Dorsomedial prefrontal neural ensembles reflect changes in task utility that culminate in task quitting.

When performing a physically demanding behavior, sometimes the optimal choice is to quit the behavior rather than persist to minimize energy expenditure for the benefits gained. The dorsomedial prefrontal cortex (dmPFC), consisting of the anterior cingulate cortex and secondary motor area, likely contributes toward such utility assessments. Here, we examined how male rat dmPFC single unit and ensemble-level activity corresponded to changes in task utility and quitting in an effortful weight lifting task. Rats carried out two task paradigms: one that became progressively more physically demanding over time and a second fixed effort version. Rats could quit the task at any time. Dorsomedial PFC neurons were highly responsive to each behavioral stage of the task, consisting of rope pulling, reward retrieval, and reward area leaving. Activity was highest early in sessions, commensurate with the highest relative task utility, then decreased until the point of quitting. Neural ensembles consistently represented the sequential behavioral phases of the task. However, these representations were modified over time and became more distinct over the course of the session. These results suggest that dmPFC neurons represent behavioral states that are dynamically modified as behaviors lose their utility, culminating in task quitting.NEW & NOTEWORTHY When carrying out a physically demanding task, animals must continually assess whether to persist or quit. In this study, we recorded neurons in the dorsomedial prefrontal cortex (dmPFC) of rats as they carried out a challenging weightlifting task, up to the point of quitting. We demonstrate that dmPFC neurons form a representation of the task that is modified, via a decrease in firing rate, by the decreasing the utility of the task that may signal quitting.

Stimulation in the Rat Anterior Insula and Anterior Cingulate During an Effortful Weightlifting Task.

When performing tasks, animals must continually assess how much effort is being expended, and gage this against ever-changing physiological states. As effort costs mount, persisting in the task may be unwise. The anterior cingulate cortex (ACC) and the anterior insular cortex are implicated in this process of cost-benefit decision-making, yet their precise contributions toward driving effortful persistence are not well understood. Here we investigated whether electrical stimulation of the ACC or insular cortex would alter effortful persistence in a novel weightlifting task (WLT). In the WLT an animal is challenged to pull a rope 30 cm to trigger food reward dispensing. To make the action increasingly effortful, 45 g of weight is progressively added to the rope after every 10 successful pulls. The animal can quit the task at any point - with the rope weight at the time of quitting taken as the "break weight." Ten male Sprague-Dawley rats were implanted with stimulating electrodes in either the ACC [cingulate cortex area 1 (Cg1) in rodent] or anterior insula and then assessed in the WLT during stimulation. Low-frequency (10 Hz), high-frequency (130 Hz), and sham stimulations were performed. We predicted that low-frequency stimulation (LFS) of Cg1 in particular would increase persistence in the WLT. Contrary to our predictions, LFS of Cg1 resulted in shorter session duration, lower break weights, and fewer attempts on the break weight. High-frequency stimulation of Cg1 led to an increase in time spent off-task. LFS of the anterior insula was associated with a marginal increase in attempts on the break weight. Taken together our data suggest that stimulation of the rodent Cg1 during an effortful task alters certain aspects of effortful behavior, while insula stimulation has little effect.

Regional Activity in the Rat Anterior Cingulate Cortex and Insula during Persistence and Quitting in a Physical-Effort Task.

As animals carry out behaviors, particularly costly ones, they must constantly assess whether or not to persist in the behavior or quit. The anterior cingulate cortex (ACC) has been shown to assess the value of behaviors and to be especially sensitive to physical effort costs. Complimentary to these functions, the insula is thought to represent the internal state of the animal including factors such as hunger, thirst, and fatigue. Using a novel weight-lifting task for rats, we characterized the local field potential (LFP) activity of the ACC and anterior insula (AI) during effort expenditure. In the task, male rats are challenged to work for sucrose reward, which costs progressively more effort over time to obtain. Rats are able to quit the task at any point. We found modest shifts in LFP theta (7-9 Hz) activity as the task got progressively more difficult in terms of absolute effort expenditure. However, when the LFP data were analyzed based on the relative progress of the rat toward quitting the task, substantial shifts in LFP power in the theta and gamma (55-100 Hz) frequency bands were observed in ACC and AI. Both ACC and AI theta power decreased as the rats got closer to quitting, while ACC and AI gamma power increased. Furthermore, coherency between ACC and AI in the delta (2-4 Hz) range shifted alongside the performance state of the rat. Overall, we show that ACC and AI LFP activity changes correlate to the relative performance state of rats in an effort-based task.

Altered Hippocampal-Prefrontal Dynamics Following Medial Prefrontal Stroke in Mouse.

Frontal infarcts can produce cognitive impairments that affect an individual's ability to function in everyday life. However, the precise types of deficits, and their underlying mechanisms, are not well-understood. Here we used a prefrontal photothrombotic stroke model in C57BL/6J mice to characterise specific cognitive changes that occur in the 6 weeks post-stroke. Behavioural experiments were paired with in vivo electrophysiology to assess whether changes in oscillatory communication between the prefrontal cortex (PFC) and the hippocampus (HPC) mirrored any observed behavioural changes. We found that mice in the stroke group exhibited a delayed onset impairment in tasks of spatial working memory (object location recognition and Y-maze) and that this correlated with reduced PFC-HPC theta band coherence (5-12 Hz) during the task. In the open field, mice in the stroke group exhibited hyperactivity as compared to controls, and stroke animals also exhibited significantly higher beta band activity (13-30 Hz) in the PFC and the HPC. Taken together our results suggest that infarcts in the PFC result in PFC-HPC oscillatory communication changes in the theta and beta bands, correlating with altered performance in spatial memory and open field tasks respectively. Of particular interest, early open field changes in PFC beta band power post-stroke correlated to later-stage spatial memory impairments, highlighting this as a potential biomarker for detecting when spatial memory impairments are likely to occur.

Anterior cingulate cortex encoding of effortful behavior.

An animal's ability to assess the value of their behaviors to minimize energy use while maximizing goal achievement is critical to its survival. The anterior cingulate cortex (ACC) has been previously shown to play a critical role in this behavioral optimization process, especially when animals are faced with effortful behaviors. In the present study, we designed a novel task to investigate the role of the ACC in evaluating behaviors that varied in effort but all resulted in the same outcome. We recorded single unit activity from the ACC as rats ran back and forth in a shuttle box that could be tilted to different tilt angles (0, 15, and 25°) to manipulate effort. Overall, a majority of ACC neurons showed selective firing to specific effort conditions. During effort expenditure, ACC units showed a consistent firing rate bias toward the downhill route compared with the more difficult uphill route, regardless of the tilt angle of the apparatus. Once rats completed a run and received their fixed reward, ACC units also showed a clear firing rate preference for the single condition with the highest relative value (25° downhill). To assess effort preferences, we used a choice version of our task and confirmed that rats prefer downhill routes to uphill routes when given the choice. Overall, these results help to elucidate the functional role of the ACC in monitoring and evaluating effortful behaviors that may then bias decision-making toward behaviors with the highest utility. NEW & NOTEWORTHY We developed a novel effort paradigm to investigate how the anterior cingulate cortex (ACC) responds to behaviors with varied degrees of physical effort and how changes in effort influence the ACC's evaluation of behavioral outcomes. Our results provide evidence for a wider role of the ACC in its ability to motivate effortful behaviors and evaluate the outcome of multiple behaviors within an environment.

A Novel Weight Lifting Task for Investigating Effort and Persistence in Rats.

Here we present a novel effort-based task for laboratory rats: the weight lifting task (WLT). Studies of effort expenditure in rodents have typically involved climbing barriers within T-mazes or operant lever pressing paradigms. These task designs have been successful for neuropharmacological and neurophysiological investigations, but both tasks involve simple action patterns. High climbing barriers may also present risk of injury to animals and/or issues with tethered recording equipment. In the WLT, a rat is placed in a large rectangular arena and tasked with pulling a rope 30 cm to trigger food delivery at a nearby spout; weights can be added to the rope in 45 g increments to increase the intensity of effort. As compared to lever pressing and barrier jumping, 30 cm of rope pulling is a multi-step action sequence requiring sustained effort. The actions are carried out on the single plane of the arena floor, making it safer for the animal and more suitable for tethered equipment and video tracking. A microcontroller and associated sensors enable precise timestamping of specific behaviors to synchronize with electrophysiological recordings. The rope and reward spout are spatially segregated to allow for spatial discrimination of the effort zone and the reward zone. We validated the task across five cohorts of rats (total n = 35) and report consistent behavioral metrics. The WLT is well-suited for neuropharmacological and/or in vivo neurophysiological investigations surrounding effortful behaviors, particularly when wanting to probe different aspects of effort expenditure (intensity vs. duration).

Regular Exercise Enhances Task-Based Industriousness in Laboratory Rats.

Individuals vary greatly in their willingness to select and persist in effortful tasks, even when high-effort will knowingly result in high-reward. Individuals who select and successively complete effortful, goal-directed tasks can be described as industrious. Trying to increase one's industriousness is desirable from a productivity standpoint, yet intrinsically challenging given that effort expenditure is generally aversive. Here we show that in laboratory rats, a basic physical exercise regimen (20 min/day, five days/week) is sufficient to increase industriousness across a battery of subsequent testing tasks. Exercised rats outperformed their non-exercised counterparts in tasks designed to tax effort expenditure, strategic decision-making, problem solving and persistence. These increases in performance led to quicker reward obtainment and greater reward gain over time, and could not be accounted for simply by increased locomotor activity. Our results suggest that a basic exercise regimen can enhance effortful goal-directed behaviour in goal-directed tasks, which highlights a potential productivity benefit of staying physically active.

Persisting through subjective effort: a key role for the anterior cingulate cortex?

One shortcoming of Kurzban et al.'s model is that it is not clear how animals persist through subjectively effortful tasks, particularly over a long time course. We suggest that the anterior cingulate cortex plays a critical role by encoding the utility of an action, and signalling where efforts should be best directed based on previous and prospected experience.

Cost-benefit analysis: the first real rule of fight club?

Competition is ubiquitous among social animals. Vying against a conspecific to achieve a particular outcome often requires one to act aggressively, but this is a costly and inherently risky behavior. So why do we aggressively compete, or at the extreme, fight against others? Early work suggested that competitive aggression might stem from an innate aggressive tendency, emanating from subcortical structures. Later work highlighted key cortical regions that contribute toward an instrumental aggression network, one that is recruited or suppressed as needed to achieve a goal. Recent neuroimaging work hints that competitive aggression is upmost a cost-benefit decision, in that it appears to recruit many components of traditional, non-social decision-making networks. This review provides a historical glimpse into the neuroscience of competitive aggression, and proposes a conceptual advancement for studying competitive behavior by outlining how utility calculations of contested-for resources are skewed, pre- and post-competition. A basic multi-factorial model of utility assessment is proposed to account for competitive endowment effects that stem from the presence of peers, peer salience and disposition, and the tactical effort required for victory. In part, competitive aggression is a learned behavior that should only be repeated if positive outcomes are achieved. However, due to skewed utility assessments, deviations of associative learning occur. Hence truly careful cost-benefit analysis is warranted before choosing to vie against another.

Neural encoding of competitive effort in the anterior cingulate cortex.

In social environments, animals often compete to obtain limited resources. Strategically electing to work against another animal represents a cost-benefit decision. Is the resource worth an investment of competitive effort? The anterior cingulate cortex (ACC) has been implicated in cost-benefit decision-making, but its role in competitive effort has not been examined. We recorded ACC neurons in freely moving rats as they performed a competitive foraging choice task. When at least one of the two choice options demanded competitive effort, the majority of ACC neurons exhibited heightened and differential firing between the goal trajectories. Inter- and intrasession manipulations revealed that differential firing was not attributable to effort or reward in isolation; instead ACC encoding patterns appeared to indicate net utility assessments of available choice options. Our findings suggest that the ACC is important for encoding competitive effort, a cost-benefit domain that has received little neural-level investigation despite its predominance in nature.

Neurons in the rat anterior cingulate cortex dynamically encode cost-benefit in a spatial decision-making task.

Optimal decision-making often requires an assessment of the costs and benefits associated with each available course of action. Previous studies have shown that lesions to the anterior cingulate cortex (ACC) impair cost-benefit decision-making in laboratory animals, but the neural mechanisms underlying the deficit are not well understood. We recorded from ACC neurons in freely moving rats as they performed a spatial decision-making task whereby, in the baseline configuration "2:6B," rats could pursue two or six food pellets, the latter obtained by climbing a barrier [high cost, high reward (HCHR)]. In this configuration, the mean percentage of HCHR choices was 69 +/- 4%, and a substantial portion of ACC neurons (63%) exhibited significantly higher firing for one goal trajectory versus the other; for 94% of these cells, higher firing was associated with the HCHR option. This HCHR bias was not simply attributable to the larger reward, the barrier, or behavioral preference. In intersession and intrasession manipulations involving at least one barrier (2:6B, 2B:6B, and 2:2B), ACC activity rapidly adapted and was consistently biased toward the economically advantageous option relative to the configuration. Interestingly, when only a difference in reward magnitude was presented (2:6, no barrier, HCHR choices of 84 +/- 4%), ACC activity was minimal and nonbiased. One interpretation of our data is that the ACC encodes a relative, integrated cost-benefit representation of available choice options that is biased toward the "better" option in terms of effort/outcome ratio. This representation may be specifically recruited when an assessment of reward and effort is required to optimally perform a task.

Alpha-1A adrenergic receptor activation increases inhibitory tone in CA1 hippocampus.

The endogenous catecholamine norepinephrine (NE) exhibits anti-epileptic properties, however it is not well understood which adrenergic receptor (AR) mediates this effect. The aim of this study was to investigate alpha(1)-adrenergic receptor activation in region CA1 of the hippocampus, a subcortical structure often implicated in temporal lobe epilepsies. Using cell-attached and whole-cell recordings in rat hippocampal slices, we confirmed that selective alpha(1)-AR activation increases action potential firing in a subpopulation of CA1 interneurons. We found that this response is mediated via the alpha(1A)-AR subtype, initiated by sodium influx, and appears independent of second messenger signaling. In CA1 pyramidal cells, alpha(1A)-AR activation decreases activity due to increased pre-synaptic GABA and somatostatin release. Examination of post-synaptic receptor involvement revealed that while GABA(A) receptors mediate the majority of alpha(1A)-adrenergic effects on CA1 pyramidal cells, significant contributions are also made by GABA(B) and somatostatin receptors. Finally, to test whether alpha(1A)-AR activation could have potential therapeutic implications, we performed AR agonist challenges using two in vitro epileptiform models. When GABA(A) receptors were available, alpha(1A)-AR activation significantly decreased epileptiform bursting in CA1. Together, our findings directly link stimulation of the alpha(1A)-AR subtype to release of GABA and somatostatin at the single cell level and suggest that alpha(1A)-AR activation may represent one mechanism by which NE exerts anti-epileptic effects within the hippocampus.

Alpha2A adrenergic receptor activation inhibits epileptiform activity in the rat hippocampal CA3 region.

Norepinephrine has potent antiepileptic properties, the pharmacology of which is unclear. Under conditions in which GABAergic inhibition is blocked, norepinephrine reduces hippocampal cornu ammonis 3 (CA3) epileptiform activity through alpha(2) adrenergic receptor (AR) activation on pyramidal cells. In this study, we investigated which alpha(2)AR subtype(s) mediates this effect. First, alpha(2)AR genomic expression patterns of 25 rat CA3 pyramidal cells were determined using real-time single-cell reverse transcription-polymerase chain reaction, demonstrating that 12 cells expressed alpha(2A)AR transcript; 3 of the 12 cells additionally expressed mRNA for alpha(2C)AR subtype and no cells possessing alpha(2B)AR mRNA. Hippocampal CA3 epileptiform activity was then examined using field potential recordings in brain slices. The selective alphaAR agonist 6-fluoronorepinephrine caused a reduction of CA3 epileptiform activity, as measured by decreased frequency of spontaneous epileptiform bursts. In the presence of betaAR blockade, concentration-response curves for AR agonists suggest that an alpha(2)AR mediates this response, as the rank order of potency was 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK-14304) >or= epinephrine >6-fluoronorepinephrine > norepinephrine >>> phenylephrine. Finally, equilibrium dissociation constants (K(b)) of selective alphaAR antagonists were functionally determined to confirm the specific alpha(2)AR subtype inhibiting CA3 epileptiform activity. Apparent K(b) values calculated for atipamezole (1.7 nM), MK-912 (4.8 nM), BRL-44408 (15 nM), yohimbine (63 nM), ARC-239 (540 nM), prazosin (4900 nM), and terazosin (5000 nM) correlated best with affinities previously determined for the alpha(2A)AR subtype (r = 0.99, slope = 1.0). These results suggest that, under conditions of impaired GABAergic inhibition, activation of alpha(2A)ARs is primarily responsible for the antiepileptic actions of norepinephrine in the rat hippocampal CA3 region.

Alpha1A-adrenergic receptors are functionally expressed by a subpopulation of cornu ammonis 1 interneurons in rat hippocampus.

The importance of adrenergic receptors (ARs) in the hippocampus has generally focused on betaARs; however, interest is growing in hippocampal alphaARs given their purported neuroprotective role. We have previously reported alpha(1)AR transcripts in a subpopulation of cornu ammonis 1 (CA1) interneurons. The goal of this study was to identify the specific alpha(1)AR subtype (alpha(1A), alpha(1B), alpha(1D)) functionally expressed by these cells. Using cell-attached recordings to measure action potential frequency changes, concentration-response curves for the selective alpha(1)AR agonist phenylephrine (PE) were generated in the presence of competitive subtype-selective alpha(1)AR antagonists. Schild regression analysis was then used to estimate equilibrium dissociation constants (K(b)) for each receptor antagonist in our system. The selective alpha(1A)AR antagonists, 5-methylurapidil and WB-4101 [2-[(2,6-dimethoxyphenoxyethyl)aminomethyl]-1,4-benzodioxane hydrochloride], produced consecutive rightward shifts in the concentration-response curve for PE when used at discriminating, nanomolar concentrations. Calculated K(b) values for 5-methylurapidil (10 nM) and WB-4101 (5 nM) correlate to previously published affinity values for these antagonists at the alpha(1A)AR. The selective alpha(1B)AR antagonist L-765,314 [(2S)-4-(4-amino-6,7-dimethoxy-2-quinazolinyl)-2-[[(1,1-dimethylethyl)amino]carbonyl]-1-piperazinecarboxylic acid], as well as the selective alpha(1D)AR antagonist BMY7378 [8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride], produced significant rightward shifts in the concentration-response curve for PE only when used at nondistinguishing, micromolar concentrations. Calculated K(b) values for L-765,314 (794 nM) and BMY7378 (316 nM) do not agree with affinity values for these antagonists at the alpha(1B) or alpha(1D)AR, respectively. Rather, these K(b) values more closely match equilibrium dissociation constants estimated for these compounds when used to identify alpha(1A)AR subtypes. Together, our results provide strong evidence to support functional expression of alpha(1A)ARs in a subpopulation of CA1 interneurons.

Adrenergic receptor characterization of CA1 hippocampal neurons using real time single cell RT-PCR.

The CA1 region of the rat hippocampus exhibits both alpha and beta adrenergic receptor (AR) responses, however, the specific AR subtypes involved and the neuronal expression patterns for these receptors are not well understood. We have employed single cell real time RT-PCR in conjunction with cell-specific immunohistochemical markers to determine the AR expression patterns for hippocampal neurons located in CA1, a region often implicated in learning and memory processes. Cytoplasmic samples were taken from 55 individual cells located in stratum oriens, pyramidale, or radiatum and reverse transcribed. All successfully amplified pyramidal neuron samples (n = 17) expressed mRNA for the beta2AR, with four cells additionally expressing mRNA for the beta1AR subtype. Positive interneurons from stratum oriens (n = 10) and stratum radiatum (n = 8) expressed mRNA for the alpha1A and/or alpha(1B)AR (n = 9/18) only when coexpressing transcripts for somatostatin. Interneurons containing neuropeptide Y or cholecystokinin (n = 9/18) were not positive for any of the nine AR subtypes, suggesting that CA1 interneuron AR expression is limited to a subset of somatostatin-positive cells. These findings suggest that only a select number of AR subtypes are transcriptionally expressed in CA1 and that these receptors are selective to specific neuronal cell types.

Functional characterization of the beta-adrenergic receptor subtypes expressed by CA1 pyramidal cells in the rat hippocampus.

Recent studies have demonstrated that activation of the beta-adrenergic receptor (AR) using the selective beta-AR agonist isoproterenol (ISO) facilitates pyramidal cell long-term potentiation in the cornu ammonis 1 (CA1) region of the rat hippocampus. We have previously analyzed beta-AR genomic expression patterns of 17 CA1 pyramidal cells using single cell reverse transcription-polymerase chain reaction, demonstrating that all samples expressed the beta2-AR transcript, with four of the 17 cells additionally expressing mRNA for the beta1-AR subtype. However, it has not been determined which beta-AR subtypes are functionally expressed in CA1 for these same pyramidal neurons. Using cell-attached recordings, we tested the ability of ISO to increase pyramidal cell action potential (AP) frequency in the presence of subtype-selective beta-AR antagonists. ICI-118,551 [(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol] and butoxamine [alpha-[1-(t-butylamino)ethyl]-2,5-dimethoxybenzyl alcohol) hydrochloride], agents that selectively block the beta2-AR, produced significant parallel rightward shifts in the concentration-response curves for ISO. From these curves, apparent equilibrium dissociation constant (K(b)) values of 0.3 nM for ICI-118,551 and 355 nM for butoxamine were calculated using Schild regression analysis. Conversely, effective concentrations of the selective beta1-AR antagonists CGP 20712A [(+/-)-2-hydroxy-5-[2-([2-hydroxy-3-(4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]phenoxy)propyl]amino)ethoxy]-benzamide methanesulfonate] and atenolol [4-[2'-hydroxy-3'-(isopropyl-amino)propoxy]phenylacetamide] did not significantly affect the pyramidal cell response to ISO. However, at higher concentrations, atenolol significantly decreased the potency for ISO-mediated AP frequencies. From these curves, an apparent atenolol K(b) value of 3162 nM was calculated. This pharmacological profile for subtype-selective beta-AR antagonists indicates that beta2-AR activation is mediating the increased AP frequency. Knowledge of functional AR expression in CA1 pyramidal neurons will aid future long-term potentiation studies by allowing selective manipulation of specific beta-AR subtypes.

Differential mechanisms of nitric oxide- and peroxynitrite-induced cell death.

Nitric oxide (NO) contributes to cellular degeneration in various disorders, particularly in the nervous system. NO targets cell proteins such as soluble guanylyl cyclase, but its detrimental effects are generally attributed to its reaction product with superoxide, peroxynitrite. To understand the mechanisms of NO-induced cell stress, we studied the effects of the NO donors diethylenetriamine and spermine NONOate and the peroxynitrite donor 5-amino-3-(4-morpholinyl)-1,2,3-oxadiazolium chloride (SIN-1) in SH-SY5Y and NG108-15 neuroblastoma cells. All three compounds induced a dose- and time-dependent decrease in viable cells, which was not blocked by the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. The two NONOates were approximately 15-fold more potent in SH-SY5Y than in NG108-15 cells, whereas the EC50 values of SIN-1 in SH-SY5Y and NG108-15 cells were in the same order. This led us to conclude that the mechanisms of NO and peroxynitrite did not converge. This was supported by our other findings. NONOates induced DNA fragmentation and an increase in cellular caspase-3 activity that preceded the gradual decline in cell viability. In contrast, SIN-1 induced a transient decline in ATP levels and a delayed loss of cell viability with no significant increase in caspase-3 activity or DNA laddering. Moreover, post-treatment with insulin inhibited caspase-3 activation and loss of cell viability in NONOate- but not in SIN-1-exposed cells. These findings suggest that NO is a potent toxin independent of peroxynitrite formation.