A theory of the functional organization of the neostriatum and the neostriatal control of voluntary movement

Direct projections from the caudal spinal trigeminal nucleus to the striatum in the cat

The results of a WGA-HRP and HRP study in the cat indicated that some neurons in the marginal zone (lamina I) of the caudal spinal trigeminal nucleus sent their axons contralaterally to the striatum; mainly to the dorsal part of the putamen, and additionally to the ventrolateral part of the caudate nucleus, at the stereotaxic rostrocaudal levels of A 13.0-A 15.5.

Neuronal phosphoproteins. Mediators of signal transduction

This article summarizes some of our knowledge concerning intracellular protein phosphorylation pathways in nerve cells. It also summarizes, very briefly, recent direct experimental evidence involving intracellular injection of protein kinases, protein kinase inhibitors, and substrates, indicating that protein phosphorylation mediates the actions of a variety of neurotransmitters on their target cells. Finally, it summarizes in somewhat greater detail the results of studies of three different types of substrate proteins that appear to regulate different types of biological responses in nerve cells: synapsin I, a substrate protein present in virtually all nerve terminals, which appears to regulate neurotransmitter release from those nerve terminals; the acetylcholine receptor, the phosphorylation of which regulates its rate of desensitization in the presence of acetylcholine; and DARPP-32, the phosphorylation of which converts it into a very potent phosphoprotein phosphatase inhibitor that may be involved in the regulation by the neuromodulator dopamine of the effects of the neurotransmitter glutamate. The identification and characterization of additional neuronal phosphoproteins can be expected to lead to the clarification of numerous additional molecular mechanisms by which signal transduction is carried out in nerve cells.

Striatal substance P cell clusters coincide with the high density terminal zones of the discontinuous nigrostriatal dopaminergic projection system in the cat: a study by combined immunohistochemistry and autoradiographic axon-tracing

A portion of the nigrostriatal projection that originates from presumably dopaminergic neurons in the caudal pars compacta of the substantia nigra and the suprajacent pars dorsalis (retrorubral area), was shown by [3H]amino acid autoradiographic tracing to distribute nonhomogeneously in the head of the caudate nucleus, such that zones of high density termination are in register with the archipelago of substance P cell clusters revealed immunohistochemically in the same and adjacent tissue sections of the cat's brain. Axons from this same portion of the substantia nigra distribute densely at caudal levels of the putamen where again substance P-immunoreactive striatal cells are numerous. In nearby tissue sections from the same cases, tyrosine hydroxylase-like immunoreactivity suggested only subtle variations in the density of the catecholamine axon network within the striatum. Thus, whereas dopamine axons are distributed densely throughout the striatum, those originating from cells in the caudal pars compacta et dorsalis of the substantia nigra and ending in the head of the caudate nucleus appear to terminate preferentially within the substance P cell clusters. These data suggest that the striatal substance P cells, which send their axons selectively to the entopeduncular nucleus and substantia nigra, but much less so the globus pallidus, are a major target of nigrostriatal dopamine transmission. This result is discussed with respect to the anatomical, neurochemical and functional organization of the striatifugal projection system.

In vivo release of [3H]gamma-aminobutyric acid in the rat neostriatum--II. Opposing effects of D1 and D2 dopamine receptor stimulation in the dorsal caudate putamen

The effects of several dopaminergic agonists and antagonists on the spontaneous release of [3H]gamma-aminobutyric acid were investigated in the dorsal striatum of halothane-anaesthetized rats. A push-pull cannula was implanted and the tissue was superfused continuously with a physiological medium containing [3H]glutamine, the precursor of [3H]GABA. Drugs were added to the superfusion medium. 2-Amino,6,7-dihydroxy,1,2,3,4-tetrahydro-naphtalene (ADTN, a mixed D1 and D2 receptor agonist) and D-amphetamine (a drug that enhances the release of endogenous dopamine) increased the release of 3H-GABA. The effect of ADTN was blocked by a D1 antagonist [R-(+),8-chloro, 7-hydroxy,2,3,4,5-tetrahydro,3-methyl,5-phenyl,1-H,3-benzazepine (SCH 23390)] but not by a D2 antagonist (S-sulpiride). Furthermore the stimulation of D1 receptors either by 2,3,4,5-tetrahydro,7,8-dihydroxy,1-phenyl,1-H,3-benzazepine or by D-amphetamine in the presence of S-sulpiride also enhanced the release of [3H]GABA. On the other hand, a selective D2 receptor agonist (3-(2-(N-3-hydroxy-phenylethyl)N-propylamino)ethyl-phenol) decreased the release of [3H]GABA. This effect was blocked in the presence of S-sulpiride. By itself the D1 receptor antagonist (SCH 23390) decreased the release of [3H]GABA whereas the D2 receptor antagonist (S-sulpiride) had no effect. It was concluded that stimulation of D1 and D2 receptors produces opposing effects on the spontaneous release of [3H]GABA in the dorsal striatum. Stimulation of D1 receptors facilitates the release of [3H]GABA whilst stimulation of D2 receptors inhibits it. The effect of D1 receptor stimulation appears to be predominant, and endogenous dopamine may activate tonically the release of GABA through these receptors in our experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Thalamic control of dopaminergic functions in the caudate-putamen of the rat--I. The influence of electrical stimulation of the parafascicular nucleus on dopamine utilization

A neurochemical response of four dopamine-rich brain regions to unilateral electrical stimulation of the parafascicular thalamic nucleus was examined in the halothane-anaesthetized rat. Tissue concentrations of dopamine and its two major metabolites, 3,4-dihydroxyphenylacetic acid and 4-hydroxy-3-methoxyphenylacetic acid, were assayed by a high performance liquid chromatographic technique in samples of caudate-putamen complex, nucleus accumbens, prefrontal cortex and substantia nigra. The ratios of metabolite to parent amine concentrations were taken as indices of dopamine utilization. Halothane anaesthesia alone evoked significant bilateral increases of dopamine utilization in every brain region studied. Electrical stimulation of one parafascicular nucleus produced further bilateral elevations of dopamine utilization in the caudate-putamen complex without altering these parameters in the substantia nigra. In the prefrontal cortex, however, thalamic stimulation resulted in significant bilateral decreases of dopamine utilization. Electrical stimulation of cortical or other thalamic areas did not evoke this regional pattern of dopamine utilization. It is argued that these indices of dopamine utilization together serve as reliable indicators of synaptic dopamine release and it is concluded that the parafascicular thalamus is capable of facilitating dopaminergic neurotransmission in the caudate-putamen by a mechanism that is probably independent of changes in dopamine cell firing rate. An anatomical analysis suggests that a thalamo-cortical-striatal route is most likely to mediate this function.

Unilateral, intranigral infusions of amphetamine produce differential, bilateral changes in unit activity and extracellular levels of ascorbate in the neostriatum of the rat

Simultaneous recordings of single-unit activity and oxidation current were obtained bilaterally from the neostriatum of rats in response to a unilateral infusion of D-amphetamine (2.0 microliters of 10 micrograms/microliter) into the substantia nigra. Whereas neuronal activity increases ipsilaterally and decreases contralaterally, the electrochemical signals, which reflect extracellular ascorbate, increase bilaterally. In each case, changes in unit activity precede the change in ascorbate release. Systemic administration of haloperidol (0.2 mg/kg) blocks the increase in oxidation current bilaterally, but reverses the neuronal activity response only on the ipsilateral side. These results lend further support to the view that intranigral amphetamine facilitates neostriatal ascorbate release, but this effect is not correlated with changes in single-unit activity.

Quantification of the dopamine innervation in adult rat neostriatum

Conditions leading to specific and integral visualization of dopamine axon terminals (varicosities) were tested in adult rat cerebral hemisphere slices incubated with [3H]dopamine and processed for high resolution radioautography. Specific visualization of the dopamine endings was achieved after incubation with 10(-6) M [3H]dopamine in the presence of a monoamine oxidase inhibitor (pargyline 10(-4) M), and of desipramine (5 X 10(-6) M), an inhibitor of catecholamine uptake by noradrenaline and serotonin neurons. [3H]Dopamine varicosity labeling was eliminated by the addition of 5 X 10(-5) M benztropine (an inhibitor of catecholamine uptake by catecholamine neurons), and was almost absent when dopamine nerve cell bodies of the midbrain had been previously destroyed with 6-hydroxydopamine. In dopamine-denervated neostriatum incubated without desipramine, a second set of labeled terminals was also visible. These were identified as serotoninergic, since their labeling was suppressed by citalopram, an inhibitor of monoamine uptake highly specific for serotonin neurons. There was no desipramine-sensitive but citalopram-resistant varicosity labeling suggestive of neostriatal noradrenaline innervation. In normal striatum, incubation at 35 degrees C always resulted in a labeling of dopamine varicosities restricted to a narrow band which followed the contours and cut surface of this anatomical region. This unusual distribution was the result of an uptake barrier generated by the tightly packed dopamine varicosities. Indeed, the striatal dopamine varicosity labeling was more widespread after partial 6-hydroxydopamine denervation or in normal tissue incubated either with a higher [3H]dopamine concentration (5 X 10(-6) M), in the presence of relatively low benztropine concentrations (10(-5) M), or at lower temperature (15 degrees C). Material incubated at 15 degrees C for 90 min was suitable for purposes of quantification: labeled varicosities were then visualized throughout the striatum and across the full thickness of the slices; moreover, the number of labeled varicosities plotted against radioautographic exposure time increased in parallel and reached a plateau at the same time in neostriatal sectors with widely different innervation densities. At a rostral transverse level across neostriatum, the dorsolateral quadrant showed hyperdense "patches" of labeled terminals distinguishable from an already dense surrounding "matrix", whereas, ventromedially, the dopamine innervation appeared more uniform and somewhat less dense.(ABSTRACT TRUNCATED AT 400 WORDS)

Substantia nigra stimulation evoked antidromic responses in rat neostriatum

Electrical stimulation of the substantia nigra of rats elicits a burst of small amplitude waves with a latency of 4-6 ms that may last for 10-15 ms throughout much of the neostriatum. Frontal cortex stimulation also elicits a burst response, which can occlude the substantia nigra response. The substantia nigra evoked burst response was still present after chronic neocortical ablation or thalamic transection or both treatments combined. The response corresponds to the first sharp negative wave of the substantia nigra evoked neostriatal field potential. Single substantia nigra evoked action potentials were recorded in neostriatum with a mean latency of 9.8 ms, ranging from 4-22 ms. These action potentials were considered to be antidromic because they were occluded during appropriate collision intervals by orthodromic action potentials elicited by frontal cortex stimulation. Subthreshold frontal cortex conditioning stimulation did not alter the threshold for activation from substantia nigra. The refractory period for the axon was at least as long as that for the soma and ranged between 0.8-2.0 ms. The antidromic responses failed to follow low frequency stimulation (less than 40 Hz for 3000 ms). This failure occurred in the axon between substantia nigra and globus pallidus. The burst response and first sharp negative wave of the field potential probably represent the antidromic activation of the ubiquitous and densely packed medium spiny neostriatal projection neurons. These responses occur at the same latency, respond in the same manner to twin pulse and repetitive stimulation and are occluded by frontal cortex stimulation in the same manner as antidromic action potentials.

Release of endogenous amino acids from striatal neurons in primary culture

Endogenous amino acid release was examined in highly purified striatal neurons obtained from fetal mouse brain, and differentiated in primary culture. This study aimed to determine which amino acids are released from striatal neurons after a brief depolarization period induced by elevated potassium concentration or veratrine. Amino acids released into the extracellular medium, subsequent to a 3-min exposure of striatal neurons, were subjected to HPLC analysis. At 14 days in vitro potassium (56 mM) depolarization elicited a 25-fold increase in gamma-aminobutyric acid release, 85% of which was calcium-dependent. This effect was small but apparent at 7 days in vitro (two-fold increase) and greatly increased between 11 and 14 days in vitro, subsequent to the appearance of synaptic vesicles in nerve terminals. gamma-Aminobutyric acid release was readily reversible within minutes of return to the resting state. Veratrine induced a quantitatively similar but calcium-independent increase in gamma-aminobutyric acid release. Similar results were observed on aspartate and glutamate release, but the increase was very small even after 14 days in vitro (62.2 and 123.3% increase over basal release, respectively). Taurine and hypotaurine release increased during and after depolarization induced by potassium. This effect remained constant between 11 and 18 days in vitro. BAY K 8644, a dihydropyridine-sensitive calcium channel agonist, augmented the effect of 15 mM potassium on gamma-aminobutyric acid release, but this effect remained very small as compared to the potassium (56 mM) or veratrine effects. In addition, nifedipine inhibited this BAY K 8644-induced release. These results demonstrate the high level of differentiation among striatal neurons containing gamma-aminobutyric acid in this in vitro system.

The neural substrates for the motor-activating properties of psychostimulants: a review of recent findings

Several different classes of pharmacological agents produce syndromes of behavioral activation in humans and infrahumans. While many of these agents, including direct and indirect sympathomimetics, methylxanthines, opiates and several neuropeptides have very distinct neurochemical profiles, it is not clear whether their behavioral stimulant action results from their action on a common neural substrate, or instead from their action on parallel but separate activation "circuits.' Using photocell measurements of motor activity in rats, it has been possible to demonstrate that some agents with very distinct neurochemical identities act on common neural substrates to produce behavioral activation, while other agents act on completely distinct brain regions. Specifically, the locomotor-activating properties of direct and indirect sympathomimetics and opiates appear to result from their action within the basal ganglia, including the ventral striatum and globus pallidus, while the activating properties of caffeine and the neuropeptide, corticotropin releasing factor (CRF) appear to be independent of this circuitry. These findings suggest the presence of at least two separate neural systems capable of mediating behavioral activation.

Substance P and Parkinson's disease: a causal relationship?

Parkinson's disease (PD) is a common condition that is thought to result from a marked degeneration of dopaminergic neurones of midbrain origin. Here I present evidence to show that PD may result from a primary loss of active tachykinin, probably substance P (SP) in the substantia nigra (SN), and that this loss leads to a secondary degeneration of the dopaminergic neurones. This raises the possibility of treating and curing patients with PD by giving them SP agonsts.

Synaptogenesis of cultured striatal neurons in serum-free medium: a morphological and biochemical study

Striatal neurons were cultured from the fetal mouse brain and maintained in serum-free medium for 14-21 days in vitro (DIV). Pretreatment of the culture dishes successively with a polycation followed by fetal calf serum resulted in rapid neuron attachment and neurite proliferation. After 9-10 DIV, electron microscope observations revealed the presence of vesicles in axon terminals forming mature synapses with axons and perikarya of adjacent neurons and in varicosities along extended axons. Synapsin I, a synaptic vesicle-specific protein, was present only in neuronal perikarya after 3 DIV, in perikarya and in varicosities along extended axons after 6 DIV, and in varicosities and contact points between axon terminals and adjacent axons or perikarya after 11-14 DIV. Neurotransmitter-stimulated intracellular formation of cAMP decreased markedly during neuronal differentiation. Inositol phosphate formation in response to neurotransmitters, however, increased significantly throughout the period of striatal neuronal development. K+ (56 mM) depolarization resulted in a 2-fold increase in endogenous gamma-aminobutyric acid (GABA) release from striatal neurons, 50% of which was Ca2+-dependent, between 3 and 11 DIV. Between 11 and 14 DIV, subsequent to synapse formation (as revealed by electron microscope observations), GABA release evoked by 56 mM K+ increased up to 5-fold, 75% of which was Ca2+-dependent. It appears that the complete differentiation of striatal neurons in serum-free medium may provide a suitable model for the study of the physiological and regulatory mechanisms involved in nerve cell development.

Glutamic acid decarboxylase and enkephalin immunoreactive axon terminals in the rat neostriatum synapse with striatonigral neurons

Synaptic interactions between striatal projection neurons and axon terminals containing immunoreactive glutamic acid decarboxylase (GAD) or Leu-enkephalin were examined in the rat neostriatum using a combined method of horseradish peroxidase retrograde transport from the substantia nigra and immunohistochemistry at the electron microscopic level. Results showed that numerous immunoreactive GAD and enkephalin boutons formed synapses with the cell bodies and dendrites of medium-sized striatonigral neurons. These findings demonstrate that within the neostriatum GABA and enkephalin directly influence caudate output pathways.

Electrophysiological study of the effects of D1 and D2 dopamine antagonists on the interaction of converging inputs from the sensory-motor cortex and substantia nigra neurons in the rat

The interaction of stimulation of the cerebral cortex and of the substantia nigra on the activity of neostriatal neurons was investigated in urethane-anesthetized rats. Neurons of the dorsal striatum were activated by single pulse stimulation of the sensory-motor cortex. The effects of nigral conditioning stimulation on this excitatory response of striatal neurons to cortical stimulation were studied in a series of parametric experiments in which the length of the train of pulses and the intensity of the nigral stimulation were varied. One and five pulses of nigral conditioning stimulation had little or no effect. Ten pulses of nigral conditioning stimulation reduced the excitatory response, the magnitude of the reduction being greater with higher current intensities. In another series of experiments, the effects of dopaminergic receptor antagonists on the interaction of cortical and nigral inputs to striatal neurons were studied. Sulpiride, a D2 antagonist, reversed the attenuating effects of nigral conditioning stimulation on the excitatory response of striatal neurons to cortical stimulation, whereas SCH 23390 a D1 antagonist, had no effect. The present findings support the hypothesis that the nigrostriatal dopaminergic pathway modulates the excitatory response of striatal neurons to cortical stimulation by means of dopamine D2 receptors.

Morphology of embryonic neostriatal cell suspensions transplanted into adult neostriata

Embryonic neostriatal cell suspensions were transplanted into intact or kainic acid-lesioned neostriata of adult host rats. These transplants survived and were sacrificed at 34-78 days posttransplantation. Nissl and Golgi preparations revealed neurons present within the transplants. Neurons with abundant dendritic spines (Spiny type I) were most frequent, but those with fewer spines (Spiny type II) and smooth dendrites (Aspiny II and III) were also present. These results indicate that neostriatal transplants are populated by the major output and internuncial neurons of the neostriatum.

Dopamine and the action of opiates: a reevaluation of the dopamine hypothesis of schizophrenia. With special consideration of the role of endogenous opioids in the pathogenesis of schizophrenia

It is suggested that the antipsychotic efficacy of opioids in patients suffering from schizophrenia may result from an interaction of opioids with the dopaminergic system. The modulatory effect of opioids on dopaminergic functions has already been demonstrated in basic experiments: Anatomical and biochemical data reveal an interaction between opioid receptors and dopamine (DA) actions on dopaminergic nerve terminals, cell bodies, and afferent nerve endings. Endogenous enkephalin levels correlate well with the endogenous dopamine content in various brain areas. Systemic or iontophoretic administration of morphine alters the spontaneous activity of ventral tegmental dopaminergic neurons. Morphine and enkephalin effectively enhance pituitary prolactin release, whereas dopamine inhibits it. Opioid agonists effectively alter DA release, DA reuptake, and DA metabolism in the striatum and substantia nigra. In reverse, chronic neuroleptic treatment enhances the synthesis and release of pituitary beta-endorphin. Opioids affect contralateral rotation elicited by dopamine agonists in animals with unilateral lesions of the nigrostriatal pathway. Phencyclidine, a psychotropic drug that shares certain pharmacological characteristics with the putative sigma-opioid receptor ligand SKF 10,047, indirectly mimics the effects of dopamine agonists on prolactin release, release of acetylcholine, etc. It is suggested that an imbalance of opiate-DA interaction might be involved in the pathogenesis of schizophrenia. Consequently, clinical studies on the effects of opioids on psychotic symptoms should also examine opioid influence on dopaminergic functions in these patients.

Altered local cerebral glucose utilization by unilateral frontal cortical ablations in rats

Alterations in local cerebral glucose utilization (LCGU) following ablations of the unilateral frontal cortex in rats were studied to elucidate the effect of the lesion on the functional activity in the related cerebral structures. Frontal cortical ablations (areas 2, 4, 6 and 10) were made by aspiration on the left side, and LCGU was evaluated at 7 days after the operation, using the [14C]deoxyglucose method. Significant decreases in LCGU in rats with unilateral frontal cortical ablations, were observed in the ipsilateral thalamic nuclei (ventroanterior-ventrolateral (VAL), ventrobasal (VB), reticular), red nucleus and pontine nucleus. The ipsilateral globus pallidus showed a significant LCGU increase. The contralateral cerebellar cortex showed a tendency toward a decrease in LCGU. The striatum, which receives direct projections from the frontal cortex, showed no LCGU change. These results indicated that ablations of unilateral frontal cortex in rats produced LCGU changes in the cerebral structures which have direct or indirect neuronal connections with the ablated area. These LCGU changes were, for the most part, brought about by alteration in the neuronal activity. Particularly, the LCGU increase in the globus pallidus which receives transsynaptic neuronal input from the frontal cortex, without changes in the striatum, which receives direct projection, was attributed to the functional alteration of the globus pallidus produced by the cortical ablation. Destructive lesion of a cerebral structure, therefore, does not necessarily cause functional depressions in the pertinent structures, but it may enhance the function of some structures, depending on the functional characteristics of each neuronal connection and functional organization of those structures.

Dopamine receptor agonists: mechanisms underlying autoreceptor selectivity. II. Theoretical considerations

In a companion article, we extensively reviewed the pharmacological actions of the enantiomers of the dopamine analogue 3-(3-hydroxyphenyl)-N-n-propylpiperidine, 3-PPP. The profiles of action exhibited by transdihydrolisuride (TDHL) and the trans-fused 7-OH-1,2,3,4,4a,5,6,10-octahydrobenzo(f)quinoline (HW 165) were also described. These latter agents, along with (-)-3-PPP, exert a variety of effects at different DA receptors depending on the anatomical location of these receptor sites and the experimental conditions. In the first part of the present article, it is suggested that the intrinsic activity of these agents in different pharmacological models is dependent on the responsiveness of the relevant DA-receptors which, in turn, is related to the degree of previous agonist occupancy of these sites. In situations where these agents exhibit partial agonist activity, their pharmacological effect is also dependent on the relative concentrations of drug and endogenous DA competing for common receptor sites. A number of theoretical implications will be discussed relevant to the suggestion that DA receptors exist in various adaptational states which can influence drug action. In the second part of this review, we will consider the behavioural profile exhibited by (-)-3-PPP in relation to that observed with classical DA antagonists. In addition, the potential clinical application of (-)-3-PPP and similar-acting agents will be discussed.

Gamma-vinyl-GABA treatment of tardive dyskinesia and other movement disorders

We conducted a single-blind trial of gamma-vinyl-GABA (GVG) in nine patients: seven with tardive dyskinesia, one with Meige syndrome, and one with Tourette syndrome. Five tardive dyskinesia patients completed the entire 11-week study and, as a group, demonstrated significant decreases in dyskinesia scores. Four of these five tardive dyskinesia patients showed clinically evident improvement, with approximately 30% reduction in dyskinetic symptoms. Other patients had no clinical benefit from GVG. Three patients had transient exacerbation of psychiatric symptoms after sudden withdrawal of GVG, and one patient experienced dose-related confusional episodes. Our results suggest that GABAergic drugs may have a role in treating patients with tardive dyskinesia.

Sensitivity changes to dopaminergic agents in fine motor control of rhesus monkeys after repeated methamphetamine administration

Long-term behavioral and neurochemical effects of repeated methamphetamine (MA) administration were investigated in rhesus monkeys trained to perform a fine motor task requiring control of exerted force for a specified time. Rhesus monkeys were trained to extend their arms into a tube to press a lever with a force between 25 and 40 g for 5 sec in order to receive 1.5 ml of water. The effects of intramuscular administration of MA, apomorphine (APO) and haloperidol (HAL) on responding were compared before and after a 2-week period of repeated MA administration. During this period, MA was given in 4 divided doses starting at a total daily dose of 4 mg/kg/day and increasing to 40 mg/kg/day. Tolerance to MA, increased sensitivity to HAL and no consistent sensitivity change to APO were observed when dose-response functions were redetermined starting 1 month after the repeated MA administration. One month after these determinations were completed, the brains of the monkeys were analyzed for changes in monoamines. Significant depletions of dopamine in the caudate nucleus and serotonin in the frontal cortex were seen. It is hypothesized that the sensitivity changes to the drugs on performance were related to the dopamine depletion.

A Golgi study of the human neostriatum: neurons and afferent fibers

The neostriatum of 20 adult humans was examined in Golgi-Kopsch and rapid Golgi preparations. At least five types of neurons and four types of afferent fibers are described. Neurons of medium size with spine-rich dendrites (spiny type I) are the most frequent type. These cells exhibit a greater morphological diversity than those previously studied in the monkey. Also, quantitative data show that, compared to the monkey, spiny type I neurons in man have a greater somal size and dendritic field radius. Although the types of spines are similar, the mean density and radial distribution of spines along dendrites differ in the two species. Morphologic features of the axon, which is usually long with extensive collateral branches, suggest that more than one process from the axon may be efferent. Medium to large neurons with sparsely spined dendrites (spiny type II) differ from type I neurons in having a poorer branching and greater radial spread of their dendrites and a lower density of spines. They also differ from spiny type I neurons in their distribution and relative proportion of various spine types. The axon of the spiny type II neuron is long and has collaterals which are poorly arborized in comparison to those of spiny type I cells. Aspiny neurons are of medium (aspiny type I) and large (aspiny type II) size. They have varicose, curved dendrites and a short axon which arborizes mostly within the dendritic field. A group of smaller neurons with more variable dendritic morphology is also seen. Observations suggest that in the human brain the proportion of medium-sized aspiny neurons and small neurons may be greater than in other species.

The biochemical basis of the behavioral disorder in the Lesch-Nyhan syndrome

An inherited complete deficiency of hypoxanthine-guanine phosphoribosyltransferase in male children is associated with a severe neurological disorder characterized by chloroform and athetoid movements, hypertonicity, mental retardation, and self-injurious behavior. In the review that follows several possible mechanisms by which the enzyme defect may cause the CNS disorder are discussed. Current evidence suggests that the primary neural deficit in the Lesch-Nyhan syndrome is a deficiency of dopamine in the basal ganglia. It is argued that this neurochemical lesion results from a deficiency of purine nucleotides which impairs arborization of nigrostriatal neurons during perinatal development. Differences in the ontogenetic timing of the neurochemical lesion may be partly responsible for the different neurological symptoms displayed by persons afflicted with the Lesch-Nyhan and Parkinson's syndromes.

Tyrosine hydroxylase-immunoreactive boutons in synaptic contact with identified striatonigral neurons, with particular reference to dendritic spines

Tyrosine hydroxylase-immunoreactive fibres in the rat neostriatum were studied in the electron microscope in order to determine the nature of the contacts they make with other neural elements. The larger varicose parts of such fibres contained relatively few vesicles and rarely displayed synaptic membrane specializations; however, thinner parts of axons (0.1-0.4 micron) contained many vesicles and had symmetrical membrane specializations, indicative of en passant type synapses. By far the most common postsynaptic targets of tyrosine hydroxylase-immunoreactive boutons were dendritic spines and shafts, although neuronal cell bodies and axon initial segments also received such input. Six striatonigral neurons in the ventral striatum were identified by retrograde labelling with horseradish peroxidase and their dendritic processes were revealed by Golgi impregnation using the section-Golgi procedure. The same sections were also developed to reveal tyrosine hydroxylase immunoreactivity and so we were able to study immunoreactive boutons in contact with the Golgi-impregnated striatonigral neurons. Each of the 280 immunoreactive boutons examined in the electron microscope displayed symmetrical synaptic membrane specializations: 59% of the boutons were in synaptic contact with the dendritic spines, 35% with the dendritic shafts and 6% with the cell bodies of striatonigral neurons. The dendritic spines of striatonigral neurons that received input from immunoreactive boutons invariably also received input, usually more distally, from unstained boutons that formed asymmetrical synaptic specializations. A study of 87 spines along the dendrites of an identified striatonigral neuron showed that the most common type of synaptic input was from an individual unstained bouton making asymmetrical synaptic contact (53%), while 39% of the spines received one asymmetrical synapse and one symmetrical immunoreactive synapse. It is proposed that the spatial distribution of presumed dopaminergic terminals in synaptic contact with different parts of striatonigral neurons has important functional implications. Those synapses on the cell body and proximal dendritic shafts might mediate a relatively non-selective inhibition. In contrast, the major dopaminergic input that occurs on the necks of dendritic spines is likely to be highly selective since it could prevent the excitatory input to the same spines from reaching the dendritic shaft. One of the main functions of dopamine released from nigrostriatal fibres might thus be to alter the pattern of firing of striatal output neurons by regulating their input.

Inhibitory response of pallidal neurons to cortical stimulation and the influence of conditioning stimulation of substantia nigra

Single pulse stimulation of the sensory motor cortex of rats anesthetized with urethane was observed to inhibit the activity of neurons in the globus pallidus. When a train of 10 pulses delivered to the substantia nigra, preceded the cortical stimulation, the inhibitory response was significantly reduced in 46 of 66 globus pallidus neurons tested. A single pulse stimulus to the substantia nigra had no effect on the inhibitory response of globus pallidus neurons to cortical stimulation. Similar interaction experiments were performed in rats treated with haloperidol (HPL), a dopamine antagonist, or with 6-hydroxydopamine. In such experiments a train of stimulus pulses delivered to the substantia nigra did not attenuate the inhibitory response of globus pallidus neurons to cortical stimulation, suggesting that the observed interactions are dopamine-mediated.

Excitatory input from sensory motor cortex to neostriatum and its modification by conditioning stimulation of the substantia nigra

Extracellular single unit responses were recorded from 381 neurons in the neostriatum of urethane-anesthetized rats. Single pulse stimulation of the sensory motor cortex produced strong excitatory responses in neostriatal neurons with a mean onset latency of 7.9 ms. A train of 10 pulses (0.15 ms, 300-600 microA) at 10 Hz delivered to the substantia nigra 100 ms before cortical stimulation attenuated the original excitatory response of 22 of 53 striatal neurons tested and enhanced the excitatory response of 12 of these neurons. These attenuating and enhancing effects were reduced or abolished by the systemic administration of haloperidol, a dopamine antagonist. Single pulse nigral stimulation 100 ms before the cortical stimulation had little or no effect on the excitatory response of neostriatal neurons. The iontophoretic application of dopamine also had attenuation and enhancement effects on the excitatory response of striatal neurons to cortical stimulation. The results suggest that the attenuation and enhancement of the excitatory responses of striatal neurons to cortical stimulation which resulted from nigral conditioning stimulation is mediated by nigrostriatal dopaminergic neurons.

Ultrastructural morphology of dopaminergic nerve terminals and synapses in the striatum of the rat using tyrosine hydroxylase immunocytochemistry: a topographical study

Structures immunoreactive for TH were examined in the rat striatum (including caudate-putamen, nucleus accumbens and globus pallidus) by electron microscopy using the indirect peroxidase-labeled antibody method. Axon profiles and nerve terminals were the only structures stained by DAB precipitates in the axoplasm. The reactive boutons frequently contained a population of large pleomorphic vesicles (40-60 nm in diameter) but their interiors remained free of reactions. The synaptic contacts formed belonged principally to the symmetric type 2 of Gray while asymmetric Gray's type 1 synapses were rarely observed. The former were mostly apposed to dendritic trunks (rarely to perikarya) and the latter to dendritic spines. In addition, numerous immunoreactive nerve terminals were often found in close contact with small structures identified as the neck of dendritic spines. The active zone of these presumed synapses was characterized by a prominent thickening of the presynaptic membrane but the post-synaptic thickening was lacking. For similar reasons, it was difficult to assert the existence of one axo-axonic synapse when a positive nerve terminal was closely apposed to another one (generally unreactive). The exact morphology of dopaminergic synapses, or even their existence, have not been firmly established owing to large discrepancies between previous reports. No synapses, or synaptic contacts of either asymmetric or symmetric type were described according to the technique used. Our work was undertaken to elucidate further this problem, and in particular, we thought that regional differences in the synaptic organization might explain the divergent data. However, regional quantitative analysis performed in this study did not show significant differences in the percentage of either kind of synapses in the various striatal regions.

Characterization of cholinergic neurons in the rat neostriatum. A combination of choline acetyltransferase immunocytochemistry, Golgi-impregnation and electron microscopy

Immunocytochemistry with a monoclonal antibody against choline acetyltransferase has been used to characterise cholinergic neurons in the rat neostriatum. The light microscopic morphology, ultrastructure and synaptic input of these neurons was compared to that of the three types of large neuron found in Golgi preparations of the striatum. The cholinergic neurons are large and have long infrequently branching dendrites. Two of the immunoreactive neurons were also Golgi-impregnated and showed characteristics of the "classical" large neurons of the striatum. Examination in the electron microscope revealed that the synaptic input to perikarya and proximal dendrites is sparse, thus distinguishing them from another large type of neuron, found in the ventral regions of the striatum, whose dendrites and perikarya are ensheathed in synaptic boutons. It is concluded that one of the three morphologically distinguishable classes of large neuron in the striatum is a cholinergic neuron.

In vivo release of [3H]GABA in cat caudate nucleus and substantia nigra. II. Involvement of different thalamic nuclei in the bilateral changes induced by a nigral application of muscimol

The contribution of motor and intralaminar thalamic nuclei to the changes of [3H]GABA release evoked in both caudate nuclei (CN) and both substantia nigra (SN) by a unilateral nigral application of muscimol (10(-6) M) was investigated on halothane-anaesthetized cats. Acute lesions were performed on one side of the thalamus at the level of either the ventralis medialis and ventralis lateralis (motor nuclei) or the centralis lateralis and paralamellar zone of the medialis dorsalis (intralaminar nuclei). The release of [3H]GABA neosynthesized from [3H]glutamine was measured by perfusing continuously a [3H]glutamine-enriched physiological medium through a push-pull cannula implanted in the 4 structures under investigation. After two hours of superfusion, muscimol (10(-6) M) was delivered for 60 min through the nigral push-pull cannula implanted ipsilaterally to the thalamic lesion. Evoked changes of [3H]GABA release were analyzed either in motor or intralaminar nuclei lesioned cats and compared to those observed in intact animals. Whatever the localization of the thalamic lesions was, an increased release of [3H]GABA was elicited locally in the SN and distally in the ipsilateral CN as in intact animals, suggesting that the responses induced ipsilaterally did not require nigro-thalamic pathways. On the contrary, in the contralateral CN changes of [3H]GABA release evoked by the nigral muscimol application were reversed by both types of thalamic lesion. Instead of a decreased release of [3H]GABA observed in intact cats, an increased release of [3H]GABA was detected in lesioned animals. In the contralateral SN, the response was reversed only after the intralaminar nuclei lesion. In this situation nigral muscimol application induced a decreased release of [3H]GABA in contrast to the enhanced release observed in intact and motor thalamic lesioned cats. The parallel increased release of [3H]GABA observed in the contralateral CN and SN in motor thalamic nuclei lesioned cats suggests an activation of the striatonigral cells by the nigral muscimol treatment. The asymmetrical changes of [3H]GABA release measured in the contralateral CN and SN in intact and intralaminar nuclei lesioned cats could indicate a presynaptic modulation of the [3H]GABA release acting either at the CN or the SN levels. The possible pathways involved in the interhemispheric transfer of information originating from one SN to the contralateral basal ganglia components are also discussed.

Efferent connections of the caudate nucleus, including cortical projections of the striatum and other basal ganglia: an autoradiographic and horseradish peroxidase investigation in the cat

Tritiated tracer was injected into the head of the caudate nucleus in cats. Following such injections, labeling is present within extensive regions of both the globus pallidus and entopeduncular nucleus, where it presents a mottled or meshlike appearance. These projections are topographically organized in that there is simple correspondence between the mediolateral, dorsoventral, and rostrocaudal origin of the caudate projection and its input to the globus pallidus and entopeduncular nucleus. Transported tracer is also present within the substantia nigra, where it is most abundant within the pars reticularis. However, distinct labeling also overlies cells of the pars compacta, and lesser amounts of labeling are present within the pars lateralis and within the retrorubral area. Following injections of horseradish peroxidase into the caudate nucleus, and subsequent tissue processing by the tetramethylbenzidine (TMB) method of Mesulam ('78), labeled anterograde fibers are present in abundance within the globus pallidus, entopeduncular nucleus, and all subdivisions of the substantia nigra, thus confirming the autoradiographic findings. Also, it is especially obvious in this HRP material that, contrary to previous degeneration studies, both the rostromedial and caudolateral parts of the pars lateralis of the substantia nigra contain numerous anterogradely labeled fibers. Retrogradely labeled neurons are also present within the substantia nigra of these same tissue sections, where they are most abundant within the pars compacta, but lesser numbers of labeled neurons are also present within the pars reticularis, pars lateralis, retrorubral area, and ventral tegmental area on the ipsilateral side, and all of these same subdivisions of the substantia nigra on the contralateral side. Also, within the subthalamic nucleus in these experiments, there are anterogradely labeled fibers, as well as retrogradely labeled neurons, which are interpreted to represent a reciprocal connection between the subthalamic nucleus and the striatum. In a separate series of experiments, horseradish peroxidase was injected into the motor cortex-specifically into the anterior sigmoidal gyrus. Following such injections, labeled neurons representing afferents to the motor cortex are found in all subcortical nuclei commonly known as the "basal ganglia," including the caudate nucleus, putamen, globus pallidus, entopeduncular nucleus, substantia innominata, nucleus of the diagonal band of Broca, medial septal nucleus, claustrum, and basolateral amygdaloid nucleus.

Acute changes in nigral substance P content induced by drugs acting on dopamine, muscarine and GABA receptors

Effects of acutely administered drugs acting on dopamine, muscarine or GABA receptors on the substance P content in rat substantia nigra were examined. Systemic injection of apomorphine caused a significant reduction in the nigral substance P content. This effect was found to be partially inhibited by atropine pretreatment. Haloperidol completely abolished the effect of apomorphine, while sulpiride did not. When administered alone, haloperidol, sulpiride or atropine had no effect on the nigral substance P content. Oxotremorine, the muscarine receptor agonist, reduced substance P content in th rostral half of the substantia nigra. Reduction in the nigral substance P content was also induced by treatment with the GABA receptor antagonist picrotoxin. On the other hand, diazepam increased the substance P content. These results suggest that the striatonigral substance P neurons could be regulated by dopaminergic, cholinergic and GABAergic systems, and that the dopaminergic influence on the substantia P neurons may be mediated, at least in part, by the cholinergic system.