Caudate intracellular response to thalamic and cortical inputs

Effective Regulation of Auditory Processing by Parvalbumin Interneurons in the Tail of the Striatum

Parvalbumin (PV) interneurons in the auditory cortex (AC) play a crucial role in shaping auditory processing, including receptive field formation, temporal precision enhancement, and gain regulation. PV interneurons are also the primary inhibitory neurons in the tail of the striatum (TS), which is one of the major descending brain regions in the auditory nervous system. However, the specific roles of TS-PV interneurons in auditory processing remain elusive. In this study, morphological and slice recording experiments in both male and female mice revealed that TS-PV interneurons, compared with AC-PV interneurons, were present in fewer numbers but exhibited longer projection distances, which enabled them to provide sufficient inhibitory inputs to spiny projection neurons (SPNs). Furthermore, TS-PV interneurons received dense auditory input from both the AC and medial geniculate body (MGB), particularly from the MGB, which rendered their auditory responses comparable to those of AC-PV interneurons. Optogenetic manipulation experiments demonstrated that TS-PV interneurons were capable of bidirectionally regulating the auditory responses of SPNs. Our findings suggest that PV interneurons can effectively modulate auditory processing in the TS and may play a critical role in auditory-related behaviors.

Generation and propagation of bursts of activity in the developing basal ganglia

The neonatal brain is characterized by intermittent bursts of oscillatory activity interspersed by relative silence. Although well-characterized for many cortical areas, to what extent these propagate and interact with subcortical brain areas is largely unknown. Here, early network activity was recorded from the developing basal ganglia, including motor/somatosensory cortex, dorsal striatum, and intralaminar thalamus, during the first postnatal weeks in mice. An unsupervised detection and classification method revealed two main classes of bursting activity, namely spindle bursts and nested gamma spindle bursts, characterized by oscillatory activity at ~ 10 and ~ 30 Hz frequencies, respectively. These were reliably identified across all three brain regions and exhibited region-specific differences in their structural, spectral, and developmental characteristics. Bursts of the same type often co-occurred in different brain regions and coherence and cross-correlation analyses reveal dynamic developmental changes in their interactions. The strongest interactions were seen for cortex and striatum, from the first postnatal week onwards, and cortex appeared to drive burst events in subcortical regions. Together, these results provide the first detailed description of early network activity within the developing basal ganglia and suggest that cortex is one of the main drivers of activity in downstream nuclei during this postnatal period.

Real-Time Object Tracking via Adaptive Correlation Filters

Although correlation filter-based trackers (CFTs) have made great achievements on both robustness and accuracy, the performance of trackers can still be improved, because most of the existing trackers use either a sole filter template or fixed features fusion weight to represent a target. Herein, a real-time dual-template CFT for various challenge scenarios is proposed in this work. First, the color histograms, histogram of oriented gradient (HOG), and color naming (CN) features are extracted from the target image patch. Then, the dual-template is utilized based on the target response confidence. Meanwhile, in order to solve the various appearance variations in complicated challenge scenarios, the schemes of discriminative appearance model, multi-peaks target re-detection, and scale adaptive are integrated into the proposed tracker. Furthermore, the problem that the filter model may drift or even corrupt is solved by using high confidence template updating technique. In the experiment, 27 existing competitors, including 16 handcrafted features-based trackers (HFTs) and 11 deep features-based trackers (DFTs), are introduced for the comprehensive contrastive analysis on four benchmark databases. The experimental results demonstrate that the proposed tracker performs favorably against state-of-the-art HFTs and is comparable with the DFTs.

Cortical and thalamic inputs exert cell type-specific feedforward inhibition on striatal GABAergic interneurons

The classical view of striatal GABAergic interneuron function has been that they operate as largely independent, parallel, feedforward inhibitory elements providing inhibitory inputs to spiny projection neurons (SPNs). Much recent evidence has shown that the extrinsic innervation of striatal interneurons is not indiscriminate but rather very specific, and that striatal interneurons are themselves interconnected in a cell type-specific manner. This suggests that the ultimate effect of extrinsic inputs on striatal neuronal activity depends critically on synaptic interactions within interneuronal circuitry. Here, we compared the cortical and thalamic input to two recently described subtypes of striatal GABAergic interneurons, tyrosine hydroxylase-expressing interneurons (THINs), and spontaneously active bursty interneurons (SABIs) using transgenic TH-Cre and Htr3a-Cre mice of both sexes. Our results show that both THINs and SABIs receive strong excitatory input from the motor cortex and the thalamic parafascicular nucleus. Cortical optogenetic stimulation also evokes disynaptic inhibitory GABAergic responses in THINs but not in SABIs. In contrast, optogenetic stimulation of the parafascicular nucleus induces disynaptic inhibitory responses in both interneuron populations. However, the short-term plasticity of these disynaptic inhibitory responses is different suggesting the involvement of different intrastriatal microcircuits. Altogether, our results point to highly specific interneuronal circuits that are selectively engaged by different excitatory inputs.

Dynamic postnatal development of the cellular and circuit properties of striatal D1 and D2 spiny projection neurons

KEY POINTS

Imbalances in the activity of the D1-expressing direct pathway and D2-expressing indirect pathway striatal projection neurons (SPNs) are thought to contribute to many basal ganglia disorders, including early-onset neurodevelopmental disorders such as obsessive-compulsive disorder, attention deficit hyperactivity disorder and Tourette's syndrome. This study provides the first detailed quantitative investigation of development of D1 and D2 SPNs, including their cellular properties and connectivity within neural circuits, during the first postnatal weeks. This period is highly dynamic with many properties changing, but it is possible to make three main observations: many aspects of D1 and D2 SPNs progressively mature in parallel; there are notable exceptions when they diverge; and many of the defining properties of mature striatal SPNs and circuits are already established by the first and second postnatal weeks, suggesting guidance through intrinsic developmental programmes. These findings provide an experimental framework for future studies of striatal development in both health and disease.

ABSTRACT

Many basal ganglia neurodevelopmental disorders are thought to result from imbalances in the activity of the D1-expressing direct pathway and D2-expressing indirect pathway striatal projection neurons (SPNs). Insight into these disorders is reliant on our understanding of normal D1 and D2 SPN development. Here we provide the first detailed study and quantification of the striatal cellular and circuit changes occurring for both D1 and D2 SPNs in the first postnatal weeks using in vitro whole-cell patch-clamp electrophysiology. Characterization of their intrinsic electrophysiological and morphological properties, the excitatory long-range inputs coming from cortex and thalamus, as well their local gap junction and inhibitory synaptic connections reveals this period to be highly dynamic with numerous properties changing. However it is possible to make three main observations. Firstly, many aspects of SPNs mature in parallel, including intrinsic membrane properties, increases in dendritic arbours and spine densities, general synaptic inputs and expression of specific glutamate receptors. Secondly, there are notable exceptions, including a transient stronger thalamic innervation of D2 SPNs and stronger cortical NMDA receptor-mediated inputs to D1 SPNs, both in the second postnatal week. Thirdly, many of the defining properties of mature D1 and D2 SPNs and striatal circuits are already established by the first and second postnatal weeks, including different electrophysiological properties as well as biased local inhibitory connections between SPNs, suggesting this is guided through intrinsic developmental programmes. Together these findings provide an experimental framework for future studies of D1 and D2 SPN development in health and disease.

Neuropilin 2 Signaling Mediates Corticostriatal Transmission, Spine Maintenance, and Goal-Directed Learning in Mice

The striatum represents the main input structure of the basal ganglia, receiving massive excitatory input from the cortex and the thalamus. The development and maintenance of cortical input to the striatum is crucial for all striatal function including many forms of sensorimotor integration, learning, and action control. The molecular mechanisms regulating the development and maintenance of corticostriatal synaptic transmission are unclear. Here we show that the guidance cue, Semaphorin 3F and its receptor Neuropilin 2 (Nrp2), influence dendritic spine maintenance, corticostriatal short-term plasticity, and learning in adult male and female mice. We found that Nrp2 is enriched in adult layer V pyramidal neurons, corticostriatal terminals, and in developing and adult striatal spiny projection neurons (SPNs). Loss of Nrp2 increases SPN excitability and spine number, reduces short-term facilitation at corticostriatal synapses, and impairs goal-directed learning in an instrumental task. Acute deletion of Nrp2 selectively in adult layer V cortical neurons produces a similar increase in the number of dendritic spines and presynaptic modifications at the corticostriatal synapse in the Nrp2 ^-/- mouse, but does not affect the intrinsic excitability of SPNs. Furthermore, conditional loss of Nrp2 impairs sensorimotor learning on the accelerating rotarod without affecting goal-directed instrumental learning. Collectively, our results identify Nrp2 signaling as essential for the development and maintenance of the corticostriatal pathway and may shed novel insights on neurodevelopmental disorders linked to the corticostriatal pathway and Semaphorin signaling.SIGNIFICANCE STATEMENT The corticostriatal pathway controls sensorimotor, learning, and action control behaviors and its dysregulation is linked to neurodevelopmental disorders, such as autism spectrum disorder (ASD). Here we demonstrate that Neuropilin 2 (Nrp2), a receptor for the axon guidance cue semaphorin 3F, has important and previously unappreciated functions in the development and adult maintenance of dendritic spines on striatal spiny projection neurons (SPNs), corticostriatal short-term plasticity, intrinsic physiological properties of SPNs, and learning in mice. Our findings, coupled with the association of Nrp2 with ASD in human populations, suggest that Nrp2 may play an important role in ASD pathophysiology. Overall, our work demonstrates Nrp2 to be a key regulator of corticostriatal development, maintenance, and function, and may lead to better understanding of neurodevelopmental disease mechanisms.

Translating striatal activity from brain slice to whole animal neurophysiology: A guide for neuroscience research integrating diverse levels of analysis

An important goal of this review is highlighting research in neuroscience as examples of multilevel functional and anatomical analyses addressing basic science issues and applying results to the understanding of diverse disorders. The research of Dr. Michael Levine, a leader in neuroscience, exemplifies this approach by uncovering fundamental properties of basal ganglia function and translating these findings to clinical applications. The review focuses on neurophysiological research connecting results from in vitro and in vivo recordings. A second goal is to utilize these research connections to produce novel, accurate descriptions for corticostriatal processing involved in varied, complex functions. Medium spiny neurons in striatum act as integrators combining input with baseline activity creating motivational "events." Basic research on corticostriatal synapses is described and links developed to issues with clinical relevance such as inhibitory gating, self-injurious behavior, and relative reward valuation. Work is highlighted on dopamine-glutamate interactions. Individual medium spiny neurons express both D₁ and D₂ receptors and encode information in a bivalent manner depending upon the mix of receptors involved. Current work on neurophysiology of reward processing has taken advantage of these basic approaches at the cellular and molecular levels. Future directions in studying physiology of reward processing and action sequencing could profit by incorporating the divergent ways dopamine modulates incoming neurochemical signals. Primary investigators leading research teams should mirror Mike Levine's efforts in "climbing the mountain" of scientific inquiry by performing analyses at different levels of inquiry, integrating the findings, and building comprehensive answers to problems unsolvable without this bold approach.

Excitatory extrinsic afferents to striatal interneurons and interactions with striatal microcircuitry

The striatum constitutes the main input structure of the basal ganglia and receives two major excitatory glutamatergic inputs, from the cortex and the thalamus. Excitatory cortico- and thalamostriatal connections innervate the principal neurons of the striatum, the spiny projection neurons (SPNs), which constitute the main cellular input as well as the only output of the striatum. In addition, corticostriatal and thalamostriatal inputs also innervate striatal interneurons. Some of these inputs have been very well studied, for example the thalamic innervation of cholinergic interneurons and the cortical innervation of striatal fast-spiking interneurons, but inputs to most other GABAergic interneurons remain largely unstudied, due in part to the relatively recent identification and characterization of many of these interneurons. In this review, we will discuss and reconcile some older as well as more recent data on the extrinsic excitatory inputs to striatal interneurons. We propose that the traditional feed-forward inhibitory model of the cortical input to the fast-spiking interneuron then inhibiting the SPN, often assumed to be the prototype of the main functional organization of striatal interneurons, is incomplete. We provide evidence that the extrinsic innervation of striatal interneurons is not uniform but shows great cell-type specificity. In addition, we will review data showing that striatal interneurons are themselves interconnected in a highly cell-type-specific manner. These data suggest that the impact of the extrinsic inputs on striatal activity critically depends on synaptic interactions within interneuronal circuitry.

Differential processing of thalamic information via distinct striatal interneuron circuits

Recent discoveries of striatal GABAergic interneurons require a new conceptualization of the organization of intrastriatal circuitry and their cortical and thalamic inputs. We investigated thalamic inputs to the two populations of striatal neuropeptide Y (NPY) interneurons, plateau low threshold spike (PLTS) and NPY-neurogliaform (NGF) cells. Optogenetic activation of parafascicular inputs evokes suprathreshold monosynaptic glutamatergic excitation in NGF interneurons and a disynaptic, nicotinic excitation through cholinergic interneurons. In contrast, the predominant response of PLTS interneurons is a disynaptic inhibition dependent on thalamic activation of striatal tyrosine hydroxylase interneurons (THINs). In contrast, THINs do not innervate NGF or fast spiking interneurons, showing significant specificity in THINs outputs. Chemospecific ablation of THINs impairs prepulse inhibition of the acoustic startle response suggesting an important behavioural role of this disynaptic pathway. Our findings demonstrate that the impact of the parafascicular nucleus on striatal activity and some related behaviour critically depend on synaptic interactions within interneuronal circuits.

The responses of striatal GABAergic interneurons to thalamic inputs are not well characterised. Here, the authors demonstrate that complex intrastriatal circuitry is responsible for thalamic-evoked monosynaptic and disynaptic excitation in NPY-NGF interneurons but a disynaptic inhibition in the NPY-PLTS.

Heterogeneous properties of central lateral and parafascicular thalamic synapses in the striatum

To understand the principles of operation of the striatum it is critical to elucidate the properties of the main excitatory inputs from cortex and thalamus, as well as their ability to activate the main neurons of the striatum, the medium spiny neurons (MSNs). As the thalamostriatal projection is heterogeneous, we set out to isolate and study the thalamic afferent inputs to MSNs using small localized injections of adeno-associated virus carrying fusion genes for channelrhodopsin-2 and YFP, in either the rostral or caudal regions of the intralaminar thalamic nuclei (i.e. the central lateral or parafascicular nucleus). This enabled optical activation of specific thalamic afferents combined with whole-cell, patch-clamp recordings of MSNs and electrical stimulation of cortical afferents, in adult mice. We found that thalamostriatal synapses differ significantly in their peak amplitude responses, short-term dynamics and expression of ionotropic glutamate receptor subtypes. Our results suggest that central lateral synapses are most efficient in driving MSNs to depolarization, particularly those of the direct pathway, as they exhibit large amplitude responses, short-term facilitation and predominantly express postsynaptic AMPA receptors. In contrast, parafascicular synapses exhibit small amplitude responses, short-term depression and predominantly express postsynaptic NMDA receptors, suggesting a modulatory role, e.g. facilitating Ca(2+)-dependent processes. Indeed, pairing parafascicular, but not central lateral, presynaptic stimulation with action potentials in MSNs, leads to NMDA receptor- and Ca(2+)-dependent long-term depression at these synapses. We conclude that the main excitatory thalamostriatal afferents differ in many of their characteristics and suggest that they each contribute differentially to striatal information processing.

Evolutionarily conserved differences in pallial and thalamic short-term synaptic plasticity in striatum

The striatum of the basal ganglia is conserved throughout the vertebrate phylum. Tracing studies in lamprey have shown that its afferent inputs are organized in a manner similar to that of mammals. The main inputs arise from the thalamus (Th) and lateral pallium (LPal; the homologue of cortex) that represents the two principal excitatory glutamatergic inputs in mammals. The aim here was to characterize the pharmacology and synaptic dynamics of afferent fibres from the LPal and Th onto identified striatal neurons to understand the processing taking place in the lamprey striatum. We used whole-cell current-clamp recordings in acute slices of striatum with preserved fibres from the Th and LPal, as well as tract tracing and immunohistochemistry. We show that the Th and LPal produce monosynaptic excitatory glutamatergic input through NMDA and AMPA receptors. The synaptic input from the LPal displayed short-term facilitation, unlike the Th input that instead displayed strong short-term synaptic depression. There was also an activity-dependent recruitment of intrastriatal oligosynaptic inhibition from both inputs. These results indicate that the two principal inputs undergo different activity-dependent short-term synaptic plasticity in the lamprey striatum. The difference observed between Th and LPal (cortical) input is also observed in mammals, suggesting a conserved trait throughout vertebrate evolution.

The primate centromedian-parafascicular complex: anatomical organization with a note on neuromodulation

In addition to the cerebral cortex, the striatum receives excitatory input from the thalamus. The centromedian (centre median, CM) and parafascicular (Pf) nuclei are an important source of thalamostriatal projections. Anterograde tract-tracing indicates the CM-Pf complex provides dense afferents to the matrix compartment of the striatum. Whereas CM projects to the entire sensorimotor territory of the striatum, the Pf provides complementary input to the entire associative sector. The Pf also provides lighter input to the nucleus accumbens. Both CM and Pf provide light to moderately dense inputs to other components of the basal ganglia in a largely complementary manner, covering motor or associative-limbic territories of the subthalamic nucleus, globus pallidus and ventral midbrain. In turn, the CM and Pf receive mainly segregated input from parallel motor and associative-limbic circuits of the basal ganglia. The CM and Pf may therefore be considered important participants in parallel processing of motor and associative-limbic information in the basal ganglia. Connections of the CM and Pf with other thalamic nuclei suggest they also participate in integrative functions within the thalamus. In addition, inputs from the brainstem reticular core, reciprocal connections with the cerebral cortex and reticular thalamic nucleus suggest a role in state-dependant information processing. Consideration of the differential connections of the CM and Pf, and better understanding of their role in pathophysiology, may eventually lead to development of an important new target for relief of a variety of neurological and psychiatric disorders.

Thalamic innervation of the direct and indirect basal ganglia pathways in the rat: Ipsi- and contralateral projections

The present study describes the thalamic innervation coming from the rat parafascicular nucleus (PF) onto striatal and subthalamic efferent neurons projecting either to the globus pallidus (GP) or to the substantia nigra pars reticulata (SNr) by using a protocol for multiple neuroanatomical tracing. Both striatofugal neurons targeting the ipsilateral SNr (direct pathway) as well as striatal efferent neurons projecting to the ipsilateral GP (indirect pathway) were located within the terminal fields of the thalamostriatal afferents. In the subthalamic nucleus (STN), both neurons projecting to ipsilateral GP as well as neurons projecting to ipsilateral SNr also appear to receive thalamic afferents. Although the projections linking the caudal intralaminar nuclei with the ipsilateral striatum and STN are far more prominent, we also noticed that thalamic axons could gain access to the contralateral STN. Furthermore, a small number of STN neurons were seen to project to both the contralateral GP and PF nuclei. These ipsi- and contralateral projections enable the caudal intralaminar nuclei to modulate the activity of both the direct and the indirect pathway.

Long-term Potentiation in the Striatum is Unmasked by Removing the Voltage-dependent Magnesium Block of NMDA Receptor Channels

We have studied the effects of tetanic stimulation of the corticostriatal pathway on the amplitude of striatal excitatory synaptic potentials. Recordings were obtained from a corticostriatal slice preparation by utilizing both extracellular and intracellular techniques. Under the control condition (1.2 mM external Mg2+), excitatory postsynaptic potentials (EPSPs) evoked by cortical stimulation were reversibly blocked by 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an antagonist of dl-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) ionotropic glutamate receptors, while they were not affected by 30 - 50 microM 2-amino-5-phosphonovalerate (APV), an antagonist of N-methyl-d-aspartate (NMDA) glutamate receptors. In the presence of 1.2 mM external Mg2+, tetanic activation of cortical inputs produced long-term depression (LTD) of both extracellularly and intracellularly recorded synaptic potentials. When Mg2+ was removed from the external medium, EPSP amplitude and duration increased. In Mg2+-free medium, cortically evoked EPSPs revealed an APV-sensitive component; in this condition tetanic stimulation produced long-term potentiation (LTP) of synaptic transmission. Incubation of the slices in 30 - 50 microM APV blocked striatal LTP, while it did not affect LTD. In Mg2+-free medium, incubation of the slices in 10 microM CNQX did not block the expression of striatal LTP. Intrinsic membrane properties (membrane potential, input resistance and firing pattern) of striatal neurons were altered neither by tetanic stimuli inducing LTD and LTP, nor by removal of Mg2+ from the external medium. These findings show that repetitive activation of cortical inputs can induce long-term changes of synaptic transmission in the striatum. Under control conditions NMDA receptor channels are inactivated by the voltage-dependent Mg2+ block and repetitive cortical stimulation induces LTD which does not require activation of NMDA channels. Removal of external Mg2+ deinactivates these channels and reveals a component of the EPSP which is potentiated by repetitive activation. Since the striatum has been involved in memory and in the storage of motor skills, LTD and LTP of synaptic transmission in this structure may provide the cellular substrate for motor learning and underlie the physiopathology of some movement disorders.

Activation of cAMP-dependent protein kinase suppresses the presynaptic cannabinoid inhibition of glutamatergic transmission at corticostriatal synapses

In a previous study, we showed that type 1 cannabinoid (CB(1)) receptor activation substantially depresses the corticostriatal glutamatergic transmission onto striatal neurons in the brain slice preparation. We now report that the adenylyl cyclase activator forskolin and cAMP analog (S)-p-8-(4-chlorophenythil) adenosine-3',5'-monophosphorothioate (Sp-8-CPT-cAMPS) strongly suppressed the synaptic depression induced by cannabimimetic aminoalkylindole, WIN 55,212-2. Application of the cAMP-dependent protein kinase (PKA) inhibitor KT5720 alone had no consistent effect on basal synaptic transmission but the synaptic enhancement elicited by forskolin was blocked. In addition, pretreatment of striatal slices with either KT5720 or another PKA inhibitor, H89, completely abolished the attenuation by forskolin on WIN 55,212-2-induced synaptic depression. The effect of forskolin on CB(1) receptor function was still observed in a low Ca(2+) bathing solution, suggesting that the forskolin's action is not attributable to its ability to saturate the presynaptic transmitter release processes. The possibility that forskolin acted by increasing CB(1) receptor phosphorylation was confirmed by demonstrating that the serine-phosphorylated component with CB(1) receptors was significantly increased after forskolin treatment. This forskolin effect was markedly attenuated in the presence of KT5720. Moreover, the activation of beta-adrenergic receptors by isoproterenol mimics forskolin to elicit a PKA-dependent inhibition of CB(1) receptor function. Together, these observations indicate that the presynaptic inhibitory action of CB(1) receptors at corticostriatal synapses could be negatively regulated by cAMP/PKA-mediated receptor phosphorylation. This effect of PKA may play a functional role in fine-tuning glutamatergic transmission at corticostriatal synapses.

Dopamine-dependent synaptic plasticity in the striatal cholinergic interneurons

The striatum, the input stage of the basal ganglia, is a critical brain structure for the learning of stimulus-response habits as well as motor, perceptual, and cognitive skills. Roles of dopamine (DA) and acetylcholine (ACh) in this form of implicit memory have long been considered essential, but the underlying cellular mechanism is still unclear. By means of patch-clamp recordings from corticostriatal slices of the mouse, we studied whether the identified striatal cholinergic interneurons undergo long-term synaptic changes after tetanic stimulation of cortico- and thalamostriatal fibers. Electrical stimulation of the fibers revealed a depolarizing and hyperpolarizing postsynaptic potential in the striatal cholinergic interneurons. The early depolarizing phase was considered to be a cortico/thalamostriatal glutamatergic EPSP, and the hyperpolarizing component was considered to be an intrastriatally evoked GABAergic IPSP. Tetanic stimulation of cortico/thalamostriatal fibers was found to induce simultaneously occurring long-term potentiation (LTP) of the EPSPs as well as the disynaptically mediated IPSPs. The induction of LTP of EPSP required a rise in intracellular Ca(2+) concentration and dopamine D(5), but not D(2) receptor activation. Ca(2+)-permeable AMPA receptors might also play a part in the LTP induction. Blockade of NMDA receptors, metabotropic glutamate receptors, or serotonin receptors had no significant effects. The long-term enhancement of the disynaptic IPSPs was caused by a long-term increase in the occurrence rate but not the amplitude of disynaptically mediated IPSP in the striatal cholinergic interneurons. This dual mechanism of synaptic plasticity may be responsible for the long-term modulation of the cortico/thalamostriatal synaptic transmission.

Presynaptic mechanisms underlying cannabinoid inhibition of excitatory synaptic transmission in rat striatal neurons

The striatum is a crucial site of action for the motor effects of cannabinoids (CBs). However, the electrophysiological consequences of activation of CB receptors on the striatal neurons have not been established. Here we report for the first time that the cannabimimetic aminoalkylindole WIN 55,212-2 and the endogenous cannabinoid anandamide substantially depress corticostriatal glutamatergic synaptic transmission onto striatal neurons in the brain slice preparation. The selective CB1 receptor antagonist SR 141716 effectively reversed this inhibition. WIN 55,212-2 significantly increased the paired-pulse facilitation of synaptically evoked EPSCs, while having no effect on the sensitivity of postsynaptic neurons to [alpha]-amino-3-hydroxy-5-methylisoxazole-4-propionic acid. WIN 55,212-2 also reduced the frequency of spontaneous, action potential-dependent EPSCs (sEPSCs) without altering their amplitude distribution. Superfusion of WIN 55,212-2 elicited a membrane hyperpolarization accompanied by a decrease in input resistance. Both effects were blocked by intracellular caesium. In contrast, intracellular caesium failed to affect WIN 55,212-2-mediated synaptic inhibition. The WIN 55,212-2-mediated synaptic inhibition was blocked by the Gi/o protein inhibitor pertussis toxin (PTX), but not by the GABA(A) receptor antagonist bicuculline or GABA(B) receptor antagonist SCH 50911. Pretreatment with the N-type Ca2+ channel antagonist [omega]-conotoxin GVIA selectively abolished the WIN-55,212-2-mediated synaptic inhibition. These results suggest that cannabinoids depress the corticostriatal glutamatergic synaptic transmission through the activation of presynaptic CB1 receptors to inhibit N-type Ca2+ channel activity, which in turn reduces glutamate release. The presynaptic action of cannabinoids is mediated by a PTX-sensitive Gi/o protein-coupled signalling pathway.

Postnatal development of electrophysiological properties of nucleus accumbens neurons

We have studied the postnatal development of the physiological characteristics of nucleus accumbens (nAcb) neurons in slices from postnatal day 1 (P1) to P49 rats using the whole cell patch-clamp technique. The majority of neurons (102/108) were physiologically identified as medium spiny (MS) projection neurons, and only these were subjected to detailed analysis. The remaining neurons displayed characteristics suggesting that they were not MS neurons. Around the time of birth and during the first postnatal weeks, the membrane and firing characteristics of MS neurons were quite different from those observed later. These characteristics changed rapidly during the first 3 postnatal weeks, at which point they began to resemble those found in adults. Both whole cell membrane resistance and membrane time constant decreased more than fourfold during the period studied. The resting membrane potential (RMP) also changed significantly from an average of -50 mV around birth to less than -80 mV by the end of the third postnatal week. During the first postnatal week, the current-voltage relationship of all encountered MS neurons was linear over a wide range of membrane potentials above and below RMP. Through the second postnatal week, the proportion of neurons displaying inward rectification in the hyperpolarized range increased steadily and after P15, all recorded MS neurons displayed significant inward rectification. At all ages, inward rectification was blocked by extracellular cesium and tetra-ethyl ammonium and was not changed by 4-aminopyridine; this shows that inward rectification was mediated by the same currents in young and mature MS neurons. MS neurons fired single and repetitive Na(+)/K(+) action potentials as early as P1. Spike threshold and amplitude remained constant throughout development in contrast to spike duration, which decreased significantly over the same period. Depolarizing current pulses from rest showed that immature MS neurons fired action potentials more easily than their older counterparts. Taken together, the results from the present study suggest that young and adult nAcb MS neurons integrate excitatory synaptic inputs differently because of differences in their membrane and firing properties. These findings provide important insights into signal processing within nAcb during this critical period of development.

Cortical and nigral deafferentation and striatal cholinergic markers in the rat dorsal striatum: different effects on the expression of mRNAs encoding choline acetyltransferase and muscarinic m1 and m4 receptors

The regulation of the striatal m1 and m4 muscarinic receptor mRNA as well as the choline acetyltransferase (ChAT) mRNA expression by nigral dopaminergic and cortical glutamatergic afferent fibres was investigated using quantitative in situ hybridization histochemistry. The effects induced by a unilateral lesion of the medial forebrain bundle and a bilateral lesion of the sensorimotor (SM) cortex were analysed in the dorsal striatum 3 weeks after the lesions. Dopaminergic denervation of the striatum resulted in a marked decrease in the levels of m4 mRNA throughout the striatum, while the levels of muscarinic m1 mRNA and ChAT mRNA in cholinergic neurons were unaffected by the lesion. In contrast, following bilateral cortical ablation, the levels of the muscarinic m1 mRNA were significantly increased in the striatal projection area of the SM cortex, whereas the expression of m4 mRNA remained unchanged. Single cholinergic cell analysis by computer-assisted grain counting revealed a decreased labelling for ChAT mRNA per neuron following cortical ablation. However, in contrast to the topographical m1 mRNA changes, the decreased ChAT mRNA expression was evenly distributed within the striatum, suggesting an indirect cortical control upon striatal cholinergic interneurons. Altogether, these data suggest that dopaminergic nigral and glutamatergic cortical afferents modulate differentially cholinergic markers, at the pre- and post-synaptic levels. Beside the fact that nigral and cortical inputs exert an opposite control on cholinergic neurotransmission, our study further shows that this control involved different muscarinic receptor subtypes: the m4 and m1 receptors, respectively.

Plasticity of responses to synaptic inputs in rat ventral striatal neurons after repeated administration of the dopamine D2 antagonist raclopride

The effects of acute and repeated systemic administration of the dopaminergic D2 antagonist raclopride on responses of ventral striatal neurons were examined in chloral hydrate-anesthetized rats. Stimulating electrodes were placed in the entorhinal and perirhinal cortices, medial thalamus, and prelimbic cortex. Stimulation in water-injected control rats evoked one or occasionally two action potentials. Results were similar in rats injected acutely with raclopride (4 or 8 mg/kg) except that a small proportion of cells (5%) produced burst responses (defined as three or more evoked action potentials). In rats injected with raclopride daily for 7-14 days, burst responses were seen in a larger proportion of cells (17%) and bursts of up to nine action potentials could be evoked. The results suggest that repeated administration of dopaminergic agents can induce striking plastic changes of excitatory responses in a subset of ventral striatal neurons.

Postnatal development of excitatory synaptic input to the rat neostriatum: an electron microscopic study

The distribution and density of asymmetric synapses including biocytin-labelled corticostriatal synapses of the rat neostriatum were examined at postnatal day 10 (P10), P15, P21 and in adults. The density of asymmetric synapses in the adult neostriatum (28.0 synapses/100 microm2) was significantly greater than that in neonates at P15 (14.4 synapses/100 microm2) and P10 (11.5 synapses/100 microm2), but not at P21 (24.2+/-1.5 synapses/100 microm2). The increased density of asymmetric synapses in the adult neostriatum was due primarily to an increase in the number of axospinous synapses. The density of axospinous synapses was greatest in adults (22.3 synapses/100 microm2) and significantly less at P21 (15.3 synapses/100 microm2), P15 (5.9 synapses/100 microm2), and P10 (2.0 synapses/100 microm2). The density of axodendritic synapses, however, remained similar at all ages (adult, 3.9+/-1.1 synapses/100 microm2; P21, 6.0+/-1.2 synapses/100 microm2; P15, 5.7+/-0.8 synapses/100 microm2 or P10, 7.2+/-1.3 synapses/100 microm2). Iontophoretic injection of biocytin into the lateral frontal agranular cortex produced labelling of corticostriatal afferents which formed asymmetric synapses in the neostriatum. The distribution of termination sites of biocytin-labelled corticostriatal boutons showed a pattern of development similar to the unlabelled asymmetric synapses. The present study shows that the increase in the overall number of asymmetric synapses over the first three postnatal weeks can be attributed to an increase in the density of asymmetric axospinous synapses. During the same period little change is noted in the number or density of asymmetric axodendritic synapses. These changes in excitatory synaptic input to medium spiny neurons may explain some of the previously described electrophysiological differences noted between the neonatal and adult neostriatum.

Effects of the cholinergic system of the rat neostriatum on learning active escape in normal animals and in animals with lesions to the intralaminar thalamic nuclei

Studies were carried out into the role of the parafascicular (Pf) nuclei of the rat thalamus in learning a conditioned active escape reflex (CAER) in a T-maze, a reflex associated with discrimination of visual stimuli, and into the regulatory effect on this learning process of activation of the neostriatal cholinergic system. The following results were obtained using 57 Sprague-Dawley rats divided into a number of experimental groups: 1) bilateral microinjection of carbacholine (0.03 microgram) into the neostriatum on days 4, 5, and 6 of training produced significant (p < 0.01) increases in the proportion of correct discriminant CAER performances; 2) bilateral lesioning of the Pf nuclei led to irreversible disruption of the previously learned CAER. Rats with initially bilaterally lesioned Pf nuclei did not learn the discriminant CAER at all after 10 days of training (16 combinations), and microinjection of carbacholine into the neostriatum of these animals was ineffective. It is concluded that the integrity of the afferent input into the Pf nuclei of the thalamus is an important factor for activation of the neuronal background of the neostriatum, and is required for cholinergic activation of the neostriatum to be effective.

Transplantation of mesencephalic cell suspension in dopamine-denervated striatum of the rat. II. Effects on corticostriatal transmission

The present study has been designed to investigate whether intrastriatal implantation of mesencephalic dopamine (DA)-synthetizing neurons into the striatum (ST) of rats whose substantia nigra (SN) was previously destroyed by 6-hydroxydopamine (6-OHDA) restores the pattern of corticostriatal transmission from the medial prelimbic and sensorimotor cortices. In 6-month-old normal animals electrical stimulation of these two functionally unrelated cortices evoked a short latency and brief excitation in 81.6% of neurons recorded in the dorsolateral ST. This percentage decreased significantly (70.6%) in age-matched animals whose dopaminergic nigrostriatal pathway was unilaterally destroyed by 6-OHDA 3 months before recording. However a significant increase in neurons (36.9%) which could be simultaneously activated from the two cortices in comparison to intact rats was noted. In addition the lesion caused a significant decrease in the threshold current required to evoke activation of striatal neurons from the sensorimotor cortex. The increase in the number of striatal neurons responding simultaneously to cortical stimulations demonstrates that destruction of the dopaminergic nigrostriatal pathway causes a loss of the focusing action of DA on corticostriatal transmission. Transplantation of embryonic mesencephalic neurons appears to reestablish this action since the number of convergent responses was significantly decreased in grafted animals (23.5%) in comparison to denervated (36.9%) and sham-grafted (35.1%) animals. Furthermore, the grafts showed a trend to increase current intensities required to evoke activation of striatal cells from both cortices. The action of grafted mesencephalic neurons over prelimbic and sensorimotor cortical inputs to the dorsal ST could be involved in recovery of grafted animals in the correct execution of complex sensorimotor tasks requiring integration of different cortical signals within the ST.

Neocortical damage alters synaptic responses of neostriatal neurons in vitro

The present experiments were designed to investigate the physiological impact of a partial decortication upon neostriatal synaptic responses using intracellular recording techniques in the in vitro brain slice preparation. In the intact rat, the locally evoked neostriatal synaptic response is primarily mediated by excitatory amino acid receptor activation. Following neocortex damage, the contributions of both N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor activation were significantly diminished, although responses remained robust in amplitude and duration. Components of the locally evoked synaptic response mediated by activation of GABAA receptors were relatively unchanged, while presynaptic inhibition mediated by activation of GABAB receptors was markedly reduced. Furthermore, the normally minimal acetylcholine contribution to the synaptic response was significantly increased after neocortical damage. This enhanced cholinergic role in the generation of the synaptic response appeared to be mediated primarily by activation of nicotinic receptors. Thus, neocortical damage leads to novel physiological relationships between intrinsic neostriatal cholinergic interneurons and the GABAergic projection neurons. One possibility is that cholinergic interneurons have the potential for substituting for the loss of excitation created by the absence of neocortical glutamatergic input.

Differential synaptic innervation of striatofugal neurones projecting to the internal or external segments of the globus pallidus by thalamic afferents in the squirrel monkey

It is well established that the centromedian nucleus (CM) is the major source of thalamic afferents to the sensorimotor territory of the striatum in monkeys. However, the projection sites of striatal neurons contacted by thalamic afferents still remain to be determined. We therefore carried out an anatomical study aimed at elucidating the hodology of striatal neurones that receive input from the CM in squirrel monkeys. Our approach was to combine the anterograde transport of Phaseolus vulgaris-leucoagglutinin (PHA-L) or biocytin from the CM with the retrograde transport of biotinylated dextran-amine (bio-dex) or PHA-L from the internal (GPi) or external (GPe) segments of the globus pallidus. Following CM injections, rich plexuses of anterogradely labelled, thin varicose fibres aggregated in the form of bands that were confined to the postcommissural region of the putamen. On the other hand, injections into the GPe or GPi led to profuse retrograde labelling of a multitude of medium-sized spiny neurones. In cases where the injections involved the caudoventral two-thirds of the GPe or GPi, the retrogradely labelled striatopallidal cells and the anterogradely labelled thalamostriatal fibres occurred in the sensorimotor territory of the putamen. After injections into either pallidal segments, clusters of retrogradely labelled cells were in register with bands of anterogradely labelled thalamic fibres. However, electron microscopic analysis of striatal regions containing both anterogradely labelled thalamic afferents and retrogradely labelled cells revealed that terminals from the CM frequently form asymmetric synapses with dendritic shafts and spines of striato-GPi cells but rarely with those of striato-GPe cells. In conclusion, our findings demonstrate that thalamic afferents from the CM innervate preferentially striatopallidal neurones projecting to the GPi in monkeys. These results indicate that the striatopallidal neurones contributing to the "direct" and "indirect" output pathways are differentially innervated by thalamic afferents in primates.

Neurophysiology of converging synaptic inputs from the rat prefrontal cortex, amygdala, midline thalamus, and hippocampal formation onto single neurons of the caudate/putamen and nucleus accumbens

Neurophysiological responses mediated by projections from five telencephalic and diencephalic regions (the infra- and prelimbic portions of the prefrontal cortex, amygdala, midline and intralaminar thalamic nuclei, entorhinal cortex and subiculum/CA1) to the caudate/putamen (CPu) and nucleus accumbens (Acb) of the dorsal and ventral striatum were studied in chloral-hydrate-anesthetized rats. Both extra- and intracellular in vivo recording techniques were used. A retrograde tracer (wheatgerm agglutinin-apo-horseradish peroxidase-5 nm colloidal Gold) was deposited in some animals in the vicinity of recording sites to confirm that stimulating electrodes were located near cells that projected to the striatum. Electrical stimulation of these five regions, respectively, evoked excitatory responses in 60%, 22%, 51%, 25%, and 17% of striatal neurons. Some responses, particularly with thalamic stimulation, showed short-term frequency potentiation in which 5/s stimulation increased the probability of spike firing. About half of responsive cells showed convergent excitation to more than one stimulating site. It was possible with convergent excitatory responses to show synaptic interactions: simultaneous activation of more than one site produced spatial and temporal summation to increase the probability of spike firing. Up to 5-way convergence onto single striatal neurons and up to 3-way interactions could be shown. These results indicate that functional influences from the hippocampal formation can converge with other excitatory input onto single striatal neurons to effect synaptic integration.

Effects of local connectivity on striatal function: stimulation and analysis of a model

Neuronal population activity was investigated by computer simulation of a network model based on the neostriatum. Three network topologies were studied, based on different assumptions about the synaptic connectivity among medium spiny neurons. In all networks neurons were interconnected by inhibitory synapses. The connectivity was either symmetric, in which case all connections between cells were reciprocal and equal in strength; or asymmetric. Simulations showed that networks with symmetric connectivity receiving randomly distributed afferent excitation produced stationary spatial activity patterns. In contrast, asymmetric connectivity in homogeneous networks produced slow travelling-wave activity across the network. We suggest that the shape of the medium spiny neurons is an important determinant of synaptic connectivity and that changes in the shape of these neurons caused by Huntington's disease would result in asymmetric connectivity. Slow travelling-wave activity produced by asymmetric connectivity in the neostriatum could explain some aspects of the choreic movement and some electromyographic features seen in Huntington's patients.

Decortication decreases paired-pulse facilitation in the neostriatal slice of the rat

Paired-pulse facilitation, a form of short-term synaptic enhancement, occurs in the neostriatum. The present experiments were designed to determine the contributions of neostriatal afferents to the maintenance of this form of short-term facilitation. There are 3 major afferents to the neostriatum: the neocortex, the substantia nigra and the medial thalamus. Since the largest inputs into the neostriatum emanate from the neocortex and substantia nigra, the effects of unilateral decortication or unilateral dopamine depletion on paired-pulse facilitation were primarily examined. Intracellular recordings were made from neostriatal neurons in brain slices 2 weeks following unilateral decortication or dopamine-depleting lesions. Statistically significant decreases in paired-pulse facilitation of the synaptic response evoked by local stimulation occurred only after neocortical damage. In contrast, paired-pulse facilitation in neostriatal neurons ipsilateral to the dopamine depleting lesion was not significantly altered. These results indicate that the corticostriatal input is primarily responsible for neostriatal short-term synaptic facilitation.

Postsynaptic integration of glutamatergic and dopaminergic signals in the striatum

The aim of this study was to achieve a better understanding of the integration in striatal medium-sized spiny neurons (MSNs) of converging signals from glutamatergic and dopaminergic afferents. The review of the literature in the first section shows that these two types of afferents not only contact the same striatal cell type, but that individual MSNs receive both a corticostriatal and a dopaminergic terminal. The most common sites of convergence are dendritic shafts and spines of MSNs with a distance between the terminals of less than 1-2 microns. The second section focuses on synaptic transmission and second messenger activation. Glutamate, the candidate transmitter of corticostriatal terminals, via different types of glutamate receptors can evoke an increase in intracellular free calcium concentrations. The net effect of dopamine in the striatum is a stimulation of adenylate cyclase activity leading to an increase in cAMP. The subsequent sections present information on calcium- and cAMP-sensitive biochemical pathways and review the regional and subcellular distribution of the components in the striatum. The specific biochemical reaction steps were formalized as simplified equilibrium equations. Parameter values of the model were chosen from published experimental data. Major results of this analysis are: at intracellular free calcium concentrations below 1 microM the stimulation of adenylate cyclase by calcium and dopamine is at least additive in the steady state. Free calcium concentrations exceeding 1 microM inhibit adenylate cyclase, which is not overcome by dopaminergic stimulation. The kinases and phosphatases studied can be divided in those that are almost exclusively calcium-sensitive (PP2B and CaMPK), and others that are modulated by both calcium and dopamine (PKA and PP1). Maximal threonine-phosphorylation of the phosphoprotein DARPP requires optimal concentrations of calcium (about 0.3 microM) and dopamine (above 5 microM). It seems favourable if the glutamate signal precedes phasic dopamine release by approximately 100 msec. The phosphorylation of MAP2 is under essentially calcium-dependent control of at least five kinases and phosphatases, which differentially affect its heterogeneous phosphorylation sites. Therefore, MAP2 could respond specifically to the spatio-temporal characteristics of different intracellular calcium fluxes. The quantitative description of the calcium- and dopamine-dependent regulation of DARPP and MAP2 provides insights into the crosstalk between glutamatergic and dopaminergic signals in striatal MSNs. Such insights constitute an important step towards a better understanding of the links between biochemical pathways, physiological processes, and behavioural consequences connected with striatal function. The relevance to long-term potentiation, reinforcement learning, and Parkinson's disease is discussed.

Synaptic relationships between dopaminergic afferents and cortical or thalamic input in the sensorimotor territory of the striatum in monkey

The cerebral cortex and the intralaminar thalamic nuclei are the major sources of excitatory glutamatergic afferents to the striatum, whereas the midbrain catecholaminergic neurones provide a dense intrastriatal plexus of dopamine-containing terminals. Evidence from various sources suggests that there is a functional interaction between the glutamate- and dopamine-containing terminals in the striatum. The aim of the present study was to determine the synaptic relationships between cortical or thalamic inputs and the dopaminergic afferents in the sensorimotor territory of the monkey striatum. To address this issue, anterograde tracing in combination with immunocytochemistry for tyrosine hydroxylase (TH) was carried out by light and electron microscopy. Squirrel monkeys received injections of biocytin in the primary motor and somatosensory cortical areas or injections of either Phaseolus vulgaris-leucoagglutinin (PHA-L) or biocytin in the centromedian nucleus (CM) of the thalamus. Sections that included the striatum were processed to visualize the anterograde tracers alone or in combination with TH immunoreactivity. The anterogradely labelled fibres from the cerebral cortex and CM display a band-like pattern and are exclusively confined to the postcommissural region of the putamen, whereas TH-immunoreactive axon terminals are homogeneously distributed throughout the entire extent of the striatum. Electron microscopic analysis revealed that the anterogradely labelled terminals from the cerebral cortex form asymmetric synapses almost exclusively with the heads of dendritic spines. The thalamic terminals also form asymmetric synapses, but in contrast to cortical fibres, predominantly with dendrites (67.4%) and less frequently with spines (32.6%). The TH-immunoreactive boutons are heterogeneous in morphology. The most common type (84% of the total population) forms symmetric synapses; of these the majority is in contact with dendritic shafts (72.1%), less with spines (22.5%) and few with perikarya (5.4%). In sections processed to reveal anterogradely labelled cortical fibres and TH-immunoreactive structures, individual spines of striatal neurones were found to receive convergent synaptic inputs from both cortical and TH-immunoreactive boutons. In contrast, anterogradely labelled thalamic terminals and TH-immunoreactive boutons were never seen to form convergent synaptic contacts on the same postsynaptic structure. These findings suggest that the dopaminergic afferents are located to subserve a more specific modulation of afferent cortical input than afferent thalamic input in the sensorimotor territory of the striatum in primates.

Identification and characterization of striatal cell subtypes using in vivo intracellular recording and dye-labeling in rats: III. Morphological correlates and compartmental localization

In the first two reports of this series, in vivo intracellular recording techniques were used to characterize the electrophysiological properties of two types of striatal neurons that had been identified by their distinct response patterns to stimulation of corticostriatal afferents. In this paper, we examined whether cells showing Type I or Type II response patterns also differed with respect to their morphology or compartmental localization by combining intracellular recording and Lucifer yellow staining with immunocytochemical localization of calbindin 28 kd immunoreactivity. In the majority of cases, both Type I and Type II neurons exhibited similar morphological characteristics, with 80% of the Type I cells (13/16) and all of the Type II cells (n = 40) being small or medium spiny neurons. In each case where the morphological class of the cell was different than the spiny cell class, the cell exhibited a Type I response pattern. These spiny neurons had somata that averaged 17.1 +/- 1.3 microns in diameter and gave rise to between four and eight primary dendrites. The axons typically arose from cell bodies (7/13 for Type I and 25/40 for Type II cells) and emitted extensive local axonal collaterals. However, the axons of Type I cells more frequently originated from the dorsal surface of the somata (9/13; 69%), whereas Type II axons more frequently arose from the ventral surface of the somata (25/35; 71%), which may account for their different extracellular waveforms. In coronally sectioned tissue (n = 18), the axons always projected laterally when the somata were located in the medial striatum and projected medially when the somata were in the lateral striatal region. In a subset of experiments (N = 22), Lucifer yellow-stained neurons were localized with respect to their position within the patch and matrix compartments of the striatum using subsequent staining for calbindin 28 kd immunoreactivity. Of the 20 labeled medium spiny neurons examined (Type II: N = 13; Type I: N = 7), 19 were located in the calbindin-positive matrix compartment. The only neuron localized to the patch compartment was a medium spiny cell that exhibited a Type II paired impulse response pattern. In addition, of the two aspiny neurons from this group with beaded dendrites, one was localized to the border between adjacent patch and matrix compartments, whereas the other was located completely within the matrix compartment. Therefore, despite their distinct paired impulse response patterns, the majority of both Type I and Type II neurons were medium spiny cells located in the matrix compartment of the striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification and characterization of striatal cell subtypes using in vivo intracellular recording in rats: I. Basic physiology and response to corticostriatal fiber stimulation

The electrophysiological characteristics of two subtypes of striatal neurons, identified by their distinct patterns of response to paired impulse stimulation of corticostriatal afferents, were compared using in vivo intracellular recordings in rats. As observed in previous extracellular recording studies, the majority of neurons (73%) were found to be of the Type II class, with the remaining cells exhibiting the Type I response pattern. For all cells, cortical stimulation elicited 5-30 mV EPSPs at latencies ranging from 2.0-5.3 msec. Increasing the stimulating current intensity caused a progressive increase in the amplitude of the evoked EPSPs without altering their latencies, suggesting that the EPSPs are monosynaptically mediated. Both the average amplitude and duration of the evoked EPSPs at spike threshold in Type I neurons (9.8 +/- 1.7 mV, 11.8 +/- 2.8 msec; mean +/- SEM) were significantly smaller than those of Type II cells (20.3 +/- 1.4 mV, 22.7 +/- 2.1 msec). Although the average latency to the onset of the EPSP was similar for both cell classes (Type I cells: 2.3 +/- 0.3 msec; Type II cells: 2.2 +/- 0.2 msec), the EPSPs in Type I cells reached peak amplitude and the spikes were triggered at significantly longer latencies than in the Type II cells (peak I: 11.2 +/- 2.5 msec vs. II: 7.6 +/- 0.7 msec; spike I: 8.0 +/- 1.2 msec vs. II: 5.7 +/- 0.4 msec). Striatal neurons had a comparatively hyperpolarized resting membrane potential (-70.2 +/- 2.1 mV) and had an average input resistance of 35.4 +/- 7.6 M omega. Overall, striatal neurons exhibited low levels of spontaneous activity (0.6 +/- 0.7 Hz) with 50% of the neurons being quiescent. Type I cells exhibited significantly higher firing rates (3.2 +/- 0.8 Hz) than Type II cells (0.8 +/- 0.3 Hz), although their resting membrane potentials were not significantly different. Spontaneously occurring spikes had an average amplitude of 72.7 +/- 3.4 mV and spike thresholds of -50.1 +/- 1.5 mV. Irregularly occurring depolarizing plateau potentials, which typically gave rise to spike discharge, were frequently observed in both spontaneously firing and quiescent neurons. A small proportion of the cells recorded (3/55) exhibited a Type I response pattern but had unique physiological characteristics that were similar to those described by others as arising from large, aspiny striatal neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

The cortico-nigral projection in the rat: an anterograde tracing study with biotinylated dextran amine

The projection from the cortex to the substantia nigra (SN) in the rat was studied using the biotinylated dextran amine (BDA) anterograde tracing method. Injections of BDA into the prefrontal cortex consistently yielded labeling of the thin nerve fibers with small boutons in the SN pars compacta (SNc) and the pars reticulata (SNr). The cortico-nigral projection had a loose medio-lateral and rostro-caudal arrangement. Injections of BDA into the precentral lateral, the parietal, the temporal, and the occipital cortices resulted in sparse or no labeling of boutons in the SN. The density of boutons in the most heavily labeled region of the SN was 0.23/10(3) micron3. For comparison, similar measurement was performed in the cortico-striatal projection. The density of the boutons in the the neostriatum was 4.9/10(3) micron3. This study indicates that the entire prefrontal cortex projects to the SNc and SNr and that the terminal density of this projection is much less than the cortico-striatal projection.

Subthalamic nucleus and globus pallidus lesions alter activity in nigrothalamic neurons in rats

Lesions of the subthalamic nucleus or the globus pallidus altered the response of substantia nigra pars reticulata neurons (antidromically identified as projecting to the thalamus) to electrical stimulation of the frontal agranular cortex. In intact animals, cortical stimulation evokes three independent responses (excitation, inhibition, excitation) that may occur singly or in various combinations. The independence of the various responses, especially the temporally coincident excitatory and inhibitory responses, suggests that the net inhibitory and excitatory pathways carrying these signals from the cortex may converge to varying degrees on individual nigrothalamic neurons. Subthalamic lesions increased total response duration (from 28.4 to 39.7 ms), increased the duration of inhibition (from 18 to 30 ms), decreased the occurrence of excitatory responses, and decreased the intensity of the second excitation (from 1.1 to 0.6 spikes/s). Lesion of the globus pallidus also increased total response duration (up to 38 ms), but by increasing the duration of the second excitation (from 15.1 up to 23.8 ms). The intensity of the second excitation (from 1.1 to 1.5 spikes/stimulus) and the number of cells showing the first and second excitations also increased. The incidence, but not the duration, of the inhibition increased. The mean firing rate increased after subthalamic nucleus lesion (34.2 spikes/s) as compared to intact (27.0) or globus pallidus lesion (25.6). These changes may reflect changes in the relative contribution of the five different pathways transmitting information from the cortex to the substantia nigra. In all cases the cortico-striato-nigral pathway is largely intact.(ABSTRACT TRUNCATED AT 250 WORDS)

Depression of excitatory synaptic input in rat striatal neurons

Intracellular recording of rat striatal neurons was performed in vitro to investigate posttetanic changes in the excitatory post-synaptic potential (EPSP) elicited by stimulation of the corpus callosum. Tetanic stimulation induced posttetanic potentiation (PTP) in 11 of 12 cells. The PTP decayed in 1-5 min and was followed by either a short or long duration depression of the EPSP in 10 of 12 neurons. The remaining two neurons examined showed a slight enhancement of the EPSP that lasted for 30 min after the tetanus. The group of cells demonstrating short-duration depression (n = 3) were characterized by a decay of the depression to the control level by 15-20 min post-tetanus. The EPSP in the remaining cells showing depression (n = 7) showed a maintained depression for the entire recording session. Blockade of GABAA receptors with bicuculline (30 microM) or NMDA receptors with APV (50 microM) did not effect the induction of long-lasting depression of the striatal EPSP. The data indicates that the corticostriatal pathway can undergo enduring forms of use-dependent synaptic plasticity. This type of synaptic modification may participate in the refinement of movement and contribute to striatal related learning and memory.

Role of primate basal ganglia and frontal cortex in the internal generation of movements. III. Neuronal activity in the supplementary motor area

This study is a part of a project investigating neuronal activity in the basal ganglia and frontal cortex and describes externally and internally induced preparatory activity in the supplementary motor area (SMA), which forms a closed neuronal loop with the striatum. Monkeys made self-initiated arm reaching movements toward a constant target in the absence of phasic external stimuli. In separate blocks of trials, animals performed in a delayed go no-go task in which an instruction cue prepared for subsequent movement or no-movement to a trigger stimulus. A total of 328 neurons were tested in the delay task. Of these, 91 responded transiently to the instruction light with a median latency of 262 ms. Three quarters of these responses were restricted to the instruction preparing for arm movement, as opposed to withholding it, and thus may be involved in movement preparation processes. Sustained activation during the instruction-trigger interval was found for 67 neurons and occurred nearly exclusively in movement trials. Activation usually increased gradually after the cue and ended abruptly upon movement onset and thus could be related to the setting and maintenance of processes underlying the preparation of movement. Time-locked responses to the trigger stimulus were found in 38 neurons and were usually restricted to movement trials (median latency 80 ms). Activity time-locked to movement execution occurred in 67 neurons, beginning up to 252 ms before movement onset. A total of 266 neurons were tested with self-initiated arm movements. Of these, 43 showed premovement activity beginning 610-3030 ms before movement onset (median 1430 ms). The activity increased slowly and reached its peak at 370 ms before movement onset. It ended before movement onset or continued until the arm began to move or reached the target. This activity appears to reflect neuronal processes related to the internal generation of movements. Two thirds of activations preceding self-initiated movements occurred in neurons not activated before externally instructed movements, suggesting a selectivity for the internal generation process. Activity related to the execution of self-initiated movements occurred in 67 neurons: it began during and up to 420 ms before movement onset and was usually not associated with premovement activity. Most of these neurons were also activated with stimulus-triggered movements, suggesting a lack of selectivity for the execution of self-initiated movements. In comparison with the striatum, more SMA neurons showed preparatory activity preceding externally instructed movements (transient 27% vs 16%, sustained 20% vs 12%) and self-initiated movements (16% vs 11%).(ABSTRACT TRUNCATED AT 400 WORDS)

Efferent connections of the centromedian and parafascicular thalamic nuclei in the squirrel monkey: a light and electron microscopic study of the thalamostriatal projection in relation to striatal heterogeneity

The organization of the thalamostriatal projections arising from the centromedian (CM) and parafascicular (Pf) thalamic nuclei in the squirrel monkey (Saimiri sciureus) was studied at both light and electron microscopic levels. Following selective injections of the anterograde axonal tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) into the CM or Pf, patterns of terminal arborization within the striatum were compared to the biochemical heterogeneity of the striatum as revealed by immunohistochemical staining for the calcium-binding protein calbindin D-28k (CaBP), and histochemical staining for the enzymes acetylcholinesterase (AChE) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-diaphorase). The PHA-L-labeled axon terminals within the striatum were further analyzed at the ultrastructural level to characterize their pattern of synaptic organization. Dense and heterogeneous terminal fields occur in the "sensorimotor" territory of the striatum after CM injections, or in the "associative" striatal territory following Pf injections. In the associative territory labeled axons arborize in a diffuse manner predominantly within areas enriched with CaBP, AChE, or NADPH-diaphorase, representing the matrix compartment, and tend to avoid areas poor in these substances, corresponding to the patch/striosome compartment. In the sensorimotor territory labeled axons form bands that occupy a subregion of the NADPH-diaphorase-rich zone in the putamen. The terminal pattern of the CM-striatal projection suggests the existence of a more complex mosaic organization within the sensorimotor territory. Ultrastructural analysis of PHA-L-labeled elements within the striatum reveals that both CM and Pf projections form asymmetric synapses upon dendrites and spines of striatal cells. A total of 339 PHA-L-labeled boutons were examined after CM injections and compared to 293 boutons following Pf injections. After CM injections, 29% of PHA-L-labeled terminals form synapses on dendritic spines and 66% on dendritic shafts, whereas after Pf injections only 12% of synapses occur on dendritic spines compared to 81% on dendritic shafts. Labeled terminals forming axosomatic or axoaxonic synapses were not seen within the striatum following either CM or Pf injections. It is concluded that in the squirrel monkey: 1) Pf-striatal fibers profusely arborize within the matrix compartment of the associative territory, 2) CM-striatal fibers form bands that occupy a subregion of the NADPH-diaphorase-rich zone within the sensorimotor territory, and 3) that both Pf- and CM-striatal projections establish asymmetric synapses with dendrites and spines of medium-sized spiny cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Functionally distinct subpopulations of striatal neurons are differentially regulated by GABAergic and dopaminergic inputs--I. In vivo analysis

Two subpopulations of striatal neurons, Type I and Type II, are distinguished by their contrasting electrophysiological responses to paired impulse stimulation of cortical afferents. Although both Type I and Type II striatal neurons are excited by the first impulse of any pair of impulses, in response to short interstimulus intervals (10-30 ms) Type I neurons display an increase in probability of spike discharge to the second impulse (facilitation), whereas Type II neurons exhibit a decrease in probability of discharge (inhibition); in response to longer interstimulus intervals (50-250 ms) Type I cells display inhibition, whereas Type II cells show facilitation. The present experiments investigated the possibility that the unique paired impulse responses of Type I and Type II neurons reflect differential regulation by GABAergic and dopaminergic afferents. Extracellular recording techniques were combined with micropressure ejection of specific antagonists for GABAA (bicuculline), GABAB (phaclofen), D1 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-IH-3-benzazepin+ ++-7-ol; SCH23390) or D2 (sulpiride) receptors; the role of dopamine was also examined using the specific neurotoxin, 6-hydroxydopamine. Results showed that bicuculline (250-500 microM) reduced stimulation threshold for spike discharge of both Type I and Type II neurons and completely antagonized the paired impulse inhibition in response to short interstimulus intervals characteristic of Type II neurons. In contrast, phaclofen (2-30 mM) had only a variable influence on spike threshold for Type II cells and no effect on the paired impulse responses of either Type I or Type II neurons. Micropressure ejection of SCH23390 (1 mM) decreased spike thresholds for both cell types and attenuated the inhibition of spike discharge to long interstimulus intervals distinctive of Type I neurons, an effect which was mimicked by dopaminergic denervation. In contrast, sulpiride (1 mM) had little effect on spike thresholds, and no influence on the paired impulse responses of either cell type. These results indicate that the excitability of both Type I and Type II neurons is tonically inhibited by GABAergic and dopaminergic input via stimulation of GABAA and D1 receptors, respectively. Moreover, the bicuculline sensitivity of Type II neurons suggests that GABAergic input to this cell class arises from neurons within a cortically driven feedforward and/or feedback loop, whereas Type I cells receive input from neurons which lie outside of such a loop. In addition, the inhibition to longer interstimulus intervals characteristic of Type I cells is, at least in part, dependent on dopaminergic input through D1 receptor stimulation.

Intracellular response of caudate neurons to variable frequency stimulation of motor cortical areas in dog

The intracellular response to electrical stimulation of motor cortex was studied in 77 neurons recorded in the head of the caudate (Cd) nucleus of dog. Single pulse stimulation of either medial, intermediate or lateral precruciate cortex produced a response in 69 neurons, 59% of which responded to more than one cortical area. Most intracellular responses were complex potentials consisting of an initial depolarization (E) followed by a longer duration hyperpolarization (I) or E-I response complex. When stimulated with trains of low frequency pulses (10 Hz), the stimulus-generated I potentials reduced the absolute amplitude of the evoked E's, often to a level below resting potential. However, at higher frequencies (50 Hz), the I potentials were attenuated and the E potentials summated into a prolonged depolarization lasting the duration of the stimulus train. A computer model of the response to multiple stimuli was generated assuming that the E-I response to each stimulus pulse in the train should temporally summate with previous responses. As the frequency of stimulation was increased, this model consistently predicted greater summation of the I potentials than was experimentally observed. These data suggest that inhibition of Cd neurons is input frequency dependent such that as the frequency of cortical input increases there is a decrease of input-generated inhibition of Cd neurons. Thus, inhibition may modulate the response of Cd neurons such that cortical input must reach a critical firing frequency before being relayed through the Cd nucleus.

Neurophysiological maturation of cat caudate neurons: evidence from in vitro studies

The membrane properties and synaptic physiology of developing cat caudate (Cd) nucleus neurons were studied in in vitro slice preparations. Recordings were obtained from 98 cells in kittens from fetal day (F) 56 to postnatal day (P) 90. With increasing age, the following maturational changes occurred; resting membrane potentials became more negative, action potential rise times decreased, action potential amplitudes increased, and action potential durations and input resistances decreased. The frequency of occurrence of afterhyperpolarizations and of anomalous rectification increased with age. The primary response to local extracellular stimulation was a depolarization usually accompanied by an action potential. Evoked hyperpolarizing responses were seen after P28 but only occurred if the membrane was depolarized by intracellular current injection. Cells identified by intracellular injection of Lucifer yellow were primarily medium-sized spiny neurons although it was not always possible to determine the cell type in slices from animals less than P5. Somatic diameter, dendritic length, and spine density increased with age. Dye-coupling occurred in slices less than P20. Its frequency decreased with age. These results show that Cd neurons undergo significant maturation during late prenatal and early postnatal periods. In contrast, substantia nigra neurons mature more rapidly and should be capable of influencing the less mature Cd neurons during development.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of aspartate in corticofugal pathways

In the present study we used immunohistochemistry, with an antibody directed against aspartate (Asp), in conjunction with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) histochemistry to examine the Asp-containing neurons in the motor and somatosensory cortices of the rat that project to the caudate/putamen or the pons. Injections of WGA-HRP in the caudate/putamen labelled cells in layer V of both cortical areas. In the motor cortex, retrogradely labelled neurons were distributed throughout layer V; 59% of these cells were also Asp-immunoreactive. In the somatosensory cortex labelled neurons were found mainly in layer Vb; 57% of these cells were double labelled. A similar percentage of cells were double labelled in this cortical area following WGA-HRP injections into the pontine nuclei. These observations taken together with previous findings (Exp. Neurol., 105 (1989) 36-44) suggest that nearly equal proportions of neurons that give rise to the corticostriatal and corticopontine pathways may use either Asp or glutamate (Glu) as putative neurotransmitters.