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Biomedical subjects

E H Boyd

Publications and source records attributed to E H Boyd.

At least 19 recordsLinked to original sources
PubMed1989

Absorption of two trimethoprim/sulphonamide combinations from the uterus of pony mares.

Plasma drug concentrations were measured after two commercially available potentiated sulphonamides, trimethoprim and sulfadoxine and trimethoprim and sulphadiazine, were infused daily for 2 and 3 days, respectively, into the uteri of pony mares which had been mated before ovulation. Intravenous administration of trimethoprim and sulfadoxine allowed uterine absorption of trimethoprim (23-43%) and sulfadoxine (29-34%) to be calculated. After intra-uterine administration trimethoprim and sulphadiazine were detected in the milk of a lactating mare. In order to maintain plasma concentrations likely to be required for clinical efficacy of both drugs they should be administered every 12 h. However, infusions of both preparations caused endometrial inflammation as assessed by cytological and histological examination and this may have been responsible for the low pregnancy rate.

Absorption↗
PubMed1988

Absorption of neomycin from the equine uterus: effect of bacterial and chemical endometritis.

Plasma concentrations of neomycin were measured after intrauterine infusion of 3.3 mg/kg neomycin sulphate. Mares infected two hours previously with an intra-uterine infusion of beta-haemolytic streptococci absorbed approximately 12 per cent of the neomycin in both the oestrous and the luteal phases of the cycle. Normal mares in oestrus absorbed 6 per cent of the neomycin infused and luteal mares absorbed 56 per cent. In infected mares the peak plasma concentrations occurred two hours after neomycin infusion, earlier than in healthy mares. Cervical flushings after neomycin infusion in infected luteal mares revealed an increased reflux of neomycin when compared with healthy mares. Prior infusion of 30 ml of 10 per cent Lugol's iodine into the uterus resulted in 31 per cent of neomycin being absorbed by oestrous mares and 64 per cent by mares in the luteal phase. Peak plasma concentrations occurred 30 minutes after infusion in both phases. In the luteal phase the mares' absorption of neomycin may have been maximal.

Absorption↗
PubMed1988

The effect of various antibacterial preparations on the in vitro morphology and chemotactic response of equine neutrophils.

Two independent assay systems were used to study the effect of three antibacterial preparations on in vitro morphology and chemotaxis of equine neutrophils. Incubation of neutrophils with high (200 micrograms/ml) and medium (20 micrograms/ml) concentrations of neomycin impaired their response to standard chemoattractants. Trimethoprim/sulfadoxine (0.4/2.0 micrograms/ml-40/200 micrograms/ml) and benzylpenicillin (0.25-25 micrograms/ml) had no effect. Neutrophils collected from geldings 2 and 24 h after neomycin (5 mg/kg) administration had impaired responses to standard chemoattractants. Benzylpenicillin (13.2 mg/kg) had no effect.

Animals↗
PubMed1987

Absorption of neomycin from the equine uterus: effect of stage of oestrous cycle and volume of vehicle.

Plasma concentrations of neomycin were measured following intrauterine infusion of 3.3 mg/kg bodyweight neomycin sulphate. Mares in oestrus absorbed approximately 6 per cent of neomycin infused whereas mares in a luteal phase absorbed 56 per cent. The volume of infusate also affected absorption as increased volume resulted in decreased absorption. The decreased absorption both during oestrus and when large volumes were used was probably due to reflux of antibiotic through the cervix.

Absorption↗
PubMed1980

The M-wave and CNV in the squirrel monkey: generality of cue modality and of reward.

Typical M-waves and CNVs were produced in squirrel monkey frontal and rostral parietal cortex by light cues, as well as by tone cues. With light cues, M-waves were about 50% as large as with tone cues, whereas CNVs were of about the same magnitude with either type of cue. Typical M-waves and CNVs were also produced when avoidance of tail-shock was substituted for food as a reinforcer. The magnitude of both ERPs appeared to follow an inverted-U function with increasing shock intensity. The use of tail-shock as a reinforcer generated more complexities both in ERP changes and in behavior than did food. In some animals, at high shock intensities, ERP increased, rather than decreased, as each session progressed. In some animals, a combination of food and avoidance of tail-shock produced a decrease, rathan than an increase, in ERPs and did not improve behavioral performance. Furthermore, animals would not perform effectively on a CNV paradigm with punishment for aborting the trial. It was also demonstrated that increased stress (immobilization of head or tail) resulted in a reduced magnitude of both the M-wave and the CNV. This may account for some of the complexities encountered with avoidance of tail-shock as a reinforcer.

Animals↗
PubMed1979

Observations on the M-wave and the CNV in the squirrel monkey.

A typical CNV paradigm, with food as reward, evokes in the squirrel monkey's post-arcuate and post-central cortices both M-waves in response to the cues and what appears to be a CNV in the interstimulus interval. Both wave forms appear to be generated locally in cortex and to be more closely related temporally to the cues than to the animal's behavioral response. The CNV, like the M-wave, appears to reflect the animal's level of interest in obtaining the reward. It is smaller when the animal misses the cues than when he responds correctly. It decreases as food pellets are consumed. It varies with the level of interest of the animal in a particular type of food pellet, as judged from the animal's behavior. At some recording sites in some animals it appears to reflect both interest in the reward and interest in manipulating the environment to obtain the reward. It can be maintained for at least 2 sec, but differs from the human CNV in that, with the paradigm used, it is not well resolved by the imperative cue. Averaging evoked activity with the animal's motor response as reference point reveals another negative wave form which just precedes the motor response.

Acoustic Stimulation↗
PubMed1978

Effects of some psychotropic drugs on M-wave and operant behavior in the squirrel monkey.

The effects of low doses of nabilone, chlorpromazine, pentobarbital, meprobamate, diazepam, chlordiazepoxiOde and d-amphetamine on behavioral responding to cues signalling the availability of food rewards, and on the M-wave, an evoked cortical potential previously reported to reflect the conditioned incentive value of the cues were determined in the squirrel monkey. Nabilone and chlorpromazine simultaneously depressed both the M-wave and behavior. Pentobarbital, meprobamate, diazepam and chlordiazepoxide could depress the M-wave without depressing behavior. This effect was most marked with diazepam. The only augmentation of the M-wave observed was the d-amphetamine, and this occurred in only one of five animals. The benzodiazepines were the only drugs to augment behavioral output. However, diazepam occasionally increased the number of cures responded to while concomitantly decreasing both total behavioral output and the amplitude of the M-wave. It is concluded that the M-wave cannot directly reflect the incentive value of the cue, but must rather reflect something that tends to parallel this value.

Animals↗
PubMed1977

A cortical evoked potential that reflects the conditioned, positive incentive value of the stimulus. I. The evoked potential.

As squirrel monkeys learned that a tone cue signalled the availability of a food reward there appeared in pre- and post-central cortex a surface negative waveform in response to the cue. This waveform disappeared, concomitantly with the animal's behavioral response, during extinction and pseudoconditioning. It was independent of changes in cue intensity sufficient to markedly alter earlier components of evoked activity and it disappeared when evoked activity was averaged with the behavioral response, rather than the cue, as reference point. It was concluded that this evoked potential reflects cortical activity somewhere in the stimulus-response sequence between the recognition of the cue and the decision to act.

Animals↗
PubMed1977

A cortical evoked potential that reflects the conditioned, positive incentive value of the stimulus. II. Drive motivation (hunger).

It was shown that the late negative wave evoked in squirrel monkey cortex by tone cues signalling the availability of reward was smaller when the animal did not respond to the cue and often disappeared if the animal ignored many cues in succession. It decreased in amplitude as a test session progressed, and the rate of this decrease increased if the rate of reinforcement was increased. In some animals the size of the evoked wave was smaller if the animal was not fasted before a test session. In some animals the average size of a significant positive correlation with the number of cues responded to and a negative correlation with the animal's average reaction time. It is concluded that the evoked wave is probably a reflection of the conditioned incentive value of the cue.

Animals↗
PubMed1977

A cortical evoked potential that reflects the conditioned, positive incentive value of the stimulus. III. Manipulative motivation and the value of the reward.

Changing animals from a schedule on which they had to bar-press after a tone cue to get a food pellet, to a schedule on which the food pellet was presented automatically after the tone cue and the manipulandum was not available, had no effect on the latency, amplitude, or shape of the M-wave evoked by the tone cue. The amplitude of the evoked wave did, however, decrease more rapidly, as a test session progressed, with the latter schedule than with the former schedule. Failure to fast animals before test sessions markedly reduced the amplitude of the M-wave. Variation in the type of food pellet used caused marked variations in the amplitude of the evoked response. In all cases, there was a high degree of correlation between M-wave amplitude and a behavioral indication of the animal's interest in the reward. It was concluded that the M-wave reflects the conditioned incentive value of the cue, or in other words, the level of interest of the animal in the reward.

Animals↗
PubMed1976

Effects of delta9-tetrahydrocannabinol and pentobarbital on a cortical response evoked during conditioning.

A surface-negative wave, evoked by tone cues, appeared in monkey post-arcuate cortex as the monkey learned that the cue signaled the availability of reward. This evoked activity was depressed, concomitantly with changes in the animal's behavioral responding, by doses of delta9-tetrahydrocannabinol (delta9-THC) as low as 0.032 mg/kg and of pentobarbital as low as 4 mg/kg. Pentobarbital tended to increase the latency of the evoked wave, an effect not seen with delta9-THC.

Acoustic Stimulation↗