Biomedical subjects

Michael H Hofmann

Publications and source records attributed to Michael H Hofmann.

10 recordsLinked to original sources

PubMed2006

Responses to dipole stimuli of anterior lateral line nerve fibres in goldfish, Carassius auratus, under still and running water conditions.

We investigated how fibres in the anterior lateral line nerve of goldfish, Carassius auratus, respond to sinusoidal water motions in a background of still or running water. Two types of fibres were distinguished: type I fibres, which most likely innervate superficial neuromasts, were stimulated by running water (10 cm s(-1)) while type II fibres, which most likely innervate canal neuromasts, were not stimulated by running water. The responses of type I fibres to sinusoidal water motions were masked in running water whereas responses of type II fibres were not masked. These findings are in agreement with previous data obtained from the posterior lateral line nerve of goldfish. Furthermore, we demonstrate here that for type I fibres the degree of response masking increased with increasing flow velocity. Finally, the ratio between responses that were masked in running water (type I) and those that were not masked (type II) increases with increasing flow velocity. Flow fluctuations that were generated by a cylinder in front of the fish did not affect ongoing activity in the flow, nor the dipole-evoked responses. The findings are discussed with respect to particle image velocimetry data of the water motions generated in the experiments.

Animals↗

PubMed2005

Temporal analysis of moving DC electric fields in aquatic media.

Many aquatic vertebrates can sense the weak electric fields generated by other animals and may also sense geoelectric or electromagnetic phenomena for use in orientation. All these sources generate stationary (dc) fields. In addition, fields from animals are modulated by respiration and other body movements. Since electroreceptors are insensitive to a pure dc field, it has been suggested that the ac modulation carries most of the relevant information for electrosensory animals. However, in a natural situation pure dc fields are rare since any relative movement between source and receiver will transform a dc field into a time varying signal. In this paper, we will describe the properties of such signals and how they are filtered at the first stage of electrosensory information processing in the brain. We will show that the signal perceived by an animal traversing a dc electric field contains all the information necessary to reconstruct the distance to the source and that the signal conditioning algorithms are perfectly adapted to preserve such information.

Algorithms↗

PubMed2005

Response properties of electrosensory afferent fibers and secondary brain stem neurons in the paddlefish.

The passive electrosense is used by many aquatic animals to detect weak electric fields from other animals or from geoelectric sources. In contrast to the active electrosense, ;passive' means that there are no electric organs, and only external fields are measured. Electroreceptors are distributed in the skin, but are different from other skin senses because they can detect and localize sources a considerable distance away. Distant sources, however, stimulate a large number of receptors at the same time and central circuits have to compute the exact location of the source from this distributed information. In order to gain insights into the algorithms involved, we compared the response properties of units in the dorsal octavolateral nucleus (DON) with primary afferent fibers in the paddlefish. The following parameters were tested: spontaneous activity, sensitivity, frequency tuning, receptive field size, movement sensitivity, and topography within the DON. Although there are some differences in spontaneous activity and receptive field size, there are no major differences between primary afferents and DON units that could reveal any substantial amount of spatial information processing. In particular the lack of any topographic order within the DON renders a lateral interaction between neighboring receptive fields unlikely.

Afferent Pathways↗

PubMed2002

Central organization of the electrosensory system in the paddlefish (Polyodon spathula).

The central connections of the electrosensory system were studied in the paddlefish Polyodon spathula by injecting biotinylated dextran amines into the dorsal octavolateral nucleus (DON), the cerebellum, and the mesencephalic tectum. The sole target of primary electrosensory fibers is the ipsilateral dorsal octavolateral nucleus. The principal neurons ascending from this nucleus project to the torus semicircularis, the lateral mesencephalic nucleus, and the mesencephalic tectum. The mesencephalic tectum projects back to the nucleus preeminentialis, which, in turn, projects to the cerebellar auricles and to the DON. The auricles are the main source of parallel fibers in the cerebellar crest ventral to the DON. The DON also receives input from the contralateral DON. These descending feedback loops are very similar to those of other electrosensory fishes. However, the paddlefish is unique in having three mesencephalic targets of electrosensory information. It is the only bony fish known to have extensive projections directly to the mesencephalic tectum and to a lateral mesencephalic nucleus in addition to the torus semicircularis.

Afferent Pathways↗

PubMed2002

A direct projection from the cerebellum to the telencephalon in the goldfish, Carassius auratus.

Recent studies showed that the cerebellum is involved in cognitive functions previously thought to be located in the telencephalon only. Various indirect connections between telencephalon and cerebellum are long known and may be the basis for the interaction of these two brain areas. By means of biotinylated dextran amine injections into the telencephalon and cerebellum in the goldfish, Carassius auratus, we found a direct projection from the valvula cerebelli to the telencephalon. Together with other studies in fish, birds, and mammals, these data suggest that direct connections between cerebellum and telencephalon are more common than previously thought and may contribute to the integration of telencephalic and cerebellar functions.

Animals↗

PubMed2002

VIEWER: a program for visualising, recording, and analysing animal behaviour.

In order to determine the influence of environmental interventions, medical substances, drugs, or diseases on an animal, it is a common to observe the behaviour of the animal in the open field or in other environments. Changes in animal behaviour can be the first indicators for an influence of a substance or an intervention on the organism and certain kinds of behavioural changes can permit speculations about the underlying physiological mechanisms. Behavioural properties which are of interest in this respect are movement parameters such as velocity or direction, activity patterns, spatial distribution and occurrence of several types of standard behaviours of an animal. Observation of simple behaviours such as determining the average activity level can help to detect general changes of the internal state of an animal, while changes in complex behaviours may point to specific influences of a substance or an intervention. Our system 'VIEWER' uses a microcomputer (IBM-compatible PC running WINDOWS 95, WINDOWS 98, WINDOWS NT, or WINDOWS 2000), a low budget framegrabber card (e.g. WinTV, Hauppauge) and a standard black-and-white video camera (if necessary with infrared sensitivity). The software records the position of the animal online with a sample rate of up to 25 frames/s. After identification of the animal in the arena, animal location and orientation with respect to time is determined. In addition, movement velocity and direction, general activity level, and several other behavioural parameters which can include complex behavioural patterns are processed online. Data are presented as graphics and/or tables. Results may also be exported into those programs that are capable of importing graphics (wmf or bmp format) or ASCII-files. VIEWER offers an inexpensive, fast and easy way for analysing simple and complex behaviours of many species of animals in a variety of behavioural situations.

Animals↗

PubMed2002

Response properties of diencephalic neurons to visual, acoustic and hydrodynamic stimulation in the goldfish, Carassius auratus.

We studied the responses to sensory stimulation of three diencephalic areas, the central posterior nucleus of the dorsal thalamus, the anterior tuberal nucleus of the hypothalamus, and the preglomerular complex. Units sensitive to acoustic (500 Hz tone burst), hydrodynamic (25 Hz dipole stimulus) and visual (640 nm light flash) stimuli were found in both the central posterior and anterior tuberal nucleus. In contrast, unit responses or large robust evoked potentials confined to the preglomerular complex were not found. In the central posterior nucleus, most units were unimodal. Many units responded exclusively to visual stimulation and exhibited a variety of temporal response patterns to light stimuli. In the anterior tuberal nucleus of the hypothalamus, most units responded to more than one modality and showed a stronger response decrement to stimulus repetitions than units in the central posterior nucleus. Our data suggest that units in the central posterior nucleus are primarily involved in the unimodal processing of sensory information whereas units in the anterior tuberal nucleus of the hypothalamus may be involved in multisensory integration.

Journal Article↗

PubMedDate not supplied

Effects of dopaminergic drugs and telencephalic ablation on eye movements in the goldfish, Carassius auratus.

The effect of the dopamine agonist apomorphine and the antagonist haloperidol on eye movements was tested in normal and telencephalon ablated goldfish. Reflex eye movements evoked by a rotating striped cylinder were not affected, which suggests that basic sensory and motor functions were not influenced by neither dopaminergic drugs nor the telencephalon. However, profound changes were observed in spontaneous eye movements. Particularly, the effect of apomorphine was similar to changes in eye movements observed in mammals after suppression of dopaminergic functions either by means of drugs or in patients suffering from Parkinson's disease or schizophrenia.

Animals↗

PubMedDate not supplied

Responses of diencephalic neurons to sensory stimulation in the goldfish, Carassius auratus.

We studied the responses to sensory stimulation in two diencephalic areas, the central posterior nucleus of the dorsal thalamus (CP) and the anterior tuberal nucleus of the hypothalamus (TA). In both the CP and the TA, units sensitive to acoustic (500-Hz sound), hydrodynamic (25-Hz dipole stimulus), and visual (640-nm light flash) stimuli were found. In the CP, most units were unimodal and responded exclusively to visual stimulation. In contrast, in the TA, most units responded to more than one modality. The data suggest that the CP is primarily involved in the unimodal processing of sensory information, whereas the TA may be involved in multisensory integration.

Acoustic Stimulation↗

PubMedDate not supplied

The electric sense of the paddlefish: a passive system for the detection and capture of zooplankton prey.

Behavioral and electrophysiological experiments have shown that the elongated paddlefish rostrum, with its extensive population of ampullae of Lorenzini, constitutes a passive electrosensory antenna of great sensitivity and spatial resolution. As demonstrated in juvenile paddlefish, the passive electrosense serves a novel function in feeding serving as the primary, if not exclusive sensory modality for the detection and capture of zooplanktonic prey. Ampullary receptors are sensitive to the weak electrical fields of plankton from distances up to 9 cm, and juvenile paddlefish capture plankton individually with great swimming dexterity in the absence of vision or other stimulus signals. Paddlefish also detect and avoid metal obstacles, the electrical signatures of which are a potential hindrance to their feeding and reproductive migrations. The ampullary receptors, their peripheral innervation and central targets in the dorsal octavolateral nucleus, are described. We also describe the ascending and descending neuronal circuitry of the electrosensory system in the brain based on tracer studies using dextran amines.

Action Potentials↗