Basal ganglia and Parkinson's disease: neurobiological and pharmacological aspects in animals and man

Intranasal delivery of liposome encapsulated flavonoids ameliorates l-DOPA induced dyskinesia in hemiparkinsonian mice

In the present study, we explored the development of a novel noninvasive liposomal drug delivery material for use in intranasal drug delivery applications in human diseases. We used drug entrapment into liposomal nanoparticle assembly to efficiently deliver the drugs to the nasal mucosa to be delivered to the brain. The naturally occurring flavonoid 7,8-dihydroxyflavone (7,8-DHF) has previously been shown to have beneficial effects in ameliorating Parkinson's disease (PD). We used both naturally occurring 7,8-DHF and the chemically modified form of DHF, the DHF-ME, to be used as a drug candidate for the treatment of PD and l-DOPA induced dyskinesia (LID), which is the debilitating side effect of l-DOPA therapy in PD. The ligand-protein interaction behavior for 7,8-DHF and 6,7-DHF-ME was found to be more effective with molecular docking and molecular stimulation studies of flavonoid compounds with TrkB receptor. Our study showed that 7,8-DHF delivered via intranasal route using a liposomal formulation ameliorated LID in hemiparkinsonian mice model when these mice were chronically administered with l-DOPA, which is the only current medication for relieving the clinical symptoms of PD. The present study also demonstrated that apart from reducing the LID, 7,8-DHF delivery directly to the brain via the intranasal route also corrected some long-term signaling adaptations involving ΔFosB and α Synuclein in the brain of dopamine (DA) depleted animals.

Revisiting the effects of Parkinson's disease and frontal lobe lesions on task switching: the role of rule reconfiguration

This study investigated the hypothesis that rule reconfiguration in task switching can isolate aspects of intact and impaired control at different stages of Parkinson's disease (PD) by comparing switches between concrete naming rules pertaining to stimulus selection, to switches between abstract rules which allocate categorization responses to these stimuli. Based on previous findings, it was hypothesized that attentional switches, where task set competition emerges at the stimulus but not response set level, highlights striatal dopaminergic function. Conversely, increasing the degree of task set competition to encompass reconfiguration of response set when switching between abstract rules, represents a condition which engages the prefrontal cortex (PFC) and renders this manipulation sensitive to frontal damage. To this end, we investigated task switching with concrete and abstract rules in unilaterally (Hoehn & Yahr stage I) and bilaterally (Hoehn & Yahr stage II) affected PD patients, as well as striatally intact frontal lesion patients. As predicted, frontal lesion patients demonstrated switching deficits only with abstract categorization rules, where switching engendered complete task set reconfiguration and a new response, as did stage II PD patients with presumed frontal cortical pathology. Replicating previous findings, stage I PD patients with relatively circumscribed striatal pathology demonstrated no such impairment. Disease severity also impacted on attentional switching indexed by naming rules, since medicated stage II but not stage I patients demonstrated switching deficits emerging from stimulus set reconfiguration, suggesting that the ameliorative efficacy of dopaminergic medication is inversely related to the severity of the striatal deficit. These findings illustrate that the nature of the rules that are switched, and its implication in terms of reconfiguring different task set elements, highlights different neural characters of cognitive flexibility. These manipulations may help decipher the differential effects of progressive neurodegeneration on parkinsonian cognition, and provide a framework in which to conceptualize the contributions of cortical and subcortical regions to cognitive control.

Cognitive impairment in Parkinson's disease: the dual syndrome hypothesis

Research into the heterogeneous nature of cognitive impairment documented in patients with Parkinson's disease (PD) has focused on disentangling deficits that vary between individuals, evolve and respond differentially to pharmacological treatments, and relate differentially to PD dementia (PDD). We summarise studies conducted in our laboratory over the last 2 decades, outlining the incremental development of our hypotheses, the starting point for which is our early work on executive deficits mirroring fronto-striatal dysfunction. We present subsequent findings linking these deficits to a model of dopaminergic function that conforms to an inverted curvilinear function. We review studies that investigated the range of dopamine-independent attentional and visuospatial memory deficits seen in PD, demonstrating that abnormalities in these domains more accurately predict PDD. We conclude with an exposition of the dual syndrome hypothesis, which distinguishes between dopaminergically mediated fronto-striatal executive impairments and a dementia syndrome with distinctive prodromal visuospatial deficits in which cholinergic treatments offer some clinical benefits.

Bidirectional plasticity in striatonigral synapses: a switch to balance direct and indirect basal ganglia pathways

There is no hypothesis to explain how direct and indirect basal ganglia (BG) pathways interact to reach a balance during the learning of motor procedures. Both pathways converge in the substantia nigra pars reticulata (SNr) carrying the result of striatal processing. Unfortunately, the mechanisms that regulate synaptic plasticity in striatonigral (direct pathway) synapses are not known. Here, we used electrophysiological techniques to describe dopamine D(1)-receptor-mediated facilitation in striatonigral synapses in the context of its interaction with glutamatergic inputs, probably coming from the subthalamic nucleus (STN) (indirect pathway) and describe a striatonigral cannabinoid-dependent long-term synaptic depression (LTD). It is shown that striatonigral afferents exhibit D(1)-receptor-mediated facilitation of synaptic transmission when NMDA receptors are inactive, a phenomenon that changes to cannabinoid-dependent LTD when NMDA receptors are active. This interaction makes SNr neurons become coincidence-detector switching ports: When inactive, NMDA receptors lead to a dopamine-dependent enhancement of direct pathway output, theoretically facilitating movement. When active, NMDA receptors result in LTD of the same synapses, thus decreasing movement. We propose that SNr neurons, working as logical gates, tune the motor system to establish a balance between both BG pathways, enabling the system to choose appropriate synergies for movement learning and postural support.

Diversity in long-term synaptic plasticity at inhibitory synapses of striatal spiny neurons

Procedural memories and habits are posited to be stored in the basal ganglia, whose intrinsic circuitries possess important inhibitory connections arising from striatal spiny neurons. However, no information about long-term plasticity at these synapses is available. Therefore, this work describes a novel postsynaptically dependent long-term potentiation (LTP) at synapses among spiny neurons (intrinsic striatal circuitry); a postsynaptically dependent long-term depression (LTD) at synapses between spiny and pallidal neurons (indirect pathway); and a presynaptically dependent LTP at strionigral synapses (direct pathway). Interestingly, long-term synaptic plasticity differs at these synapses. The functional consequences of these long-term plasticity variations during learning of procedural memories are discussed.

The age-associated changes of dopamine-acetylcholine interaction in the striatum

The age-associated decline of dopamine D2 receptor (D2R) densities is one of the notable features of aging in mammalian brains. The concept of a functional dopamine (DA)-acetylcholine (ACh) interaction in the striatum has been strongly supported. However, the effects of this decline of D2R on the striatal DA-ACh interaction still remain to be elucidated. In the current study we examined the effects of different concentrations of a D2R agonist, quinpirole, on the striatal ACh release in three groups of rats at different ages (6-, 15-, 25-months-old) by in vivo microdialysis. The ACh release in the striatum was significantly decreased by quinpirole infusion in all three age groups. The old rats showed a significantly smaller decrease of the ACh release by quinpirole than that of the middle-aged rats at the dose of 0.1 microM and that of the young rats at the dose of 1 microM. The current study suggested that the striatal DA-ACh interaction was affected by the aging process.

SKF 83959 is an antagonist of dopamine D1-like receptors in the prefrontal cortex and nucleus accumbens: a key to its antiparkinsonian effect in animals?

SKF 83959 that has a unique antiparkinson profile in animal models of Parkinson's disease is an in vitro dopamine D1 antagonist of receptors coupled to adenylyl cyclase. We hypothesized that SKF 83959, among others, interacts with dopamine D1 receptors coupled to adenylyl cyclase in the nucleus accumbens and the prefrontal cortex. Effects of intra-accumbal injections of SKF 83959 on locomotor activity were compared to effects of the dopamine D1 agonist SKF 81297 and the dopamine D1 antagonist SCH 39166. Similarly to SCH 39166, SKF 83959 did not affect locomotor activity, but counteracted SKF 81297-induced locomotor activity. Effects of unilateral intra-prefrontal injections of SKF 83959 on rotational behaviour were compared to the effects of the dopamine D1 agonist SKF 81297 and the dopamine D1 antagonists SCH 23390 and SCH 39166 in rats selected on basis of their high locomotor response to novelty and pretreated with a subcutaneous injection of 0.75 mg/kg dexamphetamine. Like SCH 39166 and SCH 23390, SKF 83959 induced a bias for contralateral rotating and blocked the SKF 81297-induced bias for ipsilateral rotating. In conclusion, SKF 83959 is an in vivo antagonist of dopamine D1 receptors that are coupled to adenylyl cyclase in the nucleus accumbens and the prefrontal cortex. The role of these receptors in the antiparkinson profile of SKF 83959 is discussed.

Morphochemical changes in brain structures in the course of chronic haloperidol treatment and the correction of these changes with tuftsin

The systemic injection of haloperidol (4 wk, 0.5 mg/kg/d) caused the increase of protein concentration and content, and the activity level of aminopeptidase in the cytoplasm of the neurons of associated type (layer III). The nucleus of these cells decreased both in sizes and in the content of proteins. In the neurons of efferent-projectory type (layer V), the decrease of studied peculiarities as compared with control level was observed. Tuftsin (300 micrograms/kg/d) injection after chronic haloperidol treatment causes the restoring action on changed parameters in sensomotor cortex. In caudate nucleus, tuftsin influence caused further reduction of neuron's cytoplasmic area and significant reduction in protein content. The received results testify to the morphobiochemical heterogenity of investigated brain structures, which is displayed both in the case of haloperidol treatment and in the case of its correction by neuropeptide tuftsin. Chronic haloperidol administration to animals can develop a model of certain symptoms and syndromes of parkinsonism. Its most pronounced manifestation is an imbalance in the neuromediator systems, especially the dopaminergic one (Mettler and Crandall, 1959; Colls, 1984; Funk et al., 1986). The research was performed in conjunction with the physiologists, whose experiments have shown that after chronic haloperidol administration, changes in animal behavior are developed that are typical for bradikinesia, and the motor regimen of integration is disturbed (Popova and Kachalova, 1991; Dovedova and Povova, 1993). Regulatory drugs, especially the tetrapeptide tuftsin, seem to correct such disturbances.

Structure of the m4 cholinergic muscarinic receptor gene and its promoter

Cholinergic muscarinic receptor genes are members of the G-protein receptor gene superfamily. In this study we describe the structure of the gene and promoter of the rat m4 muscarinic receptor gene. A rat cosmid clone containing the coding region for the m4 gene and 25 kilobases of upstream sequence was isolated. This clone directed expression of the rat m4 gene when introduced in IMR32 cells, a human neuroblastoma that expresses m4, but did not drive expression when introduced into Chinese hamster ovary cells, a line that does not express the m4 gene. S1 nuclease, modified 5'-rapid amplification of cDNA ends and polymerase chain reaction analysis of rat cosmid DNA and cDNA showed that the gene consists of a 2.6-kilobase coding exon, extending 34 base pairs (bp) upstream from the initiating ATG, separated from a 460-493 bp noncoding exon by a 4.8-kilobase intron. DNA sequence analysis shows that the non-coding exon is GC-rich and that the promoter does not contain a TATA or CAAT box and has several consensus sequences for enhancer elements including five Sp-1 binding sites, one AP-2 site, one AP-3 binding site and two E-boxes within the proximal 600 bp. A reporter construct consisting of 1440 bp of flanking DNA and 80 bp of the first exon cloned into a luciferase reporter plasmid, drove cell specific expression in transient transfection assays. Removal of 1088 bp of the 5' end of this construct resulted in expression in non-m4 expressing cell lines suggesting there is a repressor element in this region.

Enhanced locomotor reactivity to apomorphine following repeated cocaine treatment

To study the involvement of postsynaptic dopamine (DA) receptors in cocaine-induced behavioral sensitization, locomotor responses to apomorphine (APO, 360 micrograms/kg, IP), a direct DA agonist, were compared in rats repeatedly treated with cocaine (15 mg/kg, IP x 5 and one challenge injection 4 days later) and saline under different environmental conditions. When cocaine was injected under activated conditions, immediately before animal placement in activity chamber, more powerful locomotor response to the initial drug and a significant effect of repeated treatment (sensitization) were found compared to drug administration under quiet conditions, 2 h after animal placement in activity chamber. In this case, locomotor response to the initial drug was similar to that of saline, and the effect of repeated injections on locomotion was absent (no sensitization). Locomotor stimulation induced by APO was significantly enhanced in both groups of cocaine-treated animals compared to saline controls. This effect, however, was more powerful in animals treated with cocaine under activated conditions. Present data suggest that enhanced responsiveness of postsynaptic DA receptors developed due to chronic cocaine treatment may contribute to stable alteration of DA transmission thought to mediate cocaine sensitization.

Dopaminergic involvement in the mediation of morphine effects on vocalization and movement reactivity in the rat

To understand the role of dopamine in the mediation of opiate's analgesic and reinforcing activity, the influence of pharmacologically-induced increase (apomorphine in a high dose) and decrease (haloperidol and apomorphine in a low "presynaptic" dose) of dopamine neurotransmission on morphine-induced depression of vocalization and movement reactivity was investigated in freely behaving rats. Strong enhancement of morphine-induced vocalization reactivity depression and a weakening of movement reactivity depression typical to concomitant pharmacological increase of dopamine neurotransmission may represent the enhancement of its reinforcing and analgesic properties and inhibition of its depressive/sedative activity. Enhancement of MOR-induced depression of movement and vocalization reactivity characteristic of drug-induced decrease of dopamine neurotransmission may be the consequence of the blockade of opiate's reinforcing and stimulatory activity and summation of depressive/sedative actions typical to these drugs administered alone.

Reinforcing properties of morphine chronically used in aversive life conditions: place-preference paradigm, long-term changes in behavioral reactivity

To substantiate significance of the organism's functional state in the mediation of an opiate's reinforcing activity, the rats' attitude to an initially nonpreferred environment associated with chronic (10) administration of morphine (MOR 0.67 and 2.0 mg/kg) was regularly estimated after drug administrations in conditions of two-hour restraint stress. The absence of any significant changes in the quantity of entries and the time in restraint box in rats received MOR at a low dose and only a slight increase in the quantity of entries found in animals administered MOR at a high dose allowed us to propose a blockade or prominent inhibition of the drug's rewarding efficacy to be typical under these conditions. Inverted changes in movement reactivity (its increase) as response to apomorphine at low "presynaptic" doses found in animals treated by MOR may indicate the involvement of modified presynaptic dopamine receptors in the mediation of revealed changes in an opiate's reinforcing activity.

Dopaminergic involvement in nociceptive sensitivity/behavioral reactivity regulation during aversive states of different nature in the rat

To investigate the involvement of dopamine (DA) in nociceptive sensitivity-behavioral reactivity regulation in animals during aversive states of different nature, the influence of pharmacologically-induced decrease and increase of DA neurotransmission on vocalization and movement reactivity were studied in rats in free behavior, during restraint stress, after acute trauma of an extremity and under intraperitoneal acetic acid administration. The influence of longterm increase (apomorphine in a high dose) and decrease (haloperidol, apomorphine in a low dose) on suprarenals weight and gastric ulceration in animals exposed by polymodal aversive stimulation was also studied. The data obtained are discussed in relation with; 1. DA involvement in regulation of nociceptive sensitivity and behavioral reactivity in aversive environment; 2. the role of DA and endogenous opioid peptides in endogenous analgesic mechanisms; 3. the functional significance of cerebral DA in organization and realization of various types of an organism's adaptive activity produced by different environmental and homeostatic variables; and 4. the interaction of DA and endogenous opioid peptides in mediation of this activity.

Functional properties of presumed dopamine-containing and other ventral tegmental area neurons in conscious rats

To elucidate the functional significance of mesolimbocortical dopamine (DA)-containing neurons in animal adaptive activity, the properties of single units in ventral tegmental area (VTA) and adjacent regions of the midbrain were studied in conscious rats with strictly fixed skull. Analysis of spontaneous firing activity, its changes during polymodal activating and aversive stimulations and their interrelations was performed in electrophysiologically-identified presumed DA-containing (D-type, 48 cells) and other (A-B and C-type, 47 and 29 cells accordingly) neurons found in this brain area. A common feature of all cells was the dependence of their discharge changes on the biological significance of the stimulation used and the strong correlation between these firing changes and stimulation-induced or spontaneous movement activity and blood pressure oscillations. Moreover, a significant correlation between the rate of firing and its dispersion and constancy of directions of neuronal changes during experimental stimulation in single cells were found. Presumed DA-containing neurons of D-type had a high variability of all properties and heterogeneity in the pattern of their discharges and in direction changes (prevalent activations). In presumed acetylcholine (ACh)-containing A-B type cells strong tonic-like activations and in presumed GABA- or ACh-containing interneurons of C-type depressions of firing both correlated with animal movement activity were found. Present data were discussed in relation with mediator specifity of studied cells and the differences of their participation in avoidance behavior forming in aversive environment.

The striatum and cerebral cortex express different muscarinic receptor mRNAs

The existence of four distinct muscarinic acetylcholine receptor genes (m1-mr) has recently been demonstrated. cDNAs for three of these receptors have been cloned from brain (m1, m3, m4) and one from heart (m2). To gain some understanding of the physiological role of the brain muscarinic receptors, we mapped the distribution of their mRNAs in rat brain by in situ hybridization. These mRNAs are barely detectable in the hindbrain and cerebellum. Within forebrain, each mRNA has a strikingly different pattern of distribution. The highest levels of m1 mRNA are in the cerebral cortex and hippocampus followed by the striatum. m3 mRNA is also prominent in the cerebral cortex, but has very low levels in the striatum. Conversely, the levels of m4 mRNA are highest in the striatum. Since the cognitive effects of muscarinic drugs have been localized to the cerebral cortex and hippocampus, and their psychomotor effects to the striatum, these data suggest that the muscarinic receptors which subserve these responses may be different gene products. Finally, we show that these muscarinic receptors can be distinguished pharmacologically, suggesting that it may be possible to develop drugs for the selective treatment of the psychomotor vs cognitive difficulties of Parkinson's and Alzheimer's disease, respectively.