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Biomedical subjects

M F MacDonnell

Publications and source records attributed to M F MacDonnell.

17 recordsLinked to original sources
PubMed1989

Measurement of monoamines and monoamine metabolites in various brain regions of six shark species.

1. The concentrations of six monoamines or monoamine metabolites were measured in six brain regions of six shark species using high performance liquid chromatography with electrochemical detection. 2. Serotonin concentrations were greatest in the hypothalamus and tegmentum, intermediate in the midline ridge formation, spinal cord and forebrain, and lowest in the cerebellum in all species. 3. Specie differences in dopamien concentration were significant only in the forebrain; species differences in the levels of the norepinephrine, epinephrine and 5-hydroxyindoleacetic acid were significant in most brain regions, including the midline ridge formation. 4. Differences and similarities to the mammalian pattern of monoamine distribution in the brain are discussed.

Animals↗
PubMed1989

Sub/supraependymal axonal net in the brains of sharks and probable targets in parasynaptic relationship.

A sub/supraependymal system of varicose axons in the tectal midline ridge formation of shark brains is described. Lengths of axons and their terminals are seen freestanding in the cerebrospinal fluid (CSF) as well as in close contiguity with the large CSF-contacting and supraependymal mesencephalic trigeminal neurons of the midline ridge formation. The relationship of axonal varicosities and terminals to both CSF and supraependymal somata is such as to suggest a nonsynaptic association. This finding is discussed in the context of its utility in testing the concept of parasynaptic modulation in vertebrate brains. The topographical arrangement described is one in which the essential operational elements of parasynaptic activity can be identified in a neuronal assemblage whose functional association is known.

Animals↗
PubMed1986

Enhancement of optokinetic responses by lateral hypothalamic areas associated with attack in cats.

Stimulation of lateral hypothalamic sites associated with predatory attack and known to modify trigeminal reflex systems enhanced efficiency of visual following over a wide range of target velocities. Furthermore, lateral hypothalamic stimulation reversed reflex habituation seen after continuous and after repeated optokinetic stimulation. These findings support the hypothesis that the lateral hypothalamus directs behavioral responses relevant to orienting to and capturing prey, at least in part, by regulation of reflex mechanisms in different sensory modalities. Possible neural substrates for the observed effects are discussed.

Animals↗
PubMed1984

Circumventricular mesencephalic trigeminal midline ridge formation in cartilaginous fishes: species variations.

The midline ridge formation (MRF) of the trigeminal complex in 127 cartilaginous fish of 15 species was examined by scanning electron microscopy or light microscopy. Five distinct species variations of the MRF in sharks are described. The formation has not yet been observed to be present in skates and rays, but its presence in the subclass Holocephali, the sister group to the Elasmobranchii, indicates that this proposed circumventricular organ is an ancient brain characteristic of this line of vertebrates, perhaps predating the emergence of the class Chondrichthyii. The different types of MRF are compared to a current phyletic organization of the elasmobranchs and the possible functional significance of the formation is discussed briefly.

Animals↗
PubMed1983

Mesencephalic trigeminal midline ridge formation in sharks, a proposed circumventricular organ: developmental aspects.

In scanning electron microscopic (SEM) examination of 30 shark brains, a distinctive midline ridge formation on the ventricular surface of the optic tectum was found in all juveniles and adults of the three carcharhinid species (sandbar, dusky, and smooth hound) and the one lamnid species (mako) investigated. This formation is part of the mesencephalic trigeminal (Mes V) complex of these animals, and one of its remarkable features is a population of very large cerebrospinal fluid (CSF)-contacting and supraependymal Mes V neuronal somas. These cells, whose presence in the CSF compartment is heralded by distinct premonitory ependymal bulges, are not seen in contact with CSF until the sharks are well into their first postnatal year or later. Once established, the population of CSF-contacting and supraependymal Mes V neurons remains in substantial numbers over the life span of the animals into the period of sexual maturity. Age-related changes in patterns of ependymal ciliation of the midline ridge formation, tending toward a state of oligociliation, are also apparent in all species examined. Similarities between the midline ridge formation of the Mes V complex and known circumventricular organs (CVOs) are discussed and it is suggested that the formation be considered as a previously unrecognized CVO. It is hypothesized that the midline ridge formation with its contingent of CSF-immersed neurons, by monitoring one or more CSF factors, might serve to alter the excitability of the Mes V complex as a whole and, thus, regulate intensity of biting reflexes in sharks.

Aging↗
PubMed1980

Septal and amygdalar efferents to the hypothalamus which facilitate hypothalamically elicited intraspecific aggression and associated hissing in the cat. An autoradiographic study.

Septal and amygdalar sites were identified which facilitated hypothalamically elicited intraspecific agression and associated hissing in cats. Tritiated proline was injected into facilitatory sites through a Hamilton syringe modified to serve as an electrode. Efferents from septal or amygdalar facilitatory sites were traced to the hypothalamus by means of autoradiography. Amygdalar facilitatory sites projected primarily to the core and capsule of the ventromedial nucleus of the hypothalamus (VMH), while septal facilitatory sites projected only lightly to the VMH. Common to all septal facilitatory sites, and not previously reported, was a distinct and considerable projection to the medial hypothalamus, in association with the paraventricular and dorsomedial nuclei. The means by which septal and amygdalar sites may act to facilitate hypothalamically elicited intraspecific aggression are discussed.

Aggression↗
PubMed1980

Mesencephalic trigeminal nucleus in sharks. A light microscopic study.

In 22 adult sharks representing eight species, the mesencephalic trigeminal nucleus (Mes V) was examined employing the Romanes reduced silved method. Morphological evidence is presented of extensive development of neurites and intranuclear communication among Mes V cells of sharks, as well as their apparent innervation by extranuclear neurons. Species differences and the possible significance of the morphology of the Mes V in sharks to certain aspects of their behavior are discussed. A brief comparison of the Mes V of elasmobranchs and those of reptiles and mammals is included.

Animals↗
PubMed1980

Cerebrospinal fluid contacting and supraependymal mesencephalic trigeminal cells in the blue and mako sharks. A scanning electron microscopic study.

Scanning electron microscopic observations reveal cerebrospinal fluid contacting and supraependymal cell bodies of the mesencephalic trigeminal (Mes V) nucleus in adult specimens of mako and blue sharks, but not in very young specimens of the smooth dogfish shark. Possible functional roles are discussed in terms of participation of cerebrospinal fluid contacting Mes V cells in a neuroendocrine regulatory system. Comparisons are made with light microscopic observations of the relationship of Mes V cells with the ventricular wall. General features of the scanning electron microscopic appearance of the roof of the ventricle of the optic tectum in sharks are described and compared to similar general features found in the third ventricle of a variety of vertebrates.

Animals↗
PubMed1975

Hyperexcitability in the neural substrate of emotional behavior in cats after alcohol withdrawal. Evidence of a rapid development of alcohol dependence.

Substantial and prolonged withdrawal hyperexcitability in the neural substrate for affective defense was revealed by behavioral and electrophysiological measures in cats exposed to moderate to heavy doses of alcohol for periods ranging from 6 to 72 hours. The data are interpreted as indicating a rapid development of physical dependence on alcohol in this portion of the central nervous system.

Amygdala↗
PubMed1966

Control of sensory fields by stimulation of hypothalamus.

Stimulation of the cat's hypothalamus, which elicits attack, also establishes sensory fields for two reflexes related to biting. Touching a perioral region leads to head movement, bringing the stimulus to the mouth. Touching the lip-line leads to jaw opening. The size of the fields depends on the intensity of stimulation.

Animals↗