Catecholamine-containing neurons in the sheep brainstem and diencephalon: immunohistochemical study with tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) antibodies

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Neuronal projections to the lateral retrochiasmatic area of sheep with special reference to catecholaminergic afferents: immunohistochemical and retrograde tract-tracing studies

The retrochiasmatic area contains the A15 catecholaminergic group and numerous monoaminergic afferents whose discrete cell origins are unknown in sheep. Using tract-tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the retrochiasmatic area in sheep. The retrogradely labeled cells were seen by observation of the tracer by direct fluorescence or by immunohistochemistry with specific antibodies raised in rabbits or horses. Among the retrogradely labeled neurons, double immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, and serotonin were used to characterize catecholamine and serotonin FG labeled neurons. The retrochiasmatic area, which included the A15 dopaminergic group and the accessory supraoptic nucleus (SON), received major inputs from the lateral septum (LS), the bed nucleus of the stria terminalis (BNST), the thalamic paraventricular nucleus, hypothalamic paraventricular and supraoptic nuclei, the perimamillary area, the amygdala, the ventral part of the hippocampus and the parabrachial nucleus (PBN). Further, numerous scattered retrogradely labeled neurons were observed in the preoptic area, the ventromedial part of the hypothalamus. the periventricular area, the periaqueductal central gray (CG), the ventrolateral medulla and the dorsal vagal complex. Most of the noradrenergic afferents came from the ventro-lateral medulla (Al group), and only a few from the locus coeruleus complex (A6/A7 groups). A few dopaminergic neurons retrogradely labeled with flurogold were observed in the periventricular area of the hypothalamus. Rare serotoninergic fluorogold labeled neurons belonged to the dorsal raphe nucleus. Most of these afferents came from both sides of the brain, except for hypothalamic supraoptic and paraventricular nuclei. In the light of these anatomical data, we compared our results with data obtained from rats, and we discussed the putative role of these afferents in sheep in the regulation of several specific functions in which the retrochiasmatic area may be involved, such as reproduction.

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.

Oestrogen receptors in the brainstem of the female sheep: relationship to noradrenergic cells and cells projecting to the medial preoptic area

Oestrogen regulates the secretion of gonadotropin releasing hormone (GnRH) and this could be mediated by noradrenergic systems originating in the brainstem. Whilst it is known that noradrenergic cells possess oestrogen receptors (ER), it is not known whether ER-immunoreactive (-ir) cells in the brainstem project to the regions of the hypothalamus in which GnRH neurons are found. We have used dual-label immunocytochemistry to determine the extent to which ER-alpha is found in noradrenergic cells in the brainstem of the ovariectomized (OVX) ewe. Noradrenergic/adrenergic cells were identified by immunostaining for dopamine beta-hydroxylase (DBH). Cells that stained for both DBH and ER were found in both the A1 and A2 cell groups, with the highest levels found in the most caudal regions. In the A1 group, at the most caudal extent, 73% of ER-ir cells were DBH-positive and 19% of DBH-ir cells were ER-positive. The degree of co-localization decreased in a linear manner towards the rostral brainstem. In the caudal half of A2, 9-14% of ER-ir cells were DBH-positive and 20-25% of DBH cells were ER-positive. Less than 2% of DBH-ir cells in the A5 group were dual-labelled and none of the cells in the A6 and A7 groups were ER-positive. The retrograde tracer FluoroGold was injected into the preoptic area of nine OVX ewes and labelled cells were examined in the brainstem to determine the extent of co-localization of ER. Only injections in the rostroventral part of the medial preoptic area near to the organum vasculosum of the lamina terminalis resulted in the labelling of cells in the brainstem. One ewe with very strong labelling of the brainstem was selected for detailed mapping. In the ventrolateral medulla, half the ER-ir cells in the most caudal regions were retrogradely labelled. Almost all the ER-ir cells in the mid-region of the ventrolateral medulla were retrogradely labelled but no co-localization of retrograde tracer and ER was observed rostral to obex. There were many ER-ir cells and retrogradely-labelled cells in the nucleus of the solitary tract but only a few double-labelled cells. Similarly, numerous ER-ir cells and retrogradely labelled cells were observed around the lateral edges of the caudal fourth ventricle and across to the lateral parabrachial nucleus but there were few double-labelled cells. These results suggest differential regulation of noradrenergic cells by oestrogen, with a direct action of the hormone confined to the cells in the most caudal region of the A1 and A2 cell groups. The cells of the caudal ventrolateral medulla which contain ER-ir cells that project to the preoptic area may be important in the mediation by noradrenaline of the actions of oestrogen on GnRH secretion in the ewe.

Levels of dopamine beta hydroxylase immunoreactivity in the preoptic hypothalamus of the ovariectomised ewe following injection of oestrogen: evidence for increased noradrenaline release around the time of the oestrogen-induced surge in luteinizing hormone

We have measured dopamine beta hydroxylase (DBH) immunoreactivity in the preoptic hypothalamus as an index of release of noradrenaline in the ovariectomised (OVX) ewe at the time of an oestrogen-induced surge in luteinizing hormone (LH) release. OVX ewes (n=5) were given an injection of 50 microg oestradiol benzoate (or oil), which causes a surge in the secretion of LH. Blood samples were taken and sheep were killed 16 h later. Other groups (n=3) were given oil or oestrogen and killed 6 h later. Brains were collected for immunohistochemistry and image analysis. The number of DBH-stained cells and the integrated optical density of the cells was measured throughout the A1 field of the brainstem. The DBH staining was measured in the terminal beds of the hypothalamus. There was no difference between the controls and the EB-treated OVX ewes in the number of DBH positive cells or the optical density of DBH-staining cells in the A1 field. Within the preoptic area, there was reduced (P<0.02) DBH staining in the 16 h EB-treated ewes. There was no change in the DBH staining in the paraventricular nucleus or the arcuate nucleus of the hypothalamus. These data suggest that there is release of noradrenaline in the preoptic area at the time of the E-induced GnRH/LH surge in the OVX ewe.

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.

Characterization of pontine neurons which respond to hypoxia in fetal sheep

Hypoxia causes apnea and postural muscle hypotonia in fetal sheep, a response thought to arise by descending inhibition from a group of lateral pontine neurons that express FOS protein after hypoxia. To determine the neurochemical phenotype, and whether these neurons project to the cervical spinal cord, the retrograde tracer CTB-gold was injected into the C5-C8 ventral horn of four fetal sheep at 110 days gestation. Then, at 135 days each fetus was made hypoxic for 2 h by allowing the mother to breathe 7-8% O2. Immunocytochemistry showed that FOS-positive neurons in the subcoeruleus and Kolliker-Fuse regions of the pons were catecholaminergic, but not cholinergic or GABAergic, and a proportion of them contained CTB-gold particles, indicating direct connection with the cervical spinal cord. We suggest that these pontine neurons inhibit respiratory and postural muscle activities during hypoxia in fetal sheep.

The distribution of FOS-immunoreactive neurons in the brainstem, midbrain and diencephalon of fetal sheep in response to acute hypoxia in mid and late gestation

FOS immunohistochemistry was used to map the distribution of neuronal pathways activated by hypoxia in fetal sheep. Conscious pregnant sheep were exposed to hypoxia (7-9% O2, 1-2% CO2, balance N2) for 2 h at either 100-105 days (n=5) or 130-133 days gestation (n=5); term is approximately 147 days. The hypoxia caused cessation of breathing movements at both fetal ages, and increased FOS staining in the medulla (area postrema, dorsal motor nucleus of vagus, nucleus solitary tract, ventrolateral medulla); pons (locus coeruleus and subcoeruleus, lateral and medial parabrachial nuclei); midbrain (habenula, periaqueductal grey, substantia nigra, areas ventrolateral to Red Nucleus); and hypothalamus (anterior and lateral hypothalamic areas, paraventricular and supraoptic nuclei). The results were essentially the same at both gestational ages, except that hypoxia increased FOS-staining in the habenula only in the older fetuses. The presence of FOS protein in pontomedullary cardiorespiratory nuclei at 100-105 days gestation indicates that the peripheral chemoreceptors respond to hypoxia at this early age, and in the subcoeruleus and medial parabrachial regions of the pons is consistent with lesion studies suggesting these areas mediate the inhibition of fetal breathing in response to hypoxia. FOS staining in the ventrolateral periaqueductal grey and habenula was unexpected, and suggests that pathways normally involved in response to noxious stimuli, or which are part of the hypothalamic 'defense' response are activated by hypoxia in the fetus. Some FOS-labelling could arise secondarily as a consequence of the cardiovascular and endocrine responses to hypoxia.

Effects of the respiratory stimulant almitrine on breathing and FOS expression in the brain of fetal and newborn sheep

Almitrine is a piperazine derivative known to stimulate breathing in the adult but cause apnea in fetal sheep. In fetal sheep (127-133 d gestation; term = 147 d) we confirmed this finding, but found that almitrine (4 mg/kg, i.v. or intra-arterial) had a biphasic effect, briefly stimulating and then suppressing breathing movements for at least 3 h. In 2- to 3-d-old (n = 4) and 7- to 14-d-old (n = 4) lambs almitrine increased both tidal volume and breath frequency, increased arterial partial pressure of oxygen and pH, and decreased partial pressure of carbon dioxide. The changes of tidal volume, partial pressure of oxygen and partial pressure of carbon dioxide were less in the 2- to 3-d-old compared with the 7- to 14-d-old lambs. The distribution of the nuclear phosphoprotein FOS, a marker of neuronal activation was examined in fetal and newborn brains. FOS protein was increased in cardiorespiratory areas of the medulla and pons, in the periaqueductal region of the midbrain, and in the supraoptic and paraventricular regions of the hypothalamus. In the pons, FOS protein was increased in the medial parabrachial and subcoeruleus nuclei in the fetuses but not in the 2- to 3- or 7- to 14-d-old lambs. These observations are similar to those reported for hypoxia, and consistent with the hypothesis that both almitrine and hypoxia inhibit fetal breathing movements by an action on a select group of pontine neurons. Whether these neurons respond directly to these stimuli or receive input from the other centers is yet to be elucidated. The mechanisms that change the almitrine (and hypoxia) response from inhibition to excitation at birth have not been identified, but may be important in preventing apnea in the newborn.

Median eminence dopaminergic activation is critical for the early long-day inhibition of luteinizing hormone secretion in the ewe

In ewes, photoperiod modulates LH release. The median eminence (ME) dopaminergic activity seems to be implicated in the inhibition of LH secretion by photoperiod. This study investigated the functional importance of ME dopaminergic activity for LH secretion inhibition in three inhibitory photoperiodic treatments: after 33 long days (LD) (LD1 treatment), after 72 LD (LD2 treatment), and after 34 short days. Using reverse microdialysis on three groups of seven ewes, a solution of alpha-methyl-paratyrosine [alphaMPT, an inhibitor of tyrosine hydroxylase (TH); 10 mM in Ringer's lactate] was infused into the ME for 5 h, preceded by a 5-h control period during which only vehicle was infused, in each of the three photoperiodic treatments. AlphaMPT dramatically decreased the 3,4-dihydroxyphenylacetic acid concentration, similarly in all three photoperiodic treatments, suggesting a similar inhibition of TH activity. In the LD1 treatment, alphaMPT significantly increased LH pulse frequency (+1.22 +/- 0.46 pulse/5 h from control period, mean +/- SEM, n = 9; P < 0.05) and mean concentration (+51 +/- 28%; P < 0.001). In the other two photoperiodic treatments, alphaMPT had no significant effect on LH release. Thus, blockade of dopamine synthesis in the ME seems to stimulate LH secretion in early, but not long-term, inhibition by LD nor after the transition to short days. Therefore, dopaminergic activity of the ME seems to be critical for LH secretion inhibition in some photoperiodic inhibitory treatments but not in others.

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.

Blockade of tyrosine hydroxylase activity in the median eminence partially reverses the long day-induced inhibition of pulsatile LH secretion in the ewe

The photoperiod-induced stimulation of LH secretion is associated with a decrease in dopamine content, as well as in the activity of its rate limiting enzyme, tyrosine hydroxylase (TH), in the median eminence (ME) of the ewe. We therefore hypothesize that ME-TH activity can constitute a limiting factor of photoperiod-induced inhibition of LH pulsatile secretion. To test this hypothesis, we studied whether the inhibition of ME-TH activity can reverse the long day-induced inhibition of LH. Using microdialysis, a 3 mM solution of alpha methyl-p-tyrosine (alpha MPT; a competitive inhibitor of TH), was administered in the ME of ovariectomized ewes bearing a 0.5 cm oestradiol implant at the beginning of a LD-induced inhibition of LH secretion. The vehicle solution was infused for 4 h followed by a 3 mM alpha MPT solution infused for an additional 4 h. LH pulsatile secretory patterns within the same animal were compared between the control period and the alpha MPT period. alpha MPT infusion in the ME was associated with an increase in LH pulse frequency whereas it did not affect prolactin secretion. In conclusion, our results suggest that the inhibition of TH activity in the ME causes a stimulation of LH secretion in long-day inhibited ewes.

The distribution of estrogen receptors in the brainstem of female sheep

Estrogen receptors (ER) have been mapped in the brainstem of the female sheep with immunocytochemistry. A small group of ER-positive cells was found in the lateral and ventrolateral medulla and a larger number in the nucleus of the solitary tract. ER-positive cells were abundant in the area postrema. In the rostral brainstem a small number of ER-positive cells were found in the lateral and dorsal regions of the periaqueductal gray area, and some immediately lateral to the fourth ventricle. Many ER-positive cells were also present in the region around the superior cerebellar peduncle, particularly in the lateral parabrachial nucleus. These results describe for the first time the distribution of ER in the brainstem of the sheep and indicate that the majority of estrogen-containing cells are located in structures involved in the regulation of cardiovascular parameters and fluid balance.

Central connections of the ovine olfactory bulb formation identified using wheat germ agglutinin-conjugated horseradish peroxidase

Pheromonal stimuli elicit rapid behavioral and reproductive endocrine changes in the ewe. The neural pathways responsible for these effects in sheep are unknown, in part, because the olfactory bulb projections have not been examined in this species. Using the anterograde and retrograde neuronal tracer, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), we describe the afferent and efferent olfactory bulb connections of the Suffolk ewe. Injections of WGA-HRP limited to the main olfactory bulb resulted in retrograde labeling of cells in numerous telencephalic, diencephalic, and metencephalic regions. Terminal labeling was limited to layer la of ipsilateral cortical structures extending rostrally from the anterior olfactory nucleus (AON), piriform cortex, anterior-, and posterolateral-cortical amygdaloid nuclei to lateral entorhinal cortex caudally. Injections involving the accessory olfactory bulb and AON produced additional labeling of cells within the bed nucleus of the stria terminalis (BNST), medial nucleus of the amygdala, and a few cells in the posteromedial cortical nucleus of the amygdala. Terminal labeling included a small dorsomedial quadrant of BNST and also extended to the far lateral portions of the supraoptic nucleus. A clearly defined accessory olfactory tract and nucleus was not evident, perhaps due to limitations in the sensitivity of the method. With this possible exception, the afferent and efferent olfactory connections in the sheep appear similar to those reported for other species.

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.

Thyroid hormone receptor (alpha) distribution in hamster and sheep brain: colocalization in gonadotropin-releasing hormone and other identified neurons

Thyroid hormones appear to play an important role in the seasonal reproductive transitions of a number of mammalian and avian species. These seasonal transitions as well as the effects of thyroid hormones on the reproductive neuroendocrine axis are mediated by the GnRH system. How thyroid hormones affect the GnRH system is unclear. Double label immunocytochemistry was used to examine GnRH- and other neurotransmitter/neuropeptide-containing neurons for thyroid hormone receptor (alphaTHR) colocalization in two seasonal breeders, the golden hamster and the sheep. AlphaTHR was identified in hamster and sheep brain by Western blot analysis. Furthermore, alphaTHR immunoreactivity was widely distributed in brain and was colocalized in identified populations: GnRH neurons (hamster, 28%; sheep, 46%); dopaminergic neurons of the A14 (hypothalamic) and A16 (olfactory bulb) cell groups, but not in the hypothalamic A13 cell group; and neurophysin-immunoreactive neurons of the supraoptic and paraventricular nuclei. The finding of alphaTHR in GnRH and A14 dopamine neurons provides an anatomical substrate for direct thyroid hormone action on the reproductive neuroendocrine system of these two seasonally breeding species. It remains to be determined whether the GnRH gene itself or the gene of another constituent within the same GnRH neuron is responsive to thyroid hormones.

Mesopontine organization of cholinergic and catecholaminergic cell groups in the normal and narcoleptic dog

Canine narcolepsy is a unique experimental model of a human sleep disorder characterized by excessive daytime sleepiness and cataplexy. There is a consensus recognition of an imbalance between cholinergic and catecholaminergic systems in narcolepsy although the underlying mechanisms remain poorly understood. Possible substrates could be an abnormal organization, numbers and/or ratio of cholinergic to catecholaminergic cells in the brain of narcoleptic dogs. Therefore, we sought to characterize the corresponding neuronal populations in normal and narcoleptic dogs (Doberman Pinscher) by using choline acetyltransferase (ChAT), nicotinamide adenosine dinucleotide phosphate (NADPH)-diaphorase, tyrosine hydroxylase (TH), and dopamine beta-hydroxylase (DBH). Cholinergic cell groups were found in an area extending from the central to the gigantocellular tegmental field and the periventricular gray corresponding to the pedunculopontine tegmental nucleus (PPT), the laterodorsal tegmental nucleus (LDT), and the parabrachial nucleus. An almost perfect co-localization of ChAT and NADPH-diaphorase was also observed. Catecholaminergic cell groups detected included the ventral tegmental area, the substantia nigra, and the locus coeruleus nucleus (LC). The anatomical distribution of catecholaminergic neurons was unusual in the dog in two important aspects: i) TH- and/or DBH-immunoreactive neurons of the LC were found almost exclusively in the reticular formation and not within the periventricular gray, ii) very few, if any TH-positive neurons were found in the central gray and dorsal raphe. Quantitative analysis did not reveal any significant differences in the organization and the number of cells identified in the LDT, PPT, and LC of normal and narcoleptic dogs. Moreover, the cholinergic to catecholaminergic ratio was found identical in the two groups. In conclusion, the present results do not support the hypothesis that the neurochemical imbalance in narcolepsy could result from abnormal organization, numbers, or ratio of the corresponding neuronal populations.

Distribution and pharmacological characterization of somatostatin receptor binding sites in the sheep brain

Somatostatin binding sites have been localized and quantified in the sheep brain using 125I-Tyr0-DTrp8-somatostatin, by quantitative high resolution light microscopic autoradiography. Sections were analyzed by densitometry on radioautographic film, and subsequently on slides coated with photoemulsion. Specific somatostatin binding sites were concentrated in the medial habenula, superior colliculus, dorsal motor nucleus of the vagus nerve, inferior olive, spinal trigeminal nucleus, and cerebellum. In competition experiments, octreotide, a sst2/sst3/sst5 selective agonist only partially displaced 125I-Tyr0-DTrp8-somatostatin in the three cerebellar layers while it was fully active as compared to somatostatin 14 and 28 in the deeper layers of the parietal cortex. Moderate to low somatostatin receptor densities were present in the mesencephalic periaqueductal gray, dorsal raphe, thalamic paraventricular nucleus, interpeduncular nucleus, pineal gland, dorsal tegmental, dorsolateral tegmental and parabrachial nuclei, nucleus of the solitary tract. The distribution of somatostatin binding sites generally correlates with the data obtained on slides dipped in photoemulsion which provided better resolution and more precise localization. In most of the labeled areas, 125I-Tyr0-DTrp8-somatostatin receptor binding was distributed between both neuropil and perikarya. Perikarya bearing 125I-Tyr0-DTrp8-somatostatin receptors were observed in areas which did not display detectable binding sites on film such as the preoptic-anterior hypothalamic complex and arcuate nucleus and in the locus coeruleus. In conclusion, the distribution of 125I-Tyr0-DTrp8-somatostatin binding sites in sheep brain is very reminiscent of other mammals being closer to the human than to rodents.

A method for drug infusion into the lateral median eminence and arcuate nucleus of sheep

The role of catecholamines in the control of the GnRH pulse generator is unclear as studies have relied on the use of peripheral or intracerebroventricular injections, which lack specificity in relation to the anatomical site of action. Direct brain site infusions have been used, however, these are limited by the ability to accurately target small brain regions. One such area of interest in the control of GnRH is the median eminence and arcuate nucleus within the medial basal hypothalamus. Here we describe a method of stereotaxically targeting this area in a large animal (sheep) and an infusion system to deliver drugs into unrestrained conscious animals. To test our technique we infused the dopamine agonist, quinpirole or vehicle into the medial basal hypothalamus of ovariectomised ewes. Quinpirole significantly suppressed LH pulsatility only in animals with injectors located close to the lateral median eminence. This in vivo result supports the hypothesis that dopamine inhibits GnRH secretion by presynaptic inhibition in the lateral median eminence. Also infusion of quinpirole into the medial basal hypothalamus suppressed prolactin secretion providing in vivo evidence that is consistent with the hypothesis that there are stimulatory autoreceptors on tubero-infundibular dopamine neurons.

A subset of estrogen receptor-containing neurons project to the median eminence in the ewe

The neural pathways responsible for conveying the steroid feedback signals that ultimately affect reproductive neuroendocrine function remain largely undefined. One possibility involves a direct projection from estrogen receptor (ER)-containing neurons to the median eminence (ME), a site of neuroendocrine peptide release. To examine this possibility, 8 ewes received stereotaxic injections of the retrograde neuronal tract-tracing compound cholera toxin-beta subunit (CT beta) into the ME. Neurons sending projections to the ME and containing ER were identified using a dual-label immunoperoxidase method. Double-labeled cells were found in distinct regions: (1) the ER-rich arcuate nucleus (ARC) that contained the greatest number of double-labeled cells, and (2) the organum vasculosum of the lamina terminalis (OVLT) which contained a very consistent, but low, number of double-labeled cells. While a fairly large number of retrogradely-labeled ARC neurons containing ER were identified, the majority of ER-containing ARC neurons were unlabeled and thus send projections elsewhere. Other regions containing high concentrations of ER-positive cells such as the medial preoptic area (MPOA), anterior hypothalamic area, and ventrolateral portion of the ventromedial hypothalamic nucleus, were devoid of double-labeled cells. Similarly, regions rich in neuroendocrine neurons such as the periventricular hypothalamus and paraventricular and supraoptic hypothalamic nuclei contained no double-labeled cells. These results suggest that modulation of neuroendocrine secretory activity may occur directly at the level of the ME by ER-containing neurons located within restricted regions of the hypothalamus and forebrain. However, the relatively low proportion of ER-containing neurons projecting to the ME suggests that the influence of estradiol upon neuroendocrine function also may include target sites other than the ME.

Distribution of catecholamine-synthesizing enzymes and some neuropeptides in the median eminence-arcuate nucleus complex (MEARC) of the immature female pig

The presence of the catecholamine-synthesizing enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (D beta H) and some neuropeptides, including neuropeptide Y (NPY), Leu5-enkephalin (LENK), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP), galanin (GAL) and somatostatin (SOM) was investigated in nerve fibres and perikarya of the median eminence-arcuate nucleus complex (MEARC) of the sexually immature female pigs by means of the immunohistochemical avidin-biotin complex method. Although immunoreactivities to all the studied substances were found in nerve fibres of the porcine MEARC, there were differences in the distribution and density of particular subsets of nerve fibres within the complex. While loose D beta H-immunoreactive (D beta H-IR) and dense TH-, NPY- and VIP-IR nerve meshworks occurred predominantly in the internal layer of the MEARC, nerve fibres immunoreactive to TH, CGRP, SOM, SP and LENK were more numerous in the external than in the internal layer of the median eminence (ME). Numerous TH-, D beta H-, NPY-, VIP-, SP- and CGRP-IR perivascular nerve fibres were also observed within both layers of the median eminence. There were also differences in the distribution of a particular subset of neurons within the porcine MEARC: NPY-, VIP-, GAL-, SP- and TH-IR (but not D beta H-IR) perikarya were found in the arcuate nucleus, while in the median eminence only subpopulations of NPY-, VIP and GAL-IR neurons were observed.

Immunocytochemical distribution of catecholamine-synthesizing neurons in the hypothalamus and pituitary gland of pigs: tyrosine hydroxylase and dopamine-beta-hydroxylase

This study describes the distribution of catecholaminergic neurons in the hypothalamus and the pituitary gland of the domestic pig, Sus scrofa, an animal that is widely used as an experimental model of human physiology in addition to its worldwide agricultural importance. Hypothalamic catecholamine neurons were identified by immunocytochemical staining for the presence of the catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase. Tyrosine hydroxylase-immunoreactive perikarya were observed in the periventricular region throughout the extent of the third ventricle, the anterior and retrochiasmatic divisions of the supraoptic nucleus, the suprachiasmatic nucleus, the ventral and dorsolateral regions of the paraventricular nucleus and adjacent dorsal hypothalamus, the ventrolateral arcuate nucleus, and the posterior hypothalamus. Perikarya ranged from parvicellular (10-15 microns) to magnocellular (25-50 microns) and were of multiple shapes (rounded, fusiform, triangular, or multipolar) and generally had two to five processes with branched arborization. No dopamine-beta-hydroxylase immunoreactive perikarya were observed within the hypothalamus or in the adjacent basal forebrain structures. Both tyrosine hydroxylase- and dopamine-beta-hydroxylase-immunoreactive fibers and punctate varicosities were observed throughout areas containing tyrosine hydroxylase perikarya, but dopamine-beta-hydroxylase immunoreactivity was very sparse within the median eminence. Within the pituitary gland, only tyrosine hydroxylase fibers, and not dopamine-beta-hydroxylase immunoreactive fibers, were located throughout the neurohypophyseal tract and within the posterior pituitary in both pars intermedia and pars nervosa regions. Generally, the location and patterns of both catecholamine-synthesizing enzymes were similar to those reported for other mammalian species except for the absence of the A15 dorsal group and the very sparse dopamine-beta-hydroxylase immunoreactive fibers and varicosities in the median eminence in the pig. These findings provide an initial framework for elucidating behavioral and neuroendocrine species differences with regard to catecholamine neurotransmitters.

Effect of hypothalamic infusion of a dopamine D1 receptor antagonist on prolactin secretion in the ewe

In this study we investigated whether dopamine D1 receptors in the hypothalamus are involved in the control of prolactin secretion in ovariectomised, oestradiol implanted ewes. The D1 antagonist SCH23390 or vehicle was infused into either the preoptic area (POA) or the ventromedial hypothalamus (VMH). During infusion into the VMH, prolactin concentrations declined significantly and did not return to control values until more than 60 min after the infusions had stopped. In contrast, infusion into the POA had no significant effect. These results are in accord with the hypothesis that dopaminergic pathways within the hypothalamus stimulate prolactin secretion via dopamine D1 receptors in the VMH.

Immunocytochemical localization of the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the hypothalamus of cattle

Immunocytochemical staining for the presence of catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine beta-hydroxylase, was used to characterize the regional distribution of catecholaminergic neurons in the hypothalamus and adjacent areas of domestic cattle, Bos taurus. In steers, heifers and cows, tyrosine hydroxylase-immunoreactive perikarya was located throughout periventricular regions of the third cerebral ventricle, in both anterior and retrochiasmatic divisions of the supraoptic nucleus, suprachiasmatic nucleus, and ventral and dorsolateral regions of the paraventricular nucleus, dorsal hypothalamus, ventrolateral aspects of the arcuate nucleus, along the ventral hypothalamic surface between the median eminence and optic tract, and in the posterior hypothalamus. Immunostained perikarya ranged from small (10-20 microns, parvicellular) to large (30-50 microns, magnocellular) and were of multiple shapes: round, triangular, fusiform or multipolar, often with 2-5 processes of branched arborization. There were no dopamine-beta-hydroxylase immunoreactive perikarya observed within the hypothalamus and adjacent structures. However, both tyrosine hydroxylase and dopamine-beta-hydroxylase immunoreactive fibers and punctate varicosities were observed throughout regions of tyrosine hydroxylase immunoreactivity perikarya. Generally, the location and pattern of hypothalamic tyrosine hydroxylase immunoreactivity and dopamine-beta-hydroxylase immunoreactive were similar to those reported for most other large brain mammalian species, however, there were several differences with commonly used small laboratory animals. These included intense tyrosine hydroxylase immunoreactivity of perikarya within the retrochiasmatic division of the supraoptic nucleus (ventral A15 region), the absence of tyrosine hydroxylase immunoreactive perikarya below the anterior commissure or within the bed nucleus of stria terminalis (absence of the dorsal A15 region), an abundance of tyrosine hydroxylase immunoreactive perikarya within the ependymal layer of the median eminence, heavy innervation of the arcuate nucleus with dopamine-beta-hydroxylase immunoreactive fibers and varicosities, and the paucity of dopamine-beta-hydroxylase immunoreactive throughout the median eminence.

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.

Catecholaminergic region A15 in the bovine and porcine hypothalamus

Magnocellular perikarya within the retrochiasmatic division of the supraoptic nucleus of bovine and porcine hypothalami were immunoreactive (ir) with antiserum against tyrosine hydroxylase (TH), but not dopamine-beta-hydroxylase (DBH). Few cells in this region were also immunoreactive for vasopressin (VP) or oxytocin (OT). In contrast, the main division of the supraoptic nucleus contained numerous perikarya immunoreactive for VP and OT, but not TH nor DBH. Both the retrochiasmatic and principal divisions of the supraoptic nuclei contained TH- and DBH-ir fibers and varicosities. This region in bovine and porcine hypothalami corresponds to the ventral A15 catecholaminergic (dopamine-producing) cell group.

Postnatal development and laminar distribution of noradrenergic fibers in cat visual cortex

Previous studies have indicated that adrenergic receptors show significant changes either in laminar distribution or in number during the critical period of kitten visual cortex development. In order to further investigate the postnatal development of this neurotransmitter system, especially in relation to the critical period, we used a polyclonal antibody against dopamine-beta-hydroxylase to localize noradrenaline-containing afferents in visual cortex of kittens of various ages from birth to adulthood. In young kittens, less than 2 weeks of age, noradrenergic fibers were sparse, short and randomly oriented, and were concentrated in layer I and in deep cortical layers V and VI. By postnatal day 40, the fibers were present throughout all cortical layers and exhibited higher densities in layers I, II, III, V and VI, with a band of lower staining in layer IV. While tangential fibers predominated in layers I, V and VI, relatively straight radial fibers traversed layers II and III. After postnatal day 40, we did not find major changes in the laminar distribution of adrenergic fibers. This developmental laminar distribution pattern of adrenergic fibers resembles that of the beta-adrenergic receptors that we and others have studied in kitten visual cortex, but differs from that of alpha-adrenergic receptors.

Neuronal projections to the medial preoptic area of the sheep, with special reference to monoaminergic afferents: immunohistochemical and retrograde tract tracing studies

The preoptic area contains most of the luteinizing hormone releasing hormone immunoreactive neurons and numerous monoaminergic afferents whose cell origins are unknown in sheep. Using tract tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the medial preoptic area in sheep. Among the retrogradely labeled neurons, immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, phenylethanolamine N-methyltransferase, and serotonin was used to characterize catecholamine and serotonin fluorogold labeled neurons. Most of the afferents came from the ipsilateral side to the injection site. It was observed that the medial preoptic area received major inputs from the diagonal band of Broca, the lateral septum, the thalamic paraventricular nucleus, the lateral hypothalamus, the area dorsolateral to the third ventricle, the perimamillary area, the amygdala, and the ventral part of the hippocampus. Other numerous, scattered, retrogradely labeled neurons were observed in the ventral part of the preoptic area, the vascular organ of the lamina terminalis, the ventromedial part of the hypothalamus, the periventricular area, the area lateral to the interpeduncular nucleus, and the dorsal vagal complex. Noradrenergic afferents came from the complex of the locus coeruleus (A6/A7 groups) and from the ventro-lateral medulla (group A1). However, dopaminergic and adrenergic neuronal groups retrogradely labeled with fluorogold were not observed. Serotoninergic fluorogold labeled neurons belonged to the medial raphe nucleus (B8, B5) and to the serotoninergic group situated lateral to the interpeduncular nucleus (S4). In the light of these anatomical data we hypothesize that these afferents have a role in the regulation of several functions of the preoptic area, particularly those related to reproduction. Accordingly these afferents could be involved in the control of luteinizing hormone releasing hormone (LHRH) pulsatility or of preovulatory LHRH surge.

Distribution of dopamine-containing neurons and fibres in the feline medulla oblongata: a comparative study using catecholamine-synthesizing enzyme and dopamine immunohistochemistry

The distribution of dopamine-immunoreactive neurons and fibres in the feline medulla oblongata was examined by immunocytochemistry with antisera to the catecholamine-synthesizing enzymes tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase, and with antisera to the catecholamines dopamine and L-dihydroxyphenylalanine. Neurons immunoreactive for the catecholamine-synthesizing enzymes were found in two regions of the medulla, the ventrolateral A1 region and the dorsomedial A2 region. Double-staining studies with antisera to the enzymes indicated that a population of neurons within both regions were immunoreactive for tyrosine hydroxylase but not dopamine-beta-hydroxylase or phenylethanolamine-N-methyltransferase, implying that they synthesize dopamine. Studies using the dopamine antisera demonstrated the presence of dopamine-immunoreactive neurons in both the ventrolateral and dorsomedial regions of the medulla; in the dorsomedial region, they were found in the area postrema, nucleus tractus solitarius and dorsal motor vagal nucleus, mainly at levels caudal to the obex. Dopamine-immunoreactive fibres were found in several areas of the medulla including the nucleus tractus solitarius, inferior olive, dorsal motor vagal, spinal trigeminal, hypoglossal, cuneate, gracile, and raphe nuclei. Double-staining studies with antisera to dopamine and dopamine-beta-hydroxylase revealed a population of cells immunoreactive for dopamine alone. The presence of some double-stained neurons, however, implies some cross-reactivity of the dopamine antiserum with noradrenaline or adrenaline and/or recognition of dopamine present as a metabolic intermediary in some noradrenergic neurons. No L-dihydroxyphenylalanine-immunoreactive neurons were found in the medulla, although fibres were seen. These data provide evidence for the existence of catecholamine neurons which utilize dopamine as a final synthetic product within the medulla oblongata.

The catecholaminergic system of the quail brain: immunocytochemical studies of dopamine beta-hydroxylase and tyrosine hydroxylase

The distribution of dopamine beta-hydroxylase and tyrosine hydroxylase, two key enzymes in the biosynthesis of catecholamines, was investigated by immunocytochemistry in the brain of male and female Japanese quail. Cells or fibers showing dopamine beta-hydroxylase and tyrosine hydroxylase immunoreactivity were considered to be noradrenergic or adrenergic, while all structures showing only tyrosine hydroxylase immunoreactivity were tentatively considered to be dopaminergic. The major dopaminergic and noradrenergic cell groups that have been identified in the brain of mammals could be observed in the Japanese quail, with the exception of a tuberoinfundibular dopaminergic group. The dopamine beta-hydroxylase-immunoreactive cells were found exclusively in the pons (locus ceruleus and nucleus subceruleus ventralis) and in the medulla (area of the nucleus reticularis). The tyrosine hydroxylase-immunoreactive cells had a much wider distribution and extended from the preoptic area to the level of the medulla. They were, however, present in larger numbers in the area ventralis of Tsai and in the nucleus tegmenti pedunculo-pontinus, pars compacta, which respectively correspond to the ventral tegmental area and to the substantia nigra of mammals. A high density of dopamine beta-hydroxylase- and tyrosine hydroxylase-immunoreactive fibers and punctate structures was found in several steroid-sensitive brain regions that are implicated in the control of reproduction. In the preoptic area and in the region of the nucleus accumbens-nucleus stria terminalis, immunonegative perikarya were completely surrounded by immunoreactive fibers forming basket-like structures. Given that some of these cells contain the enzyme aromatase, these structures may represent the morphological substrate for a regulation of aromatase activity by catecholamines. The dopamine beta-hydroxylase-immunoreactive fibers were also present in a larger part of the preoptic area of females than in males. This sex difference in the noradrenergic innervation of the preoptic area presumably reflects the sex difference in norepinephrine content in this region.

Morphological relationships between tyrosine hydroxylase-immunoreactive neurons and dopamine-beta-hydroxylase-immunoreactive fibres in dopamine cell group A15 of the sheep

Double immunocytochemical labelling with antibodies raised against tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase was used on semi-thin sections of sheep hypothalamus to investigate possible morphological relationships between dopamine neurons of group A15 and noradrenaline afferents to this area. Dopamine-beta-hydroxylase-immunoreactive (IR) fibres were found in the close proximity of dendrites of TH-IR neurons. At electron microscopic level, single immunocytochemical staining with TH antibodies revealed the presence of synaptic contacts between labelled or unlabelled axon terminals and anti-TH labelled dendrites. These observations suggest that in the sheep, TH-IR neurons of group A15 are controlled by non-catecholaminergic and catecholaminergic afferents. Catecholamine inputs could contain either dopamine or noradrenaline. The hypothesis of noradrenaline inputs to A15 is strongly supported by the results obtained after double labelling on semi-thin sections. Tyrosine hydroxylase-immunoreactive perikarya and dendrites often seemed to be partly surrounded by glial processes. This latter observation suggests that the synaptic investment of these neurons might be controlled by glial cells.

Immunolocalization of catecholamine enzymes, serotonin, dopamine and L-dopa in the brain of Dicentrarchus labrax (Teleostei)

Antisera to serotonin (5-HT), dopamine, and L-dopa, and to the catecholamine synthesizing enzymes, tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyl transferase (PNMT), were used to localize monoamine containing neurones in the brain of Dicentrarchus labrax (sea bass). In the brain stem, 5-HT-immunoreactive (ir) neurones were recognized in the ventrolateral medulla, vagal motor area, medullary, and mesencephalic raphe nuclei and in the dorsolateral isthmal tegmentum. In the hypothalamus, liquor-contacting 5-HT neurones were seen in various regions of the paraventricular organ. Virtually all regions of the brain contained a dense innervation by 5-HT fibres and terminals. DBH-ir neurones were restricted to three brain stem areas: the locus coeruleus, the area postrema, and the reticular formation of the lower medulla. Neurones in these three groups also displayed TH-ir, and in the latter area, PNMT-ir in addition. In the locus coeruleus and area postrema, TH-ir neurones outnumbered DBH-ir neurones, an observation substantiated by the presence of dopamine-ir neurones. In the forebrain, dopamine- and TH-ir neurones were found in the olfactory bulb, ventral/central telencephalon, periventricular preoptic, and suprachiasmatic areas, dorsolateral and ventromedial thalamus, and posterior tuberal nucleus. In the paraventricular organ, the distribution and morphology of dopamine-ir neurones was similar to that observed with anti-5-HT, but the vast majority of cells were not TH-ir, suggesting accumulation of dopamine by uptake from the ventricle, rather than by synthesis. L-dopa-ir neurones were found only in the central telencephalon, preoptic recess, and dorsolateral thalamus. Fibres and terminals immunoreactive for dopamine, TH, and DBH showed a broadly similar distribution. The results are discussed in relation to the monoaminergic systems previously reported in other teleostean species and the mammalian brain.

Immunohistochemical colocalization of tyrosine hydroxylase and estradiol receptors in the sheep arcuate nucleus

In sheep, the arcuate nucleus contains numerous tyrosine hydroxylase (TH) and estradiol receptor (rE2) immunoreactive (IR) perikarya and it has been shown previously in this species that catecholaminergic neurons can mediate the gonadal steroid action on the reproductive function. In the present study, double immunohistochemical labelling with antibodies against TH and rE2 have been used to demonstrate the presence of rE2 in TH-IR neurons in the arcuate nucleus where the distribution of TH-IR and rE2-IR neurons overlap each other. Only less than 10% of all the rE2-IR perikarya presented TH immunoreactivity. It was therefore hypothesized that either such a low number of double labelled neurons can support the effects of estradiol in this area or that the effect of this steroid was indirect. In the latter case it might be first mediated by beta-endorphin neurons which have been previously described in this nucleus.

Neuropeptides and monoamines in the torus semicircularis of the carp (Cyprinus carpio)

The distribution of vasoactive intestinal polypeptide, gastrin-releasing peptide, gamma-melanocyte-stimulating hormone, alpha-neo-endorphin, angiotensin II, cholecystokinin-8, serotonin, and tyrosine hydroxylase has been studied in the nuclei lateralis and centralis of the Cyprinus carpio torus semicircularis using an indirect immunoperoxidase technique. In both nuclei, we found vasoactive intestinal polypeptide, gastrin-releasing peptide, gamma-melanocyte-stimulating hormone, alpha-neo-endorphin, serotonin, and tyrosine hydroxylase immunoreactive fibers, whereas the torus semicircularis was not immunoreactive for cholecystokinin-8 and angiotensin II. Moreover, no immunoreactive cell bodies containing peptides or monoamines were observed. The presence of these peptides and monoamines in both the nuclei lateralis and centralis suggests that such substances might be involved in the control of the visual, auditive, and/or lateral line information systems.

Dopaminergic neurons in the cat dorsal motor nucleus of the vagus, demonstrated by dopamine, AADC and TH immunohistochemistry

In the rostral part of the dorsal motor nucleus of the vagus of the cat, neurons do not contain histochemically detectable catecholamines, even though many perikarya contain both intense aromatic L-amino acid decarboxylase (AADC) immunoreactivity and strong monoamine oxidase enzymatic activity. Similarly located perikarya have distinct immunoreactivities to tyrosine hydroxylase (TH) and dopamine after treatment with colchicine. Since inhibition of monoamine oxidase fails to reveal dopamine in these cells, its absence in non-colchicine-treated animals cannot be due to rapid deamination. It appears that dopamine is synthesized by TH and AADC in dorsal motor vagal cells and is then rapidly transported from the perikarya.

Monoamine content of the stalk-median eminence and hypothalamus in adult female sheep as affected by daylength

Abstract In the ewe, plasma luteinizing hormone and prolactin concentrations exhibit seasonal variations. During long days, inhibition of pulsatile luteinizing hormone secretion is mediated by monoamines. In a model of ovariectomized ewes bearing a subcutaneous oestradiol implant, we previously showed that the steroid-dependent inhibition of luteinizing hormone involves the A15 dopaminergic nucleus of the retrochiasmatic area. In the present work, we compared the aminergic activities of tele-diencephalic structures in groups of ovariectomized ewes under artificial illumination for short versus long days (8 versus 16 h/day of light, respectively). Half the animals in each group were bearing a subcutaneous oestradiol implant. Using high-performance liquid chromatography and electrochemical detection, we measured the levels of amines and amine metabolites in 'punches' of tissues from regions containing luteinizing hormone-releasing hormone axon terminals or cell bodies and catecholaminergic structures. Concurrently, we checked the pulsatile luteinizing hormone release and plasma prolactin concentration to assess the ability of our model to mimic seasonal changes in the hormonal status. As expected, ovariectomized ewes with a subcutaneous oestradiol implant showed an inhibition of the pulsatile luteinizing hormone release under long days. A higher concentration of plasma prolactin was also observed under long days, without any effect of the steroid treatment. Under this light regimen, statistically significant higher contents of dopamine than under short days were found in the stalk-median eminence. Larger contents of homovanillic acid, a dopamine metabolite, and 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), a noradrenaline metabolite were observed in the infundibular nucleus, while the catechola-mines themselves remained unchanged. Furthermore, oestradiol also significantly increased the content of MHPG in the latter structure. During long days, animals without oestradiol treatment exhibited a significant lower content of noradrenaline in the A15 nucleus, without any alteration of the dopamine content. Daylength or oestradiol treatment had no significant effects on the levels of amines or amine metabolites in the preoptic or septal areas. Thus, our results in the ewe underline the role played by the medial basal hypothalamus in the catecholaminergic regulation of seasonal changes in hormone release and suggest modifications in the turnover of the neurotransmitters in some structures.

Preparation and characterization of a specific antibody for the immunohistochemical detection of L-dopa in paraformaldehyde-fixed rodent brains

A rat polyclonal antiserum has been obtained after coupling of L-3,4-dihydroxyphenylalanine (L-DOPA) to larger proteins using a low concentration of glutaraldehyde. The antiserum was tested for its affinity and specificity using an enzyme-linked-immunosorbent-assay (ELISA). From competition experiments, the most immunoreactive compound was found to be the non-reduced L-DOPA conjugate. Our specific L-DOPA antiserum enables us to visualize L-DOPA molecule on brain of guinea pigs and rats. We examined the immunohistochemical distribution of the polyclonal L-DOPA antiserum after the fixation of brains with a mixture of paraformaldehyde and picric acid. The presence of L-DOPA-immunoreactive (IR) neurons and fibers was described in the posterior, dorsal and periventricular hypothalamic areas and in the arcuate nucleus. Finally, the distribution of L-DOPA-IR cells was compared to that of tyrosine hydroxylase (TH)-IR cells, by means of a double staining procedure. The presence of two populations of TH-IR cells (TH-positive/L-DOPA-negative and TH-positive/L-DOPA-positive cells) was described in the dorsal part of the hypothalamus.

Distribution, morphology and number of monoamine-synthesizing and substance P-containing neurons in the human dorsal raphe nucleus

The distribution, morphology and number of serotonin-, catecholamine- and substance P-containing neurons in the human dorsal raphe nucleus were studied. Parallel series of sections were prepared from 10 human brainstems obtained at autopsy from patients without neurological disease aged between 42 and 88 years. The neurons were identified using immunohistochemistry with antibodies raised against phenylalanine hydroxylase (tryptophan hydroxylase-containing, serotonin neurons), tyrosine hydroxylase (catecholamine neurons) and substance P. A reference series of Nissl-stained sections was also prepared and data published separately were used to delineate the subnuclear divisions of the dorsal raphe nucleus and to establish the total number of neurons in each subnucleus. The following principal findings emerged. (1) Serotonin-synthesizing neurons are present in all regions of the dorsal raphe nucleus and their total number is 165,000 +/- 34,000. The same types of neurons as those seen in Nissl material characterize each of the five subnuclei (caudal, dorsal, ventral, ventrolateral and interfascicular). (2) Substance P-containing neurons mostly occupy the rostral part of the nucleus and their number is 74,600 +/- 17,600. (3) Catecholamine cells are only found in the rostral part of the dorsal raphe nucleus and their number is 5600 +/- 3400. (4) In the ventral and interfascicular subnuclei the combined number of serotonin-synthesizing and substance P-containing neurons exceeds the total number of Nissl-stained neurons suggesting that serotonin and substance P co-exist in a substantial part of the cell population of the dorsal raphe nucleus. This is further supported by the highly similar morphology and size of these neurons. It is concluded that there are demonstrable chemical differences between the various subregions of the human dorsal raphe nucleus. These differences are in harmony with the results of hodological studies in animals, which have demonstrated differential projection pathways emerging from this nucleus.