Effect of unilateral perinatal hypoxic-ischemic brain injury on striatal dopamine uptake sites and D1 and D2 receptors in adult rats

Cat Scratch Disease-associated Encephalitis Followed by Parkinsonism

Cat scratch disease (CSD) is a zoonotic infection caused by Bartonella henselae typically resulting in self-limited regional lymphadenopathy. Encephalitis is a complication with a supposedly benign prognosis, but we encountered an exceptional case. A 19-year-old Japanese woman presented with status epilepticus. She was diagnosed with CSD-associated encephalitis based on her history of contact with a kitten and a high titre of serum IgG to B. henselae. Multimodal treatment ameliorated her encephalitis, but neurological sequelae including spastic paraparesis, persisted. After several months, she developed age-disproportionate parkinsonism inconsistent with a neurodegenerative disease. In conclusion, CSD-associated encephalitis can result in severe neurological sequelae and post-encephalitic parkinsonism.

Prefrontal cortex dysfunction in hypoxic-ischaemic encephalopathy contributes to executive function impairments in rats: Potential contribution for attention-deficit/hyperactivity disorder

OBJECTIVES

The attention-deficit/hyperactivity disorder (ADHD) compromises the quality of life of individuals including adaptation to the social environment. ADHD aetiology includes perinatal conditions such as hypoxic-ischaemic events; preclinical studies have demonstrated attentional deficits and impulsive-hyperactive outcomes after neonatal hypoxic and/or ischaemic intervention, but data are missing to understand this relationship. Thus, the aim of this study was to evaluate executive function (EF) and impulsivity, and tissue integrity and dopaminergic function in the prefrontal cortex (PFC) of rats submitted to hypoxia-ischaemia (HI).

METHODS

At postnatal day (PND) 7, male Wistar rats were divided into control (n = 10) and HI groups (n = 11) and the HI procedure was conducted. At PND60, the animals were tested in the attentional set-shifting (ASS) task to EF and in the tolerance to delay of reward for assessment of impulsivity. After, morphological analysis and the dopaminergic system were evaluated in the PFC.

RESULTS

Animals subjected to HI had impairments in EF evidenced by a behavioural inflexibility that was correlated to PFC atrophy. Moreover, HI animals presented reduced D2 receptors in the ipsilateral side of ischaemia in the PFC.

CONCLUSIONS

Animals submitted to HI presented impaired EF associated with tissue atrophy and dopaminergic disturbance in the PFC.

The association between perinatal hypoxia exposure and externalizing symptoms and children's decision making in conditions of uncertainty is moderated by DRD2 genotype

Variants of the DRD2 Taq1A polymorphism, which have been shown to result in functional differences in dopamine D2 receptors (D2R), have been linked to various externalizing outcomes in adults. However, the neurobiological processes that contribute to these associations are not well understood. The current study investigates gene × environment effects on teacher-rated externalizing behaviors and probabilistic decision making in a sample of 333 children (age 9) enrolled in an ongoing longitudinal study. Findings indicate that externalizing behaviors increased as a function of hypoxic exposure only among individuals carrying the A1 (A1+) allele. Results also indicate that willingness to pursue reward under conditions of maximum uncertainty (50% probability) decreased as a function of hypoxic exposure only among A1- individuals. Among A1 carriers, no association between probability decision making and hypoxic exposure emerged. These findings suggest that hypoxia could influence neural development through different biological pathways depending on D2 receptor genotype, and provide insight into the development of individual differences in behavior and decision making.

Vulnerability of the mesencephalic dopaminergic neurons of the human neonate to prolonged perinatal hypoxia: an immunohistochemical study of tyrosine hydroxylase expression in autopsy material

Experimental studies indicate that hypoxia to the fetus, a common occurrence in many birth complications in humans, results in long-term disturbances of the central dopaminergic (DA) systems that persist in adulthood. Because dysregulation of DA systems is involved in the pathophysiology of many neurological and psychiatric disorders, we investigated the effects of perinatal hypoxia on the mesencephalic DA neurons of the human neonate using immunohistochemistry. We studied the expression of tyrosine hydroxylase (TH), the first and rate-limiting enzyme in catecholamine synthesis, in substantia nigra, and ventral tegmental area of 18 neonates in relation to the age and severity/duration of hypoxic injury estimated by neuropathological criteria. In severe/abrupt perinatal hypoxia, intense TH staining was observed in substantia nigra, ventral tegmental area, and, surprisingly, in the nonpreganglionic Edinger-Westphal nucleus. In severe/prolonged hypoxia, there was a striking reduction or even absence of TH immunoreactivity in all the mesencephalic nuclei. These observations suggest that at early states of perinatal hypoxia, there is a massive increase in dopamine synthesis and release that is followed by feedback blockage of dopamine synthesis through inhibition of TH by the end product dopamine. Early dysregulation of DA neurotransmission could predispose infant survivors of severe perinatal hypoxia to dopamine-related neurological and/or cognitive deficits later in life.

Acute and long-term response of dopamine nigrostriatal synapses to a single, low-dose episode of 3-nitropropionic acid-mediated chemical hypoxia

The goal of the present investigation was to determine the persistence of striatal (DA) dopaminergic dysfunction after a mild chemically induced hypoxic event in Fisher 344 rats. To this end, we gave a single injection of the mitochondrial complex II inhibitor 3-nitropropionic acid (3-NP; 16.5 mg/kg, i.p.) to 2-month old male F344 rats and measured various indices of striatal DA functioning and lipid peroxidation over a 3-month span. Separate groups of rats were used to measure rod walking, evoked DA release, DA content, malondialdehyde (MDA) accumulation, DA receptor binding, and tyrosine hydroxylase (TH) activity. The results showed that 3-NP exposure reduced most measures of DA functioning including motoric ability, DA release, and D(2) receptor densities for 1 to 3 months postdrug administration. Interestingly, DA content was reduced 1 week after 3-NP exposure, but rose to 147% of control values 1 month after 3-NP treatment. MDA accumulation, a measure of lipid peroxidation activity, was increased 24 h and 1 month after 3-NP treatment. 3-NP did not affect TH activity, suggesting that alterations in DA functioning were not the result of nigrostriatal terminal loss. These data demonstrate that a brief mild hypoxic episode caused by 3-NP exposure has long-term detrimental effects on the functioning of the nigrostriatal DA system.

Regional expression of dopamine D1 and D2 receptor proteins in the cerebral cortex of asphyxic newborn infants

Dopamine D(1) and D(2) receptor protein expression was examined by Western blotting in newborn infants dying from cerebral asphyxia between 31 and 42 weeks' gestation, and matched controls. Frontal, occipital, temporal, and motor cortex tissue samples were obtained at autopsy (median postmortem interval 35 hours) and frozen for storage at -80 degrees C. A total of 2 immunoreactive bands were detected with each primary antibody in infant brain, whereas a single band was present in adult human and rat tissue. Immunoreactivity varied between cortical areas for both receptors, but their regional patterns differed significantly. D(1) protein levels were higher in motor and temporal cortex than in frontal or occipital cortex. D(2) protein showed graded expression frontal > motor > occipital > temporal cortex. Asphyxia cases showed lower expression of the upper D(2) immunoreactive band, but no difference in regional pattern. Lower D(2) receptor expression may attenuate stress responses and underlie increased vulnerability to hypoxia at birth.

Dopamine D1 receptor changes due to caesarean section birth: effects of anesthesia, developmental time course, and functional consequences

There is an epidemiological association between increased obstetric complications and disorders involving CNS dopamine dysregulation, such as schizophrenia. In light of this, a rat model of global hypoxia during Caesarean section (C-section) birth has been used to directly test if birth complications can produce long-term dopaminergic dysregulation. Previous studies have shown that, compared to vaginal birth, C-section birth alone (without additional global hypoxia) is sufficient to increase D1-like receptor binding in rat brain at adulthood. The current study examined (1) the developmental time course of changes in D1-like or D2-like receptors following C-section birth; (2) whether C-section birth from isoflurane-anesthetized dams also results in altered D1-like receptor levels, as does C-section from decapitated dams; and (3) behavioral responses to D1 and D2 agonists in rats born vaginally compared to C-section. Increases in nucleus accumbens D1-like receptor binding due to C-section birth were observed only at adulthood (3 months) but not prepubertally (1 month or 2 weeks). D2-like receptor binding levels were unaffected by C-section birth across the three developmental time points. Compared to vaginal birth, D1-like receptors were increased following C-section birth from isoflurane-anesthetized dams, as well as from decapitated dams. Adult rats that had been born by C-section showed enhanced D1 potentiation of D2-induced locomotor behavior. These studies indicate that C-section birth, from either anesthetized or unanesthetized dams, results in postpubertal increases in D1-like receptor binding and enhanced functional responses to D1 receptor activation.

mRNA D(2) dopaminergic receptor expression after hypoxia-ischemia in rat immature brain

Previous studies have shown a reduction of dopaminergic D(2) receptors (D(2)R) in the striatum after hypoxia-ischemia in newborn rats. We show here an early and transient reduction of mRNA D(2)R in nonatrophic brains following hypoxia-ischemia. The left carotid artery of P7 rats was ligated followed by hypoxia for 2 h. The rats were sacrificed after 24 h, 48 h and 14 days. D(2)R mRNA was studied by in situ hybridization, the cell number by conventional histology, and neuronal and astrocyte differentiation by immunohistochemistry. A 20% reduction of striatal mRNA D(2)R occurred 24 h after hypoxia-ischemia, whereas no reduction was observed after 48 h and 14 days. There were no differences in total cell number and in the expression of neuronal (MAP-1, MAP-2) and astrocyte (GFAP) markers between both brain hemispheres nor between control and hypoxia-ischemia animals. The early decrease in mRNA D(2)R could explain the delayed reduced D(2)R after neonatal hypoxia-ischemia.

Progressive degeneration of dopamine system functions after transient cerebral oligemia in rats

A reduction in cerebral blood flow to oligemic levels was achieved in pentobarbital-anesthetized adult rats by clamping both carotid arteries (BCCA) for 60 min. To assess the extent to which the animals' dopaminergic system was affected over an increasing time span, their spontaneous locomotor activity in an unfamiliar environment and in response to the subcutaneous administration of apomorphine was tested at various times after either BCCA or sham operation. Eight to 14 days after the operation, it was possible to observe a diminished locomotor activity in response to apomorphine injection in BCCA as compared with sham-operated animals, while oral stereotypical behavior such as licking was increased. At 3 months, there was only a subtle decrease in apomorphine-induced locomotor activity, and stereotypical behavior was similar in both groups. At 7 months, the BCCA rats covered shorter distances than sham-operated controls during the habituation phase; after apomorphine injection, more stereotypic movements, such as, e.g., sniffing, were observed, and less running. Twelve months after surgery, no further differences could be observed between the two groups during the habituation phase, but the injection of apomorphine led to increased stereotypic sniffing movements, rearing and locomotor activity in BCCA animals to a greater extent than in the controls. At 12 months, sensorimotor disturbances elicited by the rota rod test, which were only transiently observed at 11 weeks and 7 months, did not appear any different from the normal age-related motor decline of the sham-operated controls. The animals' motor co-ordination in the chimney test was not significantly disturbed during the time between 7 and 12 months after surgery. At 15 months, nocturnal locomotor activities in BCCA rats were significantly decreased. In situ hybridization (ISH) histochemistry revealed decreased D1 receptor mRNA (D1RmRNA) in striatal neurons 19 months after surgery, while D2 receptor mRNA (D2RmRNA) and the neuronal number remained the same. The present results show that just as is already known for the immature rat brain, the adult rat brain, too, reacts to a transient decrease in its blood supply by appearance of long-lasting alterations in function, and that even a single oligemic episode is capable of inducing progressive dopaminergic dysfunctions and ultimately the partial loss of striatal D1RmRNA.

Neuropathological characteristics and alteration of the dopamine D2 receptor in hypoxic-ischemic basal ganglia necrosis

The neuropathological characteristics and alteration of the dopamine D2 receptor (D2R) were investigated in 27 cases of hypoxic-ischemic basal ganglia necrosis (BGN) by means of neuropathological and immunohistochemical methods. Perinatal hypoxic-ischemic BGN manifested neuronal karyorrhexis as well as eosinophilia, karyorrhexis being more predominant in preterm infants and eosinophilia more predominant in full-term infants. Immunoreactivity to D2R was detected in the cytoplasm and dendrites of small and large neurons in the basal ganglia, and increased with neuronal maturation during the late gestational period in normal human basal ganglia. The number of D2R-positive neurons was smaller in all cases of acute BGN than that in controls, the areas of decreased D2R-positive neurons corresponding to the damaged regions observed on HE staining. Furthermore, neurons showed high expression of D2R in a few cases of remote BGN, suggesting some plasticity as to the recovery of D2R. Thus, the neuropathological characteristics of perinatal hypoxic-ischemic BGN may be related to neuronal maturation during different developmental stages in each region, and D2R development may play a role in the basal ganglia vulnerability to hypoxic-ischemia.

Effects of perinatal asphyxia on the mesostriatal/mesolimbic dopamine system of neonatal and 4-week-old male rats

The present study was undertaken in order to study the effects of perinatal asphyxia on tyrosine hydroxylase (TH) activity, dopamine levels and turnover, and dopamine metabolites (3,4-dihydroxyphenylacetic acid, DOPAC, homovanillic acid, HVA, and 3-methoxytyramine, 3-MT, analyzed by high-performance liquid chromatography, HPLC) measured in the basal ganglia of the 20- to 40-min-old newborn and 4-week-old male rat. Asphyxia was induced in pups by placing the fetuses, still in their uterus horns removed by hysterectomy from pregnant rats at full term, in a 37 degrees C water bath for 15-16 min or 19-20 min. Following asphyxia, the uterus horns were opened, and the pups were removed and stimulated to breathe. A 100% and 50-80% pup survival was obtained following 15-16 min and 19-20 min of asphyxia, respectively. Acute changes were studied in brains from newborn pups 20-40 min after delivery, and long-term changes were studied in brains from 4-week-old rats. No changes in TH-activity could be observed in the substantia nigra/ventral tegmental area (SN/VTA), the striatum, or the accumbens nucleus/olfactory tubercle (ACC/TUB), in the newborn or the 4-week-old rat. In the newborn rat, 19-20 min of asphyxia increased (as compared to controls) dopamine levels in the SN/VTA to 136 +/- 14% and in the ACC/TUB to 160 +/- 10%, indicating an increased synthesis and/or release of dopamine. DO-PAC levels were increased in the SN/VTA to 150 +/- 14% and in the ACC/TUB to 151 +/- 10%, and HVA levels were increased to 152 +/- 16% in the striatum and to 117 +/- 4% in the ACC/TUB. Following 15-16 min of asphyxia, dopamine levels were increased to 130 +/- 12% in the ACC/TUB, and DOPAC levels were increased to 135 +/- 6% and 130 +/- 12% in the SN/VTA and the ACC/TUB, respectively. This suggests that the increased dopamine levels may preferably reflect an increased release of dopamine following perinatal asphyxia. In the 4-week-old rat, dopamine levels were decreased in the SN/VTA to 71 +/- 4%, in the striatum to 52 +/- 8%, and in the ACC/TUB to 53 +/- 7%, following 19-20 min of perinatal asphyxia as compared to controls. No changes were observed in DOPAC, HVA, or 3-MT levels, indicating that the reduced dopamine levels reflect a reduced dopamine synthesis following perinatal asphyxia. A decrease in dopamine utilization was observed in the striatum to 15 +/- 8% and in the ACC/TUB to 9 +/- 13% following 19-20 min of perinatal asphyxia as compared to controls. This indicates that perinatal asphyxia produced long-lasting reductions in activity in the mesostriatal/mesolimbic dopamine systems in the 4-week-old rat.

Evolution of dopamine receptors in the rat after neonatal hypoxia-ischemia: autoradiographic studies

The aim of this work was to follow the evolution of striatal dopamine D1 and D2 receptors after hypoxic-ischemic (H/I) insult in immature rats. SPET imaging of these receptors could be used as an index to assess brain dysfunctions after perinatal H/I without change in cerebral blood flow or neuronal loss. We submitted 1-week-old rat pups to unilateral ligation of the left carotid artery plus 2h exposure to 8% O2. After recovery periods of 1, 2 or 9 weeks, ex vivo and in vitro autoradiographic studies of dopamine receptors were performed on normal appearing brains using specific ligands usable in human SPET imaging. Striatal dopamine D2 receptors tended to decrease bilaterally after one week's recovery. The decrease then reached 40% at 3 weeks of age and at 10 weeks of age the level of receptors had returned to normal values. By contrast, no change in dopamine D1 receptors was seen, whatever the age studied. In conclusion, changes in dopamine D2 receptors could be a valuable index for SPET imaging to evaluate H/I brain damage in the absence of anatomical lesions.

Neuropathophysiology of movement disorders in cerebral palsy

Recent developments in understanding the pathophysiology of disordered motor control in cerebral palsy are reviewed. In spastic cerebral palsy, evidence for abnormal segmental as well as supraspinal control of motor neuron output exists. Impaired Ia inhibition of antagonist muscles has been suggested but recently contested. Evidence also supports the role of decreased presynaptic inhibition of Ia afferents and decreased nonreciprocal Ib inhibition. Furthermore, early cerebral injury results in reorganization of supraspinal (corticospinal) inputs to motor neuron pools. In extrapyramidal cerebral palsy, injury of basal ganglia or thalamus has been demonstrated. A scheme for understanding the neurochemical circuitry of the extrapyramidal system is discussed. Animal models and certain specific human diseases provide examples of how this circuitry may be disturbed, thereby resulting in an imbalance between the direct and indirect striatal output systems and in impaired motor control. Future studies employing postmortem neurochemical analysis, functional magnetic resonance imaging, and positron emission tomographic scanning may foster progress in this area.

The temporal evolution of striatal dopamine receptor binding and mRNA expression following hypoxia-ischemia in the neonatal rat

Neonatal hypoxic-ischemic (HI) brain injury in the rat alters dopamine receptors. To determine whether such changes are permanent, dopamine receptors and corresponding mRNA were examined at various time points after neonatal HI using receptor autoradiography and in situ hybridization. Rat pups underwent ligation of the left common carotid artery followed by hypoxic exposure (8.5% O2 for 3 h). Controls underwent sham surgery alone. Animals surviving for 2-80 days following HI were studied. Striatal D1 receptors (labeled by [3H]SCH23390) were reduced as early as 2 days following HI, remained depressed for 21 days, but recovered to control levels by young adulthood (3 months of age). D2 receptors (labeled by [125I] iodosulpride) did not decline until 10 days after HI, and remained uniformly depressed throughout the caudate-putamen thereafter. Changes in D1 receptor mRNA transcripts closely paralleled alterations in receptors: early reductions in D1 mRNA signal recovered by young adulthood. D2 mRNA exhibited a unique temporal profile with an early decrease (2 days following HI), and prompt, persistent recovery. Dopamine receptors and transcripts are differentially affected by HI injury early in development. Whereas D1 receptor expression recovers from neonatal HI injury, D2 receptors remain permanently affected despite the presence of normal levels of D2 receptor transcripts. A persistent, post-transcriptional effect of HI on D2 receptor expression is suggested.

Nicotine treatment counteracts perinatal asphyxia-induced changes in the mesostriatal/limbic dopamine systems and in motor behaviour in the four-week-old male rat

In the present study, the effects of nicotine treatment on the changes induced by perinatal asphyxia in exploratory and D-amphetamine-induced behaviour, and in the number of brain tyrosine hydroxylase-immunoreactive nerve cell bodies were investigated in four-week-old male rats. Asphyxia was induced in pups by placing the fetuses, still in their uterus horns removed by hysterectomy from full-term pregnant rats, in a 37 degrees C water bath for 15-16 min or 19-20 min. Surviving male pups were treated with nicotine via suckling from surrogate mothers implanted subcutaneously with Alzet minipumps containing nicotine (0.2 mumol/kg per h) for four weeks. The minipumps implanted in the mothers of sham-treated animals contained saline only. After treatment, exploratory behaviour and D-amphetamine-induced behaviour was analysed in a computerized "activity" box. After the behavioural experiments, the rats were taken for tyrosine hydroxylase immunohistochemistry, and the total number of tyrosine hydroxylase immunoreactive cell bodies were counted in the A9 and A10 regions of the substantia nigra and the ventral tegmental area, respectively. Nicotine serum levels were measured using gas chromatography in selected asphyctic and control pups at different periods after delivery. During the exploratory phase, in saline-nurtured rats, 15-16 min of asphyxia slightly increased (approximately 25%) locomotion, motility and rearing. In contrast, 19-20 min of asphyxia reduced the locomotion and rearing by approximately 50%, as compared to controls. An increase in amphetamine-induced behaviours was observed after 15-16 min, but not after 19-20 min of asphyxia, as compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of neonatal hypoxia-ischemia on nigro-striatal dopamine receptors and on striatal neuropeptide Y, dynorphin A and substance P concentrations in rats

Perinatal hypoxic-ischemic brain injury was induced in 7- to 8-day-old rats by ligating the left carotid artery with subsequent exposure to 9% oxygen atmosphere for 2.5 h. The animals were killed 7 days later and grouped according to the degree of brain injury sustained after hypoxia-ischemia. Total protein content measured in striatum ipsilateral to the ligation, and dissected from brains showing extensive damage, was reduced to 64% of contralateral tissue. The protein content was not altered in other groups including control animals exposed to air and in sham-operated animals exposed to hypoxic conditions. The concentration of (pg/mg protein) and total (pg/striatum) striatal dynorphin A-like immunoreactivity (DLI) from brains with extensive damage were increased to 481% and 285% of the contralateral side, respectively. Hypoxia-ischemia increased striatal neuropeptide Y-like immunoreactivity (NPYLI) concentration from brains with extensive damage to 157% of contralateral side, but when the results were expressed as total NPYLI content per striatum, NPYLI content in striatum with extensive damage remained unaltered. Substance P-like immunoreactivity (SPLI) concentration and total content per striatum from brains with extensive damage were reduced to 66% and 43% of the contralateral side, respectively. D1 and D2 receptor density in animals killed 10 days after injury was reduced by 24% and 22% of control, respectively, in striatum from brains with extensive damage. These results indicate complex changes in brain neuropeptides following neonatal hypoxia-ischemia. Damage in the substance P system could have functional effects on dopaminergic transmission while the increase in NPYLI and in DLI concentrations may respectively reflect the relative preservation from neuronal damage and possibly an increase in neuropeptide synthesis or decrease in release. The decrease in SPLI concentration and the increase DLI concentration induced by hypoxia-ischemia suggests that these peptides may be present in separate neurons.

Acute and persistent suppression of preproenkephalin mRNA expression in the striatum following developmental hypoxic-ischemic injury

The striatum is vulnerable to hypoxic-ischemic injury during development. In a rodent model of perinatal hypoxia-ischemia, it has been shown that striatal neurons are not uniformly vulnerable. Cholinergic neurons and NADPH-diaphorase-positive neurons are relatively spared. However, it is unknown what classes of striatal neurons are relatively sensitive. One of the major classes of striatal neurons uses enkephalin as a neurotransmitter. We have studied the effect of early hypoxic-ischemic injury on this class of neurons using a quantitative solution hybridization assay for preproenkephalin mRNA in conjunction with in situ hybridization. Hypoxia-ischemia results in an early (up to 24 h) decrease in striatal preproenkephalin mRNA, which is shown by in situ hybridization to occur mainly in the dorsal portion of the striatum. By 14 days, whole striatal preproenkephalin mRNA and total enkephalin-containing peptide levels are normal. However, at 14 days, in situ hybridization reveals that regions of complete preproenkephalin mRNA-positive neuron loss remain in the dorsal region. Normal whole striatal levels are due to an up-regulation of preproenkephalin mRNA expression in the ventrolateral region of the injured striatum. Given the important role that the enkephalin-containing striatal efferent projection plays in regulating motor function, its relative loss may be important in the chronic disturbances of motor control observed in brain injury due to developmental hypoxic-ischemic injury.

Effects of cyanide on the striatal dopamine receptor binding in the rat

In previous studies we have shown that sodium cyanide decreases the striatal dopamine levels within 60 s compared with the controls. Treatment with sodium cyanide also increases the naturally occurring 3,4-dihydroxy-L-phenylalanine (L-DOPA) in the striatum, but not in any other region studied. An increase in the in vivo synthesis of dopamine in cyanide-treated rats has also been observed. In order to further elucidate the effects on the central dopaminergic pathways the effects of sodium cyanide on the striatal dopamine D1 and dopamine D2 receptor binding were studied in vitro and after administration of sodium cyanide. In the rats injected with sodium cyanide (2.0 mg/kg, i.p.) the Bmax of the striatal dopamine D1 receptor binding was significantly decreased 15 min and 1 h after the treatment. The striatal dopamine D2 receptor binding was decreased only at 1 h after the cyanide administration. Neither sodium cyanide nor its metabolite sodium thiocyanate did significantly change the striatal dopamine D1 and D2 receptor binding in vitro. Accordingly sodium cyanide and sodium thiocyanate do not have direct effects on the dopamine receptors studied. The effects of cyanide on dopamine D1 and D2 receptors are probably in part due to the effect of cyanide on the release of dopamine.

Preserved striatal tyrosine hydroxylase activity, assessed in vivo, following neonatal hypoxia-ischemia

Previous in vitro studies have shown that biochemical indices of striatal dopaminergic systems are preserved following neonatal hypoxia-ischemia. There has been no previous assessment of these systems in vivo. Using the accumulation of striatal dopa following administration of a dopa decarboxylase inhibitor as an in vivo measure of tyrosine hydroxylase (TH) activity, we have found that baseline TH activity, and its regulation by both neuronal activity and presynaptic autoreceptors are also preserved following hypoxia-ischemia.