Effects of dopamine D1 modulation of the anterior cingulate cortex in a fear conditioning procedure

Prefrontal dopamine activity is critical for rapid threat avoidance learning

The medial prefrontal cortex (mPFC) is required for learning associations that determine whether animals approach or avoid potential threats in the environment. Dopaminergic (DA) projections from the ventral tegmental area (VTA) to the mPFC carry information, particularly about aversive outcomes, that may inform prefrontal computations. But the role of prefrontal DA in learning based on aversive outcomes remains poorly understood. Here, we used platform mediated avoidance (PMA) to study the role of mPFC DA in threat avoidance learning in mice. We show that activity in VTA-mPFC dopaminergic terminals is required for avoidance learning, but not for escape, conditioned fear, or to recall a previously learned avoidance strategy. mPFC DA is most dynamic in the early stages of learning, and encodes aversive outcomes, their omissions, and threat-induced behaviors. Computational models of PMA behavior and DA activity revealed that mPFC DA influences learning rates and encodes the predictive relationships between cues and adaptive behaviors. Taken together, these data indicate that mPFC DA is necessary to rapidly learn behaviors required to avoid signaled threats, but not for learning cue-threat associations.

The role of histamine H1 receptor in the anterior cingulate cortex on nociception level following acute restraint stress in male rats

Considering the importance of pain and stress, we decided to investigate the intra-anterior cingulate cortex (ACC) microinjection of histamine and mepyramine alone and concurrently on acute pain induced by hot plate following restraint stress in male rats. 24-gauge, 10 mm stainless steel guide cannula was implanted over the ACC in the incised scalp of 4 groups. Restraint stress in healthy rats produced a significant increase (p < .05) in the pain threshold. The simultaneous microinjection of 4 μg/side histamine and 8 μg/side mepyramine as a histaminergic system inverse agonist in healthy nonrestraint animals did not affect the pain threshold. Although Histamine decreased the threshold of pain meaningfully, mepyramine elevated it in a significant manner (p < .05). In the restrained animals, intra-ACC microinjection of histamine produced no significant impact on the pain threshold. However, intra-ACC microinjection of mepyramine before histamine, significantly (p < .01) altered the result and enhanced the threshold of pain. The results of our study demonstrated that histaminergic neurons have an important role in the processing of pain in the ACC following restraint stress.

Effects of Immediate Aversive Stimulation on Haloperidol-Induced Catalepsy in Rats

In animal models, the administration of the dopaminergic D2 antagonist haloperidol affects the nigrostriatal pathway, inducing catalepsy, a state of immobility similar to Parkinson’s disease (PD) bradykinesia and akinesia. In PD, the motor impairments are due to difficulties in selecting and executing motor actions, associated with dopamine loss in basal ganglia and cortical targets. Motor and affective limbic networks seem to be integrated via a striato-nigro-striatal network, therefore, it is not surprising that the motor impairments in PD can be influenced by the patient’s emotional state. Indeed, when exposed to aversive stimuli or life-threatening events, immobile patients are capable of performing sudden movements, a phenomenon known as paradoxical kinesia. Thus, the present study investigated the effects of unconditioned and conditioned aversive stimulation on haloperidol-induced catalepsy in rats. First, male Wistar rats received intraperitoneal administration of saline or haloperidol (1 or 2 mg/kg) and were evaluated in the catalepsy bar test to assess the cataleptic state induced by the different doses of haloperidol over time. Next, we evaluated the effects of two types of unconditioned aversive stimuli–100 lux light (1 and 20 s) or 0.6 mA footshock (1 s)–on the catalepsy. Finally, we evaluated the effects of light conditioned stimuli (Light-CS), previously paired with footshocks, on the cataleptic state. Catalepsy was observed following haloperidol 1 and 2 mg/kg administration. Exposure to footshocks, but not to light, significantly reduced step-down latency during the catalepsy test. Although unconditioned light did not affect catalepsy, paired Light-CS did reduce step-down latency. Here, we have provided evidence of face validity for the study of paradoxical kinesia. In addition to demonstrating that immediate exposure to an aversive stimulus is capable of disrupting the cataleptic state, our findings show that haloperidol-induced catalepsy seems to be differently influenced depending on the modality of aversive stimulation. Our data suggest that the selective recruitment of threat response systems may bypass the dysfunctional motor circuit leading to the activation of alternative routes to drive movement.

Does curcumin have an effect on sleep duration in metabolic syndrome patients?

OBJECTIVE

Sleep-duration is related to obesity. Curcumin can affect behavioral changes that arise from sleep deprivation in animal models. In this study, we assessed the effects of curcumin on sleep-duration in metabolic-syndrome (MetS) patients.

MATERIALS AND METHODS

This study was a double-blind clinical trial in 120 adults with MetS. All participants received crude curcuminoids in a simple formulation (n=40), phospholipidated curcuminoids (n=40) or placebo (n=40) 1 g/day during 6 weeks. Demographic data, anthropometric indices and serum biochemical factors were documented for all volunteers at baseline and after the intervention. A standard questionnaire was used for evaluating physical-activity-level (PAL) and patients' sleep-duration, including night time sleep and daily napping. Based on the time of sleep, sleeping hours were classified into: night time sleep; daily naps and total sleeping hours in 24 hours.

RESULTS

A total of 120 participants aged 38.72±10.05 years old were enrolled into the study. We did not find significant differences in biochemical factors, sleep-duration or PAL at baseline among the 3 groups (p>0·05). Moreover, curcumin did not exert any significant effect on sleep-duration before, or after, adjustment for confounding factors in the overweight and obese individuals, or in total population (p>0.05).

CONCLUSION

The results showed that curcumin does not have an effect on sleep-duration in subject with MetS.

Muscimol-induced inactivation of the anterior cingulate cortex does not impair trace fear conditioning in the rat

Previous studies suggest that trace conditioning depends on the anterior cingulate cortex (ACC). To examine the role of ACC in trace fear conditioning further, 48 rats were surgically prepared for infusion with saline or 62.5 or 125 µg/side muscimol to inactivate ACC reversibly prior to conditioning. A noise stimulus was followed by a 1 mA footshock, with or without a 10-second trace interval between these events in a conditioned suppression procedure. The trace-conditioned groups (10 seconds) showed less test suppression than the control-conditioned groups (0 seconds). Counter to prediction, there was no effect of muscimol infusion on suppression to the noise stimulus in the 10-second trace groups.

Underlying Mechanisms of Psychological Interventions in Magnetic Resonance Imaging and Image-Guided Radiology Procedures

Positive patient care and healthcare facility outcomes are associated with using various psychological interventions during magnetic resonance imaging and interventional radiology procedures. Interventions such as hypnosis, relaxation, guided imagery, and empathic communication can improve anxiety, pain, and hemodynamic stability during procedures, as well as improve claustrophobia and anxiety during magnetic resonance imaging. Little is understood as to the potential underlying mechanisms of how these interventions operate and contribute to positive outcomes. Thus, this article seeks to address that question by integrating autonomic nervous system functioning, neuropsychological concepts, and common factors theory of psychotherapy as potential underlying mechanisms. Opportunities for future directions in the field are also included.

Understanding the role of dopamine in conditioned and unconditioned fear

Pharmacological and molecular imaging studies in anxiety disorders have primarily focused on the serotonin system. In the meantime, dopamine has been known as the neurotransmitter of reward for 60 years, particularly for its action in the nervous terminals of the mesocorticolimbic system. Interest in the mediation by dopamine of the well-known brain aversion system has grown recently, particularly given recent evidence obtained on the role of D2 dopamine receptors in unconditioned fear. However, it has been established that excitation of the mesocorticolimbic pathway, originating from dopaminergic (DA) neurons from the ventral tegmental area (VTA), is relevant for the development of anxiety. Among the forebrain regions innervated by this pathway, the amygdala is an essential component of the neural circuitry of conditioned fear. Current findings indicate that the dopamine D2 receptor-signaling pathway connecting the VTA to the basolateral amygdala modulates fear and anxiety, whereas neural circuits in the midbrain tectum underlie the expression of innate fear. The A13 nucleus of the zona incerta is proposed as the origin of these DA neurons projecting to caudal structures of the brain aversion system. In this article we review data obtained in studies showing that DA receptor-mediated mechanisms on ascending or descending DA pathways play opposing roles in fear/anxiety processes. Dopamine appears to mediate conditioned fear by acting at rostral levels of the brain and regulate unconditioned fear at the midbrain level.

Dopamine D1-like receptors in the dorsomedial prefrontal cortex regulate contextual fear conditioning

RATIONALE

Dopamine D1 receptor (D1R) signalling is involved in contextual fear conditioning. The D1R antagonist SCH23390 impairs the acquisition of contextual fear when administered systemically or infused locally into the dorsal hippocampus or basolateral amygdala.

OBJECTIVES

We determined if state dependency may account for the impairment in contextual fear conditioning caused by systemic SCH23390 administration. We also examined if the dorsomedial prefrontal cortex (dmPFC), nucleus accumbens (NAc), and ventral hippocampus (VH) are involved in mediating the effect of systemic SCH23390 treatment on contextual fear conditioning.

METHODS

In experiment 1, SCH23390 (0.1 mg/kg) or vehicle was given before contextual fear conditioning and/or retrieval. In experiment 2, SCH23390 (2.5 μg/0.5 uL) or vehicle was infused locally into dmPFC, NAc, or VH before contextual fear conditioning, and retrieval was tested drug-free. Freezing was quantified as a measure of contextual fear.

RESULTS

In experiment 1, SCH23390 given before conditioning or before both conditioning and retrieval decreased freezing at retrieval, whereas SCH23390 given only before retrieval had no effect. In experiment 2, SCH23390 infused into dmPFC before conditioning decreased freezing at retrieval, while infusion of SCH23390 into NAc or VH had no effect.

CONCLUSIONS

The results of experiment 1 confirm those of previous studies indicating that D1Rs are required for the acquisition but not retrieval of contextual fear and rule out state dependency as an explanation for these findings. Moreover, the results of experiment 2 provide evidence that dmPFC is also part of the neural circuitry through which D1R signalling regulates contextual fear conditioning.

Rate and Temporal Coding Mechanisms in the Anterior Cingulate Cortex for Pain Anticipation

Pain is a complex sensory and affective experience. Through its anticipation, animals can learn to avoid pain. Much is known about passive avoidance during a painful event; however, less is known about active pain avoidance. The anterior cingulate cortex (ACC) is a critical hub for affective pain processing. However, there is currently no mechanism that links ACC activities at the cellular level with behavioral anticipation or avoidance. Here we asked whether distinct populations of neurons in the ACC can encode information for pain anticipation. We used tetrodes to record from ACC neurons during a conditioning assay to train rats to avoid pain. We found that in rats that successfully avoid acute pain episodes, neurons that responded to pain shifted their firing rates to an earlier time, whereas neurons that responded to the anticipation of pain increased their firing rates prior to noxious stimulation. Furthermore, we found a selected group of neurons that shifted their firing from a pain-tuned response to an anticipatory response. Unsupervised learning analysis of ensemble spike activity indicates that temporal spiking patterns of ACC neurons can indeed predict the onset of pain avoidance. These results suggest rate and temporal coding schemes in the ACC for pain avoidance.

Using curcumin to prevent structural and behavioral changes of medial prefrontal cortex induced by sleep deprivation in rats

Sleep Deprivation (SD) is known to result in a range of neurological consequences in chronically-afflicted subjects. Curcumin, a natural substance, has neuroprotective properties. This study aimed to evaluate the effects of curcumin on the medial Prefrontal Cortex (mPFC) of SD rats. Male rats were arbitrarily assigned to nine groups, including control, curcumin (100 mg/kg/day), olive oil, SD, SD+curcumin, SD+olive oil, grid, grid+curcumin, and grid+olive oil groups. SD was induced by a multiplatform box containing water. After a period of 21 days, the learning and memory of the rats were tested in an eight-arm radial maze. Afterwards, their brains were evaluated using stereological methods. Concomitant treatment of curcumin during SD caused fewer errors during evaluation of the working and reference memory errors in the acquisition and retention phases. The overall volume of the mPFC, Infralimbic Cortex (ILC), Prelimbic Cortex (PLC), Anterior Cingulate Cortex (ACC) and the total number of neurons and glial cells reduced by 20 %-40 % on average in the SD animals in comparison to the control group. This indicated atrophic changes and cell loss in these areas (p < 0.01). The dendrites' length and the number of spines per dendrite also reduced by 35 %-55 % in the SD rats compared to the ones in the control group (p < 0.01). Yet, treatment of the SD animals with curcumin prevented the atrophic changes of the mPFC, cell loss, and dendritic changes (p < 0.05). SD induced structural changes in the mPFC and memory impairment in the rats. However, curcumin could protect their PFC.

The dopamine D1 receptor agonist SKF81297 has dose-related effects on locomotor activity but is without effect in a CER trace conditioning procedure conducted with two versus four trials

In an appetitively motivated procedure, we have previously reported that systemic treatment with the dopamine (DA) D1 receptor agonist SKF81297 (0.4 and 0.8 mg/kg) depressed acquisition at a 2 s inter-stimulus-interval (ISI), suitable to detect trace conditioning impairment. However since DA is involved in reinforcement processes, the generality of effects across appetitively- and aversively-motivated trace conditioning procedures cannot be assumed. The present study tested the effects of SKF81297 (0.4 and 0.8 mg/kg) in an established conditioned emotional response (CER) procedure. Trace-dependent conditioning was clearly shown in two experiments: while conditioning was relatively strong at a 3-s ISI, it was attenuated at a 30-s ISI. This was shown after two (Experiment 1) or four (Experiment 2) conditioning trials conducted in – as far as possible – the same CER procedure. Contrary to prediction, in neither experiment was there any indication that trace conditioning was attenuated by treatment with 0.4 or 0.8 mg/kg SKF81297. In the same rats, locomotor activity was significantly enhanced at the 0.8 mg/kg dose of SKF81297. These results suggest that procedural details of the trace conditioning variant in use are an important determinant of the profile of dopaminergic modulation.

Potentiation rather than distraction in a trace fear conditioning procedure

Trace conditioning procedures are defined by the introduction of a trace interval between conditioned stimulus (CS, e.g. noise or light) offset and unconditioned stimulus (US, e.g. footshock). The introduction of an additional stimulus as a distractor has been suggested to increase the attentional demands of the task and to extend the usefulness of the behavioural model. In Experiment 1, the CS was noise and the distractor was provided by an intermittent light. In Experiment 2, the CS was light and the distractor was provided by an intermittent noise. In both experiments, the introduction of a 10s trace interval weakened associative learning compared with that seen in a 0s delay conditioned group. However, there was no consistent evidence of distraction. On the contrary, in Experiment 1, associative learning was stronger (in both trace and delay conditioned groups) for rats conditioned also in the presence of the intermittent light. In Experiment 2, there was no such effect when the roles of the stimuli were reversed. The results of Experiment 2 did however confirm the particular salience of the noise stimulus. The finding of increased associative learning dependent on salience is consistent with arousal-mediated effects on associative learning.