Masahiro Irifune

Ketamine-induced anesthesia involves the N-methyl-d-aspartate receptor-channel complex in mice

The role of the N-methyl-D-aspartate (NMDA) receptor-channel complex in ketamine-induced anesthesia was examined in mice. General anesthetic potencies were evaluated on a rating scale, which provided the data for anesthetic scores, loss of righting reflex, sleeping time and recovery time. All drugs were administered intraperitoneally. NMDA (60-300 mg/kg), an NMDA receptor agonist, dose-dependently antagonized the general anesthetic potencies of ketamine at a dose of 100 mg/kg which produced loss of righting reflex in more than 90% of the mice. On the other hand, a high dose of N-methyl-L-aspartate (400 mg/kg), a stereoisomer of NMDA, did not. A dose of 300 mg/kg of NMDA significantly shifted the dose-response curve of ketamine for loss of righting reflex to the right. A high dose of D-cycloserine (200 mg/kg), an agonist at the glycine site on the NMDA receptor complex, slightly but significantly shortened the sleeping time caused by ketamine (100 mg/kg). However, neither a critical subconvulsive dose of kainate (15 mg/kg), a kainate receptor agonist, nor a subconvulsive dose of quisqualate (120 mg/kg), an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor agonist, reversed general anesthesia induced by 100 mg/kg of ketamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Ketamine-induced hyperlocomotion associated with alteration of presynaptic components of dopamine neurons in the nucleus accumbens of mice.

The underlying mechanisms of ketamine-induced hyperlocomotion were examined in mice. An intraperitoneal (IP) injection of ketamine (3-150 mg/kg) increased locomotor activity in a dose-dependent fashion. A low dose of ketamine (30 mg/kg) produced peak locomotion within the first 10 min followed by a rapid decline. In contrast, a high dose (150 mg/kg) inhibited locomotor activity to the control level during the first 30 min. Thereafter the activity gradually increased and reached a peak at approximately 2 h followed by a gradual decline. The hyperactivities induced by both low and high doses of ketamine were inhibited by a low dose of haloperidol (0.10 mg/kg, IP), a dopamine (DA) receptor antagonist. However, neither a high dose of phenoxybenzamine (10 mg/kg, IP), an alpha-blocker nor a high dose of propranolol (20 mg/kg, IP), a beta-blocker inhibited the hyperactivities. Destruction of catecholaminergic terminals by 6-hydroxydopamine suppressed ketamine-induced hyperlocomotion. Regional brain monoamine assays revealed that, at peak locomotion, a low dose of ketamine (30 mg/kg) selectively increased DA turnover in the nucleus accumbens which is a forebrain region believed to be involved in the initiation and regulation of locomotor activity, while a high dose (150 mg/kg) increased not only DA but also norepinephrine and serotonin turnover in many regions of the brain. In vitro, ketamine slightly provoked [3H]DA release from nucleus accumbens and striatal slices to a similar extent, but inhibited synaptosomal uptake of [3H]DA in the nucleus accumbens to a greater degree than in the striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for GABAA receptor agonistic properties of ketamine: Convulsive and anesthetic behavioral models in mice

We examined the potentiation by ketamine of the &ggr;-aminobutyric acidA (GABAA) receptor function using convulsive and anesthetic behavioral models in adult male ddY mice. General anesthetic potencies were evaluated by a rating scale, which provided the data for anesthetic scores, loss of righting reflex, duration, and recovery time. All drugs were administered intraperitoneally. Small subanesthetic doses of ketamine did inhibit tonic seizures induced by a large dose of the GABAA receptor antagonist bicuculline (8 mg/kg). The 50% effective dose value was 15 (95% confidence limits 10–22) mg/kg. Even large anesthetic doses (100–150 mg/kg) did not suppress clonic seizures in 50% of the animals. The GABAA receptor agonist, muscimol (0.32–1.12 mg/kg), potentiated ketamine-induced anesthesia in a dose-dependent fashion (P < 0.05). Similarly, the benzodiazepine receptor agonist, diazepam (1–3 mg/kg), augmented ketamine anesthesia in a dose-dependent manner (P < 0.05). Bicuculline (2–5 mg/kg) dose-dependently antagonized ketamine-induced anesthesia (P < 0.05). Neither the benzodiazepine receptor antagonist, flumazenil (2–20 mg/kg), nor the GABA synthesis inhibitor, l-allylglycine (200 mg/kg), affected the anesthetic action of ketamine. These results suggest that ketamine has GABAA receptor agonistic properties and that ketamine-induced anesthesia is mediated, at least in part, by GABAA receptors. Implications We examined the potentiation by ketamine of the &ggr;-aminobutyric acidA receptor function using convulsive and anesthetic behavioral models in mice. Subanesthetic doses of ketamine-inhibited tonic convulsions induced by the &ggr;-aminobutyric acidA receptor antagonist bicuculline. The &ggr;-aminobutyric acidA receptor agonist, muscimol, potentiated ketamine-induced anesthesia. Bicuculline antagonized ketamine anesthesia, but the benzodiazepine receptor antagonist, flumazenil, and the &ggr;-aminobutyric acid synthesis inhibitor, l-allyglycine, did not. The effects of ketamine on the &ggr;-aminobutyric acidA receptors appear to correlate with its anesthetic actions.

Propofol-induced Anesthesia in Mice Is Mediated by γ-aminobutyric Acid-a and Excitatory Amino Acid Receptors

To elucidate the role of &ggr;-aminobutyric acid (GABA)A receptor complex and excitatory amino acid receptors (N-methyl-d-aspartate [NMDA] and non-NMDA receptors) in propofol-induced anesthesia, we examined behaviorally the effects of GABAergic and glutamatergic drugs on propofol anesthesia in mice. All drugs were administered intraperitoneally. General anesthetic potencies were evaluated using a righting reflex assay. The GABAA receptor agonist muscimol potentiated propofol (140 mg/kg; 50% effective dose for loss of righting reflex) induced anesthesia. Similarly, the benzodiazepine receptor agonist diazepam and the NMDA receptor antagonist MK-801 augmented propofol anesthesia, but the non-NMDA receptor antagonist CNQX did not. In contrast, the GABAA receptor antagonist bicuculline antagonized propofol (200 mg/kg; 95% effective dose for loss of righting reflex) induced anesthesia. However, neither the benzodiazepine receptor antagonist flumazenil, the GABA synthesis inhibitor l-allylglycine, nor the NMDA receptor agonist NMDA reversed propofol anesthesia. Conversely, the non-NMDA receptor agonist kainate enhanced propofol anesthesia. These results suggest that propofol-induced anesthesia is mediated, at least in part, by both GABAA and excitatory amino acid receptors.

Involvement of N-methyl-D-aspartate (NMDA) receptors in noncompetitive NMDA receptor antagonist-induced hyperlocomotion in mice

The role of the N-methyl-D-aspartate (NMDA) receptors in hyperlocomotion induced by (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801), a potent and selective noncompetitive NMDA receptor antagonist, was examined in male ddY mice. A low dose of MK-801 [0.2 mg/kg, intraperitoneally (IP)] produced a marked increase in locomotor activity without obvious staggering gait. In contrast, a high dose (1 mg/kg, IP) induced a typical motor syndrome characterized by increased locomotor activity, stereotyped behavior, and severe ataxia. NMDA (60-120 mg/kg, IP), an NMDA receptor agonist, dose dependently antagonized hyperlocomotion induced by a low dose of MK-801 (0.2 mg/kg). However, even a high convulsive dose of NMDA (240 mg/kg, IP) could not completely antagonize the hyperactivity induced by MK-801. On the other hand, neither a high dose of N-methyl-L-aspartate (400 mg/kg, IP), a stereoisomer of NMDA, nor a critical subconvulsive dose of kainate (10 mg/kg, IP), a non-NMDA receptor agonist, reversed MK-801-induced hyperlocomotion. The activity induced by MK-801 was potently suppressed by low doses of haloperidol (0.05-0.1 mg/kg, IP), a dopamine (DA) receptor antagonist, in a dose-dependent manner. These data for MK-801 were similar to those for phencyclidine and ketamine, other noncompetitive NMDA receptor antagonists. These results suggest that noncompetitive NMDA receptor antagonist-induced hyperlocomotion is mediated, at least in part, by NMDA receptor antagonism, although this hyperactivity may also involve dopaminergic mechanisms through indirect (perhaps by reducing NMDA receptor-mediated neurotransmission) and/or direct (by inhibiting DA uptake) effects on DA neurons.

Effects of ketamine on dopamine metabolism during anesthesia in discrete brain regions in mice: comparison with the effects during the recovery and subanesthetic phases

The effects of ketamine on the levels of dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT, serotonin) and their metabolites were examined in discrete brain regions in mice. A high dose of ketamine (150 mg/kg, i.p.) did not change DA metabolism in the frontal cortex, nucleus accumbens, striatum and hippocampus, but did decrease it in the brainstem during anesthesia. In contrast, during recovery from the ketamine anesthesia, the high dose increased the level of homovanillic acid (HVA) in all brain regions. A low subanesthetic dose of ketamine (30 mg/kg, i.p.) increased the concentrations of both 3,4-dihydroxyphenylacetic acid (DOPAC) and HVA only in the nucleus accumbens. The DA level was not affected by any ketamine treatment. During ketamine anesthesia, the content of 3-methoxy-4-hydroxy-phenylglycol (MHPG) was decreased in the brainstem, whereas during recovery from anesthesia, the MHPG level was increased in the frontal cortex, nucleus accumbens and brainstem. The NE content was not altered in any region by ketamine treatment. The concentration of 5-hydroxyindoleacetic acid (5-HIAA) was reduced in the frontal cortex, striatum, hippocampus and brainstem during ketamine anesthesia. The 5-HT level was unaltered in all regions except the brainstem where it was reduced. In contrast, after anesthesia, the concentrations of both 5-HT and 5-HIAA were increased in the striatum. During the subanesthetic phase, however, the levels of NE, 5-HT and their metabolites were unchanged. These neurochemical results are consistent with the electrophysiological findings that a high dose of ketamine does not change the basal firing rates of nigrostriatal DA neurons during anesthesia, while low subanesthetic doses significantly increase those of ventral tegmental DA neurons.

Effects of ovariectomy and calcium deficiency on learning and memory of eight-arm radial maze in middle-aged female rats

There is increasing evidence that estrogen and calcium ion are involved in learning and memory. In the present study, to examine the effect of estrogen deficiency and low-calcium diet on learning and memory, middle-aged female Wistar rats (50 weeks old) were fed either a low-calcium (0.02% Ca) or a normal-calcium (1.25% Ca) diet throughout the experiment. Rats were ovariectomized (OVX) or sham-operated (Sham). These animals were divided into four groups: 1) Sham group with normal-calcium diet [Sham-normal Ca group], 2) OVX group with normal-calcium diet [OVX-low Ca group], 3) Sham group with low-calcium diet [Sham-low Ca group], 4) OVX group with low-calcium diet [OVX-low Ca group]. Seventy-seven days after the OVX or Sham operation, the learning and memory abilities in the female rats were examined by using a radial maze task according to the method of Olton and Samuelson (regular trials) and using a delay-interposed task following regular trials. During regular trials and delay-interposed tasks, the OVX-low Ca group was inferior to all the other groups in accuracy of choice behavior. Both Sham-normal Ca and Sham-low Ca groups showed more accurate choices than the OVX-low Ca group, but were less accurate than the Sham-normal Ca group. In addition, there was no significant difference in locomotor activity between any of the groups. These results suggest that OVX or low-calcium diet may impair learning and memory, and that the combination of these factors impaired more markedly when the rats were tested in the eight-arm radial maze. These results may also imply the possibility that a woman in menopause or post-menopause suffers impairment of learning and/or memory when intakes low-calcium diet.

Effects of volatile and intravenous anesthetics on the uptake of GABA, glutamate and dopamine by their transporters heterologously expressed in COS cells and in rat brain synaptosomes

Although the neurotransmitter uptake system is considered a possible target for the presynaptic action of anesthetic agents, observations are inconsistent concerning effects on the transporter and their clinical relevance. The present study examined the effects of volatile and intravenous anesthetics on the uptake of GABA, glutamate and dopamine in COS cells heterologously expressing the transporters for these neurotransmitters and in the rat brain synaptosomes. Halothane and isoflurane, but not thiamylal or thiopental, significantly inhibited uptake by COS cell systems of GABA, dopamine and glutamic acid in a concentration-dependent manner within clinically relevant ranges for anesthesia induced by these agents. Similarly, in synaptosomes halothane and isoflurane but not thiopental significantly suppressed the uptake of GABA and glutamic acid, respectively. These results do not support the hypothesis that volatile and intravenous anesthetics exert their action via specific inhibition of GABA uptake to enhance inhibitory GABAergic neuronal activity. Rather, they suggest that presynaptic uptake systems for various neurotransmitters including GABA may be the molecular targets for volatile anesthetic agents.

Hyperlocomotion during Recovery from Isoflurane Anesthesia Is Associated with Increased Dopamine Turnover in the Nucleus Accumbens and Striatum in Mice

Background It was recently reported that isoflurane increases dopamine release in the striatum in rats both in vivo and in vitro, and that isoflurane inhibits uptake of dopamine in the rat brain synaptosomes. However, the functional role of these effects of isoflurane on dopamine neurons is uncertain. Dopaminergic mechanisms within the nucleus accumbens and striatum play an important role in the control of locomotor activity, and a change in dopamine turnover depends essentially on a change in impulse flow in the dopamine neurons. In this study, the effects of isoflurane on locomotor activity and on dopamine turnover were investigated in discrete brain regions in mice. Methods Mice were placed in individual airtight clear plastic chambers and spontaneously breathed isoflurane in 25% oxygen and 75% nitrogen (fresh gas flow, 4 l/min). Locomotor activity was measured with an Animex activity meter. Animals were decapitated after treatments with or without isoflurane, and the concentrations of monoamines and their metabolites in different brain areas were measured by high‐performance liquid chromatography. Results During the 10 min after the cessation of the 20‐min exposure to isoflurane, there was a significant increase in locomotor activity in animals breathing 1.5% isoflurane but not 0.7% isoflurane. This increase in locomotor activity produced by 1.5% isoflurane was abolished by a low dose of haloperidol (0.1 mg/kg), a dopamine receptor antagonist. Regional brain monoamine assays revealed that 1.5% isoflurane significantly increased the 3,4‐dihydroxyphenylacetic acid:dopamine ratio (one indicator of transmitter turnover) in the nucleus accumbens and striatum, but a concentration of 0.7% did not. This significant increase in dopamine turnover in these regions continued during 20 min after the cessation of the administration of 1.5% isoflurane. Conclusions These results suggest that isoflurane‐induced hyperlocomotion during emergence may be associated with increased dopamine turnover in the nucleus accumbens and striatum.

Inhibitory effects of group II mGluR-related drugs on memory performance in mice

The cAMP/protein kinase A signaling pathway is negatively modulated by group II metabotropic glutamate receptors (mGluRs), and the cross-talk that occurs between these receptors may modulate learning and memory. To examine the relationship among cAMP/PKA-signaling pathway activity, group II mGluRs, and learning and memory, mice were trained to perform a step-through-type passive avoidance task, and 10 min before each avoidance trial the following drugs were injected intracisternally (i.cist.): vehicle (0.05% dimethylsulfoxide); a specific group II mGluR agonist, DCG-IV (1-50 ng/mouse); a specific group II mGluR antagonist, LY341495 (10-300 ng); a selective inhibitor of cAMP-specific phosphodiesterase, rolipram (100-1000 ng); an activator of adenylyl cyclase, forskolin (25-250 ng); a specific inhibitor of PKA, H-89 (150 or 300 ng) or; an activator of protein kinase C, phorbol 12-myristate 13-acetate (PMA 200 ng). DCG-IV (25 and 50 ng) or LY341495 (150 and 300 ng) reduced the latency in the avoidance task. The reduction of latency by DCG-IV was not observed in mice coinjected with DCG-IV (50 ng) together with rolipram (500 ng) or forskolin (25 ng). Conversely, coinjection of LY341495 with 100 or 1000 ng rolipram, or with 25 or 250 ng forskolin tended to potentiate the LY341495-induced shortening of latency. In addition, the reduction of latency by DCG-IV (50 ng) was not observed in mice coinjected with DCG-IV and PMA together. However, the reduction of latency by LY341495 (300 ng) was potentiated when the drug was coadministered with PMA. These results suggest that changes in the cAMP/PKA-signaling pathway, mediated by group II mGluRs, influence memory in the passive avoidance task, and that both the excessive activation and deactivation of this pathway may induce the impairment of learning and memory.