Subpopulations Of Striatal Neurons Research Articles

The Gsh2 homeodomain gene controls multiple aspects of telencephalic development.

Homeobox genes have recently been demonstrated to be important for the proper patterning of the mammalian telencephalon. One of these genes is Gsh2, whose expression in the forebrain is restricted to the ventral domain. In this study, we demonstrate that Gsh2 is a downstream target of sonic hedgehog and that lack of Gsh2 results in profound defects in telencephalic development. Gsh2 mutants have a significant decrease in the expression of numerous genes that mark early development of the lateral ganglionic eminence, the striatal anlage. Accompanying this early loss of patterning genes is an initial expansion of dorsal telencephalic markers across the cortical-striatal boundary into the lateral ganglionic eminence. Interestingly, as development proceeds, there is compensation for this early loss of markers that is coincident with a molecular re-establishment of the cortical-striatal boundary. Despite this compensation, there is a defect in the development of distinct subpopulations of striatal neurons. Moreover, while our analysis suggests that the migration of the ventrally derived interneurons to the developing cerebral cortex is not significantly affected in Gsh2 mutants, there is a distinct delay in the appearance of GABAergic interneurons in the olfactory bulb. Taken together, our data support a model in which Gsh2, in response to sonic hedgehog signaling, plays a crucial role in multiple aspects of telencephalic development.

Interaction of acamprosate with ethanol and spermine on NMDA receptors in primary cultured neurons

The N-methyl- d-aspartate (NMDA) receptor has been implicated as a putative sight of action for acamprosate, a novel drug that reduces craving for alcohol. The purpose of this study was to assess the effect of acamprosate on the function of native NMDA receptors expressed in primary cultured striatal and cerebellar granule cells, as well as ethanol inhibition and spermine modulation of these receptors, using whole-cell patch-clamp electrophysiological techniques. Under all circumstances, acamprosate (0.1–300 μM) did not alter NMDA- or glutamate-induced currents. Acamprosate did not alter the inhibitory effects of ethanol (10–100 mM) on receptor function. In a subpopulation of striatal neurons, acamprosate did reverse the potentiating effects of spermine. These findings indicate that although acamprosate may modify polyamine modulation of the NMDA receptor, acamprosate alone does not alter receptor function nor does it modify ethanol inhibition of this receptor expressed in primary cultured striatal and cerebellar granule neurons.

Pharmacological mechanisms mediating phencyclidine-induced apoptosis of striatopallidal neurons: the roles of glutamate, dopamine, acetylcholine and corticosteroids

Phencyclidine (PCP) has recently been shown to induce apoptosis of a subpopulation of striatopallidal neurons which lie in the dorsomedial caudate–putamen. The pharmacological mechanisms underlying this PCP-induced striatal death were investigated in a series of small experiments. Striatal silver-methenamine-stained sections from rats injected acutely with dizocilpine (MK-801; 1.5–5 mg/kg, i.p.) were analysed to determine whether other non-competitive N-methyl- d-aspartate (NMDA) receptor antagonists could induce apoptotic-like changes in striatal cells. The effects of amphetamine (3–12 mg/kg, i.p.) were similarly investigated as PCP can elevate extracellular dopamine levels and dopamine has the potential to be neurotoxic. The potential involvement of dopamine transmission in PCP-induced striatal apoptosis was also tested by determining the effect of co-administering SCH23390 (D1 dopamine receptor antagonist) and quinpirole (D2 dopamine receptor agonist) on PCP (80 mg/kg, s.c.)-induced striatal apoptotic-like cell death. Equivalent experiments were performed using scopolamine (cholinergic antagonist) as this drug blocks PCP-induced damage of the retrosplenial cortex and RU38486 (corticosteroid receptor antagonist) as a similar subpopulation of striatal neurons undergoes apoptosis following dexamethasone administration. Injection of neither MK-801 nor amphetamine induced elevations of apoptotic-like cells in the striatum nor did co-administration of SCH23390 or scopolamine affect the levels of PCP-induced striatal cell death. In contrast, quinpirole elevated the levels of PCP-induced apoptotic-like striatal cell death and RU38486 markedly reduced it. Within the retrosplenial cortex, scopolamine lowered PCP-induced apoptotic-like cell death whereas RU38486 was without effect. These results suggest that PCP-induced striatal apoptosis results from a corticosteroid-dependent mechanism. The results further demonstrate that different pathological mechanisms underlie PCP-induced neuronal damage in the striatum and the retrosplenial cortex.

Involvement of basal ganglia and orbitofrontal cortex in goal-directed behavior

An impressive array of neural processing appears to be dedicated to the extraction of reward-related information from environmental stimuli and use of this information in the generation of goal-directed behaviors. While other structures are certainly involved in these processes, the characteristics of activations seen in mesencephalic dopamine neurons, striatal neurons and neurons of the orbitofrontal cortex provide distinct examples of the different ways in which reward-related information is processed. In addition, the differences in activations seen in these three regions demonstrate the different roles they may play in goal-directed behavior. A principal role played by dopamine neurons is that of a detector of an error in reward prediction. The homogeneity of responsiveness across the population of dopamine neurons indicates that this error signal is widely broadcast to dopamine terminal regions where it could provide a teaching signal for synaptic modifications underlying the learning of goal-directed appetitive behaviors. The responses of these same neurons to conditioned stimuli associated with reward could also serve as a signal of prediction error useful for the learning of sequences of environmental stimuli leading to reward. Dopamine neuron responses to both rewards and conditioned stimuli are not contingent on the behavior executed to obtain the reward and thus appear to reflect a relatively pure signal of a reward prediction error. It is not yet clear whether these activations, and responses to novel stimuli, have an additional function in engaging neural systems involved in the representation and execution of goal-directed behaviors. This representation of goal-directed behaviors may involve the striatal regions studied, where processing of reward-related information appears to be much more heterogeneous. Different subpopulations of striatal neurons are activated at different stages in the course of goal-directed behaviors, with largely separate populations activated following presentation of conditioned stimuli, preceding reinforcers, and following reinforcers. Neurons exhibiting each of these types of activation appear to differentiate between rewarding and non-rewarding outcomes of behavioral acts and, as a population, appear to be biased towards processing reward vs. non-reward. These activations observed in the striatum were often contingent on the behavioral act associated with obtaining reward, reflecting an integration of information not observed in dopamine neurons. Another difference between reward processing in striatal neurons and dopamine neurons is the influence of predictability on neuronal responsiveness. Unlike dopamine neurons, many striatal neurons respond to predicted rewards, although at least some may reflect the relative degree of predictability in the magnitude of the responses to reward. Thus, striatal processing of reward-related information is in some ways more complex than that observed in dopamine neurons, incorporating information on behavior and potentially providing more detailed information regarding predictability. These activations could serve as a component of the neural representation of the goal, and/or the behavioral aspects of goal-directed behaviors. As such they would be of use for the execution of appropriate goal-directed behaviors in response to known environmental stimuli, as well as for generating behaviors in response to novel stimuli that may be associated with desirable goals. Neuronal activations in the orbitofrontal cortex appear to involve less integration of behavioral and reward-related information, but rather incorporate another aspect of reward, the relative motivational significance of different rewards. These activations would serve a function similar to those striatal neurons that encode exclusively reward-related information in situations in which only a single outcome is obtainable. (ABSTRACT TRUNCATED)

Intranuclear inclusions in subtypes of striatal neurons in Huntingtonʼs disease transgenic mice

R6/2 transgenic mice express exon 1 of an abnormal human Huntington's disease (HD) gene and develop a neurological phenotype similar to HD. These mice develop ubiquitinated neuronal intranuclear inclusions (NII) which might play a central role in the pathophysiology of HD. We studied the distribution of NII in subpopulations of striatal neurons in 12-week-old R6/2 transgenic mice using fluorescent double label immunohistochemistry. We observed that most of the Calbindin-D28K positive projection neurons (89%) and the Parvalbumin positive interneurons (86%) showed ubiquitinated NII. In interneurons, however, which contain either choline acetyltransferase, neuronal nitric oxide synthase, or Calretinin, the frequency of NII was much lower (22%, 8%, 9%, respectively). Our data suggest that subpopulations of striatal neurons differ remarkably in their capability of forming ubiquitinated NII. Interneurons which are known to resist neurodegeneration in HD show less NII.

Gene expression of the GAD67 and GAD65 isoforms of glutamate decarboxylase is differentially altered in subpopulations of striatal neurons in adult rats lesioned with 6-OHDA as neonates.

The levels of mRNAs encoding for the two isoforms of glutamate decarboxylase, GAD65 and GAD67, were measured in subpopulations of striatal neurons in adult rats depleted of dopamine as neonates with 6-OHDA and chronically injected with vehicle or with the dopamine receptor agonists apomorphine or SKF-38393. In adult rats depleted of dopamine as neonates, an increase of GAD65 and GAD67 mRNA levels was measured in the striatum. These changes were paralleled by an increase in preproenkephalin (PPE) and a decrease in preprodynorphin (PPD) mRNA levels. Quantitative analysis at the cellular level indicated that GAD67 mRNA levels were increased in PPE-labeled neurons, whereas GAD65 mRNA levels were increased in PPE-unlabeled neurons. Chronic and systemic injections of apomorphine or SKF-38393 induced further increases in striatal GAD65 and GAD67 mRNA levels. These increases were only detected in the subpopulation of PPE-unlabeled neurons and were paralleled by an increase in PPD mRNA levels. The increases in GAD67, GAD65, and PPD mRNA levels induced by SKF-38393 were abolished by the administration of the D1 receptor antagonist SCH-23390. The present results provide further evidence that GAD67 and GAD65 gene expression is differentially regulated in the two subpopulations of efferent striatal neurons. They also suggest that neonatal depletions in dopamine levels induce alterations of GABA-mediated signaling in the two subpopulations of striatal efferent neurons. We speculate that these alterations are involved in the behavioral particularities exhibited by rats depleted of dopamine as neonates.

Gene expression of the GAD67 and GAD65 isoforms of glutamate decarboxylase is differentially altered in subpopulations of striatal neurons in adult rats lesioned with 6‐OHDA as neonates

Gene expression of the GAD67 and GAD65 isoforms of glutamate decarboxylase is differentially altered in subpopulations of striatal neurons in adult rats lesioned with 6‐OHDA as neonates

Subpopulations of neurons in the rat neostriatum display GABA BR1 receptor immunoreactivity

Immunoreactivity for gamma aminobutyric acid BR1 receptor (GABA BR1) was detected in the neuropilar elements as well as in the perikarya of neurons in the neostriatum. Many of the GABA BR1-immunoreactive perikarya were medium-sized with a thin rim of cytoplasm. They resembled the morphology of medium spiny neurons, the projection neurons of the neostriatum. In addition, some GABA BR1-immunoreactive neurons were densely labeled and were of medium to large in size. These neurons were characterized by double immunofluorescence using their neurochemicals as markers. Over 90% of the parvalbumin- and choline acetyltransferase-immunoreactive neurons and about 80% of the nitric oxide synthase-immunoreactive neurons displayed GABA BR1 immunoreactivity. The present results show for the first time that the major four subpopulations of striatal neurons express GABA BR1 receptor and may have a functional implication in the GABA neurotransmission in the microcircuitry of the neostriatum.

Phencyclidine induces D-1 dopamine receptor mediated Fos-like immunoreactivity in discretely localised populations of striatopallidal and striatoentopeduncular neurons in the rat

Phencyclidine (PCP), a non-competitive antagonist of the NMDA subtype of glutamate receptor, which also acts as an indirect dopamine agonist and at sigma sites, can induce a long lasting psychotic state when taken acutely. It is well established that PCP is toxic to specific limbic structures and we have recently demonstrated that it induces apoptosis of a subpopulation of striatal neurons. These neurons lie predominantly in the dorsomedial striatum and project to the globus pallidus. The mechanisms mediating this neuronal death are unclear though manipulations of dopamine transmission can induce striatal c- fos expression and continuous c- fos expression has been implicated in the molecular cascades controlling apoptosis. We accordingly undertook a series of experiments to determine the action of PCP on striatal Fos-like immunoreactivity (FLI). PCP (80 mg/kg, s.c.) elicited FLI in three distinct striatal areas, namely dorsomedial, dorsolateral and the nucleus accumbens. The level of PCP-induced FLI was consistently attenuated by the co-administration of the D-1 antagonist, SCH 23390. Vehicle injections also induced modest levels of FLI in the dorsomedial striatum and the nucleus accumbens which again were attenuated by SCH 23390. The type of striatal neuron in which PCP-induced FLI was determined by the use of a retrograde anatomical tracer. A colloidal gold tracer was thus injected into the major areas of termination of striatal projection neurons prior to the administration of PCP. This procedure demonstrated that the majority of the FLI positive striatal cells were striatopallidal neurons, though some FLI positive striatoentopeduncular neurons were also seen. The potential pharmacological mechanisms underlying the results are discussed. It is argued that the complex pattern of PCP-induced striatal FLI might be accounted for by a differential action upon extracellular dopamine levels whereby they are elevated in some striatal areas and simultaneously reduced in others.

Distinct and interactive effects of d-amphetamine and haloperidol on levels of neurotensin and its mRNA in subterritories in the dorsal and ventral striatum of the rat.

Striatal tissue concentrations of neurotensin, expression of neurotensin/neuromedin N (NT/N) mRNA, and numbers of neurotensin-immunoreactive neurons are increased by d-amphetamine (amph), which stimulates dopamine release in the striatum, and haloperidol (hal), a dopamine receptor antagonist with high affinity for D2-like receptors. The possibility that the effects of these drugs involve distinct subpopulations of striatal neurons was addressed in this study, in which the relative numbers and distributions of striatal neuron profiles containing neurotensin immunoreactivity and/or NT/N mRNA were compared following administrations of hal, amph, hal and amph co-administered, and vehicle. Fourteen striatal subterritories in caudate-putamen, nucleus accumbens, and olfactory tubercle were evaluated. Amph produced increases in the expression of neurotensin preferentially in the ventromedial and caudodorsal subterritories of the caudate-putamen, the rostrobasal cell cluster and lateral shell of the nucleus accumbens, and the olfactory tubercle. Haloperidol produced increased neurotensin expression in much of dorsal and ventral striatum, most prominently in the rostral, dorsomedial and ventrolateral quadrants of the caudate-putamen, and in the rostrobasal cell cluster, rostral pole, medial and lateral shell of the nucleus accumbens and the olfactory tubercle. The numbers of neurons responding to amph and hal in all subterritories following co-administration of the two drugs were significantly less than the summed numbers responding individually to amph and hal. Furthermore, in the subterritories where immunohistochemically detectable responses elicited by amph exceeded those produced by hal, co-administration of the two drugs resulted in responses comparable to those elicited by hal given alone. It is suggested that some of the reported anti-dopaminergic behavioral effects of basal ganglia neurotensin may be attenuated in conditions of reduced dopamine neurotransmission.

C- fos gene expression is induced in a subpopulation of striatal neurons following a single administration of a dopamine D1-receptor agonist in adult rats lesioned with 6-OHDA as neonates

The effects of the dopamine D1 receptor agonist, SKF-38393, on the levels of mRNAs encoding for the proto-oncogene c- fos and the GABA-synthesizing enzyme glutamate decarboxylase (GAD65) were measured by in situ hybridization histochemistry in the striatum of adult rats depleted of dopamine as neonates. c- fos mRNA levels exhibited a prominent increase following the acute systemic administration of SKF-38393 in dopamine-depleted but not in normal rats. Double-labeling in situ hybridization histochemistry using a radioactive c- fos probe and a digoxigenin-labeled preproenkephalin (PPE) cRNA probe indicated that c- fos mRNA levels were increased by SKF-38393 exclusively in a subpopulation of PPE-unlabeled neurons. Dopamine-depleted rats exhibited an increase in GAD65 mRNA levels relative to control rats. Acute administration of SKF-38393 did not alter GAD65 mRNA levels in control or in dopamine-depleted rats. Our results demonstrate that an acute administration of a D1-receptor agonist induces c- fos but not GAD65 gene expression in a subpopulation of presumed striato-nigral/entopeduncular neurons. They also suggest that the D1-dependent behavioral plasticity exhibited by adult rats depleted of dopamine as neonates is not the result of an altered activation of the two subpopulations of striatal efferent neurons.

Phencyclidine and corticosteroids induce apoptosis of a subpopulation of striatal neurons: A neural substrate for psychosis?

Phencyclidine, a non-competitive N-methyl- d-aspartate receptor antagonist and indirect dopamine agonist, has neuroprotective properties. Phencyclidine, however, can also exert toxic effects and causes degeneration of neurons in the retrosplenial cortex. In this paper we demonstrate that acute administration of a high dose of phencyclidine to rats, (80 mg/kg), also causes death of a subpopulation of striatal neurons. The dying cells exhibited many of the morphological and biochemical features of cells undergoing apoptosis as revealed by a silver methenamine stain, propidium iodide fluorescence histochemistry and a TUNEL procedure. The majority of the dying cells tended to be clustered within the dorsomedial aspect of the striatum. The type of striatal cell undergoing apoptosis was determined by stereotaxically injecting a colloidal gold retrograde anatomical tracer into the major areas of striatal termination prior to the administration of phencyclidine. This procedure demonstrated that phencyclidine induced striatal apoptosis is almost exclusively limited to striatopallidal neurons. A similar series of experiments was conducted to determine whether the synthetic corticosteroid, dexamethasone, also induces apoptosis of striatal neurons. Corticosteroids are known to be toxic to hippocampal neurons and interact with striatal dopamine transmission. Acute administration of dexamethasone, (20 mg/kg), induced apoptosis of a subpopulation of striatal cells. As was the case with phencyclidine, most of the dexamethasone-induced apoptotic striatal cells were striatopallidal neurons located within the dorsomedial striatum. The pathology during the early stages of Huntington's disease is restricted to an equivalent subpopulation of striatal neurons. Many Huntington's patients are extremely psychotic during this stage in the progression of the disease. Psychosis is also associated with the acute administration of both phencyclidine and dexamethasone to humans. We accordingly speculate that the selective loss of striatopallidal neurons in the dorsomedial striatum may represent the neural substrate of many forms of psychosis.

Morphologically distinct subpopulations of neurotensin-immunoreactive striatal neurons observed in rat following dopamine depletions and D 2 receptor blockade project to the globus pallidus

It has been reported in previous studies that perikaryal neurotensin immunoreactivity is largely absent in the rat striatum except following striatal dopamine depletion or blockade of dopamine D 2 receptors, after which, however, neurotensin immunoreactivity is elicited in at least two distinct subpopulations of striatal neurons [Zahm D. S. (1992) Neuroscience 46, 335–350]. One subpopulation of such cells (type I), prominent following D 2 receptor blockade, is located mainly in the matrix compartment in the rostral, dorsomedial and ventrolateral parts of the striatum, and comprises neurons at the large end of the medium-sized spectrum that exhibit intense neurotensin immunoreactivity in perikarya and proximal dendrites, but rarely display Fos immunoreactivity [Senger B. et al. (1993) Neuroscience 57, 649–660]. A second subpopulation (type II) resides predominantly in the patch (striosome) and matrix compartments in the dorsolateral quadrant of the striatum, and is prominent following administration of reserpine. These neurons are at the small end of the medium size range and exhibit very light neurotensin immunoreactivity, with little staining of dendrites. Fos immunoreactivity is frequently co-localized in striatal neurons that exhibit a type II striatal neurotensin response [Brog J. S. and Zahm D. S. (1995) Neuroscience 65, 71–86]. In the current study, neurotensin immunoreactivity was elicited in striatal neurons by ventral mesencephalic 6-hydroxydopamine lesions or administration of reserpine or haloperidol. Irrespective of which drug was given, retrogradely transported Fluoro-Gold was prominently co-localized with neurotensin-like immunofluorescence in the perikarya of striatal neurons following injections of the retrograde tracer into the globus pallidus. Few double-labeled neurons were observed following administration of any of these drugs and injections of Fluoro-Gold into the substantia nigra. It is concluded that two supopulations of neurotensin-immunoreactive striatal neurons project predominantly to the globus pallidus and minimally to the substantia nigra.

Intrastriatal implants of polymer encapsulated cells genetically modified to secrete human nerve growth factor: Trophic effects upon cholinergic and noncholinergic striatal neurons

Nerve growth factor selectively prevents the degeneration of cholinergic neurons following intrastriatal infusion but rescues both cholinergic and noncholinergic striatal neurons if the nerve growth factor is secreted from grafts of genetically modified fibroblasts. The present study evaluated whether grafted fibroblasts genetically modified to secrete human nerve growth factor could provide trophic influences upon intact cholinergic and noncholinergic striatal neurons. Unilateral striatal grafts of polymer-encapsulated cells genetically modified to secrete human nerve growth factor induced hypertrophy and significantly increased the optical density of choline acetyltransferase-immunoreactive striatal neurons one, two, and four weeks post-transplantation relative to rats receiving identical grafts missing only the human nerve growth factor construct. Nerve growth factor secreting grafts also induced a hypertrophy of noncholinergic neuropeptide Y-immunoreactive striatal neurons one, two, and four weeks post-transplantation. Glutamic acid decarboxylase-immunoreactive neurons were unaffected by the human nerve growth factors secreting grafts. The effects upon choline acetyltransferase-immunoreactive and neuropeptide Y-immunoreactive striatal neurons dissipated following retrieval of the implants. Immunocytochemistry for nerve growth factor revealed intense graft-derived immunoreactivity for up to 1000 microns from the capsule extending along the dorsoventral axis of the striatum. Nerve growth factor-immunoreactivity was also observed within a subpopulation of striatal neurons and may represent nerve growth factor consumer neurons which retrogradely transported graft-derived nerve growth factor. When explanted, grafts produced 2-4 ng human nerve growth factor/24 h over the time course of this study indicating that this level of continuous human nerve growth factor secretion was sufficient to mediate the effects presently observed.

NADPH Diaphorase-Containing Striatal or Cortical Neurons Are Resistant to Apoptosis

The small subpopulation of striatal neurons containing nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d, recently identified as nitric oxide synthase, NOS) is selectively spared in Huntington's disease. Previous search for pathogenic mechanisms capable of destroying striatal neurons but sparing NADPH-d(+) cells has identified only NMDA receptor-mediated excitotoxicity. In view of suggestions that neuronal death in Huntington's disease may occur by apoptosis, we examined the vulnerability of NADPH-d(+) neurons to apoptosis. Murine striatal or cortical cultures exposed to serum deprivation developed extensive neuronal apoptosis, but NADPH-d(+) neurons were relatively spared. This sparing was seen when cultures were exposed to several other apoptosis-inducing insults. It was not seen after toxic exposure to H2O2, and it was not blocked by NOS inhibition. The selective resistance of NADPH-d(+) neurons to several forms of apoptosis provides key support for the possibility that apoptosis may contribute to the pathogenesis of Huntington's disease.

Morphology and Fos immunoreactivity reveal two subpopulations of striatal neurotensin neurons following acute 6-hydroxydopamine lesions and reserpine administration

It was previously reported that following striatal dopamine depletion or pharmacological blockade of dopamine neurotransmission, neurotensin immunoreactivity is elicited in at least two distinct subpopulations of striatal neurons (Neuroscience Vol. 46, pp. 335-350, 1992). Recently it was shown that Fos immunoreactivity, interpreted as an indicator of enhanced neuronal activity, is appreciably co-localized in only one of the subpopulations of neurotensin-immunoreactive neurons observed following blockade of the dopamine D2 receptor (Neuroscience Vol. 57, pp. 649-660, 1993). In the present study, similar methods were used to determine the degree of co-localization of Fos and neurotensin immunoreactivity in striatal neurons in response to the dopamine-depleting effects of 6-hydroxydopamine lesions and reserpine administration. It was observed that following these treatments, a subpopulation of neurons at the small end of the medium size range exhibited light neurotensin immunoreactivity and frequent co-localization with Fos immunoreactivity. This population was predominant after reserpine administration in the dorsolateral quadrant of the striatum. Another subpopulation comprised larger neurons that exhibited intense neurotensin immunoreactivity in perikarya and proximal processes that was rarely co-localized with Fos immunoreactivity. This type of neuron was observed following all the drug treatments but was present almost to the exclusion of the smaller type of cells three days following ventral midbrain 6-hydroxydopamine lesions, being mainly located in the dorsomedial and ventrolateral portions of the striatum. The present data support the results of the preceding studies in being consistent with the existence of two subpopulations of striatal neurons that accumulate neurotensin following dopamine depletion. The possibility is considered that one subpopulation accumulates neurotensin in response to co-ordinate increases in neuronal activity and neurotensin synthesis, and the other as a result of decreased release.

Localization of ampa-selective excitatory amino acid receptor subunits in identified populations of striatal neurons

Two-color immunofluorescence histochemistry and immunohistochemistry in combination with retrograde tract-tracing techniques were used to examine the relationship of α-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA)-selective glutamate receptor subunits (GluR1, GluR2/3/4c and GluR4) to identified populations of striatal projection neurons and interneurons. The majority of striatonigral and striatopallidal neurons were double-labeled for GluR2/3/4c. These findings were confirmed using calbindin to label matrix projection neurons. In contrast, immunostaining of the GluR1 subunit was not observed to co-localize with any striatal projection neurons. Striatal interneurons immunostained for parvalbumin were also labeled by antibodies directed against the GluRl subunit. Approximately 50% of parvalbumin neurons also contained GluR2/3/4c. Somatostatin immunoreactivity did not co-localize with either the GluR1 or GluR2/3/4c subunits. GluR4-immunoreactive neurons were not observed in striatum. This study demonstrates that AMPA-selective glutamate receptors are differentially localized on subpopulations of striatal neurons and interneurons. These findings suggest that discrete striatal neuron populations may express different AMPA receptor subunit combinations which may account for their functional specificity.

Postnatal Rat NADPH-Diaphorase-Containing Myenteric Neurons Extend Processes When Transplanted into Adult Rat Corpus Striatum

Pieces of isolated myenteric plexus, freshly dissected from the colon of young inbred Fischer rats, were implanted unilaterally into the corpus striatum of adult Fischer rats which had received a prior quinolinic acid lesion. Similar implants were made into the unlesioned striatum of a second group of Fischer rats. The survival of a subpopulation of grafted neurons, and the incidence of fiber outgrowth from these neurons into the host striatum, was examined after 3 and 6 weeks using a histochemical technique for the demonstration of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) activity. This enzyme is found both in some enteric neurons and a subpopulation of striatal neurons. Grafted enteric neurons expressing NADPH-diaphorase were easily distinguished in both the lesioned and unlesioned host striata at 3 and 6 weeks postimplantation. Fibers could be found extending from NADPH-diaphorase-containing enteric neurons into both the lesioned and unlesioned corpus striatum, although fewer graft-derived fibers were seen in the unlesioned striatum. This is the first demonstration that enteric neurons transplanted into the adult mammalian brain are capable of extending processes into the surrounding CNS tissue.

Repeated NMDA receptor activation induces distinct intracellular calcium changes in subpopulations of striatal neurons in vitro

The mechanisms underlying long-term calcium changes evoked by excitatory amino acids have not been previously examined in striatal neurons. Fura-2 fluorescence measurements were used to examine intracellular calcium concentration ([Ca 2+] i) changes due to repeated N-methyl- D-aspartate (NMDA) receptor activation, in primary cultures of murine striatal neurons. Three applications of 200 μM NMDA (for 2 min, each application separated by 7 min), in 0 magnesium-containing artificial cerebral spinal fluid, elicited three distinct responses. In 50 ± 8% of the NMDA-responsive neurons, no persistent increases in [Ca 2+] i (final[Ca 2+] i ≦ 150%baseline) were observed, while in 33 ± 7%and17 ± 3% of the cells, sustained (peak response > final [Ca 2+] i > 150% baseline) and uncontrolled increases (final[Ca 2+] i ≧peak response) were observed, respectively. NMDA-responsive neurons that were intensely immunoreactive for the calcium binding protein calbindin-D 28k never exhibited uncontrolled increases in [Ca 2+] i. Removal of extracellular Ca 2+ significantly attenuated sustained, but not uncontrolled, increases in [Ca 2+] i; sustained increases in some neurons were also attenuated by application of verapamil (100 μM) or MK-801 (1 μM). Pre-treatment of striatal neurons with the protein kinase C blocker sphingosine (20 μM), virtually eliminated the development of sustained or uncontrolled increases in [Ca 2+] i. These findings suggest that specific intracellular mechanisms regulate the distinct [Ca 2+] i responses of subpopulations of striatal neurons to repeated NMDA receptor activation.

Dopa resistance in multiple‐system atrophy: Loss of postsynaptic D2 receptors

Postmortem autoradiography was used to explore the mechanisms underlying L-dopa resistance in 2 patients with multiple-system atrophy. Indices of striatal presynaptic dopamine terminal loss and dopamine (D1 and D2) receptors were provided by 3H-mazindol, 3H-SCH 23390, and 125I-sulpiride binding. Neuronal loss, gliosis, and loss of postsynaptic D2 receptors preferentially involved the middle and posterior of the putamen, that region of the striatum most intimately involved in motor function. Loss of D1 receptors in the same area occurred in only 1 patient. These findings suggest that in multiple-system atrophy, resistance to L-dopa is due to a loss of putamental D2 receptors. The differential effects on D1 and D2 receptors in 1 patient implies that different subpopulations of striatal neurons were selectively involved.