Localization of oestrogen receptors in preoptic neurons containing neurotensin but not tyrosine hydroxylase, cholecystokinin or luteinizing hormone-releasing hormone in the male and female rat.

The neurochemical identity of preoptic neurons containing oestrogen receptors was investigated in the male and female rat using a sequential double-staining immunocytochemistry procedure. Single-immunostaining revealed large populations of cells with nuclear immunoreactivity to the oestrogen receptor in the medial preoptic area of the male and female rat. Optimal double-staining of sections for the oestrogen receptor and one of several neuropeptides or tyrosine hydroxylase, was achieved with short-term (two- to four-day) gonadectomized rats treated with colchicine where necessary. Neurotensin-immunoreactive cells were distributed in a sexually dimorphic manner in the region of the anteroventral preoptic nucleus and exhibited oestrogen receptor immunoreactivity in both sexes. Double-labelled cells in this area of the female rat comprised 50% and 11% of the total neurotensin- and oestrogen receptor-containing cell populations, respectively, compared with 25% and 4% in the male (P less than 0.01). The numbers of neurotensin-immunoreactive cells in the region of the medial preoptic nucleus were similar in male and female rats with double-labelled cells making up 20-38% and 3-5% of the total numbers of cells containing neurotensin and oestrogen receptors, respectively, in both sexes. Neurons immunoreactive for tyrosine hydroxylase were distributed in a gender-specific manner within the anterior periventricular area but were not immunoreactive for the oestrogen receptor in either sex. Following colchicine treatment, cholecystokinin-immunoreactive cells were identified predominantly within periventricular regions of the preoptic area and similarly, did not possess immunoreactivity to the oestrogen receptor in either the male or the female rat. Neurons containing luteinizing hormone-releasing hormone were found immediately lateral to the cell populations containing oestrogen receptors and immunoreactivity to the oestrogen receptor was not identified within any neurons containing luteinizing hormone-releasing hormone in either the male or female rat. The absence of oestrogen receptor immunoreactivity in neurons containing tyrosine hydroxylase, cholecystokinin or luteinizing hormone-releasing hormone suggests that gonadal steroids acting through this receptor do not influence these cells directly in either sex. In particular, it appears that gender-specific patterns of luteinizing hormone secretion cannot be attributed to sex differences in oestrogen receptor localization within luteinizing hormone-releasing hormone neurons. These experiments also show that the sexually dimorphic neurotensin neurons in the preoptic area possess oestrogen receptors and that female rats have larger number of neurons co-localizing neurotensin and oestrogen receptors. As such, these neurons may be involved in mediating sex-specific actions of the gonadal steroids in the preoptic area.     

Projection of pro-opiomelanocortin neurons from the rat arcuate nucleus to the midbrain central gray as demonstrated by double staining with retrograde labeling and immunohistochemistry

Conjugate of horseradish peroxidase and wheat germ agglutinin (HRP-WGA conjugate) was injected into the midbrain central gray (MCG) of three adult rats. Frontal sections of the diencephalon were first treated with diaminobenzidine and hydrogen peroxide to detect the retrogradely transported conjugate. They were then stained immunohistochemically to detect pro-opiomelanocortin (POMC)-derived peptides (ACTH, beta-endorphin and alpha-MSH). The coexistence of the three POMC-derived peptides was confirmed by the immunohistochemistry of three consecutive sections stained with antiserum specific to each peptide. Some of the neuronal perikarya distributed in and around the arcuate nucleus were positive to the immunohistochemical stain for POMC-derived peptides, and, concomitantly, were labeled with HRP-WGA conjugate, which indicated that they projected to the MCG. They were mostly concentrated in the rostral three-fifths of the arcuate nucleus. The finding that some of the POMC neurons in the arcuate nucleus project to the midbrain central gray deserves interest, because the central gray is involved in analgesia induced by opioid peptides.     

Brainstem projections to the medial preoptic region containing the luteinizing hormone-releasing hormone perikarya in the rat. An immunohistochemical and retrograde transport study.

The afferent projections to the anterior medial preoptic area (MPA) from the brainstem have been studied, in female Wistar rats, by retrograde tracing with horseradish peroxidase (HRP). The HRP was injected by iontophoresis into the preoptic region containing the luteinizing hormone-releasing hormone (LHRH) perikarya. The brain sections including the MPA were reacted with diaminobenzidine (DAB) to reveal the injection site; the LHRH cells were then immunohistochemically identified using DAB with ammonium nickel sulphate. When the injection site incorporated the LHRH cells, the brainstem sections were reacted with the DAB nickel solution to detect lysosomal HRP and then immunohistochemically processed to locate the adrenaline-synthesizing cells using DAB alone. The results confirm the brainstem projections to the MPA from the central grey matter, ventral tegmental area, subcoeruleus area, the dorsal raphe nucleus, the lateral parabrachial nucleus, the raphe pontis nucleus, the raphe obscurus nucleus, the region of the paragigantocellular nucleus and the nucleus of the solitary tract. Given the considerable evidence implicating the ascending adrenergic systems in the regulation of LHRH, we focused our attention on the afferents from the locus coeruleus, area postrema and the adrenaline-synthesizing cell groups (C1-3). The only cells which were retrogradely labelled and immunopositive for phenylethanolamine N-methyltransferase were found in C3.     

Hypothalamic neurons projecting to the rat caudal medulla oblongata, examined by immunoperoxidase staining of retrogradely transported horseradish peroxidase

Horseradish peroxidase (HRP), injected into the rat caudal medulla oblongata, was detected by immunoperoxidase staining in 120 microns frozen sections, allowing examination of both the distribution and morphology of transporting neurons. In the hypothalamus, several groups of HRP-labeled neurons could be distinguished on the basis of location of the neurons, neural cell size and morphology of the neural processes. Most HRP-labeled neurons were found in the posterior half of the hypothalamus, although scattered single neurons were present as far rostral as the anterior hypothalamus and preoptic area. Prominent groups of HRP-labeled neurons were found in the paraventricular, dorsomedial and arcuate nuclei, near the fornix at two separate levels, and in the lateral posterior hypothalamus. Based on comparison with peptide immunohistochemistry it seems likely that many magnocellular oxytocin, vasopressin and neurophysin neurons in the paraventricular nucleus, and a few ACTH/beta-endorphin neurons in the arcuate nucleus may project to the caudal medulla oblongata.     

大鼠视前内侧区的传入性神经纤维联系,HRP,EB,NY法研究

本文应用轴突逆行运输HRP、EB、NY研究大鼠视前内侧区的传入性神经纤维联系。所用三种示踪剂结果基本一致。结果为:在外侧隔核、外侧嗅束核、杏仁内侧核、下丘脑外侧区、下丘脑腹内侧核和乳头体前腹核内观察到密集的标记细胞。在杏仁皮质核、杏仁中央核、下丘脑室旁核、下丘脑后核、弓状核、乳头体上核、丘脑腹核尾侧部、未定带、腹侧被盖区、脚间核、中缝正中核和背核内观察到较多标记细胞。在中脑中央灰质腹侧部、兰斑核、外侧臂旁核及海马腹下角内观察到少数标记细胞。     

A direct catecholaminergic projection from the brainstem to the neurohypophysis of the rat

The presence of the catecholamines dopamine and noradrenaline in the posterior pituitary is well documented. Dopaminergic terminals are thought to derive from cells in the periventricular hypothalamus including the rostral arcuate nucleus, but the origin of the noradrenergic terminals is uncertain. The majority of central noradrenaline-containing neurons are in the brainstem and lesions of the ventral noradrenergic tract significantly reduce the noradrenaline content of the neural lobe. We have explored the possibility of a direct noradrenergic projection from the brainstem to the neural lobe using as a retrograde tract tracer horseradish peroxidase alone or in combination with immunohistochemical detection of tyrosine hydroxylase. Horseradish peroxidase was injected into the neural lobes of 20 rats using a ventral approach, and the animals were perfusion fixed 12 h later. In all 20 cases, cells retrogradely labelled with horseradish peroxidase were found not only in the periventricular zone and magnocellular nuclei of the hypothalamus but also in the A2 region of the brainstem. In all six cases simultaneously processed for horseradish peroxidase and tyrosine hydroxylase immunohistochemistry, retrogradely labelled cells in both the arcuate nucleus and A2 region were found to be tyrosine hydroxylase-positive. These findings demonstrate the presence of a direct projection from catecholaminergic neurons in the A2 region of the brainstem to the neurohypophysis. Since catecholaminergic neurons in this region are known to be noradrenergic and lesions of the ventral noradrenergic tract deplete the neurohypophysis of noradrenaline, these neurons may represent an important source of noradrenaline in the neurohypophysis.     

The distribution and morphology of identified thalamocortical projection neurons and glial cells with reference to the question of interneurons in the ventrolateral nucleus of the rat thalamus

The distribution and morphology of thalamocortical projection neurons and glial cells in the ventrolateral nucleus of the rat thalamus have been investigated using light and electron microscopic techniques. In this material thalamocortical projection neurons in the ventrolateral nucleus were identified by the retrograde transport of horseradish peroxidase following the placement of multiple injections of horseradish peroxidase in the primary motor and sensorimotor overlap regions of the cerebral cortex. The location of horseradish peroxidase-labelled thalamocortical projection neurons varied with the locus of injection in the motor and sensorimotor overlap cortex; caudal injections labelled cells in the rostrolateral region of the ventrolateral nucleus while injections involving successively more rostral regions of the cortex labelled cells in more medial and caudal regions of the nucleus. Labelled thalamocortical neurons were grouped in clusters with neuron pairs often closely applied to each other via non-synaptic junctional complexes. Where the field of labelled neurons was analysed in series of 1-micron-thick sections with phase contrast light microscopy, all neurons in the field were found to be clearly labelled with horseradish peroxidase. Thalamocortical neurons comprised mainly medium-to-large, multipolar ovoid-shaped cells which showed a large centrally placed nucleus with deep invaginations of the nuclear membrane. Two types of glial cells were identified: astrocytes, identified by their characteristic pale-staining ovoid nucleus, showed a close relationship to blood vessels, synaptic complexes and neurons; oligodendrocytes, distinguished by their darkly stained nucleus and cytoplasm, were somewhat smaller and showed a close association with myelinated fibres. These findings show that the rat ventrolateral nucleus comprises a homogeneous population of thalamocortical projection neurons and thus provide indirect evidence suggesting the absence of interneurons in the ventrolateral nucleus of the rat thalamus.     

Vasopressin induces a luteinizing hormone surge in ovariectomized, estradiol-treated rats with lesions of the suprachiasmatic nucleus.

The luteinizing hormone surge in the female rat is the result of the integration of multiple signals within the medial preoptic area. The medial preoptic area contains gonadotropin-releasing hormone neurons that are responsible for the release of luteinizing hormone, neurons containing estrogen receptors and terminals originating from the suprachiasmatic nucleus with, for example, vasopressin as neurotransmitter. Both the medial preoptic area and suprachiasmatic nucleus are crucial for the occurrence of luteinizing hormone surges, since lesioning of either nucleus prevents pre-ovulatory and steroid-induced luteinizing hormone surges. In this study, we investigated whether vasopressin in the medial preoptic area could be the daily neuronal signal from the suprachiasmatic nucleus responsible for the timing of the luteinizing hormone surge. Vasopressin (50 ng/microl) or Ringer solution was administered by reverse microdialysis from Zeitgeber times 7.5 to 12.5 into the medial preoptic area of ovariectomized, estradiol-treated rats. The suprachiasmatic nucleus was lesioned to remove all cyclic luteinizing hormone secretion. This was evaluated by monitoring behavioral activity; animals that were arrhythmic were included in the experiments. Hourly blood samples were taken to measure plasma luteinizing hormone levels. Preoptic vasopressin administration induced a surge-like luteinizing hormone pattern in suprachiasmatic nucleus-lesioned animals, whereas constant, basal luteinizing hormone levels were found in the control animals. These data show that vasopressin, by itself, is able to trigger the luteinizing hormone surge in suprachiasmatic nucleus-lesioned rats. We propose that vasopressin is a timing signal from the suprachiasmatic nucleus responsible for the activation of the hypothalamo-pituitary-gonadal axis in the female rat.     

Neurons containing messenger RNA encoding glutamate decarboxylase in rat hypothalamus demonstrated by in situ hybridization, with special emphasis on cell groups in medial preoptic area, anterior hypothalamic area and dorsomedial hypothalamic nucleus

Previous deafferentation studies have suggested that most hypothalamic GABAergic innervation originates from neurons within the hypothalamus. We have investigated the distribution of GABAergic cell groups in the rat hypothalamus by means of the in situ hybridization technique, using a cDNA probe for messenger RNA encoding glutamate decarboxylase. Several major GABAergic cell groups were demonstrated, including cells of the tuberomammillary nucleus, arcuate nucleus, suprachiasmatic nucleus, medial preoptic area, anterior hypothalamic area, the dorsomedial hypothalamic nucleus, perifornical area, and lateral hypothalamic area. The most prominent glutamate decarboxylase mRNA-containing cell groups were located in the medial preoptic area, anterior hypothalamic area and dorsomedial hypothalamic nucleus, and were composed of small- to medium-sized neurons. Compared to previously well-characterized GABAergic cell groups in the tuberomammillary nucleus, reticular thalamic nucleus, and non-pyramidal cells of cerebral cortex, the cells of these GABAergic groups demonstrated only weak cDNA labelling, indicating that they contain lower levels of glutamate decarboxylase mRNA. Several types of control experiments supported the specificity of this cDNA labelling, and the GABAergic nature of these cell populations was further supported by detection of glutamate decarboxylase and GABA immunoreactivity. Abundance of GABAergic cells in many hypothalamic nuclei indicates that GABA represents quantitatively the most important transmitter of hypothalamic neurons, and may be involved in neuroendocrine and autonomic regulatory functions.     

Catecholaminergic afferents to the cat median eminence as determined by double-labelling methods.

The localization of dopaminergic and non-dopaminergic neuronal perikarya sending axons to the median eminence was investigated in the cat by using two colour double-immunostaining techniques. Unconjugated cholera toxin and wheat germ agglutinin were used as retrograde tracers and injected respectively into the median eminence and the neuro-intermediate pituitary of the same animal. As controls, cholera toxin was also injected into the arcuate (infundibular) nucleus or third ventricle. The retrograde labelling of one of the tracers was combined with tyrosine hydroxylase immunohistochemistry as a marker for dopaminergic neurons. The retrograde labelling studies of cholera toxin alone and the double-immunostaining of cholera toxin and wheat germ agglutinin on the same sections revealed that the cat median eminence receives major afferent projections originating in midline hypothalamic nuclear groups such as the anterior periventricular nucleus, the periventricular part of the paraventricular nucleus and the arcuate nucleus; minor afferent projections arise from the anterior hypothalamic area, the rostral part of the medial preoptic area around the organum vasculosum of the lamina terminalis and to a lesser extent from the posterior hypothalamic region. We further determine that the rostral part of the parvocellular arcuate neurons constitutes the main source of dopaminergic afferents to the median eminence in the cat brain.     

Beta-endorphin-, adrenocorticotrophic hormone- and neuropeptide y-containing projection fibers from the arcuate hypothalamic nucleus make synaptic contacts on to nucleus preopticus medianus neurons projecting to the paraventricular hypothalamic nucleus in the rat

The nucleus preopticus medianus is known to be situated in a key site in pathways regulating the paraventricular hypothalamic nucleus. To investigate the innervation pattern to nucleus preopticus medianus neurons by afferent fibers containing beta-endorphin, adrenocorticotrophic hormone and neuropeptide Y, a retrograde tracing method was combined with immunohistochemistry for these peptides in the rat. In the first experiment with injection of a retrograde tracer in the nucleus preopticus medianus, retrogradely labeled neurons were found in many regions throughout the brain. Among these, the arcuate hypothalamic nucleus contained a number of retrogradely labeled neurons showing immunoreactivity to the neuropeptides examined. About 20%, 20% and 40% of retrogradely labeled arcuate hypothalamic nucleus neurons showed beta-endorphin, adrenocorticotrophic hormone and neuropeptide Y immunoreactivity, respectively. About 18% and 57% of retrogradely labeled neurons in the nucleus tractus solitarius and ventrolateral medulla, respectively, were immunoreactive to neuropeptide Y. There were many more neuropeptide Y-immunoreactive projections to the nucleus preopticus medianus from the arcuate hypothalamic nucleus than those from the medulla. None of the retrogradely labeled neurons in the medulla showed immunoreactivity to beta-endorphin or adrenocorticotrophic hormone. In the second experiment with injection of a retrograde tracer in the paraventricular hypothalamic nucleus, electron microscopic observation revealed that retrogradely labeled neurons in the nucleus preopticus medianus were in synaptic contact with beta-endorphin-, adrenocorticotrophic hormone- and neuropeptide Y-immunoreactive axon terminals.The present finding indicates that nucleus preopticus medianus neurons projecting to the paraventricular hypothalamic nucleus are innervated by beta-endorphin-, adrenocorticotrophic hormone- and neuropeptide Y-containing arcuate hypothalamic nucleus neurons in addition to being innervated by neuropeptide Y-containing catecholaminergic medullary neurons which have been reported in our previous study.     

下丘脑弓状核KNDy神经元参与围绝经期潮热发生的机制

潮热是围绝经期女性最常见的特异性症状,严重危害女性的身心健康和生活质量。由于潮热的发病机制尚未明确,且现有的雌激素替代疗法存在诸多局限和禁忌,故探讨潮热的发病机制并寻找新的治疗靶点尤为迫切和重要。近年研究提示,围绝经期雌激素降低时下丘脑弓状核（ARC）中KNDy神经元异常是引起潮热的关键因素。部分学者认为,ARC中KNDy神经元通过调控促性腺激素释放激素及其下游促黄体生成素的脉冲释放参与潮热的发生;而另有学者认为,ARC中KNDy神经元通过调控下丘脑视前区的正中视前核在潮热发生过程中发挥关键作用。我们就上述两种关于ARC KNDy神经元与潮热发生之间的关系及其参与潮热的可能机制进行总结和概括,为探寻诊治围绝经期潮热的新靶点和新方法奠定理论基础。     

Anatomical relationships of monoaminergic and neuropeptide Y-containing fibres with luteinizing hormone-releasing hormone systems in the preoptic area of the sheep brain: immunohistochemical studies

Immunohistochemical double-labellings of luteinizing hormone-releasing hormone and neuropeptide Y, serotonin, tyrosine hydroxylase and dopamine-beta-hydroxylase, were performed in the preoptic area at the level of the organum vasculosum laminae terminalis. The observed neuropeptide Y-, serotonin-, tyrosine hydroxylase- and dopamine-beta-hydroxylase-immunoreactive fibres presented large varicosities when they were found within close proximity to luteinizing hormone-releasing hormone-containing perikarya. The fact that neuropeptide Y- and dopamine-beta-hydroxylase-immunoreactive fibres exhibited the same morphological characteristics and the comparison of the distribution of these two fibre populations raised the possibility of the co-localization of neuropeptide Y and dopamine-beta-hydroxylase in the same fibres. Dopamine-beta-hydroxylase- and tyrosine hydroxylase-immunoreactive fibres were morphologically different, suggesting that both dopaminergic and noradrenergic fibres could contact luteinizing hormone-releasing hormone-containing perikarya. Serotonin-immunoreactive fibres were also found close to the perikarya and to the proximal dendrite of the luteinizing hormone-releasing hormone-containing neurons. This study showed only putative sites of interactions between chemically identified fibres and luteinizing hormone-releasing hormone-containing neurons. Further ultrastructural immunocytochemical investigations are needed to ascertain the existence of synaptic contacts.     

Immunocytochemical characterization of afferents to estrogen receptor-containing neurons in the medial preoptic area of the rat.

Double-label immunocytochemistry has been employed to elucidate the chemical nature of the afferent neuronal projections to the estrogen receptor-containing neurons located in the medial preoptic area of the rat brain. To ensure a clear separation of the immunolabelled afferent profiles from the estrogen receptors, the former were visualized first and the diaminobenzidine reaction product was silver-gold intensified. Using a monoclonal antibody raised against purified human estrogen receptors, we observed an intense nuclear immunoreactivity in Vibratome, semithin and ultrathin sections. Neuropeptide-Y, serotonin-, phenylethanolamine N-methyltransferase- and adrenocorticotrophin-immunoreactive axons and varicosities were observed in close apposition to the estrogen receptor-positive cells. At the ultrastructural level, neuropeptide-Y-immunoreactive boutons were seen in synaptic contact with cells showing estrogen receptor immunoreactivity in their nucleus. These results indicate that neurons located in the medial preoptic area, one of the principal sites for the control of female reproductive function, may be influenced by both estrogen and neurotransmitters/neuropeptides via, respectively, nuclear receptors and synaptic contacts.     

Basal ganglia and other afferent projections to the peribrachial region in the rat: A study using retrograde and anterograde transport of horseradish peroxidase

The afferent projections to the peribrachial region in the rat were studied using retrograde and anterograde transport of horseradish peroxidase. Particular attention was paid to descending projections from the basal ganglia and related nuclei to the region of nucleus tegmenti pedunculopontinus. Following injection of peroxidase into nucleus tegmenti pedunculopontinus, few retrogradely-labelled neurons were found in the entopeduncular nucleus proper, but larger numbers were found with a wide distribution within the boundaries of the internal capsule and cerebral peduncle. Labelled cells were also consistently observed in the amygdala, the caudal globus pallidus, the subthalamus including zona incerta and subthalamic nucleus, the hypothalamus, the substantia nigra and the ventral tegmental area. Following iontophoretic injections of horseradish peroxidase into the entopeduncular nucleus, lateral hypothalamus, subthalamic nucleus or ventral tegmental area, terminal labelling was observed in and around the branchium conjunctivum in an area apparently corresponding to nucleus tegmenti pedunculopontinus in the rat.     

Immunocytochemical localization of estrogen receptors within neurotensin cells in the rostral preoptic area of the rat hypothalamus.

In situ hybridization procedures indicate that estrogen selectively increases neurotensin and neuromedin (NT/N) mRNA levels in the rostral preoptic area of the rat hypothalamus (RPH). Using the co-localization procedures of Axelson and Van Leeuwen, J. Neuroendocrinol., 2 (1990) 209-216, the present study examined whether NT cells in the RPH contained estrogen receptors (ER). Vibratome sections of brains from adult ovariectomized, colchicine-treated rats were first incubated with estrogen receptor antibody and stained with diaminobenzidine (DAB)-Ni+ producing a blue-black nucleus. Subsequently, NT antisera were used to provide a brown reaction product with DAB as chromogen. Approximately 25% of the NT cells in the RPH contained ER. These data support the hypothesis that NT cells in the RPH that play a role in luteinizing hormone release from the pituitary are, in part, influenced directly by estrogen feedback via nuclear ER and may act as interneurons controlling luteinizing hormone releasing hormone turnover.     

Immunohistochemical localization of estrogen receptors within aromatase-immunoreactive neurons in the fetal and neonatal rat brain

We elucidated the anatomical relationship between estrogen receptors and aromatase, the enzyme converting androgens to estrogens, in the fetal and neonatal rat brain by means of double immunohistochemical labeling, using antibodies against rat estrogen receptors and human placental aromatase cytochrome P450. Numerous aromatase-immunoreactive neurons were found in the medial preoptic area, the bed nucleus of the stria terminalis, the medial amygdaloid nucleus and the ventromedial nucleus. Estrogen receptors were also abundant in these areas. Most of the aromatase-immunoreactive neurons showed immunoreactivity for estrogen receptors in the medial subdivision of the bed nucleus of the stria terminalis and in the posterodorsal division of the medial amygdaloid nucleus. There were also many double-labeled cells in the ventromedial nucleus. However, in the medial preoptic area the localization of aromatase-immunoreactive neurons was distinct from that of neurons containing estrogen receptors. These results suggested that estrogens, which are converted from androgens in aromatase-containing neurons, are involved in the sexual differentiation of the brain through estrogen receptors within aromatase-immunoreactive neurons in the bed nucleus of the stria terminalis, the medial amygdaloid nucleus and the ventromedial nucleus, but through estrogen receptors in aromatase-immunonegative neurons in the medial preoptic area.     

Serotonin-, substance P- and tyrosine hydroxylase-like immunoreactive neurons projecting from the midbrain periaqueductal gray to the nucleus tractus solitarii in the rat.

Serotonin-, substance P- and tyrosine hydroxylase-like immunoreactive neurons in the midbrain periaqueductal gray (PAG) were observed to send their axons to the nucleus tractus solitarii in the rat by the retrograde horseradish peroxidase tracing method combined with the immunocytochemical technique. These neurons were most frequently observed in the ventrolateral subnucleus and ventral portion of the medial subnucleus of the PAG at the entire rostrocaudal levels.     

Cortical relay neurons and interneurons in the N. ventralis posterolateralis of cats: a horseradish peroxidase, electron-microscopic, Golgi and immunocytochemical study

After injections of horseradish peroxidase involving the whole primary (SI) and secondary somatosensory (SII) areas of adult cats, 16-21% out of 2220 counted neurons in the nucleus ventralis posterolateralis were unlabelled. The mean areas of perikarya of these neurons varied between 111.8 +/- 32.3 microns2 and 180.8 +/- 48.6 microns2. The size of perikarya of retrogradely-labelled neuron ranged from 256.9 +/- 100.4 microns2 to 409 +/- 163 microns2. Retrogradely-labelled and unlabelled neurons were examined under light- and high-voltage electron-microscopy. Besides 'large', mainly multipolar or oval fusiform perikarya, retrogradely-labelled neurons may display perikarya of 'small' size. Both types of neurons correlate well with Golgi-impregnated cells with a tufted dendritic pattern usually identified as thalamocortical neurons. On the other hand, the size and morphology of perikarya and initial dendrites of neurons unlabelled by retrograde transport of horseradish peroxidase correlate well with that of Golgi-impregnated neurons which are markedly different from the thalamocortical neurons, have very characteristic and profuse dendritic appendages and have been identified by previous investigators as Golgi Type II neurons. In order to probe further whether these may correspond to the GABAergic interneurons proposed by previous evidence, an immunocytochemical approach was also applied at the light- and electron-microscope level, using an antiserum prepared in sheep against rat brain glutamate decarboxylase. By this method it is shown that 19-21% of neurons in the nucleus ventralis posterolateralis of adult cats are glutamate decarboxylase-positive and that the perikaryal size of these labelled neurons ranges between 134.6 +/- 44.5 microns2 and 164.4 +/- 47.3 microns2. Histogram distribution of the number and areas of the counted immunoreactive neurons closely matches that of unlabelled neurons in experiments with retrograde transport of horseradish peroxidase. The results give support to previous evidence suggesting that part of population of neurons in the nucleus ventralis posterolateralis is represented by a distinct class of neurons which are apparently GABAergic.     

Dendritic arborization and axon trajectory of neurons in the hypothalamic arcuate nucleus of the rat

Summary Dendritic arborization patterns of neurons in the hypothalamic arcuate nucleus and the course of their axons outside the median eminence were studied using Golgi material, electron microscopic detection of degenerated axon terminals following surgical interference, and horseradish peroxidase technique.Two kinds of neurons can be distinguished in the arcuate nucleus: small fusiform and somewhat larger polygonal cells. Fusiform neurons having two, sparsely arborizing stem dendrites are localized mainly in the medial and dorsal parts of the nucleus. A variant of the fusiform neurons (pear shaped cells) has only one dendritic stem, and the axon originates at the other pole of the neuron. These latter cells are found along the ependymal wall of the third ventricle. Polygonal neurons which occupy the ventral and lateral portions of the nucleus have 4–5 repeatedly branching stem dendrites. In addition to the well known course of the axons of the arcuate neurons towards the median eminence, there are axons of both fusiform and polygonal cells which leave the nucleus in lateral or dorsolateral direction. Axons having this course frequently issue a collateral branch along the first 100–150 m of their trajectory.A knife-cut through the arcuate nucleus or along its lateral border resulted in degeneration of axon terminals in the area between the arcuate and ventromedial nuclei, and in a ventromedial sector of the ventromedial nucleus itself. A cut located in the area between the arcuate and ventromedial nuclei caused degenerated axon terminals over a large part of the ventromedial nucleus with a considerable increase in the ventromedial portion.Labeled fusiform and polygonal neurons can be seen in the arcuate nucleus following the injection of horseradish peroxidase into the lateral hypothalamus.The results suggest unequivocally that the neurons in the arcuate nucleus have efferent connections not only towards the median eminence but also to the hypothalamic ventromedial nucleus and lateral hypothalamic area.