Early and widespread normalization of dopamine-neuropeptide Y interactions in the rat striatum after transplantation of fetal mesencephalon cells.

Graft-to-host interactions were examined at cellular level, by measuring changes in the immunoreactivity of striatal interneurons expressing neuropeptide Y after dopamine denervation and transplantation of fetal mesencephalon neurons into the striatum of adult rats. Mesencephalic cell suspensions were implanted unilaterally into the dorsal part of the striatum in rats two weeks after intranigral injection of 6-hydroxydopamine. One month and three to four months later, rats showing abolition of amphetamine-induced turning were perfused. Serial brain sections containing intrastriatal grafts were treated for tyrosine hydroxylase and neuropeptide Y immunocytochemistry, and neuropeptide Y-immunoreactive neurons were quantified in various parts of the striatal surface and compared with the striatum of controls and age-matched rats with lesions. Biochemical analyses of dopamine and dihydroxyphenyl acetic acid tissue levels and [3H]dopamine uptake were also performed on striatal samples from similar groups of normal, lesioned and transplanted rats. As early as one month post-grafting, a complete reversal of the increase in the number of neuropeptide Y-immunoreactive neurons occurring after 6-hydroxydopamine lesion was observed in dopamine-grafted animals, although a partial restoration of the tyrosine hydroxylase immunostaining and a recovery of 8% dopamine tissue level were observed in the striata of grafted as compared to normal rats. This effect on the host immunoreactivity was found to be specific to dopamine grafts, since no reversal was observed in sham-spinal cord-transplanted rats. Moreover, similar degrees of normalization were recorded either in the total striatum, or in the area immediately adjacent to the graft, or even in the zone most sensitive to dopamine denervation in terms of neuropeptide Y immunoreactivity. No more pronounced functional effects were observed three to four months after transplantation. These data suggest that grafted dopamine neurons are able to induce rapid and extensive host responsiveness, possibly by means of mechanisms involving synaptic and diffuse release of dopamine and adaptive changes in the host brain. These data may provide a cellular basis for interpreting larger behavioural recoveries than those expected to occur with dopamine grafts in view of the partial restoration of the dopaminergic innervation.

Depletion in serotonin decreases neurogenesis in the dentate gyrus and the subventricular zone of adult rats.

During adulthood, neuronal precursor cells persist in two discrete regions, the subventricular zone and the hippocampal subgranular zone, as recently demonstrated in primates. To date, a few factors such as adrenal steroids and trophic factors are known to regulate adult neurogenesis. Since neuronal activity may also influence cellular development and plasticity in brain, we investigated the effects of serotonin depletion on cell proliferation occurring in these regions. Indeed, in addition to its role as a neurotransmitter, 5-hydroxytryptamine (serotonin) is considered as a developmental regulatory signal. Prenatal depletion in 5-hydroxytryptamine delays the onset of neurogenesis in 5-hydroxytryptamine target regions and 5-hydroxytryptamine promotes the differentiation of cortical and hippocampal neurons. Although in the adult brain, a few studies have suggested that 5-hydroxytryptamine may play a role in neuronal plasticity by maintaining the synaptic connections in the cortex and hippocampus, no information is actually available concerning the influence of 5-hydroxytryptamine on adult neurogenesis. If further work confirms that new neurons can be produced in the adult human brain as is the case for a variety of species, it is particularly relevant to determine the influence of 5-hydroxytryptamine on neurogenesis in the hippocampal formation, a part of the brain largely implicated in learning and memory processes. Indeed, lack of 5-hydroxytryptamine in the hippocampus has been associated with cognitive disorders, such as depression, schizophrenia and Alzheimer's disease. In the present study, we demonstrated that both inhibition of 5-hydroxytryptamine synthesis and selective lesions of 5-hydroxytryptamine neurons are associated with decreases in the number of newly generated cells in the dentate gyrus, as well as in the subventricular zone.

Behavioural recovery of rats grafted with dopamine cells after partial striatal dopaminergic depletion in a conditioned reaction-time task.

The functional effects of grafts of dopamine-rich ventral mesencephalic suspension transplanted in a partially dopamine-depleted striatum were studied in rats performing a reaction-time motor task. The animals were trained to depress a lever, hold it down and release it within a limited period of time (700 ms) after the onset of a visual conditioned stimulus to obtain a food reward. The animals' performances were tested daily for up to two months after transplantation and for up to three months in the case of the animals with lesion only (bilateral striatal 6-hydroxydopamine injection). The baseline performances of the sham-operated control animals tended to improve, whereas the performances of the lesioned rats were significantly disrupted throughout the three months test. The majority of the animals (13/21) in the lesion group showed severe deficits mainly reflected in an increase in the number of the anticipated responses (premature release of the lever before the visual stimulus), and also in the number of the delayed responses (lever release after the time limit) recorded after dopamine depletion. The remaining animals (8/21) exhibited mild deficits (delayed responses only). These differences in the performance deficits appeared to be in relation to the extent of the dopamine denervation within the striatum assessed by the tyrosine hydroxylase immunostaining. Grafted animals showed a large number of dopamine fibers in the reinnervated striata and most of them (73%) significantly improved the reaction-time performance after transplantation. In the most severely impaired animals the number of anticipated errors was totally reversed within one month post-grafting, while the number of delayed responses remained high after transplantation. The performances of the less severely impaired animals returned more rapidly (within three weeks) to the pre-operative levels. The results show that intrastriatal ventral mesencephalic transplants are able to induce substantial or complete recovery in a complex reaction-time task. In the present model for partial dopamine depletion of the striatum, the mechanisms underlying the graft-induced recovery probably involve the participation of endogenous dopamine neurons acting in addition to, and/or in synergy with the dopamine-rich grafted tissue so that a functional level of dopaminergic transmission is restored in transplanted animals.

Ultrastructural features of the serotonin innervation in adult rat hippocampus: an immunocytochemical description in single and serial thin sections.

This study was aimed at characterizing the fine-structural features of the normal serotonin (5-HT) innervation in adult rat hippocampus, by means of electron microscopic immunocytochemistry with a polyclonal antiserum against 5-HT-glutaraldehyde-protein conjugate (donated by Michel Geffard, Bordeaux). Two hippocampal sectors were examined, at mid-level along the septo-temporal axis: CA3-a of Ammon's horn and crest of the dentate gyrus (DG-c). A large number of axonal varicosities (terminals) were sampled in single ultrathin sections, to achieve a statistically significant comparison of their size and of their relative frequency of synaptic specialization, junctional targets and juxtaposed elements, between the oriens and the radiatum layer of CA3-a, and the molecular and the polymorph layer of DG-c. In both CA3-a layers, the microenvironment of the immunostained terminals was also compared to that of a population of unlabeled varicosities randomly selected from the same micrographs. Moreover, 57 varicosities from the oriens and the radiatum layer of CA3-a were visualized in a long series of thin sections, allowing for their examination from end to end in 43 instances. As measured in single sections, hippocampal 5-HT varicosities were of comparable diameter (0.57 microns on the average) in the two anatomical sectors and four neuropil layers examined. As extrapolated stereologically to whole varicosities, the proportion making a synaptic membrane specialization (synaptic incidence) ranged from 18 to 33% (average of 24%), without statistically significant differences between the two sectors and four layers. The synaptic incidence determined directly from serial sections of CA3-a (18%) was nearly identical to that extrapolated from single sections (18.1% in the oriens and 19.5% in the radiatum layer). In both CA3-a and DG-c, the 5-HT varicosities showing a junctional complex were slightly larger than their non-junctional counterparts. In CA3-a, only dendritic shafts were targeted by synaptic 5-HT varicosities, whereas in DG-c there were also a few axo-spinous synapses. The microenvironment of CA3-a 5-HT varicosities differed markedly from that of randomly selected unlabeled varicosities, due to its much lower frequency of synaptic targets and higher frequency of juxtaposed axonal varicosities, at least in the radiatum layer. In all four layers examined, other axonal varicosities were indeed the most frequently encountered neuronal element in the immediate vicinity of immunostained 5-HT varicosities. Neurites and dendritic shafts were also common, but dendritic spines (4%) were relatively infrequent.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural features of serotonin neurons grafted to adult rat hippocampus: an immunocytochemical analysis of their cell bodies and axon terminals.

Serotonin (5-HT) immunocytochemistry was used at the electron microscopic level to examine 5-HT neurons reinnervating and hyperinnervating the hippocampus of adult rat, three to four months after a total 5-HT denervation and subsequent graft of embryonic raphe cells. The study focused on immunostained nerve cell bodies, dendrites and axon terminals (varicosities) in the core of grafts, and on a large single section sampling of axon terminals from a CA3 and a dentate gyrus sector of the outgrowth, which were systematically compared to the endogenous 5-HT innervation of the same regions described in a companion paper. The shape, size and synaptic investment of the grafted 5-HT somata and their dendrites resembled those of in situ 5-HT neurons. Clusters of small, clear vesicles were sometimes seen along these 5-HT dendrites. 5-HT axonal varicosities were fairly numerous in the core. A few were directly apposed to, or made asymmetrical synaptic contact with the immunostained dendrites and perikarya, but the vast majority showed no indication of junctional specialization (synaptic incidence of 19%, as stereologically extrapolated for whole varicosities). Occasional myelinated 5-HT axons were also present in the core of grafts. In the two outgrowth sectors, the graft-borne 5-HT varicosities were similar in size, content, frequency of synaptic contact and identity of junctional and appositional elements, irrespective of their laminar location. Moreover, none of these parameters were significantly different from those of the endogenous innervation. Notably, in spite of their excessive number, the synaptic incidence of the outgrowth 5-HT varicosities remained inferior to 20%. The similarity between the respective microenvironments of the supernumerary, graft-borne 5-HT terminals and of their normal counterparts could only be explained by a random intratissular distribution of these varicosities in both the normal and the grafted hippocampus. Thus, in spite of their transplantation and growth into an abnormal milieu, and the fact that they hyperinnervated the host tissue, the grafted embryonic 5-HT neurons appeared committed to express a particular set of intrinsic and relational morphological features corresponding to their normal adult characteristics.

Selective effects of partial and severe lesions of the serotonergic systems on Met-enkephalin and substance P neurons in rat basal ganglia.

The effects of partial (80%) vs. severe (> 95%) depletion of serotonin (5-HT) on peptide expression in basal ganglia were examined using immunocytochemical and in situ hybridization histochemical approaches. Topographical analysis of the changes in Met-enkephalin (Met-enk) and substance P (SP) levels were performed on the rat striatum, globus pallidus and substantia nigra 3 weeks after injecting 3 microl (partial lesion) or 6 microl (severe lesion) 5,7-dihydroxytryptamine (6.6 microg/microl) into the anterior raphe nuclei. Both kinds of lesion led to significant increases (39-42%) in Met-enk immunoreactivity in the striatum; a corresponding increase (21%) was detected in the globus pallidus only after severe 5-HT depletion. Only the severe lesion increased the SP immunoreactivity in the striatum (32%) and substantia nigra (26%). Neither striatal preproenkephalin nor preprotachykinin levels showed significant differences with the control values. These results suggest that the neuronal accumulation of Met-enk or SP may be attributable to post-transcriptional events, such as a blockade of the peptide release, and that 5-HT may, thus, exert a facilitatory influence on the striatal output neurons. The results obtained after partial lesion indicate a preferential sensitivity of striatal Met-enk vs. SP containing terminals to the 5-HT denervation. These differences are illustrated in selective regional changes in peptide labeling. These data point to some balance exerted by the serotonergic and dopaminergic inputs on these neuronal populations.

Distribution and quantification of 5-HT nerve cell bodies in the nucleus raphe dorsalis area of C57BL and BALBc mice. Relationship between anatomy and biochemistry.

BALBc and C57BL mice have been shown to have a different 5-HT metabolism. The present study compares the number and the distribution of 5-HT cell bodies in the nucleus raphe dorsalis area (B7 + B6) of these strains. By using 5-HT immunohistochemistry, we found a higher number of 5-HT neurons in the most caudal part of NRD (B6) of BALBc mice compared to C57BL. This difference may be correlated with a higher level of endogenous 5-HT, a higher uptake capacity toward exogenous [3H]5-HT, and a lower release of the amine in this same area of BALBc mice compared to C57BL. It could also imply a significant participation of the nerve cell bodies in the regulation of 5-HT transmission inside 5-HT nuclei.

Early postnatal development of EEG and sleep-waking cycle in two inbred mouse strains.

The postnatal maturation of brain electrical activity and sleep-waking cycle were studied in two inbred mouse strains (C57BL and BALBc), previously differentiated in their sleep patterns at adult age. Genetic differences are evident during the first postnatal period (until day 12) in the maturation of electrical activity which is both earlier and slower in C57BL than in BALBc. On the other hand, from day 12 onwards, as soon as the sleep-waking cycle can be defined by using EEG morphology to select quiet sleep (QS) and active sleep (AS) C57BL is characterized by a higher amount of AS and a lower amount of waking (W) than BALBc, as found in juvenile and adult mice. These differences appear a little later when the recordings are performed on animals which are isolated instead of being left with the rest of the litter.

Sleep variations in C57BL and BALBc mice from 3 weeks to 14 weeks of age.

The evolution of sleep patterns during the diurnal period was studied in C57BL and BALBc mice from 3 to 14 weeks of age. Quantitative analysis of the hypnograms reveals that the main sleep changes occur between weeks 3 and 4 in the two strains. This period is characterized by a decrease of the percentage of paradoxical sleep in BALBc strain, due to a simultaneous drop in the mean number and duration of the episodes. During this time C57BL strain exhibits an increase in the percentage of slow wave sleep, resulting from a rise in the mean number of episodes. At the same time the percentage of awake state decreases in C57BL mice. In the adults these changes result in differences between the strains in sleep pattern that are characterized by a higher percentage of paradoxical and slow wave sleep in C57BL than in BALBc mice. As regards the results obtained, the maturation of sleep mechanisms and particularly of the paradoxical sleep seems to be different in C57BL and in BALBc mice.

Combined cholinergic and serotonergic denervation of the forebrain produces severe deficits in a spatial learning task in the rat.

The purpose of the present experiments was to study the effects of a combined cholinergic and serotonergic denervation of the rat forebrain on spatial learning using the Morris water maze task. Experiment 1 compared the acute effects of a radiofrequency lesion of the septum, an intraventricular 5,7-dihydroxytryptamine (5,7-DHT) lesion, and a combined septal plus 5,7-DHT lesion. Although the 5,7-DHT lesion alone did not produce any significant deficits in the water maze task, the lesion greatly potentiated the learning impairments produced by the septal lesion. Thus, the rats with both lesions combined showed severe difficulties in finding the platform and they did not develop any place navigational search strategy. This effect was not dependent on any effect on swimming ability or locomotor activity. The long-term effects of the combined septal and 5,7-DHT lesion was investigated in experiment 2, where the rats were tested in the water maze both 5 and 24-25 weeks after surgery. In this experiment, the rats showed the same severe deficits in spatial learning in both tests, showing that the impairments remain for long periods and after extended training. The results show that a combination of a cholinergic and a serotonergic denervation of the rat forebrain produces pronounced impairments in spatial learning in the Morris water maze task, and that this effect is long-lasting. This indicates that the recently proposed serotonergic deficit in patients with Alzheimer's disease may contribute importantly to the cognitive disabilities in these patients.

Serotonin neurons grafted to the adult rat hippocampus. II. 5-HT release as studied by intracerebral microdialysis.

Extracellular levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were monitored by microdialysis in the hippocampal formation previously denervated of its serotonergic input by an intraventricular injection of 5,7-dihydroxytryptamine (5,7-DHT), and in 5,7-DHT denervated hippocampi reinnervated by grafted fetal rat serotonin neurons. Two weeks after 5,7-DHT lesion, baseline 5-HT release was reduced to levels below detection, and KCl- and p-chloro-amphetamine-evoked release was reduced by 90-95%. In the chronically denervated hippocampus (3 months after lesion), baseline 5-HT release had recovered to near-normal levels, but KCl- and p-chloroamphetamine-evoked release remained severely impaired. Addition of the 5-HT re-uptake blocker indalpine to the perfusion medium induced a 5-6-fold increase in serotonin overflow in the normal hippocampus, while the serotonin overflow in the 5,7-DHT denervated hippocampus remained unaffected. The intrahippocampal fetal raphe transplants restored 5-HT release to near-normal levels, not only under baseline conditions but also in the presence of re-uptake blockade. Both KCl- and p-chloroamphetamine-induced release had recovered in the grafted hippocampus and the responses were even greater than those seen in normal animals. In both normal and grafted hippocampus addition of the sodium channel blocker tetrodotoxin reduced 5-HT overflow to the level seen in the denervated hippocampus. The new hippocampal serotonin innervation, established by the grafts, was markedly denser than normal, and the tissue 5-HT and 5-HIAA levels were 3-4-fold higher than normal in the grafted hippocampi. The 5-HIAA level in the perfusate collected from the grafted hippocampi showed a similar increase above normal, whereas 5-HT release was maintained within the normal range, both under baseline conditions and in the presence of re-uptake blockade. The results indicate that the grafted serotonergic raphe neurons are spontaneously active at the synaptic level, despite their ectopic location. The ability of the grafted neurons to maintain 5-HT release within the normal range suggests that local regulatory mechanisms at the terminal level can compensate for abnormalities in the graft-derived innervation density.

Serotonin neurons grafted to the adult rat hippocampus. I. Time course of growth as studied by immunohistochemistry and biochemistry.

The maturation and growth of fetal serotonergic raphe neurons have been studied immunohistochemically and biochemically between 1 week and 5 months after grafting to the hippocampal formation in 5,7-dihydroxytryptamine-pretreated adult rats. The average number of surviving neurons in each group was 1800, which is equivalent to approximately 20% of the potential number of serotonin neurons contained in the grafted cell suspension. The fetal raphe cells, which were taken from 12-14-day-old embryos, had developed strong serotonin immunoreactivity at 1 week after transplantation, and the number of serotonin cells present at 1 week was similar to that found at later time points. Fiber outgrowth was demonstrable already at 1 week but the serotonin-positive fibers were restricted to the areas close to the graft. Single fibers, however, could be traced for distances of up to 500-800 microns into the host hippocampus and dentate gyrus. At later time points, the graft-derived serotonin-immunoreactive fiber network extended to cover the entire hippocampal formation. At the longest postoperative time point, 7 weeks and 5 months, some of the animals exhibited extensive hyperinnervation patterns throughout the dorsal parts of the hippocampus and the dentate gyrus. Consistent with these immunohistochemical observations, supranormal serotonin levels developed with time after transplantation in the grafted hippocampi from an average of 5% of normal at 1 week, to 28% of normal at 3 weeks, 146% of normal at 7 weeks, and 216% of normal at 5 months. Although the recovery of 5-hydroxyindoleacetic acid (5-HIAA) paralleled that of serotonin (5-HT), the increase in the metabolite concentrations was less than that of the amine, indicating a change in the turnover or metabolism of serotonin in the grafted neurons over time. Thus, the 5-HIAA:5-HT ratio was higher than normal at 3 weeks post-grafting (when the host hippocampus was only partially reinnervated); it was similar to normal at 7 weeks, and it tended to be lower than normal in the hyperinnervated specimens at 5 months' survival. A regression analysis revealed a significant inverse correlation between the hippocampal 5-HT concentration and the 5-HIAA:5-HT ratio in the graft-reinnervated hippocampal formation. In conclusion, the grafted serotonergic raphe neurons, in contrast to other types of aminergic neurons, exhibited a prominent tendency to form extensive hyperiinnervation patterns in the previously dennervated host target.(ABSTRACT TRUNCATED AT 400 WORDS)

5-HT concentration in cat's brain.

Endogenous concentrations of TRP, 5-HT and 5-HIAA were determined in the different cortical and subcortical areas of adult cat's brain, using ion-exchange chromatography and spectrofluorimetric methods. Tryptophan is homogeneously distributed in all structures of the brain. 5-HT is mainly accumulated in the brain stem, hypothalamus and caudate nucleus, but also in cortical areas as olfactory and piriform gyrus. The ratio 5-HIAA/5-HT shows that 5-HT utilization is higher in the structures containing small amounts of 5-HT. Using the radioenzymatic assay described by Saavedra et al. (1973), the rostrocaudal distribution of 5-HT content was determined in olfactory and piriform cortex. Important concentrations of 5-HT were detected in the prepiriformis and anterior amygdaloidea areas. Using the same assay and microdissection on frozen frontal slices of the brain, the distribution of 5-HT concentration throughout the different layers of cortical areas was studied. Piriform, olfactory and sigmoid cortex present high concentrations in the superficial layers, including the molecular one. These results were confirmed by uptake studies, made on crude homogenates from frozen tissue, suggesting that 5-HT is mainly contained in the most external cortical terminals.

Selective increases in serotonin 5-HT1B/1D and 5-HT2A/2C binding sites in adult rat basal ganglia following lesions of serotonergic neurons.

Quantitative autoradiography was used to examine possible adaptive changes in serotonin 5-HT1B/1D and 5-HT2A/2C receptor binding sites in adult rat basal ganglia, after partial or severe lesions of serotonergic neurons produced by intraraphe injections of variable amounts of 5,7-dihydroxytryptamine. In controls, the 5-HT1B/1D sites labeled with S-CM-G[125I]TNH2 were evenly distributed in the core and the shell of the nucleus accumbens. The density of 5-HT1B/1D sites was higher in the ventral than dorsal part of the striatum and no regional differences were detected along the rostrocaudal axis of the structure. The 5-HT2A/2C sites labeled with [125I]DOI were preferentially distributed in the mediodorsal striatum and higher densities were detected in the shell than core of the nucleus accumbens. Following 5,7-dihydroxytryptamine injections, there were no changes in binding of either receptor subtype after partial lesions entailing 80-90% 5-HT depletions. After severe 5-HT depletions (over 95%), large increases in 5-HT1B/1D binding were observed in the substantia nigra (78%), but no changes took place in the globus pallidus. Increases in 5-HT1B/1D binding were also detected in the shell of the nucleus accumbens (27%). Similar sized increases in 5-HT2A/2C binding (22%) were restricted to the medial striatum. The present results suggest a preferential association between 5-HT1B/1D receptors and the striatonigral neurons containing substance P, as indicated by the striatal distribution of these receptors and their selective increases in the substantia nigra after severe 5-HT deprivation. We recently proposed a similar relationship between the 5-HT4 receptors and the striatopallidal neurons containing met-enkephalin. Moreover, the increases in 5-HT1B/1D binding in the substantia nigra and in the shell of the nucleus accumbens reinforce the view of an implication of this receptor subtype in motor functions. In contrast, the prominent increases in 5-HT2A/2C binding after severe 5-HT deprivation as restricted to the medial region of the striatum and suggest up-regulation of most probably 5-HT2C receptors in a region implicated in cognitive functions.

Differential effects of serotonin (5-HT) lesions and synthesis blockade on neuropeptide-Y immunoreactivity and 5-HT1A, 5-HT1B/1D and 5-HT2A/2C receptor binding sites in the rat cerebral cortex.

The present study was aimed at comparing the effects of serotonin (5-HT) synthesis blockade using chronic administration of p-chlorophenylalanine (PCPA) and 5,7-dihydroxytryptamine injections of variable volume (3 vs. 6 microl) on the density of NPY immunoreactive (Ir) neurons and binding of [3H]8-OH-DPAT, S-CM-G[125I]TNH2 and [125I]DOI to 5-HT1A, 5-HT1B/1D, and 5-HT2A/2C receptors in rat cortical regions. Three weeks after large but partial (89% depletion in 5-HT tissue concentration) lesions of 5-HT neurons no changes in neither NPY immunoreactivity nor 5-HT receptor binding were detected. The complete 5,7-DHT lesions produced increases in the number of NPY-Ir neurons in the upper regions of the cingular (134%), frontal (140%) and parietal cortex (48%) and corresponding decreases in 5-HT2A/2C binding (16-26%). No changes in 5-HT1A and 5-HT1B/1D binding were observed after lesions of this kind. After PCPA treatment, decreases in NPY-Ir neurons density (22-40%) and increases in 5-HT1A and 5-HT1B/1D receptor binding sites (20-50%) were distributed in both upper and deeper cortical regions. The lack of effect of the partial lesion suggests that spared 5-HT neurons may exert compensatory mechanisms up to a large extent. The changes in NPY immunoreactivity and 5-HT2A/2C binding detected in the upper regions of the cortex after complete 5-HT lesions probably result from local cellular rearrangements, whereas blocking 5-HT synthesis has more widespread influence on NPY neurons and on 5-HT1A and 5-HT1B/1D receptor subtypes. Moreover, decreases in DOPAC concentrations detected only after complete lesions suggest that the involvement of catecholaminergic transmission may also differentiate 5,7-DHT and PCPA treatments. Altogether, these data suggest that different receptor subtypes might be involved in 5-HT-NPY relationships.

Effect of serotonin on cyclic AMP level in rat hypothalamus slices during development.

The effect of serotonin (5-HT) on cyclic AMP levels in rat hypothalamic slices was age-dependent. The sensitivity of the cyclic AMP system to 5 X 10(-5) M 5-HT already existed in the foetus at 21 days of pregnancy. It reached a maximum on the 7th postnatal day and then decreased with age. In adult tissue the response was still present and was antagonized by two serotonergic antagonists (methiothepin and metergoline). When compared to the progressive increase of 5-HT level in the hypothalamus the data suggest a different evolution of serotonergic innervation and of 5-HT receptors.

Uptake of [3H]serotonin and [3H]noradrenaline in the raphe nuclei and the locus coeruleus of C57BL/6 Rholco and BALB/c Cenlco mice at three times of the day.

Uptake of [3H]serotonin (5-HT) and [3H]noradrenaline (NA) in the raphe nuclei and the locus coeruleus of C57BL/6 and BALB/c mice has been analysed at 3 times of the day. Daily mean results clearly show a higher uptake of [3H]5-HT and [3H]NA in the raphe dorsalis of the BALB/c strain than in C57BL/6. A higher uptake of [3H]NA is also found in the locus coeruleus of BALB/c mice than in C57BL/6. However, differences between the strains are neither visible at all times of the day nor simultaneously in the different structures.

Endogenous levels of tryptophan, serotonin and 5-hydroxyindole acetic acid in the developing brain of the cat.

Using spectrofluorimetric methods, endogenous levels of tryptophan (TRP), serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) were determined in various structures of the growing brain of cats. After one month, 5-HT metabolism is comparable to that observed in adult cats. The third week after birth is marked by increasing levels of TRP and 5-HIAA and seems to be a critical period for the maturation of serotoninergic neurons.

In vitro 3H-serotonin (5-HT) synthesis and release in BALBc and C57BL mice. II. Cell body areas.

"In vitro" 3H-5-HT and 3H-5-HIAA, newly synthesized from 3H-TRP, are measured in the brainstem, the anterior raphe nuclei and the locus coeruleus of C57BL and BALBc mice. As found for the caudate nucleus and the hippocampus, higher synthesis and release are determined in C57BL than in BALBc, for the locus coeruleus and more globally, for the brainstem. But these differences disappear when the study is carried on the raphe dorsalis and the raphe centralis nuclei. Therefore the serotonergic activity could be independently regulated at the level of cell bodies and at those of terminals. However, the 5-HT metabolism of NRD of BALBc mice could be submitted to a specific autoinhibition which could explain a lower 5-HT synthesis and release at the corresponding terminal level, compared to C57BL.

In vitro 3H-serotonin (5-HT) synthesis and release in BALBc and C57BL mice. I. Terminal areas.

"In vitro," 3H-5-HT and 3H-5-HIAA newly synthesized from 3H-TRP are measured in the caudate nucleus and the hippocampus of C57BL and BALBc mice. Higher synthesis, utilization and release are to be found in C57BL than in BALBc strain. In the hippocampus of C57BL this higher synthesis is due both to higher tryptophan hydroxylase activity and to higher tryptophan uptake ability. But in the caudate nucleus the initial accumulation of tryptophan is similar in both strains. Finally the two forms of monoamine oxidase (A and B) show also similar activities in both strain. These data will be compared to those obtained at the nerve cell body level in the paper (II).