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L S Demski

Publications and source records attributed to L S Demski.

At least 19 recordsLinked to original sources
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)

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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PubMed1978

Agonistic behavior elicited by electrical stimulation of the brain in western collared lizards, Crotaphytus collaris.

Western collared lizards, Crotaphytus collaris, were tested in three experiments using electrical stimulation of the brain. In experiment 1, agonistic behavior (defensive, aggressive and escape) responses were elicited in free-moving unanesthetized lizards. In experiment 2, areas were localized from which gular extension, a common component of defensive and aggressive behavior, could be evoked in anesthetized animals. Experiment 3 was carried out to demonstrate that defensive and aggressive behavior could be elicited from the same stimulation sites both in anesthetized and unanesthetized lizards. Initially, gular extension was evoked while the animal was anesthetized and later the animal was tested while freely moving and unanesthetized. Based on a combined plot of the sites from which defensive and aggressive behavior was evoked in experiments 1--3, the higher threshold sites (51--750 muA) were in the dorsal ventricular ridge anterior, amygdaloid complex, septal and preoptic areas, hypothalamus, thalamus and adjacent to the nucleus profundus mesencephali (NPM) and reticular formation. Lower threshold sites (up to 50 muA) are found in the NPM and the reticular formation. Escape behavior can be evoked from stimulation sites within or adjacent to areas from which defensive and aggressive behavior can be elicited.

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PubMed1976

The lateral recess of the third ventricle in teleosts: an electron microscopic and Golgi study.

The ependyma lining the lateral recess of the third ventricle of the teleost inferior lobe has been studied by light and electron microscopy, including Golgi impregnation methods. As many as five different cell types appear to line the ventricle, but some of these may be similar cells in different stages of activity. One cell type contains small dense-cored vesicles and appears to have processes extending into deeper portions of the lobe. Golgi preparations reveal subependymal cells with apical processes extending to the ventricle and basal extensions which may reach the pial surface. The present observations are discussed in relation to similar studies in other fishes, amphibians and mammals. Possible functions for the various cells observed are suggested.

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PubMed1976

The structure of the hypothalamic inferior lobes of the blacktip reef shark: scanning and transmission electron microscopic observations.

The inferior lobes of the shark hypothalamus were examined with light, transmission and scanning electron microscopy. The cells bordering the floor of the lateral recess appear to be typical liquor-contacting neurons. With scanning electron microscopy (SEM) the apical ends of these cells are seen to bulge into the ventricular lumen. In contrast, the roof is lined by a more typical ependymal cell characterized by numerous cilia and microvilli. In addition, SEM reveals several kinds of supraependymal cells with processes that appear to penetrate the ventricular lining. A periventricular nucleus underlies the ependymal cells. Neurons of the periventricular nucleus contain numerous lipofuchsin granules. The rest of the inferior lobe consists of many neuronal fibers. The morphology of the hypothalamic inferior lobe is discussed in relation to its possible role in feeding and aggressive behavior in both elasmobranchs and teleosts.

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PubMed1975

The structure of the inferior lobe of the teleost hypothalamus.

Electron microscopic and Golgi studies on the inferior lobes of sunfish and goldfish are described. The inferior lobe consists primarily of a nucleus ventricularis of densely packed cells surrounding the lateral recess of the third ventricle, and a peripherally situated nucleus diffusus consisting mostly of scattered neurons. A cell-sparse zone of dense neuropil is located between the two cellular areas. Neurons of both nuclei have spiny dendrites and axons which originate from basal dendrites. In some cases axons are found to send a collateral into the cell-sparse zone. Neurons of the nucleus diffusus possess collaterals that extend a considerable distance within the nucleus itself. The ultrastructure of cells of both nuclei reveals cytoplasmic organelles typical of most neurons. Synapses containing dense-cored and clear vesicles are present on the spines and shafts of the dendrites of both neuronal types. In only rare cases synapses were observed on the soma of neurons of the nucleus ventricularis. Possible anatomical substrates involved in the control of feeding and aggression in teleosts are considered in light of the present findings. Morphological similarities of the inferior lobes and related areas in various fishes and amphibians are discussed and their possible significance for the understanding of the evolution of hypothalamic mechanisms is considered.

Aggression↗
PubMed1975

Sperm release evoked by electrical stimulation of the fish brain: a functional-anatomical study.

Acute brain stimulation experiments were carried out in anesthetized male green sunfish, Lepomis cyanellus. Semen discharge was evoked consistently by low level electrical stimulation (100 muA or less) in the following areas: the preoptic region, dorsal hypothalamus, thalamus, midbrain tegmentum and the basolateral midbrain and medulla. Areas which were stimulated repeatedly at 100 muA and were always negative for sperm release included: the telencephalon with the exception of the preoptic region, the optic tectum, the cerebellum, the inferior lobe of the hypothalamus, the nucleus rotundus and the dorsal medulla. Removal of most of the optic tectum and cerebellum failed to block reponses evoked from the preoptic area; however, they were usually eliminated by transecting the rostral spinal cord. Electrical stimulation of an isolated 4 mm segment of spinal cord located at the third vertebral level resulted in sperm release, indicating that adequate mechanisms for semen discharge are present within the upper spinal cord. The results of this study suggest that a sperm release system in the green sunfish extends from the preoptic area to the spinal cord passing through the hypothalamus, midbrain tegmentum and basal midbrain and medulla.

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