Effects of dopamine receptor stimulants on locomotor activity of rats with electrolytic or 6-hydroxydopamine-induced lesions of the nucleus accumbens

Lactiplantibacillus plantarum PS128 Alleviates Exaggerated Cortical Beta Oscillations and Motor Deficits in the 6-Hydroxydopamine Rat Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by midbrain dopaminergic neuronal loss and subsequent physical impairments. Levodopa manages symptoms best, while deep brain stimulation (DBS) is effective for advanced PD patients; however, side effects occur with the diminishing therapeutic window. Recently, Lactiplantibacillus plantarum PS128 (PS128) was found to elevate dopamine levels in rodent brains, suggesting its potential to prevent PD. Here, the therapeutic efficacy of PS128 was examined in the 6-hydroxydopamine rat PD model. Suppression of the power spectral density of beta oscillations (beta PSD) in the primary motor cortex (M1) was recorded as the indicator of disease progression. We found that 6 weeks of daily PS128 supplementation suppressed M1 beta PSD as well as did levodopa and DBS. Long-term normalization of M1 beta PSD was found in PS128-fed rats, whereas levodopa and DBS showed only temporal effects. PS128 + levodopa and PS128 + DBS exhibited better therapeutic effects than did levodopa + DBS or either alone. Significantly improved motor functions in PS128-fed rats were correlated with normalization of M1 beta PSD. Brain tissue analyses further demonstrated the role of PS128 in dopaminergic neuroprotection and the enhanced availability of neurotransmitters. These findings suggest that psychobiotic PS128 might be used alongside conventional therapies to treat PD patients.

Psychotropic effects of Lactobacillus plantarum PS128 in early life-stressed and naïve adult mice

Ingestion of specific probiotics, namely "psychobiotics", produces psychotropic effects on behavior and affects the hypothalamic-pituitary-adrenal axis and neurochemicals in the brain. We examined the psychotropic effects of a potential psychobiotic bacterium, Lactobacillus plantarum strain PS128 (PS128), on mice subjected to early life stress (ELS) and on naïve adult mice. Behavioral tests revealed that chronic ingestion of PS128 increased the locomotor activities in both ELS and naïve adult mice in the open field test. In the elevated plus maze, PS128 significantly reduced the anxiety-like behaviors in naïve adult mice but not in the ELS mice; whereas the depression-like behaviors were reduced in ELS mice but not in naïve mice in forced swimming test and sucrose preference test. PS128 administration also reduced ELS-induced elevation of serum corticosterone under both basal and stressed states but had no effect on naïve mice. In addition, PS128 reduced inflammatory cytokine levels and increased anti-inflammatory cytokine level in the serum of ELS mice. Furthermore, the dopamine level in the prefrontal cortex (PFC) was significantly increased in PS128 treated ELS and naïve adult mice whereas serotonin (5-HT) level was increased only in the naïve adult mice. These results suggest that chronic ingestion of PS128 could ameliorate anxiety- and depression-like behaviors and modulate neurochemicals related to affective disorders. Thus PS128 shows psychotropic properties and has great potential for improving stress-related symptoms.

Central dopaminergic neurotransmission plays an important role in thermoregulation and performance during endurance exercise

Dopamine (DA) has been widely investigated for its potential role in determining exercise performance. It was originally thought that DA's ergogenic effect was by mediating psychological responses. Recently, some studies have also suggested that DA may regulate physiological responses, such as thermoregulation. Hyperthermia has been demonstrated as an important limiting factor during endurance exercise. DA is prominent in the thermoregulatory centre, and changes in DA concentration have been shown to affect core temperature regulation during exercise. Some studies have proposed that DA or DA/noradrenaline (NA) reuptake inhibitors can improve exercise performance, despite hyperthermia during exercise in the heat. DA/NA reuptake inhibitors also increase catecholamine release in the thermoregulatory centre. Intracerebroventricularly injected DA has been shown to improve exercise performance through inhibiting hyperthermia-induced fatigue, even at normal ambient temperatures. Further, caffeine has been reported to increase DA release in the thermoregulatory centre and improves endurance exercise performance despite increased core body temperature. Taken together, DA has been shown to have ergogenic effects and increase heat storage and hyperthermia tolerance. The mechanisms underlying these effects seem to involve limiting/overriding the inhibitory signals from the central nervous system that result in cessation of exercise due to hyperthermia.

Psychotropic drug-induced locomotor hyperactivity and prepulse inhibition regulation in male and female aromatase knockout (ArKO) mice: role of dopamine D1 and D2 receptors and dopamine transporters

RATIONALE AND OBJECTIVES

The aim of the present study was to investigate the possible role of oestrogen in schizophrenia by comparing aromatase knockout (ArKO) mice, which are unable to produce oestrogen, with wild-type controls using two behavioural animal models with relevance to the illness, psychotropic drug-induced locomotor hyperactivity and prepulse inhibition (PPI).

RESULTS

Baseline PPI was not different between ArKO and controls. Treatment with apomorphine, MK-801 and amphetamine caused disruption of PPI in all groups. However, in female but not male ArKO mice, the effect of both apomorphine and amphetamine was reduced. In female ArKO mice, amphetamine-induced hyperlocomotion was markedly reduced, but in male mice, the genotype difference was far smaller. Female but not male ArKO mice also showed a reduction of phencyclidine-induced locomotor hyperactivity. The density of dopamine transporters, but not D1 and D2 receptors, was significantly increased in the caudate putamen of male but not female ArKO mice compared to wild-type mice. This could represent a compensatory dopaminergic upregulation in male ArKO mice.

CONCLUSION

Because of their lack of oestrogen production, it was anticipated that ArKO mice would display enhanced effects of amphetamine on locomotor activity and PPI. Instead, in these animals, aromatase knockout appeared to be 'protective'. This may represent limitations in the ability to model a complex illness such as schizophrenia in a constitutive knockout model, such as ArKO mice. Moreover, the current results may point at the involvement of other sex steroids, which are also altered in ArKO mice, in dopaminergic control of behaviour.

An integrative neuroanatomical perspective on some subcortical substrates of adaptive responding with emphasis on the nucleus accumbens

Neuroanatomical substrates associated in the literature with adaptive responding are discussed, with a focus on the nucleus accumbens. While it is emphasized that the accumbens exhibits multiple levels of complex organization, a fairly complete list of brief descriptions of recent studies devoted specifically to the accumbens shell and core subterritories is presented in tabular format. The distinct patterns of connectivity of the accumbens core and shell and structures related to them by connections are described. Multiple inputs, outputs and abundant reciprocity of connections within the ventral parts of the basal ganglia are emphasized and the implications for "through-put" of impulses is considered. It is noted, at least on neuroanatomical grounds, that there is ample reason to expect feed forward processing from shell and structures with which it is associated to core and structures with which it is associated. Furthermore, the potential for additional feed forward processing involving several forebrain functional anatomical systems, inlcuding the ventral striatopallidum, extended amygdala and magnocellular basal forebrain complex is considered. It is intended that from the considerations recorded here a conceptual framework will begin to emerge that is amenable to further experimental substantiation as regards how multiple basal forebrain systems and the cortices to which they are related by connections work together to fashion a unitary object--the adaptive response.

Direct comparison of projections from the central amygdaloid region and nucleus accumbens shell

Certain neurochemical and connectional characteristics common to extended amygdala and the nucleus accumbens shell suggest that the two represent a single functional-anatomical continuum. If this is so, it follows that the outputs of the two structures should be substantially similar. To address this, projections from the caudomedial shell and central nucleus of the amygdala, a key extended amygdala structure, were demonstrated in Sprague-Dawley rats with different anterograde axonal tracers processed separately to exhibit distinguishable brown and blue-black precipitates. The caudomedial shell projection is strong in the ventral pallidum and along the medial forebrain bundle through the lateral preopticohypothalamic continuum into the ventral tegmental area, distal to which it thins abruptly. The central nucleus projects strongly to the bed nucleus of the stria terminalis and the sublenticular extended amygdala, but substantially to the lateral hypothalamus only at levels behind the rostral part of the entopeduncular nucleus. Innervation of the ventral tegmental area by the central amygdala is minimal, but the lateral one-third of the substantia nigra, pars compacta and an adjacent lateral part of the retrorubral field receive substantial central amygdala input. Central amygdaloid projections are robust in caudal brainstem sites, such as the reticular formation, parabrachial nucleus, nucleus of the solitary tract and dorsal vagal complex, all of which receive little input from the accumbens. The substantial differences in the output systems of the caudomedial shell of accumbens and central amygdala suggest that the two represent distinct functional-anatomical systems.

Mechanisms of action of atypical antipsychotic drugs: a critical analysis

Various criteria used to define atypical antipsychotic drugs include: 1) decrease, or absence, of the capacity to cause acute extrapyramidal motor side effects (acute EPSE) and tardive dyskinesia (TD); 2) increased therapeutic efficacy reflected by improvement in positive, negative, or cognitive symptoms; 3) and a decrease, or absence, of the capacity to increase prolactin levels. The pharmacologic basis of atypical antipsychotic drug activity has been the target of intensive study since the significance of clozapine was first appreciated. Three notions have been utilized conceptually to explain the distinction between atypical versus typical antipsychotic drugs: 1) dose-response separation between particular pharmacologic functions; 2) anatomic specificity of particular pharmacologic activities; 3) neurotransmitter receptor interactions and pharmacodynamics. These conceptual bases are not mutually exclusive, and the demonstration of limbic versus extrapyramidal motor functional selectivity is apparent within each arbitrary theoretical base. This review discusses salient distinctions predominantly between prototypic atypical and typical antipsychotic drugs such as clozapine and haloperidol, respectively. In addition, areas of common function between atypical and typical antipsychotic drug action may also be crucial to our identification of pathophysiological foci of the different dimensions of schizophrenia, including positive symptoms, negative symptoms, and neurocognitive deficits.

Excitotoxic lesions of the core and shell subregions of the nucleus accumbens differentially disrupt body weight regulation and motor activity in rat

The behavioral effects of bilateral N-methyl-D-aspartate (NMDA) lesions of the core and medial shell subregions of the nucleus accumbens were evaluated in rats. Body weight was monitored for 2 weeks following surgery. Locomotor activity and open field behavior were recorded 1 week after surgery. The core-lesion group had difficulty recovering from the lesion and had significantly lower weights throughout the experiment. The shell-lesion group had normal recovery and weighed significantly more than controls over the course of the experiment. In the activity cage test, the core-lesion group was hyperactive when compared to controls and to the shell-lesion group. Activity of the shell-lesion group was similar to that of their sham-controls. Three weeks postlesion, the core-lesion group was still significantly more active. In the open field test, peripheral locomotion scores were significantly higher in the core-lesion group when compared to their controls, whereas the scores of the shell-lesion group were similar to controls. In the other open field measures, both lesion groups were hyperactive; however, the scores of core-lesion group were significantly higher than those of the shell-lesion group on all measures. Histological analysis indicated small, discrete areas of damage within the core or medial shell accumbens regions. These preliminary results suggest that these two subregions can be behaviorally differentiated.

Dopamine receptors: molecular biology, biochemistry and behavioural aspects

The description of new dopamine (DA) receptor subtypes, D1-(D1 and D5) and D2-like (D2A, D2B, D3, D4), has given an impetus to DA research. While selective agonists and antagonists are not generally available yet, the receptor distribution in the brain suggests that they could be new targets for drug development. Binding characteristics and second messenger coupling has been explored in cell lines expressing the new cloned receptors. The absence of selective ligands has meant that in vivo studies have lagged behind. However, progress has been made in understanding the function of DA-containing discrete brain nuclei and the functional consequence of the DA's interaction with other neurotransmitters. This review explores some of the latest advances in these various areas.

Role of dopamine and GABA in the control of motor activity elicited from the rat nucleus accumbens

The application of 1.2 and 12.0 micrograms/side of the GABAA receptor agonist 3-aminopropane sulphonic acid bilaterally into the nucleus accumbens (Acb) of rats nonsignificantly depressed locomotor activity as assessed in automated Animex activity cages, while the highest dose (60 micrograms/side) significantly stimulated activity. The GABAA receptor antagonists picrotoxinin (0.0625 and 0.125 micrograms/saide) and bicuculline (0.895 micrograms/side) produced forward locomotion around the cage accompanied by a number of other behaviours. The GABAB agonist baclofen (0.023 and 0.092 micrograms/side) induced a short-lasting (18 min) locomotor depression. None of the GABAB antagonists tested (2-hydroxysaclofen 2.6 micrograms/side, two novel beta-(benzo[b]furan) analogues of baclofen 9G or 9H each 6.8 micrograms/side, 4-aminobutylphosphonic acid 1.32 micrograms/side and phaclofen 0.535 and 2 micrograms/side) significantly affected locomotor activity. In rats pretreated with reserpine and alpha-methyl-p-tyrosine, picrotoxinin (0.0625 and 0.125 micrograms/side) did not significantly alter locomotor activity. Furthermore, when picrotoxinin (0.0625 micrograms/side) was combined with either the selective dopamine (DA) D1 agonist SKF38393 or the selective D2 agonist quinpirole, no significant alteration in locomotor function occurred. When SKF38393 and quinpirole were coadministered, significant stimulation occurred which was further enhanced by the addition of picrotoxinin. It is concluded that GABAA receptors, together with D1 and D2 receptors, play a major role in modulating the control of motor function by the Acb of rats.

Possible involvement of the central nervous system in long-term effect of caerulein on amphetamine-induced hyperactivity in rats

The present experiments were performed in order to ascertain whether the long-term antagonistic effect of caerulein on amphetamine-induced hyperactivity is produced in the central nervous system. In the vagotomized rats, animals treated with a combination of caerulein and haloperidol and exposed to amphetamine on the 1st day became less sensitive to amphetamine for 24 hr to 1 week when their ambulatory activities were measured in an open field apparatus. The same results were also observed in the experiments where caerulein was applied directly into the lateral ventricle. However, the animals given caerulein in the nucleus accumbens showed no reduced susceptibility to amphetamine. Thus, the present results suggest that caerulein may indirectly modulate some dopaminergic activity in the central nervous system. One possible mechanism involved in the antagonistic effect of caerulein on amphetamine-induced hyperactivity is changes in activities of endocrine systems.

Effects of intranigral injections of dopamine agonists and antagonists, glycine, muscimol and N-methyl-D,L-aspartate on locomotor activity

Previously it has been shown that bilateral intranigral injections of dopamine into rats pretreated with a monoamine oxidase inhibitor induced prolonged stimulation of locomotor activity, while bilateral intranigral injections of haloperidol reduced the locomotor stimulation evoked by systemic amphetamine. In the present studies, the role of the substantia nigra in locomotor activity was further investigated using a variety of dopaminergic and other agonists and neuroleptics. Ergometrine, epinine, (+/-)-2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronapthalene hydrobromide (ADTN), 1,2,3,4-tetrahydro-6,7,-dihydroxyisoquinoline hydrochloride (THIQ), muscimol and glycine elicited locomotor activity when injected into the substantia nigra pars reticulata bilaterally. Additionally the non-dopaminergic agonists also elicited a degree of stereotyped behavior. Locomotor activity induced by intranigral ergometrine was blocked by systemic haloperidol but was not affected by intranigral haloperidol. Locomotor activity elicited by systemic amphetamine was blocked by bilateral intranigral alpha-flupenthixol, but that elicited by bilateral intra-accumbens ergometrine was not affected by alpha-flupenthixol or haloperidol injected into the substantia nigra pars reticulata bilaterally. The results provide further evidence that alterations of neurotransmission in the substantia nigra exert effects on locomotor activity.

Mesolimbic dopamine neurons: effects of 6-hydroxydopamine-induced destruction and receptor blockade on drug-induced rotation of rats

Bilateral injections of 6-hydroxydopamine (6-OHDA) into the nucleus accumbens greatly reduced the dopamine content of this nucleus and the olfactory tubercle and blocked the ipsilateral rotation induced by amphetamine and methamphetamine in rats with unilateral 6-OHDA lesions of the caudate nucleus. In contrast, apomorphine-induced contralateral rotation was enhanced. Similar results were obtained when the destruction of forebrain noradrenergic neurons, normally produced by the nucleus accumbens 6-OHDA lesion, was prevented by desipramine (DMI) pretreatment. Microinjections of the dopamine receptor antagonist heloperidol into the nucleus accumbens did not spread to the olfactory tubercle, as assessed by the distribution of 3H-haloperidol, and blocked circling induced by amphetamine and apomorphine. Amphetamine-induced circling was less effectively blocked by haloperidol injected into the olfactory tubercle. These results suggest that activity at nucleus accumbens dopamine receptors can greatly affect circling behavior, perhaps by amplifying asymmetries of nigrostriatal activity.