Electrophysiological study of locus ceruleus projections to central cerebellar nuclei

Evoked response (field potentials) were recorded in all cerebellar nuclei when stimulating the locus ceruleus (LC). Response occurring in the dentate and fastigial nuclei were of considerably greater amplitude and were repeated at a higher rate than in the interstitial nucleus. Blockade of beta-adrenoreceptors led to clear-cut depression of response in the dentate and fastigial nuclei and increased response in the interstitial nucleus. Neuronal response to LC stimulation in the nuclei mainly took the form of inhibition of spontaneous discharges. A less pronounced response was observed in the interstitial nucleus. The findings obtained would indicate the presence of noradrenergic afferents reaching the cerebellar nuclei, where they are unevenly distributed.Kh. Anovyan Pedagogical Institute, Armenia SSR, Erevan. L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 1, pp. 39–44, January–February, 1989.     

Electrophysiological study of corticocaudate projections in cats

The potential waves evoked in the caudate nucleus (CN) of cats by stimulation of the cerebral neocortex were stereotactically recorded. The head and the body of the caudate nucleus were systematically explored. Stimulation of the ipsilateral sigmoid gyrus and the orbitofrontal cortex evoked waves with the largest amplitude in the CN. Smaller potentials were evoked from the ipsilateral ectosylvian and suprasylvian gyri and from the sigmoid gyrus on the contralateral side. Antidromic conduction from the caudate nucleus to the cortex demonstrated the directness of the corticocaudate pathway. By stimulating the white matter and by making lesions, the corticocaudate pathway was shown to pass, in part, through the subcallosal fasciculus and, in part, through the internal capsule. Corticocaudate connections were shown to be separate from the fibers of the corticospinal tract. A staggered and extensively overlapping topographic progression of the corticocaudate projections was demonstrable along the antero-posterior axis, but was less evident in the medio-lateral direction. It was concluded that the intranuclear distribution of functional synaptic connections must be more profusely branched than was suspected from anatomical data.     

Mechanism of perception of changes in the magnetic field by ampullae of lorenzini of elasmobranchs

The mechanisms of reception of changes in the magnetic field by electroreceptor formations were investigated in experiments on Black Sea rays in which spike activity was recorded from single nerve fibers connected with the ampullae of Lorenzini. The responses of the ampullae of Lorenzini to magnetic stimulation were shown to be due to induced electric currents creating potential gradients in the body tissues of the fish and the sea water. On the basis of differences in responses of different ampullae to magnetic stimulation, it is possible to distinguish between magnetic stimuli and other stimuli acting on the electroreceptor system. Potentiation of the receptor response to magnetic stimulation was found as the fish came closer to the "shore." The mechanisms and biological importance of reception of changes in the magnetic field by the ampullae of Lorenzini are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 1, 75–83, January–February, 1978.     

Electrophysiological study of corticocaudate projections in cats.

The potential waves evoked in the caudate nucleus (CN) of cats by stimulation of the cerebral neocortex were sterotactically recorded. The head and the body of the caudate nucleus were systematically explored. Stimulation of the ipsilateral sigmoid gyrus and the orbitofrontal cortex evoked waves with the largest amplitude in the CN. Smaller potentials were evoked from the ipsilateral ectosylvian and suprasylvian gyri and from the sigmoid gyrus on the contralateral side. Antidromic conduction from the caudate nucleus to the cortex demonstrated the directness of the corticocaudate pathway. By stimulating the white matter and by amking lesions, the corticocaudate pathway was shown to pass, in part, through the subcallosal fasciculus and, in part, through the internal capsule. Corticocaudate connections were shown to be separate from the fibers of the corticospinal tract. A staggered and extensively overlapping topographic progression of the corticocaudate projections was demonstrable along the antero-posterior axis, but was less evident in the medio-lateral direction. It was concluded that the intranuclear distribution of functional synaptic connections must be more profusely branched than was suspected from anatomical data.     

Investigation of the mechanism of temperature sensitivity of the electroreceptors of ampullae of lorenzini

In experiments on Black Sea skates (Raja clavata), the potential of the receptor epithelium of the ampullae of Lorenzini and spike activity of single nerve fibers connected to them were investigated during electrical and temperature stimulation. Usually the potential within the canal was between 0 and –2 mV, and the input resistance of the ampulla 250–400 k. Heating of the region of the receptor epithelium was accompanied by a negative wave of potential, an increase in input resistance, and inhibition of spike activity. With worsening of the animal's condition the transepithelial potential became positive (up to +10 mV) but the input resistance of the ampulla during stimulation with a positive current was nonlinear in some cases: a regenerative spike of positive polarity appeared in the channel. During heating, the spike response was sometimes reversed in sign. It is suggested that fluctuations of the transepithelial potential and spike responses to temperature stimulation reflect changes in the potential difference on the basal membrane of the receptor cells, which is described by a relationship of the Nernst's or Goldman's equation type.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. I. M. Sechenov, Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Pacific Institute of Oceanology, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 67–74, January–February, 1980.     

Influence of L-serine-O-phosphate on synaptic transmission in afferent synapses of the ampullae of Lorenzini of skates

The method of superfusion of the basal membranes of the ampullae of Lorenzini of skates was used to investigate the influence of L-serine-O-phosphate (SOP) on the background and evoked activity of afferent nerve fibers, as well as on the effects of application of agonists: exciting amino acids — L-glutamate (L-GLU), kainate (KA), quisqualte (Q), and N-methyl-D-aspartate (NMDA). It was found that SOP (threshold concentration 10^–7 M) had an inhibiting effect on the background and evoked activity of the nerve fibers; depending on the concentration it decreased the stimulatory effects of L-GLU and NMDA and did not change the responses due to application of KA and Q. The data obtained suggest that the effects of SOP observed in the ampullae of Lorenzini are associated with its interaction with NMDA-type amino acid receptors.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 387–391, July–August, 1991.     

A morphological analysis of the ampullae of Lorenzini in selected skates (Pisces,Rajoidei)

A comparison of the ampullae of Lorenzini among 40 species of skates (Rajoidei) demonstrates a close relationship between inferred electroreceptive capabilities and feeding mechanisms. Three general lines of morphological modifications are noted. (1) Whereas the majority of ampullary pores are located on the ventral surface of the dorsoventrally flattened body, the relative proportion of ventral pores is significantly lower on species inhabiting aphotic waters. (2) The ventral pores on more piscivorous species are distributed over a larger portion of body surface than they are on those species that feed primarily on invertebrates. Ventral pores in this latter group are more noticeably concentrated around the mouth and their densities on the adult are inversely related to the overall mobility of preferred prey species. (3) The size of each ampulla and the number of alveoli associated with it are directly related to the habitat depth occupied by each species. Shallow-water species have smaller ampullae with fewer alveoli than deeper-dwelling (> 1,000 m) species. The general distribution of ampullary pores on deep dwelling rajoids appears to compensate for reduced visual input, whereas their relative densities are a measure of the system's resolution and reflect major differences in feeding strategies. The increased ampullary size and complexity observed in deep-sea rajoids provides mechanisms to increase both the sensitivity and signal-to-noise ratios.     

Effects of kainic acid on synaptic transmission in electroreceptors (the ampullae of Lorenzini) of skates

1. Effects of kainic acid (KA) on resting and evoked activities of the ampullary electroreceptor were studied in marine skates (Raja clavata). 2. Perfusion of the basal membrane with 10(-6)-10(-9) M KA produced significant and reversible changes in impulse activity depending on initial firing rate. 3. When synaptic transmission was blocked by perfusion with elevated Mg2+, the resting and evoked activities were restored if KA was added. 4. The results are consistent with the view that KA is a potent excitant of the ampullae receptors and its effects appear to be presynaptic.     

Preface: Biology of skates

Synopsis Skates have become a concern in recent years due to the preponderance of these elasmobranchs that are caught as bycatch or as a directed fishery. This has raised concern because skates have life history characteristics that may make them vulnerable to over-exploitation. It was due to this increasing awareness and concern about these batoids that prompted us to organize an international symposium on the “Biology of Skates”. The aims and goals of the symposium were to bring together an international group of researchers to meet, discuss, perhaps develop collaborations, and present their most recent findings. The symposium was held over two days, on 13–14 July, 2006, in conjunction with the 22nd annual meeting of the American Elasmobranch Society in New Orleans, LA. A total of 31 authors from four countries contributed 16 papers that appear in this special issue. The papers are broadly arranged into four separate categories: systematics and biogeography, diet and feeding ecology, reproductive biology, and age and growth. To the best of our knowledge this is the first dedicated book on the biology of skates. We hope that readers will find this issue of interest and that it helps encourage and stimulate future research into these fascinating fishes.     

DNA barcoding of Canada's skates

DNA-based identifications have been employed across broad taxonomic ranges and provide an especially useful tool in cases where external identification may be problematic. This study explored the utility of DNA barcoding in resolving skate species found in Atlantic Canadian waters. Most species were clearly resolved, expanding the utility for such identification on a taxonomically problematic group. Notably, one genus (Amblyraja) contained three of four species whose distributions do not overlap that could not be readily identified with this method. On the other hand, two common and partially sympatric species (Little and Winter skates) were readily identifiable. There were several instances of inconsistency between the voucher identification and the DNA sequence data. In some cases, these were at the intrageneric level among species acknowledged to be prone to misidentification. However, several instances of intergeneric discrepancies were also identified, suggesting either evidence of past introgressive hybridization or misidentification of vouchered specimens across broader taxonomic ranges. Such occurrences highlight the importance of retaining vouchered specimens for subsequent re-examination in the light of conflicting DNA evidence.     

Electrophysiological projections of pulvinar-lateralis posterior complex (P-LP) upon superior colliculus units in the cat

The effect of Pulvinar-Lateral Posterior (P-LP) electrical stimulation on superior colliculus unitary responses and eye movements is analyzed in 17 encéphale isolé cats. Twelve of them were curarized. Out of a total of 190 recorded units, 117 were localized in the superior colliculus and 73 units in the Mesencephalic Reticular Formation (MRF) below the superior colliculus. Thirty eight per cent (n = 45) of the collicular units modified their discharge frequency when the ipsilateral P-LP was electrically stimulated. The current intensity thresholds of transynaptic activation had a range between 0.5 and 2.0 mA. Most of the orthodromic responses were produced by ipsilateral P-LP stimulation and were localized in the intermediate and deep layers of the superior colliculus. Three types of responses were obtained: short latency responses between 2 and 10 ms (57%); intermediate latency responses between 15 and 40 ms (29%), and long latency responses between 50 and 200 ms (14%). Thirty one per cent (n = 18) of the units recorded in the MRF responded to P-LP stimulation with 10 ms pulse-trains duration. In the MRF 3 types of responses were observed: 1) a decrease or blockade in the resting discharge during 20 to 100 ms after stimulation (20%); simple responses with a latency between 25 and 150 ms (40%), and complex responses with an early response and a latency between 15-40 ms, and a late response with a latency between 150 and 200 ms (40%).(ABSTRACT TRUNCATED AT 250 WORDS)