No abstract

In drug addiction, environmental stimuli previously associated with cocaine use readily elicit cocaine‐associated memories, which persist long after abstinence and trigger cocaine craving and consumption. Although previous studies suggest that the medial prefrontal cortex (mPFC) is involved in the expression of cocaine‐addictive behaviors, it remains unclear whether excitatory and inhibitory neurons in the mPFC are causally related to the formation and retrieval of cocaine‐associated memories. To address this issue, we used the designer receptors exclusively activated by designer drugs (DREADD) technology combined with a cocaine‐induced conditioned place preference (CPP) paradigm. We suppressed mPFC neuronal activity in a cell‐type– and timing‐dependent manner. C57BL/6J wild‐type mice received bilateral intra‐mPFC infusion of an adeno‐associated virus (AAV) expressing inhibitory DREADD (hM4Di) under the control of CaMKII promotor to selectively suppress mPFC pyramidal neurons. GAD67‐Cre mice received bilateral intra‐mPFC infusion of a Cre‐dependent AAV expressing hM4Di to specifically silence GABAergic neurons. Chemogenetic suppression of mPFC pyramidal neurons significantly attenuated both the acquisition and expression of cocaine CPP, while suppression of mPFC GABAergic neurons affected neither the acquisition nor expression of cocaine CPP. Moreover, chemogenetic inhibition of mPFC glutamatergic neurons did not affect the acquisition and expression of lithium chloride‐induced conditioned place aversion. These results suggest that the activation of glutamatergic, but not GABAergic, neurons in the mPFC mediates both the formation and retrieval of cocaine‐associated memories.

No abstract

Cocaine-associated environmental cues elicit craving and relapse to cocaine use by recalling the rewarding memory of cocaine. However, the neuronal mechanisms underlying the expression of cocaine-associated memory are not fully understood. Here, we investigated the possible contribution of γ-aminobutyrate (GABA) ergic neurons in the nucleus accumbens (NAc), a key brain region associated with the rewarding and reinforcing effects of cocaine, to the expression of cocaine-associated memory using the conditioned place preference ( Key words nucleus accumbens; cocaine; conditioned place preference; designer receptors exclusively activated by designer drugs; γ-aminobutyrate (GABA); mouse Cocaine addiction is a chronic relapsing disease characterized by compulsive drug seeking and taking. The rewarding and reinforcing properties of cocaine are readily associated with the environmental contexts where cocaine is experienced. The cocaine-associated environmental cues elicit craving and relapse to cocaine use by recalling the rewarding memory of cocaine. However, the mechanisms by which environmental cues induce the expression of cocaine-associated memory are not fully understood. To investigate these mechanisms, the conditioned place preference (CPP) test, a widely used Pavlovian conditioning paradigm is considered to be useful. 1) In the conditioning session of the CPP, animals learn to associate the rewarding effects of cocaine and a neutral environmental context that has been paired with cocaine administration by investigators. Thereafter, in the posttest session, animals exhibit a preference for the cocaine-paired environment, likely due to the expression of cocaine-associated memory. Although previous studies revealed that the mesocorticolimbic reward system consisting of the ventral tegmental area (VTA), medial prefrontal cortex (mPFC), and nucleus accumbens (NAc) is involved in the expression of cocaine-associated memory, 2-4) the precise neuronal and circuit mechanisms underlying this behavior remain unclear.The NAc plays an important role in the expression of cocaine-seeking behavior and cocaine-associated memory. [5][6][7] Recent studies have shown that activation of glutamatergic projections from the prelimbic subregion (PL) of the mPFC to the NAc core is required for cue-induced reinstatement of cocaine seeking. 8,9) In addition, intra-NAc infusion of an AMPA receptor antagonist was found to block the expression of cocaine CPP. 2) These findings suggest that excitation of the NAc is involved in the expression of cocaine-associated memory. Considering that the vast majority of NAc neurons are γ-aminobutyrate (GABA) ergic medium spiny neurons (MSNs), 10,11) these GABAergic neurons are likely to contribute to the expression of cocaine CPP. Thus, in the present study, we addressed this issue using designer receptors exclusively activated by designer drugs (DREADD) technology. 12) We selectively expressed G i/o -coupled inhibitory DREADD hM4Di in NAc GABAergic neurons of vesicular GABA transporterCre (vGAT-Cre) mic...

Nicotine enhances attention, working memory and recognition. One of the brain regions associated with these effects of nicotine is the medial prefrontal cortex (mPFC). However, cellular mechanisms that induce the enhancing effects of nicotine remain unclear. To address this issue, we performed whole-cell patch-clamp recordings from mPFC layer 5 pyramidal neurons in slices of C57BL/6J mice. Shortly (approx. 2 min) after bath application of nicotine, the number of action potentials, which were elicited by depolarizing current injection, was increased, and this increase persisted for over 5 min. The effect of nicotine was blocked by the α4β2 nicotinic acetylcholine receptor (nAChR) antagonist dihydro-β-erythroidine, α7 nAChR antagonist methyllycaconitine, or intracellular perfusion with the Ca 2 chelator 1,2-bis(2-aminophenoxy) ethane-N,N,N′,N′-tetraacetic acid (BAPTA). Additionally, the voltage-dependent potassium 7 (Kv7) channel blocker, 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone dihydrochloride (XE-991), as well as nicotine, shortened the spike threshold latency and increased the spike numbers. By contrast, the Kv7 channel opener, retigabine reduced the number of firings, and the addition of nicotine did not increase the spike numbers. These results indicate that nicotine induces long-lasting enhancement of firing activity in mPFC layer 5 pyramidal neurons, which is mediated by the stimulation of the α4β2 and α7 nAChRs and subsequent increase in intracellular Ca 2 levels followed by the suppression of the Kv7 channels. The novel effect of nicotine might underlie the nicotine-induced enhancement of attention, working memory and recognition.

These findings suggest that 5F-AMB attenuates both excitatory and inhibitory transmission in mPFC L5 pyramidal neurons via the activation of CB1 receptors located in presynaptic terminals. Further, the net impact of 5F-AMB on L5 pyramidal neurons is inhibition due to the change in balance between excitation and inhibition. This inhibitory effect might at least partly contribute to the expression of the adverse effects induced by 5F-AMB inhalation.

We have recently found that nicotine (Nic) enhances object recognition memory (ORM) in the novel object recognition test (NOR) via stimulation of α4β2 and α7 nicotinic acetylcholine receptors (nAChRs) in the medial prefrontal cortex (mPFC) of mice. Additionally, in vitro electrophysiological analyses revealed that Nic increases firing activity of mPFC layer V pyramidal neurons, which was occluded by 4-aminopyridine (4-AP), a non-selective voltage-dependent potassium (Kv) channel inhibitor, or XE-991, a selective Kv7 channel inhibitor. According to these findings, we hypothesized that Nic increases mPFC neuronal activity by suppressing Kv channels, resulting in the enhancement of ORM. To test this hypothesis, we first observed that c-Fos expression is increased in the mPFC after systemic Nic administration and that suppression of mPFC neuronal activity with inhibitory DREADD significantly inhibits the Nic-induced ORM enhancement, indicating the importance of mPFC neuronal activity in ORM enhancement. Moreover, we found that intra-mPFC injection of 4-AP or XE-991, as well as Nic, enhances ORM. Since one of the targets of 4-AP is Kv4.3 channels, we tested the effects of NS5806, a Kv4.3 channel activator, on Nicinduced ORM enhancement and found that intra-mPFC injection of NS5806 suppressed the Nic-induced ORM enhancement. Similarly, a Kv7 channel activator retigabine also attenuated Nic-induced ORM enhancement. These data suggest that Nic enhances ORM via activation of mPFC neurons through the suppression of Kv4.3 and Kv7 channels.

Stress is one of the most frequently self-reported precipitants for seizure induction in epilepsy patients, but how stress triggers seizures remains unknown. In the medial prefrontal cortex (mPFC), stress has been known to enhance the release of noradrenaline (NA), which excites mPFC layer 5 (L5) pyramidal cells. Thus, we investigated the possible contribution of NA in the mPFC to stress-induced epileptic seizures. Intra-mPFC infusion of picrotoxin (0.1 nmol/side) and NA (10 nmol/side) induced seizures with shorter latency than that of picrotoxin alone in C57BL/6J mice. In vitro whole-cell patch-clamp recordings from mPFC L5 pyramidal cells revealed that, in the presence of picrotoxin (30 µM), bath-application of NA (10 µM) induced rhythmic and frequent epileptiform activities (EA) consisting of prolonged depolarization with burst firings in short latency, while picrotoxin alone induced sporadic and long-latency EA. The NA-induced EA were inhibited by terazosin (5 µM), but not atipamezole (3 µM) or timolol (10 µM), indicating the involvement of α1 adrenoceptors for the EA generation. These results suggest that NA released in the mPFC might contribute to the expression of stress-induced seizures in epilepsy patients.