Biomedical subjects

Y Tillet

Publications and source records attributed to Y Tillet.

At least 37 records · Page 2Linked to original sources

PubMed1998

Localization of the preprosomatostatin-mRNA by in situ hybridization in the ewe hypothalamus.

The peptidergic neurohormone somatostatin (SRIF) derives from a precursor called preprosomatostatin (PPS) by proteolysis. We have isolated by RT-PCR and sequenced a partial cDNA coding for the ovine PPS. It contains a 348 base pairs coding sequence that shares strong similarities with previously cloned mammalian cDNAs. The ovine cDNA was used to synthesize radiolabeled cRNA to probe the PPS mRNA in the ewe hypothalamus by in situ hybridization. The PPS mRNA-containing cells are widely distributed in the hypothalamus. According to the number of silver grains over a cell, they show various staining intensities. The distribution of the PPS mRNA is in good agreement with that of the peptide previously determined using immunohistochemistry. The strongest labeled areas include the periventricular region of the paraventricular nucleus and the lateral division of the ventromedial nucleus. The difference in labeling intensity observed in the diverse populations of labeled neurons could reflect various levels of neuronal activity.

Amino Acid Sequence↗

PubMed1998

Presence of galanin in dopaminergic neurons of the sheep infundibular nucleus: a double staining immunohistochemical study.

The distribution of tyrosine hydroxylase (TH) and of galanin immunoreactive (IR) neurons were examined in the sheep infundibular nucleus. Antisera raised against TH and galanin were used on adjacent sections and for double immunohistochemical staining of the same sections. There was considerable overlap in the distribution of TH and galanin-IR neurons in the medial part of the nucleus. Most of the galanin-IR neurons were also TH-IR, but less than 50% of the TH-IR neurons also expressed galanin immunoreactivity. Neurons immunoreactive to TH alone were observed close to the third ventricle and in the rostral part of the infundibular nucleus. In the median eminence, TH and galanin-IR fibres overlapped mainly in the lateral and dorsal parts of the external layer, but the colocalisation of both antigens could not be assessed on the available material. Thus, in sheep, the population of catecholaminergic neurons of the infundibular nucleus may be subdivided into different subpopulations according to their peptide content, but does not appear segregated as in rat and human.

Animals↗

PubMed1998

Effect of oestradiol and photoperiod on TH mRNA concentrations in A15 and A12 dopamine cell groups in the ewe.

In the sheep, photoperiod, through melatonin, and oestradiol negative-feedback are two major regulators of seasonal changes in luteinizing hormone (LH) and prolactin secretion. Melatonin and oestradiol act on dopamine neurons of the hypothalamus to modify the enzymatic activity of tyrosine hydroxylase (TH). To further understand how melatonin and oestradiol regulate TH activity, we have studied the level of TH mRNA by in situ hybridization with an homologous cDNA probe, in A12 and A15 dopamine neurons of four groups of ovariectomized ewes: long-day exposed ewes with or without subcutaneous oestradiol implants and short-day exposed ewes with or without oestradiol. Results were analysed in relation to the concentration of LH and prolactin in the peripheral circulation. In the A15 cell group, TH mRNA levels were elevated in the short-day, oestradiol-treated ewes compared to all other groups. In this group, the level of TH mRNA was elevated simultaneously with LH concentration. The low level of TH mRNA found in the long-day, oestradiol-treated ewes may indicate that the increase of TH enzymatic activity previously reported by this treatment is not caused by an increase of the level of enzyme. In the A12 cell group, the level of TH mRNA in both long-day and short-day oestradiol-treated ewes was significantly higher than in ewes without oestradiol replacement. Prolactin concentrations were not correlated with TH mRNA variations in the A12 cell group.

Animals↗

PubMed1998

Distribution of central catecholaminergic neurons: a comparison between ungulates, humans and other species.

In ungulates and primates, the distribution of central catecholaminergic neurons identified using antibodies raised against catecholamine synthesizing enzymes and catecholamines themselves, shows many differences if compared to rats. Catecholaminergic neurons are more loosely clustered in ungulates and primates than in rat. In the medulla oblongata, the density of noradrenergic/adrenergic neurons is lower in ungulates than in other species and, particularly in sheep, the adrenergic group C1 is not observed. The noradrenergic neurons of the locus coeruleus are present in a larger area in ungulates than in rodents. In the hypothalamus, the density of dopamine neurons is lower in ungulates and primates than in rodents. In the rostral hypothalamus of ungulates, the dorsal part of the group A14 is missing, and these species present only the ventral part of the group A15. In primates the group A15 extends into the supraoptic and paraventricular nuclei which have large tyrosine hydroxylase-immunoreactive (TH-IR) neurons not observed in other species. In addition, in all studies species, not all cells expressing catecholamine synthesizing enzymes also express catecholamines, as found in some TH-IR neurons in the arcuate nucleus, thereby demonstrating the necessity of using different markers to ascertain the true catecholaminergic nature of labeled neurons. These anatomical differences between species show the difficulty in extrapolating the distribution of catecholamine neurons from one species to another and may be related to adaptative physiological differences between mammals.

Animals↗

PubMed1997

Isolation and characterization of ovine tyrosine hydroxylase mRNA.

Tyrosine hydroxylase (TH) cDNA has been characterized in rodents and primates, but only a few studies have been developed in ungulates, except in cows. Because sheep is a species used for many physiological studies, it was of interest to clone TH cDNA in this species. Ovine TH cDNA was purified from a library of sheep adrenal glands. The entire cDNA was 1,721 bp long. It presented a higher percentage of similarity with bovine TH cDNA (93%) than with rodent cDNAs (75%). The deduced amino acid sequence was 490 amino acids long and had 96% similarity with the bovine amino acid sequence. The entire cDNA and different fragments obtained with endonuclease restriction enzymes were cloned in plasmid pUC 18 and were labeled with 35S-dATP to detect TH mRNA by in situ hybridization. Strong labelings were observed on adrenal medulla and on noradrenergic and dopaminergic neurons in the sheep but also in the cow and pig. This labeling matched completely TH immunohistochemical staining obtained on the same sections with anti-TH antibodies. Ovine TH cDNA is a useful tool to study the variations of TH mRNA levels in sheep catecholaminergic neurons.

Amino Acid Sequence↗

PubMed1997

Characterization of the short day-induced decrease in median eminence tyrosine hydroxylase activity in the ewe: temporal relationship to the changes in luteinizing hormone and prolactin secretion and short day-like effect of melatonin.

In the ewe, photoperiod modulates LH and PRL secretion as well as median eminence (ME) dopaminergic activity. The studies reported here were designed to characterize the functional significance of this photoperiodic modulation of ME dopaminergic neuron activity in relation to the regulation of LH and PRL secretion. The aim of the first experiment was to assess whether photoperiodic changes in hypothalamic dopaminergic activity were temporally linked to changes in either PRL or LH secretion. The purpose of the second experiment was to determine whether melatonin mimicked the effects of photoperiod on ME dopaminergic activity. In the first experiment, LH and PRL secretion, hypothalamic tyrosine hydroxylase (TH) activity, and catecholamine contents were determined in ovariectomized estradiol-treated ewes either during long days (LD; control group) or after 5, 25, and 76 short days (SD). SD were associated with a stimulation of LH secretion and a decrease in ME TH activity, which were both expressed only in the 76 SD group. In contrast, the SD-induced inhibition of PRL secretion was already maximal in the 25 SD group. In the second experiment, LH secretion and hypothalamic dopaminergic activity were studied in ovariectomized estradiol-treated ewes kept in LD and then treated for 0 (control), 25, or 77 days with melatonin implants producing a SD-like effect on LH secretion. Melatonin induced a decrease in PRL secretion (observed after 25 days of treatment), as well as a stimulation of LH secretion and a decrease in ME TH activity and dopamine content (observed only after 77 days of treatment). In conclusion, the decrease in ME dopaminergic activity associated with SD exposure or the SD-like effect of melatonin appears unrelated to the regulation of PRL secretion. The SD-like effect of melatonin on ME dopaminergic activity suggests that melatonin mediates the effect of SD on this activity. The regulation of ME dopaminergic activity can thus be considered a probable step in the photoperiodic regulation of LH secretion.

Animals↗

PubMed1996

Distribution of melanin-concentrating hormone (MCH)-like immunoreactivity in neurons of the diencephalon of sheep.

An immunohistochemical study with an antiserum raised against salmon melanin concentrating-hormone has demonstrated the presence of numerous melanin concentrating-hormone-immunoreactive neurons in the lateral hypothalamic areas of the sheep. The pattern of distribution of these perikarya is similar to that of rodents and primates. In sheep, however, melanin concentrating-hormone-immunoreactive neurons appeared to form two gatherings: the first is situated ventromedially to the internal capsule and the second in the dorsolateral hypothalamus. In these areas, numerous immunostained perikarya are observed. Compared to the rats, labelled neurons extended more caudally in the ventral tegmental area and more rostrally above the optic chiasma. Compared to primates, these neurons are less numerous in the periventricular area. In our study, dense networks of melanin concentrating-hormone-immunoreactive varicose fibers were observed in the supramamillary nucleus, the lateral hypothalamus, the nucleus medialis thalami and nucleus reuniens and in the bed nucleus of the stria terminalis.

Animals↗

PubMed1996

Photoperiodic modulation of monoamines and amino-acids involved in the control of prolactin and LH secretion in the ewe: evidence for a regulation of tyrosine hydroxylase activity.

Several neurotransmitters are implicated in the photoperiodic regulation of prolactin and luteinising hormone (LH) secretion in the ewe. This work investigated whether catecholamines, gamma-amino butyric acid (GABA), excitatory amino acids and serotonin diencephalic contents are affected by photoperiod and how such changes relate to the seasonal effects of photoperiod on LH and prolactin secretions. Moreover, to determine whether photoperiod can influence catecholamine biosynthesis, the activity of its rate limiting enzyme, tyrosine hydroxylase (TH) was also investigated. TH activity and the tissue content of the monoamines and their metabolites were measured in stalk-median eminence (SME), preoptic area (POA) and the mediobasal, mediodorsal and laterobasal aspects of the hypothalamus. Investigation of excitatory amino acids and GABA was limited to the POA and the SME. Ovariectomized ewes were initially maintained in long days (LD) for 70 days. Thereafter half the ewes remained exposed to long days and the other half were transferred onto short days (SD) for 63 to 66 days to induce a stimulation of LH secretion and an inhibition of prolactin secretion. In each photoperiodic regime, half the ewes were treated with a subcutaneous oestradiol implant (+E) and half were not (-E). As expected, short days induced a decrease in prolactin and an increase in pulsatile LH secretion. These neuroendocrine changes were associated with a decrease in the TH activity of the SME in both oestradiol treated and non treated animals (146.5 +/- 24.1, 167.6 +/- 26.5 U TH/g of tissue in LD-E and LD+E vs 83.5 +/- 12.4 and 95.0 +/- 30.2 U TH/g of tissue in SD-E and SD+E animals; P < or = 0.01). A similar and parallel short day-induced decrease was observed in the tissue content of dopamine and its metabolite, 3,4-dihydroxy-phenylacetic acid (SD level were 55% of LD levels, P < 0.05). In POA, a short day-induced decrease in dopamine (18%; P < or = 0.05) and GABA (16.4%; P < or = 0.05) content and an oestradiol-induced decrease in aspartate (15.6%; P < or = 0.05) content were found. This study provides the first report of a photoperiodic control of the synthesis activity of catecholaminergic neurones of the SME in the ewe. The photoperiod-induced changes in dopaminergic activity at the level of the SME were associated with changes in LH and prolactin secretion indicating that TH activity of dopaminergic neurones of the SME could be a critical component of the photoperiodic regulation of LH and/or prolactin secretion. In particular, this finding is in agreement with the hypothesis that photoperiod can control a dopaminergic pathway inhibitory of LH secretion and which ends in the median eminence.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1995

Changes in LHbeta-gene and FSHbeta-gene expression in the ram pars tuberalis according to season and castration.

Luteinizing hormone beta (LHbeta) and follicle stimulating hormone beta (FSHbeta) subunits and their mRNAs were studied in the ram pars tuberalis following different seasonal (winter vs summer) and experimental (intact vs castrated animals) conditions. Hormone-containing cells were identified by immunohistochemistry, using homologous double-stranded 35S-cDNAs. The labelling was quantified by image analysis. Immunohistochemical staining showed that cells containing LHbeta and FSHbeta were localized mainly in the ventral part of the pars tuberalis but that, in the summer, additional LHbeta containing cells were present in the dorsal part in intact rams. On the other hand, LHbeta-mRNA labelling was found in the whole pars tuberalis in wethers but only in the ventral part in intact rams. The magnitude of LHbeta-mRNA labelling was significantly greater in summer than in winter rams, and in castrated than in intact animals (P<0.001). However, the number of labelled cells was found to be the greatest in the winter (P<0.001) and was not affected by castration. FSHbeta-mRNA expression was similar to that of LHbeta-mRNA except that the level and extent were considerably lower. Thus, our results show an increase in the magnitude of gonadotropin beta subunit-mRNA in the summer and following castration; this increase appears to involve the entire pars tuberalis.

Animals↗

PubMed1995

Efferent projections from the retrochiasmatic area to the median eminence and to the pars nervosa of the hypophysis with special reference to the A15 dopaminergic cell group in the sheep.

Anterograde tracers, viz. Phaseolus vulgaris leucoagglutinin and fluorescein dextran, were used in conjunction with tyrosine hydroxylase immunohistochemistry to study the projections of the A15 dopaminergic cell group towards the median eminence and pituitary in sheep. After injection of the tracers in the retrochiasmatic area, which contains the cell group A15, fibres containing anterograde tracer were observed in the internal zone of the median eminence and in the pars nervosa of the pituitary. Numerous tyrosine hydroxylase immunoreactive fibres were present in the external zone of the median eminence and in the pars intermedia and the pars nervosa of the pituitary, with characteristic patterns of organisation in each area. Most tyrosine hydroxylase-immunoreactive fibres containing fluorescein dextran were located in the pars nervosa, whereas only a few were observed in the internal zone of the median eminence. It was concluded that at least part of the dopaminergic innervation of the pars nervosa originated from the A15 group. These results provide morphological evidence for (1) the role of dopaminergic neurons of the A15 cell group in the seasonal control of prolactin secretion via the release of dopamine in the pars nervosa, and (2) putative physiological interactions between dopamine and the secretion of neurohypophysial hormones in sheep.

Animals↗

PubMed1995

Involvement of the main but not the accessory olfactory system in maternal behavior of primiparous and multiparous ewes.

The respective roles of the main and accessory olfactory systems in the development of maternal behavior and selective suckling were investigated in parturient primiparous and multiparous ewes. Vomeronasal nerve section before parturition did not disturb either maternal behavior or maternal selectivity at suckling. By contrast, anosmia induced by zinc sulphate infusion had significant effects on the onset of maternal behavior in primiparous ewes. The onset of licking and of suckling were delayed and licking times and maternal bleats were reduced. Such disturbances were not observed in multiparous anosmic ewes, indicating that experience can compensate for the loss of olfactory information. On the other hand, anosmia prevented selective care regardless of maternal experience. Our results underline the importance of the main olfactory system for the development of adequate maternal behavior in sheep.

Animals↗

PubMed1995

Distribution of neurotransmitters in the sheep brain.

Although the general organization of the sheep brain is similar to that of other mammals, there are species differences in the fine architecture and neurotransmitter distribution. In sheep, perikarya are generally scattered, unlike the situation in rodents where they are clustered. The same organization is observed in cows and primates. The density of neurones immunoreactive for tyrosine hydroxylase in the dorsorostral diencephalon of sheep is lower than in rodents; A14 and A15 dopaminergic cell groups do not present a dorsal part. Only one adrenergic group, C2, is observed in the dorsomedial medulla oblongata. GnRH-immunoreactive neurones are mainly found in the anterior hypothalamic-preoptic areas, a few being present in the mediobasal hypothalamus. The density of several neurones containing neuropeptides (for example vasoactive intestinal polypeptide, cholecystokinin and somatostatin) in the caudal brain of sheep is lower than in other species and in the forebrain of sheep. These differences contribute to different patterns of innervation of brain areas compared with other species. For example, the suprachiasmatic nucleus does not present a dense network of fibres immunoreactive for 5-hydroxytryptamine and neuropeptide Y as observed in rats. These morphological studies constitute information necessary for further physiological investigations.

Animals↗

PubMed1994

Aromatic L-amino acid decarboxylase immunohistochemistry in the suprachiasmatic nucleus of the sheep. Comparison with tyrosine hydroxylase immunohistochemistry.

Using antisera against tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC), we have demonstrated the presence of numerous AADC immunoreactive neurons and a few TH immunoreactive neurons, homogeneously distributed throughout the suprachiasmatic nucleus. Similar results have been described in other species. These observations show that this nucleus is able to synthesize trace amines (such as phenylethylamine or tyramine) in addition to dopamine. It is hypothesized that these trace amines are possibly involved in the integration of day length variation in sheep, a species whose reproduction is closely related to photoperiod.

Animals↗

PubMed1994

Immunolocalization of aromatic L-amino acid decarboxylase in goldfish (Carassius auratus) brain.

The distribution of monoamines (catecholamines and serotonin) in fishes has been previously studied by immunohistochemistry of both the monoamines themselves and their biosynthetic enzymes. But the distribution of neurons containing aromatic L-amino acid decarboxylase, an enzyme involved in the biosynthesis of both catecholamines and serotonin, has up to now not been investigated. In order to improve knowledge about the localization of aromatic L-amino acid decarboxylase, neurons containing this enzyme were mapped immunohistochemically in the goldfish brain. Furthermore, neurons bearing aromatic L-amino acid decarboxylase immunoreactivity have been compared with those containing tyrosine hydroxylase and serotonin immunoreactivities. Our results show that distribution of aromatic L-amino acid decarboxylase immunoreactivity generally coincides with that of tyrosine hydroxylase and serotonin. Nevertheless, the presence of nine D cell groups (containing aromatic L-amino acid decarboxylase but lacking both catecholamines and serotonin) and six groups of neurons which are aromatic L-amino acid decarboxylase-immunonegative but contain tyrosine hydroxylase, and might produce L-DOPA, have been revealed. The occurrence of both D cell groups and presumptive L-DOPA neurons in goldfish brain is discussed in relation to similar findings in fish and mammalian brain.

Animals↗

PubMed1994

Postnatal development of the suprachiasmatic nucleus in the rat. Morpho-functional characteristics and time course of tyrosine hydroxylase immunopositive fibers.

According to earlier data, the suprachiasmatic nucleus of neonatal rats is highly innervated by serotonin- and tyrosine hydroxylase-immunopositive fibers [Ugrumov M. V. (1992) Zool. Sci. (Tokyo) 9, 37-45], while the latter were no longer observed in adults. This study has attempted to evaluate the timing of the innervation of the rat suprachiasmatic nucleus by tyrosine hydroxylase-immunopositive fibers, as well as to specify some morpho-functional characteristics of these fibers. According to our semi-quantitative light microscopic immunocytochemical data, few tyrosine hydroxylase-immunopositive fibers were observed in the suprachiasmatic nucleus as early as the second postnatal day. They highly increased in number neonatally reaching a maximum at the 10th postnatal day, and then decreased dramatically in adulthood. These data suggest either the provisional character of the tyrosine hydroxylase-immunopositive fibers themselves or the transient expression of tyrosine hydroxylase within permanent fibers. The tyrosine hydroxylase immunopositivity in the fibers points to their catecholaminergic nature, while the overlapping in the distribution of tyrosine hydroxylase- and serotonin-immunopositive fibers might also suggest the transient expression of tyrosine hydroxylase in serotoninergic neurons. In order to check this hypothesis, the neurotoxins of catecholamine- and serotoninergic neurons, 6-hydroxydopamine and 5,7-dihydroxytryptamine, were intraventricularly injected at the second postnatal day, while their effects were specified by the semi-quantitative immunocytochemistry eight days later. 6-Hydroxydopamine did not modify the content of tyrosine hydroxylase-immunopositive fibers in the suprachiasmatic nucleus. Conversely, the treatment with 5,7-dihydroxytryptamine resulted in a significant increase in the number of the tyrosine hydroxylase-immunopositive fibers, while reducing the amount of the serotoninergic ones.(ABSTRACT TRUNCATED AT 250 WORDS)

5,7-Dihydroxytryptamine↗

PubMed1994

Estradiol increases tyrosine hydroxylase activity of the A15 nucleus dopaminergic neurons during long days in the ewe.

In the ewe, the inhibition of LH secretion during long days results from increased negative feedback by estradiol. This effect depends on aminergic systems, mainly in the lateral retrochiasmatic area, a region that includes the dopaminergic A15 nucleus. Recently we demonstrated that the inhibition of LH secretion by estradiol under long days is accompanied by an increase in extracellular levels of amine metabolites (3,4-dihydroxyphenylacetic acid [DOPAC], homovanillic acid [HVA], and 5-hydroxyindolacetic acid [5-HIAA]) in the lateral retrochiasmatic area of the hypothalamus. The increase in catecholamine metabolite levels could be due to stimulation of tyrosine hydroxylase (TH) activity in the catecholaminergic systems of this region. In the present study, we tested this hypothesis by incorporating in vivo measurement of TH activity in the brain into our microdialysis model. We used this approach to first examine the effect of estradiol on TH activity in both the lateral retrochiasmatic area and the caudate nucleus during long days (experiment 1). Two dialysis sessions were carried out on each of six ewes: one after a 10-day estradiol treatment (s.c. implant) and the other after 10 days without estradiol treatment. Estradiol treatment reduced pulsatile LH secretion without affecting the secretion of prolactin. The steroid also significantly increased TH activity in the lateral retrochiasmatic area as assessed by the formation of L-3-4 dihydroxyphenylalanine (L-DOPA). There was no variation in the TH activity of the catecholaminergic systems of the caudate nucleus, suggesting that the effect of estradiol is specifically hypothalamic. In experiment 2, we estimated the relative contribution to the accumulation of L-DOPA in the lateral retrochiasmatic area by dopamine (DA) synthesis in the dopaminergic neurons and noradrenaline (NA) synthesis in the noradrenergic afferents of the A15 nucleus. This study also allowed us to test whether DOPAC and HVA molecules released in this medium originate from DA metabolism in dopaminergic cells of the A15 nucleus or in its noradrenergic afferents. We monitored TH activity as well as amine metabolite concentrations in the lateral retrochiasmatic area after a partial destruction of noradrenergic nerves in the brain using intracerebroventricular (i.c.v.) injections of nomifensine followed by 6-hydroxydopamine (6-OHDA) injections. We compared the responses in four experimental ewes with those in four control ewes receiving a single i.c.v. injection of nomifensine only. Decreases in extracellular concentrations of 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG) in the left lateral retrochiasmatic area and the tissue content of NA in the contralateral structure confirmed the effectiveness of the lesion of the noradrenergic endings.(ABSTRACT TRUNCATED AT 400 WORDS)

3,4-Dihydroxyphenylacetic Acid↗

PubMed1994

Effects of Trypanosoma congolense infection on the pituitary gland of Baoulé bulls: immunohistochemistry of LH- and FSH-secreting cells and response of plasma LH and testosterone to combined dexamethasone and GnRH treatment.

The effects of Trypanosoma congolense infection were investigated at the pituitary level on trypanosome resistant Baoulé bulls (aged 3-6 years), using immunohistochemistry of LH- and FSH-secreting cells and a combined dexamethasone and GnRH challenge. The pituitaries of two control and five naturally infected Baoulé bulls were removed after slaughter and the LH- and FSH-secreting cells were examined immunohistochemically, using specific polyclonal antibodies against beta LH and beta FSH. No significant impairment of the labelling and distribution of LH- and FSH-secreting cells was seen in infected bulls when compared with control animals. No parasites were found in the pituitary glands. Plasma LH and testosterone concentrations were determined in eight control and eight infected bulls by enzymeimmunoassay and radioimmunoassay techniques, respectively. Blood samples were collected at intervals of 30 min two times before and nine times after dexamethasone treatment (20 mg i.m.). GnRH (Busereline: 20 micrograms, i.m.) was injected 4.5 h later and samples were collected every 15 min for 180 min. After dexamethasone treatment, LH and testosterone concentrations declined dramatically in both groups. Four hours after treatment, the mean testosterone concentration for both groups was 0.44 ng ml-1. After GnRH injection, LH concentrations in the infected group increased rapidly to a mean maximum value of 30 ng ml-1 by 165 min. In contrast, the increase in LH concentration in non-infected bulls was more gradual and the mean maximum value, reached at the same time, was only 20 ng ml-1. Testosterone concentration increased rapidly and in a similar manner in both groups for the first 90 min (0.08 +/- 0.04 ng ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Active immunization against melatonin in Ile-de-France ewes and photoperiodic control of prolactin secretion and ovulatory activity.

An experiment was conducted to determine whether active immunization against melatonin could modify the perception of abrupt photoperiodic changes in ewes. Two groups each containing six intact Ile-de-France ewes were submitted to alternate periods of short days for 2.5 months and long days for 2.5 days for about 70 weeks. Three series of active immunizations against a melatonin conjugate were carried out during the first of the three long-day periods. Control ewes were actively immunized at the same time against human serum albumin. Blood samples were taken once a week throughout the experiment to measure antibody titre and affinity, and prolactin and progesterone concentrations. Sera of all treated ewes demonstrated higher antibody titres than those of control ewes. Antisera were highly specific, as evidenced by the absence of displacement of iodinated melatonin in the presence of ten melatonin metabolites. Significant effects of photoperiod and of the interaction between treatment and photoperiod on prolactin concentration were detected. Prolactin concentrations in plasma of the control ewes were high during long days and low during short days. However, in the treated ewes, with the exception of the first period of long days, prolactin concentrations were not influenced by photoperiodic changes. Ovulatory activity of control ewes, as demonstrated by progesterone measurements, was stimulated by short days and inhibited by long days. In contrast, ovulatory activity of treated ewes, after a response identical to that of control ewes after the first photoperiodic shift from long to short days, showed a complete desynchronization of ovulatory activity relative to photoperiodic changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗