Hypericum polyanthemum cyclohexane extract potentiates behavioral effects and neurodegeneration induced by nigral infusions of 6-hydroxydopamine in rats.

INTRODUCTION: Parkinson's Disease (PD) is a progressive neurodegenerative disorder, hallmark of which is loss of nigral dopaminergic neurons. Since a Hypericum polyanthemum extract inhibits monoamine reuptake and some of its constituents present cytotoxic properties, the aim of this study was to evaluate the effect of this extract in an animal PD model. METHODS: Adult Wistar rats (110 days old) received 6-hydroxydopamine (6-OHDA) infusions into the right medial forebrain bundle. A cyclohexane extract from aerial parts of H. polyanthemum (POL; 90 mg/kg/administration; gavage) was administered in three different regimens. In Regimens 1 and 2, rats received 3 administrations of POL starting 4 or 24 h after 6-OHDA infusion, respectively. In Regimen 3, these administrations were carried out 1 day before any evaluation of ipsilateral rotational activity induced by methylphenidate (MP, 20 mg/kg, i.p.). MP was administered 10, 45, and 85 days after 6-OHDA infusion in all groups. Nigral tyrosine hydroxylase (TH) immunocontent was evaluated 120 days after 6-OHDA infusion in animals submitted to Regimen 2 only. The effect of POL on apomorphine-induced climbing behavior in non-lesioned adult CF1 mice (60 days old) treated with POL was also evaluated. RESULTS: Regimen 2 increased MP-induced rotational activity and decreased nigral TH levels in 6-OHDA-lesioned rats. Rotational activity was not altered in regimens 1 and 3. In addition, no change in climbing behavior was observed in non-lesioned mice. CONCLUSION: Together, these results indicate that, in 6-OHDA-lesioned rats, a cyclohexane H. polyanthemum extract potentiates neurotoxicity and MP-induced motor asymmetry depending on the time of administration. In the short term, it seems to not act directly on mice dopaminergic 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.

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.

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.

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.

Catecholamines in steroid-dependent brain development.

UNLABELLED: 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.

Enhanced norepinephrine release in hypothalamus from locus coeruleus in SHR.

The hypothesis that a functional projection from the locus coeruleus (LC) to the posterior hypothalamus contributes to the development of hypertension in SHR, was tested by measuring norepinephrine (NE) in the posterior hypothalamus by brain dialysis after injections of L-glutamate (L-glu) into LC. L-glu elicited a prolonged elevation of blood pressure in both SHR and WKY. Pressor effects were significantly larger in SHR than in WKY. Extracellular NE in the posterior hypothalamus increased after LC stimulation; NE release was significantly higher in SHR than in WKY. Injections of 6-hydroxydopamine (6-OHDA) into posterior hypothalamus lowered the resting blood pressure and attenuated the pressor responses to L-glu injections into the LC in SHR. These findings suggest that the LC projects functionally to the posterior hypothalamus and that the projection can contribute to the development of hypertension in SHR.

Opioid binding in the rostral hypothalamus is reduced following lesion of the ventral noradrenergic tract in female rats.

Experiments were undertaken to establish whether opioid receptors exert a direct presynaptic influence on noradrenergic (NA) terminals in the preoptic/anterior hypothalamus (PO/AH) of the female rat. Thus, opioid binding studies were performed in rats with lesions of the ventral NA tract (VNAT; the main NA projection to the hypothalamus) to assess whether a loss of NA terminals may also result in a decrease in opioid binding in the PO/AH. In the first experiment, unilateral electrolytic lesions of the VNAT caused a significant reduction in both the NA content and specific [3H]-diprenorphine binding to membrane homogenates in the ipsilateral PO/AH. In the second experiment bilateral 6-hydroxydopamine (6-OHDA)-induced lesions of the VNAT caused a significant reduction in NA levels in the PO/AH as well as significant decreases in the density of [3H]-diprenorphine binding to tissue sections of the PO/AH when compared to control animals. These results strongly suggest that the NA input to the PO/AH is regulated by endogenous opioid peptides, and provide an anatomical substrate to explain opioid-NA interactions in the control of gonadotrophin releasing hormone (GnRH) and gonadotrophin secretion.

D1 and D2 dopamine receptor-regulated gene expression of striatonigral and striatopallidal neurons.

The striatum, which is the major component of the basal ganglia in the brain, is regulated in part by dopaminergic input from the substantia nigra. Severe movement disorders result from the loss of striatal dopamine in patients with Parkinson's disease. Rats with lesions of the nigrostriatal dopamine pathway caused by 6-hydroxydopamine (6-OHDA) serve as a model for Parkinson's disease and show alterations in gene expression in the two major output systems of the striatum to the globus pallidus and substantia nigra. Striatopallidal neurons show a 6-OHDA-induced elevation in their specific expression of messenger RNAs (mRNAs) encoding the D2 dopamine receptor and enkephalin, which is reversed by subsequent continuous treatment with the D2 agonist quinpirole. Conversely, striatonigral neurons show a 6-OHDA-induced reduction in their specific expression of mRNAs encoding the D1 dopamine receptor and substance P, which is reversed by subsequent daily injections of the D1 agonist SKF-38393. This treatment also increases dynorphin mRNA in striatonigral neurons. Thus, the differential effects of dopamine on striatonigral and striatopallidal neurons are mediated by their specific expression of D1 and D2 dopamine receptor subtypes, respectively.

Adrenergic regulation of hypothalamic proenkephalin neurons: evidence for opposite effects in subpopulations terminating in median eminence and neurointermediate pituitary.

The effect of adrenergic influences on Met-enkephalin concentrations in median eminence, neurointermediate pituitary and hypothalamus outside median eminence were examined. Met-enkephalin levels in median eminence were augmented by administration of the alpha 1-adrenergic agonist methoxamine acutely or chronically and decreased by the selective depletion of adrenergic transmitters by 6-hydroxydopamine. Met-enkephalin levels in neurointermediate lobe were decreased by methoxamine but unaffected by depletion of noradrenaline/adrenaline. These results indicate that adrenergic mechanisms maintain Met-enkephalin concentrations tonically in median eminence and deplete Met-enkephalin concentrations in neurointermediate lobe. These results suggest differential adrenergic regulation of hypothalamic proenkephalin neurons terminating in median eminence and neural lobe of pituitary.

Pressor and sympathetic responses to dorsal raphe nucleus infusions of TRH in rats.

Pressor, tachycardic, and sympathoexcitatory responses to intracerebroventricularly (icv) infused thyrotropin-releasing hormone (TRH) were recorded in urethan-anesthetized rats to identify where centrally administered TRH acts in the brain. None of these responses was altered either by electrolytic lesions in the medial preoptic, posterior, or paraventricular hypothalamus or by chemical lesions produced by destroying catecholaminergic neurons with icv infused 6-hydroxydopamine. By contrast, when serotonergic neurons were similarly destroyed with 5,7-dihydroxytryptamine, TRH-induced tachycardia was inhibited. Attendant pressor responses were also inhibited by electrolytic lesions of the dorsal, but not of the median, raphe nucleus. Pressor and sympathoexcitatory responses elicited by infusing TRH directly into the dorsal raphe nucleus resembled those produced by icv infusion, and their magnitude diminished after pentolinium-induced ganglioplegia. These results are compatible with the interpretation that icv infused TRH may produce its cardiovascular and sympathetic effects by acting, at least in part, on serotonergic mechanisms located in the dorsal raphe nucleus.

Antikindling effects of locus coeruleus stimulation: mediation by ascending noradrenergic projections.

Electrical stimulation of the noradrenergic locus coeruleus (LC) delays the generalization of partial seizures during amygdaloid kindling by increasing the time spent in the earliest stages of seizure development. To determine whether noradrenergic axons projecting to the midbrain and forebrain are involved in this antikindling effect, we examined the effects of lesions of the dorsal noradrenergic bundle, induced by intracerebral infusions of 6-hydroxydopamine (6-OHDA), on kindling and the antikindling action of stimulation of the LC. Stimulation of the LC during amygdaloid kindling increased the number of afterdischarges (ADs) spent in the early stages of partial seizure and decreased the number of ADs spent in later stages of generalized seizure, as has been described previously. LC-stimulated rats also displayed longer durations of AD during early stages of kindling. The antikindling effect of LC stimulation was blocked by lesions of the dorsal bundle, whereas the facilitatory effects of LC stimulation on generalization and on the duration of AD were unaffected by the lesions. These results suggest that the antikindling action of LC stimulation is mediated by the ascending projections of noradrenergic neurons, presumably through enhanced release of noradrenaline. On the other hand, the facilitatory effects of LC stimulation on the development of later stages of seizure and on the duration of AD appear to be independent of the ascending dorsal bundle.

Nicotine-induced catecholamine synthesis after lesions to the dorsal or ventral noradrenergic bundle.

The role of projections from coerulear (A6) and lateral tegmental (A1-A5) noradrenergic cell groups in the induced catecholamine response to (-)-nicotine was studied following lesions to the dorsal (DNAB) or ventral (VNAB) noradrenergic bundle by 6-hydroxydopamine. The lesions produced large reductions in basal noradrenaline levels in hippocampus (after DNAB lesions) and hypothalamus (after VNAB lesions), while not affecting basal levels of dopamine or 5-hydroxytryptamine. Vehicle and sham operated controls showed a significant increase in DOPA accumulation in response to (-)-nicotine (0.8 mg/kg s.c.) following inhibition of amino acid decarboxylase. In DNAB lesioned rats, the response induced by (-)-nicotine in both the hippocampus and hypothalamus was significantly attenuated, whereas in VNAB lesioned rats the induced response was still evident. The effect of (-)-nicotine was also studied in the nucleus accumbens and was found not to be affected by either lesion. These data suggest that increases in catecholamine synthesis in the hippocampus and hypothalamus reflect increased noradrenaline synthesis, and that this effect occurs specifically in noradrenergic projections originating in the locus coeruleus.

[Effects of destruction of preoptic catecholaminergic nerve terminals on acupuncture analgesia].

The effect of microinjection of 6-hydroxydopamine into the preoptic area was studied to observe the effect of destruction of catecholaminergic terminals in the preoptic area on acupuncture analgesia. It was shown that the analgesic effect of acupuncture was significantly enhanced in 6-hydroxydopamine treated group on the second and fourth day after injection as compared with those before injection or those in control group. The fluorecence of catecholamine terminals in the preoptic area disappeared almost completely on the fourth day after injection, and did not restore on the tenth day. The data indicate that the reduction of catecholamine content in the preoptic area may enhance acupuncture analgesia.

Effects of destruction of preoptic catecholaminergic nerve terminal on acupuncture analgesia.

The present work studied the effect of preoptic catecholamine on acupuncture analgesia. The catecholaminergic terminals were destructed by microinjection of 6-hydroxydopamine into the preoptic area and the destruction was checked by fluorescence histochemical method. The results showed that the destruction of catecholaminergic terminals significantly enhance acupuncture analgesia, suggesting that the reduction of catecholamine content in the preoptic area may enhance acupuncture analgesia.

Noradrenergic modulation of the masseteric reflex in behaving cats. II. Physiological studies.

Studies in the preceding paper demonstrated that the amplitude of the masseteric reflex in behaving cats is augmented by pharmacological manipulations that increase norepinephrine (NE) tone in the motor trigeminal nucleus (MoV) through exogenous means. The present studies examine whether such a relationship also exists under physiological conditions, i.e., whether physiological increases in NE synaptic activity are correlated with increases in the reflex amplitude. The masseteric reflex was elicited in behaving cats by electrical stimulation of the mesencephalic trigeminal nucleus (MesV) and the response recorded via electrodes permanently placed in the masseter muscle. Following baseline measures of the reflex amplitude, the reflex was gain elicited while cats were exposed to various environmental stimuli known to activate NE neurons: 15 min of 100-dB white noise, confrontation with a dog, or auditory clicks presented repetitively at various intervals prior to MesV stimulation. Presentation of the white noise or the dog significantly facilitated the reflex response for the duration of the exposure. The clicks produced reflex facilitation at 100 and 150 msec following their presentation and reflex suppression at 20 msec. Two approaches were then employed to determine whether NE mediated, at least in part, augmentation of the reflex produced by these environmental conditions. In the first, cats were given either the alpha-1-noradrenergic antagonist prazosin (5 mg/kg, i.p.) or the serotonin antagonist methysergide (0.5 mg/kg, i.p.). In all cases, prazosin blocked the reflex augmentation whereas methysergide was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)

[Role of noradrenaline of the dorsal hippocampus in the mechanism of self-stimulation reaction in rats]. / Rol' noradrenalina dorsal'nogo gippokampa v mekhanizme reaktsii samorazdrazheniia u krys.

In has been established that intrahippocampal bilateral injection of NA did not influence common frequency of lateral hypothalamic self stimulation. After the destruction of hippocampal NA - terminals of 6-OHDA increased the frequency of self stimulation and rearing. It is suggested that NA hippocampus inhibit the recall trace of the memory of sensory reinforcement stimuli in the course of stimulation "reward".

Effects of morphine on plasma B-endorphin and cortisol levels and on body temperature in guinea-pigs pretreated with 6-hydroxydopamine.

1. i.c.v. morphine administration (50 micrograms/10 microliters) to sham-lesioned guinea-pigs produces a decrease of body temperature 90 min after injections. 2. This effect was blocked in animals that received i.c.v. 6-OHDA injections 20 days before. 3. On the other hand, morphine injection to sham-lesioned guinea-pigs resulted 30 and 90 min later in suppressed plasma B-END and cortisol concentration. 4. This suppressive effect was increased 20 days after 6-OHDA injections. 5. These results indicate that in the guinea-pig the effects of morphine on both body temperature and plasma levels of B-END and cortisol are altered by hypothalamic DA lesions, and suggest that hypothalamic DA neurons would be one of the sites participating in morphine-induced delayed decreased in plasma B-END and cortisol.

Evidence for the involvement of the central adrenergic system in the febrile response induced by interleukin-1 in rats.

We have studied the effect of noradrenaline- and serotonin-depleting agents on the febrile response induced by an intracerebroventricular (i.c.v.) injection of interleukin-1 (IL-1) in rats. Pretreatment with an injection into the lateral ventricle of the catecholamine-depleting agent, 6-hydroxydopamine (6-OHDA), abolished the febrile response induced by IL-1. Injection of 6-OHDA into the ventral noradrenergic ascending bundle (VNAB) did not affect the pyrogenic effect of IL-1. Pretreatment with the serotonin-depleting agent, 5,7-dihydroxytryptamine (5,7-DHT), did not inhibit the febrile response to IL-1. In addition, pretreatment with a beta-adrenergic blocker (propranolol) but not an alpha-adrenergic blocker (yohimbine) attenuated the fever induced by an i.c.v. injection of IL-1. These results suggest that the integrity of the central catecholaminergic system is important in mediating the IL-1-induced fever in rats. The central serotonergic system, as well as noradrenergic neurotransmission at the hypothalamus, do not appear to participate in this endogenous pyrogen-induced febrile response.

Depletion of hypothalamic norepinephrine reduces the fever induced by polyriboinosinic acid: polyribocytidylic acid (Poly I:Poly C) in rats.

Administration of either Poly I:Poly C (0.05-0.50 micrograms) or norepinephrine (2-8 micrograms) into the anterior hypothalamic area produced a dose-related fever in rats. The fever induced by Poly I:Poly C was attenuated after selective depletion of norepinephrine in the hypothalamus. However, selective depletion of hypothalamic norepinephrine did not affect the fever induced by intrahypothalamic norepinephrine. The data indicate that Poly I:Poly C may act to induce fever through the endogenous release of norepinephrine from the rat's hypothalamus.