Tyrosine hydroxylase immunoreactivity in cerebellar Purkinje cells of the rat

Activating Lobule VI PCTH+-Med Pathway in Cerebellum Blocks the Acquisition of Methamphetamine Conditioned Place Preference in Mice

Cerebellum has been implicated in drug addiction; however, its underlying cellular populations and neuronal circuitry remain largely unknown. In the current study, we identified a neural pathway from tyrosine hydroxylase (TH)-positive Purkinje cells (PCTH+) in cerebellar lobule VI to calcium/calmodulin-dependent protein kinase II (CaMKII)-positive glutamatergic neurons in the medial cerebellar nucleus (MedCaMKII), forming the lobule VI PCTH+-MedCaMKII pathway in male mice. In naive male mice, inhibition of PCTH+ neurons activated Med neurons. During conditioned place preference (CPP) training, exposure to methamphetamine (METH) inhibited lobule VI PCTH+ neurons while excited MedCaMKII neurons in mice. Silencing MedCaMKII using a tetanus toxin light chain (tettox) suppressed the acquisition of METH CPP in mice but resulted in motor coordination deficits in naive mice. In contrast, activating lobule VI PCTH+ terminals within Med inhibited the activity of Med neurons and subsequently blocked the acquisition of METH CPP in mice without affecting motor coordination, locomotor activity, and sucrose reinforcements in naive mice. Our findings identified a novel lobule VI PCTH+-MedCaMKII pathway within the cerebellum and explored its role in mediating the acquisition of METH-preferred behaviors.

Assessing the Location, Relative Expression and Subclass of Dopamine Receptors in the Cerebellum of Hemi-Parkinsonian Rats

Parkinson's Disease (PD) is a neurodegenerative disease with loss of dopaminergic neurons in the nigrostriatal pathway resulting in basal ganglia (BG) dysfunction. This is largely why much of the preclinical and clinical research has focused on pathophysiological changes in these brain areas in PD. The cerebellum is another motor area of the brain. Yet, if and how this brain area responds to PD therapy and contributes to maintaining motor function fidelity in the face of diminished BG function remains largely unanswered. Limited research suggests that dopaminergic signaling exists in the cerebellum with functional dopamine receptors, tyrosine hydroxylase (TH) and dopamine transporters (DATs); however, much of this information is largely derived from healthy animals and humans. Here, we identified the location and relative expression of dopamine 1 receptors (D1R) and dopamine 2 receptors (D2R) in the cerebellum of a hemi-parkinsonian male rat model of PD. D1R expression was higher in PD animals compared to sham animals in both hemispheres in the purkinje cell layer (PCL) and granule cell layer (GCL) of the cerebellar cortex. Interestingly, D2R expression was higher in PD animals than sham animals mostly in the posterior lobe of the PCL, but no discernible pattern of D2R expression was seen in the GCL between PD and sham animals. To our knowledge, we are the first to report these findings, which may lay the foundation for further interrogation of the role of the cerebellum in PD therapy and/or pathophysiology.

Dopaminergic regulation of vestibulo-cerebellar circuits through unipolar brush cells

While multiple monoamines modulate cerebellar output, the mechanistic details of dopaminergic signaling in the cerebellum remain poorly understood. We show that dopamine type 1 receptors (Drd1) are expressed in unipolar brush cells (UBCs) of the mouse cerebellar vermis. Drd1 activation increases UBC firing rate and post-synaptic NMDAR -mediated currents. Using anatomical tracing and in situ hybridization, we test three hypotheses about the source of cerebellar dopamine. We exclude midbrain dopaminergic nuclei and tyrosine hydroxylase-positive Purkinje (Pkj) cells as potential sources, supporting the possibility of dopaminergic co-release from locus coeruleus (LC) axons. Using an optical dopamine sensor GRABDA2h, electrical stimulation, and optogenetic activation of LC fibers in the acute slice, we find evidence for monoamine release onto Drd1-expressing UBCs. Altogether, we propose that the LC regulates cerebellar cortex activity by co-releasing dopamine onto UBCs to modulate their response to cerebellar inputs. Pkj cells directly inhibit these Drd1-positive UBCs, forming a dopamine-sensitive recurrent vestibulo-cerebellar circuit.

The Pathophysiology and Treatment of Essential Tremor: The Role of Adenosine and Dopamine Receptors in Animal Models

Essential tremor (ET) is one of the most common neurological disorders that often affects people in the prime of their lives, leading to a significant reduction in their quality of life, gradually making them unable to independently perform the simplest activities. Here we show that current ET pharmacotherapy often does not sufficiently alleviate disease symptoms and is completely ineffective in more than 30% of patients. At present, deep brain stimulation of the motor thalamus is the most effective ET treatment. However, like any brain surgery, it can cause many undesirable side effects; thus, it is only performed in patients with an advanced disease who are not responsive to drugs. Therefore, it seems extremely important to look for new strategies for treating ET. The purpose of this review is to summarize the current knowledge on the pathomechanism of ET based on studies in animal models of the disease, as well as to present and discuss the results of research available to date on various substances affecting dopamine (mainly D3) or adenosine A1 receptors, which, due to their ability to modulate harmaline-induced tremor, may provide the basis for the development of new potential therapies for ET in the future.

The Cerebellar Dopaminergic System

In the central nervous system (CNS), dopamine (DA) is involved in motor and cognitive functions. Although the cerebellum is not been considered an elective dopaminergic region, studies attributed to it a critical role in dopamine deficit-related neurological and psychiatric disorders [e.g., Parkinson's disease (PD) and schizophrenia (SCZ)]. Data on the cerebellar dopaminergic neuronal system are still lacking. Nevertheless, biochemical studies detected in the mammalians cerebellum high dopamine levels, while chemical neuroanatomy studies revealed the presence of midbrain dopaminergic afferents to the cerebellum as well as wide distribution of the dopaminergic receptor subtypes (DRD1-DRD5). The present review summarizes the data on the cerebellar dopaminergic system including its involvement in associative and projective circuits. Furthermore, this study also briefly discusses the role of the cerebellar dopaminergic system in some neurologic and psychiatric disorders and suggests its potential involvement as a target in pharmacologic and non-pharmacologic treatments.

Catecholaminergic Innervation of the Lateral Nucleus of the Cerebellum Modulates Cognitive Behaviors

The cerebellum processes neural signals related to rewarding and aversive stimuli, suggesting that the cerebellum supports nonmotor functions in cognitive and emotional domains. Catecholamines are a class of neuromodulatory neurotransmitters well known for encoding such salient stimuli. Catecholaminergic modulation of classical cerebellar functions have been demonstrated. However, a role for cerebellar catecholamines in modulating cerebellar nonmotor functions is unknown. Using biochemical methods in male mice, we comprehensively mapped TH+ fibers throughout the entire cerebellum and known precerebellar nuclei. Using electrochemical (fast scan cyclic voltammetry), and viral/genetic methods to selectively delete Th in fibers innervating the lateral cerebellar nucleus (LCN), we interrogated sources and functional roles of catecholamines innervating the LCN, which is known for its role in supporting cognition. The LCN has the most TH+ fibers in cerebellum, as well as the most change in rostrocaudal expression among the cerebellar nuclei. Norepinephrine is the major catecholamine measured in LCN. Distinct catecholaminergic projections to LCN arise only from locus coeruleus, and a subset of Purkinje cells that are positive for staining of TH. LC stimulation was sufficient to produce catecholamine release in LCN. Deletion of Th in fibers innervating LCN (LCN-Th-cKO) resulted in impaired sensorimotor integration, associative fear learning, response inhibition, and working memory in LCN-Th-cKO mice. Strikingly, selective inhibition of excitatory LCN output neurons with inhibitory designer receptor exclusively activated by designer drugs led to facilitation of learning on the same working memory task impaired in LCN-Th-cKO mice. Collectively, these data demonstrate a role for LCN catecholamines in cognitive behaviors.SIGNIFICANCE STATEMENT Here, we report on interrogating sources and functional roles of catecholamines innervating the lateral nucleus of the cerebellum (LCN). We map and quantify expression of TH, the rate-limiting enzyme in catecholamine synthesis, in the entire cerebellar system, including several precerebellar nuclei. We used cyclic voltammetry and pharmacology to demonstrate sufficiency of LC stimulation to produce catecholamine release in LCN. We used advanced viral techniques to map and selectively KO catecholaminergic neurotransmission to the LCN, and characterized significant cognitive deficits related to this manipulation. Finally, we show that inhibition of excitatory LCN neurons with designer receptor exclusively activated by designer drugs, designed to mimic Gi-coupled catecholamine GPCR signaling, results in facilitation of a working memory task impaired in LCN-specific TH KO mice.

Purkinje Cell-Specific Knockout of Tyrosine Hydroxylase Impairs Cognitive Behaviors

Tyrosine hydroxylase (Th) expression has previously been reported in Purkinje cells (PCs) of rodents and humans, but its role in the regulation of behavior is not understood. Catecholamines are well known for facilitating cognitive behaviors and are expressed in many regions of the brain. Here, we investigated a possible role in cognitive behaviors of PC catecholamines, by mapping and testing functional roles of Th positive PCs in mice. Comprehensive mapping analyses revealed a distinct population of Th expressing PCs primarily in the posterior and lateral regions of the cerebellum (comprising about 18% of all PCs). To identify the role of PC catecholamines, we selectively knocked out Th in PCs using a conditional knockout approach, by crossing a Purkinje cell-selective Cre recombinase line, Pcp2-Cre, with a floxed tyrosine hydroxylase mouse line (Thlox/lox) to produce Pcp2-Cre;Thlox/lox mice. This manipulation resulted in approximately 50% reduction of Th protein expression in the cerebellar cortex and lateral cerebellar nucleus, but no reduction of Th in the locus coeruleus, which is known to innervate the cerebellum in mice. Pcp2-Cre;Thlox/lox mice showed impairments in behavioral flexibility, response inhibition, social recognition memory, and associative fear learning relative to littermate controls, but no deficits in gross motor, sensory, instrumental learning, or sensorimotor gating functions. Catecholamines derived from specific populations of PCs appear to support cognitive functions, and their spatial distribution in the cerebellum suggests that they may underlie patterns of activation seen in human studies on the cerebellar role in cognitive function.

Generation and characterization of a mouse line for monitoring translation in dopaminergic neurons

We developed a mouse line targeting midbrain dopamine neurons for Translating Ribosome Affinity Purification(TRAP). Here, we briefly report on the basic characterization of this mouse line including confirmation of expression of the transgene in midbrain dopamine neurons and validation of its effectiveness in capturing mRNA from these cells. We also report a translational profile of these neurons which may be of use to investigators studying the gene expression of these cells. Finally, we have provided the line to Jackson Laboratories for distribution and use in future studies.

Pramipexole at a Low Dose Induces Beneficial Effect in the Harmaline-induced Model of Essential Tremor in Rats

AIMS

The aim of the study was to examine the effects of preferential agonists of dopamine D3 receptors: pramipexole and 7-OH-DPAT on the harmaline-induced tremor in rats (a model of essential tremor, ET). To study receptor mechanisms of these drugs, rats were pretreated with dopamine D3 receptor antagonists--SB-277011-A and SR-21502, an antagonist of presynaptic D2/D3 receptors--amisulpride, or a nonselective antagonist of D2-like receptors, haloperidol, at a postsynaptic dose.

METHODS

For tremor measurement, fully automated force plate actimeters were used and data were analyzed using fast Fourier transform.

RESULTS

Harmaline (15 mg/kg ip)-triggered tremor was manifested by an increase in the power within 9-15 Hz band (AP2). Pramipexole administered at a low (0.1 mg/kg sc), but not higher doses (0.3 and 1 mg/kg sc), and 7-OH-DPAT (0.1, 0.3, and 1 mg/kg sc) reversed the harmaline-increased AP2. None of the examined dopamine antagonists: SB-277011-A (10 mg/kg ip), SR-21502 (15 mg/kg ip), haloperidol (0.5 mg/kg ip), or amisulpride (1 mg/kg ip) influenced the above effect of dopamine agonists.

CONCLUSION

The present study indicates that pramipexole reduces the harmaline-induced tremor, which may suggest its beneficial effects in ET patients. However, mechanisms underlying its action are still unclear and need further examination.

Catecholaminergic connectivity to the inner ear, central auditory, and vocal motor circuitry in the plainfin midshipman fish porichthys notatus

Although the neuroanatomical distribution of catecholaminergic (CA) neurons has been well documented across all vertebrate classes, few studies have examined CA connectivity to physiologically and anatomically identified neural circuitry that controls behavior. The goal of this study was to characterize CA distribution in the brain and inner ear of the plainfin midshipman fish (Porichthys notatus) with particular emphasis on their relationship with anatomically labeled circuitry that both produces and encodes social acoustic signals in this species. Neurobiotin labeling of the main auditory end organ, the saccule, combined with tyrosine hydroxylase immunofluorescence (TH-ir) revealed a strong CA innervation of both the peripheral and central auditory system. Diencephalic TH-ir neurons in the periventricular posterior tuberculum, known to be dopaminergic, send ascending projections to the ventral telencephalon and prominent descending projections to vocal-acoustic integration sites, notably the hindbrain octavolateralis efferent nucleus, as well as onto the base of hair cells in the saccule via nerve VIII. Neurobiotin backfills of the vocal nerve in combination with TH-ir revealed CA terminals on all components of the vocal pattern generator, which appears to largely originate from local TH-ir neurons but may include input from diencephalic projections as well. This study provides strong neuroanatomical evidence that catecholamines are important modulators of both auditory and vocal circuitry and acoustic-driven social behavior in midshipman fish. This demonstration of TH-ir terminals in the main end organ of hearing in a nonmammalian vertebrate suggests a conserved and important anatomical and functional role for dopamine in normal audition.

Role of cerebellar dopamine D(3) receptors in modulating exploratory locomotion and cataleptogenicity in rats

Dopamine D(3) receptors are highly expressed in the cerebellum; however, their pathophysiological functions are not fully understood. Here, we conducted microinjection studies to clarify the role of cerebellar D(3) receptors in modulating locomotion and cataleptogenicity in rats. Microinjection of the preferential D(3) agonist 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT) into lobe 9 of the cerebellum significantly reduced spontaneous locomotor activity with a U-shaped dose-response curve. The intracerebellar microinjection of 7-OH-DPAT did not elicit catalepsy by itself, but markedly potentiated catalepsy induction with a low dose (0.3mg/kg) of haloperidol. The catalepsy enhancement by 7-OH-DPAT occurred in a dose-dependent manner and was not associated with the locomotor inhibition. U-99194A (a selective D(3) antagonist) or AD-6048 (a preferential D(3) vs. D(2) antagonist) antagonized both the catalepsy enhancement and the locomotor inhibition with 7-OH-DPAT. In addition, U-99194A and AD-6048 per se significantly alleviated catalepsy induced by a high dose (0.5mg/kg) of haloperidol. Furthermore, microinjection of 7-OH-DPAT into the nucleus accumbens or the dorsolateral striatum neither affected spontaneous locomotor activity nor haloperidol (0.3mg/kg)-induced catalepsy. The present results illustrate for the first time the role of cerebellar D(3) receptors in modulating cataleptogenicity of antipsychotic agents, implying that blockade of cerebellar D(3) receptors contributes to the reduction of extrapyramidal side effects.

Dopamine signaling is required for depolarization-induced slow current in cerebellar Purkinje cells

Brief strong depolarization of cerebellar Purkinje cells produces a slow inward cation current. This current, called depolarization-induced slow current (DISC), is triggered by Ca influx in the Purkinje cell and is attenuated by a blocker of vesicular fusion. Previous work in other brain regions, such as the substantia nigra and ventral tegmental area, has shown that dopamine can be released from dendrites to produce paracrine and autocrine signaling. Here, we test the hypothesis that postsynaptic release of dopamine and autocrine activation of dopamine receptors is involved in DISC. Light immunohistochemistry showed that D(3) dopamine receptors, vesicular monoamine transporter type 2 (VMAT2), and dopamine plasma membrane transporters (DATs) were all expressed in cerebellar Purkinje cells. However, their expression was strongest in the gyrus region of cerebellar lobules IX and X. Comparison of DISC across lobules revealed that it was weak in the anterior portions of the cerebellum (lobules II, V, and VI) and strong in lobules IX and X. DISC was blocked by dopamine receptor antagonists (haloperidol, clozapine, eticlopride, and SCH23390). Likewise, DISC was strongly attenuated by inhibitors of VMAT (reserpine and tetrabenazine) and DAT (GBR12909 and rimcazole). These drugs did not produce DISC attenuation through blockade of depolarization-evoked Purkinje cell Ca transients. Purkinje cells in cerebellar slices derived from DAT-null mice expressed DISC, but this DISC ran down at a significantly higher rate than littermate controls. Together, these results suggest that strong Purkinje cell depolarization produces Ca-dependent release of vesicular postsynaptic dopamine that then excites Purkinje cells in an autocrine manner.

Pharmacological characterization and anatomical distribution of the dopamine transporter in the mouse cerebellum

We studied the binding parameters, the pharmacological profile and the anatomical distribution of the dopamine transporter in the mouse cerebellum by using the specific dopamine uptake antagonist [(3)H]GBR12935 and an antidopamine transporter monoclonal antibody. Competition experiments in cerebellar and striatal membrane preparations showed that [(3)H]GBR12935 binds to a specific binding site, sensitive to dopamine and low concentrations of mazindol. The affinity of dopamine for the cerebellar binding site was one order of magnitude lower than the affinity for the striatal binding site. Saturation experiments in cerebellar membrane preparations and thin frozen sections showed that the affinity of [(3)H]GBR12935 for this binding site is similar to its affinity for the striatal dopamine transporter. Saturable binding was lobule specific and in general was higher in the molecular layer compared to the granule cell layer. The immunohistochemical signal was mostly concentrated in the Purkinje cell layer and the cerebellar nuclei. The results suggest that the cerebellar dopamine transporter is similar but not identical to the striatal dopamine transporter and that it is present in the mouse cerebellum in a lobule and lamina specific pattern.

Developmentally regulated Ca2+-dependent activator protein for secretion 2 (CAPS2) is involved in BDNF secretion and is associated with autism susceptibility

The postnatal development of the cerebellum is accomplished via a series of cytogenetic and morphogenetic events encoded in the genome. To decipher the underlying genetic basis of these events we have systematized the spatio-temporal gene expression profiles during mouse cerebellar development in the Cerebellar Development Transcriptome Database (CDT-DB). Using the CDT-DB, Ca(2+)-dependent activator protein for secretion 2 (CAPS2 or CADPS2) was identified as a developmentally regulated gene that is predominantly expressed in cerebellar granule cells (GCs) with an expression peak around the first or second postnatal week. CAPS2 protein is concentrated in parallel fiber (PF) terminals and is associated with secretory vesicles containing brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3). CAPS2 enhances release of BDNF and NT-3, both of which are essential for normal cerebellar development. CAPS2-deficient (CAPS2(-/-)) mice show reduced secretion of BDNF and NT-3; consequently, the cerebella of these mice exhibit developmental deficits, such as delayed development and increased cell death in GCs, fewer branched dendrites on Purkinje cells (PCs), and loss of the intercrural fissure. The PF-PC synapses have aberrant cytoarchitectures and electrophysiological properties. These abnormal cellular and morphological phenotypes are more severe around the cerebellar vermis, in which hypoplasia has been reported in autism patients. Moreover, CAPS2(-/-) mice had fewer cortical and hippocampal parvalbumin-positive interneurons and some autistic-like behavioral phenotypes. In the CAPS2 genes of some autistic patients an aberrant splicing variant and non-synonymous SNPs have been identified. These recent studies implicate CAPS2 in autism susceptibility. Therefore, CAPS2(-/-) mice will be a useful model animal in which to study aspects of the neuropathology and behaviors characteristic of developmental disorders.

Methamphetamine induces ectopic expression of tyrosine hydroxylase and increases noradrenaline levels within the cerebellar cortex

Methamphetamine produces locomotor activation and typical stereotyped motor patterns, which are commonly related with increased catecholamine activity within the basal ganglia, including the dorsal and ventral striatum. Since the cerebellum is critical for movement control, and for learning of motor patterns, we hypothesized that cerebellar catecholamines might be a target of methamphetamine. To test this experimental hypothesis we injected methamphetamine into C57 Black mice at the doses of 5 mg/kg two or three times, 2 h apart. This dosing regimen is known to be toxic for striatal dopamine terminals. However, we found that in the cerebellum, methamphetamine increased the expression of the primary transcript of the tyrosine hydroxylase (TH) gene, followed by an increased expression of the TH protein. Increased TH was localized within Purkinje cells, where methamphetamine increased the number of TH-immunogold particles, and produced a change in the distribution of the enzyme by increasing the cytoplasmic percentage. Increased TH expression was accompanied by a slight increase in noradrenaline content. This effect was highly site-specific for the cortex of posterior vermal lobules, while only slight effects were detectable in the hemispheres. The present data indicate that the cerebellum does represent a target of methamphetamine, which produces specific and fine alterations of the catecholamine system involving synthesis, amount, and compartmentalization of TH as well as increased noradrenaline levels. This may be relevant for motor alterations induced by methamphetamine. In line with this, inherited cerebellar movement disorders in various animal species including humans are associated with increased TH immunoreactivity within intrinsic neurons of the same lobules of the cerebellar cortex.

Tyrosine hydroxylase (TH)- and aromatic-L-amino acid decarboxylase (AADC)-immunoreactive neurons of the common marmoset (Callithrix jacchus) brain: an immunohistochemical analysis

From the perspective of comparative morphology, the distribution of non-monoaminergic neurons in the common marmoset (Callithrix jacchus) was investigated using an immunohistochemical method with specific antibodies to tyrosine hydroxylase (TH) and aromatic-L-amino acid decarboxylase (AADC).TH-immunoreactive (IR) neurons (but not AADC-IR) neurons were observed in the olfactory tubercle, preoptic suprachiasmatic nucleus, periventricular hypothalamic nucleus, arcuate nucleus, paraventricular nucleus, periaqueductal gray matter, medial longitudinal fasciculus, substantia nigra, and nucleus solitaris. In contrast, AADC-IR (but not TH-IR), small, oval and spindle-shaped neurons were sparsely distributed in the following areas: the hypothalamus from the anterior nucleus to the lateral nucleus, the dorsomedial nucleus, the dorsomedial area of the medial mammillary nucleus and the arcuate nucleus; the midbrain, including the stria medullaris and substantia nigra; and the medulla oblongata, including the dorsal area of the nucleus solitaris and the medullary reticular nucleus. The distribution of AADC-IR neurons was not as extensive in the marmoset as it is in rats. However, these neurons were located in the marmoset, but not the rat substantia nigra. Furthermore, AADC-IR neurons that are present in the human striatum were absent in that of the marmoset. The present results indicate that the distribution of non-monoaminergic neurons in the brain of the common marmoset is unique and different from that in humans and rodents.

P2Y1 receptor switches to neurons from glia in juvenile versus neonatal rat cerebellar cortex

Background

In the CNS, several P2 receptors for extracellular nucleotides are identified on neurons and glial cells to participate to neuron-neuron, glia-glia and glia-neuron communication.

Results

In this work, we describe the cellular and subcellular presence of metabotropic P2Y₁ receptor in rat cerebellum at two distinct developmental ages, by means of immunofluorescence-confocal and electron microscopy as well as western blotting and direct membrane separation techniques. At postnatal day 21, we find that P2Y₁ receptor in addition to Purkinje neurons, is abundant on neuronal specializations identified as noradrenergic by anatomical, morphological and biochemical features. P2Y₁ receptor immunoreactivity colocalizes with dopamine β-hydroxylase, tyrosine hydroxylase, neurofilament light chain, synaptophysin and flotillin, but not with glial fibrillary acidic protein for astrocytes. P2Y₁ receptor is found enriched in membrane microdomains such as lipid rafts, in cerebellar synaptic vesicles, and is moreover visualized on synaptic varicosities by electron microscopy analysis. When examined at postnatal day 7, P2Y₁ receptor immunoreactivity is instead predominantly expressed only on Bergmann and astroglial cells, as shown by colocalization with glial fibrillary acidic protein rather then neuronal markers. At this age, we moreover identify that P2Y₁ receptor-positive Bergmann fibers wrap up doublecortin-positive granule cells stretching along them, while migrating through the cerebellar layers.

Conclusion

Membrane components including purinergic receptors are already known to mediate cellular contact and aggregation in platelets. Our results suggesting a potential role for P2Y₁ protein in cell junction/communication and development, are totally innovative for the CNS.

Cyto- and Chemoarchitecture of the Cerebellum of the Short-Beaked Echidna (Tachyglossus aculeatus)

The monotremes (echidnas and platypus) have been claimed by some authors to show 'avian' or 'reptilian' features in the gross morphology and microscopic anatomy of the cerebellum. We have used Nissl staining in conjunction with enzyme histochemistry to acetylcholinesterase and cytochrome oxidase and immunohistochemistry to non-phosphorylated neurofilament protein (SMI-32 antibody), calcium binding proteins (parvalbumin, calbindin and calretinin) and tyrosine hydroxylase to examine the cyto- and chemoarchitecture of the cerebellar cortex and deep cerebellar nuclei in the short-beaked echidna. Immunoreactivity for non-phosphorylated neurofilament (SMI-32 antibody) was found in the deep cerebellar nuclei and in Purkinje cells of most regions except the nodule. Purkinje cells identified with SMI-32 immunoreactivity were clearly mammalian in morphology. Parvalbumin and calbindin immunoreactivity was found in Purkinje cells with some regional variation in staining intensity and in Purkinje cell axons traversing cerebellar white matter or terminating on Lugaro cells. Calbindin immunoreactivity was also present in inferior olivary complex neurons. Calretinin immunoreactivity was found in pontocerebellar fibers and small cells in the deep granule cell layer of the ansiform lobule. We found that, although the deep cerebellar nuclei were much less clearly demarcated than in the rodent cerebellum, it was possible to distinguish medial, interposed and lateral nuclear components in the echidna. As far as we can determine from our techniques, the cerebellum of the echidna shows all the gross and cytological features familiar from the cerebellum of therian mammals.

The absence of phosphorylated tyrosine hydroxylase expression in the purkinje cells of the ataxic mutant pogo mouse

The pogo mouse is a new ataxic autosomal recessive mutant that arose in Korean wild mice (KJR/Mskist). Its ataxic phenotype includes difficulty in maintaining a normal posture and the inability to walk in a straight line. Several studies have reported that tyrosine hydroxylase (TH) is persistently ectopically expressed in particular subsets of Purkinje cells in a parasagittal banding pattern in several ataxic mutant mice, e.g. tottering alleles and pogo mice. In this present study, we examined the expression of an enzymatically active form of TH and phosphorylated TH at Ser(40) (phospho-TH) by using immunohistochemistry and double immunofluorescence in the cerebellum of pogo mice. TH immunostaining appeared in some Purkinje cells in pogo, but in only a few of Purkinje cells of their heterozygous littermate controls. In all groups of mice, no phospho-TH immunoreactive Purkinje cells were observed in the cerebellum, although subsets of TH immunoreactive Purkinje cells were found in adjacent sections. This study suggests that TH expression in the Purkinje cells of pogo abnormally increases without activation of this enzyme by phosphorylation. This may mean that TH in the Purkinje cells of these mutants does not catalyse the conversion of tyrosine to l-DOPA, and is not related to catecholamine synthesis.

Dopamine receptor and transporter levels are altered in the brain of Purkinje Cell Degeneration mutant mice

The Purkinje Cell Degeneration (Nna1pcd, pcd) mutant mouse is mainly characterized by the complete, primary loss of the Purkinje cells and the secondary, partial, retrograde loss of the granule and inferior olive neurons and is considered a model of human degenerative ataxia. We determined, by in vitro quantitative autoradiography and in situ hybridization, the effects of the Purkinje cell deprivation on the dopaminergic system of the Nna1pcd mutant mouse. The dopamine transporters, as determined by [3H]WIN35428 binding, were increased compared with wild-type mice in the ventral mesencephalic dopaminergic nuclei and in the lateral striatum, motor cortex and septum. In the cerebellum of Nna1pcd mice, the dopamine transporters showed a significant increase in the deep cerebellar nuclei, but were significantly decreased in the molecular layer. The D1-like receptors, as determined by [3H]SCH23390 binding, increased significantly in the Nna1pcd substantia nigra. The D2/D3 receptors, as determined by [3H]raclopride binding, exhibited a significant decrease in lateral divisions of the striatum. Significant increases in D2-like receptors, as determined by [3H]nemonapride binding, were observed in most divisions of the striatum as well as in septum, hippocampus, and piriform cortex. This D2-like fraction most probably corresponds to the D4 receptor subtype. In the cerebellum of Nna1pcd mice, D2-like receptors were significantly decreased in the molecular layer. The results suggest an increased excitatory input on the dopaminergic mesencephalic neurons and an alteration of the dopaminergic neurotransmission in basal ganglia, cortical and limbic regions of the Nna1pcd mutant mouse. In the cerebellum, the significant downregulation of the dopamine transporters and D2-like receptors in the mutant cerebellar molecular layer is possibly due to the absence of the Purkinje cells.

The secretory granule-associated protein CAPS2 regulates neurotrophin release and cell survival

Neurotrophins are key modulators of various neuronal functions, including differentiation, survival, and synaptic plasticity, but the molecules that regulate their secretion are poorly understood. We isolated a clone that is predominantly expressed in granule cells of postnatally developing mouse cerebellum, which turned out to be a paralog of CAPS (Ca2+-dependent activator protein for secretion), and named CAPS2. CAPS2 is enriched on vesicular structures of presynaptic parallel fiber terminals of granule cells connecting postsynaptic spines of Purkinje cell dendrites. Vesicle factions affinity-purified by the CAPS2 antibody from mouse cerebella contained significant amounts of neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF), and chromogranin B but not marker proteins for synaptic vesicle synaptophysin and synaptotagmin. In cerebellar primary cultures, punctate CAPS2 immunoreactivities are primarily colocalized with those of NT-3 and BDNF and near those of a postsynaptic marker, postsynaptic density-95, around dendritic arborization of Purkinje cells. Exogenously expressed CAPS2 enhanced release of exogenous NT-3 and BDNF from PC12 cells and endogenous NT-3 from cultured granule cells in a depolarization-dependent manner. Moreover, the overexpression of CAPS2 in granule cells promotes the survival of Purkinje cells in cerebellar cultures. Thus, we suggest that CAPS2 mediates the depolarization-dependent release of NT-3 and BDNF from granule cells, leading to regulation in cell differentiation and survival during cerebellar development.

Glucose-6-phosphate dehydrogenase supports the functioning of the synapses in rat cerebellar cortex

This study investigates heterogeneous glucose-6-phosphate dehydrogenase (G6PD) expression in the rat cerebellar cortex. G6PD activity and its electrophoretic pattern, evaluated on the cerebellar homogenate, were found to be similar to those of other brain areas. However, histochemical and immunohistochemical analyses revealed that the highest expression of G6PD activity and protein was in Purkinje's cells, followed by the molecular and granular layers. Electron microscopy analysis showed that, in Purkinje's cells, the G6PD reaction products were concentrated in the neurites while in the basket cells in the cell body. The granules showed a weaker activity everywhere. The quantitative distribution of G6PD is discussed in the light of the neurochemical function of these cells.

Ectopic expression of tyrosine hydroxylase in Zebrin II immunoreactive Purkinje cells in the cerebellum of the ataxic mutant mouse, pogo

The pogo mouse is a new ataxic autosomal recessive mutant that arose in an inbred strain (KJR/MsKist) derived from a Korean wild mouse. The phenotype includes difficulty in maintaining normal posture and the inability to walk straight. Several previous studies have associated inherited ataxia with the ectopic expression of tyrosine hydroxylase (TH) in Purkinje cells. Therefore, in the present study, the distribution of TH expression was compared with that of zebrin II in Purkinje cells of adult pogo/pogo mutant mice. In normal control littermates, tyrosine hydroxylase immunoreactivity is confined to a delicate axonal plexus ramifying through the molecular layer. In pogo/pogo, in addition to the axonal plexus, TH-immunoreactive Purkinje cells were present in all lobules of the cerebellar vermis and hemispheres, distributed as series parasagittal bands. The general pattern of expression is reproducible between individuals and symmetrical about the midline. Alternating stripes of TH expression are also seen in the hemispheres, and most Purkinje cells in the paraflocculi and flocculi are immunoreactive. In pogo/+ mice, TH-immunoreactive Purkinje cells are rare. The pattern of zebrin II expression was used to map TH immunoreactive Purkinje cells in pogo/pogo mutant mice. Double immunofluorescence labeling combining anti-zebrin II fand anti-TH showed that all TH-immunoreactive Purkinje cells are zebrin II+, but that many zebrin II+ Purkinje cells within a band do not stain with anti-TH. Taken together with the morphological changes observed in the Purkinje cell axons, this suggests that abnormal Purkinje cell function may contribute to the ataxic phenotype in pogo/pogo mice.

Neurotransmitters, neuropeptides and calcium binding proteins in developing human cerebellum: a review

Many endogenous neurochemicals that are known to have important functions in the mature central nervous system have also been found in the developing human cerebellum. Cholinergic neurons, as revealed by immunoreactivities towards choline acetyltransferase or acetylcholinesterase, appear early at 23 weeks of gestation in the cerebellar cortex and deep nuclei. Immunoreactivities gradually increase until the first postnatal month. Enkephalin is localized in the developing cerebellum, initially in the fibers of the cortex and deep nuclei at 16-20 weeks and then also in the Purkinje cells, granule cells, basket cells and Golgi cells at 23 weeks onward. Another neuropeptide, substance P, is localized mainly in the fibers of the dentate nucleus from 9 to 24 weeks but substance P immunoreactivity declines thereafter. GABA, an inhibitory neurotransmitter of the central nervous system, starts to appear at 16 weeks in the Purkinje cells, stellate cells, basket cells, mossy fibers and neurons of deep nuclei. GABA expression is gradually upregulated toward term forming networks of GABA-positive fibers and neurons. Catecholaminergic fibers and neurons are also detected in the cortex and deep nuclei at as early as 16 weeks. Calcium binding proteins, calbindin D28K and parvalbumin, make their first appearance in the cortex and deep nuclei at 14 weeks and then their expression decreases toward term, while calretinin appears later at 21 weeks but its expression increases with fetal age. The above findings suggest that many neurotransmitters, neuropeptides and calcium binding proteins (1) appear early during development of the cerebellum; (2) have specific temporal and spatial expression patterns; (3) may have functions other than those found in the mature neural systems; and (4) may be able to interact with each other during early development.

Decreased locomotor activity after microinjection of dopamine D2/D3 receptor agonists and antagonists into lobule 9/10 of the cerebellum: a D3 receptor mediated effect?

The restricted localization of dopamine (DA) D3 receptors in the rat cerebellum lobule 9/10 appears to provide a method for investigating the in vivo selectivity of dopaminergic compounds for the D3 receptor subtype. Sprague-Dawley rats implanted with a cannula aimed at lobule 9/10 were microinjected with DA receptor ligands and immediately placed into activity chambers to record their spontaneous locomotor activity for short term (0 to 20 min) and delayed (20 to 40 min) effects. The DA D2/D3 receptor agonists quinelorane (0.1 to 2.5 microg) and 7-OH-DPAT (0.1 to 10 microg) decreased locomotor activity in the first 20 min post-microinjection. In contrast, the DAD1, receptor agonist 6-Br-APB (0.1 to 10 microg) did not affect locomotor activity during this time period, but markedly increased locomotion between 20 and 40 min at the highest dose tested. The DA receptor antagonists haloperidol and raclopride (1 to 10 microg) were also found to reduce locomotor activity. Furthermore, quinelorane and 7-OH-DPAT, but not haloperidol, when microinjected into lobules 1/2 or 6/7 (where no DA D3 receptors have been detected) decreased locomotor scores. These results show that both DA receptor agonists and antagonists decrease locomotor activity when microinjected into lobule 9/10 of the cerebellum. Additionally, DA receptor agonists can reduce spontaneous locomotion when microinjected outside of lobule 9/10. This would suggest that, at least for quinelorane and 7-OH-DPAT, the locomotor decreasing effects following microinjection into cerebellar lobule 9/10 may not be mediated by activity at DA D3 receptors, and that this behavioural assay is unlikely to provide a means for studying the in vivo pharmacology of the DA D3 receptor.

4.5 kb of the rat tyrosine hydroxylase 5' flanking sequence directs tissue specific expression during development and contains consensus sites for multiple transcription factors

To delineate DNA sequences responsible for developmentally correct expression of the rat tyrosine hydroxylase (TH) gene, we analyzed a line of transgenic mice expressing high levels of human placental alkaline phosphatase (AP) under control of 4.5 kb of 5' flanking DNA from the rat TH gene in embryos and adults. Several regions, such as the accessory olfactory bulb, which were not thought to synthesize TH protein or do so only transiently, were shown to express TH protein using an improved method of antigen retrieval for TH immunohistochemistry. Many of these regions had been shown to express TH-driven reporter genes in transgenic mice. In the central nervous system, AP was detected in essentially all TH-expressing cell groups throughout development and in adults. In the peripheral nervous system, transgene expression paralleled endogenous TH expression in the developing adrenal medulla and sympathetic ganglia but not in transiently TH-positive cells in dorsal root ganglia. Peripheral expression in the adult adrenal medulla was very weak and absent in sympathetic ganglia. The specificity with which the 4.5 kb region directs transgene expression in embryos is comparable to that observed with longer 5' flanking promoter regions, implying that this region contains the control elements for appropriate expression during development. Sequence analysis of the region demonstrates a GT dinucleotide repeat, an element that resembles the neural restrictive silencer element (NRSE), which restricts transcription of neuronal genes in non-neuronal cells, and consensus sites for three families of transcription factors, Ptx1/3, Nurr1 and Gli1/2, which are required for the early differentiation of mesencephalic neurons.

Monoamine oxidase activity in noradrenaline neurons of the locus coeruleus of the rat. A double-labeling histochemical study

The aim of the present study is to examine whether noradrenergic neurons of the locus coeruleus (LC) of the rat contain monoamine oxidase (MAO) activity. Sections were processed initially for MAO enzyme histochemistry using tyramine as a substrate, followed by fluorescence immunohistochemistry for tyrosine hydroxylase (TH). In the LC, virtually all TH-immunoreactive neurons (i.e., noradrenergic neurons) were also positive for MAO. No MAO activity was found in any TH-negative neurons. Neurons in the LC have previously been shown to form dopamine during noradrenaline biosynthesis and to produce serotonin from exogenously administered l-5-hydroxytryptophan. Moreover, dopamine- and serotonin-degrading MAO activity has also been found in LC neurons. Therefore, our results indicate that MAO activity is localized within noradrenergic neurons in the LC and is likely involved in the degradation of dopamine that is endogenously synthesized, and also in the elimination of serotonin that is produced from exogenous precursors.

Integrin alpha1 localization in murine central and peripheral nervous system

The distribution of neurons expressing integrin alpha1 subunit protein (INTalpha1) was examined in adult mouse tissues of not only the central nervous system, but also the sympathetic ganglia, and the adrenal gland by immunohistochemistry and immunoelectron microscopy. INTalpha1-positive neurons were observed in most tissues examined, and most of them were found to coexpress tyrosine hydroxylase (TH) except for Purkinje cells and hippocampal neurons. Expression of INTalpha1 was also observed in the malpositioned cortical neurons in reeler mutants, and appeared not to be affected by the aberrant cell migration of the reeler cortical neurons. In situ hybridization showed that the expression of INTalpha1 mRNA was correlated with synthesis of the INTalpha1 protein in each case, and this finding indicated that expression of the protein was controlled by transcriptional regulation of the INTalpha1 gene.

CRE and TRE sequences of the rat tyrosine hydroxylase promoter are required for TH basal expression in adult mice but not in the embryo

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamine neurotransmitters, is expressed in a restricted number of areas, and subject to numerous regulations during development and in adulthood. Two transcription factor binding sites present in the proximal region of the TH gene, the TPA-responsive element (TRE) and the c-AMP responsive element (CRE), have been shown to play important roles in TH gene regulation in vitro. In order to elucidate in vivo the role of these two sites, we produced transgenic mice bearing a 5.3-kb fragment from the 5' flanking sequence of the TH gene with mutations in either the CRE-or TRE-sites. Using the intact 5.3-kb fragment fused to two different reporter genes (HSV1-tk and lacZ), we show that this promoter fragment is able to specifically direct expression in catecholaminergic tissues both in adult mice and embryos. Interestingly, the CRE- and TRE-mutated transgenes were not expressed in adult mice, contrary to the situation in embryos where they were specifically expressed in catecholaminergic regions. These results demonstrate that the CRE and TRE play an essential role in basal TH expression in adult tissues in vivo. Moreover, they suggest that distinct transcription factors are involved in TH regulation in developing and adult tissues. In support of this, gel mobility shift experiments revealed a complex present only in embryonic tissues. Taken together, these data highlight the diversity of the mechanisms underlying the establishment and maintenance of the catecholaminergic phenotype.

Galanin messenger RNA during postnatal development of the rat brain: expression patterns in Purkinje cells differentiate anterior and posterior lobes of cerebellum

Following our initial mapping of preprogalanin messenger RNA in adult brain and its presence in a subpopulation of cerebellar Purkinje neurons [Ryan M. C. and Gundlach A. C. (1996) Neuroscience 70, 709-728], the present study examined the ontogenic expression of preprogalanin messenger RNA in the postnatal rat brain focussing on the Purkinje cells of the cerebellar cortex. Using in situ hybridization histochemistry, preprogalanin messenger RNA was detected in the developing forebrain and hindbrain from postnatal day 4 to day 60 (adult). On postnatal day 4 very light hybridization signal (labelling) was observed in cells of a number of nuclei including the central amygdaloid nucleus, the medial preoptic area, paraventricular nucleus and dorsomedial hypothalamic nucleus of the forebrain while lightly-labelled cells were detected in neurons of the nucleus of the solitary tract and locus coeruleus of the hindbrain. Hybridization signal was not apparent in other nuclei until later, with positively-labelled neurons first apparent in the dorsal cochlear nucleus at postnatal day 21. The abundance of preprogalanin messenger RNA-positive neurons and the intensity of the hybridization signal increased, in most regions, until postnatal day 28 when labelling resembled that of the mature rat. Preprogalanin messenger RNA was first detected in the cerebellum on postnatal day 10 only in Purkinje cells of lobule 10 of the posterior vermis and increased in distribution throughout Purkinje cell layers of the entire cerebellar cortex by postnatal day 13. The intensity of hybridization signal in Purkinje cells varied between lobules, with Purkinje cells in lobule 10 displaying a moderate to heavy degree of labelling, while lobules 6-9 and the more posterior lobules of the hemisphere including crus 2 of the ansiform lobule, the paramedian lobule and the copula pyramis, displayed only light labelling. The intensity of labelling in the anterior vermis and the remaining lobules of the hemisphere including crus 1 of the ansiform lobule, the simple lobule, the paraflocculus and the flocculus, was homogeneously weak. By postnatal day 21, Purkinje cell labelling reached maximum intensity in all lobules. Regional differences were still apparent, however, with labelling in the posterior vermis and hemisphere ranging from moderate to heavy, with only light to moderate labelling detected in the anterior vermis. The intensity of labelling in the posterior vermis and most lobules of the hemisphere was similar from postnatal day 21 to adulthood, while, in the anterior vermis, crus 1 of the ansiform lobule and the simple lobule, the intensity of hybridization decreased slightly by postnatal day 28 and was completely absent in Purkinje cells of the adult rat. Differential expression of preprogalanin messenger RNA in Purkinje cells of the developing rat cerebellum and transient expression in certain lobules suggests that galanin gene products may have a role in both the developing and mature rat brain and that galanin gene expression may represent a useful marker for differentiating the anterior and posterior cerebellar lobes.

Distribution of tyrosine hydroxylase-immunoreactive afferents to the cerebellum differs between species

The indirect antibody peroxidase-antiperoxidase technique was used to determine the laminar and lobular distribution of catecholaminergic afferents in the adult mouse, opossum, and cat cerebellum. A monoclonal antibody to tyrosine hydroxylase (TH) revealed a plexus of thin varicose fibers that exhibited a different density and distribution pattern for each species. In the cat, TH-immunoreactive fibers were sparsely distributed to all laminae, lobules, and nuclei of the cat cerebellum except for an area of elevated density in the ventral folia of lobules V and VI. In the opossum, TH-positive fibers were uniformly and densely distributed in the granule and Purkinje cell layers; they were more abundant in vermal lobules V-VI than in more anterior and posterior lobules, particularly I and X. Numerous TH-immunoreactive fibers were found in all four cerebellar nuclei of the opossum. In the mouse, TH-positive fibers formed a dense plexus within all cerebellar lobules, laminae, and nuclei. The mouse also exhibited numerous TH-immunoreactive Purkinje cells that were localized predominantly within vermal lobules VI-X, the paraflocculus, and flocculus. In addition to the interspecies differences in the distribution of catecholaminergic fibers within the cerebellum, comparison of this plexus to that previously described for serotonin in these species reveals that the relative densities and distribution patterns of catecholaminergic and serotoninergic fibers also vary between species. It is thus hypothesized that in each species a given monoamine has a unique net effect on cerebellar output that is determined by its effects on different neuronal populations within the cerebellum.

Localization of preprogalanin messenger RNA in rat brain: identification of transcripts in a subpopulation of cerebellar Purkinje cells

Galanin, a 29 amino acid peptide, is widely distributed throughout both the peripheral and central nervous systems and is thought to be involved in multiple physiological functions including smooth muscle relaxation, stimulation of feeding, blood pressure regulation, control of hormone secretion and modulation of nociception. Galanin has been shown to co-exist with several neurotransmitters throughout the neuroaxis and in some cases to modify their presynaptic and postsynaptic actions. In the present study, the anatomical distribution of preprogalanin messenger RNA in rat brain was examined by in situ hybridization histochemistry using specific 35S-labelled oligonucleotide probes. Neurons expressing preprogalanin messenger RNA were found throughout the brain and were particularly abundant in the hypothalamus. High densities of preprogalanin messenger RNA-positive neurons were found in the anteroventral preoptic, supraoptic, paraventricular and dorsomedial nuclei of the hypothalamus, in the locus coeruleus and in the nucleus of the solitary tract. Moderate densities of preprogalanin messenger RNA-positive cells were apparent in the periventricular and arcuate nuclei of the hypothalamus, in the dorsal raphe and dorsal cochlear nuclei. Low densities of preprogalanin messenger RNA-expressing neurons were observed in the piriform cortex, medial septum and the retrochiasmatic area. These findings are consistent with results of previous in situ localization studies of preprogalanin messenger RNA and also with studies reporting the distribution of galanin-like immunoreactivity in rat brain. A novel finding, however, was the detection of preprogalanin messenger RNA in Purkinje cells in the caudal cerebellar vermis (lobules 6 to 10) and the flocculus and paraflocculus of the lateral hemispheres of the cerebellum. Galanin is presumably co-localized in these cells with GABA, which is normally present in Purkinje cells and possibly with tyrosine hydroxylase, which has recently been detected in a similar subpopulation of cerebellar Purkinje cells in both rat and mouse. Thus, the present study reveals a previously unreported site of galanin gene expression in the cerebellum which represents a novel, putative site of action for galanin to add to its already varied physiological roles.

Activation of dopamine D4 receptor inhibits an L-type calcium current in cerebellar granule cells

The functions of the D4 receptor, a newly cloned D2-like receptor, as well as the identity of cells expressing it, are still poorly defined. Using quantitative polymerase chain reaction we detected the messenger RNA of the D4, but not other D2-like receptor, in cultured granule cells from neonatal rat cerebellum. In these neurons, dopamine reduced high-voltage-activated calcium current, with a pharmacology corresponding to that of the D4 receptor. The response declined from one to three days, when calcium currents were mostly sensitive to nifedipine, to 15 days, when nifedipine-insensitive calcium currents were also present and D4 receptor messenger RNA had declined. The dopamine response was abolished after pretreatment of the cells by pertussis toxin, was potentiated and made irreversible by infusion of guanosine 5'-O-(3-thiotriphosphate) but persisted in the presence of cyclic AMP and isobutylmethylxanthine. These results indicate the presence in the neonatal cerebellum of a functional D4 receptor inhibiting an L-type calcium current, an action involving a Gi/Go protein but independent from adenylate cyclase inhibition.

Enhanced expression of tyrosine hydroxylase and aromatic L-amino acid decarboxylase in cerebellar Purkinje cells of mouse after hyperosmotic stimuli

We examined by immunohistochemistry the effect of salt loading on the expression of tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), and GTP cyclohydrolase I (GCH) in Purkinje cells of the mouse cerebellum. In control mice, only a few Purkinje cells were positive for TH or AADC. No Purkinje cells were stained for GCH. Drinking 2% sodium chloride for 2 weeks resulted in an increase in the number of TH- or AADC-positive Purkinje cells in the caudal vermis, paraflocculus and flocculus of the cerebellum. In contrast, no Purkinje cells were immunoreactive to GCH or L-DOPA after the salt loading. The present findings suggest that the salt loading differentially affects the expression of TH, AADC and GCH in Purkinje cells of the mouse cerebellum.

Phenotypical characterization of neurons expressing the dopamine D3 receptor in the rat brain

We have established the cellular distribution of the dopamine D3 receptor using tritiated 7-hydroxy-N-N-di-n-propyl-2-aminotetralin and a complementary RNA probe to visualize autoradiographically the protein in binding studies and the gene transcripts by in situ hybridization, respectively. Studies with these two markers confirm the restricted expression of the D3 receptor in few brain areas, i.e. mainly the ventral striatal complex, the substantia nigra-ventral tegmental area and the cerebellum. In nucleus accumbens, the D3 receptor was mainly expressed in medium-sized neurons of the rostral pole and ventromedial shell subdivisions, but not of the core or septal pole, i.e. accumbal subdivisions expressing the D2 receptor. In the ventromedial shell, about 60% of the D3 receptor-expressing neurons were neurotensin neurons, presumably projecting to the ventral pallidum. In the islands of Calleja, both D3 receptor binding and messenger RNA were abundant in the entire population of granule cells. These cells are known to make sparse contacts with dopaminergic axons and also to express the D1 receptor. In the mesencephalon, low levels of D3 messenger RNA were detected in few dopamine neurons of substantia nigra pars lateralis and ventral tegmental area. In addition, some D3 receptor binding but not messenger RNA was detected in medial substantia nigra and lateral ventral tegmental area, where the receptor is presumably located presynaptically on afferents. In the archicerebellum, Purkinje cell perikarya in lobules 9 and 10 expressed the D3 receptor messenger RNA, whereas binding sites were found in the molecular layer, where corresponding dendrites but no known dopaminergic projection from mesencephalon are found. The occurrence of D3 receptor gene expression in some brain areas receiving low dopamine innervation supports the hypothesis that this receptor may mediate non-synaptic actions of dopamine.

DNA regulatory sequences of the rat tyrosine hydroxylase gene direct correct catecholaminergic cell-type specificity of a human growth hormone reporter in the CNS of transgenic mice causing a dwarf phenotype

Transgenic mice bearing 4.8 kilobases (kb) of upstream rat tyrosine hydroxylase (TH) sequences linked to a human growth hormone gene (hGH) exhibited cell-specific expression of hGH in all the appropriate catecholaminergic neurons in the central nervous system (CNS), although with different penetrance in two different mouse lineages. No ectopic expression was observed in any brain or peripheral region in one founder and its progeny. In another founder there was some ectopic expression in addition to appropriate and high levels of tissue-specific expression in all catecholaminergic areas. These results identify regulatory sequences that are sufficient for targeting expression to all catecholaminergic CNS neurons. Also, expression of exogenous hGH in the hypothalamus caused a dwarf phenotype, generating a novel genetic model for GH deficiency of hypothalamic origin.

Immunohistochemical demonstration of expression of tyrosine hydroxylase in cerebellar Purkinje cells of the human and mouse

We demonstrated the expression of tyrosine hydroxylase (TH) and phenylethanolamine-N-methyltransferase (PNMT) in cerebellar Purkinje cells of human and mouse brains by immunohistochemistry. At the age of 8 months, vermal Purkinje cells in the human cerebellum were immunoreactive with anti-TH or anti-human specific PNMT antiserum. We also found TH-positive Purkinje cells in the mouse brain. TH immunoreactivity first appeared in the Purkinje cells in the caudal vermis from postnatal day 8 (P8), and enlarged numbers between P13 and P15. After gradual reduction to P19, the TH-positive Purkinje cells again multiplied the number from the age of 4 weeks, and maintained in a large number up to old stage. At the age of 11 months, the other groups of TH-positive Purkinje cells appeared in the flocculus and paraflocculus of the mouse cerebellum.