Dopamine neuron agenesis in Nurr1-deficient mice

Dopamine neurons of the substantia nigra and ventral tegmental area regulate movement and affective behavior and degenerate in Parkinson's disease. The orphan nuclear receptor Nurr1 was shown to be expressed in developing dopamine neurons before the appearance of known phenotypic markers for these cells. Mice lacking Nurr1 failed to generate midbrain dopaminergic neurons, were hypoactive, and died soon after birth. Nurr1 expression continued into adulthood, and brains of heterozygous animals, otherwise apparently healthy, contained reduced dopamine levels. These results suggest that putative Nurr1 ligands may be useful for treatment of Parkinson's disease and other disorders of midbrain dopamine circuitry.

Defects in enteric innervation and kidney development in mice lacking GDNF

Glial-lial-cell-line-derived neurotrophic factor (GDNF) has been isolated as neurotrophic factor for midbrain dopaminergic neurons. Because of its neurotrophic activity on a wide range of neuronal populations in vitro and in vivo, GDNF is being considered as a potential therapeutic agent for neuronal disorders. During mammalian development, it is expressed not only in the nervous system, but also very prominently in the metanephric kidney and the gastrointestinal tract, suggesting possible functions during organogenesis. We have investigated the role of GDNF during development by generating a null mutation in the murine GDNF locus, and found that mutant mice show kidney agenesis or dysgenesis and defective enteric innervation. We demonstrate that GDNF induces ureter bud formation and branching during metanephros development, and is essential for proper innervation of the gastrointestinal tract.

Protection and repair of the nigrostriatal dopaminergic system by GDNF in vivo

Glial-cell-line-derived neurotrophic factor (GDNF), a recently cloned new member of the transforming growth factor-beta superfamily, promotes survival of cultured fetal mesencephalic dopamine neurons and is expressed in the developing striatum. There have, however, been no reports about effects of GDNF in situ. We have used the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which produces parkinsonian symptoms in man, to determine whether GDNF might exert protective or regenerative effects in vivo in the adult nigrostriatal dopamine system in C57/B1 mice. GDNF injected over the substantia nigra or in striatum before MPTP potently protects the dopamine system, as shown by numbers of mesencephalic dopamine nerve cell bodies, dopamine nerve terminal densities and dopamine levels. When GDNF is given after MPTP, dopamine levels and fibre densities are significantly restored. In both cases, motor behaviour is increased above normal levels. We conclude that intracerebral GDNF administration exerts both protective and reparative effects on the nigrostriatal dopamine system, which may have implications for the development of new treatment strategies for Parkinson's disease.

Functional recovery in parkinsonian monkeys treated with GDNF

Parkinson's disease results from the progressive degeneration of dopamine neurons that innervate the striatum. In rodents, glial-cell-line-derived neurotrophic factor (GDNF) stimulates an increase in midbrain dopamine levels, protects dopamine neurons from some neurotoxins, and maintains injured dopamine neurons. Here we extend the rodent studies to an animal closer to the human in brain organization and function, by evaluating the effects of GDNF injected intracerebrally in rhesus monkeys that have had the symptomatology and pathophysiological features of Parkinson's disease induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The recipients of GDNF displayed significant improvements in three of the cardinal symptoms of parkinsonism: bradykinesia, rigidity and postural instability. GDNF administered every four weeks maintained functional recovery. On the lesioned side of GDNF-treated animals, dopamine levels in the midbrain and globus pallidus were twice as high, and nigral dopamine neurons were, on average, 20% larger, with an increased fibre density. The results indicate that GDNF may be of benefit in the treatment of Parkinson's disease.

Brain grafts reduce motor abnormalities produced by destruction of nigrostriatal dopamine system

In order to determine if brain tissue grafts can provide functional input to recipient central nervous system tissue, fetal rat dopamine-containg neurons were implanted adjacent to the caudate nucleus of adult recipients whose endogenous dopaminergic input had been destroyed. The grafts showed good survival and axonal outgrowth. Motor abnormalities, which had been induced by the destruction of the endogenous dopaminergic input to the caudate, were significantly reduced after grafting of the fetal brain tissue. These data suggest that such implants may be potentially useful in reversing deficits after circumscribed destruction of brain tissue.

Human fetal dopamine neurons grafted into the striatum in two patients with severe Parkinson's disease. A detailed account of methodology and a 6-month follow-up

By using stereotaxic surgical techniques, ventral mesencephalic tissues from aborted human fetuses of 8 to 10 weeks' gestational age were implanted unilaterally into the striata in two patients with advanced Parkinson's disease. The patients were treated with a cyclosporine, azathioprine, and steroid regimen to minimize the risk for graft rejection. They were examined for 6 months preoperatively and 6 months postoperatively and continued to receive the same doses of antiparkinsonian medication. There were no significant postoperative complications. No major therapeutic effect from the operation was observed. However, in the clinical tests, both patients showed small but significant increases of movement speed for repeated pronation-supination, fist clenching, and foot lifting. The rate of walking also increased in the one patient tested. For both patients, there was an initial worsening postoperatively, followed by improvement vs preoperative performance at 1 to 3 months. Both patients also showed significant improvement in the magnitude of response to a single dose of levodopa (L-dopa), but there was no increase in the duration of drug action. The motor readiness potential increased in both patients postoperatively, primarily over the operated hemisphere. Neurophysiological measurements also showed a more rapid performance of simple and complex arm and hand movements on the side contralateral to transplantation in one patient at 5 months postoperatively. Positron emission tomography demonstrated no increased uptake of 6-L-(18F)-fluorodopa in the transplanted striatum at 5 and 6 months. Taken together, these results suggest that the fetal nigral implants may have provided a modest improvement in motor function, consistent with the presence of small surviving grafts. Although our results support further scientific experimentation with transplantation in Parkinson's disease, widespread clinical trials with this procedure are probably not warranted at this time.

Glial cell line-derived neurotrophic factor reverses toxin-induced injury to midbrain dopaminergic neurons in vivo

Fischer 344 rats were unilaterally injected into the medial forebrain bundle with 6-hydroxydopamine (6-OHDA). Apomorphine-induced rotational behavior was used to select animals whose rotation exceeded 300 turns/h, corresponding to greater than 95% dopamine (DA) depletion in the ipsilateral striatum. Four weeks later, glial cell line-derived neurotrophic factor (GDNF) or vehicle was injected intranigrally ipsilateral to the lesion (0.1-100 micrograms). The highest dose of GDNF tested produced a marked decrease in rotational behavior. This dose also produced levels of DA in the ipsilateral substantia nigra (SN) which were not statistically different from the contralateral side. Vehicle-treated animals showed a marked DA depletion in the ipsilateral SN. These results demonstrate neurochemical and behavioral improvements in unilaterally DA-lesioned rats following intranigral administration of GDNF, suggesting that GDNF may develop into a useful therapy for Parkinson's disease.

Adenine nucleotides and synaptic transmission in the in vitro rat hippocampus

1 The effects of adenosine and various derivatives were examined in the in vitro hippocampal slice preparation from rat.2 The amplitudes of extracellularly recorded field potentials from the CA1 region were depressed by adenosine, and this effect could be antagonized by methylxanthines. Because presynaptic field potentials were unaffected by adenosine, while the field e.p.s.p. was depressed, adenosine would appear to act at a synaptic site to depress transmission.3 Adenosine deaminase, which breaks down adenosine to inosine, increased the amplitude of synaptic responses, while hexobendine, which blocks reuptake of adenosine, had a depressant effect. This strongly suggests that the endogenous release of adenosine from the hippocampal slice preparation is sufficient to exert a tonic inhibitory influence on the amplitude of synaptic responses.4 Cyclic adenosine 3',5'-monophosphate (cyclic AMP) and its dibutyryl derivative had depressant effects on the amplitude of field responses which were blocked by theophylline, suggesting that they are able to act at the extracellular adenosine receptor. (-)-Isoprenaline (which raises tissue cyclic AMP levels), and the 8-p-chlorophenylthio derivative of cyclic AMP both increased the amplitude of population spike responses, and these effects were not blocked by theophylline, suggesting that the physiological effects of adenosine are not mediated via a cyclic AMP-dependent mechanism.5 Since adenosine is not the transmitter at this CA1 pyramidal cell synapse, but is apparently present in the extracellular compartment in sufficient concentrations to affect the synaptic physiology of this region, this provides strong evidence in favour of the concept of a neuromodulatory role for adenosine in the central nervous system.

Correlation of apomorphine- and amphetamine-induced turning with nigrostriatal dopamine content in unilateral 6-hydroxydopamine lesioned rats

In the unilateral 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson's disease, controversy exists concerning the use of apomorphine- or D-amphetamine-induced rotations as reliable indicators of nigrostriatal dopamine depletion. Our objective was to evaluate which, if either, drug-induced behavior is more predictive of the extent of nigrostriatal dopamine depletion. Fischer 344 and Sprague-Dawley rats were unilaterally injected with 9 micrograms/4 microliters/4 min 6-hydroxydopamine into the medial forebrain bundle. The animals were behaviorally tested with apomorphine (0.05 mg/kg, s.c.) and D-amphetamine (5.0 mg/kg, s.c.). Following testing, the brains were removed and the right and left striata, substantia nigra and ventral tegmental area were dissected free and quickly frozen at -70 degrees C for analysis of catecholamine content by high performance liquid chromatography coupled with electrochemical detection. Our results indicate that an animal which has greater than a 90% depletion of dopamine in the striatum might not rotate substantially on apomorphine, without a concomitant depletion of > 50% of the DA content in the corresponding substantia nigra. No correlations were seen involving depletions of the ventral tegmental area and the extent of the lesions to the striatum. Submaximally lesioned (75-90% depleted) rats were found to rotate on D-amphetamine but not on apomorphine. In addition, control rats that did not receive lesions were often seen to rotate extensively on D-amphetamine. We therefore conclude that maximal lesions of the striatum and substantia nigra are required to generate rotations demonstrable with low dose apomorphine but not with D-amphetamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Restoration of dopaminergic function by grafting of fetal rat substantia nigra to the caudate nucleus: long-term behavioral, biochemical, and histochemical studies

Motor deficits produced in rats by unilateral substantia nigra lesions have been found to be reduced by grafts of fetal rat substantia nigra to the dopamine denervated caudate nucleus. In the present study these grafts were examined behaviorally, histochemically, and biochemically over six to 10-month periods. The grafts were found to survive in a healthy condition and contain catecholaminergic cells and fibers after eight to ten months. Concentrations of dopamine in adjoining parts of the caudate nucleus were increased when examined six months after grafting. Apomorphine induced rotation was reduced by the grafts, and these reductions persisted for at least six months. Although signs of aging were observed in the brains of the host animals when sacrificed eight to ten months after grafting, the grafts remained healthy and showed no signs of aging or deterioration. It is concluded that substantia nigra grafts can become permanent, functional constituents of the brains of host animals with prior substantia nigra lesions.

Glial cell line-derived neurotrophic factor supports survival of injured midbrain dopaminergic neurons

Glial cell-lined derived neurotrophic factor (GDNF) has been shown to promote survival of developing mesencephalic dopaminergic neurons in vitro. In order to determine if there is a positive effect of GDNF on injured adult midbrain dopaminergic neurons in situ, we have carried out experiments in which a single dose of GDNF was injected into the substantia nigra following a unilateral lesion of the nigrostriatal system. Rats were unilaterally lesioned by a single stereotaxic injection of 6-hydroxydopamine (6-OHDA; 9 micrograms/4 microliters normal saline with 0.02% ascorbate) into the medial forebrain bundle and tested weekly for apomorphine-induced (0.05 mg/kg s.c.) contralateral rotation behavior. Rats that manifested > 300 turns/hour received a nigral injection of 100 micrograms GDNF, or cytochrome C as a control, 4 weeks following the 6-OHDA lesion. Rotation behavior was quantified weekly for 5 weeks after GDNF. Rats were subsequently anesthetized, transcardially perfused, and processed for tyrosine hydroxylase immunohistochemistry. It was found that 100 micrograms GDNF decreased apomorphine-induced rotational behavior by more than 85%. Immunohistochemical studies revealed that tyrosine hydroxylase immunoreactivity was equally reduced in the striatum ipsilateral to the lesion in both cytochrome C and GDNF-injected animals. In contrast, large increments in tyrosine hydroxylase immunoreactivity were observed in the substantia nigra of animals treated with 100 micrograms of GDNF, with a significant increase in numbers of tyrosine hydroxylase-immunoreactive cell bodies and neurites as well as a small increase in the cell body area of these neurons. The results suggest that GDNF can maintain the dopaminergic neuronal phenotype in a number of nigral neurons following a unilateral nigrostriatal lesion in the rat.

Retrograde axonal transport of glial cell line-derived neurotrophic factor in the adult nigrostriatal system suggests a trophic role in the adult

The recently cloned, distant member of the transforming growth factor beta (TGF-beta) family, glial cell line-derived neurotrophic factor (GDNF), has potent trophic actions on fetal mesencephalic dopamine neurons. GDNF also has protective and restorative activity on adult mesencephalic dopaminergic neurons and potently protects motoneurons from axotomy-induced cell death. However, evidence for a role for endogenous GDNF as a target-derived trophic factor in adult midbrain dopaminergic circuits requires documentation of specific transport from the sites of synthesis in the target areas to the nerve cell bodies themselves. Here, we demonstrate that GDNF is retrogradely transported by mesencephalic dopamine neurons of the nigrostriatal pathway. The pattern of retrograde transport following intrastriatal injections indicates that there may be subpopulations of neurons that are GDNF responsive. Retrograde axonal transport of biologically active 125I-labeled GDNF was inhibited by an excess of unlabeled GDNF but not by an excess of cytochrome c. Specificity was further documented by demonstrating that another TGF-beta family member, TGF-beta 1, did not appear to affect retrograde transport. Retrograde transport was also demonstrated by immunohistochemistry by using intrastriatal injections of unlabeled GDNF. GDNF immunoreactivity was found specifically in dopamine nerve cell bodies of the substantia nigra pars compacta distributed in granules in the soma and proximal dendrites. Our data implicate a specific receptor-mediated uptake mechanism operating in the adult. Taken together, the present findings suggest that GDNF acts endogenously as a target-derived physiological survival/maintenance factor for dopaminergic neurons.

Cyclic adenosine monophosphate and norepinephrine: effects on transmembrane properties of cerebellar Purkinje cells

Electrical properties of Purkinje cells were recorded by intracellular microelectrode during extracellular electrophoretic application of gamma aminobutyrate, norepinephrine, cyclic adenosine monophosphate, and dibutyryl cyclic adenosine monophosphate. All these substances hyperpolarized Purkinje cells. Transmembrane resistance decreased during gamma aminobutyrate hyperpolarization. In contrast, norepinephrine and the cyclic nucleotides generally elevated resistance. These results show that cyclic nucleotides mimic the unique effects of norepinephrine on the bioelectric properties of neuronal membranes.

Vitamin D(3) attenuates 6-hydroxydopamine-induced neurotoxicity in rats

Previous reports have demonstrated that exogeneous administration of glial cell line-derived neurotrophic factor (GDNF) reduces ventral mesencephalic (VM) dopaminergic (DA) neuron damage induced by 6-hydroxydopamine (6-OHDA) lesioning in rats. Recent studies have shown that 1,25-dihydroxyvitamin D(3) (D3) enhances endogenous GDNF expression in vitro and in vivo. The purpose of present study was to investigate if administration of D3 in vivo and in vitro would protect against 6-OHDA-induced DA neuron injury. Adult male Sprague-Dawley rats were injected daily with D3 or with saline for 8 days and then lesioned unilaterally with 6-OHDA into the medial forebrain bundle. Locomotor activity was measured using automated activity chambers. We found that unilateral 6-OHDA lesioning reduced locomotor activity in saline-pretreated animals. Pretreatment with D3 for 8 days significantly restored locomotor activity in the lesioned animals. All animals were sacrificed for neurochemical analysis 6 weeks after lesioning. We found that 6-OHDA administration significantly reduced dopamine (DA), 3,4-dihydroxy-phenylacetic acid (DOPAC) and homovanilic acid (HVA) levels in the substantia nigra (SN) on the lesioned side in the saline-treated rats. D3 pretreatment protected against 6-OHDA-mediated depletion of DA and its metabolites in SN. Using primary cultures obtained from the VM of rat embryos, we found that 6-OHDA or H(2)O(2) alone caused significant cell death. Pretreatment with D3 (10(-10) M) protected VM neurons against 6-OHDA- or H(2)O(2)-induced cell death in vitro. Taken together, our data indicate that D3 pretreatment attenuates the hypokinesia and DA neuronal toxicity induced by 6-OHDA. Since both H(2)O(2) and 6-OHDA may injure cells via free radical and reactive oxygen species, the neuroprotection seen here may operate via a reversal of such a toxic mechanism.

Cyclic adenosine monophosphate: possible mediator for norepinephrine effects on cerebellar Purkinje cells

Microelectrophoretic application of norepinephrine or cyclic adenosine monophosphate reduces the discharge frequency of Purkinje cells in the rat cerebellum. In contrast, other nucleotides accelerate the discharge rate of most units. Parenterally administered theophylline, which inhibits the hydrolysis of cyclic adenosine monophosphate enhances the effects of norepinephrine and cyclic adenosine monophosphate. Therefore, norepinephrine may be able to regulate Purkinje cells functionally by metabolic stimulation of cyclic adenosine monophosphate synthesis.

Cellular expression of GDNF mRNA suggests multiple functions inside and outside the nervous system

Glial-cell-line-derived neurotrophic factor (GDNF) is a distant member of the transforming growth factor-beta family and has potent neurotrophic effects on several classes of neurons including dopamine neurons and motoneurons. Here, we have used in situ hybridization to describe the development of the cellular expression of GDNF mRNA pre- and postnatally. Consistent with dopaminotrophic activity, GDNF mRNA is expressed in the developing basal ganglia and the olfactory tubercle. It is also found in a thalamic nucleus, in neurons of the substantia innominata, in the developing Purkinje neurons and the developing locus coeruleus area, and in trigeminal brainstem nuclei. In the spinal cord, neuronal expression is found in Clarke's column. GDNF mRNA is also expressed in the dorsal horns during development. Additional GDNF mRNA expression in the head region includes the carotid body, the retina, the vibrissae, the inner ear, the ear canal, and epithelium in the nasal cavity. Prominent expression is also found in the developing teeth. The widespread expression of GDNF in developing skeletal muscle is consistent with trophic activity on alpha-motoneurons. The smooth muscle layers of the gastrointestinal tract are also strongly positive. A very strong signal is found in the outer mesenchyme of the developing metanephric kidney. We conclude that GDNF mRNA is expressed in many different cellular systems inside and outside the central nervous system during development, suggesting multiple functions of GDNF in the developing organism.

Alkylxanthines elevate hippocampal excitability. Evidence for a role of endogenous adenosine

The effects of four xanthines (theophylline, 8-phenyltheophylline, isobutylmethylxanthine (IBMX), and 7-benzyl-IBMX) were studied in the hippocampal slice in vitro. These agents increased the excitability of this preparation with 8-phenyltheophylline being the most potent, 7-benzyl-IBMX the least potent, and theophylline and IBMX having intermediate potencies. A similar rank order was observed in terms of the potencies of these xanthines in antagonizing a) electrophysiological responses to adenosine, and b) adenosine-stimulated cyclic AMP formation. These results indicate that the excitatory actions of xanthines in the vivo hippocampus can be most easily explained on the basis of their ability to block adenosine's actions; the CNS excitatory actions of these drugs in vivo may depend upon a similar mechanism of action.

Noradrenergic responses in rat hippocampus: evidence for medication by alpha and beta receptors in the in vitro slice

The effect of perfused norepinephrine (NE) on evoked potentials in CA1 of the in vitro rat hippocampus was examined. Weak and variable effects on population spike amplitude were observed, with lower doses of NE generally producing excitations and higher doses more often producing inhibitions. Clonidine, an alpha-receptor agonist, produced a dose-dependent inhibition of population spike amplitude; this inhibition was effectively antagonized by the alpha-antagonist, phentolamine. Isoproterenol (ISO), a beta-agonist, produced marked increases in population spike amplitude which could be antagonized by timolol, a beta-receptor antagonist. Phentolamine did not antagonize the excitations produced by ISO, and timolol had no effect on the inhibitions seen with clonidine. After pretreatment with either phentolamine or timolol, NE perfusion elicited robust and consistent elevations or reductions in the population spike, respectively. A potent cyclic AMP derivative, 8-p-chlorophenylthio cyclic AMP, produced large increases in population spike amplitude which appeared similar to the responses seen with beta-agonists. No changes in field EPSP amplitudes were observed with any of the drugs tested. Taken together, these results suggest that NE may interact with alpha-adrenergic receptors to decrease pyramidal cell excitability, and the beta-adrenergic receptors to increase pyramidal cell excitability; the beta-effect may involve cAMP.