 microgram) had no marked effects on the methamphetamine (1.0 mg/kg)-induced behavioral responses. These results suggest that the stimulation of mu but not delta opioid receptors plays an inhibitory role in the methamphetamine-induced behavioral responses.

Dopaminergic involvement in the improving effects of dynorphin A-(1-13) on scopolamine-induced impairment of alternation performance

The present study was designed to clarify whether dopamine systems are involved in the effect of dynorphin A-(1-13), an endogenous kappa-opioid receptor agonist, on the scopolamine-induced impairment of spontaneous alternation performance related to working memory in mice. Sulpiride (10 and/or 30 mg/kg), a dopamine D2-selective antagonist, markedly improved the impairment of alternation performance and significantly reduced the increase in total arm entries (i.e. locomotor activity) induced by scopolamine (1 mg/kg). In contrast, SCH 23390 (0.01, 0.03 and 0.1 mg/kg), a dopamine D1-selective antagonist, did not influence the impairment of alternation performance, whereas it dose dependently reduced total arm entries in scopolamine-treated mice RU 24213 (1 mg/kg), a dopamine D2-selective agonist, almost completely reversed the improving effect of dynorphin A-(1-13) (3 micrograms) on the scopolamine-induced impairment of alternation performance and reduced total arm entries, although it was without effects on behavioral responses in normal mice. However, SKF 38393 (3 and 10 mg/kg), a dopamine D1-selective agonist, failed to change alternation performance or total arm entries in normal or scopolamine-treated mice. These findings suggest that the impairment of spontaneous alternation performance induced by scopolamine is improved by the blockade of dopamine D2 receptors. Furthermore, the improving effect of dynorphin A-(1-13) on the scopolamine-induced impairment of spontaneous alternation performance may be based upon the inhibition of dopaminergic activity through the mediation of kappa-opioid receptors.

U-50,488H, a kappa-opioid receptor agonist, markedly prevents memory dysfunctions induced by transient cerebral ischemia in mice

Transient ischemia produced marked memory dysfunctions in mice on three different tasks, spontaneous alternation, elevated plus-maze and passive avoidance, as tested 1, 1-2, and 2-3 days after ischemic insult, respectively. U-50,488H, a kappa-opioid receptor agonist, administered 20 min before ischemic insult markedly prevented the impairment of spontaneous alternation, the prolongation of transfer latency in elevated-plus maze and the shortening of step-through latency in passive avoidance induced by transient ischemia. The protective effect of U-50,488H (30 mg/kg) on ischemia-induced memory dysfunctions observed in the three tasks was almost completely reversed by pretreatment with nor-binaltorphimine (4 micrograms, i.c.v.), a kappa-selective opioid antagonist. Although U-50,488H (30 mg/kg) did not affect body temperature in sham mice, it blocked hypothermia induced by ischemic insult. These results suggest that the protective effect of U-50,488H on memory dysfunctions in ischemic mice is associated with the activation of kappa-opioid receptors and is not based upon hypothermia.

Tyr-D-Arg-Phe-beta-Ala-NH2, a novel dermorphin analog, impairs memory consolidation in mice

Tyr-D-Arg-Phe-beta-Ala-NH2 (TAPA), a novel dermorphin analog with high selectivity and affinity for mu-opioid receptors, was administered intracerebroventricularly to mice before or immediately after training in a one-trial step-down type passive avoidance task. The pre- and post-training administration of TAPA (0.3 and/or 3 ng) impaired retention performance 24 h after training. In particular, the post-training administration of TAPA was much more effective because a lower dose (0.3 ng) of TAPA exclusively inhibited retention performance. The amnesic effects of TAPA were reversed by the mu-selective opioid antagonist beta-funaltrexamine (5 micrograms, i.c.v.). In addition, TAPA (0.3 and 3 ng) had no effects on nociceptive responses in a tail-flick test or on behavioral responses to electric shock during training. These results suggest that activation of mu-opioid receptors impairs passive avoidance learning, resulting in a dysfunction of memory consolidation, without affecting other behavioral responses.