The parafascicular thalamic nucleus concomitantly influences behavioral flexibility and dorsomedial striatal acetylcholine output in rats

The Cognitive Thalamus as a Gateway to Mental Representations

Historically, the thalamus has been viewed as little more than a relay, simply transferring information to key players of the cast, the cortex and hippocampus, without providing any unique functional contribution. In recent years, evidence from multiple laboratories researching different thalamic nuclei has contradicted this idea of the thalamus as a passive structure. Dated models of thalamic functions are being pushed aside, revealing a greater and far more complex contribution of the thalamus for cognition. In this Viewpoints article, we show how recent data support novel views of thalamic functions that emphasize integrative roles in cognition, ranging from learning and memory to flexible adaption. We propose that these apparently separate cognitive functions may indeed be supported by a more general role in shaping mental representations. Several features of thalamocortical circuits are consistent with this suggested role, and we highlight how divergent and convergent thalamocortical and corticothalamic pathways may complement each other to support these functions. Furthermore, the role of the thalamus for subcortical integration is highlighted as a key mechanism for maintaining and updating representations. Finally, we discuss future areas of research and stress the importance of incorporating new experimental findings into existing knowledge to continue developing thalamic models. The presence of thalamic pathology in a number of neurological conditions reinforces the need to better understand the role of this region in cognition.

A novel multichoice touchscreen paradigm for assessing cognitive flexibility in mice

Cognitive flexibility refers to various processes which enable behaviors to be modified on the basis of a change in the contingencies between stimuli or responses and their associated outcomes. Reversal learning is a form of cognitive flexibility which measures the ability to adjust responding based on a switch in the stimulus–outcome contingencies of, typically two, perceptually distinct stimuli. Reversal tasks have provided valuable insight into the neural basis of cognitive flexibility, implicating brain regions including the lateral orbitofrontal cortex (lOFC) and dorsomedial prefrontal cortex (dmPFC). However, with two-stimulus reversal, it is difficult to determine whether response errors are due excessive perseveration, deficient learning, or other problems with updating. To address this limitation, we developed a mouse three-choice touchscreen-based visual reversal task, in which the contingencies of two stimuli were switched on reversal but a third, simultaneously presented, stimulus was never reinforced. We found that, in male C57BL/6J mice, responding at the previously rewarded stimulus predominated over the newly and never-reinforced stimuli during early reversal. Next, we showed that acute pharmacological inhibition of lOFC, but not dmPFC, impaired early reversal performance, relative to noninactivated controls. Interestingly, however, lOFC inactivation deficits were characterized by increased choice of the never-reinforced stimulus and a decrease in (perseverative-like) responding at the previously rewarded stimulus. These effects are inconsistent with the historical notion of lOFC mediating response inhibition and closer to recent views of the lOFC's role in response/outcome tracking. Overall, these findings provide initial support the utility of this novel paradigm for studying cognitive flexibility and its underlying neural substrates.

Loss of glutamate signaling from the thalamus to dorsal striatum impairs motor function and slows the execution of learned behaviors

Parkinson’s disease (PD) is primarily associated with the degeneration of midbrain dopamine neurons, but it is now appreciated that pathological processes like Lewy-body inclusions and cell loss affect several other brain regions, including the central lateral (CL) and centromedian/parafascicular (CM/PF) thalamic regions. These thalamic glutamatergic neurons provide a non-cortical excitatory input to the dorsal striatum, a major projection field of dopamine neurons. To determine how thalamostriatal signaling may contribute to cognitive and motor abnormalities found in PD, we used a viral vector approach to generate mice with loss of thalamostriatal glutamate signaling specifically restricted to the dorsal striatum (CAV2^Cre-Slc17a6^lox/lox mice). We measured motor function and behaviors corresponding to cognitive domains (visuospatial function, attention, executive function, and working memory) affected in PD. CAV2^Cre-Slc17a6^lox/lox mice were impaired in motor coordination tasks such as the rotarod and beam-walk tests compared with controls (CAV2^Cre-Slc17a6^+/+ mice). They did not demonstrate much cognitive impairment in the Morris water maze or a water U-maze, but had slower processing reaction times in those tests and in a two-way active avoidance task. These mice could model an aspect of bradyphrenia, the slowness of thought that is often seen in patients with PD and other neurological disorders.

Mice in which glutamate signaling from the thalamus to dorsal striatum has been genetically inactivated mimic the slowness of thought that is often observed in patients with Parkinson’s disease (PD). The midbrain and striatum are the brain regions that are most affected in PD, however, it is increasingly recognized that cell loss in other areas of the brain also contribute to disease symptoms. Martin Darvas at the University of Washington, Seattle, USA, and colleagues found that disrupting the excitatory input from thalamic projection neurons into the dorsal striatum affected motor coordination and balance in mice. Although these mice did not have significant impairments in spatial learning and memory, they were slower at reacting to cues and executing learned behaviors suggesting that they could be used to test new approaches for treating this specific cognitive symptom of PD.

Differential inputs to striatal cholinergic and parvalbumin interneurons imply functional distinctions

Striatal cholinergic (ChAT) and parvalbumin (PV) interneurons exert powerful influences on striatal function in health and disease, yet little is known about the organization of their inputs. Here using rabies tracing, electrophysiology and genetic tools, we compare the whole-brain inputs to these two types of striatal interneurons and dissect their functional connectivity in mice. ChAT interneurons receive a substantial cortical input from associative regions of cortex, such as the orbitofrontal cortex. Amongst subcortical inputs, a previously unknown inhibitory thalamic reticular nucleus input to striatal PV interneurons is identified. Additionally, the external segment of the globus pallidus targets striatal ChAT interneurons, which is sufficient to inhibit tonic ChAT interneuron firing. Finally, we describe a novel excitatory pathway from the pedunculopontine nucleus that innervates ChAT interneurons. These results establish the brain-wide direct inputs of two major types of striatal interneurons and allude to distinct roles in regulating striatal activity and controlling behavior.

Disrupted striatal neuron inputs and outputs in Huntington's disease

Huntington's disease (HD) is a hereditary progressive neurodegenerative disorder caused by a CAG repeat expansion in the gene coding for the protein huntingtin, resulting in a pathogenic expansion of the polyglutamine tract in the N-terminus of this protein. The HD pathology resulting from the mutation is most prominent in the striatal part of the basal ganglia, and progressive differential dysfunction and loss of striatal projection neurons and interneurons account for the progression of motor deficits seen in this disease. The present review summarizes current understanding regarding the progression in striatal neuron dysfunction and loss, based on studies both in human HD victims and in genetic mouse models of HD. We review evidence on early loss of inputs to striatum from cortex and thalamus, which may be the basis of the mild premanifest bradykinesia in HD, as well as on the subsequent loss of indirect pathway striatal projection neurons and their outputs to the external pallidal segment, which appears to be the basis of the chorea seen in early symptomatic HD. Later loss of direct pathway striatal projection neurons and their output to the internal pallidal segment account for the severe akinesia seen late in HD. Loss of parvalbuminergic striatal interneurons may contribute to the late dystonia and rigidity.

Cholinergic interneurons in the rat striatum modulate substitution of habits

Behavioural flexibility is crucial for adaptive behaviour, and recent evidence suggests that cholinergic interneurons of the striatum play a distinct role. Previous studies of cholinergic function have focused on strategy switching by the dorsomedial or ventral striatum. We here investigated whether cholinergic interneurons in the dorsolateral striatum play a similar role at the level of switching of habitual responses. Because the dorsolateral striatum is particularly involved in habitual responding, we developed a habit substitution task that involved switching habitual lever‐press responses to one side to another. We first measured the effect of cholinergic activation in the dorsolateral striatum on this task. Chemogenetic activation of cholinergic interneurons caused an increase in the response rate for the substituted response that was significantly greater than the increase normally seen in control animals. The increase was due to burst‐like responses with shorter inter‐press intervals. However, there was no effect on inhibiting the old habit, or on habitual responding that did not require a switch. There was also no effect on lever‐press performance and its reversal before lever‐press responses became habitual. Conversely, neurochemically specific ablation of cholinergic interneurons did not significantly change habitual responding or response substitution. Thus, activation –but not ablation –of cholinergic interneurons in the dorsolateral striatum modulates expression of a new habit when an old habit is replaced by a new one. Together with previous work, this suggests that striatal cholinergic interneurons facilitate behavioural flexibility in both dorsolateral striatum in addition to dorsomedial and ventral striatum.

Functional neurochemical imaging of the human striatal cholinergic system during reversal learning

Animal studies have shown that acetylcholine (ACh) levels in the dorsal striatum play a role in reversal learning. However, this has not been studied in humans due to a lack of appropriate non-invasive techniques. Proton magnetic resonance spectroscopy (¹ H-MRS) can be used to measure metabolite levels in humans in vivo. Although it cannot be used to study ACh directly, ¹ H-MRS can be used to study choline, an ACh precursor, which is linked to activity-dependent ACh release. The aim of this study was to use functional-¹ H-MRS (fMRS) to measure changes in choline levels in the human dorsal striatum during performance of a probabilistic reversal learning task. We demonstrate a task-dependent decrease in choline, specifically during reversal, but not initial, learning. We interpret this to reflect a sustained increase in ACh levels, which is in line with findings from the animal literature. This task-dependent change was specific to choline and was not observed in control metabolites. These findings provide support for the use of fMRS in the in vivo study of the human cholinergic system.

Local and long-range circuit elements for cerebellar function

The view of cerebellar functions has been extended from controlling sensorimotor processes to processing 'contextual' information and generating predictions for a diverse range of behaviors. These functions rely on the computation of the local cerebellar microcircuits and long-range connectivity that relays cerebellar output to various brain areas. In this review, we discuss recent work on two of the circuit elements, which are thought to be fundamental for a wide range of non-sensorimotor behaviors: The role for cerebellar granule cells in multimodal integration in the cerebellar cortex and the long-range connectivity between the deep cerebellar nuclei and the basal ganglia. Lastly, we discuss how studies on synapses and circuits of the cerebellum in rodent models of autism-spectrum disorders might contribute to our understanding of the pathophysiology of this class of neurodevelopmental disorders.

Task-dependent function of striatal cholinergic interneurons in behavioural flexibility

Flexible switching of behaviours depends on integrative functioning through the neural circuit connecting the prefrontal cortex and the dorsomedial striatum (DMS). Although cholinergic interneurons modulate striatal outputs by diverse synaptic mechanisms, the roles of cholinergic interneurons in the DMS appear to vary among different models used to validate behavioural flexibility. Here, we conducted immunotoxin-mediated cell targeting of DMS cholinergic interneurons and examined the functions of these interneurons in behavioural flexibility, with the learning conditions differing in trial spacing and discrimination type in a modified T-maze. Elimination of the DMS cholinergic cell group normally spared reversal learning in place discrimination with an intertrial interval (ITI) of 15 s, but it impaired the reversal performance in response discrimination with the same ITI. In contrast, DMS cholinergic elimination resulted in enhanced reversal performance in both place and response discrimination tasks with a 10-min ITI and accelerated the reversal of response discrimination with a 20-min ITI. Our previous study also showed an enhanced influence of cholinergic targeting on place reversal learning with a 20-min ITI, and the present results demonstrate that DMS cholinergic interneurons act to inhibit both place and response reversal performance with a relatively longer ITI, whereas their functions differ between types of reversal performance in the tasks with a shorter ITI. These findings suggest distinct roles of the DMS cholinergic cell group in behavioural flexibility dependent on the trial spacing and discrimination type constituting the learning tasks.

Thalamic inputs to dorsomedial striatum are involved in inhibitory control: evidence from the five-choice serial reaction time task in rats

RATIONALE

Corticostriatal circuits are widely implicated in the top-down control of attention including inhibitory control and behavioural flexibility. However, recent neurophysiological evidence also suggests a role for thalamic inputs to striatum in behaviours related to salient, reward-paired cues.

OBJECTIVES

Here, we used designer receptors exclusively activated by designer drugs (DREADDs) to investigate the role of parafascicular (Pf) thalamic inputs to the dorsomedial striatum (DMS) using the five-choice serial reaction time task (5CSRTT) in rats.

METHODS

The 5CSRTT requires sustained attention in order to detect spatially and temporally distributed visual cues and provides measures of inhibitory control related to impulsivity (premature responses) and compulsivity (perseverative responses). Rats underwent bilateral Pf injections of the DREADD vector, AAV2-CaMKIIa-HA-hM4D(Gi)-IRES-mCitrine. The DREADD agonist, clozapine N-oxide (CNO; 1 μl bilateral; 3 μM) or vehicle, was injected into DMS 1 h before behavioural testing. Task parameters were manipulated to increase attention load or reduce stimulus predictability respectively.

RESULTS

We found that inhibition of the Pf-DMS projection significantly increased perseverative responses when stimulus predictability was reduced but had no effect on premature responses or response accuracy, even under increased attentional load. Control experiments showed no effects on locomotor activity in an open field.

CONCLUSIONS

These results complement previous lesion work in which the DMS and orbitofrontal cortex were similarly implicated in perseverative responses and suggest a specific role for thalamostriatal inputs in inhibitory control.

The role of the intrinsic cholinergic system of the striatum: What have we learned from TAN recordings in behaving animals?

Cholinergic interneurons provide rich local innervation of the striatum and play an important role in controlling behavior, as evidenced by the variety of movement and psychiatric disorders linked to disrupted striatal cholinergic transmission. Much progress has been made in recent years regarding our understanding of how these interneurons contribute to the processing of information in the striatum. In particular, investigation of the activity of presumed striatal cholinergic interneurons, identified as tonically active neurons or TANs in behaving animals, has pointed to their role in the signaling and learning of the motivational relevance of environmental stimuli. Although the bulk of this work has been conducted in monkeys, several studies have also been carried out in behaving rats, but information remains rather disparate across studies and it is still questionable whether rodent TANs correspond to TANs described in monkeys. Consequently, our current understanding of the function of cholinergic transmission in the striatum is challenged by the rapidly growing, but often confusing literature on the relationship between TAN activity and specific behaviors. As regards the precise nature of the information conveyed by the cholinergic TANs, a recent influential view emphasized that these local circuit neurons may play a special role in the processing of contextual information that is important for reinforcement learning and selection of appropriate actions. This review provides a summary of recent progress in TAN physiology from which it is proposed that striatal cholinergic interneurons are crucial elements for flexible switching of behaviors under changing environmental conditions.

Aging-Related Dysfunction of Striatal Cholinergic Interneurons Produces Conflict in Action Selection

For goal-directed action to remain adaptive, new strategies are required to accommodate environmental changes, a process for which parafascicular thalamic modulation of cholinergic interneurons in the striatum (PF-to-CIN) appears critical. In the elderly, however, previously acquired experience frequently interferes with new learning, yet the source of this effect has remained unexplored. Here, combining sophisticated behavioral designs, cell-specific manipulation, and extensive neuronal imaging, we investigated the involvement of the PF-to-CIN pathway in this process. We found functional alterations of this circuit in aged mice that were consistent with their incapacity to update initial goal-directed learning, resulting in faulty activation of projection neurons in the striatum. Toxicogenetic ablation of CINs in young mice reproduced these behavioral and neuronal defects, suggesting that age-related deficits in PF-to-CIN function reduce the ability of older individuals to resolve conflict between actions, likely contributing to impairments in adaptive goal-directed action and executive control in aging. VIDEO ABSTRACT.

Striatal Cholinergic Interneurons Modulate Spike-Timing in Striosomes and Matrix by an Amphetamine-Sensitive Mechanism

The striatum is key for action-selection and the motivation to move. Dopamine and acetylcholine release sites are enriched in the striatum and are cross-regulated, possibly to achieve optimal behavior. Drugs of abuse, which promote abnormally high dopamine release, disrupt normal action-selection and drive restricted, repetitive behaviors (stereotypies). Stereotypies occur in a variety of disorders including obsessive-compulsive disorder, autism, schizophrenia and Huntington's disease, as well as in addictive states. The severity of drug-induced stereotypy is correlated with induction of c-Fos expression in striosomes, a striatal compartment that is related to the limbic system and that directly projects to dopamine-producing neurons of the substantia nigra. These characteristics of striosomes contrast with the properties of the extra-striosomal matrix, which has strong sensorimotor and associative circuit inputs and outputs. Disruption of acetylcholine signaling in the striatum blocks the striosome-predominant c-Fos expression pattern induced by drugs of abuse and alters drug-induced stereotypy. The activity of striatal cholinergic interneurons is associated with behaviors related to sensory cues, and cortical inputs to striosomes can bias action-selection in the face of conflicting cues. The neurons and neuropil of striosomes and matrix neurons have observably separate distributions, both at the input level in the striatum and at the output level in the substantia nigra. Notably, cholinergic axons readily cross compartment borders, providing a potential route for local cross-compartment communication to maintain a balance between striosomal and matrix activity. We show here, by slice electrophysiology in transgenic mice, that repetitive evoked firing patterns in striosomal and matrix striatal projection neurons (SPNs) are interrupted by optogenetic activation of cholinergic interneurons either by the addition or the deletion of spikes. We demonstrate that this cholinergic modulation of projection neurons is blocked in brain slices taken from mice exposed to amphetamine and engaged in amphetamine-induced stereotypy, and lacking responsiveness to salient cues. Our findings support a model whereby activity in striosomes is normally under strong regulation by cholinergic interneurons, favoring behavioral flexibility, but that in animals with drug-induced stereotypy, this cholinergic signaling breaks down, resulting in differential modulation of striosomal activity and an inability to bias action-selection according to relevant sensory cues.

Roles of centromedian parafascicular nuclei of thalamus and cholinergic interneurons in the dorsal striatum in associative learning of environmental events

The thalamus provides a massive input to the striatum, but despite accumulating evidence, the functions of this system remain unclear. It is known, however, that the centromedian (CM) and parafascicular (Pf) nuclei of the thalamus can strongly influence particular striatal neuron subtypes, notably including the cholinergic interneurons of the striatum (CINs), key regulators of striatal function. Here, we highlight the thalamostriatal system through the CM-Pf to striatal CINs. We consider how, by virtue of the direct synaptic connections of the CM and PF, their neural activity contributes to the activity of CINs and striatal projection neurons (SPNs). CM-Pf neurons are strongly activated at sudden changes in behavioral context, such as switches in action-outcome contingency or sequence of behavioral requirements, suggesting that their activity may represent change of context operationalized as associability. Striatal CINs, on the other hand, acquire and loose responses to external events associated with particular contexts. In light of this physiological evidence, we propose a hypothesis of the CM-Pf-CINs system, suggesting that it augments associative learning by generating an associability signal and promotes reinforcement learning guided by reward prediction error signals from dopamine-containing neurons. We discuss neuronal circuit and synaptic organizations based on in vivo/in vitro studies that we suppose to underlie our hypothesis. Possible implications of CM-Pf-CINs dysfunction (or degeneration) in brain diseases are also discussed by focusing on Parkinson's disease.

Cognitive flexibility impairment and reduced frontal cortex BDNF expression in the ouabain model of mania

Central infusion of the Na+/K+-ATPase inhibitor, ouabain in rats serves as an animal model of mania because it leads to hyperactivity, as well as reproduces ion dysregulation and reduced brain-derived neurotrophic factor (BDNF) levels similar to that observed in bipolar disorder. Bipolar disorder is also associated with cognitive inflexibility and working memory deficits. It is unknown whether ouabain treatment in rats leads to similar cognitive flexibility and working memory deficits. The present study examined the effects of an intracerebral ventricular infusion of ouabain in rats on spontaneous alternation, probabilistic reversal learning and BDNF expression levels in the frontal cortex. Ouabain treatment significantly increased locomotor activity, but did not affect alternation performance in a Y-maze. Ouabain treatment selectively impaired reversal learning in a spatial discrimination task using an 80/20 probabilistic reinforcement procedure. The reversal learning deficit in ouabain-treated rats resulted from an impaired ability to maintain a new choice pattern (increased regressive errors). Ouabain treatment also decreased sensitivity to negative feedback during the initial phase of reversal learning. Expression of BDNF mRNA and protein levels was downregulated in the frontal cortex which also negatively correlated with regressive errors. These findings suggest that the ouabain model of mania may be useful in understanding the neuropathophysiology that contributes to cognitive flexibility deficits and test potential treatments to alleviate cognitive deficits in bipolar disorder.

Human centromedian-parafascicular complex signals sensory cues for goal-oriented behavior selection

Experimental research has shown that the centromedian-parafascicular complex (CM-Pf) of the intralaminar thalamus is activated in attentional orienting and processing of behaviorally relevant stimuli. These observations resulted in the hypothesis that the CM-Pf plays a pivotal role in goal-oriented behavior selection. We here set out to test this hypothesis with electrophysiological recordings from patients with electrodes implanted in CM-Pf for deep brain stimulation (DBS) treatment of chronic neuropathic pain. Six patients participated in (1) an auditory three-class oddball experiment, which required a button press to target tones, but not to standard and deviant tones and in (2) a multi-speaker experiment with a target word that required attention selection and a target image that required response selection. Subjects showed transient neural responses (8-15Hz) to the target tone and the target word. Two subjects additionally showed transient neural responses (15-25Hz) to the target image. All sensory target stimuli were related to an internal goal and required a behavior selection (attention selection, response selection). In group analyses, neural responses were greater to target tones than deviant and standard tones and to target words than other task-relevant words that did not require attention selection. The transient neural responses occurred after the target stimuli but prior to the overt behavioral response. Our results demonstrate that in human subjects the CM-Pf is involved in signaling sensory inputs related to goal-oriented selection of behavior.

Dopamine, fronto-striato-thalamic circuits and risk for psychosis

A series of parallel, integrated circuits link distinct regions of prefrontal cortex with specific nuclei of the striatum and thalamus. Dysfunction of these fronto-striato-thalamic systems is thought to play a major role in the pathogenesis of psychosis. In this review, we examine evidence from human and animal investigations that dysfunction of a specific dorsal fronto-striato-thalamic circuit, linking the dorsolateral prefrontal cortex, dorsal (associative) striatum, and mediodorsal nucleus of the thalamus, is apparent across different stages of psychosis, including prior to the onset of a first episode, suggesting that it represents a candidate risk biomarker. We consider how abnormalities at distinct points in the circuit may give rise to the pattern of findings seen in patient populations, and how these changes relate to disruptions in dopamine, glutamate and GABA signaling.

Uncertainty and expectancy deviations require cortico-subcortical cooperation

In a dynamic and uncertain environment it is beneficial to learn the causal structure of the environment in order to minimize uncertainty. This requires determining estimates of probable outcomes, which will guide expectations about incoming information. One key factor in this learning process is to detect whether an unexpected event constitutes a low probability, but valid outcome, or an outright error. The present 7T-fMRI study investigated the role of subcortical structures in regulating this probabilistic inferential learning process. A new task was designed, in which participants learned to calculate the value, and therefore to anticipate the outcome of different visual sequences. Three types of sequences provided unambiguous, ambiguous, and incongruent contextual evidence and each sequence had two outcomes, which differed in their probability of occurrence. We hypothesized that subcortical regions are necessary when expectations are violated, and that their involvement will depend on the nature of the unexpected event. The results show increased dorsomedial striatal and thalamic activation for less probable sequences; in addition, ambiguous sequences also display larger activation in the red nuclei. Incongruent sequences displayed a pattern of subcortical activation restricted to the dorsolateral and the posterior dorsomedial striatum. These results confirm that different subcortical structures regulate uncertainty and expectancy deviations; this is crucial not only for learning to predict events in the environment, but also for flexible cognitive control in general.

The external globus pallidus: progress and perspectives

The external globus pallidus (GPe) of the basal ganglia is in a unique and powerful position to influence processing of motor information by virtue of its widespread projections to all basal ganglia nuclei. Despite the clinical importance of the GPe in common motor disorders such as Parkinson's disease, there is only limited information about its cellular composition and organizational principles. In this review, recent advances in the understanding of the diversity in the molecular profile, anatomy, physiology and corresponding behaviour during movement of GPe neurons are described. Importantly, this study attempts to build consensus and highlight commonalities of the cellular classification based on existing but contentious literature. Additionally, an analysis of the literature concerning the intricate reciprocal loops formed between the GPe and major synaptic partners, including both the striatum and the subthalamic nucleus, is provided. In conclusion, the GPe has emerged as a crucial node in the basal ganglia macrocircuit. While subtleties in the cellular makeup and synaptic connection of the GPe create new challenges, modern research tools have shown promise in untangling such complexity, and will provide better understanding of the roles of the GPe in encoding movements and their associated pathologies.

Pedunculopontine tegmental nucleus lesions impair probabilistic reversal learning by reducing sensitivity to positive reward feedback

Recent findings indicate that pedunculopontine tegmental nucleus (PPTg) neurons encode reward-related information that is context-dependent. This information is critical for behavioral flexibility when reward outcomes change signaling a shift in response patterns should occur. The present experiment investigated whether NMDA lesions of the PPTg affects the acquisition and/or reversal learning of a spatial discrimination using probabilistic reinforcement. Male Long-Evans rats received a bilateral infusion of NMDA (30nmoles/side) or saline into the PPTg. Subsequently, rats were tested in a spatial discrimination test using a probabilistic learning procedure. One spatial location was rewarded with an 80% probability and the other spatial location rewarded with a 20% probability. After reaching acquisition criterion of 10 consecutive correct trials, the spatial location - reward contingencies were reversed in the following test session. Bilateral and unilateral PPTg-lesioned rats acquired the spatial discrimination test comparable to that as sham controls. In contrast, bilateral PPTg lesions, but not unilateral PPTg lesions, impaired reversal learning. The reversal learning deficit occurred because of increased regressions to the previously 'correct' spatial location after initially selecting the new, 'correct' choice. PPTg lesions also reduced the frequency of win-stay behavior early in the reversal learning session, but did not modify the frequency of lose-shift behavior during reversal learning. The present results suggest that the PPTg contributes to behavioral flexibility under conditions in which outcomes are uncertain, e.g. probabilistic reinforcement, by facilitating sensitivity to positive reward outcomes that allows the reliable execution of a new choice pattern.

A Brain Motivated to Play: Insights into the Neurobiology of Playfulness

Play is an important part of normal childhood development and is seen in varied forms among many mammals. While not indispensable to normal development, playful social experiences as juveniles may provide an opportunity to develop flexible behavioral strategies when novel and uncertain situations arise as an adult. To understand the neurobiological mechanisms responsible for play and how the functions of play may relate to these neural substrates, the rat has become the model of choice. Play in the rat is easily quantified, tightly regulated, and can be modulated by genetic factors and postnatal experiences. Brain areas most likely to be involved in the modulation of play include regions within the prefrontal cortex, dorsal and ventral striatum, some regions of the amygdala, and habenula. This paper discusses what we currently know about the neurobiological substrates of play and how this can help illuminate functional questions about the putative benefits of play.

Role of Striatal Cholinergic Interneurons in Set-Shifting in the Rat

The ability to change strategies in different contexts is a form of behavioral flexibility that is crucial for adaptive behavior. The striatum has been shown to contribute to certain forms of behavioral flexibility such as reversal learning. Here we report on the contribution of striatal cholinergic interneurons-a key element in the striatal neuronal circuit-to strategy set-shifting in which an attentional shift from one stimulus dimension to another is required. We made lesions of rat cholinergic interneurons in dorsomedial or ventral striatum using a specific immunotoxin and investigated the effects on set-shifting paradigms and on reversal learning. In shifting to a set that required attention to a previously irrelevant cue, lesions of dorsomedial striatum significantly increased the number of perseverative errors. In this condition, the number of never-reinforced errors was significantly decreased in both types of lesions. When shifting to a set that required attention to a novel cue, rats with ventral striatum lesions made more perseverative errors. Neither lesion impaired learning of the initial response strategy nor a subsequent switch to a new strategy when response choice was indicated by a previously relevant cue. Reversal learning was not affected. These results suggest that in set-shifting the striatal cholinergic interneurons play a fundamental role, which is dissociable between dorsomedial and ventral striatum depending on behavioral context. We propose a common mechanism in which cholinergic interneurons inhibit neurons representing the old strategy and enhance plasticity underlying exploration of a new rule.

Cognitive set shifting deficits and their relationship to repetitive behaviors in autism spectrum disorder

The neurocognitive impairments associated with restricted and repetitive behaviors (RRBs) in autism spectrum disorder (ASD) are not yet clear. Prior studies indicate that individuals with ASD show reduced cognitive flexibility, which could reflect difficulty shifting from a previously learned response pattern or a failure to maintain a new response set. We examined different error types on a test of set-shifting completed by 60 individuals with ASD and 55 age- and nonverbal IQ-matched controls. Individuals with ASD were able to initially shift sets, but they exhibited difficulty maintaining new response sets. Difficulty with set maintenance was related to increased severity of RRBs. General difficulty maintaining new response sets and a heightened tendency to revert to old preferences may contribute to RRBs.

Striatal cholinergic interneurons and cortico-striatal synaptic plasticity in health and disease

Basal ganglia disorders such as Parkinson's disease, dystonia, and Huntington's disease are characterized by a dysregulation of the basal ganglia neuromodulators (dopamine, acetylcholine, and others), which impacts cortico-striatal transmission. Basal ganglia disorders are often associated with an imbalance between the midbrain dopaminergic and striatal cholinergic systems. In contrast to the extensive research and literature on the consequences of a malfunction of midbrain dopaminergic signaling on the plasticity of the cortico-striatal synapse, very little is known about the role of striatal cholinergic interneurons in normal and pathological control of cortico-striatal transmission. In this review, we address the functional role of striatal cholinergic interneurons, also known as tonically active neurons and attempt to understand how the alteration of their functional properties in basal ganglia disorders leads to abnormal cortico-striatal synaptic plasticity. Specifically, we suggest that striatal cholinergic interneurons provide a permissive signal, which enables long-term changes in the efficacy of the cortico-striatal synapse. We further discuss how modifications in the striatal cholinergic activity pattern alter or prohibit plastic changes of the cortico-striatal synapse. Long-term cortico-striatal synaptic plasticity is the cellular substrate of procedural learning and adaptive control behavior. Hence, abnormal changes in this plasticity may underlie the inability of patients with basal ganglia disorders to adjust their behavior to situational demands. Normalization of the cholinergic modulation of cortico-striatal synaptic plasticity may be considered as a critical feature in future treatments of basal ganglia disorders.

A wireless neural recording system with a precision motorized microdrive for freely behaving animals

The brain is composed of many different types of neurons. Therefore, analysis of brain activity with single-cell resolution could provide fundamental insights into brain mechanisms. However, the electrical signal of an individual neuron is very small, and precise isolation of single neuronal activity from moving subjects is still challenging. To measure single-unit signals in actively behaving states, establishment of technologies that enable fine control of electrode positioning and strict spike sorting is essential. To further apply such a single-cell recording approach to small brain areas in naturally behaving animals in large spaces or during social interaction, we developed a compact wireless recording system with a motorized microdrive. Wireless control of electrode placement facilitates the exploration of single neuronal activity without affecting animal behaviors. Because the system is equipped with a newly developed data-encoding program, the recorded data are readily compressed almost to theoretical limits and securely transmitted to a host computer. Brain activity can thereby be stably monitored in real time and further analyzed using online or offline spike sorting. Our wireless recording approach using a precision motorized microdrive will become a powerful tool for studying brain mechanisms underlying natural or social behaviors.

Acute exacerbation of sleep apnea by hyperoxia impairs cognitive flexibility in Brown-Norway rats

STUDY OBJECTIVES

To determine whether learning deficits occur during acute exacerbation of spontaneous sleep related breathing disorder (SRBD) in rats with high (Brown Norway; BN) and low (Zucker Lean; ZL) apnea propensity.

DESIGN

Spatial acquisition (3 days) and reversal learning (3 days) in the Morris water maze (MWM) with polysomnography (12:00-08:00): (1) with acute SRBD exacerbation (by 20-h hyperoxia immediately preceding reversal learning) or (2) without SRBD exacerbation (room air throughout).

SETTING

Randomized, placebo-controlled, repeated-measures design.

PARTICIPANTS

14 BN rats; 16 ZL rats.

INTERVENTIONS

20-h hyperoxia.

MEASUREMENTS AND RESULTS

Apneas were detected as cessation of respiration ≥ 2 sec. Swim latency in MWM, apnea indices (AI; apneas/hour of sleep) and percentages of recording time for nonrapid eye movement (NREM), rapid eye movement (REM), and total sleep were assessed. Baseline AI in BN rats was more than double that of ZL rats (22.46 ± 2.27 versus 10.7 ± 0.9, P = 0.005). Hyperoxia increased AI in both BN (34.3 ± 7.4 versus 22.46 ± 2.27) and ZL rats (15.4 ± 2.7 versus 10.7 ± 0.9) without changes in sleep stage percentages. Control (room air) BN and ZL rats exhibited equivalent acquisition and reversal learning. Acute exacerbation of AI by hyperoxia produced a reversal learning performance deficit in BN but not ZL rats. In addition, the percentage of REM sleep and REM apnea index in BN rats during hyperoxia negatively correlated with reversal learning performance.

CONCLUSIONS

Acute exacerbation of sleep related breathing disorder by hyperoxia impairs reversal learning in a rat strain with high apnea propensity, but not a strain with a low apnea propensity. This suggests a non-linear threshold effect may contribute to the relationships between sleep apnea and cognitive dysfunctions, but strain-specific differences also may be important.

Contralateral disconnection of the rat prelimbic cortex and dorsomedial striatum impairs cue-guided behavioral switching

Switches in reward outcomes or reward-predictive cues are two fundamental ways in which information is used to flexibly shift response patterns. The rat prelimbic cortex and dorsomedial striatum support behavioral flexibility based on a change in outcomes. The present experiments investigated whether these two brain regions are necessary for conditional discrimination performance in which a switch in reward-predictive cues occurs every three to six trials. The GABA agonists baclofen and muscimol infused into the prelimbic cortex significantly impaired performance leading rats to adopt an inappropriate turn strategy. The NMDA receptor antagonist D-AP5 infused into the dorsomedial striatum or prelimbic cortex and dorsomedial striatum contralateral disconnection impaired performance due to a rat failing to switch a response choice for an entire trial block in about two out of 13 test blocks. In an additional study, contralateral disconnection did not affect nonswitch discrimination performance. The results suggest that the prelimbic cortex and dorsomedial striatum are necessary to support cue-guided behavioral switching. The prelimbic cortex may be critical for generating alternative response patterns while the dorsomedial striatum supports the selection of an appropriate response when cue information must be used to flexibly switch response patterns.

Thalamic neuromodulation and its implications for executive networks

The thalamus is a key structure that controls the routing of information in the brain. Understanding modulation at the thalamic level is critical to understanding the flow of information to brain regions involved in cognitive functions, such as the neocortex, the hippocampus, and the basal ganglia. Modulators contribute the majority of synapses that thalamic cells receive, and the highest fraction of modulator synapses is found in thalamic nuclei interconnected with higher order cortical regions. In addition, disruption of modulators often translates into disabling disorders of executive behavior. However, modulation in thalamic nuclei such as the midline and intralaminar groups, which are interconnected with forebrain executive regions, has received little attention compared to sensory nuclei. Thalamic modulators are heterogeneous in regards to their origin, the neurotransmitter they use, and the effect on thalamic cells. Modulators also share some features, such as having small terminal boutons and activating metabotropic receptors on the cells they contact. I will review anatomical and physiological data on thalamic modulators with these goals: first, determine to what extent the evidence supports similar modulator functions across thalamic nuclei; and second, discuss the current evidence on modulation in the midline and intralaminar nuclei in relation to their role in executive function.

Differential entrainment and learning-related dynamics of spike and local field potential activity in the sensorimotor and associative striatum

Parallel cortico-basal ganglia loops are thought to have distinct but interacting functions in motor learning and habit formation. In rats, the striatal projection neuron populations (MSNs) in the dorsolateral and dorsomedial striatum, respectively corresponding to sensorimotor and associative regions of the striatum, exhibit contrasting dynamics as rats acquire T-maze tasks (Thorn et al., 2010). Here, we asked whether these patterns could be related to the activity of local interneuron populations in the striatum and to the local field potential activity recorded simultaneously in the corresponding regions. We found that dorsolateral and dorsomedial striatal fast-spiking interneurons exhibited task-specific and training-related dynamics consistent with those of corresponding MSN populations. Moreover, both MSNs and interneuron populations in both regions became entrained to theta-band (5-12 Hz) frequencies during task acquisition. However, the predominant entrainment frequencies were different for the sensorimotor and associative zones. Dorsolateral striatal neurons became entrained mid-task to oscillations centered ∼ 5 Hz, whereas simultaneously recorded neurons in the dorsomedial region became entrained to higher frequency (∼ 10 Hz) rhythms. These region-specific patterns of entrainment evolved dynamically with the development of region-specific patterns of interneuron and MSN activity, indicating that, with learning, these two striatal regions can develop different frequency-modulated circuit activities in parallel. We suggest that such differential entrainment of sensorimotor and associative neuronal populations, acquired through learning, could be critical for coordinating information flow throughout each trans-striatal network while simultaneously enabling nearby components of the separate networks to operate independently.

Influence of parafascicular thalamic input on neuronal activity within the nucleus accumbens is mediated by nitric oxide - an in vivo study

AIMS

Thalamostriatal fibers are involved in cognitive tasks such as acquisition, learning, processing of sensory events, and behavioral flexibility and might play a role in Parkinson's disease. The aim of the present study was the in vivo electrochemical characterization of the projection from the lateral aspect of the parafascicular thalamus (Pfl) to the dorsolateral aspect of the nucleus accumbens (dNAc). Since nitric oxide (NO) plays a crucial role in striatal synaptic transmission, its implication in Pfl-evoked signaling within the dNAc was investigated.

MAIN METHODS

The Pfl was electrically stimulated utilizing paired pulses and extracellular potentials were recorded within the dNAc. Simultaneously, the dNAc was superfused using the push-pull superfusion technique for local application of compounds and for assessing the influence of NO on release of glutamate, aspartate and GABA.

KEY FINDINGS

Stimulation of the Pfl evoked a negative-going component at 9-14 ms followed by a positive-going component at 39-48 ms. The early response was current-dependent and diminished by superfusion of the dNAc with tetrodotoxin, kynurenic acid or N(G)-nitro-l-arginine methyl ester (L-NAME), while 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPA/NO) increased this evoked potential. Transmitter release was inhibited by L-NAME and facilitated by PAPA/NO.

SIGNIFICANCE

This study describes for the first time in vivo extracellular electrical responses of the dNAc on stimulation of the Pfl. Synaptic transmission within the dNAc on stimulation of the Pfl seems to be facilitated by NO.

Cortical and thalamic excitation mediate the multiphasic responses of striatal cholinergic interneurons to motivationally salient stimuli

Cholinergic interneurons are key components of striatal microcircuits. In primates, tonically active neurons (putative cholinergic interneurons) exhibit multiphasic responses to motivationally salient stimuli that mirror those of midbrain dopamine neurons and together these two systems mediate reward-related learning in basal ganglia circuits. Here, we addressed the potential contribution of cortical and thalamic excitatory inputs to the characteristic multiphasic responses of cholinergic interneurons in vivo. We first recorded and labeled individual cholinergic interneurons in anesthetized rats. Electron microscopic analyses of these labeled neurons demonstrated that an individual interneuron could form synapses with cortical and, more commonly, thalamic afferents. Single-pulse electrical stimulation of ipsilateral frontal cortex led to robust short-latency (<20 ms) interneuron spiking, indicating monosynaptic connectivity, but firing probability progressively decreased during high-frequency pulse trains. In contrast, single-pulse thalamic stimulation led to weak short-latency spiking, but firing probability increased during pulse trains. After initial excitation from cortex or thalamus, interneurons displayed a "pause" in firing, followed by a "rebound" increase in firing rate. Across all stimulation protocols, the number of spikes in the initial excitation correlated positively with pause duration and negatively with rebound magnitude. The magnitude of the initial excitation, therefore, partly determined the profile of later components of multiphasic responses. Upon examining the responses of tonically active neurons in behaving primates, we found that these correlations held true for unit responses to a reward-predicting stimulus, but not to the reward alone, delivered outside of any task. We conclude that excitatory inputs determine, at least in part, the multiphasic responses of cholinergic interneurons under specific behavioral conditions.

The thalamostriatal system in normal and diseased states

Because of our limited knowledge of the functional role of the thalamostriatal system, this massive network is often ignored in models of the pathophysiology of brain disorders of basal ganglia origin, such as Parkinson's disease (PD). However, over the past decade, significant advances have led to a deeper understanding of the anatomical, electrophysiological, behavioral and pathological aspects of the thalamostriatal system. The cloning of the vesicular glutamate transporters 1 and 2 (vGluT1 and vGluT2) has provided powerful tools to differentiate thalamostriatal from corticostriatal glutamatergic terminals, allowing us to carry out comparative studies of the synaptology and plasticity of these two systems in normal and pathological conditions. Findings from these studies have led to the recognition of two thalamostriatal systems, based on their differential origin from the caudal intralaminar nuclear group, the center median/parafascicular (CM/Pf) complex, or other thalamic nuclei. The recent use of optogenetic methods supports this model of the organization of the thalamostriatal systems, showing differences in functionality and glutamate receptor localization at thalamostriatal synapses from Pf and other thalamic nuclei. At the functional level, evidence largely gathered from thalamic recordings in awake monkeys strongly suggests that the thalamostriatal system from the CM/Pf is involved in regulating alertness and switching behaviors. Importantly, there is evidence that the caudal intralaminar nuclei and their axonal projections to the striatum partly degenerate in PD and that CM/Pf deep brain stimulation (DBS) may be therapeutically useful in several movement disorders.

Neuronal loss in the caudal intralaminar thalamic nuclei in a primate model of Parkinson's disease

In light of postmortem human studies showing extensive degeneration of the center median (CM) and parafascicular (Pf) thalamic nuclei in Parkinson's disease patients, the present study assessed the extent of neuronal loss in CM/Pf of non-human primates that were rendered parkinsonian by repeated injections of low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In order to determine the course of CM/Pf degeneration during the MPTP intoxication, motor-asymptomatic animals with partial striatal dopamine denervation were also used. The Cavalieri's principle for volume estimation and the unbiased stereological cell count method with the optical dissector technique were used to estimate the total number of neurons in the CM/Pf. We found substantial neurons loss in the CM/Pf in both, motor-symptomatic MPTP-treated monkeys in which the striatal dopamine innervation was reduced by more than 80%, and in motor-asymptomatic MPTP-treated animals with 40-50% striatal dopamine loss. In MPTP-treated parkinsonian monkeys, 60 and 62% neurons loss was found in CM and Pf, respectively, while partially dopamine-depleted asymptomatic animals displayed 59 and 52% neurons loss in the CM and Pf, respectively. Thus, our study demonstrates that the CM/Pf neurons loss is an early phenomenon that occurs prior to the development of parkinsonian motor symptoms in these animals. In contrast, the neighboring mediodorsal nucleus of the thalamus was only mildly affected (18% neurons loss) in the parkinsonian monkeys. Together with recent findings about the possible role of the CM/Pf-striatal system in cognition, our findings suggest that the pathology of the thalamostriatal system may precede the development of motor symptoms in PD, and may account for some of the cognitive deficits in attentional set-shifting often seen in these patients. Future studies in this animal model, and in monkeys with selective lesion of CM or Pf, are needed to further elucidate the role of the CM/Pf-striatal system in normal and parkinsonian conditions.

The prelimbic cortex and subthalamic nucleus contribute to cue-guided behavioral switching

Frontal cortex-basal ganglia circuitry supports behavioral switching when a change in outcome information is used to adapt response patterns. Less is known about whether specific frontal cortex-basal ganglia circuitry supports behavioral switching when cues signal that a change in response patterns should occur. The present experiments investigated whether the prelimbic cortex and subthalamic nucleus in male Long-Evans rats supports cue-guided switching in a conditional discrimination test. Rats learned in a cross-maze that a start arm cue (black or white) signaled which of two maze arms to enter for a food reward. The cue was switched every 3-6 trials. Baclofen and muscimol infused into the prelimbic cortex significantly impaired performance by increasing switch trial errors, as well as trials immediately following a switch trial (perseveration) and after initially making a correct switch (maintenance error). NMDA receptor blockade in the subthalamic nucleus significantly impaired performance by increasing switch errors and perseveration. Contralateral disconnection of these areas significantly reduced conditional discrimination performance by increasing switch and perseverative errors. These findings suggest that the prelimbic area and subthalamic nucleus support the use of cue information to facilitate an initial switch away from a previously relevant response pattern.

The role of the amygdala-striatal pathway in the acquisition and performance of goal-directed instrumental actions

The posterior dorsomedial striatum (pDMS) is essential for the acquisition and expression of the specific response-outcome (R-O) associations that underlie goal-directed action. Here we examined the role of a pathway linking the basolateral amygdala (BLA) and pDMS in such goal-directed learning. In Experiment 1, rats received unilateral lesions of the BLA and were implanted with cannula targeting the pDMS in either the ipsilateral (control) or contralateral (disconnection) hemisphere. After initial training, rats received infusions of muscimol to inactivate the pDMS immediately before sessions in which novel R-O associations were introduced. Sensitivity to devaluation by specific satiety was then assessed. Whereas rats in the ipsilateral group used the recently acquired associations to direct performance following devaluation, those in the contralateral group could not, indicating that BLA-pDMS disconnection prevented the acquisition of the new R-O associations. Indeed, evidence suggested that these rats relied instead on learning acquired during prior training to direct performance following devaluation. In Experiment 2, rats underwent similar surgery and training except they received muscimol infusions immediately before devaluation testing. Those in the ipsilateral group showed a selective devaluation effect, again based on the most recently introduced R-O associations. In contrast, rats in the contralateral group showed nonselective performance after devaluation indicating that the BLA-DMS pathway is also required for the expression of selective R-O associations. Together these results suggest that input from the BLA is essential for specific R-O learning by the pDMS.

The role of the anterior, mediodorsal, and parafascicular thalamus in instrumental conditioning

The traditional animal model of instrumental behavior has focused almost exclusively on structures within the cortico-striatal network and ignored the contributions of various thalamic nuclei despite large and specific connections with each of these structures. One possible reason for this is that the thalamus has been conventionally viewed as a mediator of general processes, such as attention, arousal and movement, that are not easily separated from more cognitive aspects of instrumental behavior. Recent research has, however, begun to separate these roles. Here we review the role of three thalamic nuclei in instrumental conditioning: the anterior thalamic nuclei (ANT), the mediodorsal (MD), and parafascicular thalamic nuclei (PF). Early research suggested that ANT might regulate aspects of instrumental behavior but, on review, we suggest that the types of tasks used in these studies were more likely to recruit Pavlovian processes. Indeed lesions of ANT have been found to have no effect on performance in instrumental free-operant tasks. By contrast the mediodorsal thalamus (MD) has been found to play a specific and important role in the acquisition of goal-directed action. We propose this role is related to its connections with prelimbic cortex (PL) and present new data that directly implicates this circuit in the acquisition of goal-directed actions. Finally we review evidence suggesting the PF, although not critical for the acquisition or performance of instrumental actions, plays a specific role in regulating action flexibility.

The thalamostriatal pathway and cholinergic control of goal-directed action: interlacing new with existing learning in the striatum

The capacity for goal-directed action depends on encoding specific action-outcome associations, a learning process mediated by the posterior dorsomedial striatum (pDMS). In a changing environment, plasticity has to remain flexible, requiring interference between new and existing learning to be minimized, yet it is not known how new and existing learning are interlaced in this way. Here we investigated the role of the thalamostriatal pathway linking the parafascicular thalamus (Pf) with cholinergic interneurons (CINs) in the pDMS in this process. Removing the excitatory input from Pf to the CINs was found to reduce the firing rate and intrinsic activity of these neurons and produced an enduring deficit in goal-directed learning after changes in the action-outcome contingency. Disconnection of the Pf-pDMS pathway produced similar behavioral effects. These data suggest that CINs reduce interference between new and existing learning, consistent with claims that the thalamostriatal pathway exerts state control over learning-related plasticity.

The selective serotonin reuptake inhibitor, escitalopram, enhances inhibition of prepotent responding and spatial reversal learning

Previous findings indicate treatment with a selective serotonin reuptake inhibitor (SSRI) facilitates behavioral flexibility when conditions require inhibition of a learned response pattern. The present experiment investigated whether acute treatment with the SSRI, escitalopram, affects behavioral flexibility when conditions require inhibition of a naturally biased response pattern (elevated conflict test) and/or reversal of a learned response pattern (spatial reversal learning). An additional experiment was carried out to determine whether escitalopram, at doses that affected behavioral flexibility, also reduced anxiety as tested in the elevated plus-maze. In each experiment, Long-Evans rats received an intraperitoneal injection of either saline or escitalopram (0.03, 0.3 or 1.0 mg/kg) 30 min prior to behavioral testing. Escitalopram, at all doses tested, enhanced acquisition in the elevated conflict test, but did not affect performance in the elevated plus-maze. Escitalopram (0.3 and 1.0 mg/kg) did not alter acquisition of the spatial discrimination, but facilitated reversal learning. In the elevated conflict and spatial reversal learning test, escitalopram enhanced the ability to maintain the relevant strategy after being initially selected. The present findings suggest that enhancing serotonin transmission with an SSRI facilitates inhibitory processes when conditions require a shift away from either a naturally biased response pattern or a learned choice pattern.

Effects of chronic low- and high-dose nicotine on cognitive flexibility in C57BL/6J mice

The addictive nature of nicotine remains a global health problem. Despite the availability of treatments for smoking cessation, relapse to smoking after quit attempts still remains very high. Here, we evaluated the effects of chronic nicotine in male C57BL/6J mice in an operant cognitive flexibility task that required the animals to progress sequentially through multiple phases including visual discrimination, strategy shifting and response reversal. As frontostriatal circuits involving discrete regions of dorsal striatum contribute directly to decision-making processes, and BDNF modulates synaptic plasticity and learning, we also assessed the effects of nicotine on striatal BDNF expression. Osmotic minipumps containing either of the two doses of nicotine (low: 6.3 mg/kg/day; high: 18 mg/kg/day) or saline (control) were implanted for chronic delivery that lasted 4 weeks. Nicotine-treated mice exhibited greater response accuracy during visual discrimination. Neither dose of nicotine affected learning of new egocentric response strategy during set-shifting. However, higher but not lower dose of nicotine impaired reversal learning by increasing perseverative responding to the previously non-reinforced stimulus. Furthermore, this effect was associated with reduced BDNF levels in the dorsal striatum. Collectively, these findings suggest that higher relapse rates often observed in high nicotine-dependent smokers may be attributed to impairments in inhibitory control processes. Moreover, striatal BDNF may play a critical role in nicotine-induced alterations in cognitive flexibility.

Identification of neuronal loci involved with displays of affective aggression in NC900 mice

Aggression is a complex behavior that is essential for survival. Of the various forms of aggression, impulsive violent displays without prior planning or deliberation are referred to as affective aggression. Affective aggression is thought to be caused by aberrant perceptions of, and consequent responses to, threat. Understanding the neuronal networks that regulate affective aggression is pivotal to development of novel approaches to treat chronic affective aggression. Here, we provide a detailed anatomical map of neuronal activity in the forebrain of two inbred lines of mice that were selected for low (NC100) and high (NC900) affective aggression. Attack behavior was induced in male NC900 mice by exposure to an unfamiliar male in a novel environment. Forebrain maps of c-Fos+ nuclei, which are surrogates for neuronal activity during behavior, were then generated and analyzed. NC100 males rarely exhibited affective aggression in response to the same stimulus, thus their forebrain c-Fos maps were utilized to identify unique patterns of neuronal activity in NC900s. Quantitative results indicated robust differences in the distribution patterns and densities of c-Fos+ nuclei in distinct thalamic, subthalamic, and amygdaloid nuclei, together with unique patterns of neuronal activity in the nucleus accumbens and the frontal cortices. Our findings implicate these areas as foci regulating differential behavioral responses to an unfamiliar male in NC900 mice when expressing affective aggression. Based on the highly conserved patterns of connections and organization of neuronal limbic structures from mice to humans, we speculate that neuronal activities in analogous networks may be disrupted in humans prone to maladaptive affective aggression.

The primate thalamostriatal systems: Anatomical organization, functional roles and possible involvement in Parkinson's disease

The striatum receives glutamatergic inputs from two main thalamostriatal systems that originate either from the centre median/parafascicular complex (CM/PF-striatal system) or the rostral intralaminar, midline, associative and relay thalamic nuclei (non-CM/PF-striatal system). These dual thalamostriatal systems display striking differences in their anatomical and, most likely, functional organization. The CM/PF-striatal system is topographically organized, and integrated within functionally segregated basal ganglia-thalamostriatal circuits that process sensorimotor, associative and limbic information. CM/PF neurons are highly responsive to attention-related sensory stimuli, suggesting that the CM/PF-striatal system, through its strong connections with cholinergic interneurons, may play a role in basal ganglia-mediated learning, behavioral switching and reinforcement. In light of evidence for prominent CM/PF neuronal loss in Parkinson's disease, we propose that the significant CM-striatal system degeneration, combined with the severe nigrostriatal dopamine loss in sensorimotor striatal regions, may alter normal automatic actions, and shift the processing of basal ganglia-thalamocortical motor programs towards goal-directed behaviors.

Differences in BTBR T+ tf/J and C57BL/6J mice on probabilistic reversal learning and stereotyped behaviors

Autism spectrum disorders (ASD) represent a class of neurodevelopmental disorders characterized by impairments in social interaction, verbal and non-verbal communication, as well as restricted interests and repetitive behavior. This latter class of symptoms often includes features such as compulsive behaviors and resistance to change. The BTBR T+ tf/J mouse strain has been used as an animal model to investigate the social communication and restricted interest features in ASD. Less is known about whether this mouse strain models cognitive flexibility deficits also observed in ASD. The present experiment investigated performance of BTBR T+ tf/J and C57BL/6J on two different spatial reversal learning tests (100% accurate feedback and 80/20 probabilistic feedback), as well as marble burying and grooming behavior. BTBR T+ tf/J and C57BL/6J mice exhibited similar performance on acquisition and reversal learning with 100% accurate feedback. BTBR T+ tf/J mice were impaired in probabilistic reversal learning compared to that of C57BL/6J mice. BTBR T+ tf/J mice also displayed increased stereotyped repetitive behaviors compared to that of C57BL/6J mice as shown by increased marble burying and grooming behavior. The present findings indicate that BTBR T+ tf/J mice exhibit similar features related to "insistence on sameness" in ASD that include not only stereotyped repetitive behaviors, but also alterations in behavioral flexibility. Thus, BTBR T+ tf/J mice can serve as a model to understand the neural mechanisms underlying alterations in behavioral flexibility, as well as to test potential treatments in alleviating these symptoms.