Relationship among recruitment order, axonal conduction velocity, and muscle-unit properties of type-identified motor units in cat plantaris muscle

A strict interpretation of the size-principle hypothesis (37, 39-41) is that a muscle's motor units should be recruited in an ascending order according to both the size of their motoneurons and the size of their innervated muscle units (for reviews see Refs. 9, 39, 73). Studies of large mixed muscles in the cat hindlimb, however, have shown that motor axonal conduction velocity and tetanic tension, which are frequently considered indices of motoneuron and muscle-unit size, respectively, are uncorrelated in the fast-twitch (type F) motor-unit subpopulation (12, 13, 23, 24, 30, 32, 63, 71, 79). Attempting to focus on type F units, we compared the recruitment order of 42 pairs of cat plantaris (PL) motor units with both axonal conduction velocity and tetanic tension as well as with other muscle-unit properties. Single PL alpha-motor axons were functionally isolated in intact L7 ventral root filaments of decerebrate cats. Tension responses produced by stimulating each isolated motor axon were used to find the tetanic tension of the muscle unit and to classify the unit (12) as either type S (slow twitch, fatigue resistant), type FR (fast twitch, fatigue resistant), type FI (fast twitch, intermediate fatigability), or type FF (fast twitch, highly fatigable). Conduction velocity of each isolated axon was computed from measurements of axonal conduction time and length. The axon's reflex discharges were recorded from the proximal end of the cut filament and compared with the discharges of another PL axon residing in a different, previously cut filament of the same cat. The recruitment order of each motor-unit pair studied was found during reflexes elicited by homonymous muscle stretch, tendon taps, or single shocks at group I intensity to the PL nerve. If either axon of the pair failed to discharge, as often was the case with the high-threshold type F units, the monosynaptic reflex was facilitated by a 500-pps conditioning train applied proximal to a complete reversible cooling block of the PL nerve. In all 42 pairs studied, the weaker motor unit had the lower functional threshold for recruitment. Recruitment also invariably followed the order S greater than FR greater than FI greater than FF units. The motor unit of a pair with the higher resistance to fatigue thus always had the lower functional threshold. In 21 of the 22 pairs containing at least one type S motor unit, the unit with the slower-conducting motor axon had the lower functional threshold for recruitment.(ABSTRACT TRUNCATED AT 400 WORDS)     

7α-O-IA-DPN:特异性碘标记阿片配体的研制和评价

目的：研制和评价新碘标阿片受体显像剂７αＯｉｏｄｏａｌｙｌｄｉｐｒｅｎｏｒｐｈｉｎｅ（７αＯＩＡＤＰＮ）。方法：选用阿片肽拮抗剂ＤＰＮ经碘代锡烷标记法成功地获得了一个原始的碘标阿片肽类似物，并对其进行理化性能、药理作用和生物学功能评价。结果：体外和体内阿片受体结合分析表明这一新的阿片配体具有非常高的亲和力（Ｋｉ＝４×１０－４μｍｏｌ／Ｌ）。注药后２０ｍｉｎ动物脑内的特异性结合占６３％，且其在脑内滞留时间较长而有利于成像。阿片抑制试验和抗痛活性研究分别反映碘标７αＯＩＡＤＰＮ可能对３种阿片受体（μ，δ，κ）都有亲和力，并保持了原有的药理特性和生物学功能。结论：碘标７αＯＩＡＤＰＮ作为新阿片受体显像剂较适于今后ＳＰＥＣＴ阿片受体研究。     

Diagnosis of bovine leukosis virus infection by solid phase radioimmunoassay for virus antibody

Solid phase radioimmunoassay for detection of anti-BLV antibodies in sera of infected animals is described. Viral antigens bound to surface of polystyrene are able selectively adsorb the antibodies from serum. Detection of bound antibodies quantitatively was done by 125I-labeled protein A from Staphylococcus aureus. Technical details of the assay are reported. The assay could be used as competitive one as well. Two different methods for detection of anti-BLV antibodies were compared with solid phase RIA. The solid phase RIA is highly sensitive, specific and available for large-scale examination. The assay is recommended for early diagnosis of bovine leukosis.     

Binding in vivo of selective mu and delta opioid receptor agonists: opioid receptor occupancy by endogenous enkephalins

The in vivo binding properties of cerebral mu and delta opioid receptors were investigated in mice after the intrastriatal injection of [3H][D-Ala2, MePhe4, Gly-ol5]enkephalin (DAGO) or [3H][D-Thr2,Leu5]enkephalyl-Thr (DTLET). Both peptides exhibited similar diffusion kinetics in the brain and 30-40% of [3H]DAGO or [3H]DTLET was shown to be present in the tissue 15 min after injection when maximal binding was observed. The specific binding of both agonists, defined as the fraction of the radioactivity bound to brain membranes which was displaced by 10 nmol of cold ligand, was reversible, saturable and displayed a pharmacological profile similar to that found in in vitro experiments. At doses producing a similar analgesic effect in the hot-plate test in mice, DTLET occupied 64% of delta sites and DAGO 15% of mu sites. However, because of the residual cross-reactivity of DTLET for mu sites, it appeared that both ligands occupied a similar number of mu receptors at their ED50 values, thus supporting a preferential involvement of mu opioid binding sites in the supraspinal pain control. [Met5]enkephalin inhibited the in vivo binding of both agonists only when the peptide was protected from degradation by the co-administration of a mixed inhibitor of enkephalin degrading enzymes RB38A (N[3(R)(hydroxyaminocarbonyl)-2-benzyl-1-oxopropyl]- L-phenylalanine). Unlike thiorphan, 5 nmol RB38A alone was able to inhibit [3H]DAGO binding by 60%. This result is the first direct demonstration of the existence of an in vivo tonic control of mu opioid receptor occupation by endogenous opioid peptides.     

Spectrum of cerebrospinal fluid findings in various stages of human immunodeficiency virus infection

This report summarizes the results of neurologic and cerebrospinal fluid (CSF) study findings in over 400 of the 649 human immunodeficiency virus-infected US Air Force personnel, evaluated as of Dec 31, 1987. Eighty percent of these patients were entirely asymptomatic and immunologically normal, 13% had low T-helper lymphocyte counts and/or cutaneous anergy, and only 7% had opportunistic infection. Sixty-three percent of all patients had some CSF abnormality. Sixty percent of the asymptomatic group had at least one abnormal result, over 25% had three or four CSF abnormalities, and over 7% had five or six abnormal values. When patients with evidence of blood-brain barrier leak were excluded, significant differences were seen between disease groups with regard to CSF glucose, CSF IgG levels, and CSF IgG synthesis. No human immunodeficiency virus-related central nervous system abnormalities were found on neurologic examination in immunologically intact asymptomatic patients regardless of CSF findings. No clear-cut predictor of impending central nervous system complications has, as yet, been identified from the CSF parameters studied.     

Absolute and comparative risk perceptions as predictors of cancer worry: moderating effects of gender and psychological distress

Risk perceptions for cancer measured on absolute scales (e.g., "What is the likelihood that you will get cancer?") and on comparative scales (e.g., "How does your risk compare with that of someone similar to you?") are independently associated with worry about cancer. We examined this finding in a large sample across several types of cancer, and explored whether these relationships are moderated by three clinically relevant variables-gender, levels of psychological distress, and cancer experience. Participants were respondents in a national survey who reported risk perceptions and worry regarding colon cancer (923 men, 1,532 women), breast cancer (2,154 women), and prostate cancer (860 men), and completed a validated measure of psychological distress. Analyses showed that absolute and comparative risk perceptions were independent predictors of worry across all cancer sites, but that absolute risk perceptions were significantly more predictive than comparative risk perceptions of worry for women (but not men). Among people who were more highly distressed, comparative risk perceptions were the only significant predictor of worry. Absolute risk and comparative risk were equally predictive of cancer worry among people who previously had been diagnosed with cancer. These findings imply that interventions highlighting the communication of comparative risk information may be differentially effective depending on the audience.