摘要:

The propatagium of gliding and flying mammals is of both functional and phylogenetic interest. The innervation of the propatagial muscle, platysma II, was studied with the axonal tracer wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) in a flying squirrel, Glaucomys volans. Injections of WGA-HRP into the proximal third of platysma II labeled motoneurons in the lateral part of the medial subdivision of the ipsilateral facial nucleus and in the ipsilateral ventral horn of the brachial enlargement. Injections into distal regions of platysma II labeled motoneurons in the ipsilateral ventral horn of spinal segments C5-C8 but not in the facial nucleus. Injections along the whole length of the muscle labeled afferent axons in the ipsilateral dorsal horn of spinal segments C4-T1. These results demonstrate a mixed facial and spinal motor innervation of propatagial musculature in the flying squirrel and indicate that this pattern of mixed innervation is more widespread among flying and gliding mammals than previously reported. Mixed facial and cervical propatagial innervation, independently derived in different flying and gliding mammals, may represent a common solution in the design of the propatagium. These findings complicate the use of propatagial muscle innervation patterns for the establishment of phylogenetic relationships among flying and gliding mammals.

ISSN:0006-8977    

DOI:10.1159/000113224

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

The sequence of appearance of major forebrain projection and commissural fibre bundles in the tammar wallaby (Macropus eugenii) during development was examined with the aid of silver and haematoxylin stained material. At the time of birth (P0), the cerebral cortex is unformed, but two prominent fibre bundles are apparent in the forebrain: the medial forebrain bundle and the stria medullaris thalami. There is also an unidentified tract (possibly thalamostriate or striothalamic), which appears to be transient, in that it cannot be identified at P8. By P2 the posterior commissure, fasciculus retroflexus and mammillothalamic tract have appeared. Fibres of the fornix were first visible at P8. Cortical projection fibres (internal and external capsular fibres) were first noted at P10 and the anterior commissure at P14. It was not until P18 that the cortical commissural bundle unique to diprotodontid metatherians, namely the fasciculus aberrans, was first seen. The hippocampal commissure was seen to develop relatively late, at P35. The sequence and tempo of development of these tracts has been compared in metatherian and eutherian forebrains. The sequence is similar in the two groups of mammals with one exception: isocortical commissural connections appear to develop considerably earlier in diprotodontid metatherians than in eutherians. With regard to the tempo of forebrain tract development, mammals with r selection reproductive patterns (large litter sizes, many litters per reproductive lifetime, rapid development of offspring, e.g. polyprotodontid metatherians, rodents) appear to have forebrain tract development occupying a relatively greater proportion of the period from conception to the attainment of behavioural autonomy than do those animals with K selection reproductive patterns (few offspring per reproductive lifetime, relatively prolonged development of offspring, e.g. diprotodontid metatherians, primates). This difference is irrespective of whether a mammal is metatherian or eutherian, independent of encephalization, and probably reflects the greater time allocated to aspects of brain development occurring after initial tract formation (elaboration of cortical and forebrain circuitry, dendritic tree growth, synapse overproduction and elimination) among K selection mammals.

ISSN:0006-8977    

DOI:10.1159/000113225

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Visual system anomalies in albino mammals are generally seen to be caused by a lack of retinal pigment and misrouting of retinofugal optic fibers. This study shows that the central visual system of white zebra finches is physiologically different from normally colored (wild type) birds, although the eye pigmentation and the retinofugal projection appear to be normal. Ipsilaterally evoked potentials in our white birds are enhanced in comparison to wild type birds, whereas in albino mammals the ipsilateral component of visually evoked potentials is reduced. Picrotoxin-induced blockade of inhibitory synapses in the ectostriatum reveals remarkable differences between wild type and white zebra finches. In wild type zebra finches, a significant shift of ipsilateral to contralateral stimulus response ratios is observed. However, there is no detectable shift in the white morph. The data suggest that inhibition of ipsilateral stimulus processing, as observed in wild type zebra finches, is significantly reduced in the white morph. Our results indicate that the effects observed in white zebra finches cannot be explained by the theories that have been developed for albinotic animals. We assume that in white zebra finches a genetic defect, which causes the white plumage, is coupled with the demonstrated deviations of inhibitory mechanisms in the central visual system.

ISSN:0006-8977    

DOI:10.1159/000113226

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

We compared the morphology, including relative volumes (RV), of some brain regions in leptocephalus larvae (10–30 mm in total length), glass eels (elvers), young, and immature pre-adults of the Japanese eel Anguilla japonica. The external brain shape of the leptocephali gradually changes from a laterally compressed one to a depressed elongated one. These changes are fundamentally due to biased growth of the telencephalon and optic tectum. The dramatic brain transformation progresses until the juvenile stage and culminates in an adult-type brain arrangement, with a developed cerebellum and eminentia granularis and a much more flattened appearance. The RVs of brain regions closely related to somatic sensory functions are quite different in larvae and juveniles. The larvae possess larger optic tecta and smaller chemo- and mechanosensory regions than the juveniles. The RV of the olfactory bulb increases, and that of the optic tectum decreases, until the adult stage, unlike the condition in a pelagic fish, Pagrus major, suggesting that adult eels are inferior to pelagic fishes in visual perception. In contrast, the brain morphology of the larvae suggests that they are equipped with a well-developed visual system, while the functional significance of the system still remains a mystery. It might be important for feeding, orientation and diurnal vertical migration of the larva

ISSN:0006-8977    

DOI:10.1159/000113227

出版商:S. Karger AG    

年代:1996

数据来源: Karger

摘要:

Adult, female praying mantises, Sphodromantis lineola (Burmeister), were presented with mechanically driven or computer generated stimuli in a series of seven experiments in order to test several hypotheses regarding visual prey recognition. When presented with a series of square black and white computer generated stimuli against a white background, mantises performed the highest rates of predatory behavior in response to those stimuli with a greater proportion of black versus white pixels (i.e., those that produced larger luminance decrements). Higher response rates to computer generated stimuli that produced larger luminance decrements were also seen when the stimuli were irregularly shaped or consisted of two small synchronized stimuli. Mantises responded characteristically to mechanically driven stimuli that were camouflaged to match the background against which they moved, preferring small (vs. large) squares and rectangles that were elongated parallel (vs. perpendicular) to their direction of movement. Finally, response rate to a small, preferred, mechanically presented or computer generated stimulus was suppressed by a concurrent large-field stimulus in inverse proportion to the distance between the two stimuli. This phenomenon is characteristic of systems that include phasic lateral inhibitory circuits. All of these results are consistent with the existence of a movement detector visual sub-system, as found in other orthopteromorph insects such as acridid grasshoppers and cockroaches.

ISSN:0006-8977    

DOI:10.1159/000113228

出版商:S. Karger AG    

年代:1996

数据来源: Karger