Search PubMed⌕ Search

Biomedical subjects

B L Roberts

Publications and source records attributed to B L Roberts.

At least 91 records · Page 5Linked to original sources
PubMed1986

The topographical organization of the vagal motor column in the elasmobranch fish, Scyliorhinus canicula L.

The location within the brainstem of vagal preganglionic motoneurons has been determined in the dogfish Scyliorhinus canicula L. by means of the retrograde transport of horseradish peroxidase and cobalt applied to the vagus nerve and its component branches. Labelled vagal motoneurones were located in the ipsilateral caudal rhombencephalon from 2.1 mm caudal to 2.73 mm rostral to obex. The motoneurons of the vagal motor column are arranged as four distinct groups. Caudal to obex the column contains dorsomedial and ventromedial divisions, whilst rostrally it consists of a single rostromedial division and a short lateral division. The cells in the ventromedial division are approximately twice the size (mean area 1,094 microns 2) of the other vagal neurons. The dorsomedial division contains neurons that supply the heart and viscera; the ventromedial division supplies the viscera. The heart is also innervated by the neurons of the lateral division and the visceral nerve also receives axons from the rostromedial division. All neurons supplying axons to the gill arches are located in the rostromedial division. There is a sequential topographical representation of the vagus nerve in the vagal motor column. Neurons supplying the gastrointestinal tract are located caudally; those supplying the cardiac nerves lie in the midportion of the column, and the proximal supply to the gills is given by the most rostral neurons. There is some overlap between the pools of neurons supplying adjacent branches of the vagus.

Animals↗
PubMed1986

Nuclear location signals in polyoma virus large-T.

We have found two mutually independent sequence elements that contribute to the nuclear location of polyoma virus large-T. The first sequence (pro lys lys282 ala arg glu asp) resembles the SV40 large-T nuclear signal (pro lys lys128 lys arg lys val) and occurs at a corresponding position within polyoma large-T. The second sequence (val ser arg lys192 arg pro arg) may be structurally related to the SV40 signal, although it has little sequence homology and falls in a region of the protein that has no counterpart in SV40 large-T. The data suggest that nuclear location signals with characteristics similar to the SV40 large-T prototype may be a more general feature of nuclear proteins, and that several such signals in a given protein can exert cooperative effects.

Amino Acid Sequence↗
PubMed1986

Central organization of the efferent supply to the labyrinthine and lateral line receptors of the dogfish.

Neurons that provide the efferent innervation of the inner ear and lateral line were located in the brain by applying horseradish peroxidase to appropriate cranial nerves. The efferent neurons are found in a rhombencephalic nucleus, called here the octavolateralis efferent nucleus, which lies at the rostral pole of the visceromotor column. Up to 40% of these neurons are contralateral. The location of efferent cells is not topographically related to the sense organs they innervate. Their axons leave the brain together with other motor axons in the facial and glossopharyngeal nerves and there is evidence that some neurons innervate both the ear and the lateral line. The efferent nucleus receives direct sensory input from the labyrinth, but not from the lateral line. The organization of the efferent neurons and the distribution of their axons indicates that their effect on the sense organs is probably widespread and nonspecific.

Animals↗
PubMed1985

The nuclear location signal.

A short sequence of predominantly basic amino acids Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val from SV40 Large T is responsible for the normal nuclear location of the protein. Alteration of Lys-128 to each of six different residues other than Arg renders Large T cytoplasmic, whereas single amino acid changes in the surrounding region impair but do not prevent nuclear accumulation. When transposed to the amino terminus of cytoplasmic Large T species, or Escherichia coli beta-galactosidase or of chicken muscle pyruvate kinase, the sequence around Lys-128 of Large T is able to direct the recipient protein to the nucleus. This demonstrates that these amino acids can be sufficient for nuclear location and can act as a nuclear location signal. A computer search of over 2500 proteins reveals that some other nuclear proteins (for example, BK virus Large T, SV40 VP2 and adenovirus 72kDa DNA binding protein) contain very similar basic tracts, but so too do some presumed non-nuclear proteins (for example, poliovirus VP3). We suggest that the related sequence acts as the nuclear location signal in the other nuclear proteins but that the sequence does not function in all cases, perhaps because it is not accessible. A similar, but shorter or less basic sequence, was detected in a number of other nuclear proteins, for example, polyoma virus Large T, SV40 VP1 and several histones. However, such sequences were also found in many other proteins. Perhaps the shorter basic sequences can also act as nuclear location signals, but to be functional they need to be exposed (for example, at the amino terminus of the protein as in SV40 VP1) or to be present in multiple copies.

Amino Acid Sequence↗
PubMed1984

Projections of cerebellar Purkinje cells in the dogfish, Scyliorhinus.

In the dogfish Scyliorhinus degenerating axons and terminals arising from Purkinje cells and resulting from small superficial lesions made in the cerebellar corpus were found to be predominantly restricted to the ipsilateral cerebellar nucleus; none was observed in the tegmentum. Horseradish peroxidase placed within the cerebellar nucleus was transported retrogradely to the Purkinje cells. It appears that in these fishes, as in mammals, cerebellar output is relayed through cerebellar nuclei.

Animals↗
PubMed1984

A short amino acid sequence able to specify nuclear location.

A short sequence of amino acids including Lys-128 is required for the normal nuclear accumulation of wild-type and deleted forms of SV40 large T antigen. A cytoplasmic large T mutant that lacks sequences from around Lys-128 localizes to the nucleus if the missing sequence is attached to its amino terminus. The implication that the sequence element around Lys-128 acts as an autonomous signal capable of specifying nuclear location was tested directly by transferring it to the amino termini of beta-galactosidase and of pyruvate kinase, normally a cytoplasmic protein. Sequences that included the putative signal induced each of the fusion proteins to accumulate completely in the nucleus but had no discernible effect when Lys-128 was replaced by Thr. By reducing the size of the transposed sequence we conclude that Pro-Lys-Lys-Lys-Arg-Lys-Val can act as a nuclear location signal. The sequence may represent a prototype of similar sequences in other nuclear proteins.

Amino Acid Sequence↗
PubMed1984

The activity of cerebellar neurones of the decerebrate dogfish Scyliorhinus during spontaneous swimming movements.

Patterns of activity of cerebellar neurones in response to cutaneous stimulation and during spontaneous, swimming-like movements were examined, using microelectrodes, in decerebrate dogfish (Scyliorhinus canicula). Continuous swimming movements, lasting for several hours, were obtained in fish in which the medial longitudinal fasciculus (m.l.f.) was lesioned in the rhombencephalon. Purkinje cells (P cells) and some stellate cells (S cells) were observed to discharge rhythmically, in phase with swimming movements. These units were distributed throughout the cerebellum, but with no apparent somatotopic distribution. After curarization, rhythmic motor discharges could still be recorded from ventral roots and phase locked P cell discharges were recorded from the cerebellum. P cells that discharged rhythmically during active swimming movements, did not do so when the body was oscillated passively during quiescent periods. Cutaneous stimulation evoked burst discharges in many P cells at long latency (ca. 100 ms) both before and after curarization and whether or not a rhythmic motor output was being generated. In rhythmically discharging units, a similar response was obtained when cutaneous stimulation was applied during that part of a cycle when the unit was most or least active. It was concluded that cerebellar neurones discharged in phase with the output of the spinal locomotory rhythm generators and independently of peripheral sensory feed-back.

Action Potentials↗
PubMed1983

Respiratory responses to stimulation of branchial vagus nerve ganglia of a teleost fish.

The effects of electrical stimulation of epibranchial vagus ganglia upon respiration of the carp were investigated. Single shocks evoked fast twitch responses in a number of respiratory muscles with latencies around 18 msec to the beginning and 30-35 msec to the peak of activity. Shocks given during abduction decreased the respiratory cycle duration by shortening abduction and accelerating adduction. Stimuli given throughout most of adduction also shortened the respiratory cycle, accelerating the adduction only. These responses are similar to vagally mediated lung receptor reflexes of mammals. Stimulation with short trains of pulses produced a rapid expansion-contraction movement. This movement resembles in all respects (shape, time in the respiratory cycle, muscle coordination) the intermediate expansion of a normal coughing movement. Continual stimulation at frequencies close to the normal respiratory rate had a synchronising influence upon respiration, speeding up or slowing down its rate. HRP applied to the third vagal ganglion showed that there is a small projection of this ganglion to the nucleus intermedius facialis, although the majority of sensory fibres terminate in the vagal lobe. The nucleus intermedius facialis is already known to connect directly with the respiratory motor centres and thus might provide a pathway for the fast twitch response. A projection was also found to the nucleus ambiguus; in mammals this nucleus plays an important role in the regulation of respiratory movements.

Animals↗
PubMed1983

The activity of cerebellar nuclear neurones in relation to stimuli which evoke a pectoral fin reflex in dogfish.

Extracellular single-unit recordings from the cerebellar nucleus were classified into type I and type II units on the basis of their spontaneous discharges. Type I units discharged at a very regular frequency, giving interspike interval histograms with narrow distributions. Type II units had irregular discharges. Type I units were identified as cerebellar nuclear units by their antidromic responses to stimulation of the contralateral brachium conjunctivum (b.c.) in the mid-brain and by their inhibitory responses to stimulation of the cerebellar cortex. Type II units were not driven antidromically by b.c. stimulation but were inhibited by stimulating the cerebellar cortex. Activity of the nuclear neurones was monitored following subcutaneous electrical stimulation of a fin that elicits a reflex elevation. 67% of units responded, the majority with an increased discharge frequency (excitation, 59%) but some with a decreased discharge frequency ('inhibition', 8%). Latencies of both excitatory and inhibitory responses were greater than 50-400 msec. Most excitatory responses lasted for at least 500 msec; several lasted for more than 10 sec. Inhibitory responses lasted for about 500 msec. With units tested by bilateral fin stimulation, the same qualitative response was obtained whichever fin was stimulated. These results are discussed in relation to the known responses of cerebellar Purkinje cells recorded under similar experimental conditions.

Action Potentials↗
PubMed1981

The activity of cerebellar neurones of an elasmobranch fish (Scyliorhinus canicula) during a reflex movement of a fin.

1. Response of neurones in the corpus cerebelli of Scyliorhinus canicula (Elasmobranchii) have been recorded in decerebrate unanaesthetized fish during the performance of pectoral fin reflexes (p.f.r.) evoked by electrical stimulation of the fins.2. Of 421 single units recorded in the posterior dorsal quadrant of the corpus, 111 (26%) had their discharges modulated when the reflex was evoked; fifty nine were Purkinje (P) cells discharging single spikes, thirteen were P cells discharging complex responses, thirty-six were stellate (S) cells and three were not positively identified.3. The responses of fifty-one units (thirty-seven P cells and fourteen S cells) were analysed in detail. In thirty-one of the P cells and all the S cells the initial response was excitatory, six P cells gave an inhibitory response only and a further three were inhibited after the initial excitation. Only one S cell had an inhibitory component in its response.4. The discharges of the S cells completely overlapped the inhibitory responses of the P cells.5. Only one cell (a P cell) was evoked at a latency shorter than that of the p.f.r. In one other P cell discharging single spikes spontaneously, the evoked response was a long latency (146 msec) complex response. Four other P cells discharged only complex responses but the pattern of their response to the p.f.r. was similar to that of P cells discharging single spikes only.6. No cerebellar responses were evoked if the fin stimulus was below the threshold necessary to evoke a p.f.r. In curarized fish, unit responses were recorded that were qualitatively similar to those recorded in unparalysed fish.7. These results suggest that (i) because of the long latency of the responses, the cerebellum is unlikely to have a role in the initiation of the p.f.r.; (ii) the responses during the p.f.r. were evoked via a mossy fibre-parallel fibre pathway; (iii) the responses were correlated with motor activity rather than sensory input.

Action Potentials↗
PubMed1980

Medullary and cerebellar projections of the statoacoustic nerve of the dogfish, Scyliorhinus canicula.

The statoacoustic nerve of the dogfish, Scyliorhinus canicula, was transected medial to the ganglion for the purpose of elucidating its central pathways and terminal fields. Following two to six weeks postoperative survival times, transverse, horizontal, and sagittal sections of the brain stem were stained by the Fink-Heimer silver-impregnation method to reveal degenerating axons and terminals. Fragmented axons enter the medulla and give rise to medial, descending, and ascending pathway. Fibers of the medial pathway terminate about the soma and lateral dendrites of the large cells that comprise nucleus magnocellularis; descending and ascending fibers terminate on the dendrites of the cells of ventral and superior nuclei respectively. In addition, fibers emanate from fascicles of the descending pathway to form a large field of degenerating axons and terminals within the ventromedial part of the medulla, and a substantial proportion of the fibers of the ascending pathway continues beyond the superior nucleus to terminate among the granule cells of the medial part of the vestibulolateral lobe of the cerebellum. No fragmented axons are traceable to the lateral part (auricles) of the vestibulolateral lobe, cerebellar nucleus or corpus, or those nuclei associated with the lateral-line lobes. It appears therefore that octavus terminal fields are separate from those of the lateral line at both cerebellar and medullary levels, at least at the level of the first-order neuron.

Animals↗
PubMed1979

Organization of vestibular afferents to the vestibular nuclei of the dogfish.

Electrophysiological and light microscopical studies were made on the vestibular area of the dogfish hindbrain. Three vestibular nuclei were distinguished: the superior nucleus (VES), the magnocellularis nucleus (VEM), and the ventral nucleus (VEV). The distribution of field potentials evoked in the hindbrain by stimulation of nerve VIII confirms the location and extent of the vestibular nuclei. It also raises the possibility of a direct contralateral projection of vestibular nerve fibres. Unit studies confirm the interpretation of the field potentials and provide evidence of mono- and polysynaptic activation of vestibular nuclear neurons by vestibular afferents.

Animals↗