Biomedical subjects

J Juranek

Publications and source records attributed to J Juranek.

5 recordsLinked to original sources

PubMed2000

Electrically evoked fictive swimming in the low-spinal immobilized turtle.

Fictive swimming was elicited in low-spinal immobilized turtles by electrically stimulating the contralateral dorsolateral funiculus (cDLF) at the level of the third postcervical segment (D(3)). Fictive hindlimb motor output was recorded as electroneurograms (ENGs) from up to five peripheral nerves on the right side, including three knee extensors (KE; iliotibialis [IT]-KE, ambiens [AM]-KE, and femorotibialis [FT]-KE), a hip flexor (HF), and a hip extensor (HE). Quantitative analyses of burst amplitude, duty cycle and phase were used to demonstrate the close similarity of these cDLF-evoked fictive motor patterns with previous myographic recordings obtained from the corresponding hindlimb muscles during actual swimming. Fictive rostral scratching was elicited in the same animals by cutaneous stimulation of the shell bridge, anterior to the hindlimb. Fictive swim and rostral scratch motor patterns displayed similar phasing in hip and knee motor pools but differed in the relative amplitudes and durations of ENG bursts. Both motor patterns exhibited alternating HF and HE discharge, with monoarticular knee extensor (FT-KE) discharge during the late HF phase. The two motor patterns differed principally in the relative amplitudes and durations of HF and HE bursts. Swim cycles were dominated by large-amplitude, long-duration HE bursts, whereas rostral scratch cycles were dominated by large-amplitude, long-duration HF discharge. Small but significant differences were also observed during the two behaviors in the onset phase of biarticular knee extensor bursts (IT-KE and AM-KE) within each hip cycle. Finally, interactions between swim and scratch motor networks were investigated. Brief activation of the rostral scratch during an ongoing fictive swim episode could insert one or more scratch cycles into the swim motor pattern and permanently reset the burst rhythm. Similarly, brief swim stimulation could interrupt and reset an ongoing fictive rostral scratch. This shows that there are strong central interactions between swim and scratch neural networks and suggests that they may share key neural elements.

Animals↗

PubMed1998

Segregation of behavior-specific synaptic inputs to a vertebrate neuronal oscillator.

Although essential for understanding the mechanisms underlying sensorimotor integration and motor control of behaviors, very little is known about the degree to which different behaviors share neural elements of the sensorimotor command chain by which they are controlled. Here, we provide, to our knowledge, the first direct physiological evidence that various modulatory premotor inputs to a vertebrate central pattern generator, the pacemaker nucleus in gymnotiform electric fish, carrying distinctly different behavioral information, can remain segregated from their various sites of origin in the diencephalon to the synaptic termination sites on different target neurons in the medullary pacemaker nucleus. During pharmacological activation of each of the premotor inputs originating from the three prepacemaker nuclei so far identified, we determined in vivo the changes in input resistance in the neuronal elements of the pacemaker nucleus, i.e., relay cells and pacemaker cells. We found that each input yields significantly different effects on these cells; the inputs from the two diencephalic prepacemaker nuclei, PPnC and PPnG, which resulted in increased oscillator activity, caused significantly lower input resistances in relay and pacemaker cells, respectively, exhibiting drastically different time courses. The input from the sublemniscal prepacemaker nucleus, which resulted in reduced oscillator activity, however, caused a significant increase in input resistance only in relay cells. Considering that the sensory pathways processing stimuli yielding these behaviors are separated as well, this study indicates that sensorimotor control of different behaviors can occur in strictly segregated channels from the sensory input of the brain all through to the synaptic input level of the final premotor command nucleus.

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PubMed1997

A sensory brain map for each behavior?

Multiple brain maps are commonly found in virtually every vertebrate sensory system. Although their functional significance is generally relatively little understood, they seem to specialize in processing distinct sensory parameters. Nevertheless, to yield the stimulus features that ultimately elicit the adaptive behavior, it appears that information streams have to be combined across maps. Results from current lesion experiments in the electrosensory system, however, suggest an alternative possibility. Inactivations of different maps of the first-order electrosensory nucleus in electric fish, the electrosensory lateral line lobe, resulted in markedly different behavioral deficits. The centromedial map is both necessary and sufficient for a particular electrolocation behavior, the jamming avoidance response, whereas it does not affect the communicative response to external electric signals. Conversely, the lateral map does not affect the jamming avoidance response but is necessary and sufficient to evoke communication behavior. Because the premotor pathways controlling the two behaviors in these fish appear to be separated as well, this system illustrates that sensory-motor control of different behaviors can occur in strictly segregated channels from the sensory input of the brain all through to its motor output. This might reflect an early evolutionary stage where multiplication of brain maps can satisfy the demand on processing a wider range of sensory signals ensuing from an enlarged behavioral repertoire, and bridging across maps is not yet required.

Animals↗

PubMed1997

A method to biotinylate and histochemically visualize ibotenic acid for pharmacological inactivation studies.

Ibotenic acid (IA) and kainic acid (KA) are commonly used tools to selectively inactivate neuronal perikarya, eventually leading to their degeneration, without affecting fibers of passage. Reversible inactivations and experimental paradigms that do not allow for long survival times, however, do not permit for histological verification of the site and extent of the lesion by identifying the area showing gliosis. We describe here a method in which IA and KA were conjugated with biotin and thus could be easily visualized histochemically. We pressure-injected biotinylated IA and KA into various hindbrain areas of the electrosensory system in electric fish while monitoring neuronal responses at the injection site and assessing effects on the behavior. Whereas the effects of biotinylated IA did not differ from those of the unbiotinylated form, biotinylated KA lost its physiological activity. Thus, only biotinylated IA could be used successfully. The size of the gliosis seen after a survival time of seven days was similar to the extent of biotin label observed after injection of comparable volumes of biotinylated IA. Moreover, this method resulted in labeling of individual neurons presumably affected by IA and yielded information about their projection patterns which was comparable to labeling seen after intracellular injections of neurobiotin or biocytin.

Animals↗

PubMed1994

Males located caudally in the uterus affect sexual behavior of male rats in adulthood.

It has been suggested that the sexual differentiation of female rats is affected by androgens from male fetuses in the uterine horn (intra-uterine position phenomenon). Effects of adjacent males, as well as of males located caudally in the uterus have been reported. The present study investigated whether male rats, like females, are affected by the presence of either caudal or adjacent male littermates. When tested in adulthood for sexual behavior, males that had male fetuses located caudally in the uterine horn showed shorter latencies to the first mount or intromission and shorter latencies to ejaculation, and exhibited more mounts and intromissions per minute than males that lacked caudal male siblings in the uterus. The presence of adjacent males did not significantly affect the parameters studied in this experiment.

Animals↗