Effects of 6-hydroxydopamine on brain and blood catecholamines, ammonia, and amino acids in rats

The effect of 6-hydroxydopamine (6-OHDA) upon brain and blood catecholamines, ammonia, and amino acids has been studied in rats subjected to increasing doses of the drug. Time dependent effects after injection have also been studied. Systemically injected 6-OHDA significantly, acutely reduced brain adrenaline (A), noradrenaline (NA), total catecholamines (TC), gamma-aminobutyric acid (GABA), and glutamic acid (Glu); concomitantly brain ammonia (NH3) increased. In blood, NA and TC were reduced and A and NH3 increased. The changes in brain monoamines are surprising since it has been reported that 6-OHDA does not cross the blood-brain barrier. We have proposed that these changes result from a general stress response or a reflex peripheral sympathetic response to falling blood pressure which in some manner communicates to the central nervous system. As the dose of 6-OHDA increased, brain NH3 increased and Glu decreased. A similar effect was seen from a single dose as the time after injection for sampling brain and blood constituents increased. Blood ammonia increases without change in Glu, glutamine, or asparagine. The source of NH3 may be from deamination of adenine nucleotide or catechols released from nerve terminals under the abnormal stimulus of 6-OHDA.     

The time course of brain and blood catecholamines, catechol O-methyltransferase, and amino acids in rats convulsed by oxygen at high pressure.

The time course of changes in blood and brain catecholamines, catechol O-methyltransferase (COMT), ammonia, and amino acids leading to convulsion by high pressure oxygen breathing (OHP) in rats has been investigated. Brain catecholamines were suppressed by OHP. They changed in phase with brain COMT concentration and consequently were not due to the action of this degrading enzyme. Convulsive actions seem not to be influenced by brain catecholamine concentration. Blood adrenaline concentrations are, however, significantly elevated both prior to and during convulsions. In both brain and blood, ammonia concentration increases, glutamate decreases, and glutamine-aspargine increases. It is proposed that the efficacy of the glutamate-glutamine ammonia buffering system in blood and brain is important in the prevention of the onset of convulsions but that when brain gamma-aminobutyric acid is depressed to critical levels, convulsions result.     

EFFECTS OF 6-HYDROXYDOPAMINE ON CATECHOLAMINE CONTAINING NEURONES IN THE RAT BRAIN

After the intraventricular injection of 6-hydroxydopamine (6-OHDA), there was a long lasting reduction in the brain concentrations of noradrenaline (NA) and dopamine (DA). The brain concentration of NA was affected by lower doses of 6-OHDA than were required to deplete DA. A high dose of 6-OHDA which depleted the brain of NA and DA by 81 per cent and 66 per cent respectively, had no significant effect on brain concentrations of 5-hydroxytryptamine (5-HT) or γ-aminobutyric acid (GABA). The fall in catecholamines was accompanied by a long lasting reduction in the activities of tyrosine hydroxylase and DOPA decarboxylase in the hypothalamus and striatum, areas in the brain which are rich in catecholamine containing nerve endings. There was, however, no consistent effect on catechol-O-methyl transferase or monamine oxidase activity in these brain regions. The initial accumulation of [³H]NA into slices of the hypothalamus and striatum was markedly reduced 22–30 days after 6-OHDA treatment. These results are consistent with the evidence in the peripheral sympathetic nervous system that 6-OHDA causes a selective destruction of adrenergic nerve endings and suggest that this compound may have a similar destructive effect on catecholamine neurones in the CNS.     

Correlation between decreases in brain gamma-aminobutyric acid levels and susceptibility to convulsions induced by hyperbaric oxygen

Abstract— The susceptibility of mice to seizures at hyperbaric pressures of oxygen (OHP) was placed on a quantitative basis and compared with the corresponding rate of decrease in brain GABA concentration. The influence of small amounts of carbon dioxide in the breathing mixture on these effects of OHP was also determined. A correlation between the rate of decrease in GABA and susceptibility to seizures was shown to exist not only over the varying oxygen pressures and varying concentrations of carbon dioxide used in the present experiments out also over varying animal species (a previous study). The critical oxygen pressure for decreases in brain GABA to occur was shown to be 30 p.s.i.g. This value agreed closely with the well documented critical pressure necessary to produce seizures in both animals and man. The probability that lowered brain GABA levels play a major role in the etiology of OHP convulsions was discussed.     

A possible role for spinal noradrenaline in the mechanisms of 6-hydroxydopamine against pentylenetetrazol induced convulsions in rats

The threshold of the generalized clonic convulsions induced by intravenous infusion of pentylenetetrazol (PTZ) was significantly increased by the intraperitoneal administration of noradrenaline (NA) neurotoxin, 6-hydroxydopamine, which produced no changes in the levels of catecholamines in discrete areas of rat brain, but the effect was accompanied by spinal depletion of NA. Moreover, the anticonvulsant effects of phenobarbitone (PB) and diphenylhydantoin (DPH) against PTZ convulsions were also significantly increased in the animals pretreated with 6-OHDA. These results suggest that the observed elevation of PTZ convulsive threshold and the potentiation of anticonvulsant activity of PB and DPH in 6-OHDA treated rats were possibly mediated through spinal cord depletion of NA.     

腹腔注射乙酰唑胺对大鼠氧惊厥潜伏期的影响

为探讨脑血流调节与氧惊厥的关系,本研究在复制大鼠氧惊厥模型的基础上,采用行为学方法测定氧惊厥潜伏期,并测定脑皮质氧化指标内二醛（maleic dialdehyde,MDA）含量,采用腹腔注射不同剂量脑血管扩张药物乙酰唑胺（acetazolamide,ACZ）,以及联合注射ACZ及其拈抗刺吲哚美辛（indomethacin,IND）后,观察脑血管扩张对氧化状态以及氧惊厥潜伏期的影响。结果观察到：（1）腹腔注射ACZ（不小于7．5mg／kg体重）后,氧惊厥潜伏期明显缩短（P〈0．05）,剂量越大,缩短越明显。腹腔注射IND对氧惊厥潜伏期无显著影响。腹腔注射IND（20mg／kg体重）,30min后再注射ACZ（7．5mg／kg体重）,ACZ的氧惊厥潜伏期缩短作川被对抗（P〈0．05）。（2）腹腔注射ACZ7．5mg／kg后,与各组相比,6及16min暴露后,脑组织MDA含量明显增多（P〈0．01,P〈0．05）;腹腔注射IND对脑皮质MDA含量无显著影响;在预注射IND,再注射ACZ后,MDA含量显著降低（P〈0．01,P〈0．05）。结果表明,ACZ外周注射加重氧化损伤,缩短氧惊厥潜伏期;而IND可以对抗其氧惊厥潜伏期缩短作用以及氧化损伤加重作用,碳酸酐酶活力变化很可能是通过影响脑血管状态而影响氧化损伤以及氧惊厥潜伏期。     

Influence of amygdala catecholamines on ovarian and adrenal medullary secretion.

The amygdaloid complex participates in the modulation of endocrine functions, and contains measurable amounts of noradrenaline (NA) and dopamine (DA). This study examined the contribution of the amygdaloid catecholaminergic systems to the regulation of the adrenal medulla and the ovary. To accomplish this the neurotoxin 6-hydroxydopamine (6-OHDA) was bilaterally injected into the basolateral nucleus of the amygdala (ABL) in cycling rats. The contents of NA and DA in right and left amygdala decreased significantly in lesioned animals with respect to sham lesioned animals, but hypothalamic levels were not different between groups. Administration of 6-OHDA to rats increased the NA, DA and adrenaline (A) contents of the adrenals compared to vehicle treated rats. In addition, lesioned animals showed a significant increase of NA and DA contents in the ovary, although A levels did not differ between groups. Serum oestradiol (O) concentrations were significantly lower in lesioned animals than in controls. These data suggest that the amygdaloid catecholaminergic systems exert an inhibitory effect on catecholamine content of the adrenals and the ovary, and influence the ovarian oestradiol secretion mechanism.     

Changes inγ-aminobutyric acid during different stages of picrotoxin-induced seizure,and the effect of pretreatment withγ-acetylenic GABA and phenobarbital

Changes in GABA content of various brain areas during different stages of picrotoxin-induced seizures and following pretreatment with the anti-convulsants phenobarbital andγ-acetylenic GABA were studied. Picrotoxin (6mg/kg) produced clonic/tonic convulsions associated with a 34% reduction in GABA content of the sensory motor cortex. A reduction of 24% was observed 1 min before the onset of seizure and the reduction in GABA content was reversible 20 min after the convulsion. No significant changes were observed in the cerebellum or spinal cord/medulla oblongata. Pretreatment with phenobarbital (100mg/kg) delayed the onset of convulsion and decreased the mortality rate without causing any change in GABA content at the pre-convulsive, convulsive or post-convulsive stages.γ-Acetylenic GABA (100mg/kg) has elevated GABA levels in different areas of the brain by 2–3-fold after 60 min treatment. This increase was reduced by 44% during the onset of picrotoxin-induced seizures. Picrotoxin convulsion can occur in the presence of normal, reduced or even elevated brain GABA content. The only consistent factor is a one-third reduction in GABA content before the onset of seizure.     

Effect of intraventricular administration of noradrenaline and dopamine on the levels of corticosterone in rats and denervation hypersensitivity resulting from intraventricular administration of 6-hydroxydopamine.

The effects of intraventricular administration of noradrenaline (NA) on the resting levels, stress-induced rises and dexamethasone-induced decreases of plasma corticosterone (B) were studied in rats. The effect of pretreatment with intraventricular administration of 6-hydroxydopamine (6-OHDA) on the effects of NA or dopamine (DA), which was injected intraventricularly, was also examined. The results obtained were as follows: 1) Intraventricular administration of 1.0 μg of NA did not cause a decrease in concentrations of plasma B. 2) Ten μg of NA injected intraventricularly resulted in a rise of the levels of plasma B. 3) The stimulating action of centrally administered NA was more marked when the pre-injection concentrations of B were lower. 4) Pretreatment with intraventricular administration of 6-OHDA facilitated the action of intraventricularly administered NA in the regulation of pituitary-adrenocortical functions. The result suggests a development of denervation hypersensitivity caused by the pretreatment. 5) Intraventricular administration of NA did not block stress-induced rises of plasma B. 6) Intraventricular administration of NA counteracted dexamethasone-induced decrements of plasma B. 7) This counteraction was enhanced by pretreatment with intraventricular administration of 6-OHDA. This also suggests a development of denervation hypersensitivity resulting from intraventricular administration of 6-OHDA. 8) Intraventricular administration of 1.0 μg of DA caused no change in the concentrations of plasma B in either control or 6-OHDA treated animals.     

乙酰唑胺对氧惊厥潜伏期的影响

为探讨脑血流调节与氧惊厥的关系,在复制大鼠氧惊厥模型的基础上,采用行为学方法测定氧惊厥潜伏期,并测定不司部位脑组织氧化与抗氧化指标,采用腹腔注射不同剂量脑血管扩张药物乙酰唑胺,观察脑血管扩张对氧化状态以及氧惊厥潜伏期的影响。观察结果为:(1)与生理盐水组相比,乙酰唑胺200、20 mg/kg体重组腹腔给药后氧惊厥潜伏期(纯氧6 ATA暴露)明显缩短(P<0.01),乙酰唑胺2 mg/kg体重组无明显改变(P>0.05);(2)腹腔给乙酰唑胺(20 mg/kg体重)或生理盐水后,各组各部位脑组织GSH-PX无显著差异(P>0.05),但随暴露时间的延长,其活力呈现先升高后降低的趋势;与对照组相比,乙酰唑胺6min组和生理盐水16min组皮层丙二醛(maleic dialdehyde,MDA)含量均明显增多(P<0.01),乙酰唑胺16 min组海马MDA含量明显增多(P<0.01)。结果表明,乙酰唑胺可缩短氧惊厥潜伏期,加重脑组织氧化损伤。     

Catecholamine Concentration in the Developing Rat Brain after γ-Hydroxybutyric Acid

The effect of the GABA receptor agonist γ-hydroxybutyric acid (GHBA) on brain catecholamine concentration was investigated in 1 to 28 day old rats. The infant rats were given GHBA in various doses (375–1500 mg/kg) and the effects on whole brain or regional brain concentration of dopamine (DA) and noradrenaline (NA) were measured. Brain DA concentration increased in a dose-dependent way already from two days of postnatal age. In the regional brain study of the 14- and 28-day-old animals the increase in DA concentration was found to be almost exclusively located in the striatal region. Generally, no changes in NA concentration were found in the whole brain or various brain regions at any of the ages after GHBA. It is concluded that the inhibitory striatal-nigral neurons, utilizing GABA as a transmitter, are functionally developed during early postnatal age.     

小鼠惊厥时孕烯醇酮及其硫酸盐对GABAA受体的调制作用

在建立稳定的红藻氨酸(KA)诱发小鼠惊厥模型的基础上,用放射配体受体结合分析法,研究孕烯醇酮(Pe)及其拮抗剂孕烯醇酮硫酸盐(Pes)对小鼠下丘脑、大脑皮层、海马和小脑四个脑区γ-氨基丁酸A(GABAA)受体的调制作用.结果显示,Pe能增加某些脑区3H-GABA与GABAA受体的结合量,下丘脑、海马和小脑差异显著(P＜0.05或P＜0.001),而大脑皮层差异不显著(P＞0.05).Pe对GABAA受体的调制作用能被印防己毒素(Pic)阻断,对KA的致惊效应具有抑制作用.Pes 能显著降低各脑区GABAA受体的结合量(P＜0.01或P＜0.001),对惊厥有促进作用.实验结果提示:孕烯醇酮具有明显的镇静和抗惊厥效应,并且可能是通过GABAA受体介导的.     

Significance of the reciprocal relationship of monoaminergic systems of the brain in the pharmacological compensation of 6-hydroxydopamine-induced behavior disorders in animals

The paper studied the methods of compensation of the abnormal emotional behaviour by means of pharmacological substances, which change the content of biogenic amines. The experiments made in the Wistar rats (n-54) whose frustration reaction was diminished by neonatal treatment of 6-OHDA. It was established that recovery of the disturbances in the frustration reaction in the animals with chronic brain system activity deprivation can be achieved not only by the activation of NA system (L-DOPA, DOPS) but also by deactivation of the 5-HT brain system activity (PCPA). These findings confirm suggestion about existence of reciprocal relationship between NA and 5-HT brain systems.     

Seizures induced by hyperbaric oxygen and cerebral gamma-aminobutyric acid in chicks during development

Abstract— The susceptibility of chicks to convulsions induced by hyperbaric oxygen increased with age during the first few weeks of life. The sensitivity of the levels of cerebral GABA to change by oxygen at high pressure (OHP) also increased with age. There was correlation between the rate of decrease in concentration of cerebral GABA and the time to onset of OHP seizures. The anti-convulsant action of intraperitoneally administered GABA was greater in 6-9-day-old chicks than in 21-23-day-old chicks, consistent with decreasing permeability of the blood-brain barrier to the amino acid with increasing age.     

Modulation of noradrenaline release in the median preoptic area by GABAergic inputs from the organum vasculosum of the lamina terminalis in the rat

Previous observations have shown that gamma-aminobutyric acid (GABA) receptor mechanisms modulate the release of noradrenaline (NA) in the median peptic nucleus (MnPO). The present study was carried out to investigate whether neural inputs from the organum vasculosum of the lamina terminalis (OVLT) to the MnPO are involved in the GABAergic modulation of NA release in the MnPO area using in vivo microdialysis techniques. In urethane-anesthetized rats, electrical stimulation (5 and 10 microA, 10Hz) of the OVLT region, but not its surrounding region, significantly enhanced dialysate NA concentration in the MnPO area. The enhancement in the NA level caused by the OVLT region stimulation was significantly increased by perfusion with either bicuculline (10 microM), a GABA(A) receptor antagonist, or phaclofen (10 microM), a GABA(B) receptor antagonist, through a microdialysis probe. The amount of the antagonist-induced increase was much greater in the phaclofen-treated group than in the bicuculline-treated group. These results show that the OVLT region may exert both excitatory and inhibitory influences on the release of NA in the MnPO area, and imply that the inhibitory influence may be mediated through GABA(B) receptors rather than GABA(A) receptors.     

脑室注射6—羟多巴胺对黄鼠科眠入眠的影响

The effect of forced depletion of brain norepinephrine (NE) on the onset of hibernation was observed in the ground squirrel (Citellus dauricus) by intraventricular injection of 6-hydroxydopamine (6-OHDA). The results showed: (1) Intraventricular injection of 100-200 micrograms 6-OHDA, which depleted 50-60% NE, markedly facilitated the onset of hibernation, i.e. the average induction period for hibernation in the treated animals was significantly shorter than that of the natural hibernating animals. (2) The average total torpor time in the treated animals was longer than that of natural hibernating animals. (3) All hibernating animals treated with 6-OHDA were able to wake up from deep hibernation spontaneously and undergo normal hibernation bouts. The results indicate the decrease of NE system activity in brain is one important factor in triggering the onset of hibernation.     

High-Affinity Choline Uptake in the Hippocampus: Its Relationship to the Physiological State Produced by Administration of Barbiturates and Other Treatments

Abstract: Choline uptake in hippocampal synaptosomes was not inhibited by pentobarbital administration when rats were decapitated immediately upon loss of the righting reflex (3–4 min) even though it was inhibited at later times post-injection, when the rats were still unable to right themselves. Choline uptake was increased when the animals were decapitated at convulsion after an injection of picrotoxin, high doses of bicuculline, or one of the convulsant barbiturates. However, another convulsant barbiturate, as well as strychnine and lower doses of bicuculline, did not increase choline uptake even though the animals also convulsed. Thus loss of righting reflex or convulsion is not directly correlated with changes in choline uptake. At 7 min after injection, levels of pentobarbital in the hippocampus (and other brain regions) were correlated with the degree of inhibition of choline uptake up to about 50% inhibition; however, greater inhibition could not be achieved with much higher brain levels of the drug. Although hippocampal uptake was partially inhibited at 1 h after septal lesions, 3 h after the lesion the inhibition was no longer apparent. Inhibition was almost complete 10–12 days after the lesion. These results suggest that other factors in addition to impulse flow influence choline uptake.     

Release of [3H]noradrenaline from perfused rat hearts by potassium and its modifications by 6-hydroxydopamine and reserpine.

The sources of noradrenaline (NA) released by excess potassium from isolated perfused rat hearts were investigated by labelling the hearts from normal, reserpine-treated, and 6-hydroxydopamine-treated (6-OHDA-treated) rats with [3H]HA, and measuring the increased rate of efflux induced by perfusion with a Krebs solution containing varying amounts of excess potassium. The [3H]NA and its metabolites in the effluent were separated by adsorption on alumina and a cation-exchange resin (Dowex-50). The release induced by potassium was a linear function of the log of the increased potassium concentration. Following a 1-h efflux period after labelling with [3H]NA, the hearts from reserpine-treated rats retained 1/5 as much [3H]NA, and released, in response to a 56mM elevation in the potassium concentration, less than 1/6 as much tritium label as the hearts from untreated (control) animals. In contrast, the hearts form 6-OHDA-treated animals retained 1/15 of the amount of [3H]NA and released 1/50 of the 3H label as did the control hearts. The potassium-induced increase of 3H-labelled substances in the effluent from the control hearts showed a large (threefold) percentage increase in the [3H]NA fraction, whereas the effluents from the hearts of reserpine- and 6-OHDA-treated animals contained only small increases in the [3H]NA fraction. Based on the assumptions that reserpine prevented retention of NA in the storage granules whereas 6-OHDA prevented almost all neuronal storage, it was concluded that more than 80% of the NA released by potassium excess from perfused normal hearts originated from the storage vesicles of the nerves, the remainder being largely from the cytoplasm of the nerves, with only a small portion from extraneuronal sources.     

Regional changes in the concentrations of glutamate,glycine, taurine,and GABA in the vitamin B-6 deficient developing rat brain: Association with neonatal seizures

It is well known that a dietary restriction of vitamin B-6 during gestation and lactation produces spontaneous seizures in neonatal animals. Since pyridoxal phosphate, one of the biologically active forms of vitamin B-6, is the cofactor for GAD the neonatal seizures have been attributed to low levels of brain GABA as a result of cofactor depletion. Although GABA levels are significantly lower in B-6 restricted neonatal rats with spontaneous seizures, seizure activity is not present in B-6 deficient adult rats or 28 day old rats in the present study, despite significantly low levels of brain GABA. These facts suggest that depletion of GABA is not the only biochemical alteration essential for the emergence of seizures. In the present study, the effect of vitamin B-6 undernutrition on the concentrations of the neuroactive amino acids, Glu, Gly, Tau, and GABA was determined in selected regions of the developing rat brain. The results show that the concentrations of Glu, Tau, and GABA were significantly lower and GLY significantly higher in selected brain regions of the B-6 restricted 14 day old rat compared to control tissue. Most of these changes were unique to 14 days of age, the time when spontaneous seizures are observed, and not present at 28 or 56 days of age when seizures are absent. This pattern of amino acid changes in the brain and the magnitude of the changes was consistent with those measured in a variety of chemically-induced animal models of epilepsy and in human epileptic foci. The regional distribution of amino acid changes was associated with brain regions which have been suggested to be responsible for the initiation and propagation of seizure activity. Two unique findings were also made in this study. First, there was a regional brain heterogeneity in the age-associated loss of brain Tau concentrations with the pons/medulla and substantia nigra appearing to be highly vulnerable and the hippocampus quite resistant to the loss of Tau. A second finding was the normalization of the neonatal GABA deficit in most brain regions by 56 days of age. The normalization of brain GABA was present in the face of continued dietary vitamin B-6 restriction. In summary, this study shows that the neuroactive amino acids Glu, Gly, Tau, and GABA are markedly altered in the seizure-prone vitamin B-6 restricted neonatal rat brain. The alterations in the brain concentration of Glu, Gly, and Tau may play an equally important role as GABA in the underlying mechanism of seizures associated with this condition.Abbreviations GAD Glutamic acid decarboxylase - GABA gamma-aminobutyric acid - Glu glutamate - Gly glycine - Tau taurine - CNS central nervous system - CTX cortex - HIPP hippocampus - C/P caudate/putamen - SN substantia nigra - Cb cerebellum - P/M pons/medulla     

Reduction of pentylenetetrazol-induced convulsions by the octadecaneuropeptide ODN

Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.