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.     

Emotional state variations in rats during recall of passive avoidance reactions after neurotensin administration into nucleus accumbens of the brain

Behavioral effects of neurotensin administration into the nucleus accumbens were studied in rats with neurotoxic lesions of serotoninergic structures of the dorsal raphe nucleus or periaqueductal grey matter. Changes in recall of passive avoidance conditioned reactions and aftereffects of painful stimulation in the locomotor activity were studied in the "open field" and elevated plus-maze and T-maze tests. The toxin administration into the dorsal raphe nucleus did not impair the recall of the passive avoidance reactions, but enhanced the oppressive aftereffects of painful stimulation, which can specify the development of anxiety in rats. The toxin administration into the periaqueductal grey matter had an opposite effect, which can be considered as a manifestation of the panic state. Neurotensin weakened the above mentioned effects of the toxin and, depending on the evoked emotional disorders, produced the anxiolytic or antipanic effects.     

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.     

Delayed effects of neurotensin microinjections into the substantia nigra on conditioned motor reactions of rats with lesions to serotoninergic neurons

Behavioral effects of neurotensin microinjections into the brain substantia nigra of rats with neurotoxic (5,7-dihydroxytryptamine) lesions of serotoninergic neurons in the dorsal raphe nucleus were studied. It was shown that neurotensin facilitated extinction of conditioned and intertrial reactions to negative (unreinforced) stimuli, but did not change the actualization of positive (with water reward) conditioned signals. Neurotensin-induced effects persisted in subsequent experiments without injections of the peptide. Neurotensin injections reduced the negative emotional states of lesioned animals in the arena during testing conditioned preference. It was concluded that the behavioral effects of neurotensin can be explained by the formation in the lesioned animals of the situational emotional state facilitating adaptive brain functions.     

Effects of pentadecapeptide BPC157 on regional serotonin synthesis in the rat brain: alpha-methyl-L-tryptophan autoradiographic measurements

A novel pentadecapeptide, BPC157, was recently reported to have a large spectrum of in vivo activities, from anti-ulcer to central action on the brain dopaminergic system. The mechanisms of these actions are not well understood. In this study, the evaluation of the effects of acute and repeated administration of BPC157 on serotonin (5-HT) synthesis in the rat brain is reported. The alpha-[14C]methyl-L-tryptophan (alpha-MTrp) autoradiographic method was used to measure regional 5-HT synthesis rates. In the first series of experiments, a single dose treatment of BPC157 (10 microg/kg) administered intraperitoneally 40 min before the alpha-MTrp tracer injection significantly reduced the regional rate of 5-HT synthesis in the dorsal thalamus, hippocampus, lateral geniculate body and hypothalamus. 5-HT synthesis rates in the substantia nigra reticulate and medial anterior olfactory nucleus in BPC157 treated rats were significantly higher than in the control rats. No significant change in the synthesis rate was observed in the raphe nuclei. In the second series of experiments, following a 7-day treatment with BPC157 (10 microg/kg; s.c.), a significant reduction in the 5-HT synthesis rate was observed in the dorsal raphe nucleus, and significant increases were observed in the substantia nigra, lateral caudate, accumbens nucleus and superior olive. This data suggests that BPC157, a gut peptide, influences brain 5-HT synthesis in rats, but we cannot determine, from this data, the mechanism of this action.     

Influence of Fluoxetine on Regional Serotonin Synthesis in the Rat Brain

Abstract: The aim of the present study was to test the hypothesis that there should be a difference between the effects of an acute and an 8-day (chronic) administration of fluoxetine (10 mg/kg) on the rate of serotonin [5-hydroxytryptamine (5-HT)] synthesis. The 5-HT synthesis rate was measured in discrete regions of the rat brain using the α-[¹⁴C]methyl- l -tryptophan autoradiographic method. The results show that the acute and chronic fluoxetine treatments influence the 5-HT synthesis rate in different ways. A single dose of fluoxetine induced a significant increase in 5-HT synthesis in the visual, auditory, and parietal cortices, substantia nigra, hypothalamus, ventral thalamus, and dorsal hippocampus. In contrast, after a chronic treatment a decrease was observed in the substantia nigra, caudate, and nucleus accumbens, the auditory, parietal, sensorimotor, and frontal cortices, and ventral tegmental area. A significant decrease in the rate of 5-HT synthesis was observed in the dorsal raphe after both the single and chronic treatments. The results suggest that extracellular 5-HT has a delayed influence on the brain 5-HT synthesis rate in structures with serotonergic terminals. The findings from the acute study could be important for patients who have just started receiving fluoxetine treatment, as an increase in the 5-HT synthesis rate might occur in the acute phase of their treatment. In addition, the findings from the chronic treatment study might give us a better understanding of how the brain serotonergic system adapts during a prolonged exposure to extracellular 5-HT.     

Reproduction of passive avoidance reactions after neurotensin microinjection into nucleus accumbens of rat brain against the background of reserpine action

The purpose of the study was to reveal the features of the influence of neurotensin injected into the nucleus accumbens on behaviour of rats after systemic administration of reserpine in the dose of 2 mg/kg. Reprodution of passive avoidance conditioned reactions, painful stimulation aftereffects on locomotor activity in the "open field", and behavior in the elevated plus-maze were studied. It was shown that reserpine administration impaired the reproduction of passive avoidance reactions and weakened the oppressing aftereffect of painful stimulation, which can be due to a decrease in anxiety in rats. Neurotensin prevented disorders in the defensive behavior evoked by reserpine and intensified the state of anxiety in the elevated plus-maze. The positive influence ofneurotensin on the reproduction of passive avoidance can be associated with the recovery of the anxiogenic effect of painful stimulation destroyed by reserpine. Thus, neurotensin injected into the nucleus accumbens could normalize the balance of brain monoaminergic systems.     

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.     

Ultrastructural differentiation within the central nervous system between indolamines and catecholamines by energy dispersive X-ray analysis following paraformaldehyde pretreatment

Dense bodies containing high amounts of chrome were localized in the perikarya of substantia nigra and dorsal raphe neurons following the cytochemical reaction of endogenous dopamine and serotonin (respectively) with glutaraldehyde-dichromate (GDC). Energy dispersive X-ray analysis of these bodies revealed chrome levels two to four times higher than those recorded from the cytoplasmic background. Pretreatment with paraformaldehyde blocked the GDC reaction within the dense bodies in the substantia nigra (chrome levels similar to background), while the chrome levels in the dense bodies of the raphe neurons remained elevated. This demonstrates that pretreatment with paraformaldehyde allows selective localization of central nervous system serotonin stores by the GDC technique.     

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.     

Effect of the administration of 5,6-dihydroxytryptamine to the amygdala and dorsal raphe nucleus on plasma renin activity

The effect of injections of 5,6-dihydroxytryptamine, a potent and selective neurotoxic of serotonin neurons, into amygdala and dorsal raphe mesencephalic nucleus on the plasma renin activity has been studied in male Wistar rats. Plasma renin activity was estimated on 2nd, 4th, Tth and 14th day after injections in both areas. The administration of 5,6-dihydroxytryptamine in amigdala produced a significant decrease in plasmatic renin activity between 2nd and 4th day, but the inverse effect between 7th and 14th day. Similar effects were found after injections in dorsal raphe nucleus. The contents of cerebral 5-HT were simultaneously evaluated in the entire brain when the drug was implanted in dorsal raphe, and only in amygdaloid tissue when the injection was restricted to this area. A significant decrease in serotonin content was produced 7th day in both places, while partial recuperation was found toward 14th day. The results, especially the ones related to the chemical lesion of dorsal raphe nucleus, suggest that serotoninergic brain systems are involved, as stimulators, in the control of the dynamics of renin-angiotensin system.     

Characterization and visualization of neurotensin binding to receptor sites in human brain

The binding of monoiodo [125I-Tyr3]-neurotensin to human brain was characterized and visualized using radioreceptorassay and autoradiographic techniques. Specific binding to homogenates of human substantia nigra at 25 degrees C was maximal at 20 min, reversible and saturable. Scatchard analysis of equilibrium data indicated the existence of two populations of binding sites with Kd values of 0.26 nM and 4.3 nM. Corresponding binding capacities were 26 and 89 fmol/mg of protein. Neurotensin analogs inhibited the binding of iodinated neurotensin with relative potencies that demonstrated the crucial role of the C-terminal hexapeptide portion of neurotensin for binding to its receptors. Autoradiography of human substantia nigra sections incubated with iodinated neurotensin revealed high levels of specific binding in the nucleus paranigralis and substantia nigra, pars compacta, and low levels in the substantia nigra, pars reticulata.     

1, 2, 3, 4-Tetrahydro-2-Methyl-4, 6, 7-Isoquinolinetriol Depletes Catecholamines in Rat Brain

1, 2, 3, 4-Tetrahydro-2-methyl-4, 6, 7-isoquinolinetriol (TMIQ) was synthesised and tested for activity as a dopamine-depleting agent in rat brain. After intracerebroventricular infusion, TMIQ caused reductions in dopamine concentrations in substantia nigra, striatum, hypothalamus, and dorsal raphe, and reduction in noradrenaline concentrations in locus coeruleus. TMIQ also reduced 5-hydroxytryptamine concentrations in dorsal raphe and substantia nigra, although with a lower potency. Comparisons between TMIQ and MPTP showed that they were approximately equipotent in depleting dopamine in the substantia nigra, hypothalamus, and dorsal raphe. Pretreatment of animals with a combination of monoamine oxidase A and B inhibitors completely prevented the TMIQ-induced reductions in dopamine concentrations in substantia nigra and hypothalamus. Direct unilateral intrastriatal injections of TMIQ produced marked ipsilateral reductions in striatal dopamine, correlating with a behavioural response consisting of turning towards the side of injection. The results suggest that TMIQ should be evaluated further as a possible MPTP-like compound, which may derive from endogenous β-hydroxylated catecholamines.     

Neurochemical effects of the endocannabinoid uptake inhibitor UCM707 in various rat brain regions

To date, UCM707, (5Z,8Z,11Z,14Z)-N-(3-furylmethyl)eicosa-5,8,11,14-tetraenamide, has the highest potency and selectivity in vitro and in vivo as inhibitor of the endocannabinoid uptake. Its biochemical, pharmacological and therapeutic properties have been intensely studied recently, but the information on its capability to modify neurotransmitter activity, which obviously underlies the above properties, is still limited. In the present study, we conducted a time-course experiment in rats aimed at examining the neurochemical effects of UCM707 in several brain regions following a subchronic administration (5 injections during 2.5 days) of this inhibitor in a dose of 5 mg/kg weight. In the hypothalamus, the administration of UCM707 did not modify GABA contents but reduced norepinephrine levels at 5 h after administration, followed by an increase at 12 h. Similar trends were observed for dopamine, whereas serotonin content remained elevated at 1 and, in particular, 5 and 12 h after administration. In the case of the basal ganglia, UCM707 reduced GABA content in the substantia nigra but only at longer (5 or 12 h) times after administration. There were no changes in serotonin content, but a marked reduction in its metabolite 5HIAA was recorded in the substantia nigra. The same pattern was found for dopamine, contents of which were not altered by UCM707 in the caudate-putamen, but its major metabolite DOPAC exhibited a marked decrease at 5 h. In the cerebellum, UCM707 reduced GABA, serotonin and norepinephrine content, but only the reduction found for norepinephrine at 5 h reached statistical significance. The administration of UCM707 did not modify the contents of these neurotransmitters in the hippocampus and the frontal cortex. Lastly, in the case of limbic structures, the administration of UCM707 markedly reduced dopamine content in the nucleus accumbens at 5 h, whereas GABA content remained unchanged in this structure and also in the ventral-tegmental area and the amygdala. By contrast, norepinephrine and serotonin content increased at 5 h in the nucleus accumbens, but not in the other two limbic structures. In summary, UCM707 administered subchronically modified the contents of serotonin, GABA, dopamine and/or norepinephrine with a pattern strongly different in each brain region. So, changes in GABA transmission (decrease) were restricted to the substantia nigra, but did not appear in other regions, whereas dopamine transmission was also altered in the caudate-putamen and the nucleus accumbens. By contrast, norepinephrine and serotonin were altered by UCM707 in the hypothalamus, cerebellum (only norepinephrine), and nucleus accumbens, exhibiting biphasic effects in some cases.     

大白鼠脚内核的传入性联系

众所周知,肉食动物和大白鼠的脚内核,相当于灵长类的内侧苍白球(Nagy et al.1978;Fox and Schmitz 1944);它们的细胞形态、传入及传出均相同。早期以及近年来的一些研究工作者,虽然在研究其他核团的投射时,联系到一些本核团的传入,但是尚缺乏对本核团传人的系统研究。本实验即是应用辣根过氧化物酶的逆行传递法来研究大白鼠脚内核的传入性联系。     

Opiocortin and catecholamine projections to raphe nuclei

Afferent projections to the nucleus raphe magnus (NRM) and dorsal raphe nucleus (DRN) were identified using retrograde transport of horseradish peroxidase conjugated wheat germ agglutinin (HRP-WGA). Neurons were labeled in important nociceptive regions including periaqueductal gray (PAG), arcuate nucleus, lateral hypothalamus and medial thalamic nuclei following both injections. We have immunocytochemically identified opiocortin/WGA neurons in the arcuate nucleus following NRM and DRN injections. Dual stained catecholamine/WGA perikarya were found in zona incerta, locus coeruleus, substantia nigra, nucleus tractus solitarius and adjacent A2, C2 and C3, lateral paragigantocellular reticular nucleus/C1 and lateral reticular nucleus/A1 following DRN injections and in zona incerta, substantia nigra, nucleus tractus solitarius/A2 and lateral reticular nucleus/A1 after NRM injections. These results provide further evidence for opiocortin and catecholamine modulation of analgesia.     

The comparative effect of serotonin agonists on the presynaptic and somatodendritic autoreceptors of serotoninergic neurons

Experimenting on the slices of cortex and dorsal raphe nucleus of midbrain of rats which were incubated with 3H-hydroxytrypta-mine (3H-HT) studies showed the influence of series of serotonin agonists on the spontaneous and electrically stimulated release of 3H-HT from the slices. It was established that the serotonin in concentration of 10(-5) mol/l similarly inhibits the release of 3H-HT from the electrically stimulated slices of the brain cortex (78.6%) and on slices of the dorsal raphe nucleus of the midbrain (81.6%) had no effect on the spontaneous release of serotonin. The serotonin agonists in order of increasing ability to inhibit the electrically stimulated release of 3H-HT from the cortex slices is as follows: ipsapirone (0%), 8-OH-DPAT (23%), kampirone (26.5%), 1.2-PP (28.6%), kaplapirone (35.7%), buspirone (48%) and TFMPP (67%). On the ability to influence the release of 3H-HT from the electrically stimulated slices of the dorsal raphe nucleus of the midbrain of the rats serotonin agonists were in the following order: TEMPP (12.3%), kampirone (40%), 1.2-PP (42.9%), ipsapirone (52%), 8-OH-DPAT (54.1%), kampirone (57.2%) and buspirone (65.3%). It is suggested that the effect of both ipsapirone, kampirone and 8-OH-DPAT is greatly localized on the somato-dendritic synapses P1A-HT receptors, TEMPP is more on the terminal axons of HT-ergic neurones while kampirone, buspirone and active metabolite 1.2-PP act on the presynaptic and somatodendritic autoreceptors of serotonin.     

In vivo release of dopamine during perfusion of neurotensin in substantia nigra of the unrestrained rat

The functional effect of neurotensin on the kinetics of dopamine (DA) release in the substantia nigra of the freely moving rat was investigated. After guide tubes for push-pull perfusion were implanted stereotaxically just above the substantia nigra, endogenous stores of DA in this structure were labelled by micro-injection of 0.02–0.05 μCi of [¹⁴C]-DA. Then an artificial cerebrospinal fluid (CSF) was perfused within the site at a rate of 20 μl/min at successive 5 min intervals. Neurotensin added to the CSF perfusate in concentrations of 0.05–0.1 μg/μl evoked an immediate, Ca⁺⁺ dependent release of DA from sites directly within the substantia nigra or a delayed efflux when the peptide was perfused at the edge of this structure. Neurotensin failed to affect the pattern of release of this monoamine at sites which were not within the substantia nigra. Further, the body temperature of the rat also was not altered by neurotensin at any of the sites of perfusions. A relatively inactive analogue of the peptide, [D-Arg]⁹ neurotensin, was essentially without effect on DA activity. In double isotope experiments in which the substantia nigra of the rat was labelled with both [³H]-5-HT and [¹⁴C]-DA, the perfusion with neurotensin failed to affect 5-HT efflux while the release of DA was enhanced. Chromatographic analysis of the metabolites of DA in samples of push-pull perfusates revealed that neurotensin enhanced significantly the level of DOPAC and HVA. Overall, these results demonstrate that in the unrestrained rat neurotensin acts selectively within the substantia nigra to alter the presynaptic, Ca⁺⁺ dependent release of DA. It is suggested that the mechanism by which the tri-decapeptide functions within this brainstem structure is through its modulation of nigral dopaminergic neurons.     

Regulation of release processes in central serotoninergic neurons

Different technical, physiological and biochemical aspects concerning the study of the release of 5-HT are discussed herein. Isotopic methods are the most suitable techniques since these allow the release of 3H-5-HT to be measured after having determined the identity of the labelled compounds formed from 3H-tryptophan by co-chromatography. Under these conditions, the 3H-amine released in the superfusates comes from serotoninergic nerve endings, since tryptophan hydroxylase is exclusively localized in serotoninergic neurons. Moreover, it appears that newly synthesized 5-HT is preferentially released. The release of 5-HT is dependent on neuronal activity, but is not always linked to the synthesis of 5-HT. The increase in the firing rate of serotoninergic cell bodies by a local application of glutamate in the area of the nucleus raphe dorsalis induces a marked increase n the release of 5-HT in the caudate nucleus; an opposite effect is observed after cooling this region. The local depolarization of serotoninergic terminals located in the caudate nucleus increases the release of this amine. This effect is blocked by TTX. LSD reduces the stimulating effect of KCl, thus indicating that the release of 5-HT can be controlled at a presynaptic level. In addition, the release of the amine is dependent on the presence of calcium. Serotoninergic neuronal activity can be controlled at the preterminal or at the cell body levels by the activity of other neuronal systems. The effects of the release of dopamine from dendrites, and that of GABA in the substantia nigra are reported herein. Furthermore, changes in the activity of the dopaminergic, gabaergic and serotoninergic systems innervating the nucleus raphe dorsalis modulate the release of 5-HT, measured both in the caudate nucleus and in the nucleus raphe magnus. Finally, it has been reported that the release of 5-HT can be estimated in the raphe nuclei dorsalis and magnus. It has been shown that the amounts of 3H-5-HT continuously formed from 3H-TRP and released in the nucleus raphe dorsalis are much greater than those estimated in the caudate nucleus or in the substantia nigra. Although the quantities of endogenous 5-HT measured in the nucleus raphe dorsalis are the highest in the brain, this structure presents only a few serotoninergic nerve endings. This raises the question of the origin of the 5-HT released in serotoninergic nuclei. A possible dendritic release of 5-HT is discussed.