Specific lesions in the extrapyramidal system of the rat brain induced by 3-nitropropionic acid (3-NPA)

Melatonin improves 3-nitropropionic acid induced behavioral alterations and neurotrophic factors levels

OBJECTIVE

This study sought to determine whether melatonin causes changes in neurotrophic factors and it protects against the mycotoxin 3-nitropropionic acid (3-NP) in brain tissue.

METHODS

Rats were given 3-NP over four consecutive days (20 mg/kg BW), while melatonin was administered over 21 days (1 mg/kg/BW), starting after the last injection of 3-NP.

RESULTS

Rats treated with 3-NP displayed significant changes in neurotrophic factor (BDNF and GDNF) levels, together with alterations in behavior; they also displayed extensive oxidative stress and a massive neuronal damage.

CONCLUSIONS

Melatonin improved behavioral alterations, reduced oxidative damage, lowered neurotrophic factor levels and neuronal loss in 3-NP-treated rats. These results suggest that melatonin exerts a neuroprotective action.

Chronic corticotropin-releasing factor type 1 receptor antagonism with antalarmin regulates the dopaminergic system of Fawn-Hooded rats

Corticotropin-releasing factor is a neuropeptide associated with the integration of physiological and behavioural responses to stress and also in the modulation of affective state and drug reward. The selective, centrally acting corticotropin-releasing factor type 1 receptor antagonist, antalarmin, is a potent anxiolytic and reduces volitional ethanol consumption in Fawn-Hooded rats. The efficacy of antalarmin to reduce ethanol consumption increased with time, suggestive of adaptation to reinforcement processes and goal-directed behaviour. The aim of the present study was to examine the effects of chronic antalarmin treatment on reward-related regions of Fawn-Hooded rat brain. Bi-daily antalarmin treatment (20 mg/kg, i.p.) for 10 days increased tyrosine hydroxylase messenger RNA expression throughout the ventral mesencephalon. Following chronic antalarmin the density of dopaminergic terminals within the basal ganglia and amygdaloid complex were reduced, as was dopamine transporter binding within the striatum. Receptor autoradiography indicated an up-regulation of dopamine D2, but no change in D1, binding in striatum, and Golgi-Cox analysis of striatal medium spiny neurones indicated that chronic antalarmin treatment increased spine density. Thus, chronic antalarmin treatment modulates dopaminergic pathways and implies that chronic treatment with drugs of this class may ultimately alter postsynaptic signaling mechanisms within the basal ganglia.

Differential gene expression in WKY and SHR brain following acute and chronic air-puff stress

This study determined the expression levels of tyrosine hydroxylase (TH), arginine vasopressin (AVP), and prepro-neuropeptide Y (NPY) mRNA in the brain following acute and chronic air-puff stress. Acute stress increased TH gene expression in the locus coeruleus of Wistar-Kyoto (WKY) rats (+80%), but only modestly in spontaneously hypertensive rats (SHR; +19%). Hypothalamic AVP mRNA in SHR was persistently elevated in the supraoptic nucleus (+24% acute; +19% chronic), but reduced in the magnocellular region of the paraventricular nucleus (-15% acute; -20% chronic). In the arcuate nucleus, NPY mRNA expression increased by 60% and 81% in response to acute and chronic air-puff stress, respectively, in SHR. These data suggest differential adaptation to air-puff stress between WKY and SHR.

Chronic cold stress regulates ascending noradrenergic pathways

Chronic exposure to cold in rats alters the activity of locus coeruleus (LC) neurons. In this study we aimed to examine the cellular effect of cold stress on catecholamine neurons, and determine whether this is specific to the LC compared with other catecholamine cell groups. Male Sprague-Dawley rats were subjected to 21 days of isolation under ambient conditions, chronic cold exposure at 5 degrees C, or after chronic cold followed by return to ambient temperature for 7 or 14 days. In the LC, chronic cold exposure significantly reduced tyrosine hydroxylase (TH) mRNA expression by approximately 45% compared with control rats, and remained significantly reduced (approximately 36%) after return to ambient conditions for 7 days; however, expression returned to normal after 14 days' recovery. There were no significant changes in TH mRNA in the substantia nigra or ventral tegmental area. Chronic cold increased expression of alpha2A adrenoceptor mRNA in the LC (approximately 27%). There were decreases in alpha2A expression in the nucleus tractus solitarius; however, this was seen only in rats returned to ambient conditions for 7 days. Additionally, alpha2A mRNA in the caudal ventrolateral medulla (A1 region) increased following cold exposure (approximately 84%) compared with controls. Binding of [125I]iodoclonidine to alpha2-like protein increased in the olfactory bulbs but decreased in the medial amygdala following cold exposure. Collectively, these data indicate robust effects of cold on central catecholamine neurons, not necessarily specific to the LC.

The effect of isolation rearing on volitional ethanol consumption and central CCK/dopamine systems in Fawn-Hooded rats

Numerous studies have demonstrated that socially isolating rats (from weaning) produces a sustained anxious phenotype and an enhanced response to psychostimulant drugs such as amphetamine and cocaine. In addition, isolation rearing has been shown to induce significant changes in the mesolimbic dopamine system. These data indicate that isolation rearing not only induces an anxiogenic phenotype but also induces neurochemical changes in reward nuclei of the brain, which is correlated with an enhanced response to psychostimulants. For these reasons, the effect of isolation rearing on volitional ethanol consumption was examined in Fawn-Hooded (FH) rats and correlated with neurochemical changes in central dopamine and cholecystokinin systems. Social isolation from weaning produced an anxiogenic phenotype as measured by a decreased time spent on the open arms of an elevated plus-maze. Interestingly, isolation-rearing induced a greater proportion of FH rats to acquire preference for ethanol while having no effect on the amount of ethanol consumed by alcohol-preferring rats. In addition, isolation rearing induced a number of changes in central CCK/dopamine systems.

The neurochemical effects of anxiolytic drugs are dependent on rearing conditions in Fawn-Hooded rats

There is a vast literature examining the neurochemical effects of anxiolytics throughout the rat brain; however, although the behavioural actions of anxiolytic drugs are routinely assessed in animal models of anxiety, the majority of neurochemical studies have been performed in rats with relatively 'normal' behavioural phenotypes. Since there is significant evidence that an anxious phenotype is associated with numerous neurochemical alterations, it is feasible that the central effects of anxiolytics may vary depending on the underlying behavioural state (and corresponding neuropathology) of the experimental animal. For this reason, the aim of the present study was to examine the effect of chronic anxiolytic drug administration on the central CCK and dopamine systems in anxious (isolated from weaning) and nonanxious (group-housed) Fawn-Hooded (FH) rats. It is important to note that these studies were performed in rats with continued access to ethanol, which may affect the responses to anxiolytic treatment. Chronic anxiolytic treatment with the selective CCK-B (CCK(2)) receptor antagonist, Ci-988 (0.3 mg/kg/day ip) or diazepam (2 mg/kg/day ip), induced numerous effects throughout the central nervous system (CNS), with Ci-988 inducing significant changes in the density of dopamine D(2) receptors, and diazepam producing marked changes in both dopamine D(2) and CCK-B receptor binding density as well as preproCCK mRNA expression. Interestingly, the neurochemical effects of these anxiolytic drugs varied significantly depending on the rearing conditions of the rats, demonstrating the importance of using adequate animal models when correlating the behavioural and central effects of drugs acting throughout the CNS.

Subacute systemic 3-nitropropionic acid intoxication induces a distinct motor disorder in adult C57Bl/6 mice: behavioural and histopathological characterisation

Data on motor behavioural disorders induced by systemic 3-nitropropionic acid, an irreversible inhibitor of mitochondrial succinate dehydrogenase and their histopathological correlates in mice, are sparse. We thus further characterised the subacute 3-nitropropionic-acid-induced motor disorder and its time course in C57Bl/6 mice using standard behavioural tests, histopathological correlates and in vivo magnetic resonance imaging. Firstly, we studied two intoxication paradigms (340 and 560 mg 3-nitropropionic acid/kg, 7 days) compared to controls. The low-dose regimen induced only slight motor changes (reduced hindlimb stride length and rearing). The high-dose regimen induced significant (P<0.05) behavioural and sensorimotor integration deficits (pole test, rotarod, stride length, open-field spontaneous activity) but with 37.5% lethality at week one. The clinical motor disorder consisted of hindlimb clasping and dystonia, truncal dystonia, bradykinesia and impaired postural control. Histopathologically, there were discrete lesions of the dorsolateral striatum in 62.5% of mice together with a 32% reduction (P<0.0001) of the striatal volume, reduced caldbindin-D28K immunoreactivity in the lateral striatum, and met-enkephalin and substance P in the striatal output pathways. There was also a significant (P<0.05) 30-40% dopaminergic cell loss within the substantia nigra pars compacta. Secondly, we validated a semi-quantitative behavioural scale to describe the time course of the motor deficits and to predict the occurrence of striatal damage. We sought to determine whether it could also be disclosed in vivo by magnetic resonance imaging. The scale correlated with the striatal volume reduction (r(2)=0.57) and striatal cell loss (r(2)=0.87) but not with the loss of striatal dopaminergic terminals (dopamine transporter binding). Increased T2-signal intensity within the striatal lesion correlated with the cell loss (r(2)=0.66). We conclude that systemic administration of 3-nitropropionic acid in C57Bl/6 mice induces a distinct motor disorder and dose-dependent striatonigral damage, which are potentially useful to model human diseases of the basal ganglia.

Neurotrophic and neuroprotective effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on mesencephalic dopaminergic neurons

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is present in many regions of the adult and developing brain as are receptors for PACAP. PACAP stimulates different signalling cascades in neurons, involving cAMP, MAP kinase, and calcium. These characteristics suggest that PACAP may influence neuronal development. Here we have studied the effects of PACAP on mesencephalic dopaminergic neurons using primary cultures from embryonic rats. PACAP increased the number of tyrosine hydroxylase (TH)-immunoreactive neurons, elevated TH protein, and enhanced tritiated dopamine uptake in these cultures. Moreover, PACAP counteracted the effects of 6-hydroxydopamine treatments, which induce cell death of dopaminergic neurons. In situ hybridisation showed that both PACAP and PACAP receptor type 1 are present in developing and adult rat mesencephalon. These results show that PACAP has a neurotrophic action on dopaminergic neurons and partially protects them against 6-OHDA induced neurotoxicity.

3-Nitropropionic acid's lethal triplet: cooperative pathways of neurodegeneration

3-Nitropropionic acid (3-NP) is a mitochondrial toxin which interferes with ATP synthesis. Accidental ingestion of 3-NP by humans as well as other mammals results in neuronal degeneration within the basal ganglia and movement dysfunction characterized by dystonia, chorea, and hypokinesia. The selective degeneration of structures of the basal ganglia occurs despite the non-selective impairment of energy metabolism throughout the brain and body. These effects of 3-NP are shared with the genetic disorder Huntington's disease (HD), which is characterized by progressive neurodegeneration of the basal ganglia and choreic motor dysfunction. These similarities have prompted further investigation of 3-NP as an animal model of HD. Metabolic compromise with 3-NP causes neurodegeneration that involves three interacting processes: energy impairment, excitotoxicity, and oxidative stress. This triplet of cooperative pathways of neurodegeneration helps to explain 3-NP's regional selectivity of neurotoxicity to the basal ganglia. This mini-review will focus on the actions of 3-NP and the related compound, malonic acid (MA), in the central nervous system, with an emphasis on the more current findings regarding their mechanisms of action.

Glial cell line-derived neurotrophic factor attenuates the locomotor hypofunction and striatonigral neurochemical deficits induced by chronic systemic administration of the mitochondrial toxin 3-nitropropionic acid

The present study investigated whether glial cell line-derived neurotrophic factor prevents the progressive striatal degeneration induced by chronic systemic administration of the mitochondrial toxin, 3-nitropropionic acid. In addition, the effects of delayed treatment with glial cell line-derived neurotrophic factor on toxin-induced behavioural and neurochemical deficits were determined. Locomotor activity in rats infused with 3-nitropropionic acid (15 mg/kg/day, for four weeks) via subcutaneous osmotic minipumps was considerably reduced compared to control rats. However, in rats given a single intracerebroventricular injection of 100 micrograms of glial cell line-derived neurotrophic factor, locomotor activity was significantly higher than in rats injected with the vehicle, an effect that was most pronounced at the onset of toxin infusion. Consistent with a protective or restorative effect in this model of striatal neurodegeneration, toxin-induced deficits in markers of neurotransmitter function were attenuated by glial cell line-derived neurotrophic factor. Thus, [3H]GABA uptake and [3H]tiagabine/GABA uptake sites in striatal target tissues (globus pallidus and substantia nigra), as well as [3H]choline uptake, choline acetyltransferase activity and dopamine receptor binding in the striatum were decreased by the toxin and restored to varying degrees by glial cell line-derived neurotrophic factor administration. As with locomotor abnormalities, effects on neurochemical deficits were most prominent when glial cell line-derived neurotrophic factor was given at the start of toxin infusion, but remained significantly higher than in the vehicle-injected rats when given up to two weeks after. Substance P, dynorphin A and [Met]enkephalin levels in the striatal target tissues also were reduced by 3-nitropropionic acid. The results show that glial cell line-derived neurotrophic factor protects striatal neurons from slow excitotoxic cell death resulting from energy deprivation, secondary to mitochondrial dysfunction. Moreover, they suggest that glial cell line-derived neurotrophic factor may be a viable therapeutic agent for slowly progressive central nervous system disorders, like Huntington's disease, that may be caused by secondary excitotoxicity resulting from abnormal energy utilization.

3-Nitropropionic acid increases the intracellular Ca2+ in cultured astrocytes by reverse operation of the Na+-Ca2+ exchanger

The effect of 3-nitropropionic acid (3-NPA) on intracellular calcium ([Ca2+]i) in cultured cortical and striatal astrocytes was examined using a calcium imaging technique with fura-2. 3-NPA (1.7 mM) increased the [Ca2+]i in cortical and striatal astrocytes. The latency for the onset of the rise in [Ca2+]i in cortical astrocytes was 22.7 +/- 0.8 min and was significantly longer in striatal astrocytes (39.2 +/- 2.4 min; P < 0.001). The maximal increase in [Ca2+]i for both astrocytes was seen after 50 min and remained at that level even after extensive washing. The maximal responses were about 125 and 140% of the initial values for striatal and cortical cells, respectively. Pretreatment (2-3 h) with creatine (25 mM) significantly delayed the onset of increase in [Ca2+]i by 3-NPA in cortical (39.8 +/- 3.7 min) and in striatal (57.8 +/- 2.5 min) astrocytes from the respective untreated cells (P < 0.05). However, the [Ca2+]i increase was similar to that of the untreated cells at 60 or 90 min. The increase in [Ca2+]i by 3-NPA was not observed in Ca2+-free or low-Na+ medium, but there was rather a 10-15% decrease under the Ca2+-free condition (P < 0.05). Superfusion of normal Ca2+ (2 mM) medium after exposure of the cells to 3-NPA in Ca2+-free medium increased the [Ca2+]i dramatically and reversibly. This increase was significantly attenuated in the presence of 2',4'-dichlorobenzamil (100 microM), nifedipine (10 microM), or Ni2+ (2 mM) or after exposure to amiloride (1 mM). The blockade was total in the case of 2',4'-dichlorobenzamil. The results indicate that the 3-NPA-induced increase in [Ca2+]i in astrocytes was due to an influx of Ca2+ by the reverse operation of the Na+-Ca2+ exchanger system, which may be responsible for the gliotoxic action of 3-NPA.

Acute 3-nitropropionic acid intoxication induces striatal astrocytic cell death and dysfunction of the blood-brain barrier: involvement of dopamine toxicity

Mechanisms underlying the selective vulnerability of the lateral striatal area to the toxic effects of 3-nitropropionic acid (3-NPA) were investigated in rats. A single exposure to 3-NPA (20 mg/kg, s.c.) induced no deficits in behavior and histology, but subsequent injection produced motor symptoms, catalepsy, lip smacking, abnormal gait, paddling, rolling, opisthotonos, tremor, recombence, somnolence and so on, in 30% of the animals within a few hours. Diffusion-weighted magnetic resonance imaging of the brains revealed an area of high signal intensity in the bilateral striata. By this stage (within a few hours), striatal astrocytes had become swollen and disintegrated. Extravasation of immunoglobulin G was detected, indicating blood-brain barrier (BBB) dysfunction. Electron microscopy revealed edema and disorganization of structures inside the astrocytic end-feet around the branches of the lateral striatal artery. Neurons were less vulnerable than astrocytes to the 3-NPA injury. Treatment of the rats with D2 receptor agonist prior to exposure to 3-NPA attenuated the behavioral abnormalities and histological damage whereas pretreatment with D2 antagonist exacerbated these changes. The concentrations of extracellular dopamine (DA) and dihydroxyphenyl acetic acid (DOPAC) were both increased in rats exposed to 3-NPA. In vitro imaging of astrocytes revealed a progressive increase in [Ca2+]i after superfusion with 3-NPA, and the 'ceiling' level was maintained even after extensive washing. DA superfusion also increased the astrocytic [Ca2+]i and this increase was reversible. Data indicate that 3-NPA-induced striatal damage was associated with astrocytic cell death and dysfunction of the BBB. Intracellular edema and extreme Ca2+ overload induced by the toxin were further aggravated by an increase in the level of DA activity. These factors acting either singly or in combination may trigger astrocyte destruction.

Unilateral 6-hydroxydopamine lesions of meso-striatal dopamine neurons and their physiological sequelae

One of the primary approaches in experimental brain research is to investigate the effects of specific destruction of its parts. Here, several neurotoxins are available which can be used to eliminate neurons of a certain neurochemical type or family. With respect to the study of dopamine neurons in the brain, especially within the basal ganglia, the neurotoxin 6-hydroxydopamine (6-OHDA) provides an important tool. The most common version of lesion induced with this toxin is the unilateral lesion placed in the area of mesencephalic dopamine somata or their ascending fibers, which leads to a lateralized loss of striatal dopamine. This approach has contributed to neuroscientific knowledge at the basic and clinical levels, since it has been used to clarify the neuroanatomy, neurochemistry, and electrophysiology of mesencephalic dopamine neurons and their relationships with the basal ganglia. Furthermore, unilateral 6-OHDA lesions have been used to investigate the role of these dopamine neurons with respect to behavior, and to examine the brain's capacity to recover from or compensate for specific neurochemical depletions. Finally, in clinically-oriented research, the lesion has been used to model aspects of Parkinson's disease, a human neurodegenerative disease which is neuronally characterized by a severe loss of the meso-striatal dopamine neurons. In the present review, which is the first of two, the lesion's effects on physiological parameters are being dealt with, including histological manifestations, effects on dopaminergic measures, other neurotransmitters (e.g. GABA, acetylcholine, glutamate), neuromodulators (e.g. neuropeptides, neurotrophins), electrophysiological activity, and measures of energy consumption. The findings are being discussed especially in relation to time after lesion and in relation to lesion severeness, that is, the differential role of total versus partial depletions of dopamine and the possible mechanisms of compensation. Finally, the advantages and possible drawbacks of such a lateralized lesion model are discussed.