Biomedical subjects

Ursula Dicke

Publications and source records attributed to Ursula Dicke.

6 recordsLinked to original sources

PubMed2005

Distribution of GABA, glycine, and glutamate in neurons of the medulla oblongata and their projections to the midbrain tectum in plethodontid salamanders.

In the medulla oblongata of plethodontid salamanders, GABA-, glycine-, and glutamate-like immunoreactivity (ir) of neurons was studied. Combined tracing and immunohistochemical experiments were performed to analyze the transmitter content of medullary nuclei with reciprocal connections with the tectum mesencephali. The distribution of transmitters differed significantly between rostral and caudal medulla; dual or triple localization of transmitters was present in somata throughout the rostrocaudal extent of the medulla. Regarding the rostral medulla, the largest number of GABA- and gly-ir neurons was found in the medial zone. Neurons of the nucleus reticularis medius (NRM) retrogradely labeled by tracer application into the tectum revealed predominantly gly-ir, often colocalized with glu-ir. The NRM appears to be homologous to the mammalian gigantocellular reticular nucleus, and its glycinergic projection is most likely part of a negative feedback loop between medulla and tectum. Neurons of the dorsal and vestibular nucleus projecting to the tectum were glu-ir and often revealed additional GABA- and/or gly-ir in the vestibular nucleus. Regarding the caudal medulla, the highest density of GABA- and gly-ir cells was found in the lateral zone. Differences in the neurochemistry of the rostral versus caudal medulla appear to result from the transmitter content of projection nuclei in the rostral medulla and support the idea that the rostral medulla is involved in tecto-reticular interaction. Our results likewise underline the role of the NRM in visual object selection and orientation as suggested by behavioral studies and recordings from tectal neurons.

Animals↗

PubMed2005

Evolution of the brain and intelligence.

Intelligence has evolved many times independently among vertebrates. Primates, elephants and cetaceans are assumed to be more intelligent than 'lower' mammals, the great apes and humans more than monkeys, and humans more than the great apes. Brain properties assumed to be relevant for intelligence are the (absolute or relative) size of the brain, cortex, prefrontal cortex and degree of encephalization. However, factors that correlate better with intelligence are the number of cortical neurons and conduction velocity, as the basis for information-processing capacity. Humans have more cortical neurons than other mammals, although only marginally more than whales and elephants. The outstanding intelligence of humans appears to result from a combination and enhancement of properties found in non-human primates, such as theory of mind, imitation and language, rather than from 'unique' properties.

Anatomy, Comparative↗

PubMed2004

Dorsal striatopallidal system in anurans.

The dorsal striatopallidal system of tetrapods consists of the dorsal striatum (caudate-putamen in mammals) and the dorsal pallidum. Although the existence of striatal and pallidal structures has been well documented in anuran amphibians, the exact boundaries of these structures have so far been a matter of debate. To delineate precisely the dorsal striatopallidal system of anurans, we used quantitative analysis of leucine-enkephalin immunohistochemistry (in Bombina orientalis, Discoglossus pictus, Xenopus laevis, and Hyla versicolor), retrograde neurobiotin tracing studies (injections in the central and ventromedial thalamic nuclei in H. versicolor), and double-labeling tracing studies (injections in the lateral forebrain bundle and the caudal striatum in B. orientalis). Immunohistochemistry revealed that enkephalin-positive neurons are located mainly in the rostral and intermediate striatum. Neurobiotin tracing studies demonstrated that neurons projecting to the central and ventromedial thalamic nuclei are found in the intermediate and caudal striatum. Double-labeling studies revealed that the population of neurons in the rostral and intermediate striatum innervating the caudal striatum is separated from neurons projecting into the lateral forebrain bundle. Neurons that project to both the caudal striatum and the lateral forebrain bundle are found only in the dorsal part of the intermediate striatum. Taken together, our results suggest that the rostral striatum of anurans is homologous to the striatum proper of mammals, whereas the caudal striatum is comparable to the dorsal pallidum. The intermediate striatum represents a transition area between the two structures.

Animals↗

PubMed2004

Activation patterns of the tongue-projector muscle during feeding in the imperial cave salamander Hydromantes imperialis.

Salamanders of the genus Hydromantes project their tongues the greatest distance of any amphibian to capture prey, up to 80% of body length or approximately 6 cm in an adult individual. During tongue projection on distant prey, the tongue is shot ballistically and the tongue skeleton leaves the body of the salamander entirely. We investigated an aspect of the motor control of this remarkable behavior by examining electromyographic patterns within different regions of the tongue-projector muscle, the subarcualis rectus (SAR). SAR activation is strongly modulated, and features of this modulation can be predicted by tongue-projection distance (i.e. prey distance). The strap-like buccal portion of the SAR is always activated first and for the longest duration, compared to any other region. It is in a position to transmit force generated by the posterior SAR to the floor of the mouth, where it originates. The posterior SAR encompasses and applies force to the epibranchial of the tongue skeleton, and its activation pattern gradually changes from a posterior-to-anterior wave of activation onset during short-distance projection to an all-at-once pattern during the most extreme long-distance (ballistic) projection. The duration of activity and EMG area of each recorded region of the SAR increase with increasing prey distance, showing greater muscle recruitment during long-distance projection. No effect of prey-capture success was observed in the EMG patterns, indicating that SAR activation is controlled in a feed-forward manner.

Analysis of Variance↗

PubMed2003

Morphology, axonal projection pattern, and responses to optic nerve stimulation of thalamic neurons in the fire-bellied toad Bombina orientalis.

Intracellular recording and biocytin labeling were carried out in the fire-bellied toad Bombina orientalis to study the morphology and axonal projections of thalamic (TH) neurons and their responses to electrical optic nerve stimulation. Labeled neurons (n = 142) were divided into the following groups: TH1 neurons projecting to the dorsal striatum; TH2 neurons projecting to the amygdala, nucleus accumbens, and septal nuclei; TH3 neurons projecting to the medial or dorsal pallium; TH4 neurons with projections ascending to the dorsal striatum or ventral striatum/amygdala and descending to the optic tectum, tegmentum, and rostral medulla oblongata; TH5 neurons with projections to the tegmentum, rostral medulla oblongata, prectectum, or tectum; and TH6 neurons projecting to the hypothalamus. TH1 neurons are found in the central, TH2 neurons in the anterior and central, TH3 neurons in the anterior dorsal nucleus, and TH4 and TH5 neurons in the posterior dorsal or ventral nucleus. Neurons with descending projections arborize in restricted parts of retinal afferents; neurons with ascending projections do not substantially arborize within retinal afferents. At electrical optic nerve stimulation, neurons in the ventral thalamus respond with excitation at latencies of 10.8 msec; one-third of them follow repetitive stimulation and possibly are monosynaptically driven. Neurons in the dorsal thalamus respond mostly with inhibition at latencies of 42.3 msec and are polysynaptically driven. This corroborates the view that neurons in the dorsal thalamus projecting to the telencephalon receive no substantial direct retinal input and that the thalamopallial pathway of amphibians is not homologous to the mammalian retinogeniculocortical pathway.

Animals↗

PubMed2002

The effect of stimulus features on the visual orienting behaviour of the salamander Plethodon jordani.

The effects of the visual features of prey-like objects on the orienting behaviour of the salamander Plethodon jordani were studied. Two stimuli (cricket dummies, rectangles), moving in opposite directions, were presented simultaneously on a computer screen. They differed in size, contrast, velocity and movement pattern of the entire body or the body appendages. Size and velocity appeared to be the dominant features; shape was of lesser importance. Contrast and movement pattern were of intermediate importance and local motion of little importance. This rank order was the same when the probability of a response to the different stimuli was estimated by means of the maximum-likelihood method. Cluster analysis revealed that in all animals stimuli could be grouped into five clusters. Among individuals, the rank order of stimuli was similar for high- and low-ranking stimuli and varied for those of intermediate rank; stimuli could be grouped into 3-5 clusters. Our findings favour the view that, in amphibians, prey recognition is guided by a number of visual features acting either alone or in combination and depending on internal motivational or attentional states and individual experience.

Animals↗