Action-Outcome Expectancies Require Orbitofrontal Neurotrophin Systems in Naïve and Cocaine-Exposed Mice

Cocaine disrupts action flexibility via glucocorticoid receptors

Many addictive drugs increase stress hormone levels. They also alter the propensity of organisms to prospectively select actions based on long-term consequences. We hypothesized that cocaine causes inflexible action by increasing circulating stress hormone levels, activating the glucocorticoid receptor (GR). We trained mice to generate two nose pokes for food and then required them to update action-consequence associations when one response was no longer reinforced. Cocaine delivered in adolescence or adulthood impaired the capacity of mice to update action strategies, and inhibiting CORT synthesis rescued action flexibility. Next, we reduced Nr3c1, encoding GR, in the orbitofrontal cortex (OFC), a region of the brain responsible for interlacing new information into established routines. Nr3c1 silencing preserved action flexibility and dendritic spine abundance on excitatory neurons, despite cocaine. Spines are often considered substrates for learning and memory, leading to the discovery that cocaine degrades the representation of new action memories, obstructing action flexibility.

Cocaine Elevates Calcium-Dependent Activator Protein for Secretion 2 in the Mouse Orbitofrontal Cortex

Calcium-dependent activator protein for secretion 2 (CAPS2; also referred to as CADPS2) is a dense core vesicle-associated protein that promotes the activity-dependent release of neuropeptides including neurotrophins. Addictive drugs appear to prime neurotrophin release in multiple brain regions, but mechanistic factors are still being elucidated. Here, experimenters administered cocaine to adolescent mice at doses that potentiated later cocaine self-administration. Experimenter-administered cocaine elevated the CAPS2 protein content in the orbitofrontal cortex (OFC; but not striatum) multiple weeks after drug exposure. Meanwhile, proteins that are sensitive to brain-derived neurotrophic factor (BDNF) release and binding (phosphorylated protein kinase B and phosphoinositide 3-kinase, and GABAAα1 levels) did not differ between cocaine-exposed and naive mice in the OFC. This pattern is consistent with evidence that CAPS2 primes stimulated release of neurotrophins like BDNF, rather than basal levels. Thus, cocaine administered at behaviorally relevant doses elevates CAPS2 protein content in the OFC, and the effects are detected long after cocaine exposure.

Cell Adhesion Factors in the Orbitofrontal Cortex Control Cue-Induced Reinstatement of Cocaine Seeking and Amygdala-Dependent Goal Seeking

Repeated cocaine exposure causes dendritic spine loss in the orbitofrontal cortex, which might contribute to poor orbitofrontal cortical function following drug exposure. One challenge, however, has been verifying links between neuronal structural plasticity and behavior, if any. Here we report that cocaine self-administration triggers the loss of dendritic spines on excitatory neurons in the orbitofrontal cortex of male and female mice (as has been reported in rats). To understand functional consequences, we locally ablated neuronal β1-integrins, cell adhesion receptors that adhere cells to the extracellular matrix and thus support dendritic spine stability. Degradation of β1-integrin tone: (1) caused dendritic spine loss, (2) exaggerated cocaine-seeking responses in a cue-induced reinstatement test, and (3) impaired the ability of mice to integrate new learning into familiar routines, a key function of the orbitofrontal cortex. Stimulating Abl-related gene kinase, overexpressing Proline-rich tyrosine kinase, and inhibiting Rho-associated coiled-coil containing kinase corrected response strategies, uncovering a β1-integrin-mediated signaling axis that controls orbitofrontal cortical function. Finally, use of a combinatorial gene silencing/chemogenetic strategy revealed that β1-integrins support the ability of mice to integrate new information into established behaviors by sustaining orbitofrontal cortical connections with the basolateral amygdala.SIGNIFICANCE STATEMENT Cocaine degenerates dendritic spines in the orbitofrontal cortex, a region of the brain involved in interlacing new information into established behaviors. One challenge has been verifying links between cellular structural stability and behavior, if any. In this second of two related investigations, we study integrin family receptors, which adhere cells to the extracellular matrix and thereby stabilize dendritic spines (see also DePoy et al., 2019). We reveal that β1-integrins in the orbitofrontal cortex control food- and cocaine-seeking behaviors. For instance, β1-integrin loss amplifies cocaine-seeking behavior and impairs the ability of mice to integrate new learning into familiar routines. We identify likely intracellular signaling partners by which β1-integrins support orbitofrontal cortical function and connectivity with the basolateral amygdala.

Edaravone alleviated propofol-induced neural injury in developing rats by BDNF/TrkB pathway

As a variety of free radical scavenger, edaravone has shown its potential in producing antioxidant, anti-inflammatory and neuroprotective effects in various disease models. However, the underlying mechanism behind the neuroprotective effects of edaravone remained unclear. This study is aimed at determining the effects of edaravone on neuroprotection and anti-inflammatory through a propofol-induced neural injury rat model. Firstly, an observation was made of apoptosis and neuroinflammation in the hippocampus of developing under the influence of propofol. It was found out that propofol could produce inflammatory effects in the hippocampus by enhancing the astrogliosis (GFAP) activation and elevating the level of neuronal nitric oxide synthase (nNOS), pro-inflammatory cytokines interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α). Meanwhile, the increase of apoptosis cells and the decrease of neurons (NeuN) were speculated to aggravate neural injury. Furthermore, it was demonstrated that edaravone intervention can reverse the neural apoptosis and inflammation. Additionally, the intraperitoneal injection of edaravone, the intraperitoneal injection of the brain-derived neurotrophic factor (BDNF)-mimicking small compound (7,8 dihydroxyflavone) and the intracranial injection of the exogenous BDNF were all respectively effective in alleviating the propofol-induced neural apoptosis and inflammation in the hippocampus. It was also found out that edaravone-activated downstream signalling through tyrosine kinase receptor B (TrkB) receptors in astrocyte, microglia and neuron. However, the neural injury of propofol had no impact on long-term learning and memory, except causing a short-term neurotoxicity. In conclusion, edaravone could alleviate the propofol-induced neural injury in developing rats through BDNF/TrkB pathway.

Involvement of the rodent prelimbic and medial orbitofrontal cortices in goal-directed action: A brief review

Goal-directed action refers to selecting behaviors based on the expectation that they will be reinforced with desirable outcomes. It is typically conceptualized as opposing habit-based behaviors, which are instead supported by stimulus-response associations and insensitive to consequences. The prelimbic prefrontal cortex (PL) is positioned along the medial wall of the rodent prefrontal cortex. It is indispensable for action-outcome-driven (goal-directed) behavior, consolidating action-outcome relationships and linking contextual information with instrumental behavior. In this brief review, we will discuss the growing list of molecular factors involved in PL function. Ventral to the PL is the medial orbitofrontal cortex (mOFC). We will also summarize emerging evidence from rodents (complementing existing literature describing humans) that it too is involved in action-outcome conditioning. We describe experiments using procedures that quantify responding based on reward value, the likelihood of reinforcement, or effort requirements, touching also on experiments assessing food consumption more generally. We synthesize these findings with the argument that the mOFC is essential to goal-directed action when outcome value information is not immediately observable and must be recalled and inferred.