Circling behaviour produced by unilateral lesions in the region of the locus coeruleus in rats

Noradrenaline is crucial for the substantia nigra dopaminergic cell maintenance

In Parkinson's disease, degeneration of substantia nigra dopaminergic neurons is accompanied by damage on other neuronal systems. A severe denervation is for example seen in the locus coerulean noradrenergic system. Little is known about the relation between noradrenergic and dopaminergic degeneration, and the effects of noradrenergic denervation on the function of the dopaminergic neurons of substantia nigra are not fully understood. In this study, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) was injected in rats, whereafter behavior, striatal KCl-evoked dopamine and glutamate releases, and immunohistochemistry were monitored at 3 days, 3 months, and 6 months. Quantification of dopamine-beta-hydroxylase-immunoreactive nerve fiber density in the cortex revealed a tendency towards nerve fiber regeneration at 6 months. To sustain a stable noradrenergic denervation throughout the experimental timeline, the animals in the 6-month time point received an additional DSP4 injection (2 months after the first injection). Behavioral examinations utilizing rotarod revealed that DSP4 reduced the time spent on the rotarod at 3 but not at 6 months. KCl-evoked dopamine release was significantly increased at 3 days and 3 months, while the concentrations were normalized at 6 months. DSP4 treatment prolonged both time for onset and reuptake of dopamine release over time. The dopamine degeneration was confirmed by unbiased stereology, demonstrating significant loss of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra. Furthermore, striatal glutamate release was decreased after DSP4. In regards of neuroinflammation, reactive microglia were found over the substantia nigra after DSP4 treatment. In conclusion, long-term noradrenergic denervation reduces the number of dopaminergic neurons in the substantia nigra and affects the functionality of the nigrostriatal system. Thus, locus coeruleus is important for maintenance of nigral dopaminergic neurons.

Antidepressant drug induced alterations in binding to central dopamine transporter sites in the Wistar Kyoto rat strain

The Wistar Kyoto (WKY) rat has been proposed as an animal model of depressive behavior. Exposing WKY rats to stress stimulation produces symptoms such as anhedonia, psychomotor retardation, ambivalence and negative memory bias. Given the role of the mesolimbic dopamine (DA) system in cognitive, emotional and motivational behaviors, we previously examined the distribution of DA transporter (DAT) sites in the brains of WKY compared to Wistar (WIS) and Sprague-Dawley (S-D) rats. WKY rats exhibited significant differences in DAT binding sites in the cell body as well as mesolimbic areas compared to the other strains. It was reasoned that these differences may lead to altered synaptic levels of DA in specific brain regions thus contributing to the behavioral differences observed in this rat strain. Thus, the present study examined whether repeated treatment with antidepressant drugs that block the uptake of DA (nomifensine and bupropion) would modify [3H]-GBR12935 binding to DAT sites in WKY rats compared to WIS and S-D rats. The results indicate that while nomifensine and bupropion increased the binding of [3H]-GBR12935 to DAT sites in the mesocorticolimbic regions in WKY rats, these drugs increased the binding of [3H]-GBR12935 to DAT sites in the cell body areas in WIS rats but not in S-D and WKY rats. The data from this study suggest that antidepressant induced alterations in DAT sites in the mesocorticolimbic brain regions may play a role in the behavioral improvement seen in WKY rats, as measured by the Open Field Test (OFT) and the Porsolt Forced Swim Test (FST).

Effects of low dose N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine administration on exploratory and amphetamine-induced behavior and dopamine D2 receptor function in rats with high or low exploratory activity

Individual differences in behavioral traits are associated with sensitivity to various neurochemical and psychopharmacological manipulations. In this study exploratory and amphetamine-induced behavior in rats with persistently high or low exploratory activity (HE and LE, respectively) was examined before and after a partial denervation of the locus coeruleus (LC) projections with the selective neurotoxin DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine; 10 mg/kg). Partial LC denervation prevented the increase in exploratory activity over repeated test sessions in the LE animals, but had no effect in HE-rats. Amphetamine- (0.5 mg/kg) induced locomotor activity was attenuated by DSP-4 pretreatment only in HE-rats. These results suggest differential involvement of LC noradrenergic transmission in novelty- and amphetamine-induced behavior in animals with persistent differences in novelty-related behavior. In addition to partial noradrenaline depletion in the frontal cortex and hippocampus, which occurred in both HE- and LE-rats, DSP-4 treatment also decreased the content of dopamine and its metabolites in the nucleus accumbens, and the metabolite levels in striatum, but only in the LE-animals. 5-HIAA levels were also reduced in the nucleus accumbens and striatum in LE-rats by the neurotoxin. D(2) receptor function, as determined by dopamine-stimulated [(35)S]GTPgammaS binding, was increased by DSP-4 treatment in the striatum of LE-rats, but reduced in HE-rats. No effect of partial LC denervation was found on dopamine-stimulated [(35)S]GTPgammaS binding in the nucleus accumbens. Together these findings suggest that LC noradrenergic neurotransmission is differently involved in dopaminergic mechanisms which mediate novelty-related vs amphetamine-induced behavior.

Gross mapping of α1-adrenoceptors that regulate behavioral activation in the mouse brain

Brain alpha1-adrenoceptors that participate in behavioral activation were mapped in the mouse brain by determining where microinjection of the alpha1-antagonist, terazosin, inhibited behavioral activity in a novel cage test. A total of 5 out of 23 tested regions were shown to be involved including the dorsal pons/locus coeruleus region (DP/LC), the dorsal raphe/periaqueductal gray area (DR/PAG), the vermis cerebellum (CER), the nucleus accumbens (ACC) and the medial preoptic area (MPOA). Injection in the 4th ventricle was also effective perhaps by acting on several of these regions simultaneously. A partial inhibition was obtained from the motor cortex. Coinjection of the alpha1/2-agonist, 6-fluoronorepinephrine (6FNE) but not the alpha2-agonist, dexmedetomidine (DMT) reversed the behavioral inhibition in all regions. It is hypothesized that brain motoric alpha1-receptors elicit behavioral activation by coordinately exciting several monoaminergic, motor and motivational systems.

Flotillin-1 in the substantia nigra of the Parkinson brain and a predominant localization in catecholaminergic nerves in the rat brain

The substantia nigra cells of a normal and Parkinson's disease human brain were obtained by the micropunch procedure and total RNA was isolated. Differential display RT-PCR of the total RNA revealed differentially expressed cDNAs that were identified by sequencing. This resulted in the identification of a panel of known and unknown differentially expressed genes. Complex I (NADH ubiquinone oxidoreductase) and Complex IV (cytochrome oxidase) whose expressions are decreased in Parkinson's disease were reduced in the Parkinson brain. Of the various differentially expressed genes, flotillin-1, also known as reggie-2, was of great interest to us. It is a relatively new protein which is an integral membrane component of lipid rafts and has been implicated in signal transduction pathway events. In situ hybridization histochemical studies with human and rat brain sections revealed the presence of this mRNA in discrete neuronal (and possibly glial) cells of the substantia nigra, locus coeruleus, cortex, hippocampus, hypothalamus, thalamus, motor nuclei, nucleus basalis, raphe nucleus, and other brain regions. Immunohistochemical studies revealed that flotillin-1 is not present in all the regions where the message was found. In the rat brain, the most prominent observation was the revelation of all catecholamine cells (dopamine, norepinephrine, epinephrine) by the flotillin-1 antibody (1:100 dilution). At a more concentrated dilution (1:10) other neuronal cells (e.g., cortex, thalamus, hindbrain) were observed. At both dilutions dense dopaminergic fibers were observed in the rat caudate-putamen, nigrostriatal tract, and substantia nigra. It is significant that there is an increased gene expression of flotillin-1 in the Parkinson substantia nigra/ventral tegmental area. The role of flotillin in these cells is unclear although it is interesting that the reggie-2/flotillin-1 gene was upregulated during retinal axon regeneration in the goldfish visual pathway (Schulte et al., Development 124:577-87, 1997) which suggests that flotillin-1/reggie-2 might play a role in axonal growth from the remaining substantia nigra cells of the Parkinson brain.

Role of locus coeruleus ?1-adrenoceptors in motor activity in rats

The question of whether or not the locus coeruleus (LC) participates in the control of motor activity has been controversial due to difficulties in demonstrating permanent motor deficits after neurotoxic lesions of this nucleus or of the dorsal noradrenergic bundle (DNB). In the present experiments it was shown in rats that acute local blockade (with terazosin) or stimulation (with phenylephrine) of LC alpha(1)-adrenoceptors respectively blocked or stimulated exploratory behavior in a novel cage and the home cage. Moreover, previous lesion of the DNB by i.p. DSP4 abolished the behavioral changes to local LC alpha(1)-receptor manipulation but did not affect motor activity in the novel or home cage by itself. These findings are consistent with the hypothesis that the intact LC does contribute to motor activity control, exerted in part by its alpha(1)-receptors; however, the permanent loss of this nucleus is compensated for by remaining CNS motor structures.

Strain differences in the distribution of dopamine transporter sites in rat brain

The Wistar Kyoto (WKY) rat has long been proposed as an animal model of depressive behavior. Exposure to stress produces symptoms such as anhedonia, psychomotor retardation, ambivalence, and negative memory bias. Autoradiographic studies have revealed significant differences in the density of norepinephrine transporter (NET) and serotonin transporter (5-HTT) sites in several brain regions in WKY rats compared to Sprague-Dawley (S-D) rats. Since the mesolimbic dopamine (DA) system is involved in cognitive, emotional, and motivational behaviors, this study examined the distribution of dopamine transporter (DAT) sites in the brains of WKY compared to Wistar (WIS) and S-D rats. DAT sites were labeled with [3H]-GBR12935 (1 nM), and mazindol (50 microM) was used to define nonspecific binding. Quantitative analysis of the specific binding indicated that WKY rats exhibited significant differences in DAT binding sites in the cell body as well as mesolimbic areas in comparison to WIS and S-D rats. While the binding of [3H]-GBR to DAT sites was significantly decreased in the nucleus accumbens (NAc), the amygdala, the ventral tegmental area (VTA), and the reticular part of the substantia nigra (P<.05), the binding was significantly increased in the hippocampal subregions and the hypothalamus (P<.05) in WKY rats compared to the other two strains. In contrast, no strain differences were found in the caudate-putamen. The observed differences in the density and distribution of DAT sites in WKY rats may lead to altered modulation of synaptic DA levels in the cell body and mesolimbic regions, thereby contributing to the noted depression-like behaviors reported in this rat strain.

Pharmacological evidence for the role of central alpha 1B-adrenoceptors in the motor activity and spontaneous movement of mice

Central alpha 1-noradrenergic neurotransmission has been shown to be an important complement of dopaminergic transmission in the control of motor activity but the identity of the responsible alpha 1 receptor subtype has not yet been identified. This was investigated in the present experiment by measuring the effects of intraventricular administration of a series of alpha 1 antagonists varying in affinities for the three known receptor subtypes--1a, 1b and 1d--on active behavior in mice in response to a cage change. It was found that the potency of the drugs to block both gross and small movements correlated highly with published affinities for the cloned 1b receptor but not for those of either the cloned 1a or 1d receptors. It is concluded that central alpha 1B receptors are critically involved in the mediation of the (nor)adrenergic influence on active behavior, a finding which has implications for basic and clinical research in both movement and mood disorders.

Locus coeruleus lesions potentiate neurotoxic effects of MPTP in dopaminergic neurons of the substantia nigra

The observation that Parkinson's disease (PD) is associated with locus coeruleus (LC) noradrenergic neuronal degeneration suggests that the LC noradrenergic system may be involved in the pathogenesis and natural progression of the destruction of the substantia nigra (SN) dopaminergic neurons in Parkinson's disease. The relationship of these two systems was examined by injection of subtoxic doses of MPTP into unilateral LC 6-hydroxydopamine (6-OHDA) lesioned mice. A significant loss of dopaminergic cells was only found in the SN on the side of the LC lesions. These results suggest that the LC may have protective effects on SN dopaminergic neurons.

Unilateral damage to the ventral tegmental area facilitates feeding induced by stimulation of the contralateral ventral tegmental area

Unilateral lesions of the ventral tegmental area (VTA) facilitated feeding induced by electrical stimulation of the homologous VTA tissue in the contralateral hemisphere. The lesions shifted the function relating latency to begin feeding to stimulation frequency to the left simultaneously causing a reduction of frequency threshold for feeding reaction. Facilitation of feeding was immediate (with a peak on the 2nd postlesion day) and in some animals persisted up to the end of the 2-week experimental period. No facilitation of VTA stimulation-induced feeding was found in the control animals in which comparable lesions were performed in the contralateral lateral hypothalamus or the antero-dorsal thalamus which suggests that the effect was site specific. Individual differences in the magnitude and duration of the facilitatory effect on feeding may be related to the variability in the medio-lateral localization of the lesions. The results are interpreted in terms of compensatory increase in the dopaminergic transmission and/or decrease of the GABA-ergic inhibitory tone in the contralateral hemisphere after unilateral lesion to the mesencephalic dopaminergic systems. A possible involvement of the noradrenergic transmission is also discussed.

Effects of locus coeruleus lesions on vigilance and attentive behaviour in cat

Previous data have suggested that in the cat, expectancy behaviour (waiting for a target to appear) and associated electrocortical, focal, synchronized activity ('mu' rhythms) are modulated by a noradrenergic system possibly originating from the locus coeruleus (LC). To test the latter hypothesis, we have examined the behavioural and ECoG changes induced after bilateral LC lesions. Our results demonstrated that destruction of the anterior 3/4th of the LC (A6 noradrenergic cell group) resulted in a considerable increase of mu rhythms and expectancy behaviour, without episodes of drowsiness that normally occur. Destruction of the posterior fourth of LC (A4 noradrenergic group) only increased the duration of slow sleep. Extending the A6 lesion to include the dorsal ascending noradrenergic bundle also increased the expectancy behaviour and mu rhythms. Finally, when the nucleus subcoeruleus was also involved, the duration of slow sleep and the frequency of paradoxical sleep episodes increased. These findings indicate that the LC exerts an inhibitory effect on structures involved in the induction and persistence of expectancy behaviour with accompanying mu rhythms.

The effects of L-threo-3,4-dihydroxyphenylserine on the total norepinephrine and dopamine concentrations in the cerebrospinal fluid and freezing gait in parkinsonian patients

We studied the effects of L-threo-DOPS (L-DOPS) on the concentrations of total (conjugated and unconjugated) dopamine (DA) and norepinephrine (NE) in the cerebrospinal fluid (CSF) of parkinsonian patients with freezing phenomenon. The NE concentration increased remarkably and dose-dependently after administration of L-DOPS in both L-dopa/carbidopa-pretreated and untreated patients. The DA concentration also increased mildly but significantly in L-dopa/carbidopa-untreated patients. Freezing phenomenon improved in 6 out of 8 patients at Hoehn and Yahr's stage III, and 1 out of 5 patients at stage IV. These results indicate that L-DOPS administration increases the NE concentration dose-dependently, and is effective for freezing of gait of moderate severity.

The locus coeruleus and dopaminergic function in rat brain: implications to parkinsonism

Clinical and experimental evidence suggests that degeneration of the locus coeruleus (LC) may be responsible for certain symptoms of Parkinson's disease (PD). We have, therefore, studied the effects of LC lesion on dopamine (DA) metabolism in the rat striatum. Unilateral depletion of norepinephrine (NE) was obtained by stereotaxic injection of 6-hydroxydopamine (6-OHDA) into the dorsal NE bundle (DNEB). Rats were sacrificed 1 or 3 weeks after lesioning. 6-OHDA induced approximately 50% depletion of NE in the ipsilateral hippocampus at 1 week postinjection, and over 75% depletion after 3 weeks. DNEB lesions had no effect on DA or DOPAC levels in the ipsi- or contralateral striatum at either time point. Lesions also failed to affect DA synthesis or utilization in either striatum. The metabolism of exogenous levodopa in the striatum was also unaffected. It is suggested that any possible effect of the LC on DA transmission in the striatum is not mediated by the DNEB.

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

Effects of an alpha 2 antagonist in a 20-year-old Java monkey with MPTP-induced parkinsonian signs

The study attempted to verify whether activation of locus coeruleus neurons by alpha 2 antagonists might improve parkinsonian signs. Treatment with the racemic alpha 2 antagonist R 47 243 of a monkey with MPTP-induced parkinsonian signs normalized blink rate, reduced resting tremor, and improved several other parkinsonian signs. In a second experiment, the (-)-isomer R 62 651 produced a gradual change in tremor which was the inverse of the mannner in which tremor had become installed as the result of progression earlier upon the MPTP challenge. It is proposed that further research be conducted to determine whether alpha 2 antagonists may beneficially influence the progression of Parkinson's disease.

Destruction of norepinephrine terminals in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice reduces locomotor activity induced by L-dopa

There is little information concerning the effects of norepinephrine (NE) depletion on clinical features of patients with Parkinson's disease. By inducing two types of experimental parkinsonism, one with a dopamine (DA) deficiency alone and the other with both a DA and NE deficiency, we attempted to evaluate the differences in locomotor activity and behavioral responses between the two groups after L-DOPA administration. The results of the study revealed that increases in locomotor activity were markedly suppressed in the DA and NE deficient group. This may suggest that with striatal DA deficiency the central NE terminals play a significant role in the increase in locomotor activity after L-DOPA administration.

Effects of locus coeruleus lesions on the release of endogenous dopamine in the rat nucleus accumbens and caudate nucleus as determined by intracerebral microdialysis

Bilateral 6-hydroxydopamine lesions of the rat locus coeruleus (a) depleted forebrain norepinephrine levels by 67%, (b) reduced the basal release of dopamine in the nucleus accumbens and caudate nucleus by 26% and 19%, respectively, and (c) reduced (+)-amphetamine-induced release in the nucleus accumbens and caudate nucleus. The locus coeruleus appears to exert a tonic excitatory influence on striatal and limbic dopamine release in vivo.

Central catecholaminergic dysfunction and behavioural disorders following hypoxia in adult rats

Wistar male rats, 3-4 months old, were made to breathe for 6 h a sub-lethal hypoxic atmosphere consisting of 8% oxygen and 92% nitrogen. Following this treatment, these rats were subjected to a series of behavioral and biochemical tests starting 30 days and ending at about 180 days after the hypoxic insult. an age-matched control group was subjected to the same series of tests. The following findings were made at the time interval indicated, relative to controls: (1) At 30-35 days, diurnal (3 h) and nocturnal (12 h) locomotor activities decreased by about 25%. (2) At 40-45 days, amphetamine in the dose range of 0.25-1 mg/kg proved less effective in eliciting an increase in motor activity and stereotypic behavior. (3) At about 50 days, apomorphine in the dose range 0.25-0.5 mg/kg caused an increase in stereotypic behavior. (4) At 60-65 days, alpha-methyl-p-tyrosine at the dose of 50 mg/kg caused a more pronounced hypoactive syndrome and a slower rate of recovery of motor activity. (5) At 75-90 days, performance in the active avoidance test was inferior to that of controls. (6) At 180 days, and one hour after a dose of 200 mg/kg alpha-methyl-p-tyrosine, the turnover rates of hippocampal norepinephrine and caudate-putamen dopamine were much below control. One may tentatively conclude that one of the effects of hypoxia in adult rats is a lesion producing long-term behavioral disorders which are partly ascribed to dopaminergic and, possibly noradrenergic, dysfunction.

Specific α2-adrenoreceptor antagonists induce behavioural activation in the rat

The behavioural effects of the specific and selective α(2)-adrenoreceptor antagonists, idazoxan, efaroxan and RX811059, have been investigated in the rat. All three drugs induced periods of behavioural activation characterized by increased locomotion and exploration (rearing and hole dipping). However, these effects were only apparent in animals which were fully habituated to their environments and thus displayed low baseline activity. The behaviour observed lay within the normal range of activity and was not apparent under conditions when exploration was stimulated such as in a novel environment. α( 2)-Adrenoreceptor antagonist- induced activation was a weak response when compared with the intense and prolonged hyperactivity, in both novel and non-novel environments, induced by the amine releaser D- amphetamine. Possible mechanisms involving a direct action of noradrenaline at postsynaptic α( 1)-adrenoreceptors (subsequent to enhanced presynaptic α(2)-receptor feedback blockade) or an indirect action of α(2)-antagonists on dopamine function in mesolimbic pathways are discussed.

The iminodipropionitrile (IDPN)-induced dyskinetic syndrome: behavioral and biochemical pharmacology

Chronic administration of iminodipropionitrile causes a persistent behavioral syndrome which is characterized by lateral and vertical head shakes, random circling, hyperactivity and increased acoustic startle response in rodents. These behavioral abnormalities are similar to those observed after the acute administration of serotonin (5-HT) and dopamine (DA) agonists, and of some peptides including thyrotropin-releasing hormone (TRH) and the enkephalins. The data available so far indicate that the 5-HT system which interacts with some other neurotransmitters such as DA and norepinephrine (NE) in both reciprocal and nonreciprocal ways may be primarily involved in the manifestations of this persistent dyskinetic syndrome. Preliminary evaluation of the peptidergic systems has also revealed possible involvement of opiate peptides in the IDPN-induced dyskinetic phenomena. More studies are needed to assess the role of specific molecular events which may occur at cortical, subcortical, and/or spinal levels to cause this interesting psychomotor syndrome.

Determination of monoamines and both forms of monoamine oxidase in the rat's substantia nigra during postnatal development

Changes in biogenic amine content in the substantia nigra and in both forms of monoamine oxidase in substantia nigra and striatum of the rat during postnatal development (15-180 days) have been studied. Dopamine and serotonin had the same levels at day 15, however, each monoamine showed a different developmental profile. Dopamine levels and their metabolites (except 3-methoxytyramine) decreased during postnatal development. Serotonin levels and their main metabolite, 5-hydroxyindolacetic acid, underwent an increase during all stages studied. There were no statistically significant changes in noradrenaline levels until day 180 when they increased with respect to day 15. The highest activity of the monoamine oxidase-A in substantia nigra coincided with the highest 5-hydroxyindolacetic acid:serotonin ratio. Monoamine oxidase-A in the striatum did not change contrary to that which happened in substantia nigra. The monoamine oxidase-B:monoamine oxidase-A ratio increased during development both in the substantia nigra and the striatum. The significance of these changes is discussed.

Alpha 1- and alpha 2-adrenoreceptor antagonists differentially influence locomotor and stereotyped behaviour induced by d-amphetamine and apomorphine in the rat

The importance of dopamine (DA) in mediating locomotor, exploratory and stereotyped behaviour in rodents is well established. Evidence also indicates a modulatory role for noradrenaline (NA) although, due to nonspecificity. of previously available agents, a precise role remains undefined. The effects of the specific and selective alpha-adrenoreceptor antagonists idazoxan (alpha 2) and prazosin (alpha 1) on behaviour induced by amphetamine and apomorphine have been investigated in the rat. d-Amphetamine (2 mg/kg) induced hyperactive locomotion and exploration. Pretreatment with prazosin (1 mg/kg) markedly reduced these responses. In contrast, pretreatment with idazoxan (20 mg/kg) only marginally altered d-amphetamine hyperactivity. Apomorphine (0.5 mg/kg) induced biphasic locomotor and exploratory activity. Neither alpha-antagonist affected the initial burst of activity (60 min), although prazosin inhibited whereas idazoxan potentiated the secondary phase (90-180 min). At higher dosage, amphetamine (6 mg/kg) and apomorphine (2 mg/kg) induced stereotyped behaviours. Prazosin pretreatment enhanced stereotyped gnawing and decreased sniffing and locomotion, whereas idazoxan increased locomotion and decreased amphetamine-induced mouth movements. These data indicate that DA-induced locomotor and stereotyped behaviours are differentially influenced (in opposite directions) by both alpha1- and alpha 2-adrenoreceptor antagonists. NA may thus modulate the expression and character of behaviour by influencing DA function in certain brain areas.

Which is responsible for circling behavior in rats, locus coeruleus or dorsolateral pontine tegmentum?

Unilateral electrolytic lesions restricted to the locus coeruleus (LC) in rats did not produce postural asymmetry or circling behavior, while similar lesions in the dorsolateral pontine tegmentum (DLPT) closely ventral to the LC caused a circling behavior toward the contralateral side. The circling behavior was potentiated by intraperitoneal injection of dopamine agonists, apomorphine or methamphetamine, and was abolished by the dopamine antagonist, haloperidol. Neurochemical analysis using a gas chromatographic-mass spectrometric method was made 4, 10 and 20 days after LC coagulation, resulting in a gradual decrease of noradrenaline level in the frontal cortex on the lesioned side. Dopamine content in the striatum in these rats was not significantly affected. Unilateral lesioning of the DLPT produced no significant change in contents of dopamine of homovanillic acid in the striatum or of noradrenaline in the frontal cortex. These results indicate that the LC is not involved in the circling behavior, without a modulatory effect on the dopamine metabolism in the striatum, whereas the DLPT closely ventral to the LC is responsible for circling behavior by subserving as a descending neural pathway conveying striopallidal function on the contralateral side.

Spasmodic torticollis relieved by removal of a cervical foreign body

Images

Activation of alpha 2-adrenoreceptors enhances haloperidol-induced suppression of operant behavior

Inhibition of catecholamine synthesis by alpha-methyl paratyrosine (alpha-MT) was previously shown to potentiate the behavioral suppression caused by dopamine-receptor antagonists. This effect of alpha-MT is in all probability due to inhibition of the compensatory increase in dopamine turnover induced by the dopamine receptor antagonists. In the present study we investigated the effect of the alpha 2-adrenoreceptor agonist clonidine on the haloperidol-induced suppression of food-reinforced lever-pressing behavior (fixed ratio 40:1) in rats. Small behaviorally inactive doses of clonidine were found, in analogy with alpha-MT, to enhance the haloperidol-induced suppression of the lever-pressing behavior. The haloperidol-induced increase in dopamine synthesis (measured as the accumulation of DOPA after inhibition of aromatic amino acid decarboxylate) was antagonized by clonidine in the striatum as well as in the dopamine rich limbic regions. Prazosin, a selective alpha 1-adrenoreceptor antagonist had no effect on the clonidine induced behavioral changes. Idazoxane, a selective alpha 2-adrenoreceptor antagonist, counteracted both the behavioral and biochemical effects of clonidine, indicating that these effects of clonidine are mediated via its action on alpha 2-adrenoreceptors. The present findings provide support for the notion that alpha 2-adrenoreceptors may participate in the regulation of nigro-striatal as well as meso-limbic dopaminergic activity. It is suggested that alpha 2-adrenoreceptor agents, especially in combination with classical antipsychotics, might be of therapeutic value in the treatment of disorders associated with abnormal dopaminergic activity.

The effectiveness of yohimbine in blocking rat central dopamine autoreceptors in vivo

The influence of various alpha-adrenoceptor antagonists (10 mg/kg i.p.) upon the rate of turnover of dopamine (DA) in the rat brain was investigated. Taking the levels of the DA metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) as a measure of the rate of DA turnover, it was found that prazosin and phenoxybenzamine decreased, whereas piperoxane and yohimbine increased the turnover rate both in the corpus striatum and in the tuberculum olfactorium. Azapetine, phentolamine and tolazoline as well as the beta-adrenoceptor antagonist propranolol were without a significant effect, whereas the DA antagonist haloperidol increased DOPAC and HVA levels and decreased the levels of DA itself. The possibility that the yohimbine-induced increase in the DA turnover rate was produced by a direct blockade of DA autoreceptors, was investigated under conditions where influences other than those elicited via DA autoreceptors are thought to be eliminated, i.e. in rats treated with reserpine or gamma-butyrolactone (GBL). In rats that were pretreated with reserpine, yohimbine (10 mg/kg i.p.) was found to be ineffective in antagonizing the reduction of the accumulation of 3,4-dihydroxyphenylalanine (DOPA) following decarboxylase inhibition, that was produced by the DA agonist apomorphine (2.0 mg/kg i.p.). In rats pretreated with reserpine, yohimbine (10 mg/kg i.p.) was also ineffective in antagonizing the reduction of the DOPAC and HVA levels produced by apomorphine (2.0 mg/kg i.p.), but it was effective in antagonizing the reduction of the HVA level that was produced by the selective DA autoreceptor agonist N,N-di-n-propyl-7-hydroxy-2-aminotetralin (DP-7-AT, 1.0 mg/kg i.p.).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the noradrenaline neurotoxin DSP 4 on monoamine neurons and their transmitter turnover in rat CNS

Regional effects of DSP 4 on monoamine neurons have been analyzed by chemical assay of endogenous monoamines and their metabolites in rat CNS. The results confirmed that the neurotoxic action of DSP 4 is predominantly on noradrenaline nerve terminal projections originating from locus coeruleus, with the most marked effects on terminal fields localized most distant from the noradrenaline perikarya. DSP 4 treatment (10 days) caused no alteration of the regional DA levels, except in cingulate cortex, where a moderate increase (+40%) was observed, possibly at least partially related to a sprouting of dopamine nerve terminals following the noradrenaline denervation. 5-hydroxytryptamine levels were generally unaltered after DSP 4, except for an about 10-25% reduction in cerebral cortex and hippocampus. There was with time a certain noradrenaline recovery, most likely related to regeneration of noradrenaline nerve terminals, although this process was relatively slow (months). Analysis of catecholamine decline after tyrosine hydroxylase inhibition and metabolite/monoamine ratios, as indices for transmitter utilization rate, indicated an increased noradrenaline turnover in terminals spared by DSP 4, while dopamine turnover appeared to be reduced in many regions (i.a. cerebral cortex, striatum, accumbens, olfactory tubercle and spinal cord), most pronounced in cingulate cortex. The results indicate that noradrenaline neurons have a facilitatory action on dopamine neurons. The DSP 4 treatment did not cause any significant effect on 5-hydroxytryptamine turnover in any of the individual regions analyzed.

Indirect effects of apomorphine on serotoninergic neurons in rats

We have studied the effects of apomorphine on central serotoninergic system by using fluorescence histochemistry and high performance liquid chromatography coupled with electrochemical detection. Apomorphine has been shown selectively to elevate intracellular serotonin fluorescence in dorsal raphe neurons and serotonin and/or 5-hydroxyindoleacetic acid concentrations in the major terminal area of the dorsal raphe, the striatum. Apomorphine has no effect on serotonin neurons in the median raphe or its corresponding projection site, the hippocampus. In the present study, intraventricular 6-hydroxydopamine, when administered together with desimipramine and pargyline, antagonized the apomorphine-induced elevations of serotonin fluorescence in the dorsal raphe and serotonin and 5-hydroxyindoleacetic acid levels in the striatum. This antagonism was found when 6-hydroxydopamine was given either 3 or 10 days before 3 mg/kg apomorphine. Apomorphine also elevated extraperikaryal serotonin fluorescence and catecholamine fluorescence in the dorsal raphe selectively and these effects were also blocked by 6-hydroxydopamine. Additionally, 6-hydroxydopamine accelerated striatal serotonin turnover when it was given 10 days prior to death. This phenomenon probably reflects some compensatory change of mesostriatal serotonin neurons in response to the prolonged depletion of brain dopamine. The above results suggest that the observed effects of apomorphine on the serotoninergic system are mediated indirectly through dopaminergic neurons and that postsynaptic dopamine receptors are probably not responsible for apomorphine's effects.

On the mechanism of central stimulation action of fencamfamine

The stereotypy induced by fencamfamine (10 mg/kg i.p.) was compared in different groups of rats which had been pretreated with catecholaminergic drugs. Pretreatment with alpha-methyl-p-tyrosine (alpha-MpT) did not abolish the stereotypy, however the combination of alpha-MpT plus reserpine decreased, while reserpine alone increased this response. Pretreatment with haloperidol or metoclopramide reduced the intensity of stereotyped behaviour induced by fencamfamine, while phenoxybenzamine increased this behaviour. Fencamfamine showed low affinity for binding sites of [3H]haloperidol and [3H]dihydroergocriptine. These results support the view that fencamfamine is an indirectly acting drug of the non-amphetamine class, which releases both norepinephrine (NE) and dopamine (DA) from presynaptic terminals leading to stereotyped behaviour.

Behavioral effects of lesions of the central noradrenergic bundles in the rat

Rats with bilateral lesions of the dorsal noradrenergic bundle (DB) or of the ventral noradrenergic bundle (VB) were studied in different behavioral test situations. All lesioned animals defecate less than sham operated animals in the open-field (OF) or in the conditioning apparatus described by Henderson [16]. These data suggest a decrease of emotional reactivity in lesioned animals. However, the DB rats' level of exploration was higher than that of VB rats. No effect on the amplitude of the startle response has been shown after lesioning. The lesions of the dorsal noradrenergic bundle induce a decrease in cortical noradrenaline hypothalamic catecholamines. The lesions of the ventral noradrenergic bundle induce a decrease in hypothalamic catecholamines without change in the cortex. These results do not support the postulation [22] that the dorsal bundle and the ventral bundle play an opposite role in behavior. Yet, a selective participation of each bundle is suggested in modulating responses to novel environments and anxiogenic situations.

The effects of postnatal anoxia on behaviour and on the muscarinic and beta-adrenergic receptors in the hippocampus of the developing rat

Exposure of rats to 25 min anoxia within 24 h following birth caused behavioural as well as biochemical changes during their development and maturity. Following postnatal anoxia, a significant increase in the concentration of the cholinergic muscarinic receptors in the hippocampus was noted at the early stages of development, between 6 and 20 days of age, but reached normal values at 40 days of age. However, at this age, significant increase in the concentration of beta-adrenergic receptors in the hippocampus was found, which remained significantly high during maturity and adulthood, as compared to controls. Rats submitted postnatally to anoxia exhibited hyperactivity in the open field which was maximal at 20-25 days of age and declined towards normal values at 40 days of age. At maturity, between 60 and 80 days of age, these rats showed poor performance in a complex 6-choice discrimination learning but not in simple differential conditioning. Possible correlations between the behavioural and biochemical findings are discussed.

Role of ventral mesencephalic reticular formation and related noradrenergic and serotonergic bundles in turning behaviour as investigated by means of kainate, 6-hydroxydopamine and 5,7-dihydroxytryptamine lesions

A unilateral kainate (KA) infusion (2 x 0.15 micrograms, 2 x 0.25 micrograms) in the ventral mesencephalic reticular formation (MRF) resulted in spontaneous contraversive turning lasting only a few days. Upon challenge with apomorphine (0.5 mg/kg s.c.) or amphetamine (5 mg/kg i.p.) the contraversive turning could be reinstated. The incidence, as well as the intensity, of the drug-induced response decreased over the 45 days of observation. KA infused in the ventral MRF induced typical lesions after doses of 2 x 0.15 micrograms but resulted in demyelination after 2 x 0.25 micrograms. These lesions failed to reduce noradrenaline (NA), serotonin (5 HT) or dopamine (DA) in various forebrain areas. Unilateral lesion of ascending NA projections by 6-OHDA infusion (4 micrograms) within the NA bundles coursing in the mesencephalon or near the locus coeruleus, failed to induce motor asymmetries. Unilateral selective lesion of the ventral NA bundle by local 6-OHDA (2 micrograms) infusion also failed to induce motor asymmetries, either spontaneously or in response to dopaminergic drugs. Unilateral lesion of ascending 5-HT projections by the tegmental infusion of 5,7-dihydroxytryptamine (10 micrograms) also failed to induce motor asymmetries in response to dopaminergic drugs but resulted in contraversive circling in response to 5-hydroxytryptophan. These data indicate that intrinsic neurones of the ventral MRF play a role in turning behaviour and exclude, in contrast with previous studies, a role of NA or 5-HT projections in the contraversive turning responses to DA receptor agonists obtained after lesions of the ventral MRF.

The pontine reticular formation is part of the output pathway for amphetamine- and apomorphine-induced lateral head movements: evidence from experimental lesions in the rat

Electrolytic lesions in the caudal part of the medial pontine reticular formation (PRF) in the rat abolished apomorphine- or amphetamine-induced stereotypic lateral head movements and turning to the damaged side. Rats with unilateral PRF lesions turned and circled only to the intact side, and rats with bilateral lesions did not turn at all. PRF lesions were also effective in abolishing or reducing amphetamine-induced circling in rats with unilateral nigrostriatal bundle damage. Thus, head movements induced by dopamine agonists are added to the class of head movements mediated by the PRF. It is proposed that the decussations of the motor pathways for drug-induced turning are located between the midbrain and caudal pons.

Noradrenaline and 5-hydroxytryptamine modulation of brain dopamine function: implications for the treatment of Parkinson's disease

1 Dopamine deficiency in the brain is the prime biochemical deficit in Parkinson's disease, but loss of noradrenaline and 5HT also may contribute. 2 In rats, 5HT-containing neurones originating from the dorsal and median raphe nuclei innervate forebrain dopamine-containing areas so as to impose an inhibitory regulatory tone on dopamine function. However, this interaction between brain dopamine and 5HT-containing neuronal systems is complex, and the effect produced appears dependent on the relative activity of each system. 3 Anatomical evidence for innervation of dopamine-containing brain regions by noradrenaline fibres in the rat is scanty, but functional studies suggest the existence of inputs which facilitate dopamine function. 4 Drug therapy designed to increase or decrease brain 5HT function has had no consistent effect in Parkinson's disease. 5 Manipulation of brain noradrenergic activity in Parkinson's disease had little effect, although the noradrenaline precursor L-threo-DOPS may reduce freezing attacks. 6 Until more specific drug molecules are available the role of brain noradrenergic and 5HT mechanisms in Parkinson's disease remains uncertain.

Lesion-produced telencephalic catecholamine imbalances and altered operant pecking rates in pigeons

Pigeons with bilateral neurotoxic or electrolytic lesions within ventral mesencephalon, in nucleus tegmenti pedunculo pontinus (TP) (equivalent to substantia nigra) or area ventralis of Tsai (AVT), were found to have catecholamine (CA) depletion in the telencephalon, including the paleostriatum augmentatum (PA) and lobus parolfactorius (LPO), avian basal ganglia rich in CA. Joint telencephalic concentrations of dopamine (DA) and norepinephrine (NE) within individuals were found to vary with sustained fixed interval (FI) pecking rate increases or decreases following surgery. Low (below 75% of controls) DA/normal NE concentrations were found in individuals showing a marked reduction in their key pecking rates; low DA/low NE concentrations were found in individuals showing a marked increase in their pecking rates. The fit of these data with the NE-DA interaction hypothesis of Antelman and Caggiula [2] was acknowledged but the nature of that interaction remains to be clarified.

Dopamine-norepinephrine interaction in hyperactive boys treated with d-amphetamine

We studied the relationship between the excretion of 3-methoxy-4-hydroxyphenylglycol, the main metabolite of central nervous system norepinephrine, and homovanillic acid, the main metabolite of dopamine, in 16 hyperactive boys and ten controls who were admitted to a clinical research center. We further examined the effect of d-amphetamine (0.5 mg/kg body weight daily for two weeks) on that relationship. The correlation coefficients r between MHPG and HVA excretion were significantly negative in hyperactive boys and significantly positive in controls when the relational effects of age, body surface, and 24-hour urinary creatinine with MHPG and HVA excretion were removed. Furthermore, the correlation coefficient r in hyperactive boys and in responders at baseline differed significantly from the correlation coefficients in post-treatment and in controls. The post-treatment correlation coefficient in hyperactive boys and responders did not differ from that in controls. We suggest an altered relationship between DA and NE activity in hyperactive children. Meaningful interpretation of the data should await the availability of more information on the amount of contribution of central NE and DA metabolism to urinary MHPG and HVA in both hyperactive and normal children.