Function In Lower Vertebrates Research Articles

Neuroscience of the mechanisms of mind and behavior

Reflexes, compound movements, and innate behavior are basic neural functions in lower vertebrates, and are executed by the spinal cord and brain stem. These functions are made goal-oriented by the limbic system, stable by the basal ganglia, adaptive by the cerebellum, and restorable by the wakefulness-sleep centers in the brain stem. Elaborate sensorimotor functions of the cerebral neocortex have evolved after birds, and mental functions have developed in the association cortex of primates, particularly in humans. To understand the neuronal mechanisms operating in each of these executive and regulatory systems of brains, a number of obstacles must be overcome, as reviewed here from the perspective of recent studies on the cerebellum.

Gravity, blood circulation, and the adaptation of form and function in lower vertebrates

Gravitational force influences musculoskeletal systems, fluid distribution, and hydrodynamics of the circulation, especially in larger terrestrial vertebrates. The disturbance to hydrodynamics and distribution of body fluids relates largely to the effects of hydrostatic pressure gradients acting in vertical blood columns. These, in turn, are linked to the evolution of adaptive countermeasures involving modifications of structure and function. Comparative studies of snakes suggest there are four generalizations concerning adaptive countermeasures to gravity stress that seem relevant to lower vertebrates generally. First, increasing levels of regulated arterial blood pressure are expected to evolve with some relation to gravitational stresses incurred by the effects of height and posture on vertical blood columns above the heart. Second, aspects of gross anatomical organization are expected to evolve in relation to gravitational influence incurred by habitat and behavior. Third, natural selection coupled to gravitational stresses has favored morphological features that reduce the compliance of perivascular tissues and provide an anatomical "antigravity suit." Fourth, natural selection has produced gradients or regional differences of vascular characteristics in tall or elongated vertebrates that are active in high gravity stress environments. Consideration or awareness of these principles should be incorporated into interpretations of structure and function in lower vertebrates.

Gravity, blood circulation, and the adaptation of form and function in lower vertebrates

Gravitational force influences musculoskeletal systems, fluid distribution, and hydrodynamics of the circulation, especially in larger terrestrial vertebrates. The disturbance to hydrodynamics and distribution of body fluids relates largely to the effects of hydrostatic pressure gradients acting in vertical blood columns. These, in turn, are linked to the evolution of adaptive countermeasures involving modifications of structure and function. Comparative studies of snakes suggest there are four generalizations concerning adaptive countermeasures to gravity stress that seem relevant to lower vertebrates generally. First, increasing levels of regulated arterial blood pressure are expected to evolve with some relation to gravitational stresses incurred by the effects of height and posture on vertical blood columns above the heart. Second, aspects of gross anatomical organization are expected to evolve in relation to gravitational influence incurred by habitat and behavior. Third, natural selection coupled to gravitational stresses has favored morphological features that reduce the compliance of perivascular tissues and provide an anatomical “antigravity suit.” Fourth, natural selection has produced gradients or regional differences of vascular characteristics in tall or elongated vertebrates that are active in high gravity stress environments. Consideration or awareness of these principles should be incorporated into interpretations of structure and function in lower vertebrates. © 1996 Wiley-Liss, Inc.

The pineal and melatonin: Regulators of circadian function in lower vertebrates

The pineal has been identified as a major circadian pacemaker within the circadian system of a number of lower vertebrates although other pacemaking sites have been implicated as well. The rhythmic synthesis and secretion of the pineal hormone, melatonin, is suggested as the mechanism by which the pineal controls circadian oscillators located elsewhere. Both light and temperature cycles can entrain the pineal melatonin rhythm. The pineal, therefore, acts as a photo and thermoendocrine transducer which functions to synchronize internal cycle with cycles in the environment. A model is presented which portrays the pineal as a major component of a 'multioscillator' circadian system and which suggests how these multiple circadian clocks are coupled to each other and to cycles of light and temperature in the external world.

The pineal and melatonin: Regulators of circadian function in lower vertebrates

The pineal and melatonin: Regulators of circadian function in lower vertebrates

Serotonin-like immunoreactive cells in the pulmonary epithelium of ancient fish species

The pulmonary mucosa of three species of ancient fish was studied immunohistochemically to show the distribution of serotonin, regarded as the main monoamine of mammalian bronchopulmonary paraneurons. Serotonin-like immunoreactive cells, dispersed through the airway epithelium as single cells, were found in all the fish species studied. They are presumably equivalent to the neuroendocrine cells reported in the lungs of mammalian and submammalian vertebrates. However, the precise role and the function of these cells remain unknown. Since the species studied belong to the most primitive extant groups of ancient fish, the present investigation suggests that serotonin is widely distributed in the lungs of the vertebrates. Several peptides, known to be specific cytochemical markers for the identification of the pulmonary neuroendocrine cells of mammals, are being investigated in the lungs of the fish species studied. They may help to trace the phylogeny of the pulmonary neuroendocrine cell system and to elucidate its function in lower vertebrates.

Evolution of Endocrine Regulation of Gastrointestinal Function in Lower Vertebrates

The information available concerning the evolution of endocrine regulation of three gastrointestinal functions in lower vertebrates—gastric acid secretion, gallbladder contraction, and pancreatic enzyme secretion—is reviewed. The actions of hormones of the cholecystokinin/gastrin family of peptides have been the most widely studied and are emphasized. It is concluded that regulation of pancreatic enzyme secretion is a primitive action of cholecystokinin and that the sensitivity of gallbladder muscle and gastric acid-secreting cells to these peptides evolved later, possibly in the ancestral lineage that led to the gnathostomes. The need for increased digestive efficiency to support the higher levels of activity made possible by the evolution of jaws is suggested as a strong selection pressure leading to this pattern of evolution of endocrine regulation of gastrointestinal function.

Evolution of Pineal Control of Endocrine Function in Lower Vertebrates

Pineal bodies, and other associated parietal structures, are remarkably varied among vertebrates These organs apparently assumed, in the primitive vertebrates, a principal role in integration of photic information. The pineal photoreceptor cell seems to have evolved into the secretory pinealocyte that is found in most of the higher vertebrates. Along with the evolution of the photoreceptor element into the pinealocyte, there is a concomitant shift in the neural connection of the pineal organ. The pinealo-fugal, sensory innervation gives way to an autonomic, pinealo-petal motor innervation. Thus, direct photosensitivity was superceded by indirect, optically-mediated control of the now secretory pineal gland. Even though pineal organs display such unusual plasticity and diversity across groups, responsivenses to light remains a constant feature. Photoperiod may modify the diurnallyrhythmic patterns of melatonin secretion across seasons and invoke appropriate “programs” which permit an animal to anticipate seasonal changes. Thus, melatonin may be a key molecule, attuned to photoperiodicity, which has been selected through evolution to effect adaptation to annual events.

Brain Mechanisms of Behaviour in Lower Vertebrates

Contributors Preface Introduction P. R. Laming Part I. Evolutionary Perspectives in Vertebrate Neuroethology: 1. An introduction to the functional anatomy of the brains of fish and amphibians (with comments on the reptiles) P. R. Laming 2. Evolution of telencephalic function in lower vertebrates L. R. Aronson 3. Interspecific variability in brain organisation and its possible relation to evolutionary mechanisms S. O. E. Ebbesson Part II. Sensory Mechanisms and Behaviour: 4. The properties of the visual pathway of a common freshwater fish in relation to its visual behaviour D. M. Guthrie 5. The telstean optic tectum: neuronal substrates for behavioural mechanisms H. Vanegas 6. Behavioural and electrophysiological studies of chemosensory reactions in fish T. J. Hara 7. Neural coding of 'worms' and 'antiworms' in the brain of toads: the question of hardwired and softwired systems J. P. Ewert Part III. Sleep, Wakefulness and Arousal: 8. Sleep ontogeny in fish C. M. Shapiro, C. J. Woolf and D. Borsook 9. An electrophysiological study of wakefulness and sleep-like states in fish and amphibians I. G. Karmanova, A. I. Belich and S. G. Lazarev 10. The physiological basis of alert behaviour in fish P. R. Laming Part IV. Neuronal Substrates of Appetitive Behaviour: 11. Hypothalamic mechanisms of feeding fishes L. S. Demski 12. The telencephalon and reproductive behaviour in the teleost Macropodus opercularis: effects of lesions on the incidence of spawning and egg cannibalism R. E. Davis, J. Kassel and M. Martinez Part V. Learning and Memory Mechanisms: 13. Learning in teleost fish: role of the telencephalon N. Bohac Flood and J. B. Overmier 14. Electrical stimulation of the telencephalon and learning in a teleost fish G. E. Savage and D. E. Wright 15. Pituitary peptides and memory in fish D. Borsook, C. J. Woolf, D. Vellet, I. S. Abramson and C. M. Shapiro Index.

Comparative Histophysiology of the Pancreatic Islets

The embryological origin of the islet tissue from a common entodermal anlage with the exocrine pancreas has been questioned recently. The islet tissue may be of. neural crest origin, and the ancestral islet cells may have been “taste cells in the gut.” Whether the separation of exocrine and endocrine tissue in the cyclostomes is an original one or not remains an open phylogenetic key question. One or more islet hormones affect the exocrine pancreas tissue. However, the islet topography in various groups shows that intrapancreatic islet dissemination is not a general prerequisite for the normal function of the exocrine tissue. The D-cell is now generally recognized as the source of a third islet hormone. A fourth granular cell type (X-cell) may well secrete a fourth islet hormone. The significance of the amphiphil islet cells, found in various species, and of the “light” cells of the cyclostomes requires further studies. The islet function in lower vertebrates is largely unknown. So far, neither the islet cytology nor the known effects of pancreatectomy allow far-reaching conclusions. The evolution of the islet functions may be only understood when their interactions with the pituitary functions become clear.