Dopaminergic neuron development in rats: biochemical study from prenatal life to adulthood

Co-treatment with natural HMGB1 inhibitor Glycyrrhizin exerts neuroprotection and reverses Parkinson's disease like pathology in Zebrafish

ETHNOPHARMACOLOGICAL RELEVANCE

Parkinson's disease (PD) is the second most devastating age-related neurodegenerative diseases after Alzheimer diseases (AD) and is characterized by the loss of dopaminergic (DA) neurons in the substantia nigra (SN) and aggregation of α-synuclein (α-syn). The precise etiology of PD is not yet fully understood and lacks the disease-modifying therapeutic strategies that could reverse the ongoing neurodegeneration. In the quest of exploring novel disease modifying therapeutic strategies, natural compounds from plant sources have gained much attention in recent days. Glycyrrhizin (GL) is the main active ingredient of the roots and rhizomes of licorice (Glycyrrhiza glabra L), which are generally used in the treatment of inflammatory diseases or as a tonifying herbal medicine. In Persia, GL is a conventional neuroprotective agent that are used to treat neurological disorders. The traditional use of GL in Japan is to treat chronic hepatitis B. In addition, GL is a natural inhibitor of high mobility group box 1 (HMGB1) which has exerted neuroprotective effect against several HMGB1 mediated pathological conditions.

AIM OF THE STUDY

The study is aimed to evaluate therapeutic effect of GL against PD in zebrafish.

MATERIAL AND METHODS

PD in zebrafish larvae is induced by administration of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Apoptosis was assessed with TUNEL assay. Gene expression was performed to assess the modulation in genes related to neuroinflammatory and autophagy.

RESULTS

We observed that GL co-treatment increased the length of DA neurons, decreased the number of apoptotic cells in zebrafish brain, and inhibited the loss of vasculature and disorganized vasculature induced by MPTP. GL co-treatment relieved the MPTP-induced locomotor impairment in zebrafish. GL co-treatment suppressed MPTP-induced upregulated mRNA expression of inflammatory markers such as hmgb1a, tlr4b, nfκb, il1β, and il6. GL co-treatment suppressed the autophagy related genes α-syn and atg5 whereas increased the mRNA expression level of parkin and pink1. In addition, molecular docking study reveals that GL has binding interaction with HMGB1, TLR4, and RAGE.

CONCLUSION

Hence, the effect of GL co-treatment on MPTP-induced PD-like condition in zebrafish is to alleviate apoptosis and autophagy, as well as suppress inflammatory responses.

Neuroprotective effect of YIAEDAER peptide against Parkinson's disease like pathology in zebrafish

Parkinson's disease (PD) is characterized by the loss of dopaminergic (DA) neurons in the substantia nigra (SN) and aggregation of α-synuclein (α-syn). Current PD therapies merely provide symptomatic relief, lacking the disease-modifying therapeutic strategies against that could reverse the ongoing neurodegeneration. In the quest of exploring novel disease modifying therapeutic strategies, compounds from natural sources have gained much attention in recent days. YIAEDAER (Tyr-Ile-Ala-Glu-Asp-Ala-Glu-Arg) peptide is a multi-functional peptide isolated and purified from the visceral mass extract of Neptunea arthritica cumingii (NAC) with plethora of pharmacological activities, however its neuroprotective effect against MPTP induced PD model is not yet reported. We found YIAEDAER peptide co-treatment could suppressed the MPTP-induced locomotor impairment in zebrafish, ameliorates the MPTP induced degeneration of DA neurons, inhibited the loss of vasculature and loss of cerebral vessels, suppressed α-syn levels. Moreover, YIAEDAER peptide modulates several genes related to autophagy (α-syn, pink1, parkin, atg5, atg7, beclin1, ulk1b, ulk2, and ambra1a), and oxidative stress (sod1, sod2, gss, gpx4a, gsto2, and cat). Hence, our finding suggests that YIAEDAER peptide might be a potential therapeutic candidate against MPTP-induced PD like condition.

Comprehensive Analysis of Neurotoxin-Induced Ablation of Dopaminergic Neurons in Zebrafish Larvae

Neurotoxin exposure of zebrafish larvae has been used to mimic a Parkinson’s disease (PD) phenotype and to facilitate high-throughput drug screening. However, the vulnerability of zebrafish to various neurotoxins was shown to be variable. Here, we provide a direct comparison of ablative effectiveness in order to identify the optimal neurotoxin-mediated dopaminergic (DAnergic) neuronal death in larval zebrafish. Transgenic zebrafish, Tg(dat:eGFP), were exposed to different concentrations of the neurotoxins MPTP, MPP⁺, paraquat, 6-OHDA, and rotenone for four days, starting at three days post-fertilization. The LC₅₀ of each respective neurotoxin concentration was determined. Confocal live imaging on Tg(dat:eGFP) showed that MPTP, MPP⁺, and rotenone caused comparable DAnergic cell loss in the ventral diencephalon (vDC) region while, paraquat and 6-OHDA caused fewer losses of DAnergic cells. These results were further supported by respective gene expression analyses of dat, th, and p53. Importantly, the loss of DAnergic cells from exposure to MPTP, MPP⁺, and rotenone impacted larval locomotor function. MPTP induced the largest motor deficit, but this was accompanied by the most severe morphological impairment. We conclude that, of the tested neurotoxins, MPP⁺ recapitulates a substantial degree of DAnergic ablation and slight locomotor perturbations without systemic defects indicative of a Parkinsonian phenotype.

A Comparative Study of Preparation Techniques for Improving the Viability of Nigral Grafts using Vital Stains, in Vitro Cultures, and in Vivo Grafts

The intracerebral transplantation of embryonic dopaminergic nigral neurons, although relatively successful, leads to a fairly low yield of surviving cells. Many factors may influence the viability of dopaminergic grafts and one of these is the preparation of the tissue prior to transplantation. We have investigated the effects of different steps during the preparation and storage of embryonic rat nigral cell suspensions on their subsequent survival at a variety of different time points using a combination of techniques and studies. For studies concerned with the first 24 h we employed vital stains, in the period covering the next 7 days we used in vitro cultures, and in the long term experiment we used in vivo grafts. The results suggest that nigral cell suspensions may remain sufficiently viable for grafting for much longer periods than previously reported. In addition a number of parameters which affect cell survival have been characterised, including the age of the embryonic donor tissue, the use of proteolytic enzymes and the trituration procedure used during the preparation of the suspension. The optimal preparation technique, therefore, uses E13-E14 embryos with the dissected ventral mesencephalon being incubated in purified 0.1% trypsin solutions for 60 min and triturated using a flame polished Pasteur pipette. This may have important implications in improving intracerebral transplantation for Parkinson's disease.

Cocaine exposure during the early postnatal period diminishes medial frontal cortex Gs coupling to dopamine D1-like receptors in adult rat

The effect of cocaine exposure during early postnatal ages on coupling of dopamine (DA) D(1)- and D(2)-like receptors to their respective Gs/olf and Gi was examined in striatum and medial frontal cortex (MFC). Sprague-Dawley rats were subcutaneously injected with either 50 mg/kg cocaine or vehicle during postnatal day (PnD) 11-20 and dopaminergic D(1)- and D(2)-like receptor signaling was evaluated at PnD 60. Results showed that cocaine exposure did not affect the magnitude of both DA D(1)- and D(2)-like receptor coupling to their respective Gs/olf and Gi in striatum. However, in the medial frontal cortex, the basal and the DA D(1)-like receptor and Gs association were reduced in cocaine-exposed brains. However, there was no change in basal or DA D(2)-like receptor-Gi linkage in medial frontal cortex. Since frontal cortex plays a critical role in regulating cognition and working memory, disruption of DA-modulated circuits or alteration of dopaminergic activity resulting from postnatal cocaine exposure may result in abnormal responses to environmental challenges leading to long-term behavioral changes.

Elevated levels of impulsivity and reduced place conditioning with d-amphetamine: two behavioral features of adolescence in mice

Human adolescents may have experience with easily available psychoactive drugs. Impulsivity and/or peculiarities in reward systems may play a role. These variables were studied in adolescent (Postnatal Day [PND] 30-49) and adult (PND > 60) CD-1 mice. In Experiment 1 (impulsivity), food-restricted mice were tested in operant chambers with 2 nose-poking holes that delivered 1 food pellet immediately or 5 pellets after a delay, respectively. Delay length was increased over days (0-100 s). Adolescent mice showed a shift to the left in the intolerance-delay curve, as well as enhanced demanding when nose-poking was not reinforced. In Experiment 2 (place conditioning with d-amphetamine at 0.0. 1.0, 2.0, 3.3, or 5.0 mg/kg for 3 days), adolescent mice showed no reliable evidence of place conditioning when compared with adults. Hence, 2 main features of adolescence were elevated impulsivity and restlessness, and low (or absent) rewarding efficacy of amphetamine.

Developmental neurobiology: implications for pediatric psychopharmacology

Pediatric psychopharmacology can only be properly understood within the context of developmental neurobiology. Normal maturation of the brain is characterized by the complex anatomic, molecular, and organizational changes required for optimal adaptive functioning. In many areas of the developing nervous system, neurons, cell processes, neurotransmitters, and trophic nerve growth factors are produced in far greater numbers and in different areas than in the mature brain. Psychopathology and stressful environments can lead to enduring changes in brain structure and functioning. A few select psychopharmacological treatments are reviewed to assess their potential impact on CNS development. More clinical and basic science studies are needed to determine whether current treatments have neurotoxic or neuroprotective effects when administered over extended critical early periods of the lifespan.

Adolescent nicotine exposure produces immediate and long-term changes in CNS noradrenergic and dopaminergic function

Animal studies have only recently begun to address whether nicotine evokes unique or persistent effects on brain structure or function during adolescence, the period in which smokers typically begin their habit. In the current study, we examined the impact of adolescent nicotine treatment on catecholaminergic synaptic function in rats infused with nicotine on postnatal days 30-47.5, using a paradigm that reproduces the plasma levels of nicotine found in smokers. We assessed norepinephrine and dopamine content, turnover (an index of neural activity), and the response to an acute challenge dose of nicotine. In the midbrain, the region most closely associated with addiction, both norepinephrine and dopamine turnover were activated during the infusion period, an effect not seen in any other region for norepinephrine, and only in the striatum for dopamine. In the immediate post-infusion period (PN50-60), there was a decrement in midbrain catecholamine turnover restricted to males, whereas there was a later-emerging (PN80) activation of these pathways. Again, this pattern was not observed in any other region: the cerebral cortex showed post-treatment increases in turnover without gender selectivity, the striatum showed late-emerging deficits in dopamine turnover and the hippocampus displayed a profound deficit in noradrenergic activity that was limited to females. We also assessed the catecholaminergic response to an acute challenge with nicotine (0.3 mg/kg s.c.). The midbrain once more displayed unique properties; there was initial suppression of responses followed by post-treatment rebound elevations that were more prominent in males and eventual deficits that, in the case of dopamine, were selective for males. With the exception of the cerebellum, other regions showed the initial loss of response during the infusion period but no persistent changes in responsiveness. The current results indicate that adolescent nicotine produces immediate and long-term changes in CNS catecholaminergic systems, with regional targeting and gender selectivity corresponding to the changes seen previously in nicotinic receptor upregulation or indices of cell damage. These effects may underlie long-term behavioral changes associated with adolescent nicotine exposure.

Ontogeny of ethanol-induced locomotor activity and hypothermia differences in selectively bred FAST and SLOW mice

The replicate lines of selectively bred FAST and SLOW mice differ in locomotor response to 2 g/kg ethanol (EtOH). FAST mice show enhanced locomotion; SLOW mice exhibit no change or locomotor depression. Little is known about the responses of FAST and SLOW mice to EtOH during development. We assessed the locomotor responses of FAST and SLOW mice at postnatal days (P) 10, 15, 30, and 60. A genetically correlated response, EtOH-induced hypothermia, was also investigated. Although all animals demonstrated their respective selection phenotypes in adulthood, developing FAST mice exhibited ethanol stimulation by P15 (replicate 1) or P30 (replicate 2). At these ages, responses of FAST mice differed from those of SLOW. The stimulant response in FAST mice was adult-like at P30. EtOH-induced hypothermia was seen in SLOW mice by P15. These data suggest that sensitivity to the locomotor stimulant effects of EtOH changes during postnatal development, and may mirror developmental profiles for certain neurotransmitter systems.

Behavioral changes in rats with early ventral hippocampal damage vary with age at damage

Our previous work demonstrated that neonatal (on postnatal day 7, PD7) excitotoxic damage of the ventral hippocampus (VH) results in delayed emergence of behaviors related to dopaminergic (DA) transmission. In this study, the developmental effects of VH lesions induced at two other ages were investigated in the rat. Ibotenic acid or artificial cerebrospinal fluid was infused into the VH of 3- (PD3) or 14- (PD14)-day-old rat pups. Amphetamine-induced (1.5 mg/kg, i.p.) locomotor activity was assessed in the sham and lesioned rats prior to (PD35) and after puberty (PD56 and PD86). Apomorphine-induced (0.75 mg/kg s.c.) stereotypic behaviors were measured on PD56. Similar VH lesions resulted in different profiles of behavioral abnormalities depending upon the age at which they were induced. The PD3 lesioned rats displayed hyperlocomotion to amphetamine only after puberty, while the PD14 lesioned rats manifest hyperlocomotion as early as 3 weeks after surgery (at PD35). Moreover, the PD3 lesioned rats tended to show more stereotypic behaviors in response to apomorphine than the sham-operated controls, while the PD14 rats had a profoundly diminished stereotypic response. The behavioral changes in the PD3 lesioned rats are reminiscent of those previously described in animals lesioned at PD7. In contrast, the deficits in the PD14 lesioned animals resemble those seen before in rats lesioned in adulthood. These results indicate that the pattern of impairments associated with the excitotoxic VH lesion varies with age at lesion, i.e. a similar pattern seems to be associated with lesions up to PD7, but not by PD14. To the extent that the neonatal VH lesion in the rat models certain phenomenological aspects of schizophrenia, including the temporal pattern of symptom onset, these results provide evidence that the model requires an early defect in limbic cortical development.

Antennal lobe neurons of the honey bee, Apis mellifera, express a D2-like dopamine receptor in vitro

We have used the D2-specific dopamine receptor ligand spiperone [N-(p-aminophenethyl) spiperone; NAPS] coupled to the fluorophore 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD) to visualize dopamine receptors expressed in vitro by neurons of the primary antennosensory centers (antennal lobes) of the brain of the honey bee, Apis mellifera. Changes in the percentage of antennal lobe neurons exhibiting spiperone binding sites over time in culture and at different stages of metamorphic adult development have been investigated. Neurons obtained from animals at all stages of development exhibited spiperone binding sites, but only after 2 days or more in vitro. The percentage of antennal lobe neurons in vitro expressing spiperone binding sites increased significantly with the development of the antennal lobe neuropil. Fluorescently labelled spiperone (120 nM) could be displaced effectively by 1 mM dopamine but not by the same concentration of tyramine, octopamine, or serotonin. In addition, the D2 antagonist spiperone and the D2/D1 antagonist fluphenazine were more effective at displacing the fluorescent ligand than the D1-specific antagonist SCH23390. Our results indicate that Apis antennal lobe neurons in culture express a dopamine receptor and that this receptor is more likely to be D2-like than D1-like in nature. The receptor is expressed early in the metamorphic adult development of the antennal lobe neuropil of the brain.

Maternal ingestion of tyrosine during rat pregnancy modifies the offspring behavioral lateralization

It was previously reported that oral administration of tyrosine (500 mg/kg) to pregnant rats increases tyrosine and monoamines level in the fetal brain and modifies locomotion during postnatal life. In the present study, it was found that this treatment alters behavioral lateralization in the offspring. Neonatal rats whose mothers received tyrosine during the second half of gestation showed a low level of absolute and population laterality in both tail and head movements. The alteration of behavioral lateralization was also found during postnatal development and during adulthood. The T-maze behavioral ontogeny was different for tyrosine-mother and sham-treated or untreated mother rats. During adulthood, the T-max lateralization after stress sessions (a procedure that decreases alternation behavior and facilitates the quantification of behavioral lateralization) was also different in control and tyrosine-mother groups. Neonatal and adult rats showed an increase in right-side movements probability. These data provide evidence that maternal ingestion of a catecholamine precursor during gestation may induce a long-lasting modification of the behavioral lateralization of the offspring.

Postnatal changes in [3H]mazindol-labelled dopamine uptake sites in the rat striatum following prenatal cocaine exposure

The present study showed that prenatal cocaine exposure (60 mg/kg/day) has a transient effect on the [3H]mazindol-labelled dopamine uptake sites in the striatum of the rat offspring examined from postnatal week 0-32. There is a 39% and 21% decrease in the number of binding sites (Bmax) in the cocaine-exposed group at postnatal weeks 3 and 4, respectively, with a recovery to near normal values by postnatal week 8.

Tyrosine ingestion during rat pregnancy alters postnatal development of dopaminergic neurons in the offspring

It has been previously reported that tyrosine ingestion by the mother rat during gestation modifies different behavioral patterns in the adult offspring. In the present study, the action of maternal mother tyrosine ingestion on the postnatal development of the dopaminergic system of the offspring was evaluated. The offspring of tyrosine-treated mothers showed a decrease in dopamine (DA) levels during the first 15 days of postnatal life and an increase in DA levels from day 30 to adulthood. The DOPAC level and the DOPAC/DA index were higher in the tyrosine group from postnatal life to adulthood. These differences reach statistical significance in both forebrain and mesencephalon. During adulthood the DA concentration in both s. nigra and ventral tegmental area were higher in the tyrosine group than in the control group. The behavioral postsynaptic response to a DA receptor agonist (apomorphine) was higher in the offspring of tyrosine treated rats than in the control group. These data suggest that the bioavailability of the DA precursor tyrosine during gestation may modify during postnatal life DA synapsis at both pre- and postsynaptic level.

Ontogenic development of brain asymmetry in dopaminergic neurons

In the present study the right-left brain asymmetry of central dopamine (DA) systems during postnatal brain development is evaluated. DA and dihydroxyphenylacetic acid (DOPAC) levels increased from neonatal to adult life in both the forebrain and mesencephalon. This increase was not similar in the right and left brain sides. From neonatal life to adulthood a fall was observed in (a) DA percentage in the DA high-brain side in the mesencephalon and (b) DOPAC percentage in the DOPAC high-brain side in both the forebrain and mesencephalon. The percentage of lateralized rats (more than 65% of DA or DOPAC levels in either brain side) also decreased during ontogeny. Thus, biochemical lateralization decreases during ontogeny. The right-left brain correlation for DA level and DA turnover was used to evaluate the inter-hemispheric regulation of dopaminergic systems. The correlation coefficient was near to 0 during postnatal life and around -0.8 during adulthood in both forebrain and mesencephalon. Taken together, these data suggest that the ontogenic decrease of in brain asymmetry for DA or DOPAC levels is related to the postnatal development of an inter-hemispheric regulatory system that control dopaminergic neurons activity.