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A H Bass

Publications and source records attributed to A H Bass.

65 records · Page 4Linked to original sources
PubMed1986

Androgen binding in the brain and electric organ of a mormyrid fish.

The mormyrid fish of Africa produce a weak electric pulse called an Electric Organ Discharge (EOD) that functions in electrical guidance and communication. The EOD waveform describes the appearance of a single pulse which is produced by the electric organ's excitable cells, the electrocytes. For some species, there is a sex difference in the appearance and duration of the EOD waveform, which is under the control of gonadal steroid hormones. We now show, using biochemical techniques, that the steroid-sensitivity of the myogenic electric organ correlates with the presence of comparatively high levels of androgen-binding activity in the cytosol of electrocytes. The EOD rhythm describes the rate at which the electric organ fires and is under the control of a central electromotor pathway. Sex differences have also been described for the EOD rhythm. Using steroid autoradiographic techniques, we found uptake of tritium-labelled dihydrotestosterone (3H-DHT) by cells within the reticular formation that lie adjacent to the medullary 'relay nucleus' which innervates the spinal electromotoneurons that excite the electric organ. However, no DHT-binding was observed in the relay or electromotor nuclei. Steroid-concentrating cells were also found in several other brainstem regions, the hypothalamus, and the thalamus. In particular, a group of DHT-concentrating, motoneuron-like cells were observed in the caudal medulla and were identified as a swimbladder or sonic motor nucleus. The biochemical data suggest that the electric organ has evolved a sensitivity to gonadal steroid hormones that may underlie the development of known sex differences in the EOD waveform. The autoradiographic results suggest that if steroids do affect the development of sex differences in the EOD rhythm, it is at some level removed from known spinal and medullary electromotor nuclei.

Androgens↗
PubMed1986

Steroid-sensitive neuroeffector pathways for sonic and electric communication in fish.

A neuroeffector pathway for communication consists of at least two elements: a peripheral effector organ and a central motor nucleus. Two communication systems are discussed here: the sonic motor and electromotor systems of fish. The electromotor system is used to illustrate species diversity of a peripheral effector, the electric organ. The sonic motor system is discussed in the context of species differences in the organization of a central motor nucleus for communication. Both systems share several anatomical and physiological features related to the generation of a stereotyped communication signal. Moreover, both systems appear to be sensitive to the influences of gonadal steroid hormones in the development of sexually dimorphic communication signals.

Animal Communication↗
PubMed1985

Sonic motor pathways in teleost fishes: a comparative HRP study.

Among marine teleost fishes, one neuroeffector pathway for sonic communication consists of two components: a peripheral effector organ that consists of a swimbladder with associated 'drum' muscles, and a swimbladder or 'sonic' motor nucleus (SMN) located at the junction of the spinal cord and the medulla oblongata. Here, the organization of the SMN is compared in two unrelated groups of teleosts, the midshipmen, Porichthys notatus and P. myriaster, and the sea robin, Prionotus carolinus. Horseradish peroxidase (HRP), used as a retrograde tracer, revealed the position of the SMN in each species. While the SMN is a fused midline structure in midshipmen, it is bilateral in sea robins. The functional significance of these two contrasting patterns of organization remains to be explored. A third study group included mormyrid freshwater electric fish, which are also sonic. Mormyrids were included in part because an earlier study identified androgen-binding cells at a brain level comparable to that of the SMN of marine fishes. Using HRP methods, a swimbladder motor nucleus was identified at the caudal pole of the vagal motor column. However, the nucleus in mormyrids lies dorsal to the fourth ventricle and central canal, not ventral as it does in midshipmen and sea robins. Its position corresponds to the steroid-concentrating cells identified in a previous study.

Air Sacs↗
PubMed1983

Hormonal control of sexual differentiation: changes in electric organ discharge waveform.

Males and females of some mormyrid electric fishes generate electrical pulses that differ in waveform and duration. For one such species, testosterone or dihydrotestosterone induces females and immature males to produce the mature male electric organ discharge which is two times the duration of the female or immature discharge. Estradiol has only a weak effect. For a second species where males and females have similar electric organ discharges, testosterone produces no effect. The data suggest that androgens affect the electric organ itself.

Animals↗
PubMed1983

Visual activity in the telencephalon of the painted turtle, Chrysemys picta.

Multiple unit activity in response to visual stimulation was recorded in the following telencephalic areas of the painted turtle: lateral and medial divisions of the dorsal cortex, lateral and medial divisions of the dorsal ventricular ridge, and the striatum. The data confirm anatomical evidence for ascending visual input to the dorsal cortex, the lateral dorsal ventricular ridge and the striatum. The identification of a new visual zone in a medial division of the dorsal ventricular ridge suggests that turtles, and perhaps other reptiles, possess at least 3 visual pallial areas.

Animals↗
PubMed1981

Retinal recipient nuclei in the painted turtle, Chrysemys picta: an autoradiographic and HRP study.

Retinofugal pathways in the painted turtle were examined with autoradiographic and HRP methods. The majority of the retinal fibers decussate at the optic chiasm and course caudally to terminate in 12 regions of the diencephalon and mesencephalon. The pars dorsalis of the lateral geniculate nucleus is the densest target in the thalamus. Two nuclei dorsal to pars dorsalis--the dorsal optic and dorsal central nuclei--receive optic input. Three nuclei ventral to pars dorsalis and retinal targets--the ventral geniculate nucleus, nucleus ventrolateralis pars dorsalis, and nucleus ventrolateralis pars ventralis. Contralateral fibers course through the pretectum where they terminate in nucleus geniculatis pretectalis, nucleus lentiformis mesencephali, nucleus posterodorsalis, and the external pretectal nucleus. Retinal fibers also terminate within the superficial zone of the optic tectum. HRP material demonstrates three optic fiber layers--laminae 9, 12, and 14. Optic fibers leave the main optic tract as a distinct accessory tegmental optic pathway and terminate in the basal optic nucleus. Ipsilateral retinal terminals occur in a pars dorsalis and a pars ventralis of the lateral geniculate nucleus, the dorsal optic nucleus, nucleus posterodorsalis, the basal optic nucleus, and in laminae 9 and 12 of the optic tectum. Rostrally, the ipsilateral tectal fibers occupy two zones along the medial and lateral tectal roof; these zones converge caudally and are continuous along the caudal wall of the tectum.

Animals↗
PubMed1981

Temporal coding of species recognition signals in an electric fish.

An electric fish in the African family Mormyridae recognizes members of its own species by "listening" to electric organ discharges, which are species-specific signatures. Reactions of fish in the field and of individual electroreceptors to both normal and modified computer-synthesized discharges emphasize the importance of the waveform (time-domain cues) in species recognition.

Animal Communication↗
PubMed1981

Primary retinal targets in the Atlantic loggerhead sea turtle, Caretta caretta.

Autoradiographic analysis distinguished twelve primary retinal targets in the diencephalon and the mesencephalon of the Atlantic loggerhead sea turtle, Caretta caretta. While the majority of fibers terminate contralaterally, sparse labelling is seen over ipsilateral thalamic nuclei. The dorsal optic nucleus is the most expansive retinal target in the dorsal thalamus. Four nuclei ventral and one dorsal, to the dorsal optic nucleus, receive retinal input. Before terminating in the optic tectum, labelled fibers pass through the pretectum terminating in four nuclei. Within the superficial zone of the optic tectum, three terminal zones are recognized. A distinct accessory tegmental tract separates from the main optic tract terminating in the basal optic nucleus. While such a multiplicity of retinal targets occurs among other reptiles, birds and mammals, it is presently impossible to accurately recognize visual homologies among amniotic vertebrates.

Animals↗
PubMed1981

Telencephalic efferents in channel catfish, Ictalurus punctatus: projections to the olfactory bulb and optic tectum.

Telencephalic projections to the olfactory bulb and optic tectum were examined with horseradish peroxidase (HRP) methods in catfish. Olfactory bulb afferents arise from the mitral cell layer of the contralateral olfactory bulb and the ipsilateral telencephalon. The majority of labelled cells appear within the ventral and dorsal nuclei of area ventralis telencephali and two divisions of the central zone of area dorsalis telencephali. Excepting one division of the dorsal central zone, all afferent sources are secondary olfactory targets. Tectal HRP injections reveal labelled cells in a third division of the dorsal central zone.

Afferent Pathways↗
PubMed1977

Effects of lesions of the optic tectum on the ability of turtles to locate food stimuli.

In a previous experiment, it was demonstrated that the removal of portions of the optic tectum in a turtle, Podocnemis unifilis, impaired its ability to perform a horizontal vs. vertical line discrimination task. To further elucidate the nature of this deficit, turtles (P. unifilis) were operantly conditioned to locate a food object at varying positions in an aquarium. Preoperatively, all of the animals approach a food object in a direct manner. Animals with a bilateral lesion of the optic tectum approach the food object in an indirect manner. One animal, with a unilateral lesion approached the food object in both an indirect and a direct manner depending on the position of the object in the visual field.

Animals↗