Biomedical subjects

Horst Bleckmann

Publications and source records attributed to Horst Bleckmann.

14 recordsLinked to original sources

PubMed2006

Neural responses of goldfish lateral line afferents to vortex motions.

The lateral line system of fish is sensitive to weak water motions. We recorded from posterior lateral line nerve afferents while stimulating goldfish, Carassius auratus, with unidirectional water flow and with a vortex ring. Posterior lateral line afferents of goldfish were either flow sensitive or flow insensitive. Both types of afferents responded to a vortex ring that passed the fish laterally with one to three reproducible patterns of neural activity, followed by activity patterns that were less reproducible. Using particle image velocimetry, we visualized and quantified the water motions in the vertical plane next to the surface of the fish while recording from lateral line afferents. Early response components correlated with the direction of water motions that occurred at the position of the neuromast recorded from. By contrast, neural activity that occurred after the vortex had passed the fish barely predicted the direction of water motions. These results are in agreement with the known directional sensitivity of hair cells and indicate that fish might be able to extract sensory information from complex stimuli like vortices by comparing the activity of a whole array of neuromasts. The stimulus used in this study is novel to lateral line research and resembles some of the hydrodynamic stimuli that fish might encounter in their natural environments. We expect that by combining naturalistic hydrodynamic stimuli and central nervous recordings, we will learn if and how hydrodynamic feature detection is accomplished by the lateral line system.

Action Potentials↗

PubMed2005

Sea snakes (Lapemis curtus) are sensitive to low-amplitude water motions.

The sea snake Lapemis curtus is a piscivorous predator that hunts at dusk. Like land snakes, sea snakes have scale sensillae that may be mechanoreceptive, i.e. that may be useful for the detection of water motions produced by prey fish. In addition, inner ear hair cells of sea snakes may also be involved in the detection of hydrodynamic stimuli. We generated water motions and pressure fluctuations with a vibrating sphere. In the test range 50-200 Hz evoked potentials were recorded from the midbrain of L. curtus in response to vibrating sphere stimuli. In terms of water displacement the lowest threshold amplitudes were in the frequency range 100-150 Hz. In this range peak-to-peak water displacement amplitudes of 1.8 microm (at 100 Hz) and 2.0 microm (150 Hz) generated a neural response in the most sensitive animal. Although this low sensitivity may be sufficient for the detection of fish-generated water motions, it makes it unlikely that L. curtus has a special hydrodynamic sense.

Animals↗

PubMed2005

Spatial memory and orientation strategies in the elasmobranch Potamotrygon motoro.

We investigated whether juvenile freshwater stingrays (Potamotrygon motoro) can solve spatial tasks by constructing a cognitive map of their environment. Two experimental conditions were run: allocentric and ego-allocentric. Rays were trained to locate food within a four-arm maze placed in a room with visual spatial cues. The feeding location (goal) within the maze (room) remained constant while the starting position varied for the allocentrically but not for the ego-allocentrically trained group. After training, all rays solved the experimental tasks; however, different orientation strategies were used within and between groups. Allocentrically trained rays reached the goal via novel routes starting from unfamiliar locations, while ego-allocentrically trained rays primarily solved the task on the basis of an egocentric turn response. Our data suggest that P. motoro orients by constructing a visual cognitive map of its environment, but also uses egocentric and/or other orientation strategies alone or in combination for spatial orientation, a choice which may be governed by the complexity of the problem. We conclude that spatial memory functions are a general feature of the vertebrate brain.

Animals↗

PubMed2004

Coding of lateral line stimuli in the goldfish midbrain in still and running water.

We investigated in goldfish, Carassius auratus, how running water affects the responses of toral lateral line units to a stationary vibrating sphere or to a non-vibrating sphere that moves along the side of the fish. Experiments were conducted in the presence of running water (hydrodynamic noise) to further explore the sensory capabilities of the lateral line with special focus on the morphological sub-modalities. Previous recordings from lateral line nerve fibres in various fish species and the first nucleus of the ascending lateral line pathway in goldfish revealed flow-sensitive and flow-insensitive units. These physiological differences represent, at least in part, the differences in morphology of the lateral line, superficial and canal neuromasts. Following up on these findings we recorded flow-sensitive and flow-insensitive units in the Torus semicircularis of goldfish. In still water, both types of units responded to a vibrating or moving sphere. In running water, neural responses were weaker when the sphere was moved with the flow but were comparable or slightly stronger when the sphere was moved against the flow. In running water, responses of flow-sensitive fibres to the vibrating sphere were masked. In contrast, the responses of units insensitive to water flow were not masked. Our data confirm previous findings but also indicate differences when compared to previous reports. We discuss these differences with respect to lateral line morphology, sub-modalities and convergence of different channels of information at higher brain stations.

Journal Article↗

PubMed2004

The hydrodynamic trails of Lepomis gibbosus (Centrarchidae), Colomesus psittacus (Tetraodontidae) and Thysochromis ansorgii (Cichlidae) investigated with scanning particle image velocimetry.

The hydrodynamic trails of fish belonging to the families Centrarchidae, Tetraodontidae and Cichlidae were investigated. Water movements were measured in six horizontal planes, spaced 10-12 mm apart, for up to 5 min after the passage of a fish, using a computer controlled array of modulated laser diodes. We measured continuously and non-continuously swimming fish. Water velocities decayed rapidly in the leading seconds after the passage of a fish, but could still be measured for a period considerably longer than that. In still water (median water velocity <0.5 mm s(-1)), the hydrodynamic trails of Lepomis gibbosus lasted for more than 5 min. The trails of Colomesus psittacus and Thysochromis ansorgii could be detected for more than 30 s and more than 3 min, respectively. The water disturbance left behind by these fish was sufficient to be sensed by a piscivorous predator at a distance where vision or hearing frequently fail. Acoustic stimuli estimated from a dipole model in a distance that would be covered by the tested fish in 1 min (4-25 m) were 1.5 x 10(-7) to 3.1 x 10(-10) m s(-2), while the hearing threshold of a perch is three orders of magnitude above that. By contrast, the fish wakes after 1 min (except for one Colomesus wake) contained water velocities between 0.95 and 2.05 mm s(-1), which are within the detection range of hydrodynamic sensory systems. The three species differed with respect to water velocities, the spatial extent of the fish-generated water disturbances and the structure of the wake.

Animals↗

PubMed2003

Effects of running water on lateral line responses to moving objects.

We investigated in goldfish, Carassius auratus, and trout, Oncorhynchus mykiss, how running water affects the responses of afferent fibers in the posterior lateral line nerve and of lateral line units in the brainstem medial octavolateralis nucleus to an object that is moved from anterior to posterior or opposite along the side of the fish. In still water, nerve fibers in both species responded to the moving object with alternating periods of increased and decreased firing rate. Most fibers in goldfish but none in trout discharged bursts of spikes in response to the object's wake. Responses of brainstem units were more variable and less distinct than nerve fiber responses. Bursting activity in response to the object's wake was found in only one brainstem unit. In running water, responses of goldfish nerve fibers were weaker than in still water. This effect was independent of object motion direction. Responses of trout fibers were weaker when the object was moved with the flow but were slightly stronger when the object was moved against the flow. In general, running water affected the responses of goldfish nerve fibers more strongly than the responses of trout fibers. Compared to still water, brainstem units in both species responded more weakly when the object was moved with the flow. When the object was moved against the flow, brainstem responses were on average comparable to those in still water. Measurements of changes in pressure and water velocity caused by the moving object indicate that the observed effects can largely be explained by peripheral hydrodynamic effects. However, physiological differences between goldfish and trout units indicate that the lateral line systems in these two species are adapted to different hydrodynamic conditions.

Animals↗

PubMed2003

A hydrodynamic topographic map in the midbrain of goldfish Carassius auratus.

Sensory systems often consist of several parallel pathways. Within each pathway, sensory information may be processed in topographically arranged maps or in maps derived by neuronal computation. Parallel pathways have so far not been described in the central lateral line system of teleost fish at levels higher than the medulla, and evidence for midbrain lateral line maps in fish is still weak. We found two classes of units with different response patterns in the central lateral line nucleus in the torus semicircularis of the goldfish Carassius auratus. Units of one class responded to a passing sphere and to the wake caused by that sphere with excitation. Units of the second class also responded to the moving sphere. However, these units did not respond to the wake behind the sphere. Hydrodynamic information received by class two units was topographically organized in the torus semicircularis of goldfish in that anterior body areas projected to rostral midbrain and posterior body areas to caudal midbrain. Units that responded only to the passing sphere were on average located more ventrally in the lateral TS than the units that responded exclusively to a vibrating sphere.

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

A new type of insect infrared organ of low thermal mass.

The Australian beetle Acanthocnemus nigricans is attracted by forest fires and has a pair of complex infrared (IR) receptor organs on the first thoracic segment. Each organ consists of a tiny sensory disc (diameter 120-130 microm) which serves as an absorbing structure for IR radiation. The disc is arranged above an air-filled cavity which is located just anteriorly to the coxae of the prothoracic legs. Inside the disc, about 30 multipolar thermoreceptors (warmth receptors) are tightly attached to the cuticle which is directed to the outside. The many dendrites of each multipolar neuron are tightly wrapped around the soma and contain a large number of mitochondria. Absorption of IR radiation by the disc causes an increase in temperature which is measured by the warmth receptors. Therefore, the IR receptors of A. nigricans can be classified as microbolometers with reduced thermal mass and in principle can be compared to the IR organs of pit vipers.

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↗

PubMed2002

Brainstem lateral line responses to sinusoidal wave stimuli in still and running water.

The fish lateral line consists of superficial and canal neuromasts. In still water, afferent fibers from both types of neuromast respond equally well to a sinusoidally vibrating sphere. In running water, responses to a vibrating sphere of fibers innervating superficial neuromasts are masked. In contrast, responses of fibers innervating canal neuromasts are barely altered. It is not known whether this functional subdivision of the peripheral lateral line is maintained in the brain. We studied the effect of running water on the responses to a 50 Hz vibrating sphere of single units in the medial octavolateralis nucleus (MON) in goldfish Carassius auratus. The MON is the first site of central processing of lateral line information. Three types of units were distinguished. Type I units (N=27) were flow-sensitive; their ongoing discharge rates either increased or decreased in running water, and as a consequence, responses of these units to the vibrating sphere were masked in running water. Type II units (N=7) were not flow-sensitive; their ongoing discharge rates were comparable in still and running water, so their responses to the vibrating sphere were not masked in running water. Type III units (N=7) were also not flow-sensitive, but their responses to the vibrating sphere were nevertheless masked in running water. Although interactions between the superficial and canal neuromast system cannot be ruled out, our data indicate that the functional subdivision of the lateral line periphery is maintained to a large degree at the level of the medial octavolateralis nucleus.

Animals↗

PubMedDate not supplied

3-D-orientation with the octavolateralis system.

Fish detect and localize a sound source with inner ear receptors and with the mechanosensory lateral line. The inner ear of fish is sensitive to the water displacements caused by sound waves through a direct, inertial response by hair cell epithelia of the ear. Hearing specialists, such as goldfish and herring, have accessory peripheral structures that provide additional sensitivity to the pressure component of a sound wave. While the inner ear of fish responds to the whole body motions caused by sound waves and--in case of hearing specialists--to sound pressure, the lateral line is only sensitive to water motions relative to the surface of the fish and to local pressure gradients. Using lateral line and/or acoustic input, some fish can determine the direction and the distance to a sound source. Most likely they do so by exploiting some of the mechanisms described in this paper. Piscivorous fish may use lateral line input to detect the wakes caused by swimming fish. Even in the absence of light catfish, for instance, can follow a 10 s old, three-dimensional wake left by a prey fish over distances up to 55 prey-body length.

Acoustic Stimulation↗

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↗