Urban Ungerstedt

Quantitative recording of rotational behavior in rats after 6-hydroxy-dopamine lesions of the nigrostriatal dopamine system

Abstract Several studies show that unilateral increase or decrease of the activity in the nigrostriatal dopamine system will cause an asymmetry in the movements and posture of animals. The symptoms may range from unilateral hypokinesia to vigorous rotation towards one side. In the present paper the nigrostriatal dopamine system of rats is unilaterally lesioned by intracerebral injection of 6-hydroxy-dopamine which produces an almost complete and selective lesion. The remaining contralateral dopamine system is activated by systemic treatment with amphetamine. The evoked rotational behavior is automatically registered as turns per minuteversus time in a specially designed ‘rotometer’ where the animal moves on a spherically shaped surface while connected to the registering device by a thin wire. The rotational behavior is highly reproducible and dose dependent, and it seems very probable that this rotational behavior is quantitatively related to the degree of dopamine receptor stimulation. The method is suggested for studies of different functional states in the nigrostriatal dopamine system.

6-hydroxy-dopamine induced degeneration of central monoamine neurons

Abstract Intracerebral injection of 6-hydroxy-dopamine induced degeneration of central dopamine and noradrenaline neurons. Injection into the substantia nigra produced an anterograde degeneration of the whole nigro-neostriatal dopamine neuron system. This was associated with marked motor disturbances. It is suggested that intracerebral administration of 6-hydroxy-dopamine may be used as a tool for anatomical and functional studies on central monoamine neurons.

Receptor activity and turnover of dopamine and noradrenaline after neuroleptics.

Abstract Fifteen neuroleptics of the phenothiazine, thioxanthene, dibenzazepine, butyrophenone or diphenylbutylamine type were studied in rats. The dopamine (DA) receptors in the corpus striatum were blocked by all the drugs. The effects on noradrenaline (NA) receptors in the spinal cord varied. Chlorpromazine blocked the two receptors about equally. Haloperidol, perphenazine, clothiapine and particularly spiroperidol had a greater effect on DA receptors. Pimozide and fluspirilene blocked only DA receptors. Turnover of DA and NA was studied using biochemical and histochemical techniques, after tyrosine hydroxylase inhibition. Perphenazine and clothiapine accelerated turnover of both amines whereas spiroperidol only accelerated that of DA. Pimozide and fluspirilene increased turnover of DA and, at higher doses, NA. The high doses usually reduced the endogenous DA and NA levels. Thus, the most potent and specific neuroleptics seemed to influence mainly the brain DA mechanisms, both functionally and chemically.

In Vivo Measurement of Dopamine and Its Metabolites by Intracerebral Dialysis: Changes After d-Amphetamine

Abstract: By using a new technique, intracerebral dialysis, in combination with high performance liquid chromatography and electrochemical detection, it was possible to recover and measure endogenous extracellular dopamine, together with its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) from the striatum and nucleus accumbens of anaesthetized or freely moving rats. In addition, measurements of extracellular 5‐hydroxyindoleacetic acid, ascorbic acid, and uric acid were made. Basal extracellular concentrations of dopamine and DOPAC in the striatum were estimated to be 5 × 10−8M and 5 × 10−6M, respectively. d‐Amphetamine (2 mg/kg s.c.) increased dopamine levels in the striatum perfusates by 14‐fold, whereas levels of DOPAC and HVA decreased by 77% and 66%, respectively.

Changes in cortical extracellular levels of energy-related metabolites and amino acids following concussive brain injury in rats

The aim of this study was to measure extracellular chemical changes in the cerebral cortex in response to compression contusion trauma in rats. Energy-related metabolites (i.e., lactate, pyruvate, adenosine, inosine, and hypoxanthine) and amino acids were harvested from the extracellular fluid (ECF) using microdialysis and analyzed by high-performance liquid chromatography. The measurements were performed in cortical tissue, where neuronal injury occurs in this model. The severity of the trauma was varied by using different depths of impact: mild trauma, 1.5 mm; severe trauma, 2.5 mm. The trauma induced a dramatic increase in the ECF levels of energy-related metabolites that was conditioned by the severity of the insult. The ECF level of taurine, glutamate, aspartate, and γ-aminobutyric acid (GABA) also rose markedly, while other amino acids did not change significantly. The results suggest that the trauma induced a transient, profound focal disturbance of energy metabolism in the cortical tissue, probably as a result of mechanically induced disruption of ion homeostasis and reduced blood flow in combination. The data support the potential role of glutamate and aspartate as mediators of traumatic brain injury. However, the concomitantly released adenosine, GABA, and taurine may be protective and ameliorate excitotoxicity. In analogy with the reported cumulative damaging effects of repeated ischemic insults, the observed ECF changes may help explain the vulnerability of traumatized brain tissue to secondary ischemia.

In vivo measurement of extracellular dopamine and DOPAC in rat striatum after various dopamine-releasing drugs; implications for the origin of extracellular DOPAC.

In order to further examine the likely origin of the dopamine (DA) metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), certain drugs known to release DA from different intraneuronal pools were tested for their effects on extracellular striatal DA and DOPAC levels by means of brain microdialysis in the halothane-anaesthetized rat. Amphetamine (10(-6) and 10(-5) M), nomifensine (10(-5) M), potassium chloride (30 and 60 mM), methylphenidate (10(-5) and 10(-4) M) and tyramine (10(-5) M), when added to the perfusion medium and administered locally into the striatum via the dialysis membrane, increased the level of DA in striatal perfusates during the 20 min of application. In comparison, the level of DOPAC in the perfusates was decreased by both amphetamine (10(-5) M) and potassium chloride (60 mM), but was not significantly changed by nomifensine, methylphenidate or tyramine. The effect of amphetamine (10(-6) M) and nomifensine (10(-5) M) on DA and DOPAC levels was further studied by administering the drugs over a longer period of time (3 X 20 min). Although both of these treatments produced a similar increase of DA, only amphetamine reduced the levels of DOPAC. DA (10(-4) but not (10(-5) M) increased the levels of DOPAC but this effect was also seen in DA-denervated animals. These data indicate that when the DA nerve terminal is exposed to drugs which release newly synthesized DA, DOPAC declines possibly because intraneuronal monoamine oxidase is deprived of its main substrate. We suggest that these findings support the hypothesis that a major portion of the DA metabolite, DOPAC, is derived from an intraneuronal pool of newly synthesized DA.

A direct comparison of amphetamine-induced behaviours and regional brain dopamine release in the rat using intracerebral dialysis

An intracerebral microdialysis method was used in awake rats to directly compare the effect of amphetamine on dopamine (DA) release in the striatum and nucleus (n.) accumbens with alterations in behaviour. Amphetamine (0.5-5.0 mg/kg, s.c.) caused a dose-dependent release of DA in both brain regions; however the n. accumbens appeared for the most part more sensitive to amphetamine than the striatum. At each individual dose of the drug, 0.5, 2.0 and 5.0 mg/kg s.c., DA release was closely followed over the time course by the overall behavioural syndrome. Certain components of behaviour showed a regional-specific association with DA release. The intensity of stereotyped head and forepaw movements was closely correlated over the dose range with the amount of DA released in striatum but not n. accumbens. Over the time course, however, the occurrence of this behaviour was delayed compared to increased striatal DA release. In contrast, increased locomotor activity was correlated with the time course change in, and amount of, DA released in n. accumbens by low doses of amphetamine, but not at any dose with DA released in striatum. Repetitive sniffing was better correlated with DA released in n. accumbens than striatum. These in vivo measurements of DA release add further support to the hypothesis that amphetamine-induced stereotypy and locomotion are mediated via DA released in striatum and n. accumbens, respectively. Our data suggest that the occurrence of intense stereotypy rather than locomotor activity at high doses of amphetamine is not due to a selection action in striatum but probably competition between the two behaviours.(ABSTRACT TRUNCATED AT 250 WORDS)

Purine levels in the intact rat brain. Studies with an implanted perfused hollow fibre.

A thin dialysis tube was implanted stereotaxically under halothane anesthesia in the caudate nucleus of Sprague-Dawley rats and perfused with Ringer solution at a rate of 2 microliters/min. Initially there was a high rate of purine outflow but after 1-2 h of perfusion the rate was essentially constant (anesthetized - adenosine 0.4 +/- 0.04 microM, inosine 0.8 +/- 0.2 microM; non-anesthetized - adenosine 0.33 +/- 0.03 microM, inosine 0.21 +/- 0.07 microM). Hypoxia (9% O2) increased the levels more than 3-fold. The adenosine deaminase inhibitor erythro-2-(2-hydroxy-3-nonyl)adenine (EHNA) increased the adenosine level and decreased the inosine level. In vitro recovery of adenosine was about 30%. Therefore, we conclude that the free exchangable concentration of adenosine in the rat brain is likely to be 102 micro M. This level is high enough to potentially affect central nervous function.

Dynamics of Extracellular Metabolites in the Striatum after Middle Cerebral Artery Occlusion in the Rat Monitored by Intracerebral Microdialysis

The aim of this study was to measure changes in the extracellular fluid (ECF) concentration of lactate, pyruvate, purines, amino acids, dopamine, and dopamine metabolites in the striatum of rats subjected to focal cerebral ischemia, using intracerebral microdialysis as the sampling technique. Microdialysis probes were inserted into the lateral part of the caudate-putamen bilaterally 2 h before the experiment. Ischemia was induced by permanent middle cerebral artery occlusion (MCAO) on the left side. Microdialysis samples were analyzed by high performance liquid chromatography. Following MCAO, the concentration of lactate, adenosine, inosine, and hypoxanthine rose markedly in the ECF on the occluded side, while there was no significant change in pyruvate. These changes were accompanied by dramatically elevated levels of aspartate, glutamate, taurine, γ-aminobutyric acid, and dopamine. There was also a marked increase in alanine/tyrosine, while minor or no changes occurred with other amino acids. Concomitantly, the ECF level of the dopamine metabolites 3,4–dihydroxyphenylacetate and homovanillic acid decreased. There was no significant increase in any of the metabolites measured on the right, nonoccluded side. In relation to the concept of excitotoxicity in brain ischemia, it is concluded that during the acute stage of focal cerebral ischemia, the ECF is flooded with both potentially harmful (e.g., aspartate, glutamate, and DA) and protective (e.g., taurine, GABA, and adenosine) agents. The relative importance of these events for the development of cell death in the ischemic penumbra needs to be elucidated. In addition, lactate, inosine, and hypoxanthine, measured in the ECF by intracerebral microdialysis, may prove to have diagnostic and/or prognostic value in neurometabolic monitoring of the ischemic brain.

Morphological and Functional Aspects of Central Monoamine Neurons

Publisher Summary This chapter provides an overview of the morphology of central monoamine neurons and the function of central monoamine neurons. The Nigro–Neostriatal neurons perform both the motor and mental functions. Their degeneration causes hypokinesia and rigidity while overstimulation of neostriatal dopamine (DA) receptors causes stereotyped behavior. The tubro-infundibular DA neurons probably act by way of inhibiting the release of luteinizing hormone releasing factor (LHRF) from the median eminence. The central noradrenaline (NA) neurons perform various functions, such as function in wakefulness, emotion, behavior, neuroendocrine function, and function in reflex activity. The central 5-hydroxytryptamine (5-HT) neurons contribute to the function in mood, wakefulness, thought process, behavior, neuroendocrine function, and function in reflex activity. The NA neurons probably are essential for conditioned processes as are the DA neurons while a destruction of the 5-HT neurons results in insomnia. Increased NA receptor activity results in aggression. The descending bulbospinal 5-HT neurons participate in the control of autonomic and somatic reflex activity, especially in the lumbosacral part.