Adolescent impatience decreases with increased frontostriatal connectivity

Adolescence is a developmental period associated with an increase in impulsivity. Impulsivity is a multidimensional construct, and in this study we focus on one of the underlying components: impatience. Impatience can result from (i) disregard of future outcomes and/or (ii) oversensitivity to immediate rewards, but it is not known which of these evaluative processes underlie developmental changes. To distinguish between these two causes, we investigated developmental changes in the structural and functional connectivity of different frontostriatal tracts. We report that adolescents were more impatient on an intertemporal choice task and reported less future orientation, but not more present hedonism, than young adults. Developmental increases in structural connectivity strength in the right dorsolateral prefrontal tract were related to increased negative functional coupling with the striatum and an age-related decrease in discount rates. Our results suggest that mainly increased control, and the integration of future-oriented thought, drives the reduction in impatience across adolescence.

From ventral-medial to dorsal-lateral striatum: neural correlates of reward-guided decision-making

The striatum is critical for reward-guided and habitual behavior. Anatomical and interference studies suggest a functional heterogeneity within striatum. Medial regions, such as nucleus accumbens core and dorsal medial striatum play roles in goal-directed behavior, while dorsal lateral striatum is critical for control of habitual action. Subdivisions of striatum are topographically connected with different cortical and subcortical structures forming channels that carry information related to limbic, associative, and sensorimotor functions. Here, we describe data showing that as one progresses from ventral-medial to dorsal-lateral striatum, there is a shift from more prominent value encoding to activity more closely related to associative and motor aspects of decision-making. In addition, we will describe data suggesting that striatal circuits work in parallel to control behavior and that regions within striatum can compensate for each other when functions are disrupted.

Anatomo-proteomic characterization of human basal ganglia: focus on striatum and globus pallidus

BACKGROUND

The basal ganglia (BG) are a complex network of subcortical nuclei involved in the coordination and integration of the motor activity. Although these independent anatomical structures are functionally related, the proteome present in each isolated nucleus remains largely unexplored. In order to analyse the BG proteome in a large-scale format, we used a multi-dimensional fractionation approach which combines isolation of anatomically-defined nuclei, and protein/peptide chromatographic fractionation strategies coupled to mass spectrometry.

RESULTS

Using this workflow, we have obtained a proteomic expression profile across striatum and globus pallidus structures among which 1681 proteins were located in caudate nucleus (CN), 1329 in putamen, 1419 in medial globus pallidus (GPi), and 1480 in lateral globus pallidus (GPe), establishing a BG reference proteome to a depth of 2979 unique proteins. Protein interactome mapping highlighted significant clustering of common proteins in striatal and pallidal structures, contributing to oxidative phosphorylation, protein degradation and neurotrophin signalling pathways. In silico analyses emphasized specific pathways represented in striatal and pallidal structures highlighting 5-hydroxytryptamine degradation, synaptic vesicle trafficking, and dopamine, metabotropic glutamate and muscarinic acetylcholine receptor pathways. Additional bioinformatic analyses also revealed that: i) nearly 4% of identified proteins have been previously associated to neurodegenerative syndromes, ii) 11% of protein set tends to localize to synaptic terminal, and iii) 20% of identified proteins were also localized in cerebrospinal fluid (CSF).

CONCLUSIONS

Overall, the anatomo-proteomic profiling of BG complements the anatomical atlas of the human brain transcriptome, increasing our knowledge about the molecular basis of the BG and the etiology of the movement disorders.

The distribution of phosphodiesterase 2A in the rat brain

The phosphodiesterases (PDEs) are a superfamily of enzymes that regulate spatio-temporal signaling by the intracellular second messengers cAMP and cGMP. PDE2A is expressed at high levels in the mammalian brain. To advance our understanding of the role of this enzyme in regulation of neuronal signaling, we here describe the distribution of PDE2A in the rat brain. PDE2A mRNA was prominently expressed in glutamatergic pyramidal cells in cortex, and in pyramidal and dentate granule cells in the hippocampus. Protein concentrated in the axons and nerve terminals of these neurons; staining was markedly weaker in the cell bodies and proximal dendrites. In addition, in both hippocampus and cortex, small populations of non-pyramidal cells, presumed to be interneurons, were strongly immunoreactive. PDE2A mRNA was expressed in medium spiny neurons in neostriatum. Little immunoreactivity was observed in cell bodies, whereas dense immunoreactivity was found in the axon tracts of these neurons and their terminal regions in globus pallidus and substantia nigra pars reticulata. Immunostaining was dense in the medial habenula, but weak in other diencephalic regions. In midbrain and hindbrain, immunostaining was restricted to discrete regions of the neuropil or clusters of cell bodies. These results suggest that PDE2A may modulate cortical, hippocampal and striatal networks at several levels. Preferential distribution of PDE2A into axons and terminals of the principal neurons suggests roles in regulation of axonal excitability or transmitter release. The enzyme is also in forebrain interneurons, and in mid- and hindbrain neurons that may modulate forebrain networks and circuits.

A functional and structural investigation of the human fronto-basal volitional saccade network

Almost all cortical areas are connected to the subcortical basal ganglia (BG) through parallel recurrent inhibitory and excitatory loops, exerting volitional control over automatic behavior. As this model is largely based on non-human primate research, we used high resolution functional MRI and diffusion tensor imaging (DTI) to investigate the functional and structural organization of the human (pre)frontal cortico-basal network controlling eye movements. Participants performed saccades in darkness, pro- and antisaccades and observed stimuli during fixation. We observed several bilateral functional subdivisions along the precentral sulcus around the human frontal eye fields (FEF): a medial and lateral zone activating for saccades in darkness, a more fronto-medial zone preferentially active for ipsilateral antisaccades, and a large anterior strip along the precentral sulcus activating for visual stimulus presentation during fixation. The supplementary eye fields (SEF) were identified along the medial wall containing all aforementioned functions. In the striatum, the BG area receiving almost all cortical input, all saccade related activation was observed in the putamen, previously considered a skeletomotor striatal subdivision. Activation elicited by the cue instructing pro or antisaccade trials was clearest in the medial FEF and right putamen. DTI fiber tracking revealed that the subdivisions of the human FEF complex are mainly connected to the putamen, in agreement with the fMRI findings. The present findings demonstrate that the human FEF has functional subdivisions somewhat comparable to non-human primates. However, the connections to and activation in the human striatum preferentially involve the putamen, not the caudate nucleus as is reported for monkeys. This could imply that fronto-striatal projections for the oculomotor system are fundamentally different between humans and monkeys. Alternatively, there could be a bias in published reports of monkey studies favoring the caudate nucleus over the putamen in the search for oculomotor functions.

Neuroanatomical and neurochemical substrates of timing

We all have a sense of time. Yet, there are no sensory receptors specifically dedicated for perceiving time. It is an almost uniquely intangible sensation: we cannot see time in the way that we see color, shape, or even location. So how is time represented in the brain? We explore the neural substrates of metrical representations of time such as duration estimation (explicit timing) or temporal expectation (implicit timing). Basal ganglia (BG), supplementary motor area, cerebellum, and prefrontal cortex have all been linked to the explicit estimation of duration. However, each region may have a functionally discrete role and will be differentially implicated depending upon task context. Among these, the dorsal striatum of the BG and, more specifically, its ascending nigrostriatal dopaminergic pathway seems to be the most crucial of these regions, as shown by converging functional neuroimaging, neuropsychological, and psychopharmacological investigations in humans, as well as lesion and pharmacological studies in animals. Moreover, neuronal firing rates in both striatal and interconnected frontal areas vary as a function of duration, suggesting a neurophysiological mechanism for the representation of time in the brain, with the excitatory-inhibitory balance of interactions among distinct subtypes of striatal neuron serving to fine-tune temporal accuracy and precision.

[Morpho-functional and hodological peculiarities of ascending dopaminergic system of Rhodeus sericeus (Cyprinidae)]

Using the methods of tyrosine hydroxylase (TH) immunohistochemistry combined with nerve fiber labeling with carbocyanin dye DiI (1,1',dioctadecyl-3,3;3',3'-tetramethylindocarbocyanine perchlorate), the distribution of catecholaminergic (CE) neurons and their ascending projections to the basal telencephalon were studied in adult Amur cypriniform fish Rhodeus sericeus. Highly specialized complex of CE neurons was demonstrated in diencephalon. Six populations of TH-immunopositive neurons were detected in the area of posterior tuberculum, two of them were double-labeled, indicating the presence of dopaminergic projections to the ventral portion of the telencephalon (striatum). In the posteriotuberal area, two populations of CE cells were identified (small round neurons and large pear-shaped cells) which probably could correspond to the populations of sensomotor and limbic cells in mammals.

Reward-guided learning beyond dopamine in the nucleus accumbens: the integrative functions of cortico-basal ganglia networks

Here we challenge the view that reward-guided learning is solely controlled by the mesoaccumbens pathway arising from dopaminergic neurons in the ventral tegmental area and projecting to the nucleus accumbens. This widely accepted view assumes that reward is a monolithic concept, but recent work has suggested otherwise. It now appears that, in reward-guided learning, the functions of ventral and dorsal striata, and the cortico-basal ganglia circuitry associated with them, can be dissociated. Whereas the nucleus accumbens is necessary for the acquisition and expression of certain appetitive Pavlovian responses and contributes to the motivational control of instrumental performance, the dorsal striatum is necessary for the acquisition and expression of instrumental actions. Such findings suggest the existence of multiple independent yet interacting functional systems that are implemented in iterating and hierarchically organized cortico-basal ganglia networks engaged in appetitive behaviors ranging from Pavlovian approach responses to goal-directed instrumental actions controlled by action-outcome contingencies.

Spatiotemporal pattern of striatal ERK1/2 phosphorylation in a rat model of L-DOPA-induced dyskinesia and the role of dopamine D1 receptors

BACKGROUND

We examined the activation pattern of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and its dependence on D1 versus D2 dopamine receptors in hemiparkinsonian rats treated with 3,4-dihydroxyphenyl-L-alanine (L-DOPA).

METHODS

6-Hydroxydopamine-lesioned rats were treated acutely or chronically with L-DOPA in combination with antagonists for D1 or D2 receptors. Development of dyskinesia was monitored in animals receiving chronic drug treatment. Phosphorylation of ERK1/2, mitogen- and stress-activated protein kinase-1 (MSK-1), and the levels of FosB/DeltaFosB expression were examined immunohistochemically.

RESULTS

L-DOPA treatment caused phosphorylation of ERK1/2 in the dopamine-denervated striatum after acute and chronic administration. Similar levels were observed in matrix and striosomes, and in enkephalin-positive and dynorphin-positive neurons. The severity of dyskinesia was positively correlated with phospho-ERK1/2 levels. Phosphorylation of ERK1/2 and MSK-1 was dose-dependently blocked by SCH23390, but not by raclopride. SCH23390 also inhibited the development of dyskinesia and the induction of FosB/DeltaFosB.

CONCLUSIONS

L-DOPA produces pronounced activation of ERK1/2 signaling in the dopamine-denervated striatum through a D1-receptor-dependent mechanism. This effect is associated with the development of dyskinesia. Phosphorylated ERK1/2 is localized to both dynorphinergic and enkephalinergic striatal neurons, suggesting a general role of ERK1/2 as a plasticity molecule during L-DOPA treatment.

Imaging of striatal dopamine release elicited with NMDA antagonists: is there anything there to be seen?

Increased release of striatal dopamine, indexed with in vivo imaging of the D(2) receptor, has been reported following an acute challenge with N-methyl-D-aspartate (NMDA) antagonist ketamine in humans. Replications of this result have not been consistently successful. The aim of this manuscript is to evaluate in vivo imaging examination of NMDA antagonism on striataL dopamine release in published reports of humans and pre-clinical species. The literature is evaluated in conjunction with insights on the effect of NMDA antagonism on dopamine release, elicited from microdialysis and tissue turnover studies, and suggestions for future studies are made.

Genetic evidence implicating DARPP-32 in human frontostriatal structure, function, and cognition

Dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32), encoded by PPP1R1B, is a pivotal integrator of information in dopaminoceptive neurons, regulating the response to neuroleptics, psychotomimetics, and drugs of abuse, and affecting striatal function and plasticity. Despite extensive preclinical work, there are almost no data on DARPP-32 function in humans. Here, we identify, through resequencing in 298 chromosomes, a frequent PPP1R1B haplotype predicting mRNA expression of PPP1R1B isoforms in postmortem human brain. This haplotype was associated with enhanced performance on several cognitive tests that depend on frontostriatal function. Multimodal imaging of healthy subjects revealed an impact of the haplotype on neostriatal volume, activation, and the functional connectivity of the prefrontal cortex. The haplotype was associated with the risk for schizophrenia in 1 family-based association analysis. Our convergent results identify a prefrontal-neostriatal system affected by variation in PPP1R1B and suggest that DARPP-32 plays a pivotal role in cognitive function and possibly in the pathogenesis of schizophrenia.

The nerve cells of the neostriatum in the common shrew (Sorex araneus) and bank vole (Clethrionomys glareolus): a Golgi comparative study

The studies were carried out on 12 brains derived from adult representatives of two mammalian orders, Insectivora and Rodentia. The neostriatum was compared in the common shrew (Sorex araneus) and bank vole (Clethrionomys glareolus). Three main types of striatal neuron were distinguished in the common shrew and five types of neurons in the bank vole. The fifth type of bank vole neurons was additionally divided into two subtypes with respect to dendritic pattern.

Pharmacological MRI of stem cell transplants in the 3-nitroproprionic acid-damaged striatum

Blood oxygen level dependent (BOLD) pharmacological magnetic resonance imaging (phMRI) affords the non-invasive visualization of brain activity resulting from the administration of pharmacological compounds. Once the compound-responsive cells are lost, no change in activity is expected to occur. This principle therefore allows the assessment of neuronal loss or lack of signal transmission. These investigations can provide evidence of pathology in the absence of significant tissue loss and can be highly specific to determine which type of cell has been lost. Conversely, transplantation of cells replacing the lost neurons should restore normal signal transmission. We here demonstrate the application of phMRI to differentiate between rats with 3-nitroproprionic acid (3-NPA)-induced striatal lesions and 3-NPA-lesioned animals with neural stem cell transplants or controls. 3-NPA-induced lesions mainly involve striatal projection neurons that are responsive to dopamine agonists. The D2-agonist bromocriptine acts on these projection cells and loss of these through 3-NPA administration resulted in a significant decrease of locomotor activity and a substantial attenuation of the BOLD-response in the striatum. In contrast, lesioned animals that were grafted with neural stem cells exhibited an activity pattern akin to controls. Hence, grafting of neural stem cells exerts a functionally significant effect on striatal signal transmission that could underpin behavioral recovery.

Topography of cortical projections to the dorsolateral neostriatum in rats: multiple overlapping sensorimotor pathways

In rodents, the whisker representation in primary somatosensory (SI) cortex projects to the dorsolateral neostriatum, but the location of these projections has never been characterized with respect to layer IV barrels and their intervening septa. To address this issue, we injected a retrograde tracer into the dorsolateral neostriatum and then reconstructed the location of the labeled corticostriatal neurons with respect to the cytochrome oxidase (CO)-labeled barrels in SI. When the tracer was restricted to a small focal site in the neostriatum, the retrogradely labeled neurons formed elongated strips that were parallel to the curvilinear orientation of layer IV barrel rows. After larger tracer injections, labeled neurons were distributed uniformly across layer V and were aligned with both the barrel and septal compartments. Labeled projections from the contralateral SI barrel cortex, however, were much fewer in number and were disproportionately associated with the septal compartments. A comparison of the labeling patterns in the ipsilateral and contralateral hemispheres revealed symmetric, mirror-image distributions that extended across primary motor cortex (MI) and multiple somatosensory cortical regions, including the secondary somatosensory (SII) cortex, the parietal ventral (PV) and parietal rhinal (PR) areas, and the posteromedial (PM) region. Examination of the thalamus revealed labeled neurons in the intralaminar nuclei, in the medial part of the posterior nucleus (POm), and in the ventrobasal complex. These results indicate that the dorsolateral neostriatum integrates sensorimotor information from multiple sensorimotor representations in the thalamus and cortex.

The limbic lobe and its output channels: implications for emotional functions and adaptive behavior

Current dissatisfaction with the limbic system concept reflects a desire to move beyond the limbic system in efforts to explain key facets of emotional functions and motivational behavior. This review promotes an anatomical viewpoint, which originated as a result of histotechnical advances. These improvements paved the way for anatomical discoveries, which in turn led to the concepts of the ventral striatopallidal system and extended amygdala. These two systems, together with the basal nucleus of Meynert and the septum-diagonal band system, serve as output channels for an expanded version of the classic limbic lobe of Broca, which contains all non-isocortical parts of the cortical mantle together with the large laterobasal-cortical amygdaloid complex. Thus defined, the limbic lobe contains all of the major cortical (e.g. orbitofrontal, cingulate and insular cortices in addition to the hippocampal formation) and cortical-like (laterobasal-cortical amygdala) structures known to be especially important for emotional and motivational functions. In their role as output channels for the limbic lobe, the basal forebrain functional-anatomical systems contribute to the establishment of a number of cortico-subcortical circuits, which provide an important part of the anatomical substrate for the elaboration of emotional functions and adaptive behavior.

Magnetic resonance imaging at microscopic resolution reveals subtle morphological changes in a mouse model of dopaminergic hyperfunction

Structural abnormalities of the basal ganglia have been documented in several neuropsychiatric conditions associated with dysregulation of the dopamine system. However, the histological nature underlying these changes is largely unknown. Using magnetic resonance imaging at microscopic resolution (MRI, 9.4 T with 43 microm isotropic spatial resolution) and stereological techniques, we have investigated the effect of increased dopamine neurotransmission on brain morphology in mice with elevated extracellular dopamine, the dopamine transporter knockout (DAT-KO) mice. We first demonstrate the usefulness of MRI at microscopic resolution for the accurate identification and measurement of volumes of specific subregions, accounting for less than 0.03% (0.16 mm(3)) of the volume of a mouse brain. Furthermore, the MRI analysis reveals a significantly lower volume (-9%) of the anterior striatum of DAT-KO mice, while the volume of other dopamine-related structures such as the posterior striatum and the substantia nigra pars reticulata is unchanged in comparison to wild type littermates. Stereological analysis performed in the same brains reveals that one important structural factor accounting for this selective change in volume is a reduction of 18% in the absolute number of neuronal cell bodies. The feasibility of assessing accurately small morphological alterations in mouse models, where the molecular and histological pathologies can be easily compared in a controlled manner, provides a paradigm to examine the relevance of selective brain volumetric changes associated with a number of neuropathological conditions.

Asymmetrical changes of dopamine receptors in the striatum after unilateral dopamine depletion

Dopamine plays an important role in modulating synaptic transmission in the striatum and has great influence on the function of the basal ganglia. Degeneration of dopamine neurons in the substantia nigra (SN) is the major cause of many neurological disorders, and the reduction of dopamine innervation results in alterations of dopamine receptors in the striatum. It has been shown that the nigrostriatal dopamine system has functional and neurochemical asymmetry. To investigate the lateralization of dopamine receptors in the striatum after dopamine denervation, the present study used quantitative autoradiography to compare the changes in dopamine receptor binding in the left and right striatum in rats after unilateral dopamine depletion. In comparison to control levels, dopamine D1)-like receptor binding, labeled with [3H]-SCH23390, in the dorsal striatum was reduced 2 weeks after unilateral lesions of the SN with 6-hydroxydopamine. D1-like receptor binding was decreased in the ipsilateral striatum following unilateral lesions of either the left or right SN. The left and right striatum responded similarly to unilateral SN lesions, as there were no significant differences in the percent decrease in D1-like binding in the two striata. In contrast, D2-like receptor binding, labeled with [3H]-spiroperidol, was significantly increased in the dorsal striatum following an ipsilateral SN lesion. Furthermore, the up-regulation of D2-like receptors in the right striatum was significantly greater than that in the left striatum after an ipsilateral lesion. The asymmetrical up-regulation of striatal D2 receptors after extensive dopamine depletion might contribute to the lateralization of the nigrostriatal system observed in some pathological conditions.

Enhanced binding of dopamine D1receptors in caudate-putamen subregions in High-Yawning Sprague-Dawley rats

Previous reports have shown that the inbred High-Yawning (HY) and Low-Yawning (LY) rats differ in several behavioral characteristics related to mesolimbic and nigrostriatal dopamine (DA) function. To determine if differential expression of DA receptors or DA transporter may mediate the behavioral differences in these two sublines of the Sprague-Dawley rat, we performed a quantitative autoradiography study of the DA D1-like, D2-like, and DA-transporter binding in the basal ganglia and nucleus accumbens. The results show that levels of the D1 binding in the caudate-putamen of the HY rat were higher than in the LY animals, whereas no significant differences in the DA D2 receptors and DA transporter were noted in these sublines. These data suggest that the differences in DA receptors in D1 binding in HY rats may in part have contributed to the behavioral differences related to DA functions such as grooming and penile erection. Our findings are consistent with previous reports showing a decrease in the behavioral responses after systemic administration of DA agonist in LY compared to HY rats.

Functional mapping of the prosencephalic systems involved in organizing predatory behavior in rats

The study of the neural basis of predatory behavior has been largely neglected over the recent years. Using an ethologically based approach, we presently delineate the prosencephalic systems mobilized during predation by examining Fos immunoreactivity in rats performing insect hunting. These results were further compared with those obtained from animals killed after the early nocturnal surge of food ingestion. First, predatory behavior was associated with a distinct Fos up-regulation in the ventrolateral caudoputamen at intermediate rostro-caudal levels, suggesting a possible candidate to organize the stereotyped sequence of actions seen during insect hunting. Insect predation also presented conspicuous mobilization of a neural network formed by a distinct amygdalar circuit (i.e. the postpiriform-transition area, the anterior part of cortical nucleus, anterior part of basomedial nucleus, posterior part of basolateral nucleus, and medial part of central nucleus) and affiliated sites in the bed nuclei of the stria terminalis (i.e. the rhomboid nucleus) and in the hypothalamus (i.e. the parasubthalamic nucleus). Accordingly, this network is likely to encode prey-related motivational values, such as prey's odor and taste, and to influence autonomic and motor control accompanying predatory eating. Notably, regular food intake was also associated with a relatively weak Fos up-regulation in this network. However, during regular surge of food intake, we observed a much larger mobilization in hypothalamic sites related to the homeostatic control of eating, namely, the arcuate nucleus and autonomic parts of the paraventricular nucleus. Overall, the present findings suggest potential neural systems involved in integrating prey-related motivational values and in organizing the stereotyped sequences of action seen during predation. Moreover, the comparison with regular food intake contrasts putative neural mechanisms controlling predatory related eating vs. regular food intake.

Three-dimensional topography of corticopontine projections from rat sensorimotor cortex: comparisons with corticostriatal projections reveal diverse integrative organization

The major cortical-subcortical re-entrant pathways through the basal ganglia and cerebellum are considered to represent anatomically segregated channels for information originating in different cortical areas. A capacity for integrating unique combinations of cortical inputs has been well documented in the basal ganglia circuits but is largely undefined in the precerebellar circuits. To compare and quantify the amount of overlap that occurs in the first link of the cortico-ponto-cerebellar pathway, a dual tracing approach was used to map the spatial relationship between projections originating from the primary somatosensory cortex (SI), the secondary somatosensory cortex (SII), and the primary motor cortex (MI). The anterograde tracers biotinylated dextran amine and Fluoro-Ruby were injected into homologous whisker representations of either SI and SII, or SI and MI. The ensuing pontine labeling patterns were analyzed using a computerized three-dimensional reconstruction approach. The results demonstrate that whisker-related projections from SI and MI are largely segregated. At some locations, the two projections are adjoining and partly overlapping. Furthermore, SI contributes significantly more corticopontine projections than MI. By comparison, projections from corresponding representations in SI and SII terminate in similar parts of the pontine nuclei and display considerable amounts of spatial overlap. Finally, comparison of corticopontine and corticostriatal projections in the same experimental animals reveals that SI-SII overlap is significantly larger in the pontine nuclei than in the neostriatum. These structural differences indicate a larger capacity for integration of information within the same sensory modality in the pontocerebellar system compared to the basal ganglia.

Neurotensin receptor antagonist SR 142948A alters Fos expression and extrapyramidal side effect profile of typical and atypical antipsychotic drugs

Antipsychotic drugs (APDs) have previously been shown to alter Fos expression in a regionally specific manner. Increases in Fos expression in the nucleus accumbens (NAcc) are common to all clinically effective APDs. In contrast, APD-induced Fos expression increases in the caudate-putamen (CPu) and prefrontal cortex (PFC) are associated with the extrapyramidal side effect liability of typical APDs or the effectiveness against negative symptoms of atypical APDs, respectively. Considerable evidence suggests that the neuropeptide neurotensin (NT) mediates some of the effects of APDs. To determine whether NT neurotransmission is also involved in APD-induced Fos expression in brain regions relevant for therapeutic efficacy, the NT receptor antagonist SR 142948A (10 or 100 microg/kg i.p.) was coadministered with APDs (haloperidol (2.0 mg/kg s.c.), olanzapine (5 mg/kg i.p.), or clozapine (20 mg/kg s.c.)). Fos expression was evaluated in the PFC, NAcc shell, dorsomedial, and dorsolateral CPu and the lateral septum. SR 142948A attenuated haloperidol-induced Fos expression in the CPu but, in contrast, increased olanzapine-induced Fos expression in this brain region. The effects of the NT receptor antagonist were paralleled by its effects on catalepsy in olanzapine--but not haloperidol--treated animals.

Contributions of striatal subregions to place and response learning

The involvement of different subregions of the striatum in place and response learning was examined using a T-maze. Rats were given NMDA lesions of the dorsolateral striatum (DLS), anterior dorsomedial striatum (ADMS), posterior dorsomedial striatum (PDMS), or sham surgery. They were then trained to retrieve food from the west arm of the maze, starting from the south arm, by turning left at the choice point. After 7 d of training, with four trials a day, a probe test was given in which the starting arm is inserted as the north arm, at the opposite side of the maze. A left turn would indicate a "response" strategy; a right turn, a "place" strategy. The rats were then trained for 7 more days, followed by a second probe test. Unlike rats in the other groups, most of the rats in the PDMS group turned left, using the response strategy on both probe tests. These results suggest that the PDMS plays a role in spatially guided behavior.

Staging and preparation of human fetal striatal tissue for neural transplantation in Huntington's disease

Transplantation of human fetal central nervous system tissue has been shown to be of benefit in Parkinson's disease, and is currently being explored as a therapeutic option in Huntington's disease. The success of a neural transplant is dependent on a number of factors, including the requirement that donor cells are harvested within a given developmental window and that the cell preparation protocols take account of the biological parameters identified in animal models. Although many of the criteria necessary for a successful neural transplant have been defined in animal models, ultimately they must be validated in human studies, and some issues can only ever be addressed in human studies. Furthermore, because neural transplantation of human fetal tissue is limited to small numbers of patients in any one surgical center, largely due to practical constraints, it is crucial that tissue preparation protocols are clearly defined and reproducible, so that (i) multicenter trials are possible and are based on consistent tissue preparation parameters, and (ii) results between centers can be meaningfully analyzed. Here we describe the preparation of human fetal striatum for neural transplantation in Huntington's disease, and report on the validation of a method for estimating the developmental stage of the fetus based on direct morphometric measurements of the embryonic tissue.

Dorsal striatum and stimulus-response learning: lesions of the dorsolateral, but not dorsomedial, striatum impair acquisition of a simple discrimination task

In the present experiment, the effects of neurotoxic lesions (quinolinic acid) of the dorsolateral or dorsomedial striatum were investigated on a simple instrumental discrimination task (CS+/CS-). Rats with lesions of the dorsolateral striatum were found to be impaired in the acquisition of this task, as compared to rats with either dorsomedial striatal or sham lesions. Furthermore, dorsolateral striatal lesioned animals had significantly lower levels of responding across the course of discrimination training, as assessed both by overall rate of response during CS+ presentations and number of CS+ trials without a response, despite having shown levels of responding during variable interval training that did not differ from that of sham lesioned animals. In contrast, animals with lesions of the dorsomedial striatum did not show an impairment in acquisition of the present task, but had slightly higher rates of responding during CS- presentations. It is argued that the poor acquisition and low response rates observed in animals with dorsolateral striatal lesions reflect a failure in stimulus-response learning, while the performance of animals with dorsomedial striatal lesions may have been the result of an increase in overall activity rate.

Escalating dose methamphetamine pretreatment alters the behavioral and neurochemical profiles associated with exposure to a high-dose methamphetamine binge

The neurotoxic effects of methamphetamine (METH) have been characterized primarily from the study of high-dose binge regimens in rodents. However, this drug administration paradigm does not include a potentially important feature of stimulant abuse in humans, that is, the gradual escalation of stimulant doses that frequently occurs prior to high-dose exposure. We have argued that pretreatment with escalating doses (EDs) might significantly alter the neurotoxic profile produced by a single high-dose binge. In the present study, we tested this hypothesis by pretreating rats with saline or gradually increasing doses of METH (0.1-4.0 mg/kg over 14 days), prior to an acute METH binge (4 x 6 mg/kg at 2 h intervals). These animals, whose behavior was continuously monitored throughout drug treatment, were then killed 3 days later for determination of caudate-putamen dopamine (DA) content, levels of [(3)H]WIN 35,428 binding to the DA transporter, and levels of [(3)H]dihydrotetrabenazine ([(3)H]DTBZ) binding to the vesicular monoamine transporter. ED pretreatment markedly attenuated the stereotypy response, as well as the hyperthermia and indices of sympathetic activation associated with the acute binge. In addition, ED pretreatment prevented the decline in [(3)H]WIN 35,428 binding, and significantly diminished the decrease in DA levels, but did not affect the decrease in [(3)H]DTBZ binding associated with the acute binge. We suggest that further study of the effects produced by a regimen which includes a gradual escalation of doses prior to high-dose METH binge exposure could more accurately identify the neurochemical and behavioral changes relevant to those that occur as a consequence of high-dose METH abuse in humans.

IMHV lesions caused deficits in conspecific discrimination in chicks but not in adult quail

An experiment was conducted to investigate whether there is a functional difference in IMHV between chicks and adults using the conditioned individual preference (CIP) method, a modified conditioned place preference paradigm. CIP training of the quail involved 8 days of alternate injections of morphine or saline followed by associations with a stimulus quail in one compartment of the preference box. After the CIP training, the subject quail were given a choice between the morphine-associated and the saline-associated stimulus quail. All adult and chicks with neostriatum lesion showed a preference for the morphine-associated stimulus quail. However, the chicks receiving bilateral IMHV lesions before CIP did not show any preference for either stimulus quail. These results suggest that there is a functional difference in IMHV between chicks and adults.

Inhibitory effects of D2 agonists by striatal injection on excessive release of dopamine and hyperactivity induced by Bay K 8644 in rats

We investigated by means of behavioral and neurochemical studies the effects of either D(1) or D(2) agonist on excessive dopamine release and hyperactivity induced by the microinjection of Bay K 8644, and an L-type Ca(2+) channel stimulant, into the rat caudate putamen under a novel environmental condition. Hyperactivity (locomotor activity and rearing counts) and significant increases in extracellular dopamine levels induced by Bay K 8644 were concomitantly observed. D(1) agonist, SKF81297, administered into the caudate putamen did not block Bay K 8644-induced hyperactivity measured by monitoring both animal activity and increases in extracellular dopamine levels detected by microdialysis. Pretreatment with the D(2) agonists, bromocriptine, talipexole and pramipexole, into the caudate putamen significantly blocked Bay K 8644-induced hyperactivity for 45 min after Bay K 8644 administration, although the single administration of these agonists significantly potentiated locomotor activity and rearing behavior. Furthermore, these agonists significantly suppressed Bay K 8644-induced extracellular dopamine levels. Our results indicate that these D(2) agonists (1) act on postsynaptic neuronal D(2) receptors under conditions of normal or low dopamine release in the caudate putamen, and (2) act on presynaptic D(2) receptors (autoreceptors) when excessive levels of dopamine are released or hyperdopamine neuronal activity is induced. Consequently, the effect of D(2) agonists in the clinical treatment of Parkinson's disease may be due to stimulation of postsynaptic D(2) receptors rather than presynaptic autoreceptors.

Switching memory systems during learning: changes in patterns of brain acetylcholine release in the hippocampus and striatum in rats

This experiment measured acetylcholine (ACh) release simultaneously in the hippocampus and striatum while rats were trained in a cross maze. Consistent with past findings, rats initially showed learning on the basis of place (i.e., turning to the correct position relative to the room), but after extensive training, rats shifted to learning on the basis of response (i.e., turning to the right/left to find the food). Profiles of ACh release in the hippocampus and striatum were markedly different during training. In the hippocampus, ACh release increased by approximately 60% at the onset of training and remained at that level of release throughout training, even after the rats began to show learning on the basis of turning rather than place. In the striatum, increases in ACh release occurred later, reaching asymptotic increases of 30-40%, coincident with a transition from expressing place learning to expressing response learning. These findings suggest that the hippocampal and striatal systems both participate in learning in this task, but in a manner characterized by differential activation of the neural systems. The hippocampal system is apparently engaged first before the striatum is activated and, to the extent the hippocampus is important for place learning, promotes the use of a place solution to the maze. Later in training, although the hippocampus remains activated, the striatum is also activated in a manner that may enable the use of a response strategy to solve the maze. These findings may offer a neurobiological marker of a transition during skill learning from declarative to procedural learning.

Organization of the ectostriatum based on afferent connections in the zebra finch (Taeniopygia guttata)

In birds with laterally-located eyes, such as zebra finches and pigeons, the tectofugal visual pathway is the most prominent route from the retina to the telencephalon. However, little is known about exactly how the visual information is processed in this pathway, especially at the core region of the ectostriatum (Ec) in the telencephalon. In order to reveal a detailed organization of Ec, we decided to systematically analyze the afferent connections of Ec by injecting small amounts of sensitive tracers (biotinylated dextran amine and cholera toxin subunit B) selectively into different regions of Ec and the thalamic center of the tectofugal pathway (the nucleus rotundus, Rt). The present study revealed a clearer picture of the organization of Ec subdivisions than previously known. The present results showed that the anterior portion of Rt sent a heavy projection to the ventral region of the anterior Ec, whereas the more caudal subdivisions of Rt sent projections to more caudal and dorsal portions in Ec. The results suggest that Ec subdivisions appear to be arranged along an axis 'rotated' in the anterior direction, almost parallel to other major telencephalic laminae. These results may clarify the physiological and chemical heterogeneity of Ec found in the previous studies. The present findings also provide an insight into the possible organization of a visual processing center in a non-mammal.

Marginal division of the neostriatum: a subcortical memory center

The marginal division (MrD) is a pan-shaped subdivision in the caudal margin of the neostriatum newly discovered in the brains of the rat, cat, monkey and humans. A variety of intensely expressed neuropeptides and monoamines and their receptors were identified in the fibers, terminals and neuronal somata in the MrD with immunohistochemical and patch clamp methods. The MrD was shown to be involved in learning and memory by double-blind studies of Y-maze learning and long-term potentiation in rats. c-Fos expression and tract-tracing techniques with immunoelectronmicroscopy indicated that the MrD is a new component of the limbic system and is a key linking area between the limbic system and the basal nucleus of Meynert. Functional magnetic resonance image (fMRI) studies illustrated that the MrD and the prefrontal cortex are involved in digital working memory in the human brain. A cerebral hemorrhage case report confirmed the findings with fMRI. In conclusion, based on the position of the MrD, its advanced development in higher mammalian brains, abundant blood supply and diverse connections with other memory-related structures, MrD is likely to be an important subcortical center of learning and memory.

Effects of chronic dermal exposure to nonlethal doses of methyl parathion on brain regional acetylcholinesterase and muscarinic cholinergic receptors in female rats

The in vivo and in vitro effects of methyl parathion, a phosphorothionate insecticide, on cholinergic neurotransmitter systems in the brain of rats were investigated. Three groups of adult female rats received 0, 0.1, or 1.0 mg/kg methyl parathion via dermal exposure for 95 days. Exposure to 0.1 mg/kg methyl parathion produced inhibition of AChE in the caudate-putamen and thalamic nuclei, whereas 1.0 mg/kg resulted in inhibition of AChE in most brain regions. The same doses of methyl parathion had no effect on [(3)H]QNB binding to muscarinic receptors in the brain regions examined. The in vitro study demonstrated that methyl parathion causes preferential inhibition of AChE and [(3)H]QNB binding in specific brain regions. As an inhibitor of AChE, methyl paraoxon was 1,000-fold more potent than was methyl parathion. Similarly, methyl paraoxon showed brain region-specific inhibition of the enzyme. Generally, the brain stem was highly sensitive to organophosphate-induced inhibition of AChE activity and [(3)H]QNB binding. Because central respiratory neurons gather in the brain stem, preferential effects there and in other brain regions may underlie lethal toxicity of methyl parathion and other organophosphates.

Unilateral destruction of the dorsocentral striatum in rats produces neglect but not extinction to bilateral simultaneous stimulation

A number of previous studies have indicated that lesions of the medial agranular cortex (AGm) in rats induce multimodal neglect and extinction to bilateral simultaneous stimulation (extinction), the two major symptoms of the neglect syndrome in humans. A recent study demonstrated that lesions of dorsocentral striatum (DCS), the site of AGm projections to the striatum, produce multimodal neglect qualitatively similar to that found with AGm lesions. In the present study, the behavioral effects of unilateral DCS lesions were examined in more detail for the major manifestations of neglect: hemineglect, extinction, and allesthesia/allokinesia. Subjects were tested for extinction to bilateral simultaneous stimulation of the forepaws three times a week for 3 weeks. Neglect testing occurred twice weekly and the subjects were tested for the presence of neglect by rating the magnitude of orientation to visual, tactile, and auditory stimulation. The results indicated that DCS operates, while demonstrating severe neglect, failed to demonstrate extinction or allesthesia/allokinesia. These findings suggest that the neural mechanisms that underlie neglect and extinction are dissociable in this system. A better understanding of the neural mechanisms that underlie extinction is particularly important because humans that have recovered from neglect often continue to demonstrate the debilitating symptoms of extinction.

Changes in sleep-waking cycle after striatal excitotoxic lesions

Huntington's disease (HD) patients show severe diurnal choreic movements, while during slow-wave sleep (SWS) abnormal movements subside. Sleep disturbances in HD, including irregular delta activity and decreases in SWS, have also been reported. Striatal excitotoxic lesions have been shown to induce increased nocturnal spontaneous locomotor activity in rodents. In order to characterize the changes in circadian activity and sleep patterns and their correlation with motor activity after striatal excitotoxic lesions, Sprague-Dawley rats were implanted and lesioned; their locomotor and EEG activities were recorded for either 4 or 24 h during baseline or 7 and 30 days post-lesion. Locomotor activity increased significantly at 7 days post-lesion during the dark phase of the light-dark cycle. In contrast, total time spent in wakefulness (W) increased at 30 days post-lesion during the light phase of the cycle. This increase was at the expense of SWS duration. No disruption of the circadian curves was observed. Increases in the number of W-bouts and decreases in the duration of SWS-bouts were also observed. These results suggest the possible participation of the striatum in the regulation of the sleep-waking cycle, independent of locomotor activity. The increase in W could be due to loss of inhibition of target structures involved in regulation of the sleep-waking cycle.

Nonspatial and subdivision-specific working memory deficits after selective lesions of the avian prefrontal cortex

Association areas in the avian forebrain are shown to subserve higher cognitive functions, including working memory. One of these areas, the neostriatum caudolaterale (NCL) of pigeons, has been functionally compared with the mammalian prefrontal cortex (PFC) because of its prominent role in spatial delay and reversal tasks and its innervation by the dopaminergic system that modulates these functions. However, whereas the PFC maintains in working memory information of different domains, the essential role of the NCL in working memory has been demonstrated only for spatial tasks. To investigate whether the avian NCL is also crucial for nonspatial working memory functions, pigeons were tested in an object-related (color) delayed matching-to-sample (DMTS) task. Bilateral lesions were placed in the entire, dorsal, or ventral NCL to test for possible functional subdivisions that were proposed to exist on the basis of neurochemical and behavioral data. Pigeons with total, dorsal, and ventral NCL lesions showed significant deficits in their DMTS performance, whereas controls were not impaired. Thus, the avian NCL is critically involved in nonspatial working memory processes. Recovery from performance deficits was observed in animals with ventral or total NCL lesions, whereas animals with dorsal NCL lesions showed no improvement. Ventral NCL may mediate perseverative behavior, whereas dorsal NCL might be involved in active working memory. Differences in the connections of these subdivisions with striatal areas and other association areas in the frontomedial forebrain underline functional differences. The data indicate a possible segregation of functions in the avian NCL.

Social change affects the survival of new neurons in the forebrain of adult songbirds

Many new neurons are added to the adult avian brain. Most of them die 3-5 weeks after they are born (Nature (Lond.) 335 (1988) 353; J. Comp. Neurol 411 (1999) 487). Those that survive replace, numerically, older ones that have died (Neuron 25 (2000) 481). It has been suggested that the new neurons enhance the brain's ability to acquire new long-term memories (review in Sci. Am. 260 (1989) 74). If so, perhaps an increase in social complexity affects the survival of new neurons in a social species. To test this hypothesis, we treated adult zebra finches (Taeniopygia guttata) with [3H]-thymidine immediately before introducing them into one of three different social environments that differed in complexity and killed them 40 days later. There was a significant difference between experimental groups in the number of [3H]-labeled neurons in neostriatum caudale (NC), high vocal center (HVC) and Area X, three forebrain regions that are involved in vocal communication. In these regions, birds placed in a large heterosexual group had more new neurons than birds kept singly or as male-female pairs. Regulation of new neuron survival by extent of circuit use may be a general mechanism for ensuring that neuronal replacement is closely attuned to environmental change.

NMDA antagonist effects on striatal dopamine release: microdialysis studies in awake monkeys

Brain imaging studies have suggested that the NMDA antagonist ketamine is as potent a releaser of striatal dopamine as amphetamine. This conclusion contradicts microdialysis findings in the rodent that NMDA antagonists, in contrast to amphetamine, have little or no effect on striatal dopamine release. The present study addressed two mechanisms that could account for this discrepancy: 1) whether there is a species difference, i.e., rodents vs. primates, in the responsivity of striatal dopamine to NMDA antagonists, and 2) whether rapid uptake of dopamine prevents reliable measures of synaptic dopamine release by microdialysis in response to NMDA antagonists. MRI-directed in vivo microdialysis was used to compare the effects of psychotomimetic NMDA antagonists phencyclidine (PCP), ketamine, and amphetamine on extracellular striatal dopamine levels in awake rhesus monkeys. The effect of PCP was also investigated in the presence of intrastriatally applied nomifensine, a dopamine uptake blocker. Amphetamine (0.1 or 0.4 mg/kg) produced robust and dose-dependent increases in dopamine release ranging 2-10-fold above baseline. PCP at 0.1 mg/kg had no effect and at 0.3 mg/kg produced a small 50% increase over baseline. Ketamine, at the relatively high dose of 5 mg/kg, produced only a 30% increase in dopamine release. Intrastriatal application of nomifensine did not influence the effect of PCP, suggesting that rapid uptake of dopamine is not preventing the detection of a PCP-induced increase in dopamine release. These findings suggest that in the primate, ketamine and PCP are not effective dopamine releasers, as has been suggested by previous imaging studies.

Imaging of striatal dopamine D(2) receptors with a PET system for small laboratory animals in comparison with storage phosphor autoradiography: a validation study with (18)F-(N-methyl)benperidol

Several groups have developed high-resolution PET systems and shown the feasibility of in vivo studies on small laboratory animals. In this investigation, one of these systems was validated for the performance of receptor imaging studies. For this, the radiotracer concentrations obtained in the same animals with PET and with autoradiography were quantified, and the correspondence between both methods was assessed by means of correlation analysis.

METHODS

Striatal radioactivity was measured in 10 Sprague-Dawley rats after injection of 60 +/- 10 MBq of the dopamine D(2) receptor ligand (18)F-(N-methyl)benperidol in 6 time frames of 6 min each. On completion of the scans, animals were killed, and their brains were removed and sectioned using a cryostat microtome. Coronal slices were subjected to storage phosphor autoradiography with BaFBr:Eu(2+)-coated imaging plates. Striatal radioactivity was quantified in both modalities using region-of-interest analysis and activity standards.

RESULTS

After partial-volume correction, the median of striatal radioactivity concentration measured with PET was 0.40 MBq/cm(3) (25th percentile, 0.32; 75th percentile, 0.44). Radioactivity concentrations determined by means of storage phosphor autoradiography amounted to 0.42 MBq/cm(3) (25th percentile, 0.24; 75th percentile, 0.51). Correlation of striatal radioactivity values yielded a Pearson correlation coefficient of 0.818 (P = 0.002). Radioactivity accumulation in Harder's glands led to an overestimation of striatal activity concentrations by approximately 5%. The median of striatal radioactivity concentration after spillover correction decreased slightly to 0.38 MBq/cm(3) (25th percentile, 0.30; 75th percentile, 0.43). Correlation of striatal radioactivity values after spillover correction yielded a Pearson correlation coefficient of 0.824 (P = 0.002).

CONCLUSION

The results show a significant positive correlation between radioactivity values obtained with PET and storage phosphor autoradiography used as the gold standard. Because we applied a selective dopamine D(2) receptor radioligand and because radioactivity concentrations could be reliably quantified in the target region, we may infer that in vivo receptor binding studies will be possible in small laboratory animals.

Similarity of the song nuclei of male and female Australian magpies (Gymnorhina tibicen)

The organisation of the song control nuclei of the Australian magpie (Gymnorhina tibicen), a species with highly complex song, was investigated. In contrast to most of the songbirds studied so far, the Australian magpie sings throughout the year and both males and females sing. All of the forebrain song nuclei, including the high vocal centre (HVC), the robust nucleus of the archistriatum (RA), Area X and the lateral and medial magnocellular nuclei of the anterior neostriatum (lMAN and mMAN) were found to be well developed in both male and female magpies. Consistent with the known vocal competence of juvenile magpies, all of the song nuclei were also well-developed in juvenile magpies (2--3 months old). HVC in both male and female magpies consists of a rostrolateral and a caudomedial region. The ventromedial part of RA differs from the dorsolateral part by having medium-sized neurons packed in higher density. The HVC to RA projections were labelled anterogradely by DiI and DiA. However, no HVC to Area X projections were labeled by DiI or DiA, suggesting a possible difference from songbirds studied previously.

Identification of the source of the bilateral projection system from cortex to somatosensory neostriatum and an exploration of its physiological actions

Microinjections of cholera toxin B subunit were made into the area of the neostriatum that receives input from the primary somatosensory barrel cortex (SI) in the rat. Studies of the cortices then allowed retrograde identification of the cortical cells supplying the striatal input. When injections were restricted to the neostriatum, retrograde labelling was found in layer V of both SI cortices. Ipsilateral to the injection, cells were retrogradely filled with toxin in all parts of the barrel field, in adjacent parietal cortex, in the motor cortex and in prefrontal areas. A similar distribution across cortical areas was seen contralaterally; however, the stained cells in the SI were between rather than within barrel columns. An earlier anterograde study suggested two inputs from the SI to the neostriatum. The present results indicate that one input to the somatosensory area of the neostriatum arises bilaterally from neurons between the barrels of the SI, while the topographic pathway from below the barrels is present only ipsilaterally. These anatomical results indicate that separate stimulation of the two corticostriatal pathways from the barrel cortex is possible. Electrical stimulation of the contralateral cortex will activate the bilateral pathway, while electrical stimulation of the whisker pads activates the barrels and hence the topographic pathway. Neurons in the somatosensory region of the striatum responded to stimuli in the contralateral cortex and in the contralateral whisker pad. In spite of very different path lengths, stimuli via the two routes gave rise to excitatory postsynaptic potentials in the striatal cells with similar latencies. The excitatory postsynaptic potentials to whisker pad stimulation had a rapid rise time and usually resulted in at least one action potential. Responses to stimulation of the contralateral cortex rose to a peak more slowly and were more variable in latency, but also gave rise to an action potential in the majority of cases. All the neurons had the physiological characteristics of medium-sized densely spiny cells and after intracellular filling with biocytin had the appropriate morphology. In summary, we propose that two corticostriatal pathways arise from layer V cells in the barrel area of the somatosensory cortex; one is bilateral and arises from cells mainly below the septa, while a topographical pathway arises from cells below the barrels. Both pathways can raise the spiny output cells of the striatum to firing threshold. The latencies from the contralateral cortex imply slowly conducting fibres with considerably more temporal dispersion than the pathway from below the barrels, which we excited from the contralateral periphery.

Are memories for stimulus-stimulus associations or stimulus-response associations responsible for serial-pattern learning in rats?

Previous research has provided convincing evidence that rats can learn to anticipate the individual elements of a stimulus series consisting of differing amounts of food reinforcement. Rats prepared with lesions of the dorsal striatum or hippocampus were initially trained to acquire a three-element series consisting of 21 sucrose pellets, followed by 0- and 7-pellets (Noyes standard), respectively. During the initial 30 days of training, the animals were run in two adjacent runways; the runways included either of a white, rough runway or a black, smooth runway as additional series cues. Thus, training included both floor (S-R) cues and the series (inter-item memory) cues. Anticipation was defined as faster running on the 21- than on the 7-pellet element and 7- than on the 0-pellet element. While anticipation developed more slowly in the lesion groups than in the control group, all animals eventually demonstrated the ability to track the elements of the series. Reversal of the floor cues disrupted tracking in the hippocampus-lesioned and control animals; dorsal striatum-lesioned rats were also affected but did continue tracking. As a final test, shifting the order of the series produced a marked disruption in performance in the dorsal striatum-lesioned rats but not in the hippocampus-lesioned or control rats. The results are consistent with the proposal that integrated neural mediation is required for anticipation, with a system that includes the dorsal striatum necessary for the promotion of a reinforced approach response and a system that includes the hippocampus necessary for associating and temporarily maintaining an internal record of the different elements of the stimulus series.

Effects of reversible inactivation of thalamo-striatal circuitry on delayed matching trained with retractable levers

The intralaminar thalamic nuclei are characterized by their prominent projections to striatum. Lesions of the intralaminar nuclei have been found to impair delayed matching trained with retractable levers. Comparable impairments have been observed for rats with lesions of the olfactory tubercle, involving ventral areas of striatum and pallidum. We conducted two experiments to test the functional dependence of thalamic and striatal lesions on the delayed matching task. In experiment 1, we determined the effects of inactivating the intralaminar nuclei with bilateral lidocaine infusions. In experiment 2, we compared the effects of unilateral thalamic inactivations in rats with unilateral olfactory tubercle lesions. We trained rats to perform the delayed matching task to criterion and then implanted dual cannulas aimed at the bilaterally symmetrical areas in the intralaminar nuclei. Rats in experiment 2 were also given a unilateral olfactory tubercle lesion. The results of experiment 1 showed dose-dependent impairments for bilateral infusions that were qualitatively similar, although of lesser severity than delayed matching impairments observed in previous studies for rats with lesions involving extensive areas of the intralaminar nuclei. A comparable impairment was observed in experiment 2 when thalamus was inactivated on the side opposite the olfactory tubercle lesion. Performances were significantly worse when thalamus was inactivated on the contra-lesion than on the ipsi-lesion side of the brain. These results are discussed in terms of the role of ventral striatum and related thalamic nuclei in memory.

The teleostean (zebrafish) dopaminergic system ascending to the subpallium (striatum) is located in the basal diencephalon (posterior tuberculum)

Tyrosine hydroxylase immunohistochemistry is used to demonstrate catecholaminergic neuronal populations in the fore- and midbrain of adult zebrafish (Danio rerio). While no catecholaminergic neurons are found in the midbrain, various immunoreactive populations were found in the diencephalon (hypothalamus, posterior tuberculum, ventral thalamus, pretectum) and telencephalon (preoptic region, subpallium, olfactory bulb). The posterior tubercular catecholaminergic cells include three cytological types (small round, large pear-shaped, and bipolar liquor-contacting cells). Furthermore, the retrograde neuronal tracers DiI or biocytin were applied to demonstrate ascending projections to the basal telencephalon (incl. the striatum). A double-label approach was used - together with tyrosine hydroxylase immunohistochemistry - in order to visualize neurons positive for tyrosine hydroxylase and a retrograde tracer. Double-labeled cells were identified in two locations in the posterior tuberculum (i.e, small round neurons in the periventricular nucleus of the posterior tuberculum and large pear-shaped cells adjacent to it). They are interpreted as the teleostean dopaminergic system ascending to the striatum, since previous work [16] established that no noradrenergic neurons exist in the forebrain of the adult zebrafish.

Considerations on the thalamostriatal system with some functional implications

The thalamostriatal projections are largely neglected in current reviews dealing with basal ganglia function. In the past few years, however, several studies have re-evaluated these projections and have postulated their implication in more complex tasks within the basal ganglia organization. In this review, we try to focus on the morphological and functional importance of this system in the basal ganglia of the rat, cat and monkey. Special attention is paid to the thalamus as an important place for interaction between the input and the output systems of the basal ganglia through the thalamostriatal projections. Thus, we stress on the overlapping thalamic territories between the thalamic projection of the output nuclei of the basal ganglia and the thalamostriatal neurons. Our experimental data support the existence of several thalamic feedback circuits within the basal ganglia functional design. Finally, some considerations are provided upon the functional significance of these thalamic feedback circuits in the overall organization of the basal ganglia in health and disease.

Relative size of the hyperstriatum ventrale is the best predictor of feeding innovation rate in birds

Within the avian telencephalon, the dorsal ventricular ridge (DVR) contains higher order and multimodal integration areas. Using multiple regressions on 17 avian taxa, we show that an operational estimate of behavioral flexibility, the frequency of feeding innovation reports in ornithology journals, is most closely predicted by relative size of one of these DVR areas, the hyperstriatum ventrale. Neither phylogeny, juvenile development mode, nor species sampled account for the relationship. Similar results are found when the hyperstriatum ventrale is lumped with a second DVR structure, the neostriatum. In simple correlations, size of the wulst and the striatopallidal complex is associated with feeding innovation rate, but the two structures are eliminated from the multiple regressions. Our results parallel those on primates showing a correlation between innovation rate and neocortex size and support the idea that the mammalian neocortex and the neostriatum-hyperstriatum ventrale complex in birds have similar integrative roles.

More than meets the eye: significant regional heterogeneity in human cortical T1

Segmented k-space acquisition of data was used to decrease the acquisition time and to increase the imaging resolution of the precise and accurate inversion recovery (PAIR) method of measuring T(1). We validated the new TurboPAIR method by measuring T(1) in 158 regions of interest in 12 volunteers, using both PAIR and TurboPAIR. We found a 3% difference between methods, which could be corrected by linear regression. After validation, the TurboPAIR method was used to test a hypothesis that there is significant regional heterogeneity in cortical T(1). We measured cortical gray matter T(1) in 11 right-handed volunteers, in 48 regions of interest scattered over frontal and parietal cortex, and in 46 ROIs along the central sulcus (CS). We found that T(1) in the CS is less than T(1) elsewhere in the cortex (p<0.001), and that there is considerable hemispheric asymmetry in T(1) in gray matter, but not in white matter. In central gray structures (caudate, thalamus, nucleus pulvinarus), and in the posterior CS (sensory cortex), right hemisphere T(1) was significantly greater than left hemisphere T(1) (p< or =0.004). In cortical gray matter of the frontal lobe and anterior CS (motor cortex), left hemisphere T(1) was significantly greater than right hemisphere T(1) (p< or =0.003). These findings demonstrate that there is considerable regional heterogeneity in human cortical T(1) that is unexplained by differences in tissue iron content, but may be evidence of an inherent anatomic asymmetry of the brain.

Strain differences in basal and cocaine-evoked dopamine dynamics in mouse striatum

In vivo microdialysis was used to characterize basal dopamine (DA) dynamics and cocaine-evoked DA levels in the striatum of 129/Sv-ter, C57BL/6J, DBA/2J, and Swiss-Webster mice. Basal dialysate levels of DA did not differ in the four strains tested. Similarly, the no net flux method of quantitative microdialysis revealed no difference in extracellular levels between strains. However, the in vivo extraction fraction of DA was significantly less in 129/Sv-ter (53%) mice compared with C57BL/6J (68%), DBA/2J (69%), and Swiss-Webster (67%) mice, indicating a lower rate of basal DA uptake in the 129/Sv-ter strain. Perfusion of K(+) (60 and 100 mM) through the microdialysis probe significantly increased dialysate DA levels and there was no difference between strains in the magnitude of this effect. The acute administration of cocaine (5-20 mg/kg i.p.) increased DA levels in the four strains tested. Cocaine-evoked DA levels (in nanomoles) were significantly greater in 129/Sv-ter compared with C57BL/6J, DBA/2J, or Swiss-Webster mice after administration of either 5, 10, or 20 mg/kg cocaine. However, the percentage increase in DA did not differ across strains. These data demonstrate that there are strain-related differences in basal DA dynamics in the striatum of the mouse. Basal DA uptake was reduced in striatum of 129/Sv-ter mice compared with C57BL/6J, DBA/2J, or Swiss-Webster mice. In addition, the response of DA levels to cocaine may be enhanced in 129/Sv-ter compared with C57BL/6J, DBA/2J, or Swiss-Webster mice.

Detection of the effects of dopamine receptor supersensitivity using pharmacological MRI and correlations with PET

Receptor supersensitivity is an important concept for understanding neurotransmitter and receptor dynamics. Traditionally, detection of receptor supersensitivity has been performed using autoradiography or positron emission tomography (PET). We show that use of magnetic resonance imaging (MRI) not only enables one to detect dopaminergic supersensitivity, but that the hemodynamic time course reflective of this fact is different in different brain regions. In rats unilaterally lesioned with intranigral 6-hydroxydopamine, apomorphine injections lead to a large increase in hemodynamic response (cerebral blood volume, CBV) in the striato-thalamo-cortico circuit on the lesioned side but had little effect on the intact side. Amphetamine injections lead to increases in hemodynamic responses on the intact side and little on the lesioned side in the same animals. The time course for the increase in CBV after either amphetamine or apomorphine administration was longer in striatum and thalamus than in frontal cortex. (11)C-PET studies of ligands which bind to the dopamine transporter (2-beta-carbomethoxy-3-beta-(4-fluorophenyl)tropane 1, 5-naphthalnendisulfonate, WIN 35, 428 or CFT) and D2 receptors (raclopride) confirm that there is a loss of presynaptic dopamine terminals as well as upregulation of D2 receptors in striatum in these same animals. Pharmacologic MRI should become a sensitive tool to measure functional supersensitivity in humans, providing a complementary picture to that generated using PET studies of direct receptor binding.