Biomedical subjects
L Mendell
Publications and source records attributed to L Mendell.
Are breast patterns a risk index for breast cancer? A reappraisal.
A retrospective study was designed to test J.N. Wolfe's theory that xeromammographic breast patterns can be used as a risk index for breast cancer. After analyzing breast types of all breast cancer patients over a 4 year period at the Jewish General Hospital, Montreal, who had xeromammography prior to surgery, we were unable to support Wolfe's hypothesis. We conclude that an inherent bias in the design of his experiment led to erroneous conclusions.
Individual e.p.s.p.s in chronic spinal cats [proceedings].
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The effect of axotomy on root potentials in the frog spinal cord.
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Analysis of moving supernumerary limbs of Xenopus laevis.
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Area specific reflexes from normal and supernumerary hindlimbs of Xenopus laevis.
Two area specific reflexes elicited by natural stimulation of different regions of the hindlimbs of Xenopus laevis have been identified. Light or intense mechanical stimulation of the foot evokes reflex activity in the ipsilateral knee flexor nerve; moderate pressure applied to the calf evokes reflex activity predominantly in the ipsilateral knee extensor nerve. The reflex responses have been recorded electrophysiologically to overcome the limitations of behavioral observations for determining the presence of activity in particular muscles. Normal area specific reflexes are elicited in the normal ipsilateral hindlimb by stimulation of grafted supernumerary hindlimbs innervated either by hindlimb (lumbar) or by non-limb (thoracic) spinal cord segments. The area specific reflexes can be elicited only if the limb is grafted to a host younger than stage 54-55 of Nieuwkoop and Faber ('56), the stage at which reflex movements are first observed behaviorally. Abnormal reflex responses are evoked by stimulation of supernumerary limbs innervated by either thoracic or lumbar segments when the limb buds are grafted to older larvae. Supernumerary forelimbs grafted at early stages and innervated by either thoracic or lumbar spinal cord segments generally fail to elicit area specific reflex responses in the normal hindlimb. Single-unit recordings of afferent fibers supplying the normal and supernumerary hindlimbs show that each limb receives a separate nerve supply. No evidence for branched afferent fibers has been found. The implications of these results for theories of neuronal specification are discussed, particularly the hypothesis that peripheral tissues are able to specify the central actions of afferent fibers that innervate them.
Two negative dorsal root potentials evoke a positive dorsal root potential.
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Properties and distribution of peripherally evoked presynaptic hyperpolarization in cat lumbar spinal cord.
1. The action of peripheral nerve volleys on the polarization of presynaptic terminals of inactive sensory fibres in cat lumbar spinal cord has been investigated by recording (a) the dorsal root potential (DRP), (b) intracellular changes in polarization of single preterminal axons (PAD or PAH), and (c) changes in excitability of populations of preterminal axons.2. Presynaptic hyperpolarization (positive DRP-PAH) can be evoked by stimulation of muscle group III afferents as well as by volleys in cutaneous Abeta, Adelta and C afferents. These volleys can also produce presynaptic depolarization (negative DRP-PAD).3. The positive DRP is observed in the decerebrate state and increases in amplitude following spinalization.4. Picrotoxin blocks the positive DRP at the same dosages required to block the negative DRP. Test negative DRPs are depressed during a conditioning positive DRP. These results are used to support earlier suggestions that the positive DRP results from inhibition of interneurones mediating the negative DRP.5. Trains of group III stimuli at 20/sec evoke a steady positive DRP. Trains of the same intensity at 200/sec evoke a phasic negative DRP. This frequency dependence is observed for PAD and PAH in single sensory axons.6. The DRPs recorded from different dorsal root filaments in response to a given stimulus vary widely in the ratio of negative to positive DRP.7. Intracellular recording from single axons reveals that the same stimuli evoke widely varying ratios of PAD and PAH.8. Stimulation of FRA evokes PAH > PAD in PBST group I afferents, PAD > PAH in sural A fibres and intermediate effects in G-S group I units.9. It is suggested that activation of flexor reflex afferents may selectively potentiate the synaptic efficacy of large muscle afferents mediating the flexor reflex rather than large skin afferents or large afferents from extensor muscles.
Positive dorsal root potentials produced by stimulaton of small diameter muscle afferents.
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