Coincident stimulation of convergent cortical inputs enhances immediate early gene induction in the striatum

Hyperactivity of indirect pathway-projecting spiny projection neurons promotes compulsive behavior

Compulsive behaviors are a hallmark symptom of obsessive compulsive disorder (OCD). Striatal hyperactivity has been linked to compulsive behavior generation in correlative studies in humans and causal studies in rodents. However, the contribution of the two distinct striatal output populations to the generation and treatment of compulsive behavior is unknown. These populations of direct and indirect pathway-projecting spiny projection neurons (SPNs) have classically been thought to promote or suppress actions, respectively, leading to a long-held hypothesis that increased output of direct relative to indirect pathway promotes compulsive behavior. Contrary to this hypothesis, here we find that indirect pathway hyperactivity is associated with compulsive grooming in the Sapap3-knockout mouse model of OCD-relevant behavior. Furthermore, we show that suppression of indirect pathway activity using optogenetics or treatment with the first-line OCD pharmacotherapy fluoxetine is associated with reduced grooming in Sapap3-knockouts. Together, these findings highlight the striatal indirect pathway as a potential treatment target for compulsive behavior.

The cortico-striatal circuitry in autism-spectrum disorders: a balancing act

The basal ganglia are major targets of cortical inputs and, in turn, modulate cortical function via their projections to the motor and prefrontal cortices. The role of the basal ganglia in motor control and reward is well documented and there is also extensive evidence that they play a key role in social and repetitive behaviors. The basal ganglia influence the activity of the cerebral cortex via two major projections from the striatum to the output nuclei, the globus pallidus internus and the substantia nigra, pars reticulata. This modulation involves a direct projection known as the direct pathway and an indirect projection via the globus pallidus externus and the subthalamic nucleus, known as the indirect pathway. This review discusses the respective contribution of the direct and indirect pathways to social and repetitive behaviors in neurotypical conditions and in autism spectrum disorders.

Cellular activation in limbic brain systems during social play behaviour in rats

Positive social interactions during the juvenile and adolescent phases of life are essential for proper social and cognitive development in mammals, including humans. During this developmental period, there is a marked increase in peer-peer interactions, signified by the abundance of social play behaviour. Despite its importance for behavioural development, our knowledge of the neural underpinnings of social play behaviour is limited. Therefore, the purpose of this study was to map the neural circuits involved in social play behaviour in rats. This was achieved by examining cellular activity after social play using the immediate early gene c-Fos as a marker. After a session of social play behaviour, pronounced increases in c-Fos expression were observed in the medial prefrontal cortex, medial and ventral orbitofrontal cortex, dorsal striatum, nucleus accumbens core and shell, lateral amygdala, several thalamic nuclei, dorsal raphe and the pedunculopontine tegmental nucleus. Importantly, the cellular activity patterns after social play were topographically organized in this network, as indicated by play-specific correlations in c-Fos activity between regions with known direct connections. These correlations suggest involvement in social play behaviour of the projections from the medial prefrontal cortex to the striatum, and of amygdala and monoaminergic inputs to frontal cortex and striatum. The analyses presented here outline a topographically organized neural network implicated in processes such as reward, motivation and cognitive control over behaviour, which mediates social play behaviour in rats.

Molecular and anatomical signatures of sleep deprivation in the mouse brain

Sleep deprivation (SD) leads to a suite of cognitive and behavioral impairments, and yet the molecular consequences of SD in the brain are poorly understood. Using a systematic immediate-early gene (IEG) mapping to detect neuronal activation, the consequences of SD were mapped primarily to forebrain regions. SD was found to both induce and suppress IEG expression (and thus neuronal activity) in subregions of neocortex, striatum, and other brain regions. Laser microdissection and cDNA microarrays were used to identify the molecular consequences of SD in seven brain regions. In situ hybridization (ISH) for 222 genes selected from the microarray data and other sources confirmed that robust molecular changes were largely restricted to the forebrain. Analysis of the ISH data for 222 genes (publicly accessible at http://sleep.alleninstitute.org) provided a molecular and anatomic signature of the effects of SD on the brain. The suprachiasmatic nucleus (SCN) and the neocortex exhibited differential regulation of the same genes, such that in the SCN genes exhibited time-of-day effects while in the neocortex, genes exhibited only SD and waking (W) effects. In the neocortex, SD activated gene expression in areal-, layer-, and cell type-specific manner. In the forebrain, SD preferentially activated excitatory neurons, as demonstrated by double-labeling, except for striatum which consists primarily of inhibitory neurons. These data provide a characterization of the anatomical and cell type-specific signatures of SD on neuronal activity and gene expression that may account for the associated cognitive and behavioral effects.

The integrative function of the basal ganglia in instrumental conditioning

Recent research in instrumental conditioning has focused on the striatum, particularly the role of the dorsal striatum in the learning processes that contribute to instrumental performance in rats. This research has found evidence of what appear to be parallel, functionally and anatomically distinct circuits involving dorsomedial striatum (DMS) and dorsolateral striatum (DLS) that contribute to two independent instrumental learning processes. Evidence suggests that the formation of the critical action-outcome associations mediating goal-directed action are localized to the dorsomedial striatum, whereas the sensorimotor connections that control the performance of habitual actions are localized to the dorsolateral striatum. In addition to the dorsal striatum, these learning processes appear to engage distinct cortico-striatal networks and to be embedded in a complex of converging and partially segregated loops that constitute the cortico-striatal thalamo-cortical feedback circuit. As the entry point for the basal ganglia, cortical circuits involving the dorsal striatum are clearly in a position to control a variety of motor functions but, as recent studies of various neurodegenerative disorders have made clear, they are also involved in a number of cognitive and executive functions including action selection, planning, and decision-making.

Intratelencephalic corticostriatal neurons equally excite striatonigral and striatopallidal neurons and their discharge activity is selectively reduced in experimental parkinsonism

Striatonigral and striatopallidal neurons form distinct populations of striatal projection neurons. Their discharge activity is imbalanced after dopaminergic degeneration in Parkinson's disease. Striatal projection neurons receive massive cortical excitatory inputs from bilateral intratelencephalic (IT) neurons projecting to both the ipsilateral and contralateral striatum and from collateral axons of ipsilateral neurons that send their main axon through the pyramidal tract (PT). Previous anatomical studies in rats suggested that IT and PT inputs preferentially excite striatonigral and striatopallidal neurons, respectively. Here we used electrophysiological criteria to identify them with antidromic stimulations. We show that the spontaneous discharge activity of IT neurons is depressed, whereas that of PT neurons is not affected in the rat cortex ipsilateral to 6-hydroxydopamine injection. However, our functional experiments do not support the hypothesis of a differential cortical input to striatal pathways. Firstly, although the conduction velocity of PT neurons is 4.6 times faster than that of IT neurons, identified striatopallidal and striatonigral neurons exhibit identical latencies of their spike responses to electrical stimulation of the ipsilateral cortex. Secondly, although PT neurons are ipsilateral, both striatal populations exhibit similar sensitivity to the stimulation of the ipsilateral and contralateral cortex. We suggest that IT neurons provide the main excitatory input to both striatal populations and that the corticostriatal PT input is weaker. Therefore, our functional data do not support our previous hypothesis that the deficit of IT neurons associated with the dopaminergic depletion might contribute to the striatal imbalance. This imbalance might rather result from intrinsic striatal mechanisms.

Food-associated cues alter forebrain functional connectivity as assessed with immediate early gene and proenkephalin expression

Background

Cues predictive of food availability are powerful modulators of appetite as well as food-seeking and ingestive behaviors. The neurobiological underpinnings of these conditioned responses are not well understood. Monitoring regional immediate early gene expression is a method used to assess alterations in neuronal metabolism resulting from upstream intracellular and extracellular signaling. Furthermore, assessing the expression of multiple immediate early genes offers a window onto the possible sequelae of exposure to food cues, since the function of each gene differs. We used immediate early gene and proenkephalin expression as a means of assessing food cue-elicited regional activation and alterations in functional connectivity within the forebrain.

Results

Contextual cues associated with palatable food elicited conditioned motor activation and corticosterone release in rats. This motivational state was associated with increased transcription of the activity-regulated genes homer1a, arc, zif268, ngfi-b and c-fos in corticolimbic, thalamic and hypothalamic areas and of proenkephalin within striatal regions. Furthermore, the functional connectivity elicited by food cues, as assessed by an inter-regional multigene-expression correlation method, differed substantially from that elicited by neutral cues. Specifically, food cues increased cortical engagement of the striatum, and within the nucleus accumbens, shifted correlations away from the shell towards the core. Exposure to the food-associated context also induced correlated gene expression between corticostriatal networks and the basolateral amygdala, an area critical for learning and responding to the incentive value of sensory stimuli. This increased corticostriatal-amygdalar functional connectivity was absent in the control group exposed to innocuous cues.

Conclusion

The results implicate correlated activity between the cortex and the striatum, especially the nucleus accumbens core and the basolateral amygdala, in the generation of a conditioned motivated state that may promote excessive food intake. The upregulation of a number of genes in unique patterns within corticostriatal, thalamic, and hypothalamic networks suggests that food cues are capable of powerfully altering neuronal processing in areas mediating the integration of emotion, cognition, arousal, and the regulation of energy balance. As many of these genes play a role in plasticity, their upregulation within these circuits may also indicate the neuroanatomic and transcriptional correlates of extinction learning.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

Motor-skill learning-associated gene regulation in the striatum: effects of cocaine

Psychostimulant-induced molecular changes in cortico-basal ganglia-cortical circuits play a critical role in addiction and dependence. These changes include alterations in gene regulation particularly in projection neurons of the sensorimotor striatum. We previously showed that cocaine-induced gene regulation in such neurons is dependent on the behavior performed during drug action. Rats trained on a running wheel under the influence of cocaine for 4 days subsequently displayed greater c-fos induction by cocaine than untrained controls. This effect was selective for the sensorimotor striatum, which is known to mediate forms of motor learning. In the present study, we investigated whether this enhanced cellular responsiveness was associated with learning of wheel running or with prolonged running (exercising), by assessing c-fos inducibility after 1, 2, or 8 days of training. Wheel training was performed after injection of cocaine (25 mg/kg) or vehicle, and c-fos induction by a cocaine challenge was measured 24 h later. Rats that trained under cocaine (but not vehicle) showed a greater c-fos response in the striatum compared to locked-wheel controls. This effect was present after the 1-day training, peaked after 2 days, and dissipated by 8 days of training. Similar effects were found for substance P, but not enkephalin, expression. These changes in striatal gene regulation paralleled improvement in wheel running, which was facilitated by cocaine. Thus, these training-induced molecular changes do not appear to represent exercising effects, but may reflect motor learning-associated neuronal changes altered by cocaine. Such cocaine effects may contribute to aberrant motor learning implicated in psychostimulant addiction.

Potential contributions of efferents from medial prefrontal cortex to neural activation following sexual behavior in the male rat

The limbic system plays an important role in the regulation of sexual motivation and reward. At the core of this system is an interconnected mesocorticolimbic circuit, comprised of the ventral tegmental area, nucleus accumbens and medial prefrontal cortex. Previously, our laboratory showed that sexual behavior causes neural activation in the ventral tegmental area of male rats. The main goal of this study is to identify afferent inputs to ventral tegmental area neurons that may contribute to their activation during sexual behavior. Hence, the anterograde tracer biotinylated dextran amine was injected into subregions of the rat medial prefrontal cortex, which is known to project to the ventral tegmental area. Visualization of biotinylated dextran amine-labeled axons was combined with immunostaining for sex-induced Fos expression. Quantitative analysis showed that the majority of sex-activated ventral tegmental area neurons receive putative contacts from the infralimbic and prelimbic--but not the anterior cingulate--subregions of the medial prefrontal cortex. Thus, inputs from infralimbic area and prelimbic are in an anatomical position to provide a major source of input during sexual behavior. A second goal of this study was to determine if the medial prefrontal cortex projects to sex-activated neurons in other brain regions important for sexual behavior and motivation. Infralimbic area and prelimbic area sent projections to nucleus accumbens, medial preoptic area, principal nucleus of the bed nucleus of the stria terminalis, basolateral amygdala, and parvocellular subparafasicular thalamic nucleus. Thus, the infralimbic and prelimbic subregions of the medial prefrontal cortex may also influence sexual behavior and motivation via brain regions other than the ventral tegmental area.