Biomedical subjects

Y Tillet

Publications and source records attributed to Y Tillet.

At least 19 recordsLinked to original sources

PubMed1999

Small intensely fluorescent cells of the rat paracervical ganglion synthesize adrenaline, receive afferent innervation from postganglionic cholinergic neurones, and contain muscarinic receptors.

In the paracervical ganglion (PCG) of the rat, double-labelling immunofluorescence for catecholamine-synthesizing enzymes and HPLC measurement of catecholamine contents were first performed to evaluate whether intraganglionic small intensely fluorescent (SIF) cells are capable of synthesizing adrenaline. Immunolabelling for tyrosine hydroxylase (TH), dopamine beta-hydroxylase and phenylethanolamine-N-methyl transferase (PNMT) occurred in all SIF cells of the PCG, thus demonstrating the presence of all the enzymes required for adrenaline biosynthesis. Adrenaline levels were undetectable in the PCG but to test the hypothesis that PNMT is active in SIF cells, catecholamines were measured in ganglia of rats pretreated with pargyline, an inhibitor of the monoamine oxidase, the major enzyme involved in the catecholamine degradation. Pargyline treatment increased adrenaline levels in the PCG, thus demonstrating that SIF cells are capable of adrenaline synthesis. The undetectable levels of adrenaline in the PCG of untreated rats suggested a slow rate of biosynthesis of adrenaline in the ganglion. Furthermore, the use of double-labelling showed that SIF cells of the PCG were stained for muscarinic receptors and were approached by varicose ChAT-immunoreactive nerve fibres. Nerve fibres immunoreactive for ChAT were also observed associated with nerve cell bodies of ganglion neurones. Following deafferentation of the PCG, the ChAT-immunoreactive nerve fibres surrounding nerve cell bodies totally disappeared indicating their preganglionic origin, while those associated with SIF cells did not degenerate, which demonstrate that they derived from intraganglionic cholinergic neurones. Taken together, the results show that adrenaline may be a transmitter for SIF cells in the PCG and suggest that cholinergic neurones of the parasympathetic division of the PCG can modulate the SIF cell activity through the activation of muscarinic receptors.

Afferent Pathways↗

PubMed1999

Afferents to the rostral olfactory bulb in sheep with special emphasis on the cholinergic, noradrenergic and serotonergic connections.

The olfactory bulb (OB) is involved in the processing of olfactory information particularly through the activation of its afferents. To localize their cell origin in sheep, a specific retrograde fluorescent tracer, Fluoro-Gold, was injected into the olfactory bulb of seven ewes. By using immunocytochemical techniques, retrogradely labeled neurons were colocalized with choline acetyltransferase, tyrosine hydroxylase, dopamine-beta-hydroxylase and serotonin to characterize cholinergic, noradrenergic and serotonergic Fluoro-Gold-labeled neurons. Most afferents originated from the ipsilateral side of the injection site. The OB received major inputs from the anterior olfactory nucleus (AON), the piriform cortex (PC), the olfactory tubercle, the diagonal band of Broca (DBB) and the amygdala. Other retrogradely labeled neurons were observed in the taenia tecta, the septum, the nucleus of the lateral olfactory tract, the preoptic area, the lateral hypothalamic area, the mediobasal hypothalamus, the lateral part of the premammillary nucleus, the paraventricular nucleus of the hypothalamus, the paraventricular thalamic nucleus, the central grey, the substantia nigra (SN), the ventral tegmental area (VTA), the lateral nucleus to the interpeduncular nucleus (IIP), the raphe and the locus coeruleus (LC). Contralateral labeling was also found in the AON, the PC, the SN compacta, the VTA, the IIP and the LC. Cholinergic Fluoro-Gold-labeled neurons belonged to the horizontal and vertical branch of the DBB. Noradrenergic afferents came from the LC and serotoninergic afferents came from the medial raphe nuclei and the 1IP. These data are discussed in relation with olfactory learning in the context of maternal behavior in sheep.

Animals↗

PubMed1999

Distribution of galanin immunoreactivity in the sheep diencephalon.

Although the physiological role of galanin has been demonstrated in several endocrine regulations in sheep, the anatomical characteristics of this neuronal system has never been studied. The distribution of galanin-containing neurones was described by immunohistochemistry using galanin antiserum in the diencephalon of adult ewes, both ovariectomized or treated with colchicine. Galanin-immunoreactivity was found throughout the diencephalon. In the ovariectomized ewes, galanin-immunoreactive neurones were mainly observed in the medial preoptic area and the infundibular nucleus. The highest density of immunoreactive fibres was found in the external layer of the median eminence. Numerous galanin-immunoreactive fibres were also observed in the preoptic area, the mediobasal hypothalamus, the periphery of the supraoptic and the paraventricular nuclei. With colchicine treatment, the number of labelled neurones increased, and additional galanin-immunoreactive perikarya were observed in the bed nucleus of the stria terminalis, the lateral septum, the supraoptic, the paraventricular and the periventricular nuclei and the paraventricular nucleus of the thalamus. In the caudal part of the diencephalon, the density of labelled neurones was lower in both groups of animals than in other species studied. Regardless of treatment, labelling was not seen in the suprachiasmatic nucleus and only rarely in the ventromedial nucleus. These results describe, for the first time, the distribution of galanin-immunoreactive neurones in the sheep diencephalon. Compared to other species studied, distribution in the sheep diencephalon has several distinct differences. In ovariectomized animals, the medial preoptic area presents more labelled neurones in sheep than in monkeys, whereas in the supraoptic nucleus the density of labelled neurones is lower in sheep than in humans or opossums. After colchicine treatment only very few differences were observed between sheep and rats, but in contrast to other species, the suprachiasmatic nucleus of the sheep does not contain labelled neurones.

Animals↗

PubMed1999

Localization of estrogen-receptive neurons projecting to the GnRH neuron-containing rostral preoptic area of the ewe.

Estrogen exerts important feedback effects upon the biosynthetic and secretory behavior of gonadotropin-releasing hormone (GnRH) neurons to control reproductive functioning. The mechanism of estrogen action upon these neurons is unclear and seems likely to involve the transsynaptic regulation of GnRH neurons. The objective of the present study was to identify the estrogen-receptive neural populations which project to the general vicinity of the GnRH perikarya in the rostral preoptic area and diagonal band of Broca (rPOA/DBB) of the ewe. Intact breeding-season ewes received an injection of the retrograde tracer fluorogold (FG) into the rPOA/DBB, and their hypothalami and brainstems examined for the presence of FG and estrogen receptor alpha (ERalpha) immunocytochemistry. Retrogradely labeled neurons were identified principally within the lateral septum (LS), lamina terminalis, bed nucleus of the stria terminalis, POA, arcuate nucleus (ARN), ventromedial nucleus (VMN) and median eminence. Smaller numbers of FG-immonoreactive cells were found in the caudal brainstem where they resided mostly in the ventrolateral medulla (VLM). Dual-labeled cells exhibiting both FG and ERalpha staining were prominent in the POA, LS and at all rostrocaudal levels of the VMN and ARN. Small numbers of dual-labeled cells were found in the VLM. These observations indicate that a number of distinct ERalpha-expressing neural populations project to the rPOA/DBB where the majority of the GnRH perikarya are found in the ewe. Although it is not possible to determine the direct connectivity of these projections with GnRH neurons, the findings provide an initial neuroanatomical framework through which the transsynaptic actions of estrogen on ovine GnRH neurons may be tested.

Animals↗

PubMed1998

Histaminergic neurons in the sheep diencephalon.

The distribution of histaminergic neurons in the sheep brain was studied by immunohistochemistry by using antibodies raised against histamine. For the first time in this species, the presence of histamine-immunoreactive neurons was described in the caudal diencephalon, around the mammillary bodies, and in the tuberomammillary area. The general pattern of distribution of these neurons was similar to that described previously in other species, i.e., rodents and humans. The distribution in the five neuronal groups described in rodents was not easy to demonstrate in sheep, because the boundaries between each group were not clear. The labeled neurons appeared to form a continuous cell system, as in humans. Numerous histamine-immunoreactive mast cells were found in the habenula and the thalamus. Histamine-immunoreactive fibers were found in almost all of the structures studied. The highest density of fibers was seen in the tuberomammillary area, from which dense bundles of fibers ran rostrally and dorsally along the third ventricle in a parasagittal plane. Numerous immunostained fibers were found close to the wall of the ventricles; some of them appeared to reach the cerebrospinal fluid through the ependymal cell layer. Some fibers were also observed in the optic tract, and the lowest density was found in the supraoptic and paraventricular nuclei. These results should be useful for developing further physiological studies on the role of histaminergic neuronal systems in sheep.

Animals↗

PubMed1998

Immunolocalization of aromatic L-amino acid decarboxylase, tyrosine hydroxylase, dopamine, and serotonin in the forebrain of Ambystoma mexicanum.

To improve basic knowledge about the neurochemical organization of the urodele brain, and to study discrepancies in the localization of monoaminergic markers, we immunohistochemically charted the distribution of four such markers (tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine, and serotonin) in the axolotl (Ambystoma mexicanum) forebrain. Catecholaminergic and serotoninergic systems were found in similar locations to those seen in other Urodela. As seen in other vertebrates, the localization of the different monoaminergic markers reveals some inconsistencies. Cells that are exclusively tyrosine hydroxylase-immunoreactive are observed in the olfactory bulb, anterior olfactory nucleus/nucleus accumbens region, the epichiasmatic portion of the preoptic nucleus, and in the pars intercalaris thalami, whereas cells that are only labelled by aromatic L-amino acid decarboxylase are seen in the anterior olfactory nucleus/nucleus accumbens region, the bed nuclei of the anterior commissure, the posterior portion of the preoptic nucleus, the ventral hypothalamus, and the pars intercalaris thalami. The presence of cells solely serotonin (5-HT)-immunoreactive is suggested for the nucleus infundibularis dorsalis. Conversely, there were no areas that appeared to be exclusively immunoreactive for dopamine. Double-labelling for aromatic L-amino acid decarboxylase/tyrosine hydroxylase and aromatic L-amino acid decarboxylase/serotonin, together with cell counting, confirmed the existence of neurons that express only one monoaminergic marker in amphibian, supporting the hypothesis that these cells are universally present in the central nervous system of vertebrates.

Ambystoma↗

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

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↗