Lothar Jennes

Centrifugal innervation of the retina by luteinizing hormone releasing hormone (LHRH)-immunoreactive telencephalic neurons in teleostean fishes

SummaryIn cichlid, poecilid and centrarchid fishes luteinizing hormone releasing hormone (LHRH)-immunoreactive neurons are found in a cell group (nucleus olfactoretinalis) located at the transition between the ventral telencephalon and olfactory bulb. Processes of these neurons project to the contralateral retina, traveling along the border between the internal plexiform and internal nuclear layer, and probably terminating on amacrine or bipolar cells. Horseradish peroxidase (HRP) injected into the eye or optic nerve is transported retrogradely in the optic nerve to the contralateral nucleus olfactoretinalis where neuronal perikarya are labeled. Labeled processes leave this nucleus in a rostral direction and terminate in the olfactory bulb. The nucleus olfactoretinalis is present only in fishes, such as cichlids, poecilids and centrarchids, in which the olfactory bulbs border directly the telencephalic hemispheres. In cyprinid, silurid and notopterid fishes, in which the olfactory bulbs lie beneath the olfactory epithelium and are connected to the telencephalon via olfactory stalks, the nucleus olfactoretinalis or a comparable arrangement of LHRH-immunoreactive neurons is lacking. After retrograde transport of HRP in the optic nerve of these fishes no labeling of neurons in the telencephalon occurred. It is proposed that the nucleus olfactoretinalis anatomically and functionally interconnects and integrates parts of the olfactory and optic systems.

LHRH systems in the brain of platyfish

The luteinizing hormone-releasing hormone (LHRH) system of the platyfish Xiphophorus has been studied using immunohistochemistry and retrograde transport of horseradish peroxidase (HRP). Three different populations of LHRH-positive cell bodies are present in the brain, one in the ventral telencephalon at the border to the olfactory bulb (nucleus of olfactoretinalis), one lateral to the n. preopticus (nucleus preopticus basalis lateralis) and one in the midbrain. LHRH neurons from the nucleus olfactoretinalis project via the medial olfactory tract to the olfactory bulb and to olfactory nerves. A second projection from this nucleus enters the optic tract, crosses in the optic chiasm, and courses rostrally in the outer layer of the optic nerve to the retina, where LHRH-positive nerve fibers terminate near amacrine and bipolar cells. HRP injections into the eye or into the cut optic nerve result in retrograde transport of the enzyme to the contralateral LHRH nucleus olfactoretinalis. Projections from LHRH neurons in the lateral preoptic region can be followed medially to surround the interhemispheric ventricle and laterally to border the optic tract. At the level of the postoptic commissure, LHRH fibers condense to form a fascicle which reaches the pituitary stalk to arborize throughout the hypophysis. LHRH fibers, probably in part from the midbrain LHRH neurons, project to the optic tectum, torus semicircularis, corpus and valvula of the cerebellum, as well as to the medulla oblongata. Associations of LHRH projections with sensory systems and with endocrine-autonomic systems in hypothalamus-pituitary and lower brain stem suggest a role in the modulation and integration of sensory, autonomic, behavioral and hypophyseotrophic functions.

LHRH-Systems in the Brain of the Golden Hamster

SummaryVibra tome sections of male hamster brains were treated immunohistochemically with LHRH antiserum, and the anatomical distribution of LHRH immunoreactive cells and nerve fibers was assessed. LHRH-cell bodies are found in the ventral hypothalamus that includes its preoptic, anterior and central parts, in the septum, the olfactory tubercle, the main and accessory olfactory bulb, and the prepiriform cortex. In addition, extracerebral LHRH-neurons and ganglia exist in LHRH-positive nerves at the ventromedial surface of the olfactory tubercle and bulb as well as in olfactory nerves. Dense networks of LHRH-immunoreactive fibers are found in all regions where LHRH-cell bodies exist. Intraseptal connections reach the organum vasculosum of the lamina terminalis, the subfornical organ, and the lateral ventricle. Dorsolateral projections from the septum can be traced via the fimbria hippocampi and alveus to the ventral hippocampus, via the stria terminalis to the amygdala and piriform cortex. Ventrolateral projections extend from the level of the olfactory tubercle and preoptic-anterior hypothalamic area via the ventral amygdalofugal pathway to the prepiriform and piriform cortex as well as the amygdala. Dorsal supracallosal projections via the stria longitudinalis are seen in the induseum griseum and the cingulate cortex. Caudal efferents reach the habenula, interpeduncular nucleus, midbrain raphe, and central gray of the rostral fourth ventricle via the stria medullaris and fasciculus retroflexus and by a ventral projection via the periventricular and subventricular hypothalamus. A major portion of this ventrocaudal projection gives rise to a dense network in the median eminence. Anatomical relationships of LHRH-fibers to certain regions of the inner ventricular and outer brain surface are noted.

Anatomical relationships of serotoninergic and noradrenalinergic projections with the GnRH system in septum and hypothalamus

SummaryImmunahistochemical double staining for gonadotropin releasing hormone (GnRH) and serotonin or dopamine-β-hydroxylase reveals close appositions of fibers which contain serotonin or norepinephrine to GnRH producing neurons in the septo-preoptic region. In the organum vasculosum of the lamina terminalis and in the median eminence extensive anatomical overlap exists in the distribution of GnRH and serotoninergic fibers but little of GnRH and noradrenalinergic fibers. It is proposed that serotonin plays a major role in the regulation of GnRH secretion via contacts in all of the regions studied and that the influence of norepinephrine on GnRH-secretion in the median eminence is exerted mainly via involvement of dopaminergic tuberoinfundibular neurons.

Expression of ionotropic glutamate receptor subunit mRNAs in the hypothalamic paraventricular nucleus of the rat.

The hypopthalamic paraventricular nucleus (PVN) coordinates multiple aspects of homeostatic regulation, including pituitary‐adrenocortical function, cardiovascular tone, metabolic balance, fluid/electrolyte status, parturition and lactation. In all cases, a substantial component of this function is controlled by glutamate neurotransmission. In this study, the authors performed a high‐resolution in situ hybridization analysis of ionotropic glutamate receptor subunit expression in the PVN and its immediate surround. N‐methyl‐D‐aspartate (NMDA) receptor 1 (NMDAR1), NMDAR2A, and NMDAR2B mRNAs were expressed highly throughout the PVN and its perinuclear region as well as in the subparaventricular zone. NMDAR2C/2D expression was limited to subsets of neurons in magnocellular and hypophysiotrophic regions. In contrast with NMDA subunit localization, AMPA (α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐propionate)‐preferring and kainate (KA)‐preferring receptor subunit mRNAs were expressed heterogeneously in the PVN and surround. Glutamate receptor 1 (GluR1) mRNA labeling was most intense in preautonomic subregions, whereas GluR2, GluR4, GluR5, and KA2 were expressed in hypophysiotrophic cell groups. It is noteworthy that GluR5 mRNA expression was particularly robust in the dorsolateral region of the medial parvocellular PVN, suggesting localization in corticotropin‐releasing hormone neurons. All four AMPA subunits and GluR6 and GluR7 mRNAs were expressed highly in the perinuclear PVN region and the subparaventricular zone. These data suggest the capacity for multifaceted regulation of PVN function by glutamate, with magnocellular neurons preferentially expressing NMDA subunits, preautonomic neurons preferentially expressing AMPA subunits, and hypophysiotrophic neurons preferentially expressing KA subunits. Localization of all species in the perinuclear PVN suggests that glutamate input to the immediate region of the PVN may modulate its function, perhaps by communication with local γ‐aminobutyric acid neurons. J. Comp. Neurol. 422:352–362, 2000.

Expression of gonadotropin-releasing hormone and gonadotropin-releasing hormone receptor mRNAs in various non-reproductive human tissues

Recently, cloning of the gonadotropin-releasing hormone (GnRH) receptor from the human breast tumor cell line (MCF-7) and from an ovarian tumor, and its expression in various other human tumors, tumor cell lines and reproductive organs have been reported (Kakar et al., Mol. Cell. Endocrinol., 106 (1994) 145-149). In the present studies, we investigated the expression of GnRH and GnRH receptor mRNAs in normal human non-reproductive tissues. Using reverse transcriptase-polymerase chain reaction (RT-PCR) techniques and specific oligonucleotide primers derived from the placental GnRH cDNA sequence, PCR products of the expected size were obtained from human liver, heart, skeletal muscle, kidney, placenta, and pituitary. The authenticity of the PCR products was confirmed by Southern blot analysis with an internal oligonucleotide primer as probe. Similarly, using specific oligonucleotide primers for the GnRH receptor selected from the human pituitary GnRH receptor cDNA sequence, PCR products of the expected size were amplified from human liver, heart, skeletal muscle, kidney, placenta, and pituitary, and these strongly hybridized with the human GnRH receptor cDNA on Southern blot. Cloning and nucleotide sequencing of the PCR products for the GnRH and GnRH receptor from heart revealed identical sequences when compared to the human placental GnRH and pituitary GnRH receptor cDNAs, respectively. These data demonstrate for the first time the existence of GnRH and GnRH receptor mRNAs in normal human non-reproductive tissues and suggest that GnRH and its receptor may play an important role in the regulation of cellular functions in an autocrine or paracrine manner, in addition to regulating the secretion of gonadotropins from the anterior pituitary.

Distribution of ionotropic glutamate receptor subunit mRNAs in the rat hypothalamus.

The excitatory amino acid neurotransmitter glutamate participates in the control of most (and possibly all) neuroendocrine systems in the hypothalamus. This control is exerted by binding to two classes of membrane receptors, the ionotropic and metabotropic receptor families, which differ in their structure and mechanisms of signal transduction. To gain a better understanding about the precise sites of action of glutamate and the subunit compositions of the receptors involved in the glutamatergic neurotransmission in the hypothalamus and septum, in situ hybridization was used with 35S‐labeled cRNA probes for the different ionotropic receptor subunits, including glutamate receptor subunits 1–4 (GluR1–GluR4), kainate‐2, GluR5–GluR7, N‐methyl‐D‐aspartate (NMDA) receptor 1 (NMDAR1), and NMDAR2A–NMDAR2D. The results showed that subunits of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole‐propionate‐preferring, kainate‐preferring, and NMDA‐preferring receptor subunits are distributed widely but heterogeneously and that the GluR1, GluR2, kainate‐2, NMDAR1, NMDAR2A, and NMDAR2B subunits are the most abundant in the hypothalamus. Thus, GluR1 subunit mRNA was prominent in the lateral septum, preoptic area, mediobasal hypothalamus, and tuberomammillary nucleus, whereas kainate‐2 subunit mRNA was abundant in the medial septum‐diagonal band, median and anteroventral preoptic nuclei, and supraoptic nuclei as well as the magnocellular portion of the posterior paraventricular nucleus. Regions that contained the highest levels of NMDAR1 subunit mRNA included the septum, the median preoptic nucleus, the anteroventral periventricular nucleus, and the supraoptic and suprachiasmatic nuclei as well as the arcuate nucleus. Together, the extensive distribution of the different GluR subunit mRNAs strengthen the view that glutamate is a major excitatory neurotransmitter in the hypothalamus. The overlap in the distribution of the various subunit mRNAs suggests that many neurons can express GluR channels that belong to different families, which would allow a differential regulation of the target neurons by glutamate. J. Comp. Neurol. 434:101–124, 2001.

Gonadotropin-Releasing Hormone and Its Receptors in Rat Brain

Since the chemical identification of gonadotropin-releasing hormone (GnRH) in 1971, significant progress has been made in understanding the mechanisms by which GnRH action is mediated in the anterior pituitary. In contrast, relatively little information is available which identifies the intracerebral sites and mechanisms of action of GnRH in the brain. Early immunohistochemical studies of GnRH distribution in the central nervous system, together with behavioral and electrophysiological experiments, suggested that GnRH functioned as a neurotransmitter and was, possibly, involved in the expression of reproductive behaviors. The subsequent identification and characterization of GnRH receptors in the brain further strengthened the view that GnRH caused specific effects in select regions of the brain known to be involved in the neuroendocrine regulation of the anterior pituitary and in the generation of reproductive behaviors. After the mouse pituitary GnRH receptor was cloned it became possible to identify brain neurons which contained the GnRH receptor mRNA. Comparison of the locations of the GnRH peptide, the GnRH receptor protein, and the neurons which contain the GnRH receptor mRNA suggests that the GnRH neuronal system itself can potentially provide a direct link between the neuroendocrine regulation of anterior pituitary function and the intracerebral regulation of reproductive behaviors; furthermore, it is possible that the GnRH neuronal system takes an active part in intracerebral feedback loop systems between the mediobasal hypothalamus and the septum-diagonal band which regulate GnRH release from the median eminence.

Gonadotropin-releasing hormone immunoreactive neurons with access to fenestrated capillaries in mouse brain

Gonadotropin-releasing hormone (GnRH) producing neurons which have access to fenestrated capillaries were identified through a combination of indirect immunofluorescence for GnRH with a fluorescein-taged second antibody and histochemical demonstration of the localization of blood borne and retrogradely transported horseradish peroxidase. In the mouse, GnRH positive neurons were present in the septum, which includes neurons originating from the nervus terminalis, the nucleus medialis and triangularis septi, and the nucleus of the diagonal band. Also, GnRH immunoreactive neurons could be seen in the lateral anterior hypothalamus, the nucleus preopticus medianus, the rostral nucleus periventricularis hypothalami and, to a lesser extent, the nucleus preopticus medialis. Single GnRH positive neurons were found in the nucleus supraopticus, the bed nucleus of the stria terminalis and the cingulate cortex. GnRH neurons which showed uptake of horseradish peroxidase were located in all of these regions and intermingled with unlabeled GnRH neurons. No preferential topographical concentration of GnRH neurons with access to the fenestrated vasculature was apparent. In animals in which GnRH secretion was stimulated by castration for 2 weeks, 65% of all GnRH neuronal perikarya contained horseradish peroxidase. This was reduced to 35% after a 2-week treatment of ovariectomized animals with 10 micrograms/day estradiol while the total number of immunoreactive GnRH cells remained unchanged. No differences in the number of GnRH-horseradish peroxidase positive cells was seen when the dose of horseradish peroxidase of the survival time were increased. While the presence of certain GnRH neurons with dual actions via collaterals cannot be excluded, the results suggest that there are two populations of GnRH neurons, one with access to fenestrated capillaries which is probably related to neurosecretory endocrine regulation of anterior pituitary gonadotropin secretion, and one without access to fenestrated capillaries which is probably related to intracerebral neurotransmission only.

Anatomical relationships of dopaminergic and GABAergic systems with the GnRH-systems in the septo-hypothalamic area

SummaryImmunohistochemical double staining for gonadotropin releasing hormone (GnRH) and tyrosine hydroxylase (TH) or glutamic acid decarboxylase (GAD) reveals in the septo-preopticdiagonal band complex of the rat brain close spatial associations between GnRH-immunoreactive perikarya and TH and GAD immunoreactive fibers. In the organum vasculosum laminae terminalis, no close spatial relationships could be observed between TH-or GAD-positive fibers and the GnRH-containing system. In contrast, in the median eminence substantial overlap exists in the distribution of GnRH with TH and GAD containing nerve fibers. This overlap is most intense for TH throughout the lateral palisade zone, while for GAD it is more restricted to the outermost portion of the external palisade zone. The results suggest that dopamine and GABA influence GnRH secretion via axosomatic contacts in the septo-preoptic-diagonal band complex, as well as via axo-axonic interactions in the median eminence, while no such interactions seem to exist in the organum vasculosum laminae terminalis. Since dopaminergic cell bodies in the ventral hypothalamus are closely apposed by GnRH and GAD containing fibers, the existence of feedback circuits among GnRH, dopamine and GABA systems is proposed.