Regional distribution of DARPP-32 (dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein of Mr = 32,000) mRNA in mouse brain

PLPP/CIN-mediated DARPP-32 serine 97 dephosphorylation delays the seizure onset in response to kainic acid in the mouse hippocampus

Dopamine and cAMP-regulated phosphoprotein, 32 kDa (DARPP-32)-mediated protein phosphatase 1 (PP1) inhibition leads to the increase in phosphorylation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor (AMPAR), which potentiates channel activity and current and thereby may facilitate seizure activity. In the present study, we found that pyridoxal-5'-phosphate phosphatase/chronophin (PLPP/CIN) transiently dephosphorylated DARPP-32 serine (S) 97 site in the early time window, and casein kinase 2 (CK2) subsequently phosphorylated this site in the later time points after kainic acid (KA) injection, which increased the latency of seizure onset in response to KA, but exacerbated the intensity (severity), duration and progression of seizures. TMCB (a CK2 inhibitor) delayed the seizure onset in response to KA, concomitant with the reduced DARPP-32 S97 phosphorylation. Therefore, our findings suggest that PLPP/CIN may play an important role in the latency of seizure onset via DARPP-32-PP1-AMPAR signaling pathway, and may be one of the potential therapeutic targets for medication of seizure or epilepsy.

Immunohistochemical Localization of DARPP-32 in the Brain of Two Lungfishes: Further Assessment of Its Relationship with the Dopaminergic System

The distribution of DARPP-32 (a phosphoprotein related to the dopamine D1 receptor) has been widely used as a means to clarify the brain regions with dopaminoceptive cells, primarily in representative species of tetrapods. The relationship between dopaminergic and dopaminoceptive elements is frequently analyzed using the catecholamine marker tyrosine hydroxylase (TH). In the present study, by means of combined immunohistochemistry, we have analyzed these relationships in lungfishes, the only group of sarcopterygian fishes represented by 6 extant species that are the phylogenetically closest living relatives of tetrapods. We used the Australian lungfish Neoceratodus forsteri and the African lungfish Protopterus dolloi. The DARPP-32 antibody yields a distinct and consistent pattern of neuronal staining in brain areas that, in general, coincide with areas that are densely innervated by TH-immunoreactive fibers. The striatum, thalamus, optic tectum, and torus semicircularis contain intensely DARPP-32-immunoreactive cell bodies and fibers. Cells are also located in the olfactory bulbs, amygdaloid complex, lateral septum, pallidum, preoptic area, suprachiasmatic nucleus, tuberal hypothalamic region, rostral rhombencephalic reticular formation, superior raphe nucleus, octavolateral area, solitary tract nucleus, and spinal cord. Remarkably, DARPP-32-immunoreactive fibers originating in the striatum reach the region of the dopaminergic cells in the mesencephalic tegmentum and represent a well-established striatonigral pathway in lungfishes. Double immunolabeling reveals that DARPP-32 is present in neurons that most likely receive TH input, but it is absent from the catecholaminergic neurons themselves, with the only exception of a few cells in the suprachiasmatic nucleus of Neoceratodus and the solitary tract nucleus of Protopterus. In addition, some species differences exist in the localization of DARPP-32 cells in the pallium, lateral amygdala, thalamus, prethalamus, and octavolateral area. In general, the present study demonstrates that the distribution pattern of DARPP-32, and its relationship with TH, is largely comparable to those reported for tetrapods, highlighting a shared situation among all sarcopterygians.

Motor Skill Learning Is Associated with Phase-Dependent Modifications in the Striatal cAMP/PKA/DARPP-32 Signaling Pathway in Rodents

Abundant evidence points to a key role of dopamine in motor skill learning, although the underlying cellular and molecular mechanisms are still poorly understood. Here, we used a skilled-reaching paradigm to first examine changes in the expression of the plasticity-related gene Arc to map activity in cortico-striatal circuitry during different phases of motor skill learning in young animals. In the early phase, Arc mRNA was significantly induced in the medial prefrontal cortex (mPFC), cingulate cortex, primary motor cortex, and striatum. In the late phase, expression of Arc did not change in most regions, except in the mPFC and dorsal striatum. In the second series of experiments, we studied the learning-induced changes in the phosphorylation state of dopamine and cAMP-regulated phosphoprotein, 32k Da (DARPP-32). Western blot analysis of the phosphorylation state of DARPP-32 and its downstream target cAMP response element-binding protein (CREB) in the striatum revealed that the early, but not late, phase of motor skill learning was associated with increased levels of phospho-Thr34-DARPP-32 and phospho-Ser133-CREB. Finally, we used the DARPP-32 knock-in mice with a point mutation in the Thr34 regulatory site (i.e., protein kinase A site) to test the significance of this pathway in motor skill learning. In accordance with our hypothesis, inhibition of DARPP-32 activity at the Thr34 regulatory site strongly attenuated the motor learning rate and skilled reaching performance of mice. These findings suggest that the cAMP/PKA/DARPP-32 signaling pathway is critically involved in the acquisition of novel motor skills, and also demonstrate a dynamic shift in the contribution of cortico-striatal circuitry during different phases of motor skill learning.

Genetic variation in dopamine-related gene expression influences motor skill learning in mice

Several neurodevelopmental disorders with a strong genetic basis, including attention-deficit/hyperactivity disorder, autism spectrum disorders and developmental coordination disorder, involve deficits in fine motor skills. This phenotype may depend on heritable variation in components of the dopamine (DA) system, which is known to play a critical role in motor skill learning. In this study, we took advantage of two inbred strains of mice (BALB/c and C57BL/6) that differ markedly in the number of midbrain DA neurons in order to investigate the influence of such naturally occurring genetic variation on the acquisition and performance of fine motor skills. Gene expression analysis of midbrain, frontal cortex and striatum showed significant differences in the expression of presynaptic and postsynaptic dopaminergic (DAergic) markers (e.g. tyrosine hydroxylase, DA transporter, DA D4 receptor, DA D5 receptor and DARPP-32) between these two strains. BALB/c mice had lower learning rate and performance scores in a complex skilled reaching task when compared with C57BL/6 mice. A negative correlation was found between the motor learning rate and level of DARPP-32 mRNA expression in the frontal cortex contralateral to the trained forelimb. The rate of motor learning was also negatively correlated with the levels of DARPP-32 and DA D1 receptor mRNAs in the striatum. Our results suggest that genetically driven variation in frontostriatal DAergic neurotransmission is a major contributor to individual differences in motor skill learning. Moreover, these findings implicate the D1R/cAMP/DARPP-32 signaling pathway in those neurodevelopmental disorders that are associated with fine motor skill deficits.

Cell signaling underlying epileptic behavior

Epilepsy is a complex disease, characterized by the repeated occurrence of bursts of electrical activity (seizures) in specific brain areas. The behavioral outcome of seizure events strongly depends on the brain regions that are affected by overactivity. Here we review the intracellular signaling pathways involved in the generation of seizures in epileptogenic areas. Pathways activated by modulatory neurotransmitters (dopamine, norepinephrine, and serotonin), involving the activation of extracellular-regulated kinases and the induction of immediate early genes (IEGs) will be first discussed in relation to the occurrence of acute seizure events. Activation of IEGs has been proposed to lead to long-term molecular and behavioral responses induced by acute seizures. We also review deleterious consequences of seizure activity, focusing on the contribution of apoptosis-associated signaling pathways to the progression of the disease. A deep understanding of signaling pathways involved in both acute- and long-term responses to seizures continues to be crucial to unravel the origins of epileptic behaviors and ultimately identify novel therapeutic targets for the cure of epilepsy.

Effect of KEPI (Ppp1r14c) deletion on morphine analgesia and tolerance in mice of different genetic backgrounds: when a knockout is near a relevant quantitative trait locus

We previously identified KEPI as a morphine-regulated gene using subtractive hybridization and differential display PCR. Upon phosphorylation by protein kinase C, KEPI becomes a powerful inhibitor of protein phosphatase 1. To gain insights into KEPI functions, we created KEPI knockout (KO) mice on mixed 129S6xC57BL/6 genetic backgrounds. KEPI maps onto mouse chromosome 10 close to the locus that contains the mu-opioid receptor (Oprm1) and provides a major quantitative trait locus for morphine effects. Analysis of single nucleotide polymorphisms in and near the Oprm1 locus identified a doubly-recombinant mouse with C57BL/6 markers within 1 Mb on either side of the KEPI deletion. This strategy minimized the amount of 129S6 DNA surrounding the transgene and documented the C57BL/6 origin of the Oprm1 gene in this founder and its offspring. Recombinant KEPIKO mice displayed (a) normal analgesic responses and normal locomotion after initial morphine treatments, (b) accelerated development of tolerance to analgesic effects of morphine, (c) elevated activity of protein phosphatase 1 in thalamus, (d) attenuated morphine reward as assessed by conditioned place preference. These data support roles for KEPI action in adaptive responses to repeated administration of morphine that include analgesic tolerance and drug reward.

State-dependent modulation of amygdala inputs by dopamine-induced enhancement of sodium currents in layer V entorhinal cortex

Interaction between the entorhinal cortex (EC) and basolateral amygdala (BLA) may be a fundamental component in the consolidation of many forms of affective memory, such as inhibitory avoidance. Dopamine (DA) in the EC is necessary for, and may facilitate, this form of learning. This effect of DA on affective behaviors may be accomplished in part through modulation of amygdala inputs. Although it is known that DA can modulate neuronal activity in the EC, it is not known whether DA modulates inputs from the BLA. In this study, we used in vitro patch-clamp recordings and Ca2+ imaging of layer V neurons in the rat lateral EC to determine whether DA modulates the integration of inputs from the BLA and the mechanism for this modulation. We found that DA exerted actions that depended on the neuronal state. Near resting membrane potentials, DA suppressed integration of inputs, whereas at depolarized potentials, DA enhanced integration. DA enhanced the integration by a D2-mediated enhancement of Na+ currents, via phospholipase C. These experiments demonstrate that DA can exert actions in the EC that depend on the membrane voltage. This effect of DA may affect a wide range of inputs. Functionally, by enhancement of amygdala inputs that arrive in concert with other inputs, or during depolarized states, DA can facilitate the impact of affect on memory in a subset of conditions.

Novel genes differentially expressed in cortical regions during late neurogenesis

Differential gene expression across the embryonic cerebral cortex is assumed to play a role in the subdivision of the cortex into distinct areas with specific morphology, physiology and function. In a search for genes that may be involved in the cortical regionalization during late neurogenesis in mouse, we performed an extensive in-situ expression analysis at embryonic day (E)16 and E18. The examined candidate genes were selected beforehand by a microarray screen by virtue of their preferential expression in the anlagen of the motor, somatosensory, visual and cingulate cortices or hippocampus. We present new information about graded or regionally enriched expression of 25 genes (nine of which are novel genes) across the mouse embryonic cortex, in progenitor cells as well as in the cortical plate. The established differential expression of most of these genes is persistent at both stages studied, suggesting that their expression is regulated by an intrinsic programme. For some of the genes, the concept of intrinsic regulation is further substantiated by the high similarity of the reported expression patterns at E16 and E18 and published data from earlier stages. Few genes with robust expression in the E16 caudal cortex showed a more restricted pattern at E18, possibly because of their response to extrinsic cues. In addition, several genes appeared to be suitable novel markers for amygdalar and diencephalic nuclei. Taken together, our findings reveal novel molecular partitions of the late mouse cortex that are in accordance with the model of a leading role of intrinsic mechanisms in cortical arealization.

Phosphodiesterase 1B differentially modulates the effects of methamphetamine on locomotor activity and spatial learning through DARPP32-dependent pathways: evidence from PDE1B-DARPP32 double-knockout mice

Mice lacking phosphodiesterase 1B (PDE1B) exhibit an exaggerated locomotor response to D-methamphetamine and increased in vitro phosphorylation of DARPP32 (dopamine- and cAMP-regulated phosphoprotein, M r 32 kDa) at Thr34 in striatal brain slices treated with the D1 receptor agonist, SKF81297. These results indicated a possible regulatory role for PDE1B in pathways involving DARPP32. Here, we generated PDE1B x DARPP32 double-knockout (double-KO) mice to test the role of PDE1B in DARPP32-dependent pathways in vivo. Analysis of the response to d-methamphetamine on locomotor activity showed that the hyperactivity experienced by PDE1B mutant mice was blocked in PDE1B-/- x DARPP32-/- double-KO mice, consistent with participation of PDE1B and DARPP32 in the same pathway. Further behavioral testing in the elevated zero-maze revealed that DARPP32-/- mice showed a less anxious phenotype that was nullified in double-mutant mice. In contrast, in the Morris water maze, double-KO mice showed deficits in spatial reversal learning not observed in either single mutant compared with wild-type mice. The data suggest a role for PDE1B in locomotor responses to psychostimulants through modulation of DARPP32-dependent pathways; however, this modulation does not necessarily impact other behaviors, such as anxiety or learning. Instead, the phenotype of double-KOs observed in these latter tasks may be mediated through independent pathways.

Effect of Ethanol on DARPP-32 Phosphorylation in Transgenic Mice That Express Human Type VII Adenylyl Cyclase in Brain

BACKGROUND

Dopamine and cyclic adenosine monophosphate-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32) is a bidirectional signaling protein found in dopaminergically innervated brain areas. The characteristics and direction of DARPP-32 effects are regulated by phosphorylation of this protein. Phosphorylation of DARPP-32 on threonine-34 (T34) is regulated through the activation of dopamine (D1) receptors and stimulation of adenylyl cyclase (AC) and protein kinase A activity and by calcineurin. Phosphorylation of DARPP-32 on threonine-75 (T75) is regulated by cyclin-dependent kinase 5 and protein phosphatase 2A. DARPP-32 has been implicated in the motivational effects of ethanol.

METHODS

The authors characterized transgenic mice that overexpress an ethanol-sensitive isoform of AC (AC7) in brain by measuring basal and ethanol-modulated DARPP-32 phosphorylation. Phosphorylated and total DARPP-32 were measured by immunoblotting in brain areas associated with the motivational and anxiolytic effects of ethanol (nucleus accumbens, striatum, and amygdala).

RESULTS

AC7 transgenic mice had higher basal levels of T34 DARPP-32 than wild-type mice in striatum and amygdala, whereas basal levels of T75 DARPP-32 did not differ between wild-type and transgenic mice. Ethanol administration increased T34 DARPP-32 in nucleus accumbens and amygdala (but not in the striatum) of wild-type and transgenic mice (with a greater effect in amygdala of transgenic mice than wild-type mice). Ethanol administration increased T75 DARPP-32 in amygdala of only the wild-type mice and in nucleus accumbens and striatum of both the transgenic and wild-type mice.

CONCLUSIONS

The effect of ethanol on the balance of DARPP-32 phosphorylation, especially in amygdala of wild-type versus transgenic mice, may contribute to differential motivational effects of ethanol in these animals.

A field guide to the anterior olfactory nucleus (cortex)

While portions of the mammalian olfactory system have been studied extensively, the anterior olfactory nucleus (AON) has been relatively ignored. Furthermore, the existing research is dispersed and obscured by many different nomenclatures and approaches. The present review collects and assembles the relatively sparse literature regarding the portion of the brain situated between the olfactory bulb and primary olfactory (piriform) cortex. Included is an overview of the area's organization, the functional, morphological and neurochemical characteristics of its cells and a comprehensive appraisal of its efferent and afferent fiber systems. Available evidence suggests the existence of subdivisions within the AON and demonstrates that the structure influences ongoing activity in many other olfactory areas. We conclude with a discussion of the AON's mysterious but complex role in olfactory information processing.

DARPP-32 genomic fragments drive Cre expression in postnatal striatum

To direct Cre-mediated recombination to differentiated medium-size spiny neurons (MSNs) of the striatum, we generated transgenic mice that express Cre recombinase under the regulation of DARPP-32 genomic fragments. In this reported line, recombination of an R26R reporter allele occurred postnatally in the majority of medium-size spiny neurons of the dorsal and ventral striatum (caudate nucleus and nucleus accumbens/olfactory tubercle), as well as in the piriform cortex and choroid plexus. Although regulatory fragments were selected to target MSNs, low levels of Cre-recombinase expression, as detected by beta-galactosidase activity from the R26R reporter gene, were also apparent in widely dispersed areas or cells of the forebrain and hindbrain. These included the primary and secondary motor cortex, and association cortex, as well as in the olfactory bulb and cerebellar Purkinje cells. Notably, expression in these regions was well below that of endogenous DARPP-32. Analysis of colocalization of beta-galactosidase, as detected either by histochemistry or immunocytochemistry, and DARPP-32 revealed double-labeling in almost all DARPP-32-expressing MSNs in the postnatal striatum, but not in extrastriatal regions. The DARPP-32Cre transgenic mouse line thus provides a useful tool to specifically express and/or inactivate genes in mature MSNs of the striatum.

Environmental enrichment rescues protein deficits in a mouse model of Huntington's disease, indicating a possible disease mechanism

Huntington's disease (HD) is a devastating neurodegenerative disorder caused by a CAG repeat expansion encoding an extended polyglutamine tract in the huntingtin protein. Transgenic mice expressing a human huntingtin transgene containing an expanded CAG repeat (R6/1 model) develop a neurodegenerative disorder closely resembling human HD. Previous work demonstrated that environmental enrichment delays the onset of motor symptoms in this mouse model. We confirmed that at 5 months of age, enrichment ameliorates motor symptoms (assessed using the rotarod test) and prevents loss of body weight induced by the HD transgene. We further examined molecular consequences of enrichment by determining changes in protein levels in the neostriatum, hippocampus, and anterior cortex using quantitative Western blot analysis. Non-enriched HD mice have severe reductions in BDNF in the hippocampus and striatum at 5 months, which are entirely rescued by enrichment. BDNF levels are unaltered by HD in the anterior cortex, suggesting that enrichment might prevent HD-induced impairment of anterograde transport of this neurotrophin to the striatum. NGF is unaffected by HD. Non-enriched HD mice also exhibit deficits in dopamine and cAMP-regulated phosphoprotein (32 kDa) in striatum and anterior cortex. Environmental enrichment rescues the cortical but not the striatal deficit at 5 months. These results suggest that environmental enrichment benefits animals at early stages of the disease by rescuing protein deficits, possibly through rescuing transcription or protein transport problems.

Tyrosine dephosphorylation and ethanol inhibition of N-Methyl-D-aspartate receptor function

The inhibitory effect of ethanol on N-methyl-d-aspartate receptors (NMDARs) is well documented in several brain regions. However, the molecular mechanisms by which ethanol affects NMDARs are not well understood. In contrast to the inhibitory effect of ethanol, phosphorylation of the NMDAR potentiates channel currents (Lu, W. Y., Xiong, Z. G., Lei, S., Orser, B. A., Dudek, E., Browning, M. D., and MacDonald, J. F. (1999) Nat. Neurosci. 2, 331-338). We have previously shown that protein kinase C activators induce tyrosine phosphorylation and potentiation of the NMDAR (Grosshans, D. R., Clayton, D. R., Coultrap, S. J., and Browning, M. D. (2002) Nat. Neurosci. 5, 27-33). We therefore hypothesized that the ethanol inhibition of NMDARs might be due to changes in tyrosine phosphorylation of NMDAR subunits. In support of this hypothesis, we found that tyrosine phosphorylation of both NR2A and NR2B subunits was significantly reduced following in situ exposure of hippocampal slices to 100 mm ethanol. Specifically, phosphorylation of tyrosine 1472 on NR2B was reduced 23.5%. These data suggest a possible mechanism by which ethanol may inhibit the NMDAR via activation of a tyrosine phosphatase. Electrophysiological studies demonstrated that ethanol inhibited NMDAR field excitatory postsynaptic potential slope and amplitude to a similar degree as previously reported by our laboratory and others (Schummers, J., Bentz, S., and Browning, M. D. (1997) Alcohol Clin. Exp. Res. 21, 404-408). Inclusion of bpV(phen), a potent phosphotyrosine phosphatase inhibitor, in the recording chamber prior to and during ethanol exposure significantly reduced the inhibitory effect of ethanol on NMDAR field excitatory postsynaptic potentials. Taken together, these data suggest that phosphatase-mediated dephosphorylation of NMDAR subunits may play an important role in mediating the inhibitory effects of ethanol on the N-methyl-D-aspartate receptor.

Immunohistochemical localization of DARPP-32 in the brain of the lizard, Gekko gecko: co-occurrence with tyrosine hydroxylase

To assess the relationship between dopaminergic neuronal structures and dopaminoceptive structures in a reptile, single and double immunohistochemical procedures with antibodies directed against DARPP-32 (dopamine- and cAMP-regulated phosphoprotein with an apparent molecular mass of 32,000 daltons),a phosphoprotein related to the dopamine D(1)-receptor, and tyrosine hydroxylase (TH) were applied to the brain of the lizard, Gekko gecko. The DARPP-32 antibody yielded a well-differentiated pattern of staining in the brain of Gekko. In general, areas that are densely innervated by TH-immunoreactive, putative dopaminergic fibers, such as the nucleus accumbens, striatum, dorsal ventricular ridge, and amygdaloid complex, display strong immunoreactivity for DARPP-32 in somata and neuropil. Distinct cellular DARPP-32 immunoreactivity was also found in the lateral cortex, ventral hypothalamus, habenula, central nucleus of the torus semicircularis, midbrain tectum, parvicellular isthmic nucleus, raphe nuclei, caudal rhombencephalic tegmentum, and spinal cord. Striatal projections to the midbrain and their target, i.e., the substantia nigra pars reticulata, were found to be strongly immunoreactive. Double immunofluorescence staining revealed that dopaminergic cells generally do not stain for DARPP-32, except for cells in the ventral hypothalamus and at caudal rhombencephalic levels. In conclusion, the distribution of DARPP-32 in the brain of the lizard Gekko gecko largely resembles the pattern observed in birds and mammals, at least as far as basal ganglia structures are concerned. On the other hand, there are several specific features of DARPP-32 distribution in the gekkonid brain that deserve further attention, such as cellular colocalization of DARPP-32 and TH immunoreactivity in hypothalamic and caudal rhombencephalic areas, and cellular DARPP-32 immunoreactivity in the tectum and central nucleus of the torus semicircularis of the midbrain, the superior and inferior raphe nuclei, and the spinal cord.

Distribution of DARPP-32 immunoreactive structures in the quail brain: anatomical relationship with dopamine and aromatase

We recently demonstrated that dopamine (DA) as well as different DA receptor agonists and antagonists are able to decrease within a few minutes the aromatase activity (AA) measured in vitro in homogenates or in explants of the quail preoptic area - hypothalamus. In addition, DA also appears to regulate AA, in vivo presumably by modifying enzyme synthesis. The cellular mechanisms and the anatomical substrate that mediate these controls of AA by DA are poorly understood. Tyrosine hydroxylase-immunoreactive (TH-ir) fibers and punctate structures have been previously observed in close vicinity of aromatase-immunoreactive (ARO-ir) cells in the quail medial preoptic nucleus (POM) and bed nucleus striae terminalis (BST) but these fibers could reflect a noradrenergic innervation. We also do not know whether aromatase cells are dopaminoceptive. The main goal of the present study was therefore to bring more information on the anatomical relationships between aromatase expressing neurons and the dopaminergic system in the quail brain. The visualization by immunocytochemistry of DA and of the D1 receptor associated protein DARPP-32 was used to address these questions. DA-ir fibers were observed in the quail forebrain and overlapped extensively with nuclei that contain high densities of ARO-ir cells such as the POM and BST. This confirms that the previously reported TH-ir innervation of ARO-ir cells is, at least in part, of dopaminergic nature. DARPP-32-immunoreactive cells were found in periventricular position throughout the hypothalamus. DARPP-32-ir cells were also observed in telencephalic and mesencephalic areas (hyperstriatum accessorium, paleostriatum, nucleus intercollicularis, optic tectum). DARPP-32-ir fibers were widespread in tel-, di-, and mes-encephalic areas. The highest densities of immunoreactive fibers were detected in the lobus parolfactorius, paleostriatum augmentatum and substantia nigra/area ventralis of Tsai. In double-labeled sections, appositions between DARPP-32 fibers and ARO-ir cells were present in the dorsolateral POM and BST but DARPP-32 immunoreactivity was not detected in the ARO-ir perikarya (no colocalization). These data confirm the presence of a dopaminoceptive structures within the main cell clusters of ARO-ir cells in the quail brain but provide no evidence that these ARO-ir cells are themselves dopaminoceptive. Because DARPP-32 is not present in all types of cells expressing DA receptors, the presence of DA receptors that would not be associated with DARPP-32 in ARO-ir cells still remains to be investigated

Dopamine receptor immunohistochemistry in the rat choroid plexus

1. Earlier studies have demonstrated a high density of dopamine D1-like receptor binding in the choroid plexus by light microscope autoradiography, but the dopaminergic specificity of this binding was questioned. 2. In this study the localization of dopamine receptor subtypes was investigated in the rat choroid plexus by Western blot analysis and immunohistochemistry using antibodies raised against dopamine D1-D5 receptor protein. 3. Western blot analysis revealed reactivity with immune bands of approximately 50 and 51 KDa corresponding to dopamine D1 and D5 receptors, respectively. Dopamine D1-like (D1 and D5) receptor protein immunoreactivity insensitive to superior cervical ganglionectomy was located in smooth muscle of choroid arteries and to a larger extent within choroid plexus epithelium. 4. Western blot analysis revealed reactivity with immune bands of approximately 53 KDa and 40-42 KDa corresponding to dopamine D2 and D4 receptors, respectively, and no dopamine D3 receptor reactivity. Dopamine D2-like receptor protein immunoreactivity displayed a distribution similar to that of tyrosine-hydroxylase (TH)-immunoreactive sympathetic fibres and disappeared after superior cervical ganglionectomy. It consisted in the expression of dopamine D2 and to a lesser extent of D4 receptor protein immunoreactivity perivascularly and associated with choroid epithelium. No D3 receptor protein immunoreactivity was found in rat choroid plexus. 5. The above results indicate that rat choroid plexus expresses dopamine receptor protein, being dopamine D1-like receptors predominant in epithelium and arterial smooth muscle and D2-like receptors in sympathetic nerve fibres supplying choroid plexus epithelium and vasculature. 6. These findings suggests that dopamine receptors with a different anatomical localization may modulate production of cerebrospinal fluid.

DARPP-32 knockout mice exhibit impaired reversal learning in a discriminated operant task

The current study was conducted to examine the performance of mice with a targeted deletion of the gene for DARPP-32 in a discriminated operant task using food reinforcement. DARPP-32 plays a central role in regulating the efficacy of dopaminergic neurotransmission. Initially, wild-type and DARPP-32 knockout mice were trained to nose-poke for food on a continuous reinforcement schedule. The minimum response requirement was increased every 5 days until the animals were responding on an FR-15 schedule of reinforcement. At the completion of extensive operant training, reversal learning was assessed. Wild-type and DARPP-32 knockout mice exhibited equivalent performance during acquisition of this task, with both groups increasing operant responding as the schedule of reinforcement was raised. However, significant differences in discrimination learning were observed during the reversal phase, with DARPP-32 knockout mice requiring significantly more trials to reach criterion than wild-type controls. These results provide evidence for a functional role of DARPP-32 in the mediation of processes underlying learning and memory.

Neurochemical development of the hippocampal region in the fetal rhesus monkey. II. Immunocytochemistry of peptides, calcium-binding proteins, DARPP-32, and monoamine innervation in the entorhinal cortex by the end of gestation

Material for the study came from one 126 day-old rhesus monkey fetus and two 3 day-old neonates. The immunocytochemical detection of somatostatin, neurotensin (NT), parvalbumin, calbindin D-28K, DARPP-32 as well as tyrosine hydroxylase (TH), dopamine-beta-hydroxylase and serotonin (5-HT), was carried out on serial cryostat sections of the entorhinal cortex. The authors reported in a previous paper the precocious differentiation of the entorhinal cortex in rhesus monkey fetuses and featured the conspicuous expression of calbindin D-28K, somatostatin, neurotensin, and the monoaminergic innervation during the first half of gestation. The present study shows distinct temporal profiles of neurochemical development during the second half of gestation: the dense neuropeptidergic innervation remained a constant feature; the three aminergic systems gradually increased in density; parvalbumin, unlike calbindin D-28K, was primarily expressed during the last quarter of gestation. Three other prominent features of the last quarter of gestation are illustrated: the refinement of the modular neurochemical organization of the lamina principalis externa, the delayed chemoanatomical development of the rhinal sulcus area, and the establishment of a distinct rostrocaudal pattern of neurochemical distribution. In correspondence with the cluster-like organization of the lamina principalis externa, the authors observed in the olfactory, rostral, and intermediate fields of the neonate monkey entorhinal cortex, a particular subset of pyramidal-shaped neurons: located in layer III, they were characterized by fasciculated apical dendrites ascending between the cellular islands of the discontinuous layer II and the coexpression of calbindin D-28K and DARPP-32. Besides, most of the other chemical systems displayed a distinct, area-specific, patchy distribution, except for the homogeneously distributed noradrenergic innervation. In the olfactory and rostral fields, TH positive dopaminergic fibers accumulated on the neuronal islands of layers II-III, and parvalbumin labeled fibers on those of layer III, whereas patches of 5-HT and NT-like reactive terminals were segregated between the cellular islands, overlapping the DARPP-32/calbindin D-28 K labeled dendritic bundles. At the opposite, in the intermediate field, 5-HT positive terminals overlapped the cellular islands of layer II and thin fascicles of dopaminergic fibers ran in the inter island spaces. The somatostatin-LIR innervation was apparently too dense to reveal a patchy distribution that existed at earlier developmental stages. In the caudal field, the patchy pattern was replaced by a predominant bilaminar type of distribution of NT, 5-HT, and TH-like positive afferents.(ABSTRACT TRUNCATED AT 400 WORDS)