Role of toll-like receptor 4 and sex in 6-hydroxydopamine-induced behavioral impairments and neurodegeneration in mice

Parkinson's disease (PD) is a neurodegenerative disease characterized by progressive loss of the nigrostriatal dopaminergic neurons that are associated with motor alterations and non-motor manifestations (such as depression). Neuroinflammation is a process with a critical role in the pathogenesis of PD. In this regard, toll-like receptor 4 (TLR4) is a central mediator of immune response in PD. Moreover, there are gender-related differences in the incidence, prevalence, and clinical features of PD. Therefore, we aimed to elucidate the role of TLR4 in the sex-dependent response to dopaminergic denervation induced by 6-hydroxydopamine (6-OHDA) in mice. Female and male adult wildtype (WT) and TLR4 knockout (TLR4-/-) mice were administered with unilateral injection of 6-OHDA in the dorsal striatum, and non-motor and motor impairments were evaluated for 30 days, followed by biochemistry analysis in the substantia nigra pars compacta (SNc), dorsal striatum, and dorsoventral cortex. Early non-motor impairments (i.e., depressive-like behavior and spatial learning deficits) induced by 6-OHDA were observed in the male WT mice but not in male TLR4-/- or female mice. Motor alterations were observed after administration of 6-OHDA in both strains, and the lack of TLR4 was also related to motor commitment. Moreover, ablation of TLR4 prevented 6-OHDA-induced dopaminergic denervation and microgliosis in the SNc, selectively in female mice. These results reinforced the existence of sex-biased alterations in PD and indicated TLR4 as a promising therapeutic target for the motor and non-motor symptoms of PD, which will help counteract the neuroinflammatory and neurodegenerative processes.

Crosstalk between 6-OHDA-induced autophagy and apoptosis in PC12 cells is mediated by phosphorylation of Raf-1/ERK1/2

Parkinson's disease (PD) is a degenerative brain disorder characterized by motor symptoms and loss of dopaminergic (DA) neurons in the substantia nigra. The mechanisms for DA cell death in PD have been extensively investigated using PC12 cells treated with a dopamine neurotoxin 6-hydroxydopamine (6-OHDA). 6-OHDA may induce both autophagy and apoptosis in PC12 cells. However, it remains unclear whether crosstalk occurs between autophagy and apoptosis in PC12 cells treated with 6-OHDA and whether Raf-1/ERK1/2 and their phosphorylation status play a role in autophagy. In this study, we used MDC staining assay and flow cytometry and found that 6-OHDA induced autophagy in PC12 cells. This induction was inhibited by the autophagy inhibitor 3-MA. Our electron microscopy observations also supported 6-OHDA induced autophagy in PC12 cells. Apoptosis of PC12 cells was increased with inhibition of autophagy by 3-MA. In addition, Inhibition of Raf-1 resulted in a decreased 6-OHDA-induced autophagy rate among PC12 cells. Phosphorylation levels of Raf-1 and ERK1/2 were increased in PC12 cells treated with 6-OHDA and inhibited by co-treatment with 6-OHDA and 3-MA. These data suggest that crosstalk between 6-OHDA-induced apoptosis and autophagy in PC12 cells may be regulated via the Raf-1/ERK1/2 signaling pathway. Our data suggest a mechanism for 6-OHDA toxicity in PC12 cells, contributing to our understanding of the pathogenesis of PD.

[NON-RESPIRATORY FUNCTION OF THE LUNGS IN THE NIGROSTRIATAL DOPAMINERGIC SYSTEM DYSFUNCTION]

The study presents a comprehensive of the metabolism and the fractional composition of li- pids surfactant, water balance, hemostatic activity of the lungs in neyrodegeneration substantia nigra of the brain induced by stereotaxic microinjection of 6--hydroxydopamine and systemic administration of haloperidol. It is shown that a breach of dopaminergic neurotransmission leads to deterioration of surface-active properties of the alveolar lining of the complex against a decrea- se of phospholipids, cholesterol, phosphatidylcholine and lysophospholipids enhance the pulmo- nary surfactant in the activation of phospholipase hydrolysis and lipid peroxidation. Intranigral introduction neurotoxin accompanied by increased blood supply to the lungs and the blood coagu- lation potential of the pulmonary circulation, the blockade D2-receptors--hyporhydration lung tissue. The results obtained indicate the formation of dysregulation pneumopathy dysfunction nigrostriatal dopaminergic system.

Peripheral catecholamines mediate certain responses to central cholinergic receptor stimulation by oxotremorine

The role of peripheral catecholamines in mediating the pressor and tremorigenic effects of oxotremorine were investigated in conscious rats. At time of peak tremor intensity induced by oxotremorine, plasma adrenaline and noradrenaline were increased 3--4-fold. Tremor intensity was substantially reduced by either adrenal medullectomy, chemical sympathectomy with 6-hydroxydopamine, or injection of 2.5 mg/kg L-propranolol. The pressor response to oxotremorine was not reduced by adrenal denervation, which however prevented the usual rise in plasma adrenaline but not that of noradrenaline. It is concluded that central cholinergic receptor stimulation activates the sympatho-adrenal system. While both adrenaline and intact sympathetic nerves are necessary for the mediation of the full tremorigenic effect, the pressor response to oxotremorine is mainly due to the effect of noradrenaline on vascular alpha-receptors.

Hypoglycemia differentially regulates hypothalamic glucoregulatory neurotransmitter gene and protein expression: role of caudal dorsomedial hindbrain catecholaminergic input

The hypothalamic neurochemicals neuropeptide Y (NPY), orexin-A (ORX), and oxytocin (OXY) exert glucoregulatory effects upon intracerebral administration, findings that support their potential function within neural pathways that maintain glucostasis. Current understanding of how these neurotransmitter systems respond to the diabetes mellitus complication, insulin-induced hypoglycemia, is limited to knowledge of neuropeptide gene transcriptional reactivity. We investigated the hypothesis that hypoglycemia elicits hypothalamic site-specific alterations in levels of these neurochemicals, and that adjustments in local neurotransmitter availability may be regulated by catecholaminergic (CA) input from the caudal dorsomedial hindbrain. The arcuate (ARH) and paraventricular (PVH) hypothalamic nuclei and lateral hypothalamic area (LHA) were each microdissected from adult male rats pretreated by caudal fourth ventricular administration of the selective CA neurotoxin, 6-hydroxydopamine (6-OHDA), or vehicle prior to insulin (INS)-induced hypoglycemia. Hypoglycemia stimulated ARH NPY gene expression and NPY accumulation in the ARH and LHA, but not PVH. 6-OHDA pretreatment did not modify the positive NPY mRNA response to INS, but blunted hypoglycemic augmentation of ARH and LHA NPY content while increasing PVH NPY levels in response to hypoglycemia. INS-treated rats exhibited diminished LHA ORX gene expression and increased [ARH; LHA] or decreased [PVH] tissue ORX protein levels. 6-OHDA+INS animals showed a comparable decline in ORX transcripts, but attenuated augmentation of ARH and LHA ORX content and elevated PVH ORX levels. OT mRNA and protein were respectively decreased or unchanged during hypoglycemia, responses that were uninfluenced by hindbrain CA nerve cell destruction. These results illustrate divergent adjustments in glucoregulatory neurotransmitter gene expression and site-specific protein accumulation in the hypothalamus during hypoglycemia. Evidence that 6-OHDA pretreatment does not modify NPY or ORX transcriptional reactivity to hypoglycemia, but alters hypoglycemic patterns of NPY and ORX accretion implicates dorsomedial hindbrain CA neurons in regulation of translation/post-translational processing and site-specific availability of these neurotransmitters in the hypothalamus during hypoglycemia.

Human interleukin-10 gene transfer is protective in a rat model of Parkinson's disease

In Parkinson's disease (PD) chronic inflammation occurs in the substantia nigra (SNc) concurrently with dopaminergic neurodegeneration. In models of PD, microglial activation precedes neurodegeneration in the SNc, suggesting that the underlying pathogenesis involves a complex response in the nigrostriatal pathway, and that the innate immune system plays a significant role. We have investigated the neuroprotective effect of an adeno-associated viral type-2 (AAV2) vector containing the complementary DNA (cDNA) for human interleukin-10 (hIL-10) in the unilateral 6-hydroxydopamine (6-OHDA) rat model of PD. AAV2-hIL-10 reduced the 6-OHDA-induced loss of tyrosine hydroxylase (TH)-positive neurons in the SNc, and also reduced loss of striatal dopamine (DA). Pretreatment with AAV2-hIL-10 reduced glial activation in the SNc but did not attenuate striatal release of the inflammatory cytokine IL-1beta. Assessment of rotational behavior in response to apomorphine challenge showed absence of asymmetry, confirming protection of dopaminergic innervation of the lesioned striatum. At baseline, 6-OHDA-lesioned animals displayed a deficit in contralateral forelimb use, but pretreatment with AAV2-hIL-10 reduced this forelimb akinesia. Transcriptional analyses revealed alteration of a few genes by AAV2-hIL-10; these alterations may contribute to neuroprotection. This study supports the need for further investigations relating to gene therapies aimed at reducing neuroinflammation in early PD.

6-Hydroxydopamine (6-OHDA) induces Drp1-dependent mitochondrial fragmentation in SH-SY5Y cells

Mitochondrial alterations have been associated with the cytotoxic effect of 6-hydroxydopamine (6-OHDA), a widely used neurotoxin to study Parkinson's disease. Herein we studied the potential effects of 6-OHDA on mitochondrial morphology in SH-SY5Y neuroblastoma cells. By immunofluorescence and time-lapse fluorescence microscopy we demonstrated that 6-OHDA induced profound mitochondrial fragmentation in SH-SY5Y cells, an event that was similar to mitochondrial fission induced by overexpression of Fis1p, a membrane adaptor for the dynamin-related protein 1 (DLP1/Drp1). 6-OHDA failed to induce any changes in peroxisome morphology. Biochemical experiments revealed that 6-OHDA-induced mitochondrial fragmentation is an early event preceding the collapse of the mitochondrial membrane potential and cytochrome c release in SH-SY5Y cells. Silencing of DLP1/Drp1, which is involved in mitochondrial and peroxisomal fission, prevented 6-OHDA-induced fragmentation of mitochondria. Furthermore, in cells silenced for Drp1, 6-OHDA-induced cell death was reduced, indicating that a block in mitochondrial fission protects SH-SY5Y cells against 6-OHDA toxicity. Experiments in mouse embryonic fibroblasts deficient in Bax or p53 revealed that both proteins are not essential for 6-OHDA-induced mitochondrial fragmentation. Our data demonstrate for the first time an involvement of mitochondrial fragmentation and Drp1 function in 6-OHDA-induced apoptosis.

Behavioural effects of substance P through dopaminergic pathways in the brain

Some of the highest concentrations of substance P in forebrain are found in areas where dopaminergic neurons arise or terminate. In the rat, native substance P has been injected directly into brain areas where interactions between substance P and dopamine are suspected. In the ventral tegmental area (A10 dopamine neurons), bilateral infusions of substance P induce locomotor activity and exploration. It is concluded that substance P activates A10 dopamine neurons innervating the limbic system because (i) the behavioural effects resemble those seen after systemic treatment with low doses of d-amphetamine, a drug response known to depend on the integrity of the A10 dopamine neurons; (ii) lesions to the A10 dopamine neurons abolish the behavioural response to intracerebrally infused substance P; and (iii) dopamine antagonist drugs abolish the response to substance P. In parallel experiments substance P was injected into the origins of the nigrostriatal (A9 dopamine neurons) system and found to produce stereotyped behaviour. Substance P analogues protected from enzymic degradation have been studied in these model systems. The prolongation of the behavioural effects is correlated with the presence of undegraded substance P in the ventral tegmental area. Unrelated behavioural responses are also observed, which appear not to be mediated by dopamine neurons, and probably reflect the spread of stable substance P from the ventral tegmental area to other brain sites.

Persistent dopamine functions of neurons derived from embryonic stem cells in a rodent model of Parkinson disease

The derivation of dopamine neurons is one of the best examples of the clinical potential of embryonic stem (ES) cells, but the long-term function of the grafted neurons has not been established. Here, we show that, after transplantation into an animal model, neurons derived from mouse ES cells survived for over 32 weeks, maintained midbrain markers, and had sustained behavioral effects. Microdialysis in grafted animals showed that dopamine (DA) release was induced by depolarization and pharmacological stimulants. Positron emission tomography measured the expression of presynaptic dopamine transporters in the graft and also showed that the number of postsynaptic DA D(2) receptors was normalized in the host striatum. These data suggest that ES cell-derived neurons show DA release and reuptake and stimulate appropriate postsynaptic responses for long periods after implantation. This work supports continued interest in ES cells as a source of functional DA neurons.

Cognitive Inflexibility after Prefrontal Serotonin Depletion Is Behaviorally and Neurochemically Specific

We have previously demonstrated that prefrontal serotonin depletion impairs orbitofrontal cortex (OFC)-mediated serial discrimination reversal (SDR) learning but not lateral prefrontal cortex (PFC)-mediated attentional set shifting. To address the neurochemical specificity of this reversal deficit, Experiment 1 compared the effects of selective serotonin and selective dopamine depletions of the OFC on performance of the SDR task. Whereas serotonin depletions markedly impaired performance, OFC dopamine depletions were without effect. The behavioral specificity of this reversal impairment was investigated in Experiment 2 by examining the effect of OFC serotonin depletion on performance of a modified SDR task designed to distinguish between 3 possible causes of the impairment. The results showed that the reversal deficit induced by prefrontal serotonin depletion was not due to a failure to approach a previously unrewarded stimulus (enhanced learned avoidance) or reduced proactive interference. Instead, it was due specifically to a failure to inhibit responding to the previously rewarded stimulus. The neurochemical and behavioral specificity of this particular form of cognitive inflexibility is of particular relevance to our understanding of the aetiology and treatment of inflexible behavior apparent in many neuropsychiatric and neurodegenerative disorders involving the PFC.

6-Hydroxydopamine-induced alterations in blood-brain barrier permeability

Vascular inflammation is well known for its ability to compromise the function of the blood--brain barrier (BBB). Whether inflammation on the parenchymal side of the barrier, such as that associated with Parkinson's-like dopamine (DA) neuron lesions, similarly disrupts BBB function, is unknown. We assessed BBB integrity by examining the leakage of FITC-labeled albumin or horseradish peroxidase from the vasculature into parenchyma in animals exposed to the DA neurotoxin 6-hydroxydopamine (6OHDA). Unilateral injections of 6OHDA into the striatum or the medial forebrain bundle produced increased leakage in the ipsilateral substantia nigra and striatum 10 and 34 days following 6OHDA. Microglia were markedly activated and DA neurons were reduced by the lesions. The areas of BBB leakage were associated with increased expression of P-glycoprotein and beta 3-integrin expression suggesting, respectively, a compensatory response to inflammation and possible angiogenesis. Behavioural studies revealed that domperidone, a DA antagonist that normally does not cross the BBB, attenuated apomorphine-induced stereotypic behaviour in animals with 6OHDA lesions. This suggests that drugs which normally have no effect in brain can enter following Parkinson-like lesions. These data suggest that the events associated with DA neuron loss compromise BBB function.

Novel potential neuroprotective agents with both iron chelating and amino acid-based derivatives targeting central nervous system neurons

Antioxidants and iron chelating molecules are known as neuroprotective agents in animal models of neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). In this study, we designed and synthesized a novel bifunctional molecule (M10) with radical scavenging and iron chelating ability on an amino acid carrier likely to be a substrate for system L, thus targeting the compound to the central nervous system (CNS). M10 had a moderate iron affinity in HEPES buffer (pH 7.4) with logK(3)=12.25+/-0.55 but exhibited highly inhibitory action against iron-induced lipid peroxidation, with an IC(50) value (12microM) comparable to that of desferal (DFO). EPR studies indicated that M10 was a highly potent *OH scavenger with an IC(50) of about 0.3 molar ratio of M10 to H(2)O(2). In PC12 cell culture, M10 was at least as potent as the anti-Parkinson drug rasagiline in protecting against cell death induced by serum-deprivation and by 6-hydroxydopamine (6-OHDA). These results suggest that M10 deserves further investigation as a potential agent for the treatment of neurodegenerative disorders such as AD and PD.

Molecular cloning and characterization of rat karyopherin α1 gene: structure and expression

Dopamine denervation in the striata of patients with Parkinson's disease (PD) leads to changes in neural plasticity. However, the mechanisms leading to the changes are still poorly understood. In an effort to study the molecular events in the denervated striatum, we identified and cloned rat karyopherin alpha 1 (KPNA1), a member of the importin/karyopherin alpha (KPNA) family. DNA sequence analysis revealed that the full-length cDNA, encoding rat KPNA1, was 4975 bp with a short 5'-untranslated region (UTR) of 70 bp, a putative coding sequence of 1617 bp, and an unusually long 3'-UTR of 3266 bp. The gene shared a high degree of similarity with its mouse and human homologs at both cDNA and protein levels. By computational analysis of its genomic sequence, the transcription unit was shown to span a 44-kb region and consist of 13 exons varying in size from 89 (6th exon) to 3454 bp (13th exon), and 12 introns varying in size from 0.3 to 8.9 kb. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis demonstrated that KPNA1 transcript existed in various adult tissues. Both Northern blot and semi-quantitative RT-PCR analysis showed that the expression level of KPNA1 mRNA was altered in the denervated striatum post-lesion in a time-dependent manner, reaching the maximum at 2 weeks post-lesion. Our results suggest involvement of KPNA1 in the striatal responses to denervation following 6-hydroxydopamine (6-OHDA)-induced lesion.

Protective effects of green tea polyphenols and their major component, (-)-epigallocatechin-3-gallate (EGCG), on 6-hydroxydopamine-induced apoptosis in PC12 cells

Green tea polyphenols exert a wide range of biochemical and pharmacological effects, and have been shown to possess antimutagenic and anticarcinogenic properties. Oxidative stress is involved in the pathogenesis of Parkinson's disease. However, although green tea polyphenols may be expected to inhibit the progression of Parkinson's disease on the basis of their known antioxidant activity, this has not previously been established. In the present study, we evaluated the neuroprotective effects of green tea polyphenols in the Parkinson's disease pathological cell model. The results show that the natural antioxidants have significant inhibitory effects against apoptosis induced by oxidative stress. 6-Hydroxydopamine (6-OHDA)-induced apoptosis in catecholaminergic PC12 cells was chosen as the in vitro model of Parkinson's disease in our study. Apoptotic characteristics of PC12 cells were assessed by MTT assay, flow cytometry, fluorescence microscopy and DNA fragmentation. Green tea polyphenols and their major component, EGCG at a concentration of 200 microM, exert significant protective effects against 6-OHDA-induced PC12 cell apoptosis. EGCG is more effective than the mixture of green tea polyphenols. The antioxidant function of green tea polyphenols may account for this neuroprotective effect. The present study supports the notion that green tea polyphenols have the potential to be effective as neuropreventive agents for the treatment of neurodegenerative diseases.

Signaling pathways mediate the neuroprotective effects of GDNF

We show that the glial cell line-derived neurotrophic factor (GDNF) activates the PI3K/Akt-signaling pathway in human neuroblastoma cells that express functional Ret-receptor complexes. Consistent with this finding we show PI3K-dependent Bad-inactivation by binding to 14-3-3 proteins in response to GDNF. Using differential display techniques we detected several cDNA clones differentially expressed after treatment with GDNF or 6-OHDA.

Interactions of the neurotoxin 6-hydroxydopamine with glyceraldehyde-3-phosphate dehydrogenase

The neurotoxin 6-hydroxydopamine (6-OHDA) oxidised sulphydryl groups in glyceraldenyde-3-phosphate dehydrogenase (GAPDH) with loss of the dehydrogenase activity of the enzyme. 5-Hydroxydopamine behaved similarly at higher concentrations. This oxidation was accompanied by a transient rise in the acyl phosphatase (non-phosphorylating) activity of GAPDH. Treatment with arsenite resulted in loss of the acyl phosphatase activity and restoration of the dehydrogenase activity, consistent with the process involving sulphydryl-group oxidation to the corresponding sulphenate. Prolonged incubation with 6-OHDA resulted in a loss of both enzyme activities. Arsenite was unable to reverse this inhibition, indicating further oxidation, perhaps to sulphinate and sulphonate, to have occurred. RNA, but not DNA, was a partial inhibitor of both the dehydrogenase and acyl phosphatase activities of GAPDH, whereas DNA (both single- and double-stranded) was ineffective. Both single-stranded DNA and RNA inhibited the esterase activity of GAPDH, an activity that requires the absence of NAD+, in a process that was relieved at higher polynucleotide concentrations. Except at very high concentrations (1 mM), treatment of GAPDH 6-OHDA was ineffective at abolishing its to single-stranded DNA. Since GAPDH is an essential enzyme in glycolysis and also plays a role in apoptotic cell death, these results suggest that the effects on this enzyme may contribute to the neurotoxicity of 6-OHDA.

Use of 6-hydroxydopamine to deplete brain catecholamines in the rhesus monkey: effects on urinary catecholamine metabolites and behavior

The purpose of this study was to determine: 1) whether 6-hydroxydopamine (6-OHDA), previously shown to deplete brain catecholamines (CA) in rodents, depletes brain CA in rhesus monkeys; 2) whether depletion of brain CA produces changes in behavior; and, 3) whether urinary output of 3-methoxy-4-hydroxyphenylglycol (MHPG) reflects brain norepinephrine (NE) depletions. Repeated intracerebroventricular (ICV) injection of 6-OHDA (N = 20; 15.5-73.3 mg/subject) produced chronic changes in social behavior and, at higher dosages, reduced output of urinary MHPG. However, 4 weeks after the last ICV 6-OHDA injection, urinary MHPG excretion returned to baseline values and whole brain CA content was not reliably different from control. A single treatment with 6-OHDA microinjected into the substantia nigra (SN) (N = 12; 120-240 microgram/subject) produced chronic whole brain depletions of brain CA without depleting serotonin. Reductions in brain CA were associated with a specific set of motor behaviors, aphagia, and adipsia. SN 6-OHDA produced greater brain NE depletions than ICV 6-OHDA, but urinary MHPG output was not reduced. SN 6-OHDA treated subjects showed chronic changes in social behavior and were more sensitive to the operant response rate decreasing effects of alpha-methyl-para-tyrosine (AMPT) than control subjects. Subjects with the largest depletions of brain dopamine (DA) (greater than 90%) were hypokinetic, rigid, and had a distal limb tremor. These results show that SN but not ICV injection of 6-OHDA can deplete brain CA in the rhesus monkey. The most prominent behavioral changes were characterized by disturbances in motor function. Urinary MPHG output does not reflect depletions of brain NE in this species.

In vitro loading of human synovial membrane with 5-hydroxydopamine: evidence for dense core secretory granules in type B cells

Ultrastructural studies of the synovial membrane were performed on tissue samples obtained from the human lumbar facet joint. Ultrastructural changes in synoviocytes were studied after loading synovial samples with 5-hydroxydopamine (5-OHDA) in an oxygenated Krebs' solution, prior to fixation. Synoviocytes were set loosely in the intimal matrix and classified into type A (phagocytic) and type B (secretory) cells. In general, type A cells populated the surface of the synovial lining, whereas type B cells were located deeper in the tissue, extending a process into the synovial fluid. Type B cells in control samples contained sparse secretory granules. Free nerve endings were not found in the synovial intima. In response to incubation in 5-OHDA, a precursor of biogenic monoamines, synoviocytes clustered and established contact. The ultrastructure of type B cells in the loaded group clearly differed from controls. They possessed typical membrane-bound vesicles, containing an electron dense interior surrounded by a lucent space. The size of these dense core vesicles ranged from 100 to 260 nm (on average 180 nm). They were in relation to microtubules and located preferentially in the marginal area of the cytoplasm, close to the Golgi complex. The ultrastructure of type A cells was not significantly altered. The present observations provide morphological evidence for the amine-handling properties of type B cells, indicating that they might be added to the list of 'APUD' cells of the diffuse neuroendocrine system. A recepto-secretory function for type B cells is discussed.

GABAA receptor subunit expression in intrastriatal ventral mesencephalic transplants

To compare the expression of GABAA receptor subunits in the normal substantia nigra and in fetal mesencephalic neurons ectopically transplanted into the dopamine-depleted striatum, we have employed single and double immunocytochemical approaches using tyrosine hydroxylase (TH) and alpha 1, alpha 2, alpha 3, and beta 2/3 GABAA receptor subunit specific antibodies. In the substantia nigra, alpha 1 and beta 2/3 GABAA receptor subunits were labeled in processes in the pars compacta (SNc) and, more intensely, in both somata and processes in the pars reticulata (SNr). There was no clear TH and alpha 1 or beta 2/3 colocalization, with the exception of some TH-immunoreactive (-ir) neurons that showed a weak immunoreactivity for beta 2/3. Sections immunolabeled for alpha 2 showed a faint diffuse labeling for this subunit both in the SNr and in the SNc. Scattered somata were immunopositive for alpha 2, and some of them were also TH-ir. The labeling for alpha 3 and TH showed that TH-positive neurons expressed intense alpha 3 immunoreactivity, although some TH-negative somata in the SNr expressed weak alpha 3 immunoreactivity. In the transplants, double immunostaining procedures showed that the labeling for alpha 1 or beta 2/3 appeared particularly concentrated in patches of intensely immunoreactive neuronal processes that surrounded TH-ir cells, but these processes were not TH-ir. In the case of alpha 2, diffuse immunostaining was observed all over the graft, with some scattered positive somata. Only a few of them were also TH positive. Sections immunoreacted for alpha 3 and TH revealed that TH-ir neurons expressed intense alpha 3 immunoreactivity, and that only a few TH-negative neurons were weakly positive for alpha 3. These results show that mesencephalic tissue ectopically grafted into the striatum develops a pattern of GABAA receptor expression similar to that normally expressed in situ, and particularly that the grafted dopaminergic neurons express similar GABAA receptors, including the alpha 3 subunit. This might be due to the similarity of GABAergic afferents to these neurons in the SNc and the graft, or that at the time of transplantation this expression had already been determined.

Spontaneous synaptogenesis in ex vivo sympathetic ganglion and the blockade by serum treatment

Central denervation for more than 1 month has been shown to cause an increase in the number of adrenergic synapses in sympathetic ganglia in vivo. Here, we report several lines of evidence that adrenergic synapses may be generated de novo in ex vivo superior cervical ganglion (SCG) of adult rats only several hours after the isolation. Structures immunoreactive for synaptophysin, a marker of presynaptic elements, were drastically decreased 6 days after the preganglionic denervation. A significant increase in number of synaptophysin positive boutons was observed over 3-8 hours in the denervated SCGs maintained ex vivo at 36 degrees C in oxygenated physiologic saline, and this increase was blocked by adding normal serum in the saline. Electron microscopic analysis confirmed that the number of adrenergic synapses specifically labeled with 5-hydroxydopamine was increased by several-fold under the same condition. Intracellular labeling of SCG neurons revealed an increase in the incidence (from 8 to 50%) of neurons having dendritic plexus after the in vitro incubation. No evidence of axonal sprouting within the ganglion was observed. Intracellular recordings from single neurons of denervated SCGs revealed that maximum amplitudes of inhibitory postsynaptic potentials, which were completely blocked by yohimbine, an alpha2-adrenoceptor antagonist, in response to focal stimulation were increased over the several hours. These results suggest that dendrites of SCG neurons rapidly develop and exhibit local efferent characteristics that underlie the inhibitory synaptic transmission once they are subjected to serum deprivation.

Stimulant-induced exocytosis from neuronal somata, dendrites, and newly formed synaptic nerve terminals in chronically decentralized sympathetic ganglia of the rat

Loss of preganglionic neurones underlies the autonomic failure of human multiple system atrophy. In rat sympathetic ganglia decentralization leads to new synapse formation. We explored whether these synapses are functional, and whether chronically decentralized neurones respond normally to activation, in terms of exocytosis. Potassium depolarization and cholinergic agonists were applied to freshly excised rat superior cervical sympathetic ganglia, preganglionically denervated with prevented reinnervation 5 months earlier. Ganglia were incubated and stimulated in the presence of tannic acid, which stabilizes released vesicle cores for subsequent electron microscopy. In denervated ganglia exocytosis was observed from newly formed synaptic nerve terminals, and from nonsynaptic surfaces of neurone somata and dendrites. The results demonstrated that the new intraganglionic synapses, which are mostly catecholaminergic, can function and that chronically decentralized sympathetic neurones remain capable of stimulant-induced exocytosis from somata and dendrites. The maximal release upon potassium depolarization did not differ significantly between denervated and contralateral ganglia. Relative to this, the exocytotic responses of decentralized somata and dendrites to nicotine resembled those of contralateral ganglia. Responses to muscarine were significantly less in denervated than in contralateral ganglia, indicating inhibition in dendrites. Responses to carbachol suggested interactions between nicotinic and excitatory muscarinic effects. Nerve terminals in denervated ganglia showed high basal release. Their responses to muscarine and carbachol resembled those of the decentralized neurones, from which most may originate. Their response to nicotine evidenced inhibition. Their actions, coupled with nonsynaptic effects of soma-dendritic exocytosis, might modulate responses of the decentralized neurone population to other surviving inputs. This modulation could be influential in disease-induced decentralization in man.

Caffeine-mediated induction of c-fos, zif-268 and arc expression through A1 receptors in the striatum: different interactions with the dopaminergic system

Adenosine and the adenosine receptor antagonist, caffeine, modulate locomotor activity and striatal neuropeptide expression through interactions with the dopaminergic system by mechanisms which remain partially undetermined. We addressed this question by using quantitative immunocytochemistry and in situ hybridization, combined with retrograde tracing of striatal neurons, to characterize the mechanism(s) leading to the striatal increase in the immediate early genes (IEG), c-fos, zif-268 and arc, following a single injection of caffeine or the A1 antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). Caffeine and DPCPX induced c-fos, zif-268 and arc expression, both at mRNA and protein levels, in large proportions of striatonigral and striatopallidal neurons. The involvement of dopamine systems was evaluated by manipulations of the dopaminergic transmission. Quinpirole, a D2 agonist, almost completely blocked the caffeine-induced IEG increase in both striatopallidal and striatonigral neurons. Conversely, the lesion of the nigrostriatal pathway and the D1 antagonist SCH23390 abolished the caffeine effects in striatonigral neurons but had no or slight effect, respectively, on its action in striatopallidal neurons. These observations demonstrate that caffeine- and DPCPX-mediated IEG inductions involved different mechanisms in striatonigral and striatopallidal neurons through blockade of A1 receptors. Immediate early gene inductions result from a stimulation of dopamine release in striatonigral neurons and from activation of glutamate release and probably also acetylcholine release in striatopallidal neurons. These results also support the idea that, besides A2A receptors, adenosine acting at the A1 receptor plays pivotal functions in the basal ganglia physiology and that blockade of these receptors by specific or nonspecific antagonists, DPCPX and caffeine, may influence a broad range of neuronal functions in the striatum.

Contribution of opioid receptors on primary afferent versus sympathetic neurons to peripheral opioid analgesia

Opioid receptors are synthesized in dorsal root ganglia and transported into peripheral terminals of primary afferent neurons. Activation of such receptors results in antinociceptive effects that are most prominent in inflammation. In addition, opioid receptors located on sympathetic postganglionic neuron terminals may be involved in these effects. This study investigates the peripheral analgesic efficacy of the mu, delta and kappa receptor agonists [D-Ala2,N-Me-Phe4,Gly-ol5]-enkephalin, [D-Pen2,5]-enkephalin and trans-(+/-)3, 4-Dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneacetamid e, the effective number of peripheral mu, delta and kappa receptors in relation to the development of inflammation and the contribution of sympathetic vs. sensory neurons by use of capsaicin and 6-hydroxydopamine, respectively. In Wistar rats with Freund's adjuvant-induced hindpaw inflammation, antinociceptive effects of intraplantar [D-Ala2,N-Me-Phe4,Gly-ol5]-enkephalin (1.0-32 microg), [D-Pen2,5]-enkephalin (10-100 microg) and trans-(+/-)3, 4-Dichloro-N-methyl-N-[2-(l-pyrrolidiny)-cyclohexyl]-benzeneace tam ide (10-100 microg) were evaluated by paw pressure test. These effects increased linearly between 6 and 24 hr, but did not change between 24 and 96 hr of inflammation, whereas the doses of the irreversible antagonists beta-funaltrexamine, [D-Ala2,Leu5,Cys6]enkephalin or (+/-)-(5beta,7a,8beta)-3, 4-dichloro-N-[3-methylene-2-oxo-8-(1-pyrrolidinyl)-1-oxaspir[4, 5]dec-7-yl]benzeneacetamide required to abolish the respective agonist effects increased between 12 and 96 hr. Pretreatment with capsaicin (30, 50, 70 mg/kg s.c. over 3 days) but not with 6-hydroxydopamine (75 mg/kg i.p. over 3 days) reversed the hyperalgesia in inflamed paws and almost abolished antinociceptive effects of all three agonists. These results suggest that the increased opioid agonist efficacy is due to an increased number of peripheral opioid receptors at later stages of inflammation and that peripheral opioid antinociceptive effects are primarily mediated by mu, delta and kappa opioid receptors on primary afferent neurons.

In vivo chronoamperometric measures of extracellular serotonin clearance in rat dorsal hippocampus: contribution of serotonin and norepinephrine transporters

The effects of blockade of serotonin (5-HT) and norepinephrine (NE) transporters (SERT and NET, respectively) on the removal of locally applied 5-HT from extracellular fluid (ECF) were examined using in vivo chronoamperometry. Male Sprague-Dawley rats were anesthetized with chloralose/urethane, and a Nafion-coated, carbon fiber electrode attached to a multibarrel micropipette was positioned into either the dentate gyrus or CA3 region of the dorsal hippocampus. Pressure ejection of 5-HT elicited reproducible electrochemical signals of similar peak amplitude and time course in both structures. Local application of the selective serotonin reuptake inhibitors (SSRI) fluvoxamine and citalopram prolonged the clearance of 5-HT in both brain regions and also increased signal amplitude in the CA3 region. These effects were abolished in rats pretreated with 5, 7-dihydroxytryptamine (5,7-DHT), a selective 5-HT neurotoxin. The NE uptake inhibitors desipramine (DMI) and protriptyline did not alter the 5-HT signal in the CA3 region but prolonged the clearance of 5-HT in the dentate gyrus; this effect was absent in rats pretreated with 6-hydroxydopamine (6-OHDA), a selective catecholamine neurotoxin. The prolongation of the removal of 5-HT from the ECF in the dentate gyrus caused by fluvoxamine or desipramine was of comparable magnitude and was dose dependent. Furthermore, per picomole of 5-HT applied, the signal amplitude and clearance time were significantly increased in the dentate gyrus of rats lesioned with either 5,7-DHT or 6-OHDA. Only 5,7-DHT treatment caused this effect in the CA3 region. From these data, it is inferred that in certain regions of brain (dentate gyrus), both the SERT and NET contribute to the active clearance of exogenously applied 5-HT.

Locus coeruleus lesions suppress the seizure-attenuating effects of vagus nerve stimulation

PURPOSE

Although vagus nerve stimulation (VNS) is now marketed throughout most of the world as a treatment for drug-resistant epilepsy, the therapeutic mechanism of action of VNS-induced seizure suppression has not yet been established. Elucidation of this mechanism is an important first step in the development of strategies to improve VNS efficacy. Because the locus coeruleus (LC) has been implicated in the antinociceptive effects of VNS, we chemically lesioned the LC in the present study to determine if it is a critical structure involved in the anticonvulsant mechanisms of VNS.

METHODS

Rats were chronically depleted of norepinephrine (NE) by a bilateral infusion of 6-hydroxydopamine (6-OHDA) into the LC. Two weeks later, they were tested with maximal electroshock (MES) to assess VNS-induced seizure suppression. In another experiment, the LC was acutely inactivated with lidocaine, and seizure suppression was tested in a similar fashion.

RESULTS

VNS significantly reduced seizure severities of control rats. However, in animals with chronic or acute LC lesions, VNS-induced seizure suppression was attenuated.

CONCLUSIONS

Our data indicate that the LC is involved in the circuitry necessary for the anticonvulsant effects of VNS. Seizure suppression by VNS may therefore depend on the release of NE, a neuromodulator that has anticonvulsant effects. These data suggest that noradrenergic agonists might enhance VNS-induced seizure suppression.

Dissociation of morphine-induced potentiation of turning and striatal dopamine release by amphetamine in the nigrally-lesioned rat

Morphine has been reported to increase extracellular levels of dopamine in the brain of intact rats and to potentiate turning induced by amphetamine in nigrally-lesioned rats. The present study tested the hypothesis that there is a causal relationship between these two effects of morphine. We tested morphine alone, amphetamine alone, and the combination in separate groups of nigrally-lesioned rats for effects on turning and, by microdialysis, on extracellular dopamine levels. Morphine (3.0 or 10 mg/kg) did not produce significant turning but amphetamine (1.0 mg/kg) did. The lower dose, but not the higher dose, of morphine potentiated amphetamine-induced turning. Amphetamine, but not morphine, produced increases in extracellular dopamine levels. In contrast to what occurred with turning, 10 mg/kg but not 3.0 mg/kg morphine potentiated amphetamine-induced increases in extracellular dopamine levels. These results show that the potentiation of amphetamine-induced turning by morphine in nigrally-lesioned rats is not due to the potentiation of dopamine release in the intact striatum.

[Biomedical aspects of health preservation strategy: role of catecholaminergic neuronal populations]

Lifestyle, environmental factors, genetics, and medical care are the main factors that determine the health status of man. Of particular attention are biological mechanisms ensuring the body's adaptation to constantly changing environmental conditions. The noradrenergic neuronal populations, the sympathetic nervous system in particular, modulate metabolic processes and supports a variety of activities, making them relevant to changing living conditions. There is a clear correlation between the life span and the number of sympathetic nerve cells functioning during postnatal ontogenesis. The exposures that reduce the activity of peripheral and central noradrenergic neurons and slow down aging processes in them loosen the relationships between the inner and outer world to prevent hyperactivity and to prolong life.

Dopaminergic control of light-adaptive synaptic plasticity and role in goldfish visual behavior

Dopamine has been implicated in processes of retinal light and dark adaptation. In goldfish retina, horizontal cell dendrites elaborate neurite processes (spinules) into cone terminals, in a light- and dopamine-dependent manner. However, the functions of retinal dopamine and the horizontal cell spinules in visual behavior are unknown. These issues were addressed in behavioral, electroretinographic, and anatomical studies of normal fish and those with unilateral depletion of retinal dopamine induced by intraocular (i.o.) injections with 6-hydroxydopamine (6-OHDA). Dopamine interplexiform cells (DA-IPC) disappear within 2 weeks after 6-OHDA injection; cell bodies appear at the marginal zone within 6 weeks at which time neurites slowly reinnervate the retina with a sparse plexus over the next 12 months. We found that dopamine depletion increased light sensitivity at photopic but not scotopic backgrounds by 2.5 log units, an effect mimicked by i.o. injections of dopamine D1 and D2 antagonists. The ERG b-wave increment thresholds were the same for control and dopamine depleted eyes, indicating a normal transition from rod to cone systems in the ON pathway. Light-dependent spinule formation was reduced by about 60% in dopamine-depleted retinas, but returned to normal by 3 months and 9 months after injection in the entire retina, even areas not directly innervated with DA-IPC processes. Spinule formation in vivo was inhibited 50% with i.o. injection of SCH 23390 in control retinas as well as throughout 3 month 6-OHDA injected retinas, including DA-IPC free areas. This latter result indicates a volume effect of dopamine, diffusing laterally through the retina over several millimeters, in regulating spinules. We conclude that DA-IPCs regulate sensitivity to background at photopic levels not via the ON pathway, but perhaps the OFF pathway. Goldfish display both increased sensitivity to light and a normal Purkinje shift in the ERG b-wave whether or not horizontal cell spinules are present, indicating that dopamine control of photopic vision in fish is not mediated through light-induced spinule formation of horizontal cell dendrites.

Reduction of red-green discrimination by dopamine D1 receptor antagonists and retinal dopamine depletion

Reduction of wavelength discrimination ability in the 560-640 nm range, but not in the 404-540 nm range, has been demonstrated in goldfish after intravitreal injection of D1-dopamine receptor antagonists. Intravitreal injection of the dopaminergic neurotoxin 6-OH-dopamine severely reduced wavelength discrimination ability in the 540-661 nm range within 3 days. Discrimination ability could be reconstituted by the D1-agonist SKF 38393. Animals recovered from injection of 6-OH-dopamine within 14-16 days. No change of wavelength discrimination was induced by 6-OH-dopamine in the 461-540 nm range. We conclude that under photopic conditions dopamine modulates retinal mechanisms involved in red-green colour coding via D1-dopamine receptor-like binding sites.

Fetal ventral mesencephalon of human and rat origin maintained in vitro and transplanted to 6-hydroxydopamine-lesioned rats gives rise to grafts rich in dopaminergic neurons

Free-floating roller tube cultures of human fetal (embryonic age 6-10 weeks post-conception) and rat fetal (embryonic day 13) ventral mesencephalon were prepared. After 7-15 days in vitro, the mesencephalic tissue cultures were transplanted into the striatum of adult rats that had received unilateral injections of 6-hydroxydopamine into the nigrostriatal bundle 3-5 weeks prior to transplantation. Graft survival was assessed in tyrosine hydroxylase (TH)-immunostained serial sections of the grafted brains up to post-transplantation week 4 for the human fetal xenografts and post-transplantation week 11 for the rat fetal allografts. D-amphetamine-induced rotation was monitored up to 10 weeks after transplantation in the allografted animals and compared with that of lesioned-only control animals. All transplanted animals showed large, viable grafts containing TH-immunoreactive (ir) neurons. The density of TH-ir neurons in the human fetal xenografts and in rat fetal allografts was similar. A significant amelioration of the amphetamine-induced rotation was observed in the animals that received cultured tissue allografts. These results promote the feasibility of in vitro maintenance of fetal human and rat nigral tissue prior to transplantation using the free-floating roller tube technique.

The effects of 5-hydroxydopamine on salivary flow rates and protein secretion by the submandibular and parotid glands of rats

The secretory effects of 5-hydroxydopamine (5-OHDA) were tested in Nembutal-anaesthetized adult male Sprague-Dawley rats injected I.V. over a wide range of doses, with and without various autonomic antagonists and Ca2+ channel blockers. Polyacrylamide disc gel (15%) and iso-electric focusing (IEF) electrophoresis by the PhastSystem were used to separate and determine the types of protein in submandibular saliva. Amylase activity of parotid saliva was determined by the blue dextran method. Salivation by the submandibular glands following application of 5-OHDA was completely abolished by both prazosin and propranolol, whereas salivation by the parotid glands was completely abolished by propranolol alone. Following application of 5-OHDA, there was a dose-related increase in flow rates and total output of protein, but not in the protein concentration and amylase activity, from both salivary glands. The effect of 5-OHDA on submandibular saliva was significantly reduced by alpha-adrenoceptor blockers, but not by beta-adrenoceptor and cholinergic blockers, nor by any Ca2+ channel blocker. The effect of 5-OHDA on the parotid gland was not significantly altered by atropine and phentolamine. However, after pretreatment with reserpine, a 95% reduction was observed in the salivation from the submandibular gland. This implies that 5-OHDA is mostly acting indirectly via release of noradrenaline. The proteins in submandibular saliva following treatment with 5-OHDA alone or 5-OHDA in combination with beta-adrenoceptor blockers were mainly of the alpha-type, whereas after treatment with 5-OHDA in combination with alpha-adrenoceptor blockers they were of the beta-type. The alpha-type was found in saliva after treatment with each of three Ca2+ channel blockers.

Catecholamines in steroid-dependent brain development

Sex-specific peculiarities of catecholamine (CA) content and turnover in neuroendocrine brain areas and their modification with neonatal steroids or prenatal stress (PS) in Wistar rats were studied. No changes in noradrenaline (NA) content and turnover rate were found in the preoptic area (POA), meanwhile dopamine (DA) turnover rates in the POA and mediobasal hypothalamus (MBH) were increased in neonatally androgenized 10-day-old females. Treatment of female neonates with various catecholestrogens increased hypothalamic NA content by 30-95% but only 4-hydroxyestradiol-17 beta induced anovulation. 6-Hydroxydopamine had no significant impact on hypothalamic CA content in neonates and did not prevent testosterone-induced persistent estrous. Maternal stress (restriction for 1 h a day, 15-21st days of pregnancy) resulted in a decrease of hypothalamic NA and blood plasma corticosterone response to acute stress in adult male offspring. Sex differences in CA content in the POA and MBH disappeared in 10-day-old prenatally stressed rats.

CONCLUSIONS

(1) sexual brain differentiation needs co-operative actions of sex steroids and CA to be completed; and (2) early changes in CA content and turnover induced by PS or neonatal steroid exposure predetermine long-term alterations of the stress responsiveness, reproductive behaviour and neuroendocrine control of ovulation.

5-hydroxydopamine-labeled dopaminergic axons: three-dimensional reconstructions of axons, synapses and postsynaptic targets in rat neostriatum

Previous studies employing 5-hydroxydopamine to identify nigrostriatal dopaminergic axons and their synapses found that labeled axons made few synapses or that asymmetric contacts predominated. In contrast, recent studies using tyrosine hydroxylase or dopamine antibody techniques indicate that presumed dopaminergic axons form small symmetric contacts. We re-examined 5-hydroxydopamine-labeled material from the rat neostriatum using serial three-dimensional reconstruction techniques to characterize the morphology of labeled axons, synapses and postsynaptic targets. This ultrastructural analysis revealed a class of heavily labeled axons that are small (0.06-1.5 microns in diameter) and lack large varicosities. These axons form small (0.011-0.09 microns 2), en passant, symmetric synapses, mainly onto dendritic spines and spiny dendritic shafts and, in some cases, onto aspiny dendritic segments near branch points. The sites of these synapses along the axon appeared unrelated to the locations of axonal enlargements, suggesting that counting varicosities may not be an accurate indication of the extent of dopaminergic innervation in the neostriatum. The characteristics of these 5-hydroxydopamine-labeled elements correspond in all respects to axons and synapses identified as dopaminergic by immunohistochemistry in previous studies. In tissue in which all labeled and unlabeled synapses were classified, approximately 9% of all synapses were identified as dopaminergic by this type of label. Three-dimensional reconstructions provided additional insight concerning the interaction of dopaminergic afferents with postsynaptic striatal targets and their relation to other afferents to these neurons. They reveal that a short, unbranched dopaminergic axonal segment can make multiple synapses onto dendritic spines, shafts and branch points of one or more dendrites. In addition, one dendrite can receive contacts from several labeled axons. Dopamine synapses onto spines are always associated with unlabeled, asymmetric synapses onto the same spine. Synapses of various morphologies with a distinctly different, lighter form of labeling were much rarer, and may represent other aminergic afferents to the neostriatum. The presence of this second form of label in earlier 5-hydroxydopamine studies may have contributed to the long-standing controversy over the appearance of dopaminergic synapses examined by different techniques. Our results help to resolve this controversy and confirm that the nigrostriatal projection makes small symmetric synapses with a variety of striatal targets.

A microdialysis study on striatal dopamine, 5-HT and metabolites in conscious rats after various treatments: evidence for extravesicular release of dopamine

The effects of death and various treatments that affect the status of nigrostriatal neurones on striatal release of dopamine (DA) and 5-hydroxytryptamine (5-HT) and their metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxy-4-hydroxyphenylethylamine (3-MT), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were studied by in vivo microdialysis. In conscious rats, DA and 5-HT levels were very low compared with their metabolites except 3-MT which was rarely detectable. Upon death by pentobarbitone overdose, there was an immediate surge of the DA level reflecting massive release of the neurotransmitter. This increase was accompanied by a significant increase in 3-MT level but not the other two DA metabolites. Post mortem release of 5-HT was also observed but to a much smaller extent than that of DA. The amounts of amines released appeared to be proportional to the amine stores. When L-dihydroxyphenylalanine (DOPA) was administered to reserpinized rats, the extracellular levels of both DOPAC and HVA increased but not that of DA. However, marked release of DA occurred at death in contrast to reserpinized rats not injected with the precursor. It is evident that exogenous L-DOPA is taken up into the dopaminergic nerve endings and is converted to releasable extravesicular DA, and that this releasable DA is released, at least in part, in accordance with neuronal activities.

Localisation of nitric oxide synthase within non-adrenergic, non-cholinergic nerves in the mouse anococcygeus

Immunocytochemical staining of whole mount preparations of the mouse anococcygeus muscle, using antibodies to rat brain nitric oxide synthase (NOS), revealed a dense network of NOS-immunoreactive nerve fibres running through the tissue. These fibres were resistant to the sympathetic neurotoxin 6-hydroxydopamine and are therefore likely to be the non-adrenergic nerves which mediate relaxation of this smooth muscle. Further, NOS-immunoreactive fibres were absent following denervation by cold-storage (4 degrees C; 72 h), which has been shown to abolish non-adrenergic, non-cholinergic (NANC) relaxations. The results provide strong support for the hypothesis that the L-arginine:NO pathway is responsible for the generation of the NANC transmitter in the anococcygeus.

Dopaminergic neuronal sprouting and behavioral recovery in hemi-parkinsonian rats after implantation of amnion cells

Cells obtained from human, monkey, or rat term amnion membrane produce an activity which, in vitro, increases process outgrowth from rat sympathetic neurons and from dopaminergic neurons of the rat ventral mesencephalon. To determine if these cells could induce sprouting of dopaminergic nerve fibers in vivo, the substantia nigra of rats was lesioned unilaterally with 6-hydroxydopamine and live-rat-term amnion cells, or killed-rat-term amnion cells were implanted into the denervated striata. A control group of rats received saline injections into the denervated striata. Rats implanted with live amnion cells had a significant decrease in turning in response to amphetamine. The lesioned and implanted striata of live-amnion-cell-implanted rats contained significantly greater areas of tyrosine hydroxylase-immunoreactive fibers than the lesioned and implanted striatum of rats in the killed-amnion-cell or saline groups. Differences in the area of tyrosine hydroxylase-immunoreactive fibers in the implanted striata or in amphetamine-induced rotation between killed amnion cell-implanted and saline-injected rats did not reach significance. Implants of live amnion cells into the striatum of a parkinsonian animal model can evoke the de novo appearance of dopaminergic fibers in the denervated striatum and behavioral recovery, most likely through a trophic mechanism.

Effects of 5-hydroxydopamine and 6-hydroxydopamine on the ultrastructure of type I cells in paraganglia of the rat recurrent laryngeal nerve

The ultrastructure of the Type I cells in paraganglia of rat recurrent laryngeal nerve (RLN) was studied after the administration of 5-hydroxydopamine (5-OHDA) and 6-hydroxydopamine (6-OHDA). Normal Type I cells of RLN-paraganglia contained abundant organelles and their cytoplasm was characterized by the presence of numerous membrane-bounded dense-cored vesicles (DCVs). The DCVs were round in profile (diameter 107.67 +/- 0.06 nm, all values expressed as mean +/- s.e.m. in the present study) and possessed dense cores of moderate to low electron density. After 5-OHDA treatment (single injection, 100 mg/kg b.w., i.v.), the majority of DCVs were filled with a material of high electron density. No significant difference was observed between the profile diameter of the DCVs in 5-OHDA-treated rats (104.96 +/- 0.06 nm) and that in normal rats. After 6-OHDA treatment (three injections, 100 mg/kg b.w. each at 12 h intervals i.p.), no significant alteration in the electron density of the core was noted. However, most of the DCVs were enlarged and round, elliptical or irregular in profile (190.57 +/- 2.77 nm x 130.34 +/- 2.09 nm). The dense core of DCVs was centrally or eccentrically located in DCVs. The results of the present study indicate that: 1) there is only one type of granulated glomus cell (i.e., Type I cells) in the rat RLN-paraganglia under normal physiological condition; and 2) since the ultrastructural morphology of DCVs in Type I cells of rat RLN-paraganglia is altered after 5-OHDA or 6-OHDA treatment, these cells may possess mechanisms for the uptake of false adrenergic neurotransmitter and/or neurotoxin.

Behavioral quantification of striatal dopaminergic supersensitivity after bilateral 6-hydroxydopamine lesions in the mouse

Quantitative studies using dopamine (DA) agonist-induced rotational behavior after denervation have found that the behavioral sensitivity is much greater than would be predicted on the basis of striatal DA receptor upregulation alone. The sensitivity to DA agonists after chronic treatment with neuroleptics, which elicits striatal receptor alterations equal to denervation, displays increases more consistent with alterations in striatal receptor density. Since the behavioral paradigms used to assess agonist supersensitivity after denervation are different than that for chronic neuroleptic treatment (rotational vs. stereotypic behavior), we measured the behavioral supersensitivity after bilateral denervation using stereotypic behavior. The increase in sensitivity to apomorphine after bilateral nigrostriatal 6-hydroxydopamine lesions was consistent with the increases measured previously with rotational behavior. These data suggest that the quantitative difference observed in behavioral supersensitivity resulting from the different preparations lies with the biological consequences of denervation rather than with the behavioral paradigm.

Catecholamine and serotonin depletion from rat spinal cord: effects on morphine and footshock induced analgesia

Using a methodology that causes a selective degeneration of spinal cord catecholaminergic or serotoninergic pathways but not those of the brain, it has been possible to study more precisely the role played by the spinal cord monoaminergic systems that underly the mechanism through which morphine and endogenous opioids modulate nociceptive inputs. Both noradrenaline (NA) and serotonin (5-HT) appear to be involved: first, the noradrenergic and only subsequently, with higher doses of the opiate, the serotoninergic pathways.

Differential dopaminergic regulation of proenkephalin and prodynorphin mRNAs in the basal ganglia of rats

Proenkephalin and prodynorphin mRNA levels in the caudate-putamen and in the nucleus accumbens of rats were measured by in situ hybridization 2, 4 and 8 weeks following unilateral lesion of the medial forebrain bundle by 6-hydroxydopamine (6-OHDA). After 2 weeks a 60% increase of the levels of proenkephalin mRNA in the ipsilateral caudate-putamen was observed which declined to 20% above control after 8 weeks. A smaller increase in the levels of proenkephalin mRNA of about 20% was observed in the nucleus accumbens after 2 weeks and no significant alteration could be observed 4 and 8 weeks after lesioning. The levels of prodynorphin mRNA in the ipsilateral caudate-putamen decreased 20% below control and returned to control levels 4 and 8 weeks post-lesion. In contrast, in the nucleus accumbens a persistent ipsilateral decrease of prodynorphin (20-30%) was found 2, 4 and 8 weeks post-lesion. These findings indicate, that lesions of the mesostriatal dopamine (DA) system differentially influences opioidergic gene expression in distinct areas of the caudate-putamen. The lesions cause an increase in proenkephalin mRNA levels which was higher in the caudate-putamen than in the nucleus accumbens and tend to be reversible. Conversely, the lesion caused a persistent decrease in the levels of prodynorphin mRNA in the nucleus accumbens and a small and transient decrease in the caudate-putamen.

Expression of acidic and basic fibroblast growth factors in the substantia nigra of rat, monkey, and human

The distribution of acidic (aFGF) and basic (bFGF) fibroblast growth factor mRNA and protein were examined in mesencephalon by immunohistochemistry, immunoblot analysis, in situ hybridization histochemistry, and RNA analysis. Coexistence of aFGF or bFGF with tyrosine hydroxylase protein in nigral cells was observed with immunohistochemistry. Both aFGF and bFGF mRNAs were found in the substantia nigra. Unilateral 6-hydroxydopamine lesions of nigrostriatal neurons resulted in a loss of aFGF and tyrosine hydroxylase [L-tyrosine, tetrahydropteridine: oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] mRNA-positive neurons on the lesioned side. The distribution of aFGF mRNA in monkey brain was similar to that seen in the rat. RNA and immunoblot analysis confirmed the presence of both aFGF and bFGF mRNAs and proteins in the substantia nigra of rat, monkey, and human.

Neurokinin receptors differentially mediate endogenous acetylcholine release evoked by tachykinins in the neostriatum

The regulation of neostriatal cholinergic function by tachykinins (TKs) has been studied by measuring endogenous ACh released from rat neostriatal slices. Septide (SEP; a highly selective substance P analog), neurokinin A (NKA), and neurokinin B (NKB) elicited endogenous ACh release in a concentration-dependent manner. The rank order in potency was the following: NKB (EC50 approximately 0.5 nM) greater than NKA (EC50 approximately 7 nM) greater than SEP (EC50 approximately 12 nM). Spantide (SPA) was less effective (39% inhibition) than [D-Arg6, D-Trp7,9, N-Methyl-Phe8]-substance P fragment 6-11 (53% inhibition) at antagonizing ACh release evoked by SEP and NKA. Smaller doses of the antagonists inhibited the effects of SEP compared to NKA, and the effects of NKB could only be antagonized by SPA. These findings suggest the involvement of the three neurokinin (NK) receptors in ACh release evoked by TKs with the following rank order: NK3 greater than NK2 greater than NK1. 6-Hydroxydopamine lesions of nigrostriatal neurons and tetrodotoxin (TTX) intoxication of striatal tissue revealed two different patterns of regulation of cholinergic function by TKs. On the one hand, SEP and NKA evoked ACh release, independently of the nigrostriatal dopaminergic system, by acting on NK1 and NK2 receptors that are probably localized on the somatodendritic field of cholinergic neurons receiving substance P terminals. On the other hand, dopaminergic terminals seem to regulate NKB neurons that modulate cholinergic neurons, because NKB-evoked ACh release decreased by 24% in the denervated striata. In addition, TTX partially blocked (50%) ACh release evoked by NKB, suggesting that NKB acts on NK3 receptors at both the nerve terminals and the somatodendritic field of cholinergic neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

A5 noradrenergic unit activity and sympathetic nerve discharge in rats

Unit recording experiments were designed to determine whether A5 noradrenergic neurons contribute to the generation of the splanchnic sympathetic nerve discharge (SSND) of halothane-anesthetized rats. Neurons (presumed A5 cells) were selected on the following bases: location in the ventrolateral tegmentum rostrolateral to facial nucleus (FN), antidromic (AD) activation from thoracic spinal cord, and complete inhibition by clonidine (10-15 micrograms/kg iv). These cells (n = 59) had low rates of spontaneous firing (1.4 +/- 0.2 spikes/s) and slow conduction velocities (2.6 +/- 0.2 m/s). The AD activation of seven of eight neurons was abolished within 1 h after intraspinal microinjection of 6-hydroxydopamine (4 micrograms), but the drug failed to affect the AD responses of eight sympathoexcitatory cells located caudal to the FN (control cells). The terminal fields of 16 A5 area neurons were found in the intermediolateral cell column of the spinal cord. Most neurons (63%, 37/59) were inhibited by raising arterial pressure and by train stimulation of the aortic depressor nerve (ADN, 47%, 9/20). A few cells responded to ADN stimulation but not to arterial pressure elevation or vice versa. The discharge of the cells was correlated to the SSND and preceded a peak of SSND by 69 +/- 6 ms (12/29 in intact and 3/9 in debuffered rats). We conclude that 40% of A5 cells may have a visceral vasomotor sympathoexcitatory function.

Functional enhancement of intrastriatal dopamine-containing grafts by the co-transplantation of sciatic nerve tissue in 6-hydroxydopamine-lesioned rats

Peripheral nerve "bridges" demonstrate the ability to facilitate axonal growth and regenerate adult and fetal central nervous system tissue. The purpose of this study was to determine if co-grafted peripheral nerve tissue could enhance the ability of fetal dopamine (DA) cell transplants to reinnervate host striatum that had been denervated unilaterally. Male Fisher-344 rats were unilaterally lesioned with 6-hydroxydopamine to eliminate the nigrostriatal DA pathway. A total of 31 rats demonstrated a pattern of rotation indicative of a greater than 98% depletion in DA. Rats were kept as nongrafted controls (n = 6), grafted with sciatic nerve (PN) minces (n = 6), grafted with fetal ventral mesencephalon (VM; n = 10), or co-grafted with VM and PN minces (n = 9). All groups were then tested for changes in apomorphine-induced rotational behavior. The PN control group showed no significant differences in rotation when compared to pregrafting levels and to the lesioned nongrafted group. Both the VM-grafted group and the VM-PN co-grafted group showed significant (P less than 0.01, one-way ANOVA) decreases in rotations beginning at 1.5 weeks postgrafting. There was a progressive decrease in rotations up to 12 weeks, the last test point examined. Interestingly, the co-graft group revealed a significantly greater decrease in rotation (P less than 0.05) than the VM group beginning at 5 weeks and continuing out to the 12-week test point. Histological and immunocytochemical studies showed good survival of both PN and VM grafts. The augmented recovery could not be accounted for by increased DA cell survival or host brain DA reinnervation in the co-graft group. Taken together, these findings suggest that PN tissue enhances the ability of fetal VM grafts to reinnervate host brain.