Mesencephalic Dopamine Cell Research Articles

The role of midbrain dopamine cells projecting to the insular cortex in mediated performance: Implications for animal models of reality testing.

A growing body of literature indicates that mediated learning techniques have specific utility for tapping into reality testing in animal models of neuropsychiatric illness. In particular, recent work has shown that animal models that recapitulate various endophenotypes of schizophrenia are particularly vulnerable to impairments in reality testing when undergoing mediated learning. Multiple studies have indicated that these effects are dopamine receptor 2-dependent and correlated with aberrant insular cortex (IC) activity. However, until now, the connection between dopamine and the IC had not been investigated. Here, we utilized a novel intersectional approach to label mesencephalic dopamine cells that specifically project to the insular cortex in both wild-type controls and transgenic mice expressing the dominant-negative form of the Disrupted-in-Schizophrenia-1 (DISC-1) gene. Using these techniques, we identified a population of cells that project from the ventral tegmental area (VTA) to the IC. Afterward, we conducted multiple studies to test the necessity of this circuit in behaviors ranging from gustatory detection to the maintenance of effort and, finally, mediated performance. Our results indicate that perturbations of the DISC-1 genetic locus lead to a reduction in the number of cells in the VTA → IC circuit. Behaviorally, VTA → IC circuitry does not influence gustatory detection or motivation to acquire sucrose reward; however, inactivation of this circuit differentially suppresses Pavlovian approach behavior in wild-type and DISC-1 transgenic mice during mediated performance testing. Moreover, under these testing conditions, inactivation of this circuit predisposes wild-type (but not DISC-1) mice to display impaired reality testing. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Learning, memory and consolidation mechanisms for behavioral control in hierarchically organized cortico-basal ganglia systems.

This article aims to provide a synthesis on the question how brain structures cooperate to accomplish hierarchically organized behaviors, characterized by low‐level, habitual routines nested in larger sequences of planned, goal‐directed behavior. The functioning of a connected set of brain structures—prefrontal cortex, hippocampus, striatum, and dopaminergic mesencephalon—is reviewed in relation to two important distinctions: (a) goal‐directed as opposed to habitual behavior and (b) model‐based and model‐free learning. Recent evidence indicates that the orbitomedial prefrontal cortices not only subserve goal‐directed behavior and model‐based learning, but also code the “landscape” (task space) of behaviorally relevant variables. While the hippocampus stands out for its role in coding and memorizing world state representations, it is argued to function in model‐based learning but is not required for coding of action–outcome contingencies, illustrating that goal‐directed behavior is not congruent with model‐based learning. While the dorsolateral and dorsomedial striatum largely conform to the dichotomy between habitual versus goal‐directed behavior, ventral striatal functions go beyond this distinction. Next, we contextualize findings on coding of reward‐prediction errors by ventral tegmental dopamine neurons to suggest a broader role of mesencephalic dopamine cells, viz. in behavioral reactivity and signaling unexpected sensory changes. We hypothesize that goal‐directed behavior is hierarchically organized in interconnected cortico‐basal ganglia loops, where a limbic‐affective prefrontal‐ventral striatal loop controls action selection in a dorsomedial prefrontal–striatal loop, which in turn regulates activity in sensorimotor‐dorsolateral striatal circuits. This structure for behavioral organization requires alignment with mechanisms for memory formation and consolidation. We propose that frontal corticothalamic circuits form a high‐level loop for memory processing that initiates and temporally organizes nested activities in lower‐level loops, including the hippocampus and the ripple‐associated replay it generates. The evidence on hierarchically organized behavior converges with that on consolidation mechanisms in suggesting a frontal‐to‐caudal directionality in processing control.

Decreased expression of ErbB4 and tyrosine hydroxylase mRNA and protein in the ventral midbrain of aged rats

Decreased availability or efficacy of neurotrophic factors may underlie an increased susceptibility of mesencephalic dopaminergic cells to age-related degeneration. Neuregulins (NRGs) are pleotrophic growth factors for many cell types, including mesencephalic dopamine cells in culture and in vivo. The functional NRG receptor ErbB4 is expressed by virtually all midbrain dopamine neurons. To determine if levels of the NRG receptor are maintained during aging in the dopaminergic ventral mesencephalon, expression of ErbB4 mRNA and protein was examined in young (3 months), middle-aged (18 months), and old (24–25 months) Brown Norway/Fischer 344 F1 rats. ErbB4 mRNA levels in the substantia nigra pars compacta (SNpc), but not the adjacent ventral tegmental area (VTA) or subtantia nigra pars lateralis (SNl), were significantly reduced in the middle-aged and old animals when compared to young rats. Protein expression of ErbB4 in the ventral midbrain was significantly decreased in the old rats when compared to the young rats. Expression of tyrosine hydroxylase (TH) mRNA levels was significantly reduced in the old rats when compared to young animals in the SNpc, but not in the VTA or SNI. TH protein levels in the ventral midbrain were also decreased in the old animals when compared to the young animals. These data demonstrate a progressive decline of ErbB4 expression, coinciding with a loss of the dopamine-synthesizing enzyme TH, in the ventral midbrain of aged rats, particularly in the SNpc. These findings may implicate a role for diminished NRG/ErbB4 trophic support in dopamine-related neurodegenerative disorders of aging such as Parkinson's disease.

The role of dorsal vs ventral striatal pathways in cocaine-seeking behavior after prolonged abstinence in rats

Recent studies have implicated an important role for the dorsal striatum during craving for cocaine and in cocaine-seeking after abstinence in rats. We compared the effects of pharmacological inactivation of mesencephalic dopamine (DA) cell body regions and dorsal vs ventral striatal terminal fields in an animal model of relapse after chronic cocaine self-administration. Rats self-administered cocaine for 2 h/day for ten sessions, followed by 2 weeks of abstinence (i.e., no extinction training). Immediately before being returned to the self-administration chamber, we assessed the effects of gamma-aminobutyric acid agonist inhibition of midbrain DA regions (substantia nigra [SN] and ventral tegmental area [VTA]) and striatum (dorsolateral caudate-putamen, nucleus accumbens core, and nucleus accumbens shell) on relapse to cocaine-seeking in the absence of reinforcement. Further testing examined daily extinction responding subsequent to the initial relapse test. Inactivation of the dorsal caudate-putamen and midbrain regions attenuated cocaine seeking, while inactivation of the ventral striatum had no such effects. However, subsequent sessions under extinction conditions revealed a rebound in cocaine seeking in animals that had undergone inactivation in all regions except the dorsolateral caudate-putamen. The dorsal but not ventral striatum plays a critical role in cocaine seeking immediately after abstinence. These data support the theory that chronic cocaine may shift activity from the ventral to dorsal striatum during drug seeking under certain conditions. While not necessary at the time of relapse, the ventral striatum appears to be involved in processing critical information of the relapse event.

Reactive oxygen species generation by the ethylene- bis-dithiocarbamate (EBDC) fungicide mancozeb and its contribution to neuronal toxicity in mesencephalic cells

Previous in vitro studies in our laboratory have shown that mancozeb (MZ) and maneb (MB), both widely used EBDC fungicides, are equipotent neurotoxicants that produce cell loss in mesencephalic dopaminergic and GABAergic cells after an acute 24 h exposure. Mitochondrial uncoupling and inhibition were associated with fungicide exposure. Inhibition of mitochondrial respiration is known to increase free radical production. Here the mechanism(s) of neuronal damage associated with MZ exposure was further explored by determining the role that reactive oxygen species (ROS) played in toxicity. Damage to mesencephalic dopamine and GABA cell populations were significantly attenuated when carried out in the presence of ascorbate or SOD, indicative of a free radical-mediated contribution to toxicity. ROS generation monitored by hydrogen peroxide (H 2O 2) production using Amplex Red increased in a dose-dependent manner in response to MZ. Inhibition of intracellular catalase with aminotriazole had little effect on H 2O 2 generation, whereas exogenously added catalase significantly reduced H 2O 2 production, demonstrating a large extracellular contribution to ROS generation. Conversely, cells preloaded with the ROS indicator dye DCF showed significant MZ-induced ROS production, demonstrating an increase in intracellular ROS. Both the organic backbone of MZ as well as its associated Mn ion, but not Zn ion, were responsible and required for H 2O 2 generation. The functionally diverse NADPH oxidase inhibitors, diphenylene iodonium chloride, apocynin, and 4-(2-aminoethyl)benzene-sulfonyl fluoride hydrochloride significantly attenuated H 2O 2 production by MZ. In growth medium lacking cells, MZ produced little H 2O 2, but enhanced H 2O 2 generation when added with xanthine plus xanthine oxidase whereas, in cultured cells, allopurinol partially attenuated H 2O 2 production by MZ. Minocycline, an inhibitor of microglial activation, modestly reduced H 2O 2 formation in mesencephalic cells. In contrast, neuronal-enriched cultures or cultures treated with MAC-1-SAP to kill microglia, did not show an attenuation of ROS production. These findings demonstrate that Mn-containing EBDC fungicides such as MZ and MB can produce robust ROS generation that likely occurs via redox cycling with extracellular and intracellular oxidases. The findings further show that microglia may contribute to but are not required for ROS production by MZ.

Aberrant trajectory of ascending dopaminergic pathway in mice lacking Nkx2.1

In the embryonic brain, the transcription factor Nkx2.1 is localized in the medial ganglionic eminence and the ventromedial part of the hypothalamus. In the present study, we examined the development of mesencephalic dopamine (DA) neuron system in mice lacking Nkx2.1. In normal mice, tyrosine hydroxylase-immunoreactive axons from mesencephalic DA cells extended bilaterally in the lateral hypothalamus at embryonic day 12.5 (E12.5) and project to the ipsilateral striatum by E14.5. In the mutant brain, mesencephalic DA cell groups appeared to develop normally, but the majority of their ascending axons were observed to cross the ventral midline of the caudal hypothalamus and project to the contralateral striatum. DiI, a fluorescent dye, placed in the ventrolateral mesencephalon of E14.5 mutant mice, further revealed that majority of DiI-labeled axons projected to the contralateral striatum, while a minor ipsilateral projection was also observed. In the ventromedial hypothalamus of mutants, the neuroepithelium of third ventricle was missing, and immunoreactivity of semaphorin 3A, a soluble type of axon repellent, which was normally localized in the neuroepithelium, was remarkably reduced. Together with the recent evidence that the expression of slit2, another axon-repellent diffusible factor, is also eliminated in the hypothalamic neuroepithelium of Nkx2.1-deficient mice, the abnormal crossing of ascending DA axons observed may be attributed to the elimination of these chemorepulsive signals in the medial part of the mutant hypothalamus.

The midbrain dopaminergic system: anatomy and genetic variation in dopamine neuron number of inbred mouse strains.

The mesotelencephalic dopamine system is genetically variable and affects motor behavior, motivation, and learning. Here we examine the genetic variation of mesencephalic DA neuron number in a quasi-congenic RQI mouse strain and its background partner and in a recombinant inbred strain with different levels of mesencephalic tyrosine hydroxylase activity (TH/MES). We used B6.Cb4i5-alpha6/Vad, C57BL/6By, and CXBI, which are known to express high, intermediate, and low levels of TH/MES, respectively. Unbiased stereological sampling with optical disector counting methods were employed to estimate the number of TH-positive neurons in the A8-A9-A10 cell groups. Morphometric studies on the mesencephalic dopamine cell groups indicated that male mice of the B6.Cb4i5-alpha6/Vad strain were endowed with a significantly lower number of TH-positive cells than CXBI mice. In all strains studied, the right retrorubral field (A8 area) had a higher number of dopamine neurons compared to the left A8 area. The results suggest an inverse relationship between TH/MES and number of dopamine neurons in the A9-A10 cell groups and significant lateral asymmetry in the A8 cell group. A detailed anatomical atlas of the mesencephalic A8-A9-A10 dopaminergic cell groups in the mouse is also presented to facilitate the assignment of TH-positive neurons to specific cell groups.

Fate of Mesencephalic AHD2-Expressing Dopamine Progenitor Cells in Nurr1 Mutant Mice

The orphan nuclear receptor NURR1 was previously demonstrated to be required for the generation of mesencephalic dopamine (DA) cells. However, even in the absence of NURR1, which is normally expressed as cells become postmitotic, neuronal differentiation is induced and expression of several genes detected in developing dopamine cells appears normal during early stages of development. These include the homeobox transcription factors engrailed and Ptx-3 as well as aldehyde dehydrogenase 2, here defined as the earliest marker identified in developing DA cells, expressed already in mitotic DA progenitors. We have used the expression of these dopaminergic markers, retrograde axonal tracing, and apoptosis analyses to study the fate of the DA progenitor cells in the absence of NURR1. We conclude that NURR1 plays a critical role in the maturation, migration, striatal target area innervation, and survival of differentiating mesencephalic DA cells.

Immunocytochemical localization of the dopamine transporter in human brain.

The dopamine transporter (DAT) was localized in normal human brain tissue by light microscopic immunocytochemistry by using highly specific monoclonal antibodies. Regional distribution of DAT was found in areas with established dopaminergic circuitry, e.g., mesostriatal, mesolimbic, and mesocortical pathways. Mesencephalic DAT-immunoreactivity was enriched in the dendrites and cell bodies of neurons in the substantia nigra pars compacta and ventral tegmental area. Staining in the striatum and nucleus accumbens was dense and heterogeneous. Mesocortical DAT immunoreactivity in motor, premotor, anterior cingulate, prefrontal, entorhinal/perirhinal, insular, and visual cortices was detected in scattered varicose and a few nonvaricose fibers. Varicose fibers were relatively enriched in the basolateral and central subnuclei of amygdala, with sparser fibers in lateral and basomedial subnuclei. Double-labeling studies combining DAT and tyrosine hydroxylase (TH) immunostaining in the ventral mesencephalon showed two subpopulations of dopaminergic neurons differentiated by the presence or absence of DAT-immunoreactivity in the A9 and A10 cell groups. In other dopaminergic cell groups (All, A13-A15), TH-positive hypothalamic neurons showed no detectable DAT-immunoreactivity. However, fine DAT-immunoreactive axons were scattered throughout the hypothalamus, particularly concentrated along the medial border, with more coarse axons present along the lateral border. These findings demonstrate that most mesotelencephalic dopamine neurons of human brain express high levels of DAT throughout their entire somatodendritic and axonal domains, whereas a smaller subpopulation of mesencephalic dopamine cells and all hypothalamic dopamine cell groups examined express little or no DAT. These data indicate that different subpopulations of dopaminergic neurons use different mechanisms to regulate their extracellular dopamine levels.

Expression of trkB and trkC mRNAs by adult midbrain dopamine neurons: a double-label in situ hybridization study.

The documented trophic actions of the neurotrophins brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5) upon ventral mesencephalic dopamine neurons in vitro and in vivo are presumed to be mediated through interactions with their high-affinity receptors TrkB (for BDNF and NT-4/5) and TrkC (for NT-3). Although both neurotrophin receptor mRNAs have been detected within the rat ventral midbrain, their specific association with mesencephalic dopaminergic cell bodies remains to be elucidated. The present study was performed to determine the precise organization of trkB and trkC mRNAs within rat ventral midbrain and to discern whether the neurotrophin receptor mRNAs are expressed specifically by dopaminergic neurons. In situ hybridization with isotopically labeled cRNA probes showed that trkB and trkC mRNAs were expressed in all mesencephalic dopamine cell groups, including all subdivisions of the substantia nigra and ventral tegmental area, and in the retrorubral field, rostral and caudal linear raphe nuclei, interfascicular nucleus, and supramammillary region. Combined isotopic/nonisotopic double-labeling in situ hybridization demonstrated that virtually all of the tyrosine hydroxylase (the catecholamine biosynthetic enzyme) mRNA-containing neurons in the ventral midbrain also expressed trkB or trkC mRNAs. Additional perikarya within these regions expressed the neurotrophin receptor mRNAs but were not dopaminergic. The present results demonstrate that essentially all mesencephalic dopaminergic neurons synthesize the neurotrophin receptors TrkB and TrkC and thus exhibit the capacity to respond directly to BDNF and NT-3 in the adult midbrain in vivo. Moreover, because BDNF and NT-3 are produced locally by subpopulations of the dopaminergic cells, the present data support the notion that the neurotrophins can influence the dopaminergic neurons through autocrine or paracrine mechanisms.

Widespread origin of the primate mesofrontal dopamine system.

The dopaminergic innervation of the frontal cortex, commonly implicated in psychiatric and neurological disorders, has traditionally been associated with a circumscribed midline group of ventral tegmental area (VTA) neurons. We have employed a combination of retrograde tracing, using fluorescent dyes, and tyrosine hydroxylase (TH) immunohistochemistry to amplify knowledge of frontal cortex-projecting dopamine (DA) neurons in non-human primates. Injections of retrograde fluorochromes were made in areas 46, 8B/6M, 12, 4, 24, and the prelimbic (PL) and infralimbic areas (IL) of the rhesus monkey. The mesencephalic distribution of neurons exhibiting both retrograde labeling and TH immunoreactivity or retrograde labeling alone was examined from the level of the mammillary bodies to the locus coeruleus. DA afferents innervating the macaque frontal cortex as a whole originate from an unexpectedly widespread continuum of neurons distributed in the dorsal aspects of all three of the mesencephalic DA cell groups [A9, A10 and A8; generally corresponding to the DA cells of the substantia nigra (SN), VTA, and the retrorubral area (RRA) respectively]. A large number of these retrogradely labeled neurons are non-dopaminergic. The dorsal frontal cortex (areas 46, BB/6M and 4) receive DA projections primarily from the full medial-lateral extent of A9 cells dorsal to the SN pars compacta (i.e. A9 dorsalis), the RRA and to a lesser extent from the A10 parabrachial pigmented nucleus (PBPG) and linear nuclei, the latter of which have been associated with the mesocortical DA system. In contrast, the ventromedial PL and IL exhibit a significantly more robust input from the PBPG and midline linear VTA nuclei than from the lateral groups. The anterior cingulate cortex (area 24) is innervated by a group of DA neurons primarily located between these laterally and medially concentrated populations. These findings demonstrate a degree of compartmentalization of the mesofrontal DA system in primates, and suggest that this projection should no longer be viewed as a unitary midline system.

Co-transplantation of Fetal Lateral Ganglionic Eminence and Ventral Mesencephalon Can Augment Function and Development of Intrastriatal Transplants

Methods to increase the development and sustained function of embryonic mesencephalic dopamine cells after transplantation into dopamine (DA)-depleted striatum are currently under investigation. Elements that are crucial for the maturation and connectivity of neurons during normal development of the brain may also play a role in the development and integration of grafted embryonic tissue. Based onin vitroandin vivoobservations of the enhancing effects of striatal tissue on nigral dopaminergic cell development and survival, we demonstrate that inclusion of embryonic striatal cells, specifically from the lateral ganglionic eminence (LGE), produces dopaminergic transplants with augmented functional effects. Rats neonatally DA-depleted and co-transplanted with embryonic nigral and LGE cells developed improved functional outcome when compared with animals receiving only nigral cells, and they required the transplantation of fewer nigral cells to produce a strong behavioral effect. Anatomically, the inclusion of LGE cells produced increased DA cell survival, a higher density of reinnervation into the DA-depleted host striatum, and patches of DA fibers within the co-transplants. There were also an increased number of host striatal cells which induced the immediate-early gene c-fos in co-transplanted animals compared to animals receiving nigral cells alone, indicating a higher degree of host-cell activation. The ability to enhance function, cell survival, reinnervation, and host activation with nigral-striatal co-transplants in the presence of fewer nigral cells supports the hypothesis of a trophic influence of striatal cells on nigral DA cells.

Repeated treatment with haloperidol and clozapine exerts differential effects on dye coupling between neurons in subregions of striatum and nucleus accumbens

The delayed onset of action of antipsychotic drugs (APDs) during the treatment of schizophrenia has been hypothesized to temporally correlate with the induction of depolarization block in rat mesencephalic dopamine (DA) cell groups. Nevertheless, it is unknown whether these drugs also exert a delayed action on the dopaminoceptive postsynaptic target cells in the striatal complex. Using in vivo intracellular recording and dye labeling techniques, the effects of APDs on dye coupling were examined in subregions of the striatal complex defined by double staining for calbindin immunoreactivity. Rats treated repeatedly with APDs were found to exhibit a 66-71% higher incidence of coupling that occurred in a drug- and a region-specific manner, that is, both drug treatments increased dye coupling in the limbic-associated accumbens shell region whereas only haloperidol increased dye coupling in the motor-related striatal matrix and accumbens core regions. In addition, cells located in regions in which dye coupling was altered also showed significantly higher input resistance. These changes were not observed in response to DA receptor blockade by acute drug administration or when haloperidol was administered for a period sufficient to induce DA receptor supersensitivity but not DA cell depolarization block (i.e., 2 weeks). Therefore, alteration in dye coupling appears to be correlated temporally with the induction of DA cell depolarization block. The finding that both APDs exert a common action on neurons in the accumbens shell region is consistent with its identification as the site of therapeutic drug actions, whereas the capacity of haloperidol to also affect cells in the motor-related matrix and core regions correlates with its high propensity to induce extrapyramidal side effects.

Transplantation of mesencephalic cell suspensions from wild-type and heterozygous weaver mice into the denervated striatum: Assessing the role of graft-derived dopaminergic dendrites in the recovery of function

The Weaver ( wv) mutation leads to a loss of mesencephalic dopamine cells and nigrostriatal dopamine axons in homozygosity ( wv/wv) and to a deficiency of nigral dopaminergic dendrites without a concomitant loss of dopamine cell somata or axons in heterozygosity ( wv/+). Previous studies have shown that grafts of foetal dopamine cells from wild-type (+/+) donors can survive when implanted into the wv/wv striatum, supply both an axonal and a dendritic innervation to the host, establish synaptic connections with host striatal neurons, and bring about a functional recovery evidenced by rotational asymmetry tests. The aims of the present study were to examine whether wv/+ dopamine cells maintain a “dendrite-poor” phenotype after transplantation to the denervated striatum, and to compare their functional effects with those of wild-type (+/+) grafts in reversing amphetamine-induced turning behaviour. To that end, +/+ and wv/+ ventral mesencephalic tissue (dissected out from E10-E12 foetal mice and made into a cell suspension by enzymatic and mechanical dissociation) was stereotactically grafted into the right striatum of either wv/wv hosts or +/+ hosts subjected in advance to 6-OHDA lesions of the right substantia nigra. Viability and morphology of grafted neurons were assessed by tyrosine hydroxylase immunocytochemistry on serial sections of the host forebrains. Dopamine cell bodies survived in comparable numbers in the grafts regardless of donor genotype; however, grafts of either genotype contained fewer dopaminergic cells when they were hosted in the wv/wv striatum as compared to the striatum of +/+ mice with 6-OHDA lesions. Despite the survival of cell somata, the dendritic arborisation of wv/+ cells was strikingly poorer than that of +/+ cells in grafts placed into both host types, most likely reflecting their in situ phenotypic abnormality. Recipient wv/wv mice with +/+ and wv/+ grafts exhibited 88% and 83% left rotations, respectively; 6-OHDA hosts with +/+ and wv/+ grafts showed 178% and 165% reversals of asymmetry, respectively. The differences between the effects of +/+ and wv/+ grafts were not statistically significant. We conclude that (i) wv/+ and +/+ dopamine cell somata survive in comparable numbers after intrastriatal grafting; (ii) grafted wv/+ dopamine cells express an anatomical phenotype consistent with that seen in the wv/+ substantia nigra in situ; and (iii) the axonal innervation supplied by wv/+ grafts to the denervated striatum induces a functional recovery comparable to that brought about by +/+ cells, which in addition supply a substantial dendritic innervation to the host; (iv) the wv/wv host environment may be associated with smaller numbers of graft dopamine neurons compared to the environment of +/+ mouse hosts with 6-OHDA lesions.

Transplantation of mesencephalic cell suspensions from wild-type and heterozygous Weaver mice into the denervated striatum: assessing the role of graft-derived dopaminergic dendrites in the recovery of function.

The Weaver (wv) mutation leads to a loss of mesencephalic dopamine cells and nigrostriatal dopamine axons in homozygosity (wv/wv) and to a deficiency of nigral dopaminergic dendrites without a concomitant loss of dopamine cell somata or axons in heterozygosity (wv/+). Previous studies have shown that grafts of foetal dopamine cells from wild-type (+/+) donors can survive when implanted into the wv/wv striatum, supply both an axonal and a dendritic innervation to the host, establish synaptic connections with host striatal neurons, and bring about a functional recovery evidenced by rotational asymmetry tests. The aims of the present study were to examine whether wv/+ dopamine cells maintain a "dendrite-poor" phenotype after transplantation to the denervated striatum, and to compare their functional effects with those of wild-type (+/+) grafts in reversing amphetamine-induced turning behaviour. To that end, +/+ and wv/+ ventral mesencephalic tissue (dissected out from E10-E12 foetal mice and made into a cell suspension by enzymatic and mechanical dissociation) was stereotactically grafted into the right striatum of either wv/wv hosts or +/+ hosts subjected in advance to 6-OHDA lesions of the right substantia nigra. Viability and morphology of grafted neurons were assessed by tyrosine hydroxylase immunocytochemistry on serial sections of the host forebrains. Dopamine cell bodies survived in comparable numbers in the grafts regardless of donor genotype; however, grafts of either genotype contained fewer dopaminergic cells when they were hosted in the wv/wv striatum as compared to the striatum of +/+ mice with 6-OHDA lesions. Despite the survival of cell somata, the dendritic arborisation of wv/+ cells was strikingly poorer than that of +/+ cells in grafts placed into both host types, most likely reflecting their in situ phenotypic abnormality. Recipient wv/wv mice with +/+ and wv/+ grafts exhibited 88% and 83% left rotations, respectively; 6-OHDA hosts with +/+ and wv/+ grafts showed 178% and 165% reversals of asymmetry, respectively. The differences between the effects of +/+ and wv/+ grafts were not statistically significant.(ABSTRACT TRUNCATED AT 400 WORDS)

Fetal Dopamine Cell Survival after Transplantation Is Dramatically Improved at a Critical Donor Gestational Age in Nonhuman Primates

Mesencephalic tissue containing newly generated dopamine neurons was collected from brains of embryonic African green monkeys at 44 and 49 days of gestation and stereotaxically implanted into multiple sites in the caudate nucleus of adult monkeys previously treated with the dopamine protoxin, 1-methyl-4-phenyl-1,2,3,6-tetrathydropyridine. Ultrasonography was utilized to assess the developmental stage prior to hysterotomy. Brains were removed for combined histochemical and biochemical analyses at 312 months after grafting to determine the extent of graft survival and growth. The dopamine content of the target nucleus was assessed from microdissected "punches" placed in proximity to grafts identified in unfixed brain slices prior to fixation. Tissue dopamine levels adjacent to the grafts were elevated markedly, reaching 25-50% of control levels at some sites in the caudate nucleus. Morphometric analysis of graft size and dopamine cell numbers was performed with computer-enhanced, video-based imaging. Exceptionally large grafts that far exceeded their initial size at the time of implantation were seen at each placement site. The dopamine cell count was as high as 3500 in a single graft from E44 tissue, but only as high as 550 from the E49 donor. Up to 15,000 tyrosine hydroxylase-positive neurons were stained in the host monkey that received E44 tissue; only 110 as many were seen in each of the recipients of E49 day samples. The earlier donor grafts occupied as much as 15% of the caudate nucleus as seen in a single coronal section; summation of all sections that contained grafts at each placement from the E44 donor revealed average areas occupied by the grafts ranging from 3 to 8% of the caudate nucleus. In comparison, grafts produced from an E49 donor averaged between 2.4 and 5.4% of the area of the target. Qualitatively, grafts from each gestational stage showed well-developed dopamine neurons with morphological characteristics equivalent to those of all three ventral mesencephalic dopamine cell groups. The attainment of large, well-differentiated grafts with thousands of dopaminergic neurons from early gestation tissue suggests that optimal cell survival in primates is dependent on the degree of postgerminal development of the dopamine neuron. Neurite extension may be critical in this regard as well as other, at present, undefined factors. Maximal graft development and cell survival may be a critical element in the ability of neural grafts to reverse a neurological disability and to maintain improvement in the event of continued degeneration of host dopamine neurons.

Differential effects of conditioned and unconditioned stress on the neurotensin content of dopamine cell body groups of the ventral mesencephalon.

The findings of this study extend the observations of Deutch et al. who suggested that NT in the ventral mesencephalon may be involved in the environmentally elicited activation of selectively responsive populations of mesotelencephalic dopamine neurons. The unconditioned response of NT-LI to electric footshock was observed only at an intensity of 500 microA and only in the lateral subdivision of the VTA. The selective effect of footshock stress on the NT content of a specific cell body group of the ventral mesencephalon suggests that NT mechanisms in the lateral VTA may, in part, underlie the stress-induced activation of dopamine neurons that originate in the lateral VTA. However, it should be noted that populations of dopamine neurons are activated by footshock intensities less than 500 microA, while NT concentrations of mesencephalic dopamine cell body groups are not altered by these shock intensities. The disparity weakens the possibility of a role for NT in the stress-induced activation of brain dopamine neurons unless NT mechanisms may be involved in transducing the effects of higher intensity stressors versus low intensity stressors. However, it should be noted that changes in the concentration of NT-LI represent an endpoint of unknown sensitivity and functional significance and best serve as an initial approximation of the effects of a manipulation on NT-containing neurons. It is plausible that NT mechanisms in the ventral mesencephalon may act in concert with other neuropeptides such as substance P and Met-enkephalin to transduce the effects of stressors on alterations in the activity of mesotelencephalic dopamine neurons that originate in the ventral mesencephalon. An examination of the effects of footshock stress on the content of prepro-NT mRNA in the dopamine cell body groups of the ventral mesencephalon would be of interest in assessing whether stress enhances NT gene expression or alters the characteristics of release of this neuropeptide in the ventral mesencephalon. Lacking NT receptor antagonists, it would also be of interest to determine the effects of the passive immunoneutralization of NT in the ventral mesencephalon on footshock-induced increases in the biochemically estimated activity of mesotelencephalic dopamine neurons to better understand the involvement of NT as a transducer of the effects of stress on dopamine neuronal activity. The distinct topography of conditioned versus unconditioned stress on the concentration of NT-LI in the dopamine cell body groups of the ventral mesencephalon suggests that NT may be involved in the differential activation of distinct dopamine neuronal populations by these different stressors.(ABSTRACT TRUNCATED AT 400 WORDS)

Transplantation of Human Fetal Dopamine Cells for Parkinson's Disease

In an effort to improve the clinical signs of Parkinson's disease, we have implanted mesencephalic dopamine cells from a 7-week human embryo into the caudate and putamen of a 52-year-old man with Parkinson's disease. Fetal tissue was obtained from elective abortion. The woman and the patient with Parkinson's disease were unknown to each other. The woman gave specific consent and was not paid. The patient had a 20-year history of parkinsonism treated with multiple drug therapies including levodopa/carbidopa (Sinemet) every 2 1/2 hours. His symptoms were worse on the left side. For 5 months prior to transplantation, the patient underwent clinical evaluations by both a neurologist and a computer system installed in his home for daily measurement of walking and hand movements. Preoperative positron emission tomographic scanning with 6-L[18F]fluorodopa (fluorodopa) demonstrated severe dopamine depletion bilaterally. Fetal tissue was matched to the patient for ABO blood antigens, and maternal serum was screened for hepatitis B and human immunodeficiency virus type 1 prior to surgery. Fetal tissue was implanted stereotactically throughout the caudate and putamen on the right side of the brain via 10 needle tracks. The patient was not immunosuppressed. Results 12 months after surgery showed 42% improvement in left-hand speed before the first morning dose of drug and 40% greater response to drug therapy. Right-hand speed increased 15% before drug therapy and 23% after drug therapy. Reaction time was unaffected. Walking speed increased 33% after drug administration, although walking speed before the first morning dose of drugs declined 40%. Walking speed on an all-day basis improved 17%.(ABSTRACT TRUNCATED AT 250 WORDS)

Spatial relationship of the striatonigral and mesostriatal pathways: double-label immunocytochemistry for DARPP-32 and tyrosine hydroxylase

Antibodies to tyrosine hydroxylase and DARPP-32 were used to examine the spatial arrangement between mesostriatal dopamine projections and the reciprocal pathway from DARPP-32-containing neurons in the basal forebrain. Use of a double-labeling immunocytochemical procedure demonstrated that the mesostriatal and striatonigral pathways run in close proximity throughout the rostral mesencephalon and basal forebrain. The majority of descending axons immunoreactive for DARPP-32 appear to originate in the striatum, including the nucleus accumbens, and run through the internal capsule to innervate the globus pallidus, entopeduncular nucleus, and all subdivisions of the substantia nigra. The ventral tegmental area is sparsely invested with DARPP-32-immunoreactive axons. At all levels, there are also fascicles of DARPP-32-containing fibers which run ventromedial to the internal capsule in the medial forebrain bundle, and which are coextensive with ascending axons of the mesencephalic dopamine cell groups. Tyrosine hydroxylase-immunoreactive axons are coextensive with DARPP-32-immunoreactive axons in the internal capsule, entopeduncular nucleus, and globus pallidus, as well as much of the remainder of the basal forebrain. Although the main source of descending DARPP-32 immunoreactive axons would appear to be the striatum, other possible sources are also discussed.

Layer-specific innervation of the dopamine-deficient frontal cortex in weaver mutant mice by grafted mesencephalic dopaminergic neurones.

The dopamine innervation of the frontal cortex originates in the A9 and A10 mesencephalic dopamine cell groups. In weaver mutant mice, there is a 77% frontocortical dopamine deficiency associated with losses of dopamine neurones in areas A9 and A10. The dopamine-depleted cortical areas of weaver mutant mice are receptive to reinnervation by afferent fibres originating in dopamine-containing mesencephalic grafts from normal donor embryos. In the anteromedial frontal lobe, reinnervation by tyrosine hydroxylase immunoreactive fibres is largely confined to the basal cortical layers whereas in the anterior cingulate cortex, tyrosine hydroxylase immunoreactive fibres also occupy superficial layers, including the molecular layer. Normally, the dopaminergic innervation of the anteromedial frontal lobe is distributed among the basal cortical layers (IV-VI), and the dopaminergic innervation of the cingulate cortex occupies both basal and superficial cortical layers. The pattern of innervation following transplantation indicates that, in repopulating dopamine-deficient cortical areas of recipient weaver mutants, graft-derived dopamine fibres show a preference for those layers which are normally invested by dopamine afferents.