Cytology and immunocytochemistry of the nucleus extrolateralis anterior of the mormyrid brain: possible role of GABAergic synapses in temporal analysis

Summary Mormyrid fish use their electrosensory/electromotor system for both electrolocation and electrocommunication. One type of electroreceptor, the knollenorgan, has a low threshold and is used strictly for detecting a conspecifie's electric organ discharge. Knollenorgan afferents terminate with mixed synapses (gap junctions and asymmetric chemical synapses) on neurons of the nucleus of the lateral line lobe (nLLL), which in turn projects to a midbrain nucleus — the nucleus extrolateralis anterior (ELa). ELa contains numerous granule cells, which are adendritic, and scattered larger neurons, here termed interstitial cells, which possess several branched dendrites. Because of the overall paucity of dendrites, the neuropil of ELa is scarcely developed and myelinated fibers predominate in between the cell bodies. Axons presumed to originate in nLLL make mixed synapses on both the interstitial and the granule cells. The interstitial neurons are immunoreactive for glutamic acid decarboxylase (GAD), the synthetic enzyme for the inhibitory neurotransmitter gammma-aminobutyric acid (GABA), while the granule cells are GAD-negative. Many GAD-positive synapses are found on each granule cell soma; at smaller densities, GAD-positive boutons also synapse on the cell bodies and dendrites of interstitial cells. The GAD-positive boutons have pleomorphic vesicles and make symmetric synapses. Such boutons presumably originate from a plexus of interstitial cell axons. Mormyrid fish use their knollenorgan afferents for precise temporal discriminations, and this information is needed for electrocommunication. The ELa, with its relatively simple neuronal circuitry, is the most likely site for precise temporal analysis in the knollenorgan afferent pathway, and we propose that the GABAergic synapses on the granule cells may be essential for accurate detection of specific time intervals.     

Tyrosine hydroxylase-immunoreactive cell groups in the brain of the teleost fishGnathonemus petersii

Different antibodies against tyrosine hydroxylase (TH) were used to obtain detailed information about the distribution, morphology and chemical differentiation of catecholaminergic neurons in the highly differentiated brain of the electric mormyrid fishGnathonemus petersii. The results show that the distribution of catecholaminergic neurons is much more widespread than was previously thought on the basis of dopamine and noradrenaline immunohistochemistry. Tyrosine hydroxylase-immunoreactive neurons were observed not only in clearly dopaminergic regions (the suprachiasmatic nucleus, the magnocellular hypothalamic nucleus and the area postrema) and noradrenergic cell groups (the locus coeruleus and inferior reticular cell group), but also in regions that do not, or only fragmentarily, display dopamine or noradrenaline immunoreactivity, including the ventral and intermediate telencephalon, the anterior and posterior preoptic cell group, the ventromedial thalamus, the pretectal region and the nucleus of the solitary tract, suggesting that they either represent depleted dopaminergic cell groups orl-dihydroxy phenlalanine- producing nuclei. Most TH-immunoreactive neurons are rather small (<10 μm) and have only a few slender processes, but neurons in the magnocellular hypothalamic nucleus and the inferior reticular formation are multipolar and larger (10–20 μm), while those of the locus coeruleus are even more than 20 μm in diameter. The hypothalamic paraventricular organ, which is strongly dopamine and noradrenaline immunoreactive, displays minimal TH immunoreactivity, suggesting that its cerebrospinal fluid-contacting neurons do not synthesize catecholamines, but acquire them from external sources.

Comparison with other teleosts shows that the catecholaminergic system in the brain of Gnathonemus is similarly organized as inCarassius, Gasterosteus, Anguilla andAperonotus, with some variations that may partly be due to technical reasons, and partly reflect true species differences. However, TH-immunoreactive neurons in the midbrain tegmentum were not observed, confirming previous conclusions that a major difference between teleosts and mammals concerns the absence of dopaminergic midbrain groups and correlated mesencephalo-telencephalic projections in teleosts.     

Interaction between neuropeptide Y immunoreactive neurons and galanin immunoreactive neurons in the brain of the masu salmon, Oncorhynchus masou

We investigated the immunohistochemical localization of neuropeptide Y (NPY) and galanin (GAL) in the brain of the masu salmon Oncorhynchus masou in order to clarify the interaction between these neuropeptide hormones in the brain. NPY-immunoreactive (ir) cell bodies were observed in the ventral and lateral regions of the ventral telencephalon (Vv and Vl, respectively), and in the dorsolateral midbrain tegmentum. NPY-ir fibers were observed throughout the brain, mainly in the ventral telencephalon, hypothalamus, optic tectum, and midbrain. GAL-ir cell bodies were observed in the nucleus preopticus parvicellularis anterioris (PPa) and the ventral zone of the periventricular hypothalamus (Hv). Both GAL-ir and NPY-ir fibers were observed throughout the brain. Furthermore, we examined the interaction between the NPY neurons and GAL neurons by performing double-staining immunohistochemistry. Some GAL-ir fibers were in close contact with the NPY-ir cell bodies in the Vv and Vl. In addition, some NPY-ir fibers were in close contact with the GAL-ir cell bodies in the PPa and Hv. These findings suggest that reciprocal connections exist between the NPY neurons and GAL neurons in the brain of the masu salmon.     

Histamine-immunoreactive neurons in the brain of the teleost Gasterosteus aculeatus L. Correlation with hypothalamic tyrosine hydroxylase- and serotonin-immunoreactive neurons

The distribution of putative histaminergic neurons in the brain of a teleost, the three-spined stickleback, was investigated by means of immunocytochemistry using specific antibodies against histamine (HA), and conventional microscopy as well as confocal laser scanning microscopy. Histamine-immunoreactive (HAir) neurons form discrete populations ventral to the nucleus of the posterior recess (NRP) and in the nucleus saccus vasculosus (NSV), which belong to the periventricular hypothalamic nuclei. The neuronal somata are subependymally located, and do not possess apical neurites contacting the cerebrospinal fluid. They give rise to both long-range and local axonal projections. The local projections give rise to a field of dense punctate immunoreaction dorsal to the NRP and lateral to the NSV. Long-range projections are comprised of ascending projections to the thalamus, habenula, preoptic area and dorsal telencephalon; and descending projections via the posterior tuberal nucleus, ventrally to the nucleus interpeduncularis, and dorsally into the central gray. HAir neurons occur together with serotoninergic cerebrospinal fluid-contacting (CSFc) neurons in the NRP, and with tyrosine hydroxylase-immunoreactive (THir) neurons in the NSV. Although HAir elements occur together with THir ones in many brain areas, direct contacts between the two neurotransmitter systems are rare. The putative histaminergic neurons in the brain of the three-spined stickleback constitute a very discrete neuronal system, with a major projection area in the dorsal telencephalon in a region which is considered homologous with the dorsal pallium of land vertebrates.     

Seasonal sexually dimorphic distribution of neuropeptide Y-like immunoreactive neurons in the forebrain of the lizard Podarcis hispanica

Since neuropeptide Y (NPY) is involved in several sex-specific physiological and behavioral processes, a sexual dimorphic distribution is expected in forebrain areas that take part in the control of reproduction physiology and sexual behavior. This question has been studied in the lizard Podarcis hispanica by comparing the distribution of NPY-like immunoreactive cells in several forebrain areas of males and females during the season of active (spring/summer) and inactive (fall/winter) reproductive activity. Both qualitative observations and statistical analysis (analysis of variance) indicate that the number of reactive cells within two forebrain areas, the lateral septum and the periventricular preoptic nucleus, depends on the sex (P = 0.02) and season (P = 0.03) and that, in fact, intersexual differences depend on the season of the reproductive annual cycle (P = 0.046). Other areas, such as the amygdaloid nucleus sphericus, show neither sexual dimorphism (P = 0.67), nor seasonal variation in the number of reactive cells (P = 0.18), nor seasonal variation of the intersexual differences (P = 0.75). When analyzed independently, the lateral septum shows a clear sexual dimorphism in favour of females (P = 0.003) whereas the number of reactive cells in the periventricular preoptic nucleus is significantly higher (P = 0.006) in males than in females. In the case of the preoptic nucleus, this sexual dimorphism is clearly accentuated during the season of reproductive activity (P = 0.007), but this dependence is not so clear for the lateral septum (P = 0.059). In the light of these findings the possible roles of NPY on the regulatory mechanisms of sexual behavior and other aspects of the physiology of reproduction are discussed.     

Localization of neurons containing immunoreactive delta sleep-inducing peptide in the rat brain: An immunocytochemical study

Delta sleep-inducing peptide has been found in the peripheral circulation of animals entering slow-wave, or delta, sleep. An antiserum to this peptide was used to localize immunoreactive-like delta sleep-inducing peptide in the rat brain. The peptide was shown to have a rather widespread distribution. In the forebrain, the majority of these neurons were found to extend in a continuous rostral-caudal band in the ventral one-third of the brain from the primary olfactory cortex to the lateral hypothalamus. Neurons were also present in the basal ganglia, amygdala, septum, and thalamus. In the brainstem, the neurons were widespread and associated with the reticular formation, raphe nuclei, nuclei of the trigeminal complex, several auditory nuclei—nuclei of the lateral lemniscus, cochlear nuclei, and inferior colliculus—, cerebellum, locus ceruleus, periventricular gray, and vagal and hypoglossal nuclei. Immunoreactive fibers were, in general, difficult to demonstrate; they were seen mainly in the vicinity of the third ventricle and near blood vessels.The function of delta sleep-inducing peptide is unknown and its role in sleep is still under investigation. The distribution of delta sleep-inducing peptide in the present study suggests that the peptide is a component of several systems—arousal, locomotion, auditory, visual and sensory—both somatic and vestibular. The widespread distribution of the peptide, the lack of demonstrable immunoreactive fiber tracts, and the presence of these neurons in areas known to contain aminergic and peptidergic neurons, raises the possibility that neurons containing delta sleep-inducing peptide may exert their effect by projecting directly into blood vessels and/or interacting with neurons in their immediate vicinity.     

An immunogold electron microscopic analysis of FMRFamide-like immunoreactive neurons in the CNS ofHelix pomatia: ultrastructure and synaptic connections

Summary The ultrastructure and synaptic connections of FMRFamide-like immunoreactive neurons were investigated in the CNS of the snailHelix pomatia, following the application of a post-embedding immunogold method. For comparison, first, we analyzed the ultrastructure and granule content of the identified FMRFamide-containing C3 neuron in the cerebral ganglion. Three types of unidentified immunoreactive neuronal perikarya, and five types of varicosities could be distinguished on the basis of granule content. The different granule types revealed a highly selective accumulation of gold particles. One granule type contained by one FMRFamide-like immunoreactive neuron type (N1) and by one varicosity type (T₂) showed similar ultrastructure to that of the granules seen in the C3 cell. In the neuropil, the majority of FMRFamide-like immunoreactive varicosities (four of the five varicosity types) established specialized synaptic contacts with unidentified postsynaptic profiles. In the connective tissue sheath around the ganglia, three types of FMRFamide-like immunoreactive varicosities were found to establish unspecialized contacts with smooth muscle fibres or to be free in the mass of collagen fibres. On the basis of these observations, we suggest (1) an extensive diversity of the localization of FMRFamide (and related substances) at the ultrastructural level; (2) the involvement of FMRFamide-like immunoreactive varicosities in synaptic, modulatory and neurohormonal regulatory processes in theHelix nervous system.     

Distribution of neuropeptide Y in the prosencephalon of man and Cotton-head Tamarin (Saguinus oedipus): colocalization with somatostatin in neurons of striatum and amygdala

Summary The presence, chromatographic properties and localization of neuropeptide Y was demonstrated in postmortem human brain areas of neurologically and neuropsychiatrically normative controls using immunocytochemistry and high performance liquid chromatography combined with radioimmunoassay. NPY-immunoreactivity was found in many regions of the prosencephalon. Numerous perikarya and fibers were present in the neocortex, basal ganglia and limbic-hypothalamic areas. A moderate number of neurons and fibers was observed in the basal forebrain, including the septal complex. A comparative immunohistochemical investigation in perfusion-fixed brains of the old-world ape Saguinus oedipus revealed an almost identical distribution of NPY-immunoreactivity with only minor differences. Colocalization experiments on 1–2 m thin consecutive paraffin sections revealed a large number of NPY neurons throughout the human neostriatum and amygdaloid complex that were also positive for somatostatin. Our findings indicate that detection of neuropeptides in fresh or fixed post-mortem human tissue by different immunochemical methods may actually reflect the in vivo conditions. In addition, the wide distribution of NPY throughout the human brain and its colocalization with other neurotransmitters suggests a physiological role as neuroactive substance, i.e. neuromodulator in the primate central nervous system.     

Morphological effects of isoflavones (daidzein and genistein) on hypothalamic oxytocin neurons in the neonatal mouse brain slice cultures

We investigated the immunohistochemical localization of immunoreactive (ir) cell bodies and fibers of neuropeptide Y (NPY) and galanin (GAL), and the anatomical relations between these neurons in the brain of the Siberian sturgeon Acipenser baeri to clarify the interactions between these neuropeptides. Furthermore, the anatomic relations between NPY and gonadotropin-releasing hormone (GnRH) in the brain were also examined. NPY-ir cell bodies were observed in the ventral part of the ventral telencephalon (Vv). NPY-ir fibers were observed throughout the brain, primarily in the ventral telencephalon, hypothalamus, optic tectum, and midbrain. GAL-ir cell bodies were observed in the Vv, nucleus anterioris tuberis (NAT), nucleus lateralis tuberis (NLT), and nucleus recessus posterioris (NRP). GAL-ir fibers were also observed throughout the brain. Neither NPY-ir fibers nor GAL-ir fibers were detected in the pituitary. Dual-label immunohistochemistry revealed that some GAL-ir fibers were in close contact with NPY-ir cell bodies in the Vv, and some NPY-ir fibers were in close contact with GAL-ir cell bodies in the NAT. Furthermore, some NPY-ir fibers were in close contact with GnRH-ir cell bodies in the preoptic area, and some GnRH-ir fibers were in close contact with NPY-ir cell bodies in the Vv. These findings suggest that reciprocal connections exist between the NPY and GAL neurons and between the NPY and GnRH neurons in the brain of the Siberian sturgeon.