Ketamine-induced rotation: interaction with GABA-transaminase inhibitors and picrotoxin

Profiling of behavioral effects evoked by ketamine and the role of 5HT2 and D2 receptors in ketamine-induced locomotor sensitization in mice

Ketamine has addictive potential, a troublesome fact due to its promising use as a therapeutic drug. An important phenomenon associated with drug addiction is behavioral sensitization, usually characterized as augmented locomotion. However, other behaviors may also be susceptible to sensitization, and/or interfere with locomotor activity. Thus, this study drew a comprehensive behavioral 'profiling' in an animal model of repeated administration of ketamine. Adult Swiss mice received single daily ketamine injections (30 or 50 mg/Kg, i.p.), which were followed by open field testing for 7 days (acquisition period, ACQ). A ketamine challenge (sensitization test, ST) was carried out after a 5-day withdrawal. Locomotion, rearing, grooming, rotation and falling were assessed during ACQ and ST. All behaviors were affected from the first ACQ day onwards, with no indication of competition between locomotion and the other behaviors. Only locomotion in response to 30 mg/Kg of ketamine both escalated during ACQ and expressed increased levels at ST, evidencing development and expression of locomotor sensitization. Considering the involvement of serotonin 5HT₍₂₎ and dopamine D₍₂₎ receptors on addiction mechanisms, we further tested the involvement of these receptors in ketamine-induced sensitization. Ketanserin (5HT₂ antagonist, 3 mg/Kg, s.c.) prevented ketamine-evoked development of locomotor sensitization. However, ketanserin pretreatment during ACQ failed to inhibit its expression during ST. Raclopride (D₂ antagonist, 0.5 mg/Kg, s.c.) evoked less robust reductions in locomotion but prevented the development of ketamine-evoked sensitization. Pretreatment during ACQ further inhibited the expression of sensitization during ST. These results indicate that a partial overlap in serotonergic and dopaminergic mechanisms underlies ketamine-induced locomotor sensitization.

Effects of midazolam, pentobarbital and ketamine on the mRNA expression of ion channels in a model organism Daphnia pulex

Background

Over the last few decades intensive studies have been carried out on the molecular targets mediating general anesthesia as well as the effects of general anesthetics. The γ-aminobutyric acid type A receptor (GABA_AR) has been indicated as the primary target of general anaesthetics such as propofol, etomidate and isoflurane, and sedating drugs including benzodiazepines and barbiturates. The GABA_AR is also involved in drug tolerance and dependence. However, the involvement of other ion channels is possible.

Methods

Using reverse transcription and quantitative PCR techniques, we systematically investigated changes in the mRNA levels of ion channel genes in response to exposure to midazolam, pentobarbital and ketamine in a freshwater model animal, Daphnia pulex. To retrieve the sequences of Daphnia ion channel genes, Blast searches were performed based on known human or Drosophila ion channel genes. Retrieved sequences were clustered with the maximum-likelihood method. To quantify changes in gene expression after the drug treatments for 4 hours, total RNA was extracted and reverse transcribed into cDNA and then amplified using quantitative PCR.

Results

A total of 108 ion channel transcripts were examined, and 19, 11 and 11 of them are affected by midazolam (100 μM), pentobarbital (200 μM) and ketamine (100 μM), respectively, covering a wide variety of ion channel types. There is some degree of overlap with midazolam- and pentobarbital-induced changes in the mRNA expression profiles, but ketamine causes distinct changes in gene expression pattern.

In addition, flumazenil (10 μM) eliminates the effect of midazolam on the mRNA expression of the GABA_A receptor subunit Rdl, suggesting a direct interaction between midazolam and GABA_A receptors.

Conclusions

Recent research using high throughput technology suggests that changes in mRNA expression correlate with delayed protein expression. Therefore, the mRNA profile changes in our study may reflect the molecular targets not only in drug actions, but also in chronic drug addiction. Our data also suggest the possibility that hypnotic/anesthetic drugs are capable of altering the functions of the nervous system, as well as those non-nerve tissues with abundant ion channel expressions.

The disruptive effects of ketamine on passive avoidance learning in mice: involvement of dopaminergic mechanism

The involvement of dopaminergic mechanisms in ketamine-induced disruption of one trial step-through passive avoidance performance was assessed through the coadministration with the dopamine D1 antagonist SCH 23390, the dopamine D2 antagonist YM-091512 and the dopamine autoreceptor agonist at low doses, apomorphine, in mice. Pretraining (10 min before) administration of ketamine (0; saline, 2.5, 5 and 10 mg/kg SC) dose-dependently reduced the latency in the retention trial conducted 24 h after the training. However, ketamine did not affect the retention latency when administered immediately after the training or prior to retention. YM-09151-2 (0.01 and 0.03 mg/kg SC) and apomorphine (0.01 and 0.03 mg/kg SC), but not SCH 23390 (0.01 and 0.03 mg/kg SC), ameliorated the impaired reduction by ketamine (10 mg/kg) in a dose-dependent manner. These results suggest that ketamine obstructs the acquisition of the passive avoidance task, and that this effect is induced by stimulation of dopamine D2 receptors through dopamine release from the presynaptic terminals.

Prenatal chlordiazepoxide effects on metrazol seizures and benzodiazepine receptors density in adult albino rats

Adult offsprings of rats treated with daily injection of chlordiazepoxide (10 mg/kg, i.p.) during pregnancy showed a significant decrease in benzodiazepine receptors in the cortex and the cerebellum without apparent changes in receptor affinity. A reduced susceptibility to metrazol-induced epileptogenesis paralleled this change. These findings are discussed in relation to the differential vulnerability of various types of benzodiazepine receptors.

Ketamine-induced locomotion in rats in an open-field

The effects of ketamine on locomotion in an open-field were determined in hooded rats. Animals were given intraperitoneal injections of saline, or of 1, 10, 50 or 100 mg ketamine/kg body weight on separate days. Open-field behavior was examined for 60 min following injection. The 50 mg/kg dose of ketamine produced an increase in locomotion which peaked approximately 30 min after injection. A cataleptic immobility produced by the 100 mg/kg dose was followed by postanesthetic locomotion. The ketamine-induced locomotion consisted largely of ambulation about the perimeter of the field and was accompanied by ataxia, but included relatively little tight circling (rotation) during the peak of activity. Comparisons with the results of past research suggests that test-chamber design influences the type of locomotion induced by ketamine.

Responses of striatal neurons to anesthetics and analgesics in freely moving rats

The effects of anaesthetics and analgesics on striatal neurons were examined in freely moving rats by recording extracellular action potentials of neurons in the striatum. Spontaneous multiple unit activity was reduced to less than 20% of control firing rates following either pentobarbital 35 mg/kg i.p., halothane 3%, chloral hydrate 400 mg/kg i.p., or urethane 1.5 g/kg i.p. Morphine 15 mg/kg i.p., decreased striatal neuronal firing whereas ketamine, 50 mg/kg i.p., excited striatal neurons. The only analgesic agent tested that did not significantly affect striatal neuronal firing was nitrous oxide (70% N2O/30% O2). These findings demonstrate that nitrous oxide is a suitable analgesic which can be used to alleviate stress and pain associated with immobilization procedures without appreciably altering spontaneous striatal discharge rates.

Ketamine: convulsant or anti-convulsant?

Ketamine hydrochloride in doses producing narcotic-cataleptic effects (50--100 mg/kg, IP) reduced the intensity of picrotoxin convulsions and eliminated seizures caused by metrazol administration. Subcataleptic doses (5--20 mg/kg) increased the duration of mitigated convulsive symptoms (abortive grand mal fits, jerks) especially those evoked by picrotoxin. Narcotic-cateleptic doses of ketamine considerably increased the duration of the period of single and multiple jerks produced by picrotoxin administration. Both convulsants transformed 1--2 Hz "ketamine complexes" into 2--4 Hz Wave spike discharges which appeared in a quasi-periodic fashion alternating with periods of relatively suppressed electrocortical activity. Electroencephalographic grand mal patterns were typically dissociated from behavioral manifestations under 50--100 mg/kg of ketamine, followed by a short period of postictal depression and a rapid recovery of preseizure electrographic patterns. Findings suggest that mechanisms involved in seizure alleviation may be responsible for sustaining mitigated convulsive phenomena. Neuro-chemical processes underlying antiepileptic ketamine potency remain unknown.