Telencephalon Size Research Articles

The evolution of stereopsis and the Wulst in caprimulgiform birds: a comparative analysis

Owls possess stereopsis (i.e., the ability to perceive depth from retinal disparity cues), but its distribution amongst other birds has remained largely unexplored. Here, we present data on species variation in brain and telencephalon size and features of the Wulst, the neuroanatomical substrate that subserves stereopsis, in a putative sister-group to owls, the order Caprimulgiformes. The caprimulgiforms we examined included nightjars (Caprimulgidae), owlet-nightjars (Aegothelidae), potoos (Nyctibiidae), frogmouths (Podargidae) and the Oilbird (Steatornithidae). The owlet-nightjars and frogmouths shared almost identical relative brain, telencephalic and Wulst volumes as well as overall brain morphology and Wulst morphology with owls. Specifically, the owls, frogmouths and owlet-nightjars possess relatively large brains and telencephalic and Wulst volumes, had a characteristic brain shape and displayed prominent laminae in the Wulst. In contrast, potoos and nightjars both had relatively small brains and telencephala, and Wulst volumes that are typical for similarly sized birds from other orders. The Oilbird had a large brain, telencephalon and Wulst, although these measures were not quite as large as those of the owls. This gradation of owl-like versus nightjar-like brains within caprimulgiforms has significant implications for understanding the evolution of stereopsis and the Wulst both within the order and birds in general.

Proliferation zones in the salmon telencephalon and evidence for environmental influence on proliferation rate

Cell proliferation occurs in the brain of fish throughout life. This mitotic activity contributes new neurons to some brain subdivisions, suggesting potential for plasticity in neural development. Recently we found that the telencephalon in salmonids (salmon, trout) is significantly reduced in fish reared in hatcheries compared to wild fish, and that these differences resulted in part from rearing conditions. Here, we describe localized areas of cell proliferation in the telencephalon of juvenile coho salmon ( Oncorhynchus kisutch) and begin to explore whether mitotic activity in these areas is sensitive to environmental conditions. Using the 5-bromo-2′-deoxyuridine (BrdU) cell birth-dating technique, we localized proliferating cells in the telencephalon to three distinct zones (proliferation zones 1a, 1b, and 2). We measured the volumes of these zones and showed that they grew at different rates relative to body size. We also found that variation in environmental rearing conditions altered the density of BrdU-labeled cells in proliferation zone 2, but not in zones 1a or 1b. However, this change in mitotic activity did not generate a difference in telencephalon size. These results suggest that environmental conditions, and associated changes in swimming activity or social structure, may influence rates of cell proliferation in the fish forebrain.

The relationships between brain regions and forelimb dexterity in marsupials (Marsupialia): a comparative test of the principle of proper mass

A behavioural index of forelimb dexterity and comparative statistics were used to analyse the relationships between proximal (shoulder, upper and lower forelimb) and distal (wrist, forepaw, digits) forelimb dexterity and four aspects of brain morphology (overall brain, cortex, cerebellum and telencephalon sizes) in 18 species of marsupials. On the basis of the principle of proper mass, it was expected that an increase in forelimb dexterity (either proximal or distal) would be positively correlated with the size of the brain and the three brain components. Using independent contrast analysis to remove the effects of phylogeny revealed three significant correlations between: cortex size and distal dexterity, cerebellum size and proximal dexterity, and telencephalon size and distal dexterity. The relationship between cortex size and distal dexterity was subsequently corroborated by Spearman rank correlations. These results suggest that the execution of finely coordinated forelimb movements may not be dependent upon overall brain size, but may be dependent upon the size of brain components, thus supporting the principle of proper mass.

Seasonal changes of hippocampus volume in parasitic cowbirds

Avian brain plasticity has been demonstrated by seasonal variations in neuroanatomy correlated with changes in singing and hoarding behaviour. We report a new instance of plasticity. Brood parasitism in South American cowbirds involves memory for location of hosts' nests, and is associated with an enlarged hippocampus relative to telencephalon size. This effect holds between sexes and species during the breeding season. We report that for two parasitic species, relative hippocampal volume is smaller during the non-breeding than the breeding season, and that sexual dimorphism present in summer in one of the species is not found in winter. These results support the hypothesis that the avian hippocampal formation shows neuroanatomical plasticity associated with seasonal changes in spatial memory demands.

In vitro teratogenicity of ethylenethiourea in the rat.

We have demonstrated that ethylenethiourea (ETU) is a potent teratogen to the rat embryo developing in vitro. Sprague Dawley rat embryos were explanted on gestation day 10 and cultured for 48 hours in the presence of 40-200 micrograms/ml ETU. This resulted in a dose-related inhibition of growth and differentiation as assessed by crown-rump length, protein and DNA content, and somite number and in an increase in the frequency of abnormalities. A variety of anomalies was produced, including fluid accumulation in the brain (hydrocephalus), decreased mandibular size, decreased telencephalon size, abnormal dorsiflexion, as well as subectodermal blisters on the tail and limb buds and maxilla. Frank malformations have been observed at these same sites--hydrocephalus, brachygnathia, kyphosis, limb and tail defects, cleft palate--in the term fetus in vivo. The presence of abnormal fluid accumulation in the embryos--distended neural tube and subectodermal blisters--suggesting that the osmotic environment of the embryo had been altered by ETU exposure. Osmolality of the exocoelomic fluid (ECF) surrounding the embryo was measured after 48 hours of exposure to a concentration of ETU that caused nearly a 100% incidence of subectodermal blisters. ECF osmolality was found to be significantly lower than that of control embryos. Lowered osmolality would cause water to move out of the ECF, presumably causing the observed fluid accumulation in the embryo. It is speculated that altered osmotic balance and localized edema in the embryo are contributory steps in the formation of defects after ETU exposure.