The attenuation of suppression of motility by triazolam in the conditioned fear stress task is exacerbated by ethanol in mice

Mechanisms of alcohol influence on fear conditioning: a computational model

A connection between stress-related illnesses and alcohol use disorders is extensively documented. Fear conditioning is a standard procedure used to study stress learning and links it to the activation of amygdala circuitry. However, the connection between the changes in amygdala circuit and function induced by alcohol and fear conditioning is not well established. We introduce a computational model to test the mechanistic relationship between amygdala functional and circuit adaptations during fear conditioning and the impact of acute vs. repeated alcohol exposure. In accordance with experiments, both acute and prior repeated alcohol decreases speed and robustness of fear extinction in our simulations. The model predicts that, first, the delay in fear extinction in alcohol is mostly induced by greater activation of the basolateral amygdala (BLA) after fear acquisition due to alcohol-induced modulation of synaptic weights. Second, both acute and prior repeated alcohol shifts the amygdala network away from the robust extinction regime by inhibiting the activity in the central amygdala (CeA). Third, our model predicts that fear memories formed in acute or after chronic alcohol are more connected to the context. Thus, the model suggests how circuit changes induced by alcohol may affect fear behaviors and provides a framework for investigating the involvement of multiple neuromodulators in this neuroadaptive process.

Dopamine Restores Limbic Memory Loss, Dendritic Spine Structure, and NMDAR-Dependent LTD in the Nucleus Accumbens of Alcohol-Withdrawn Rats

Alcohol abuse leads to aberrant forms of emotionally salient memory, i.e., limbic memory, that promote escalated alcohol consumption and relapse. Accordingly, activity-dependent structural abnormalities are likely to contribute to synaptic dysfunctions that occur from suddenly ceasing chronic alcohol consumption. Here we show that alcohol-dependent male rats fail to perform an emotional-learning task during abstinence but recover their functioning by l-3,4-dihydroxyphenylalanin (l-DOPA) administration during early withdrawal. l-DOPA also reverses the selective loss of dendritic "long thin" spines observed in medium spiny neurons of the nucleus accumbens (NAc) shell of alcohol-dependent rats during abstinence, as well as the reduction in tyrosine hydroxylase immunostaining and postsynaptic density-95-positive elements. Patch-clamp experiments in NAc slices reveal that both in vivo systemic l-DOPA administration and in vitro exposure to dopamine can restore the loss of long-term depression (LTD) formation, counteract the reduction in NMDAR-mediated synaptic currents and rectify the altered NMDAR/AMPAR ratio observed in alcohol-withdrawn rats. Further, in vivo microdialysis experiments show that blunted dopaminergic signaling is revived after l-DOPA treatment during early withdrawal. These results suggest a key role of an efficient dopamine signaling for maintaining, and restore, neural trophism, NMDA-dependent LTD, and ultimately optimal learning.SIGNIFICANCE STATEMENT Blunted dopamine signaling and altered glutamate connectivity in the nucleus accumbens represent the neuroanatomical basis for the impairment in aversive limbic memory observed during withdrawal in alcohol dependence. Supplying l-DOPA during withdrawal re-establishes synaptic morphology and functional neuroadaptations, suggesting a complete recovery of nucleus accumbens glutamatergic synaptic plasticity when dopamine is revived. Importantly, restoring dopamine transmission allows those synapses to encode emotionally relevant information and rescue flexibility in the neuronal circuits that process limbic memory formation. Under these conditions, drugs capable of selectively boosting the dopaminergic function during the "fluid" and still responsive state of the early withdrawn maladaptive synapses may help in the treatment of alcohol addiction.

Rapid reacquisition of contextual fear following extinction in mice: effects of amount of extinction, acute ethanol withdrawal, and ethanol intoxication

RATIONALE

Many studies have found that ethanol intoxication and withdrawal impair initial acquisition or extinction of learned behaviors. Rapid reconditioning following extinction is a form of post-extinction re-emergence of conditioned behavior that has not been studied for its interaction with ethanol intoxication or withdrawal.

OBJECTIVES

The goals of this paper were to define the parameters that allow rapid post-extinction reacquisition of fear in mice and investigate the effect of acute ethanol withdrawal and intoxication on acquisition, extinction, and post-extinction reconditioning.

METHODS

We examined acquisition, extinction, and post-extinction reconditioning of contextual fear in male C57BL/6 mice. Acute ethanol withdrawal occurred 6 h following a 4 g/kg injection of 20% ethanol and acute ethanol intoxication occurred 5 min following a 1.5 g/kg injection of 20% ethanol.

RESULTS

A weak context-shock pairing caused rapid reacquisition of conditioned freezing following moderate, but not extensive extinction. Acute ethanol intoxication impaired initial conditioning and acute ethanol withdrawal impaired rapid reacquisition after extinction, but not reconditioning or extinction itself.

CONCLUSIONS

These findings show that rapid reconditioning occurs following moderate but not extensive extinction in C57BL/6J mice. Additionally, acute ethanol withdrawal and intoxication may differentially affect different phases of conditioning. Results are discussed in terms of current ideas about post-extinction behavior and ethanol's effects on memory.

Substance abuse, memory, and post-traumatic stress disorder

A large body of literature demonstrates the effects of abused substances on memory. These effects differ depending on the drug, the pattern of delivery (acute or chronic), and the drug state at the time of learning or assessment. Substance use disorders involving these drugs are often comorbid with anxiety disorders, such as post-traumatic stress disorder (PTSD). When the cognitive effects of these drugs are considered in the context of the treatment of these disorders, it becomes clear that these drugs may play a deleterious role in the development, maintenance, and treatment of PTSD. In this review, we examine the literature evaluating the cognitive effects of three commonly abused drugs: nicotine, cocaine, and alcohol. These three drugs operate through both common and distinct neurobiological mechanisms and alter learning and memory in multiple ways. We consider how the cognitive and affective effects of these drugs interact with the acquisition, consolidation, and extinction of learned fear, and we discuss the potential impediments that substance abuse creates for the treatment of PTSD.

SSRIs and conditioned fear

Among drugs that act on serotonergic neurotransmission, selective serotonin (5-HT) reuptake inhibitors (SSRIs) are now the gold standard for the treatment of anxiety disorders. The precise mechanisms of the anxiolytic actions of SSRIs are unclear. We reviewed the literature related to the effects of SSRIs and the neurochemical changes of 5-HT in conditioned fear. Acute SSRIs and 5-HT(1A) receptor agonists reduced the acquisition and expression of contextual conditioned fear. Chronic SSRI administration enhanced anxiolytic-like effects. Microinjection studies revealed the amygdala as the target brain region of both classes of serotonergic drugs, and the hippocampus as the target of 5-HT(1A) receptor agonists. These findings highlight the contribution of post-synaptic 5-HT receptors, especially 5-HT(1A) receptors, to the anxiolytic-like effects of serotonergic drugs. These results support the new 5-HT hypothesis of fear/anxiety: the facilitation of 5-HT neurotransmission ameliorates fear/anxiety. Furthermore, these behavioral data provide a new explanation of neurochemical adaptations to contextual conditioned fear: increased 5-HT transmission seems to decrease, not increase, fear.

Superadditive effects of ethanol and flunitrazepam: implications of using immunopharmacotherapy as a therapeutic

While benzodiazepine intoxication alone may elicit sedative and antianxiety effects, alcohol coingestion greatly amplifies this central nervous system depression. As a result, this drug combination gained notoriety for its role in cases of facilitated sexual assault and fatal overdose. We previously validated the ability of the novel antiflunitrazepam monoclonal antibody (mAb) RCA3A3 to bind flunitrazepam (FLU) in vivo and block FLU-induced impairment of locomotion and memory. A therapeutically relevant application of this high affinity mAb (K(d,app) = 200 nM), however, is to the more tenuous indication of flunitrazepam (FLU) and alcohol cointoxication. Employing a murine behavioral model, passive immunization with mAb RCA3A3 before injection of ethanol (EtOH: low-dose, 1 g/kg, or high-dose, 1.5 g/kg), FLU (0.06 mg/kg), or a cocktail of both drugs offered partial to full restoration of motor activity levels in co-drug treated and FLU-treated mouse groups (n = 12), respectively. Whereas all drug treatments left contextual learning intact, auditory cued learning was severely disrupted. Prophylactic administration of mAb RCA3A3 prevented this deficit in cued learning in FLU-treated mice but not in the FLU- and EtOH-treated mice, in which co-drug exposure exacerbated the impairment in cued fear conditioning. To substantiate this finding, a dose-response study was performed, and the changes in locomotor activity incurred by different FLU (low-dose, 0.06 mg/kg, or high-dose, 0.09 mg/kg), EtOH (1.0 g/kg, 1.5 g/kg), and mAb RCA3A3 (14.5 mg/kg, 21.8 mg/kg) dose combinations illustrated the potentiation in motor effects by concomitant exposure to FLU and EtOH. Thus, motor activity and fear conditioning results demonstrated that both the amount of FLU left unbound by antibody and the pharmacological additivity between FLU and EtOH, a GABA mimetic, were limiting factors in the therapeutic efficacy of mAb RCA3A3. In sum, our study highlights the complex nature of psychomotor impairment upon co-drug versus singular drug exposure, which may pose a unique challenge to therapeutic treatment.

Potentiation of Ethanol in Spatial Memory Deficits Induced by Some Benzodiazepines

Triazolam caused no significant increase in the total error at 0.05 and 0.1 mg/kg. However, at 0.2 mg/kg, it caused a significant increase in total error. Almost the same findings were observed with brotizolam and rilmazafone. That is, at 0.2 and 0.5 mg/kg of brotizolam, 0.5 and 1.0 mg/kg of rilmazafone caused no significant increase in the total error. However, brotizolam at 1.0 mg/kg and rilmazafone at 2.0 mg/kg caused a significant increase in total error. Triazolam (0.05 mg/kg) and ethanol (1.0 g/kg) showed no significant effect on the numbers of errors when used alone separately, but the simultaneous use of triazolam and ethanol caused a significant increase in total error. Almost the same findings were observed with the coadministration of brotizolam (0.2 mg/kg) or rilmazafone (0.5 mg/kg) with ethanol. These results clearly indicate that all the short-acting benzodiazepines used in the study showed potentiation by ethanol in spatial memory deficits in mice.

Characterization of the anxiolytic-like effects of fluvoxamine, milnacipran and risperidone in mice using the conditioned fear stress paradigm

It has been known that rodents exhibit the immobility when tested in the same environment in which they had been previously exposed to aversive stimuli. This behavior is called conditioned fear stress-induced freezing behavior, and has been used as a model of anxiety. Using this animal model, the present study tried to characterize the anxiolytic-like effects of fluvoxamine, a selective serotonin reuptake inhibitor, milnacipran, a serotonin noradrenaline reuptake inhibitor and risperidone, an atypical antipsychotic in mice. Fluvoxamine (1.25-10 mg/kg, intraperitoneally (i.p.)) and milnacipran (0.5-4 mg/kg, i.p.) each dose-dependently and significantly suppressed the conditioned fear stress-induced freezing behavior in mice, an indicator of anxiety, and milnacipran had a weaker effect than fluvoxamine. While risperidone also significantly suppressed freezing behavior at a low dose (0.01 mg/kg, i.p.), a high dose (0.04 mg/kg, i.p.) decreased spontaneous motor activity. On the contrary, sulpiride, a typical antipsychotic (2-8 mg/kg, i.p.), did not affect freezing behavior. In a combination study, the suppressive effect of a low dose of risperidone (0.01 mg/kg, i.p.) on freezing behavior was significantly antagonized by the co-administration of low/middle doses of fluvoxamine (1.25 and 2.5 mg/kg, i.p.), whereas a high dose of fluvoxamine (10 mg/kg, i.p.) was unaffected. Additionally, the co-administration of milnacipran (0.5-2 mg/kg, i.p.) also tended to inhibit the suppressive effect of risperidone (0.01 mg/kg, i.p.). These findings indicate that fluvoxamine, milnacipran and risperidone may each be clinically effective at treating anxiety disorders, but their effects may be attenuated in combination with other medications.

Ethanol disrupts fear conditioning in C57BL/6 mice

Ethanol has been demonstrated to disrupt numerous forms of learning. For example, ethanol disrupts fear conditioning in rats. Surprisingly, the opposite result was reported for mice. Because of the importance of mouse models in ethanol research and the predominance of transgenic mice generated on a C57BL/6 background, the present study examined the effects of acute ethanol administration on fear conditioning in C57BL/6 mice. Fear conditioning was chosen because of the apparent contradiction in results between mice and rats, because of its popularity in assessing forebrain-dependent learning and because the task examines two types of learning: (i) the hippocampus-dependent contextual learning and (ii) the hippocampus-independent conditioned stimulus-unconditioned stimulus learning. Dose-response curves were generated for ethanol (0.5, 1.0 and 1.5 g/kg) given on either training day, testing day, or both days. Ethanol, in a dose-dependent manner, disrupted fear conditioning when given on training day or given on both training and testing days. Ethanol given on testing day only did not disrupt fear conditioning. The present results demonstrate that ethanol disrupts fear conditioning in C57BL/6 mice.

Pretreatment with diazepam suppresses the reduction in defensive freezing behavior induced by fluvoxamine in the conditioned fear stress paradigm in mice

The effects of the selective serotonin (5-hydroxytryptamine (5-HT)) reuptake inhibitor fluvoxamine, given alone or in combination with the benzodiazepine anxiolytic diazepam on the defensive freezing behavior of mice in the conditioned fear stress paradigm were examined. Fluvoxamine (5-20 mg/kg, i.p.) induced a dose-dependent reduction in freezing behavior. In contrast, while low doses of diazepam (0.125 and 0.25 mg/kg, i.p.) reduced the freezing behavior, such effects were not observed with high doses of diazepam (0.5 and 1 mg/kg, i.p.). In the combination study, fluvoxamine (20 mg/kg, i.p. ) did not reduce the freezing behavior in mice that had been pretreated with diazepam (0.125-1 mg/kg, i.p.). None of the doses of fluvoxamine and diazepam used in the present study had any effects on motor activity under non-stressed conditions. These results suggest that benzodiazepines may negatively influence the clinical efficacy of selective 5-HT reuptake inhibitors in the treatment of anxiety disorders.

Neuroactive neurosteroids as endogenous effectors for the sigma1 (sigma1) receptor: pharmacological evidence and therapeutic opportunities

Neuroactive neurosteroids, including progesterone, allopregnanolone, pregnenolone and dehydroepiandrosterone, represent steroid hormones synthesized de novo in the brain and acting locally on nervous cells. Neurosteroids modulate several neurotransmitter systems such as gamma-aminobutyric acid type A (GABA(A)), N-methyl-D-aspartate (NMDA) and acetylcholine receptors. As physiologic consequences, they are involved in neuronal plasticity, learning and memory processes, aggression and epilepsy, and they modulate the responses to stress, anxiety and depression. The sigma1-receptor protein was recently purified and its cDNA was cloned in several species. The amino-acid sequences are structurally unrelated to known mammalian proteins, but shared homology with a fungal sterol C8-C7 isomerase. The sigma1-receptor ligands exert a potent neuromodulation on excitatory neurotransmitter systems, including the glutamate and cholinergic systems. Consequently, selective sigma1 agonists show neuroprotective properties and beneficial effects in memory processes, stress and depression. The evidence of a direct interaction between neurosteroids and sigma1 receptors was first suggested by the ability of several steroids to inhibit the binding of sigma1-receptor radioligands in vitro and in vivo. A crossed pharmacology between neurosteroids and sigma1-receptor ligands was described in several physiological tests and behavioral responses. This review will detail the recent evidence for a common mechanism of action between neurosteroids and sigma1-receptor ligands and focus on the potential therapeutic interests of such interaction in the physiopathology of learning and memory impairments, stress, depression and neuroprotection.

Developmental and pharmacological features of mouse emotional piloerection

We demonstrated emotional piloerection in mice given conditioned fear stress by means of a pass-through apparatus. The emotional piloerection was first assessed in mice of different ages. The results showed that the piloerection changed with age. Pharmacological studies showed that the piloerection was inhibited by an alpha 1-adrenoceptor antagonist prazosin, but, surprisingly, was not inhibited by anxiolytic diazepam. These findings strongly suggest that the neuronal system of piloerection is different from that of freezing behavior, and that the neuronal system of piloerection develops with age.