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Biomedical subjects

M Meredith

Publications and source records attributed to M Meredith.

53 records · Page 3Linked to original sources
PubMed1987

The nervus terminalis of the shark: the effect of efferent impulses on ganglion cell activity.

Tonic activity was recorded extracellularly in the nervus terminalis of the bonnethead shark. Cutting or cooling the nerve central to its ganglion eliminated these spikes, and was followed by an increase in multi-unit activity which appeared to arise from the ganglion. After cutting centrally, electrical stimulation of the distal stump of the nerve suppressed this multi-unit activity. The data suggest that efferent impulses may normally suppress ganglion cell activity.

Action Potentials↗
PubMed1987

Convergence of main and accessory olfactory pathways onto single neurons in the hamster amygdala.

Chemoreceptor pathways from the vomeronasal organ (VNO), and main olfactory system are known to be separate as they pass into the brain, at least until the level of the amygdala. In the amygdala, vomeronasal pathways project to the posteromedial cortical nucleus (PMCN), and medial nucleus (MN). The main olfactory pathways have terminations in the posterolateral cortical nucleus (PLCN), and anterior cortical nucleus (ACN), both of which project to the PMCN and MN. The anatomy thus suggests that the PMCN and MN are sites for convergence of input from the main and accessory olfactory pathways. We have recorded single units in the amygdala and found that electrical stimulation of either the main olfactory bulbs or the VNO could drive some of the same units in the PMCN. Units were also found that were driven by one system but not the other, and units in which activity driven by one system was suppressed by stimulation of the other system.

Action Potentials↗
PubMed1986

Vomeronasal organ removal before sexual experience impairs male hamster mating behavior.

Removal of vomeronasal chemoreceptors before sexual experience in male hamsters resulted in complete failure to mate in some animals but removal of these receptors after sexual experience had no effect. Animals were tested for mating behavior with intact behaviorally receptive females and also with anesthetized males scented with vaginal fluid. The two tests produced essentially the same result. Histological analysis of the lesions and radioimmunoassay of androgen levels showed no group differences, other than vomeronasal organ removal, that could account for the results. The behavioral data suggest that the vomeronasal system may be concerned with the production of preprogrammed behavior.

Androgens↗
PubMed1986

Patterned response to odor in mammalian olfactory bulb: the influence of intensity.

Responses of single neurons in the olfactory bulb of anesthetized hamsters were recorded extracellularly while odors of defined concentration and time course were delivered to the olfactory system at constant flow. Responses could be either excitatory or suppressive, as judged by the first distinguishable change in firing rate during odor delivery. However, when the time course of the response was examined in more detail, approximately one-third of all tests and one-half of the tests at high concentration resulted in complex temporal patterns of firing rate that involved both increases and decreases with respect to spontaneous activity. Approximately two-thirds of all tests produced responses where increased firing rate preceded any distinguishable suppression. Excitatory and suppressive responses were each classified into four groups according to their temporal patterns. Different patterns were not equally represented in the data and the proportions of patterns elicited by the same odor changed with stimulus intensity. Complex responses, where temporal patterns included periods of firing rate above and below spontaneous rate, were increasingly common and intensity was increased. Magnitude of response is difficult to define when a single response includes both increases and decreases of firing rate but more than half of the neurons that responded to more than one stimulus concentration clearly had nonmonotonic intensity-response functions. Forty-one out of 101 neurons were classified as output cells because they could be driven at short constant latency by lateral olfactory tract stimulation. Their responses were not clearly different from the remaining cells that could not be classified as output cells. The contribution of the inhibitory circuits of the olfactory bulb to the generation of patterned response and to changes in pattern with intensity are discussed. The lateral inhibitory circuits of the bulb appear to be sufficient to explain the data presented here.

Action Potentials↗
PubMed1984

Effects of volatile and nonvolatile chemical signals on male sex behaviors mediated by the main and accessory olfactory systems.

Estrous hamster vaginal discharge (HVD) contains both volatile and nonvolatile chemical signals which collectively elicit both male attraction to females and male mating behavior. These two aspects of normal sexual behavior are differentially affected by lesions involving afferents of the main and the accessory olfactory systems. The results of lesions that involve the main olfactory system suggest that it provides information primarily concerning those volatile components of HVD that normally signal the presence of a female. Lesions restricted to the accessory olfactory system do not impair a male's interest in or relative preference for HVD but do significantly interfere with subsequent stages of sexual behavior by reducing the amount of mating obtained upon exposure to HVD. Stimulation of the accessory olfactory system by nonvolatile components of HVD has thus been implicated in the production of mating behavior. In these experiments, male hamsters were attracted to female odor and engaged in significant amounts of mating behavior with surrogate females when only the volatile components of HVD were available to them. These behaviors were further enhanced when both volatile and nonvolatile components of HVD were provided. Lesion studies of the afferents involved reinforce the hypothesis that the main olfactory system is preferentially involved with processing those volatile chemical signals in HVD that denote female attractiveness whereas the accessory olfactory system is preferentially involved with processing those chemical signals, both volatile and nonvolatile, that evoke subsequent steps in male sexual behavior.

Animals↗
PubMed1980

Vomeronasal pump: significance for male hamster sexual behavior.

Vomeronasal chemoreceptors segregated within the vomeronasal organ are important for male hamster sexual behavior. An autonomically controlled vascular pump, previously demonstrated in anesthetized animals, can transport stimuli to the receptors. Interruption of the efferent nerves controlling the pump results in behavioral deficits similar to those produced by interruption of the afferent nerves carrying information from the vomeronasal organ to the brain. Pump activation is thus a prerequisite for normal vomeronasal stimulation in behaving animals.

Animals↗
PubMed1979

Efferent control of stimulus access to the hamster vomeronasal organ.

Previous workers had identified the vomeronasal organ, on anatomical evidence, as an accessory olfactory organ, present in most terrestrial vertebrates. Lesion experiments had demonstrated its importance in sexual behaviour in the hamster. Howevever, the sequestered position of the vomeronasal receptor epithelium within the organ raised questions concerning the access of olfactory stimuli. Using electrophysiological and pharmacological methods we have now demonstrated the following. 1. A pumping mechanism exists, powered by vasomotor movements, which can suck stimulus substances into the vonmeronasal organ. 2. A mechanism also exists for the active expulsion of the contents of the vomeronasal organ. 3. These mechanisms are activated by fibres running in the nasopalatine nerve. 4. The suction mechanism is controlled by sympathetic, probably adrenergic, fibres from the superior cervical sympathetic ganglion. Control of the expulsion mechanism has not been definitely established but does not appear to be sympathetic. 5. The vomeronasal organ can be adequately stimulated by activation of the pumping mechanism in the presence of odour. 6. Odour responses of single units in the accessory olfactory bulb have been recorded for the first time. 7. The time course of neuronal response in the accessory olfactory bulb is more rapid than predicted by many authors. The response is sufficiently fast that the vomeronasal system cannot be ruled out as a possible sensory pathway in many odour related behaviours. Possible modes of action of the pumping mechanism in awake animals are discussed.

Adrenergic Fibers↗
PubMed1978

Patterned response to odor in single neurones of goldfish olfactory bulb: influence of odor quality and other stimulus parameters.

Responses of 75 single units in the goldfish olfactory bulb were analyzed in detail for their relationship to the time-course of the change in odor concentration during each odor stimulus. Odor stimuli were controlled for rise time, duration, and peak concentration by an apparatus developed for the purpose. This apparatus enabled aqueous odor stimuli to be interposed into a constant water stream without changes in flow rate. The time-course of the concentration change within the olfactory sac was inferred from conductivity measurements at the incurrent and excurrent nostrils. Temporal patterns of firing rate elicited by stimuli with relatively slow rising and falling phases could be quite complex combinations of excitation and suppression. Different temporal patterns were produced by different substances at a single concentration in most units. Statistical measures of the temporal pattern of response for a small number of cells at a given concentration were more characteristic of the stimulus substance than any of three measures of magnitude of response. The temporal patterns change when the peak concentration, duration, and rise time of the stimuli are varied. The nature of these changes suggests that the different patterns are due primarily to the combined influence of two factors: (a) a stimulus whose concentration varies over time and (b) a relationship between concentration and impulse frequency which varies from unit to unit. Some units produce patterns suggestive of influence by neural events of long time constant. The importance of temporal patterns in odor quality and odor intensity coding is discussed.

Amino Acids↗
PubMedDate not supplied

The issue of substance abuse in the health care industry. A preliminary survey of managerial thinking.

Substance abuse in the workplace has been a growing concern in recent years and ways to detect employees and applicants who use drugs has been the subject of much debate. In this article, the results of a survey on the attitudes of medical practice human resource managers on drug testing of both employees and applicants are given. For this study, 273 human resource managers were sent questionnaires detailing various attitude statements and were asked for their level of agreement. Categories of questions included the administrators' general philosophy of drug testing, their attitudes toward the organizational impact of drug testing, their attitudes toward the implementation of drug testing and their attitudes toward specific issues pertinent to drug testing in medical groups.

Attitude of Health Personnel↗