Biomedical subjects

K Caesar

Publications and source records attributed to K Caesar.

At least 19 recordsLinked to original sources

PubMed2000

Temporal coupling between neuronal activity and blood flow in rat cerebellar cortex as indicated by field potential analysis.

1. Laser-Doppler flowmetry and extracellular recordings of field potentials were used to examine the temporal coupling between neuronal activity and increases in cerebellar blood flow (CeBF). 2. Climbing fibre-evoked increases in CeBF were dependent on stimulus duration, indicating that increases in CeBF reflected a time integral in neuronal activity. The simplest way to represent neuronal activity over time was to obtain a running summation of evoked field potential amplitudes (runSigmaFP). RunSigmaFP was calculated for each stimulus protocol and compared with the time course of the CeBF responses to demonstrate coupling between nerve cell activity and CeBF. 3. In the climbing fibre system, the amplitude and time course of CeBF were in agreement with the calculated postsynaptic runSigmaFP (2-20 Hz for 60 s). This suggested coupling between CeBF and neuronal activity in this excitatory, monosynaptic, afferent-input system under these conditions. There was no correlation between runSigmaFP and CeBF during prolonged stimulation. 4. Parallel fibre-evoked increases in CeBF correlated with runSigmaFP of pre- and postsynaptic potentials (2-15 Hz for 60 s). At higher stimulation frequencies and during longer-lasting stimulation the time course and amplitudes of CeBF responses correlated with runSigmaFP of presynaptic, but not postsynaptic potentials. This suggested a more complex relationship in this mixed inhibitory-excitatory, disynaptic, afferent-input system. 5. This study has demonstrated temporal coupling between neuronal activity and CeBF in the monosynaptic, excitatory climbing-fibre system. In the mixed mono- and disynaptic parallel fibre system, temporal coupling was most clearly observed at low stimulation frequencies. We propose that appropriate modelling of electrophysiological data is needed to document functional coupling of neuronal activity and blood flow.

Action Potentials↗

PubMed2000

A longitudinal study of Escherichia coli strains isolated from captive mammals, birds, and reptiles in Trinidad.

A longitudinal study was conducted of the prevalence and characteristics of Escherichia coli in mammals, birds, and reptiles housed at the Emperor Valley Zoo, Trinidad. During a 6-mo study period, swabs were obtained from fecal samples that were randomly collected from the enclosures of animals from these three taxonomic groups every 3 wk. With snakes, both cloacal and fecal swabs were obtained. Fecal and cloacal swabs were cultured for E. coli on eosin methylene blue agar. The production of mucoid colonies and hemolytic colonies and non-sorbitol fermenter status were identified. The occurrence of O157 strains was determined amongst E. coli isolates that were non-sorbitol fermenters, and the disc diffusion method was used to determine the antibiograms of isolates. The frequency of E. coli isolation was significantly higher in mammals compared with birds and reptiles. Overall, the frequencies of isolation of E. coli from omnivores. herbivores, and carnivores, 87.2%, 70.0%, and 57.3%, respectively, regardless of animal class, were significantly different. Most (99.6%) of the E. coli isolates tested for antibiotic sensitivity exhibited resistance to one or more of the eight antimicrobial agents used. The possession of phenotypic virulence markers by the E. coli isolates studied and the generally high resistance to antimicrobial agents may have health implications for the zoological collection.

Animals↗

PubMed2000

Retrospective and longitudinal study of salmonellosis in captive wildlife in Trinidad.

Morbidity and mortality of captive wildlife at the Emperor Valley Zoo, Trinidad from 1993 to 1996 were analysed to determine involvement of Salmonella spp. A 6 mo longitudinal study was conducted to determine the frequency of isolation of Salmonella spp. from apparently healthy, sick and dead wild mammals, birds, and reptiles. The antibiograms of Salmonella isolates were determined using the disc diffusion method. Fecal samples randomly selected from animal enclosures and cloacal swabs of snakes were cultured for Salmonella spp. following enrichment in tetrathionate and selenite cystine broths. For the 1993-96 period, Salmonella spp. was implicated in 17 (12%) of 141 sick or dead animals and the predominant serotype was S. typhimurium. During the 6 mo prospective study in a mean animal population of 1,186, there were 20 (2%) and 14 (1%) animals that were sick and died respectively; Salmonella spp. was implicated in only one mortality. Overall, of 1,012 samples from apparently healthy wildlife cultured, 66 (7%) yielded 24 serotypes of Salmonella. The predominant serotype were S. seigburg (16 isolates), S. gaminara (6 isolates), and S. thompson (6 isolates). None of the samples yielded S. typhimurium. The frequency of isolation of Salmonella spp. in reptiles (14%) was significantly higher than found in either mammals (7%) or birds (3%). Sixty-five (99%) of 66 Salmonella spp. isolates exhibited resistance to one or more of the nine antimicrobial agents tested. Resistance was high to cephalothin (92%), moderate to streptomycin (35%) and tetracycline (29%), but significantly low to gentamicin (2%), chloramphenicol (0%), and sulphamethoxazole/trimethoprim (0%). The prevalence of asymptomatic infections by Salmonella spp. in zoo animals was high and the very high prevalence of antimicrobial resistance could be a problem when treating salmonellosis.

Animals↗

PubMed1999

Modification of activity-dependent increases in cerebellar blood flow by extracellular potassium in anaesthetized rats.

1. The hypothesis that potassium ions mediate activity-dependent increases of cerebral blood flow was examined in rat cerebellar cortex using ion-selective microelectrodes and laser-Doppler flowmetry. Increases of cerebellar blood flow (CeBF) and extracellular potassium concentration ([K+]o) were evoked by stimulation of parallel fibres and climbing fibres, and by microinjection of KCl into the cortex. 2. For parallel fibre stimulation, there was a maximal increase in [K+]o to 6.3 +/- 0.5 mM and in CeBF of 122 +/- 11 %. Climbing fibre stimulation gave a maximal increase in [K+]o to 4.4 +/- 0.2 mM and in CeBF of 157 +/- 20 %. This indicates different maxima for [K+]o and CeBF, dependent on the afferent system activated. 3. [K+]o and CeBF responses evoked by parallel or climbing fibre stimulation increased rapidly at the onset of stimulation, but exhibited different time courses during the remainder of the stimulation period and during return to baseline. 4. Microinjections of KCl into the cortex increased [K+]o to levels comparable to those evoked by parallel fibre stimulation. The corresponding CeBF increases were the same as, or smaller than, for parallel fibre stimulation, and much smaller than for climbing fibre stimulation. This suggests that mediators other than [K+]o are important for activity-dependent cerebral blood flow increases. 5. The present study showed that increased [K+]o is involved in CeBF regulation in the parallel fibre system, but is of limited importance for CeBF regulation in the climbing fibre system. The hypothesis that K+ is a major mediator of activity-dependent blood flow increases is probably not generally applicable to all brain regions and all types of neuronal stimulation.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1998

Modification of activity-dependent increases of cerebral blood flow by excitatory synaptic activity and spikes in rat cerebellar cortex.

1. Mechanisms of activity-dependent increases in cerebral blood flow (CBF) were examined in rat cerebellar cortex using the laser Doppler flow technique and extracellular recordings of single unit activity and field potentials. 2. Stimulation of the monosynaptic climbing fibre system evoked long-lasting complex spikes in Purkinje cells, and extracellular field potentials with a characteristic profile that indicated contributions from both passive and active membrane mechanisms. The concomitant CBF increases were reproducible at fairly short intervals, and suggest that both synaptic activity and spikes may contribute to increased CBF. 3. Stimulation of the disynaptic parallel fibre system inhibited the spiking activity in Purkinje cells, while the postsynaptic activity increased as indicated by the simultaneously recorded field potential. Nevertheless, CBF always increased. The inhibition of spike firing activity was partly dependent on GABAergic transmission, but may also relate to the intrinsic membrane properties of Purkinje cells. 4. The CBF increases evoked by parallel or climbing fibre stimulation were highly correlated to the sum of neural activities, i.e. the negativity of field potentials multiplied by the stimulus frequency. This suggests a robust link between extracellular current flow and activity-dependent increases in CBF. 5. AMPA receptor blockade attenuated CBF increases and field potential amplitudes, while NMDA receptor antagonism did not. This is consistent with the idea that the CBF responses are of neuronal origin. 6. This study has shown that activity-dependent CBF increases evoked by stimulation of cerebellar parallel fibres are dependent on synaptic excitation, including excitation of inhibitory interneurones, whereas the net activity of Purkinje cells, the principal neurones of the cerebellar cortex, is unimportant for the vascular response. For the climbing fibre system, not only synaptic activity but also the generation of complex spikes from Purkinje cells contribute to the increases in CBF. The strong correlation between CBF and field potential amplitudes suggests that extracellular ion fluxes contribute to the coupling of brain activity to blood flow.

Animals↗

PubMed1998

Some bacterial enteropathogens in wildlife and racing pigeons from Trinidad.

Fecal and cloacal swabs or feces of wild mammalian, avian and reptilian species, either farmed or free-ranging, and of racing pigeons (Columba livia) kept in lofts were cultured for Salmonella spp., Campylobacter spp., and Yersinia spp. Of 291 free-ranging mammals tested, 6 (2%) and 1 (< 1%) yielded positive cultures of Salmonella spp. and Campylobacter spp., respectively. Salmonella newport was the predominant serotype isolated and the opossum (Didelphis marsupialis insularis) had the significantly highest prevalence (29%) of Salmonella spp. infection compared to other species such as deer (Mazama americana trinitatis), lappe (Agouti paca), tattoo (Dasypus novemcinctus), agouti (Dasyprocta leporina), and wild hog (Tayassu tajacu). Among 14 species of farmed wildlife studied, 13 (7%) and 10 (5%) of 184 fecal or cloacal samples tested were positive for Salmonella spp. and Campylobacter spp., respectively. Salmonella javiana accounted for 50% of the Salmonella spp. isolates and C. jejuni represented 90% of the Campylobacter spp. cultured. Only 1 (1%) of 124 cloacal swabs of free-flying avian species yielded Salmonella spp. compared to 21 (17%) samples positive for Campylobacter spp. Of 171 racing pigeons which originated from 8 fanciers, 8 (5%) yielded Salmonella spp. all of which were serotype typhimurium while only 1 (1%) was positive for Campylobacter spp. Seven (88%) of 8 Salmonella spp. isolates were recovered from one fancier. Yersinia spp. was not cultured from any of the above samples. Although the prevalences of Salmonella spp. and Campylobacter spp. in wildlife in Trinidad are low, the practice of wildlife farming and the increased consumption of meat from wildlife may increase the health risk to human consumers.

Animals↗

PubMed1998

Prevalence of Salmonella and Campylobacter species in animals at Emperor Valley Zoo, Trinidad.

The prevalence of Salmonella and thermophilic Campylobacter species in animals kept at the Emperor Valley Zoo, Trinidad, was determined. Of the 433 animals from a total of 30 species sampled, 28 (6.5%) and 11 (2.5%) were positive for Salmonella and Campylobacter, respectively. The difference was statistically significant (P < or = 0.001: chi2). Overall, 12 stereotypes of Salmonella were isolated, with S. miami accounting for eight (25.8%) of 31 isolates. All Campylobacter isolates were C. jejuni, with nine (81.8%) of 11 isolates originating from birds. Reptiles had a high prevalence of Salmonella infection with a high probability for salmonellosis, but the risk of campylobacteriosis appears to be very low.

Animals↗

PubMed1989