Effects of midazolam on acquisition and extinction of conditioned taste aversion memory in rats

Activation of multiple neuromodulatory systems in alert rats acquiring conditioned taste aversion revealed by positron emission tomography

Conditioned taste aversion (CTA) is an essential ability for animals to consume food safely and is regulated by neuromodulatory systems including the dopamine, noradrenaline, serotonin, and acetylcholine systems. However, because few studies focused on a comprehensive understanding of whole-brain activities, how these neuromodulators contribute to the process of CTA remains an open issue. 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) can visualize activated regions within the whole brain simultaneously and noninvasively. This study aimed to understand the mechanisms of CTA, especially focusing on the retrieval process after CTA acquisition by FDG-PET imaging. CTA was established in rats who received an intraoral application of saccharin solution (IOAS) on the first day (Day 1), a LiCl i.p. injection after an IOAS on Day 2, and an IOAS on Day 3 (CTA group). The subtraction images of Day 3 of the SHAM group, which received a 0.9 % NaCl (saline) injection instead of a LiCl on Day 2, from those of Day 3 of the CTA group revealed increases in FDG signals in multiple brain regions including the substantia nigra, ventral tegmental area, locus coeruleus, dorsal raphe, and nucleus basalis magnocellularis, in addition to the hippocampus and nociception-related regions, including the parabrachial nucleus and solitary nucleus. On the other hand, the visceral pain induced by the LiCl injection increased FDG signals in the primary and secondary somatosensory and insular cortices in addition to the parabrachial nucleus and solitary nucleus. These results suggest that the retrieval process of CTA induces brain regions producing neuromodulators and pain-related brainstem.

Midazolam impairs the retrieval of conditioned taste aversion via opioidergic transmission in mice

Midazolam is a benzodiazepine agonist that affects the acquisition, retention, and retrieval of malaise-induced conditioned taste aversion (CTA) in rats. Our previous study suggested that the palatability-enhancing rather than amnesic effects of midazolam were responsible for impaired retrieval of conditioned aversion to palatable conditioned stimuli (CSs). However, it remains unclear whether this effect is opioid-dependent. In the present study, we examined the involvement of opioid signaling with the ability of peripheral midazolam administration to transiently impair CTA retrieval in mice. CTA was established by pairing 5mM saccharin ingestion (conditioned stimulus, CS) with an intraperitoneal (i.p.) injection of 0.15M lithium chloride (LiCl, 2% body weight) (unconditioned stimulus) for two consecutive days. Conditioned mice that received midazolam (1.5mg/kg, i.p.) before the first retention test consumed significantly more saccharin (CS) than conditioned mice that received vehicle (phosphate-buffered physiological saline, PBS; i.p.). On the next day, both conditioned groups showed strong aversions to the CS. Next, naloxone, an opioid receptor antagonist, was peripherally administered prior to the midazolam injection before the retention test. Pre-administration of naloxone but not PBS attenuated midazolam-induced increases in CS intake. Finally, we examined aversive orofacial taste reactions (TRs) to an oral infusion of the CS with pre-administration of naloxone or PBS prior to midazolam using a taste reactivity test. Conditioned mice that received midazolam showed significantly longer latencies to express aversive orofacial TRs than those that received PBS. Pre-administration of naloxone eliminated the effect of midazolam on latency to express aversive TRs. Taken together, these data suggest that midazolam activates opioidergic transmission and opioid-dependent palatability enhancement of the CS to eliminate conditioned aversion to a sweet taste.

Limitation in monitoring depth of anesthesia: a case report

Although we describe a clinical situation that most likely occurs in hundreds of operatory rooms in the world, we report this case as provocation. It concerns an unexpected awakening from an appropriate depth of anesthesia, although the BIS monitor showed a BIS index of less than 50 for a prolonged period before and after the event. Approximately 30 min after induction of anesthesia, the patient had a hypothetic sudden arousal of consciousness, with spontaneous movements, facial muscle activation, intolerance to the tracheal tube, and tearing. After immediate intravenous administration of midazolam (4 mg), the patient returned to a depth of anesthesia status, and surgery was completed uneventfully. The patient had no recall of the event when questioned during the episode, at emergence, or at 24 h, 36 h, and 7 days after surgery. Were these events spinal reflexes to pain or stimulation although the cortex was still anesthetized? Maybe this is the more rational explanation. Was the patient awake but not aware? Is it possible that our patient experienced only a transient arousal from consciousness, and that he did not have recall because the arousal time was short and we blocked memory consolidation? The latter hypothesis provides an opportunity to discuss the evidence that at the moment there is no device to assess the depth of anesthesia. We also focus on the possibility of interfering with memory processing under anesthesia.

Gene Network Analysis in Amygdala following Taste Aversion Learning in Rats

Conditioned taste aversion (CTA) is an adaptive behavior that benefits survival of animals including humans and also serves as a powerful model to study the neural mechanisms of learning. Memory formation is a necessary component of CTA learning and involves neural processing and regulation of gene expression in the amygdala. Many studies have been focused on the identification of intracellular signaling cascades involved in CTA, but not late responsive genes underlying the long-lasting behavioral plasticity. In this study, we explored in silico experiments to identify persistent changes in gene expression associated with CTA in rats. We used oligonucleotide microarrays to identify 248 genes in the amygdala regulated by CTA. Pathway Studio and IPA software analyses showed that the differentially expressed genes in the amygdala fall in diverse functional categories such as behavior, psychological disorders, nervous system development and function, and cell-to-cell signaling. Conditioned taste aversion is a complex behavioral trait which involves association of visceral and taste inputs, consolidation of taste and visceral information, memory formation, retrieval of stored information, and extinction phase. In silico analysis of differentially expressed genes is therefore necessary to manipulate specific phase/stage of CTA to understand the molecular insight.

The memory stages of a spatial Y-maze task are not affected by a low dose of ketamine/midazolam

Anesthetics, such as the ketamine/midazolam combination, are used in research with animals and in human clinical practice; thus, it is essential to clarify the potential effects of these anesthetics on memory. This study aimed to evaluate how a low dose of the ketamine/midazolam combination affects the acquisition, consolidation, or recall of a spatial memory task. Thirty-three adult male C57BL/6 mice were divided into four treatment groups: unanesthetized control animals and three groups of animals treated with 40 mg/kg of ketamine and 10mg/kg of midazolam administered in a single intraperitoneal injection. The different treatment groups received the same anesthetic dose at different time points, to study the acquisition, consolidation, and recall of spatial memory in the Y-maze task. The percentage of correct choices was measured. Six mice were killed 4 days and 12 days after anesthesia for histopathological analyses. There were no differences between treatment and control groups regarding the acquisition of spatial memory, measured as the slope of the learning curve, or in the percentage of correct choices in the consolidation or recall periods of the task. Similarly, no differences were detected between groups regarding the number of cells per square millimeter in the visual and retrosplenial cortex, in the dentate gyrus, and in the CA1 and CA3 regions of the hippocampus. Hence, a low dose of the ketamine/midazolam combination did not impair memory processes or brain integrity in adult mice, suggesting that this combination is unlikely to cause cognitive complications.

The effect of androgen on the retention of extinction memory after conditioned taste aversion in mice

Conditioned taste aversion (CTA) induced by the application of a novel taste such as sodium saccharin (Sac) as the conditioned stimulus (CS) and a malaise-inducing agent as the unconditioned stimulus (US), results in acquisition of CTA memory to Sac. In contrast, CTA is extinguished by repeated presentations of the CS without the US, resulting in acquisition of the extinction memory. We examined the effects of androgenic hormones on acquisition and retention of extinction memory in mice. We gonadectomized sexually immature mice and continuously administered androgens to these animals. After sexual maturation, the mice underwent a conditioning period followed by an extinction period. Retrieval tests revealed that the androgen-treated group showed significantly greater retention of extinction memory than the non-treated group 5 weeks later, whereas such significant difference was not observed in acquisition of extinction memory. These results demonstrate the enhancing effect of androgens on retention of extinction memory.

The anaesthetic combination of ketamine/midazolam does not alter the acquisition of spatial and motor tasks in adult mice

The ketamine/midazolam association of a dissociative with a sedative agent is used for the induction and maintenance of anaesthesia in laboratory animals. Anaesthesia may interfere with research results through side-effects on the nervous system, such as memory impairment. It is known that ketamine and midazolam affect cognition; however, their effects have not been clarified when used in a context of balanced anaesthesia. Thus, this study evaluated the effects of ketamine/midazolam on the acquisition of motor and of a spatial memory task in adult mice. Twenty-eight C57BL/6 adult male mice were divided into three groups: untreated control, treated with ketamine/midazolam (75 mg/kg / 10 mg/kg) and treated with midazolam (10 mg/kg) groups. Respiratory rate, heart rate and systolic pressure were measured every 5 min in the animals treated with ketamine/midazolam, as this was the only group that exhibited loss of the righting reflex. One day after treatment, animals were tested in the open field, rotarod and radial arm maze. There were no differences between treatments regarding open-field activity, rotarod performance or number of working and reference memory errors in the radial arm maze task. In conclusion, the learning process of spatial and motor tasks was not disrupted by the anaesthetic combination of ketamine/midazolam. These results suggest its safe use in adult mice in projects where acquisition of a spatial and motor task is necessary.

Behavioral and neural analysis of GABA in the acquisition, consolidation, reconsolidation, and extinction of fear memory

The current review systematically documents the role of gamma-amino-butyric acid (GABA) in different aspects of fear memory-acquisition and consolidation, reconsolidation, and extinction, and attempts to resolve apparent contradictions in the data in order to identify the function of GABA(A) receptors in fear memory. First, numerous studies have shown that pre- and post-training administration of drugs that facilitate GABAergic transmission disrupt the initial formation of fear memories, indicating a role for GABA(A) receptors, possibly within the amygdala and hippocampus, in the acquisition and consolidation of fear memories. Similarly, recent evidence indicates that these drugs are also detrimental to the restorage of fear memories after their reactivation. This suggests a role for GABA(A) receptors in the reconsolidation of fear memories, although the precise neural circuits are yet to be identified. Finally, research regarding the role of GABA in extinction has shown that GABAergic transmission is also disruptive to the formation of newly acquired extinction memories. We argue that contradictions to these patterns are the result of variations in (a) the location of drug infusion, (b) the dosage of the drug and/or (c) the time point of drug administration. The question of whether these GABA-induced memory deficits reflect deficits in retrieval is discussed. Overall, the evidence implies that the processes mediating memory stability consequent to initial fear learning, memory reactivation, and extinction training are dependent on a common mechanism of reduced GABAergic neurotransmission.