Impact of the COMT Val(108/158)Met polymorphism on the mu-opioid receptor system in the human brain: mu-opioid receptor, met-enkephalin and beta-endorphin expression

The Val^108/158Met polymorphism of the catechol-O-methyltransferase gene (COMT) is known to interact with the function of various neuroreceptor systems in the brain. We have recently shown by post-mortem receptor autoradiography that the number of mu-opioid (MOP) receptor binding sites depends on the number of COMT Met^108/158 alleles in distinct human brain regions. We now investigated COMT Val^108/158Met related levels of the MOP receptor protein and its endogenous ligands met-enkephalin and beta-endorphin in the human frontal cortex, thalamus and basal ganglia. Semiquantitative immunostaining and in situ hybridization were applied in a cohort of 17 human brain tissues from healthy donors. MOP receptor protein levels paralleled previous ligand binding results with a significantly higher MOP receptor expression in the mediodorsal nucleus of the thalamus of COMT Met^108/158 allele carriers. Also met-enkephalin peptide levels correlated with the genotype in this structure, with the lowest expression in COMT Met^108/158 homozygous individuals. Beta-endorphin was not detectable in the cortex, basal ganglia or thalamus, and therefore is unlikely to contribute to changes of the MOP receptor system. These results confirm the impact of the COMT Val^108/158Met polymorphism on the MOP receptor system and may support the hypothesis of an enkephalin related turnover of MOP receptors at least in some brain structures.     

Correlation of iron deposition and change of gliocyte metabolism in the basal ganglia region evaluated using magnetic resonance imaging techniques: an in vivo study

Introduction

We assessed the correlation between iron deposition and the change of gliocyte metabolism in healthy subjects’ basal ganglia region, by using 3D-enhanced susceptibility weighted angiography (ESWAN) and proton magnetic resonance spectroscopy (¹H-MRS).

Material and methods

Seventy-seven healthy volunteers (39 female and 38 male subjects; age range: 24–82 years old) were enrolled in the experiment including ESWAN and proton MRS sequences, consent for which was provided by themselves or their guardians. For each subject, the mean phase value gained by ESWAN was used to evaluate the iron deposition; choline/creatine (Cho/Cr) and mI/Cr ratios gained by ¹H-MRS were used to evaluate gliocyte metabolism in the basal ganglia region of both sides. The paired t test was used to test the difference between the two sides of the basal ganglia region. Linear regression was performed to evaluate the relation between mean phase value and age. Pearson''s correlation coefficient was calculated to analyze the relationship between the result of ESWAN and ¹H-MRS.

Results

There was no difference between the two sides of the basal ganglia region in the mean phase value and Cho/Cr. But in mI/Cr the mean phase value of each nucleus in bilateral basal ganglia decreased with increasing age. There are 16 r-values between the mean phase value and Cho/Cr and mI/Cr in bilateral basal ganglia region. And each of all p-values is less than 0.001 (p < 0.001).

Conclusions

Iron deposition in the bilateral basal ganglia is associated with the change of gliocyte metabolism with increasing age. Iron deposition in each nucleus of the basal ganglia region changes with age.     

Neurogenesis in the basal forebrain of the Chinese hamster (Cricetulus griseus). I. Time of neuron origin.

Summary The time of neuron origin has been determined in the basal ganglia and related basal forebrain structures of the Chinese hamster with the aid of ³H-thymidine autoradiography. Large-celled structures like the globus pallidus, nucleus of the horizontal limb of the diagonal band of Broca as well as large cells in the rostral part of the substantia innominata, in the caudate-putamen-complex and in the olfactory tubercle arise early (E₁₂–E₁₆), whereas medium-sized and small cells in the basal forebrain have a persistent origin over a much longer period. Neuron formation in the basal forebrain persists decrementally until P₄. A clear caudorostral spatiotemporal gradient as well as a distinct outside-in gradient have been observed in the caudate-putamen-complex. Medium-sized neurons in the neostriatum and in the nucleus accumbens, generated simultaneously, are usually arranged in scattered clusters. The present data on time of neuron origin strongly support other evidence which points to the conclusion that the nucleus accumbens can be considered as a ventromedial extension of the caudate-putamen-complex.     

Expression of cholecystokinin, somatostatin, thyrotropin-releasing hormone, glutamic acid decarboxylase and tyrosine hydroxylase genes in the central nervous motor systems of the genetically dystonic hamster

In the dt ^sz mutant hamster with idiopathic generalized dystonia, functional abnormalities of several neurotransmitters have been suggested to play a role in the development of symptoms. In the present study, we have used histochemistry with ³⁵S-ATP labeled oligonucleotides to determine whether these abnormalities are associated with modulation in the expression of neurotransmitter genes in motor regions. We examined the expression of genes encoding cholecystokinin (CCK), somatostatin (SRIF), thyrotropin-releasing hormone (TRH), glutamic acid decarboxylase (GAD), tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP43) in the cortex and basal ganglia of dystonic hamsters and of non-dystonic control hamsters of a related inbred line and of a non-related outbred line. The distribution of these mRNAs in normal hamster brain was similar to that in normal rat brain. In all cortical regions studied (frontal, parietal and piriformis), the expression of CCK was similar in dystonic and inbred controls but was significantly greater than in outbred controls. In the anterior thalamus, CCK expression was lower in dystonic hamsters than in both control groups. SRIF expression was significantly decreased in the cortex and striatum of dystonic animals than in inbred and outbred control hamsters. GAD expression was lower in the striatum and substantia nigra, pars reticulata of dystonic than in outbred hamsters, but similar values were found in all groups in the other regions studied. TH was lower in the substantia nigra of dystonic than in inbred controls. No changes were found in GAP43 expression. This study demonstrates that changes in modulation of the expression of some peptides and neurotransmitter enzymes can be found in the dystonic hamster, which is in contrast to other animal models such as the dystonic rat, where no such changes have been found. The present data are consistent with previous findings in dt ^sz hamsters that suggest a dysfunction within the basal ganglia-thalamocortical circuits. Received: 29 June 1998 / Accepted: 17 May 1999     

Primate models of dystonia

Several models of dystonia have emerged from clinical studies providing a comprehensive explanation for the pathophysiology of this movement disorder. However, several points remain unclear notably concerning the specific role of brainstem, basal ganglia nuclei and premotor cortex. We review data collected in sub-human primate to see whether they might provide new insights into the pathophysiology of dystonia. As in human patients, lesions of the putamen induce dystonia, as well as pharmacological manipulations of the dopaminergic system. In addition, primate studies revealed that lesions in brain stem areas involved in the control of muscular tone and GABAergic manipulations in various basal ganglia nuclei or thalamus also lead to dystonia. Moreover, there is a dramatic disruption in the processing of proprioceptive information with abnormal large receptive fields in the basal ganglia, thalamus, primary somesthetic cortex and premotor cortex of dystonic monkeys. These data highlight the idea that dystonia is associated with aberrant sensory representations interfering with motor control. Considering that the supplementary motor area (SMAp) is the target of basal ganglia projections within the motor loop, we propose a model of dystonia in which abnormal excitability, associated with alteration in sensory receptive fields within the SMAp, leads to an abnormal synchronization between primary motor cortex columns. Such a phenomenon might account for the co-contractions of antagonist muscles favored by action and the abnormal postures observed in dystonia.     

In - Vitro Propagation and Antimycotic Potential of Extracts and Essential Oil of Roots of Aristolochia Bracteolata Linn. (Aristolochiaceae)

In spite of the therapeutic importance of Aristolochia bracteolata Linn. in Nigerian ethnomedicine, it is largely collected from the wild. Owing to the acclaimed potency of the plant and the difficulty in treating candidiasis, the anticandidal activity and in vitro propagation of the plant were investigated. Phytochemical screening and preparation of extracts of the roots were done using standard procedures. Clinical isolates of Candida albicans were screened against extracts and essential oil of Aristolochia bracteolata root using agar-well diffusion method. Minimum Inhibitory Concentration (MIC) of the ethanol extract was determined using broth dilution method. The nodal cuttings of A. bracteolata were cultured on Murashige and Skoog (MS) basal media. A. bracteolata contained alkaloids, saponins and cardenolides. The water extract was inactive on all isolates. The ethanol extract (500 mg/ml) and essential oil (undiluted) exhibited anticandidal activity on 9 out of 10 isolates at 10¹ − 10⁶ cfu/ml inoculums concentration. Green growth and callus formation were observed in explants cultured on MS basal media after 30 days. A. bracteolata could be a source of anticandidal phytomedicine and the in vitro propagation confirmed its sustainability as anticandidal agent.     

Motor deficits and neurofibromatosis type 1 (NF1)‐associated MRI impairments in a mouse model of NF1

Neurofibromatosis type 1 (NF1) is a genetic disorder characterized inter alia by cognitive and motor dysfunction and appearance of high‐signal foci on T2‐weighted images in the brain. Nf1^+/? mice are useful models for studying aspects of NF1, including cognitive deficits. Here we assessed their motor performance and used quantitative transverse T2 relaxation MRI to identify structural abnormalities in their brains. Nf1^+/? mice exhibited both enhanced and reduced T2 signals in distinct brain regions compared to wild‐type mice, and their motor performance was impaired. As in NF1 patients, enhanced T2 signals in Nf1^+/? mice were observed in the thalamus and basal ganglia. Reduced T2 signals were seen in motor‐associated regions along the motor pathway, predominantly in the white matter of the cerebral peduncle and the optic tract. Correlation analysis between T2 signals and motor performance suggested that the motor deficits are associated with impairments in the cerebral peduncle and the amygdala. Copyright © 2010 John Wiley & Sons, Ltd.     

Nax-deficient mice show normal vasopressin response to dehydration

In dehydrated animals, the antidiuretic hormone vasopressin (VP) is released from the nerve terminals of magnocellular neurons of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) into the systemic circulation at the posterior pituitary. Increases in sodium (Na⁺)-level and osmolality in body fluids upon dehydration are reportedly sensed by a Na⁺-sensor and/or an osmosensor, respectively. However, it is still unknown whether both are involved in the regulation of production and/or release of VP. Na_x is the cerebral Na⁺-level sensor and Na_x-knockout mice do not stop ingesting salt even when dehydrated. Here we examined VP production/release in Na_x-knockout mice, and found that they are normal in the VP response to dehydration or intraperitoneal-administration with hypertonic saline. In situ hybridization using an intron-specific probe showed that VP gene expression in the SON did not differ from wild-type mice when dehydrated. Also, there was no significant difference in the activity of subfornical organ neurons projecting to the SON between the two genotypes when stimulated by water deprivation. Furthermore, Na_x-knockout mice showed a normal response in urine excretion to dehydration. All these results indicate that the information of Na⁺-level increase detected by Na_x does not contribute to the control of VP production/release.     

A paleostriatal-thalamic-telencephalic path in pigeons

The efferent connections of the thalamic nucleus dorsointermedius posterior were studied in the pigeon. In pigeons, this thalamic nucleus receives both paleostriatal (basal ganglia) and cerebellar input and has been compared to nuclei of the mammalian thalamic ventral tier on this basis. The present results show that neurons of nucleus dorsointermedius posterior project upon a crescent-shaped neuronal field within the neostriatum intermedium as well as upon the ventral paleostriatum and nucleus intrapeduncularis. The relationship of the neostriatum intermedium field to avian motor pathways is discussed and it is suggested that nucleus dorsointermedius posterior thalami of birds may play a role comparable to that of the mammalian ventral tier nuclei in the neural control of motor functions.The efferent projections of dorsointermedius posterior were contrasted with those of adjacent structures within the avian posterior thalamic complex. Neurons within nucleus dorsomedialis posterior appear to be related to the avian limbic system and project to a neuronal field within the rostromedial portion of the neostriatum intermedium. Neurons in nucleus dorsolateralis posterior have been shown to receive input from the optic tectum;¹² efferents from dorsolateralis posterior were traced to a small triangular wedged-shaped field within the ventromedial portion of the periectostriatal belt.     

SGCE isoform characterization and expression in human brain: implications for myoclonus–dystonia pathogenesis?

Myoclonus–dystonia (M–D) is a neurological movement disorder with involuntary jerky and dystonic movements as major symptoms. About 50% of M–D patients have a mutation in ɛ-sarcoglycan (SGCE), a maternally imprinted gene that is widely expressed. As little is known about SGCE function, one can only speculate about the pathomechanisms of the exclusively neurological phenotype in M–D. We characterized different SGCE isoforms in the human brain using ultra-deep sequencing. We show that a major brain-specific isoform is differentially expressed in the human brain with a notably high expression in the cerebellum, namely in the Purkinje cells and neurons of the dentate nucleus. Its expression was low in the globus pallidus and moderate to low in caudate nucleus, putamen and substantia nigra. Our data are compatible with a model in which dysfunction of the cerebellum is involved in the pathogenesis of M–D.     

Association between the Catechol-O-Methyltransferase (COMT) Val158Met Polymorphism and Alexithymia in Patients with Obsessive-Compulsive Disorder

PurposeAlexithymia, defined as a deficit in the ability to recognize and describe one''s own feelings, may be related to the development and maintenance of obsessive-compulsive symptoms. The aim of this study was to evaluate the association between the catechol-O-methyltransferase (COMT) Val¹⁵⁸Met polymorphism and alexithymia in patients with obsessive-compulsive disorder (OCD).ResultsPatients with the COMT Val/Val genotype had significantly higher total and "difficulty identifying feelings" (DIF) subdimension scores than those with the Val/Met or Met/Met genotypes. Patients with the COMT Val/Val genotype had significantly higher "difficulty describing feelings" (DDF) subdimension scores than those with the COMT Val/Met genotype. However, there were no differences in the scores for the "externally oriented thinking" (EOT) subdimension among the three genotypes.ConclusionThese results indicate that the high-activity Val allele of the COMT Val¹⁵⁸Met polymorphism is associated with increased alexithymic traits in patients with OCD. The present finding suggests that alexithymia is an endophenotype of OCD that is mediated by the COMT Val¹⁵⁸Met polymorphism.     

A single amino acid in the helicase domain of PMMoV-S is responsible for its enhanced accumulation in C. chinense (L(3)L(3)) plants at 32°C

In Capsicum chinense (L³L³) plants a higher accumulation of the tobamovirus Pepper mild mottle virus strain S (PMMoV-S) as compared to the Italian strain PMMoV-I is detected when plants are grown at 32 °C. By using a reverse genetic approach, we have established that a single amino acid at position 898 in the helicase domain of the polymerase protein, outside of the conserved regions of the helicase, is critical for the higher accumulation of PMMoV-S observed. It also is necessary for both increased accumulation of viral RNA of both polarities in pepper protoplasts and enhanced cell-to-cell movement in C. chinense plants. The influence of thermoresistance of PMMoV-S, a P_1,2 pathotype, and its prevalence on pepper cultivars over PMMoV-I, a P_1,2,3, pathotype, is discussed.     

Selective blockade of serotonin2C receptor enhances Fos expression specifically in the striatum and the subthalamic nucleus within the basal ganglia

Serotonin_2C (5-HT_2C) receptors are widely expressed in the basal ganglia, a group of brain regions involved in the control of motor behavior. However, it remains unclear whether their tonic influence on neuronal activity is distributed in these regions. We have addressed this question by measuring the product of the proto-oncogene c-Fos in rats after peripheral administration of the non-selective 5-HT antagonist mianserin, the 5-HT_2C/2B antagonist SER-082 or the selective 5-HT_2C antagonist SB 243213. The intraperitoneal administration of 1 mg/kg of SB 243213 or SER-082, but not mianserin, enhanced Fos-immunoreactive cells in the subthalamic nucleus and the striatum, primarily its medial portion. None of these treatments significantly affected Fos expression in the external globus pallidus, the entopeduncular nucleus (the internal globus pallidus in primate) or the substantia nigra pars reticulata. The data suggest that selective blockade of 5-HT_2C receptors is necessary to unmask a tonic regulation of neuronal activity by this receptor in the basal ganglia and that this effect is restricted to the two structures receiving cortical entries, the striatum and the subthalamic nucleus.     

Pathophysiology of idiopathic dystonia: findings from genetic animal models

Dystonia is a common movement disorder which is thought to represent a disease of the basal ganglia. However, the pathogenesis of the idiopathic dystonias, i.e. the neuroanatomic and neurochemical basis, is still a mystery. Research in dystonia is complicated by the existence of various phenotypic and genotypic subtypes of idiopathic dystonia, probably related to heterogeneous dysfunctions.In neurological diseases in which no obvious neuronal degeneration can be found, such as in idiopathic dystonia, the identification of a primary defect is difficult, because of the large number of chemically distinct, but functionally interrelated, neurotransmitter systems in the brain.The variable response to pharmacological agents in patients with idiopathic dystonia supports the notion that the underlying biochemical dysfunctions vary in the subtypes of idiopathic dystonia. Hence, in basic research it is important to clearly define the involved type of dystonia.Animal models of dystonias were described as limited. However, over the last years, there has been considerable progress in the evaluation of animal models for different types of dystonia.Apart from animal models of symptomatic dystonia, genetic animal models with inherited dystonia which occurs in the absence of pathomorphological alterations in brain and spinal cord are described.This review will focus mainly on genetic animal models of different idiopathic dystonias and pathophysiological findings. In particular, in the case of the mutant dystonic (dt) rat, a model of generalized dystonia, and in the case of the genetically dystonic hamster (dt^sz), a model of paroxysmal dystonic choreoathetosis has been used, as these show great promise in contributing to the identification of underlying mechanisms in idiopathic dystonias, although even a proper animal model will probably never be equivalent to a human disease.Several pathophysiological findings from animal models are in line with clinical observations in dystonic patients, indicating abnormalities not only in the basal ganglia and thalamic nuclei, but also in the cerebellum and brainstem. Through clinical studies and neurochemical data several similarities were found in the genetic animal models, although the current data indicates different defects in dystonic animals which is consistent with the notion that dystonia is a heterogenous disorder.Different supraspinal dysfunctions appear to lead to manifestation of dystonic movements and postures. In addition to increasing our understanding of the pathophysiology of idiopathic dystonia, animal models may help to improve therapeutic strategies for this movement disorder.     

The corticosterone receptive system in the brain of Tupaia belangeri visualized by in vivo autoradiography

Summary The present investigation deals with in vivo binding of ³H-corticosterone in the brains of tree shrews as visualized by autoradiography. Tree shrews were injected with ³H-corticosterone and brain sections were mounted on slides which were subsequently exposed on tritium sensitive film. The relative labeling of 20 different brain structures was determined densitometrically. The indusium griseum, which demonstrated the highest binding for corticosterone of all brain regions in the autoradiograms, was taken as reference and defined as 100% relative labeling (RL). As in other species, the hippocampal subdivisions of the tree shrew retained high amounts of the steroid (60 to 80% RL). In other parts of the limbic system, medium labeling intensities were observed with approximately 40% RL in the lateral septum. The amygdala was less intensely labeled revealing around 30% RL in the basal accessory, the cortical, central, and the lateral nuclei. Autoradiographic grey values in the ventral striatum and pallidum were comparable to those in the amygdala, but in the islands of Callejae they were approximately as high as in the lateral septum (44% RL). In contrast to previous reports dealing with other species, the tree shrew cerebellum also demonstrated a high binding capacity for corticosterone. The RL was nearly 60% in the cerebellar granular layer. This finding may indicate that the cerebellum also plays a role in mediating the effects of corticosterone in the central nervous system.Abbreviations Acb nucleus accumbens - ADX adrenalectomy - BAA nucleus basalis accessorius amygdalae - BLA nucleus basalis lateralis amygdalae - BMA nucleus basalis medialis amygdalae - bv blood vessel - CD nucleus caudatus - Ce nucleus centralis amygdalae - ChP plexus choroideus - Co nucleus corticalis amygdalae - DG fascia dentata; gran, granule cells - Hip hippocampus - I nucleus intercalatus amygdalae - ICj insulae Callejae - Ig indusium griseum - IO nucleus olivaris inferior - LA nucleus lateralis amygdalae - LS nucleus lateralis septi - OT optic tract - RL relative labeling - S subiculum - SFi septofimbrial nucleus - SI substantia innominata - SHy nucleus septohypothalamicus - Tu olfactory tubercle     

Thalamic cholinergic innervation is spared in Alzheimer disease compared to parkinsonian disorders

There are two major sources of cholinergic projections in the brain. The nucleus basalis of Meynert provides the principal cholinergic input of the cortical mantle and the pedunculopontine nucleus–laterodorsal tegmental complex (PPN–LDTC; hereafter referred to as PPN) provides the major cholinergic input to the thalamus. Cortical cholinergic denervation has previously been shown to be part of Alzheimer and parkinsonian dementia but there is less information about subcortical thalamic cholinergic denervation. We investigated thalamic cholinergic afferent integrity by measuring PPN–Thalamic (PPN–Thal) acetylcholinesterase (AChE) activity via PET imaging in Alzheimer (AD), Parkinson disease without dementia (PD), Parkinson disease with dementia (PDD) and dementia with Lewy bodies (DLB). AD (n = 13; mean age 75.4 ± 5.5), PD (n = 11; age 71.4 ± 6.4), PDD (n = 6; age 70.8 ± 4.7), DLB (n = 6; age 68.0 ± 8.6) and normal controls (NC; n = 14; age 69.0 ± 7.5) subjects underwent AChE [¹¹C]-methyl-4-piperidinyl propionate (PMP) PET imaging. PPN–Thal PET data were analyzed using the Nagatsuka method. There were no significant differences in mean age between the groups (F = 1.86, p = 0.134). Kruskal–Wallis testing demonstrated a significant group effect for PPN–Thal AChE hydrolysis rates (F = 9.62, p < 0.0001). Compared to NC, reduced thalamic k3 hydrolysis rate was noted in subjects with PDD (−19.8%; AChE k3 hydrolysis rates 0.1072 ± 0.0143 min⁻¹), DLB (−17.4%; 0.1103 ± 0.0112 min⁻¹) and PD (−12.8%; 0.1165 ± 0.0114 min⁻¹). Each of these 3 subgroups was statistically different from AD subjects (−0.7%; 0.1326 ± 0.0095 min⁻¹) who showed relatively spared thalamic k3 hydrolysis rates which were comparable to NC (0.1336 ± 0.0142 min⁻¹). Thalamic cholinergic denervation is present in PD, PDD, and DLB but not in AD. Neurodegenerative involvement of thalamic cholinergic afferent projections may contribute to disease-specific motor and cognitive abnormalities.     

Membrane resonance and its ionic mechanisms in rat subthalamic nucleus neurons

The oscillatory activity in the basal ganglia is believed to have an important function, but little is known about its actual mechanisms. We studied the resonance characteristics of subthalamic nucleus (STN) neurons and their ionic mechanisms using whole-cell patch-clamp recordings in rat brain slices. A swept-sine-wave current with constant amplitude and linearly increasing frequency was applied to measure the resonance frequency (f_res) of STN neurons. We also used single-frequency sine wave current to evoke firing. We found that the resonance of STN neurons was temperature- and voltage-dependent. The f_res of STN neurons was about 4 Hz when the temperature was maintained at 38 °C and holding potential was at −70 mV. The f_res increased with more negative holding potentials and decreased with lower temperature. Action potentials fired most readily when the input frequency was near f_res. After application of drug ZD7288 (20 μM), the resonance of STN neurons was blocked and the spikes evoked by both impedance amplitude profile (ZAP) current and single-frequency sine wave current arose readily at the lowest frequencies, indicating that hyperpolarization-activated cation current (I_h) generated the resonance and mediated a preferential coupling at frequencies near f_res between inputs and firing. In conclusion, there is a θ-frequency resonance mediated by I_h in STN neurons. The resonance characteristics are temperature- and voltage-dependent. The resonance mediates a frequency-selective coupling between inputs and firing.     

Systematic differences in time of dopaminergic neuron origin between normal mice and homozygous weaver mutants

Immunocytochemical labeling for tyrosine hydroxylase and [³H]thymidine autoradiography were combined in wild-type mice and in mice homozygous for the weaver mutant gene (wv) to see whether the neurogenetic patterns of midbrain dopaminergic neurons was normal in the mutants and whether the degeneration of dopaminergic neurons was linked to their time of origin. Dams of wild-type and homozygous weaver mice were injected with [³H]thymidine on embryonic days (E) 11–E12, E12–E13, E13–E14, and E14-E15 to label neurons in the retrorubral field, the substantia nigra pars compacta, the ventral tegmental area, and the interfascicular nucleus as they were being generated. The quantitatively determined time of origin profiles indicated that wv/wv mice have the same time span of neurogenesis as +/+ mice (E10 to E14), but have significant deficits in the proportion of late-generated neurons in each dopaminergic population. In the retrorubral field and substantia nigra, weaver homozygotes had substantial losses of dopaminergic neurons and had a greater deficit in the proportion of neurons generated late while, in the ventral tegmental area and interfascicular nucleus, there were slight losses of dopaminergic neurons and only slight deficits in the proportion of late-generated neurons. These findings lead to the conclusion that the weaver gene is specifically targeting dopaminergic neurons that are generated late, mainly on E13 and E14.