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L S Demski

Publications and source records attributed to L S Demski.

At least 19 recordsLinked to original sources
PubMed1996

Organization of GnRH and FMRF-amide systems in two primitive bony fishes (order polypteriformes).

To investigate the evolution of the neural organization of gonadotropin-releasing hormone (GnRH), we have examined GnRH-immunoreactivity in two brachiopterygian fishes (Polypterus palmas and Calamoichthys calabaricus). Distal regions of the terminal nerve (TN) within the medial olfactory nerve contained clusters of GnRH-immunoreactive (ir) perikarya (< 10 microns). More proximal, isolated GnRH-ir neurons were present among TN fascicles as they penetrated the ventral forebrain, and a few ir neurons were observed accompanying GnRH-ir fibers in the rostromedial telencephalon. GnRH-ir neurons were not observed in the preoptic area or ventral hypothalamus. In contrast, a small group of GnRH-ir neurons was localized in the periventricular nucleus of the posterior tuberculum. GnRH-ir fibers were present in widespread areas of the brain, including the olfactory bulb, telencephalon, optic nerve, hypothalamus, thalamus, habenula, optic tectum, tegmentum, pituitary and spinal cord. To further characterize projections of TN neurons, we utilized antiserum to FMRF-amide, a small peptide produced by TN cells in other vertebrates. Perikarya that were FMRF-amide-ir within the TN were similar in distribution to GnRH-TN neurons, and the distribution of FMRF-amide-ir fibers overlapped those of GnRH-ir fibers, thus providing a useful marker for identifying TN projections. An additional population of FMRF-amide-ir neurons was present in the periventricular hypothalamus. Our results suggest that in the polypteriformes, GnRH and FMRF-amide neurons of the TN are similar to those observed in other vertebrates; however, the paucity of GnRH cells in the basal forebrain may be unique to primitive actinopterygians and elasmobranchs, and may result from the lack of migration of GnRH neurons into the forebrain, a phenomenon that likely occurs in all other vertebrate classes. Finally, the identification of GnRH-ir neurons in the posterior tuberculum is consistent with similar, and perhaps homologous, GnRH neurons present in nearly all other vertebrate classes.

Animals↗
PubMed1993

Terminal nerve complex.

Cranial nerve 0 or the terminal nerve (nervus terminalis: TN) refers to a nerve or in some cases possibly a complex of nerves that most likely derive from the olfactory placodes and relate the most anterior forebrain derivatives to nasal and olfactory structures. Such a nerve(s) has been observed in at least some stages of development in all major groups of vertebrates save myxinoids or hagfish. The phylogenetic variation of TN components is presented in some detail. The functions of TN components are not yet well identified, but some indications are that it is sensory but not chemosensory, controls blood vessels and glands in the nose and has peptide-containing fibers that may control reproductive development and behavior as well as other neural functions. This paper has three parts: (1) a historical review, which provides a conceptual framework necessary for understanding current problems in the anatomy and physiology of the TN; (2) a section on recent studies in areas selected for their potential impact on understanding the TN, and (3) a brief summary, which provides some tentative answers to the questions 'what is the TN and what does it do?' and suggests directions for continued research on the TN.

Anatomy, Comparative↗
PubMed1992

Chromatophore systems in teleosts and cephalopods: a levels oriented analysis of convergent systems.

The neural control of chromatophore display in cephalopod mollusks and teleost fishes is reviewed in the context of convergence of functional-anatomical pathways and mechanisms at several levels of organization. The effector elements or chromatophores are different in origin and design in the two groups of animals. Major functional differences appear to be in the speed of response (greatest in cephalopods) and the magnitude of non-neural control mechanisms (greatest in teleosts). Despite the differences, the elements demonstrate striking overall functional similarity. Elements of different types form highly organized array patterns of similar general complexity. Innervation patterns in cephalopods and teleosts seem comparable, with control being unidirectional (albeit in opposite directions); some elements demonstrate polyaxonal innervation. Motor units in both groups are generally composed of many chromatophores. Packard's concept of 'cronological units' of similar age-classes of chromatophores being innervated by similar age-classes of motor neurons greatly simplifies the understanding of relationships between the static arrays and the physiological units that utilize them to produce chromatic displays. The lower motor control areas for both groups have been grossly identified. Chromatomotor neurons in cephalopods are mostly located in the chromatophore lobes of the subesophageal brain while comparable systems in teleosts are situated in sympathetic chain ganglia (preganglionics) and the rostral spinal cord (postganglionics). Chromatic components are the simplest visually detectable units of color display, e.g. vertical bands and fin spots. They combine to form more complex chromatic patterns, which, in turn, are integrated with components of skin texture, posture and movement to produce display behaviors. Complexity of such systems seems to be of the same order of magnitude in both cephalopods and teleosts. Areas of the CNS related to each of the categorical levels have not been clearly defined. Crude patterning may take place in the basal and, perhaps, peduncle lobes in cephalopods and in the lower and intermediate medulla in teleosts. In both groups, higher level control relates to areas involved in sensorimotor integration and mediation of agonistic, sexual, and, perhaps, other types of behavior: the peduncle and optic lobes in cephalopods and the hypothalamus, tegmentum, otic tectum, torus semicircularis, thalamus and telencephalon in fishes. The systems appear to parallel each other in being organized hierarchically, with similar levels of complexity. Some of the regions may be especially important for regulating color patterns in response to visual input. Overall, chromatomotor control systems in cephalopods and teleosts demonstrate many apparent convergent features. Possible factors responsible for the similarities are discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Gonadotropin hormone-releasing hormone (GnRH) immunoreactivity in the mesencephalon of sharks and rays.

Other than association with the terminal nerve (TN), little is known concerning the distribution of gonadotropin hormone-releasing hormone (GnRH) in elasmobranchs. The purpose of this study was to identify GnRH immunoreactivity in the brains of three elasmobranch species with special regard to the mesencephalon. The round stingray (Urolophus halleri), thornback guitarfish (Platyrhinoidis triseriata), and leopard shark (Triakis semifasciatus) were used and immunocytochemistry was performed with antisera to both salmon and mammalian GnRH. A large GnRH-immunoreactive (ir) nucleus extends rostrocaudally for approximately 1.5 mm along and adjacent to the midline of the midbrain near the area of the oculomotor nerve. GnRH-ir fibers surround the nucleus and are found diffusely throughout the mesencephalon; some of the fibers may contact the ventricle. The medulla and spinal cord contain ir fibers that most likely originate from the midbrain nucleus. Mesencephalic GnRH-ir cell groups have been reported in representatives of all vertebrate classes with the exception of agnathans and mammals. Such a well-developed cell group in elasmobranchs may aid in understanding the evolution of GnRH systems with regard to the mesencephalon as well as providing insight to the functional significance of this cell group. Possible homologies to mesencephalic GnRH systems reported in other vertebrates is discussed as well.

Animals↗
PubMed1990

The terminal nerve of dolphins: gross structure, histology and luteinizing-hormone-releasing hormone immunocytochemistry.

The terminal nerve (TN) of several dolphins was examined using gross dissection aided by osmium staining, routine light and electron microscopy, and immunocytochemistry with antibodies to mammalian luteinizing-hormone-releasing hormone (LHRH). The TN consists of numerous pial strands which emanate from large paired ganglia located in the dura near the frontal lobe of the hemisphere. The strands are largely composed of myelinated axons which extend to basal forebrain areas including the anterior perforated substance. Peripheral branches of the ganglia run through foramina in the ethmoid bone into the region of the nasal sacs and blowhole. Round to oval ganglion cells are scattered along the nerve and thousands of similar cells are found in the dural ganglia where they are encapsulated by satellite cells. A second, less prevalent cell type is also found in the ganglia. These neurons are fusiform, lack a well-defined capsule and are LHRH-immunoreactive. The results are compared to observations of the anatomy and functions of the TN in other mammals, which unlike toothed whales have retained an olfactory system. Involvement in reproduction and control of secretions and/or circulation of the nasal sac vocalization system are suggested functions of the TN in dolphins.

Animals↗
PubMed1988

Dense-cored vesicle-containing components of the terminal nerve of sharks and rays.

This paper describes electron microscopic observations of dense-cored vesicle-containing axons, cell bodies, and endings of the terminal nerve in several elasmobranchs. The vesicles are found in two apparent cell types, one with a polymorphic nucleus and another with an oval nucleus. The types may correspond to cells producing one each of two neuropeptides (LHRH and FMRF-amide) that have previously been localized in the nerve. Dense-cored vesicles are found in many unmyelinated fibers in both the terminal nerve proper and its major ganglia. Some of these form complicated structures with interdigitation and wrapping of membranes. Vesicle-containing fibers branch from the nerve, run along nearby blood vessels, and appear to end adjacent to endothelial cells which demonstrate vesicular activity. The observations suggest terminal nerve neurosecretion into the cerebral circulation. Synapses are found in and near the ganglia where they appear to be axodendritic, with multiple contacts in some cases.

Animals↗
PubMed1988

Functional-anatomical studies of neural control of heart rate in goldfish.

Neural control of heart rate (HR) was investigated in goldfish, Carassius auratus, using electrical stimulation of the brain. Three types of HR response were evoked by stimulation: HR decreases during stimulation (type I); HR increases during stimulation (type II), and HR decreases during stimulation, followed by increased rates at the offset (type III). Type I bradycardias were evoked by stimulation of the preoptic area and diencephalon, specifically in the ventral thalamus-dorsal hypothalamus transitional area, and the region dorsal and medial to the nucleus glomerulosus. Additional sites were located above crossing tectobulbar fibers in the midbrain and in basolateral medullary reticular areas, motor nucleus of the vagus and caudalmost vagal roots. Type II tachycardias were evoked by stimulation of sites in the dorsal telencephalon, inferior lobes of the hypothalamus and dorsomedial region of the vagal lobes. Type III rebound tachycardias were evoked from sites dorsal and medial to the nucleus glomerulosus and in the inferior lobe of the hypothalamus. The location of cardioactive sites in the brain in goldfish is comparable to that in other vertebrates; however, these cardiac responses may be mediated by faciliatory or inhibitory pathways to the vagal motor nuclei rather than sympathetic cardiac nerves.

Animals↗
PubMed1987

Localization of immunoreactive tyrosine hydroxylase in the goldfish brain.

This report describes the distribution of tyrosine hydroxylase immunoreactive (TH-ir) structures in the brain of the goldfish (Carassius auratus). The localization of TH-ir cell groups revealed by immunocytochemical techniques is largely in accordance with catecholamine distribution previously reported in teleosts by using monoamine fluorescence; however, in the telencephalon and diencephalon, several new cell groups are elucidated. In the telencephalon, TH-ir cell bodies are observed in the olfactory bulb, area ventralis telencephali, and the central zone of the area dorsalis telencephali. TH-ir fibers and terminals are moderately dense throughout the telencephalon except for a sparse innervation of the area dorsalis, pars medialis. Immunostained cells are present in the suprachiasmatic nucleus and magnocellular and parvicellular components of the preoptic nucleus. Immunoreactive fibers from preoptic cells can be traced caudally in two main tracts to the infundibulum. Dense immunoreactivity around cells in the pituitary provides anatomical support for catecholamine involvement in the neuroendocrine axis probably via preopticohypophysial connections. At middiencephalic levels, immunoreactive cells are present in the ventral thalamus, nucleus pretectalis periventricularis, pars ventralis, and paraventricular organ pars anterioris. In the caudal diencephalon, TH-ir cells are seen within the posterior tuberal nuclei and dorsal to posterior recess. No immunostained cells are observed in the midbrain. In the hindbrain, tyrosine hydroxylase containing cells comprise three groups similar to that described using Falck-Hillarp histofluorescence (Parent et al., '78), i.e., isthmal, central medullary, and medullospinal groups. Tyrosine hydroxylase immunoreactivity is interpreted as evidence for the presence of catecholamines and not only provides an anatomical basis for the functional significance of catecholamines in teleosts, but may be useful in elucidating homologous structures in tetrapod vertebrates, although certain sites of immunoreactivity may prove to be unique to teleosts.

Animals↗
PubMed1986

Thalamic stimulation evokes sex-color change and gamete release in a vertebrate hermaphrodite.

Sperm and egg release and sex-color patterns specific for the male and female phases of reproductive behavior were elicited by electrical stimulation in the thalamus of anesthetized sea bass. Thalamic switching of the sex-role specific motor activities in response to visual signals from the mate is considered an important feature regulating the complex mating activity of these simultaneous hermaphrodites.

Animals↗
PubMed1986

Sperm duct contractions mediate centrally evoked sperm release in goldfish.

In order to determine the peripheral mechanisms underlying sperm release (SR) in goldfish, the contractile activity of the sperm ducts (SD) and testes were monitored during SR responses evoked by electrical stimulation of the brain. Electrical stimulation of the brain triggered testicular and SD contractions, and SR, while electrical stimulation of the genital nerve branch to the SD evoked only SD contractions and SR. Centrally activated SD contractions and SR were blocked by sectioning the SD genital nerve, while testicular contractions were unaffected. Testicular contractions do not appear necessary for centrally evoked SR since the response can be elicited from preparations in which the testes were separated from the SD. The results indicate that SR in goldfish is primarily mediated by the SD and not the testes. Testicular contractions may, however, serve to load the SD with milt. The functional significance of the central pathway(s) associated with SD and testicular contractions are discussed.

Animals↗
PubMed1985

A direct magnocellular-preopticospinal pathway in goldfish: implications for control of sex behavior.

Neurons in the pars magnocellularis and gigantocellularis of the goldfish magnocellular preoptic nucleus concentrate horseradish peroxidase by retrograde transport following its placement into sectioned spinal cord. Implants at rostral levels labeled the greatest number of preoptic cells. The pathway demonstrated is primarily ipsilateral and appears equivalent to the paraventricular-spinal system of tetrapods. In goldfish it may control sperm release and other stereotyped reproductive responses.

Animals↗
PubMed1984

Functional-anatomical studies on sperm release evoked by electrical stimulation of the olfactory tract in goldfish.

Sperm release was evoked by electrical stimulation of the olfactory tracts in male goldfish. Thresholds as low as 5 microA were obtained using suction electrodes while slightly higher currents were necessary using metal electrodes (lowest thresholds of 15-20 microA). Several control procedures were carried out to insure that current-spread to nearby structures was not responsible for the evoked responses. Testing olfactory tract stimulation following transection of one or more divisions of the olfactory tract revealed that connections to the olfactory bulb and pathways involving the lateral olfactory tract were not necessary for the stimulation effect, whereas the medial olfactory tract appears to be both sufficient and necessary for mediation of evoked sperm release. The results are discussed with respect to possible involvement of each of the 3 known functional components constituting the medial olfactory tract: (1) secondary olfactory afferents; (2) olfactory efferents; and (3) fibers of the terminal nerve. The possibility that female sex pheromones normally influence central sperm release mechanisms via pathways in the medical olfactory tract is also considered.

Animals↗
PubMed1983

The terminal nerve: a new chemosensory system in vertebrates?

Ganglion cells of the terminal nerve in goldfish are located in the olfactory nerve and bulb and send peripheral processes into the olfactory epithelium and central processes to the supracommissural nuclei of the telencephalon as well as to the retina. Correlations between terminal nerve projections and neurobehavioral studies suggest that the terminal nerve mediates responses to sex pheromones.

Animals↗
PubMed1980

Vertical banding evoked by electrical stimulation of the brain in anaesthetized green sunfish, Lepomis cyanellus, and bluegills, Lepomis macrochirus.

A pattern of dark vertical bands is a characteristic agonistic display in the green sunfish, Lepomis cyanellus and the bluegill, L. macrochirus. The rapidity with which the display can appear and disappear indicates that it is neurally controlled. Electrical stimulation of the brain was carried out in anaesthetized green sunfish and bluegills to map those regions from which this colour change can be elicited. Banding was evoked by stimulation of sites near the midline in the preoptic area, ventral thalamic-dorsal hypothalmic transition zone, the midbrain tegmentum (just dorsal to the nucleus prerotundus pars medialis), in and near the torus semicricularis, in the basal midbrain (region of the crossing tectobulbar tracts), and in the rostral basomedial medulla. A 'transition' zone was located basally in the middle medulla, caudal to which only paling was evoked. Areas found to be negative for evoked banding included the telencephalic lobe, the inferior lobe of the hypothalamus, the optic tract, the optic tectum, the body and valvula of the cerebellum and the caudal medulla. It is postulated that the vertical banding pattern is made up of a separate, selectively controlled system of dermal melanophores. The possible neural mechanisms controlling banding are discussed.

Animals↗