Effects of neurotensin on active and passive avoidance performance in rats with lesions of serotoninergic neurons

After a lesion of serotoninergic neurons performed by administration of 5.7-dihydroxytriptamine into the dorsal raphe nucleus, effects of neurotensin microinjections into the substantia nigra on rat behavior were investigated. Serotoninergic lesions resulted in enhanced fear of rats manifested as an increase in the number of intersignal avoidance reactions and intensification of escape reactions. Neurotensin microinjections into the substantia nigra diminished the neurotoxin action thus increasing the adaptive character of defensive behavior of rats with deficit of functions of serotonin neurons.     

Effect of neurotensin on the behavior of rats with damaged serotoninergic neurons under immobilization stress

It was shown that the immobilization of animals has led to reducing of vertical and horizontal locomotor activity in the "open field" and decreasing of number of conditioned food-procuring reactions into T-maze. The damages of serotoninergic neurons produced via local injections of selective neurotoxin 5, 7-dihydroxytriptamine into dorsal raphe nucleus intensified behavior alterations. Neurotensin administrations reduced effects of neurotoxin: the rats locomotor activity and quantity of conditioned reactions into T-maze were kept at the phone level just after immobilization as well as next two days. The results indicate the important protective significance of neurotensinergic brain structures for ensuring of adaptive behavior of animals with damaged serotoninergic neurons under emotional stress conditions. It is supposed that neurotensin normalizing influences on behavior is connected to a restoration of balance of dopamine-and serotoninergic brain structures interaction.     

In vivo gene transfer to dopamine neurons of rat substantia nigra via the high-affinity neurotensin receptor

BACKGROUND: Recently, we synthesized a nonviral gene vector capable of transfecting cell lines taking advantage of neurotensin (NT) internalization. The vector is NT cross-linked with poly-L-lysine, to which a plasmid DNA was bound to form a complex (NT-polyplex). Nigral dopamine neurons are able to internalize NT, thus representing a target for gene transfer via NT-polyplex. This hypothesis was tested here using reporter genes encoding green fluorescent protein or chloramphenicol acetyl transferase. MATERIALS AND METHODS: NT-polyplex was injected into the substantia nigra. Double immunofluorescence labeling was used to reveal the cell type involved in the propidium iodide-labeled polyplex internalization and reporter gene expression. RESULTS: Polyplex internalization was observed within dopamine neurons but not within glial cells, and was prevented by both hypertonic sucrose solution and SR-48692, a selective nonpeptide antagonist of NT receptors. Reporter gene expression was observed in dopamine neurons from 48 hr up to 15 days after NT-polyplex injection, and was prevented by SR-48692. However, no expression was seen when the NT-polyplex was injected into the ansiform lobule of the cerebellum, which contains low- but not high-affinity NT receptors. Neither internalization nor expression was observed in cultured glial cells, despite the NT-polyplex binding to those cells that was prevented by levocabastine, a low-affinity NT receptor antagonist. CONCLUSIONS: These results suggest that high-affinity NT receptors mediate the uptake of NT-polyplex with the subsequent reporter gene expression in vivo. NT polyfection may be used to transfer genes of physiologic interest to nigrostriatal dopamine neurons, and to produce transgenic animal models of dopamine-related diseases.     

Neuroprotective effects of iron chelator Desferal on dopaminergic neurons in the substantia nigra of rats with iron-overload

The aim of the present study was to investigate whether the iron chelator Desferal prevents the degeneration of dopaminergic neurons in the substantia nigra (SN) induced by iron-overload in rats. Using fast cyclic voltammetry, tyrosine hydroxylase (TH) immunohistochemistry, Perls' iron staining, and high-performance liquid chromatography-electrochemical detection, we measured the degeneration of dopaminergic neurons and increased iron content in the SN of rats overloaded with iron dextran and assessed the effects of treatment with Desferal. The results showed that iron dextran overload increased the iron content in the SN, decreased dopamine release and content, and reduced the numbers of TH-immunoreactive neurons. Treatment with Desferal prevented the increased iron content in the SN. As a result, dopamine release and content remained at almost normal levels, while the numbers of TH-immunoreactive neurons remained at control values. This study suggests that the iron chelator Desferal is neuroprotective against iron-overload, so iron chelators that can cross the blood-brain barrier may have the potential to treat cases where abnormal iron accumulation in the brain is associated with the degenerative processes, as in Parkinson's disease.     

Supersensitivity of substantia nigra pars reticulata neurons to GABAergic drugs after striatal lesions

Rats were given unilateral, intrastriatal injections of kainic acid in order to destroy striatal and pallidal GABAergic projections to the substantia nigra. Two to 3 weeks after the lesions were made, a population of neurons in the substantia nigra pars reticulata was found to be significantly more sensitive to the inhibitory actions of iontophoretically appled GABA, although their responsiveness to iontophoresed glycine was not significantly altered. The increased sensitivity was reflected by a 48% decrease in the IT₅₀ value for GABA. In addition, pars reticulata cells became more sensitive to the inhibitory actions of i.v. muscimol, a GABA agonist. While the change in sensitivity was not statistically significant at 2–3 weeks, cells were markedly more sensitive to i.v. muscimol by 5–6 weeks after the lesions were made. This increased sensitivity was indicated by a 2.5 fold shift to the left in the cumulative dose-response curve and a significant decrease in the ED₅₀ value for muscimol. These results (1) demonstrate that a population of substantia nigra pars reticulata neurons becomes “functionally” supersensitive to GABAergic agents after destruction of the striatonigral GABA pathway, and (2) support the idea that these cells lie postsynaptic to striatonigral GABAergic fibers. The implications of these findings with respect to the etiology and treatment of tardive dyskinesia are discussed.     

Chronic intrastriatal dopamine infusions in rats with unilateral lesions of the substantia nigra

This study examined the effects of continuously supplied dopamine delivered directly into the dopamine-deficient striatum. Rats received unilateral lesions of the substantia nigra by stereotaxic administration of 6-hydroxydopamine and were tested for apomorphine-induced rotational behavior and general activity. Osmotic mini-pumps were filled with dopamine in various concentrations, implanted subcutaneously and connected to a cannula implanted directly into the striatum. The system delivered solution at a rate of .5 microliter/hr for two weeks. Dopamine in a dosage of 0.5 microgram/per hour reduced apomorphine-induced rotational behavior by a mean of 52 +/- 5.8% (mean +/- SEM, n = 20) with a maximal individual decrease of 99%. There was no change in general activity or increase in stereotyped behavior. Infusions of vehicle solutions did not decrease rotational behavior. Spread of the infused dopamine and its metabolites was estimated by adding 3H-dopamine to the pumps in tracer quantities. Radioactivity was highly concentrated at the infusion site and decreased rapidly within a few mm from the infusion site. Continuous infusion methods may eventually prove to be effective in the treatment of nigro-striatal degenerative disease.     

Influence of neurotensin on behavior of rats with lesions in serotonergic neurons

After serotonergic lesion by administration of 5,7-dihydroxytryptamine into the dorsalis raphe nucleus, effects of neurotensin microinjections into the caudate nucleus and substantia nigra on rat behavior were compared. Serotonergic lesions resulted in motivated excitement of rats manifested as an increase in the number of intersignal motor reactions during realization and, particularly, extinction of thirst conditioned reflex. Neurotensin microinjections into the caudate nucleus facilitated extinction of the conditioned reflex both in operated and control rats, but such microinjection into the substantia nigra facilitated this process only in operated animals. Neurotensin did not change conditioned reflex realization in both groups of animals but decreased emotional excitement of rats in the "open field". The behavioral effects of neurotensin in operated rats are connected with normalization of motivational and emotional states of animals and may be explained by recovery of interaction between the dopamine- and serotonergic systems. It is suggested that the mechanisms of this normalizing effects of neurotensin at the levels of the caudate nucleus and substantia nigra are different and are associated preferentially with its action either on dopamine- or serotonergic structures.     

Effect of neurotensin injections into caudate nuclei on realization and extinction of conditioned motor reflex in rats

It was shown that neurotensin microinjections into the caudate nuclei facilitated of a conditioned reflex but not affected its realization. Besides, neurotensin was shown to have a positive aftereffect on extinction. Motor activity of rats in the "open field" was augmented after neurotensin administration. A conclusion was drawn that the functional effect of neurotensin administration into the caudate nuclei is connected with the normalization of the motivational and emotional state of an animal rather than with the regulation of the motor function.     

Phencyclidine-induced ipsilateral rotation in rats with unilateral 6-hydroxydopamine-induced lesions of the substantia nigra

The effect of phencyclidine (PCP) on rotational behavior in rats with unilateral 6-hydroxydopamine (6-OHDA)-induced lesions of the substantia nigra was examined and compared to the effects of d-amphetamine and apomorphine. PCP, like d-amphetamine, induced ipsilateral rotation indicating a presynaptic effect on dopamine (DA) neurons whereas apomorphine, a direct acting agonist, caused contralateral rotation. Pretreatment with alpha-methyparatyrosine inhibited PCP-induced rotation approximately to the same extent as it inhibited d-amphetamine-induced rotation, but did not significantly reduce apomorphine-induced contralateral turning, further indicating that PCP has a presynaptic effect on DA neurons. Anti-cholinergic effects on PCP may also contribute to the ipsilateral rotation noted.     

Rotation in response to selective dopamine receptor agonists in rats with electrolytic substantia nigra lesions

Rats with unilateral, electrolytic substantia nigra (ESN) lesions were tested for rotation following systemic injections of the D1 dopamine receptor agonist SKF38393 or the D2 agonist quinpirole. Only quinpirole produced significant levels of rotation, which was ipsilateral in direction. This rotation was potentiated by coadministration of the D1 agonist, and was significantly reduced by injections of either a D1 or D2 receptor antagonist. Other groups of lesioned animals were treated with reserpine for 5 days and were then tested for rotation in response to the agonists. In this case, SKF38393 produced significant levels of contralateral rotation, while quinpirole-induced rotation remained ipsilateral; coadministration of the D1 and D2 agonists resulted in pronounced ipsilateral rotation. These results stress a role for D1 receptor mechanisms in producing rotation, and suggest that different striatal efferent pathways mediate rotation in response to selective agonists following ESN lesions.     

Firing properties of substantia nigra dopaminergic neurons in freely moving rats

Single unit recordings were obtained from putative dopaminergic neurons in the substantia nigra of awake, freely moving rats. The cells exhibited waveforms, range of firing rates and types of firing patterns identical to those of identified DA neurons of anesthetized or paralyzed rats. Two firing patterns were observed: single spike activity and a bursting mode with spikes of progressively diminished amplitude and increased duration within each burst. The degree of burst firing varied considerably among the cells and individual cells sometimes switched from one pattern of firing (e.g. predominantly single spike) to another (e.g. bursting), although the determinants of these transitions are, at this time, unclear. Putative DA neurons were inhibited by i.v. apomorphine and excited by i.v. haloperidol. Haloperidol also reversed the apomorphine-induced inhibition of firing. Inhibitions and excitations were associated with a reduction and elevation, respectively, in burst firing. The effects of the two drugs were identical to their effects in immobilized rats. In several cases, a putative DA neuron was observed to fire all of its spikes in near coincidence with at least one other cell with identical electrophysiological characteristics. This form of interaction (i.e. presumed electrical coupling) between DA cells is only rarely observed in anesthetized or paralyzed rats and may play a significant role in the normal functioning of the nigrostriatal DA system.     

Morphological picture of lesions to substantia nigra of rats following intracardial administration of quinolinic acid

Quinolinic acid is tryptophan metabolite and one of the known endogenous substance of selective neurotoxic properties. Morphological studies on noxious effect of quinolinic acid on the black substance of the brain of rats following intracardial administration of this acid were carried out. Dependence of the lesions on the dose and time of use were analysed. No lesions to the black substance were noted following a series of everyday injections of quinolinic acid in the dose of 30 mol/ml for 4 and 8 days. Degenerative changes in the neurons of black substance appeared after a dose of 60 mol/ml injected everyday for 4 days. These changes exacerbated significantly after 8 days. Generalized neuronal defects and intensive degenerative lesions in the preserved neurons with signs of decomposition of fibrous elements of tissular basis followed an administration of quinolinic acid in the dose of 100 mol/ml for 4 and 8 consecutive days.     

Activity of dopaminergic neurons of the substantia nigra following lesions of the neostriatum by kainic acid

Neostriatal lesions by kainic acid provide a good model for studying Huntington's chorea. The pattern of discharge of nigral dopaminergic neurons of rats subjected to a kainate lesions of the caudate nucleus was compared to the nigral activity in control (saline-injected) and normal rats. The observed changes suggest that neostriatal degeneration does not simply induce a nigral dopaminergic hyperactivity but rather a disorganization of their slow and rhythmic pattern of discharge, thus eliciting in the nigral neurons abnormal messages which may reach the motoneurons and participate in the genesis of choreic movements.     

Perikaryal RNA changes within neurons of the caudate-putamen and substantia nigra in soman intoxicated rats

Quantitative azure B cytophotometry was employed to monitor neuronal ribonucleic acid (RNA) metabolism within cholinergic and noncholinergic brain compartments following single sc injections of either 0.5, 0.9 or 1.5 LD₅₀ soman (pinacolyl methylphosphonofluoridate). Dose-dependent losses in neuronal RNA were observed within the cholinergic caudate-putamen (CP) and dopaminergic substantia nigra pars compacta (SNPC), whereas levels of RNA were generally maintained or elevated within the gabaergic substantia nigra pars reticulata (SNPR). CP acetylcholinesterase was inhibited in a dose-dependent fashion. These neuronal RNA changes are perhaps related to seizure activity. The overall data lend support to the hypothesis that alterations in noncholinergic activity contribute to certain manifestations of soman neurotoxicity, such as seizures, which probably stem from an impairment in the functional integrity of both excitatory and inhibitory neuronal elements.     

Specifics of the neurotensin effect on rat motor responses to positive and negative conditioned stimuli

Comparative analysis of effects of neurotensin microinjections into caudate nucleus and substantia nigra on thirst-motivated motor conditioned reactions in rats, was performed. The microinjections facilitated extinction of conditioned reactions in response to negative stimuli and did not affect realization of responses to positive conditioned signals. Behavioral effects of neurotensine in rats are connected with the normalising of motivational and emotional states of animals and may be explained by restoration of monoaminergic systems interaction.