在双脉冲光刺激下瞳孔系统的采样控制特性

本文用实验揭示了瞳孔对光动态反应具有采样控制特性。实验中采用各种不同时间间隔的双脉冲光,以开环的方式(Maxwellian View)刺激瞳孔,当双脉冲之间间隔较长时,瞳孔反应相当于对双脉冲光的两次脉冲分别产生瞬态收缩;当双脉冲时间间隔短于0.6s 时,其反应就成了一次瞬态收缩,与单个光脉冲所引起的瞳孔反应一样。同—受试者的多次实验结果相同,不同受试者所得结果也基本一致。故瞳孔对脉冲刺激光引起反应后,必须至少约隔0.6s 才能对另一次脉冲光产生反应,这就说明了瞳孔动态反应具有离散的采样控制特性。实验还进一步证明,瞳孔系统的控制机制是双重模式的控制:不同的刺激条件下,瞳孔反应可呈现为瞬态反应(AC)或持续反应(DC),瞬态反应的 AC 通道为离散的采样控制,持续反应的 DC 通道为连续控制。     

左旋四氢巴马汀加强电针对兔大脑皮层牙髓诱发电位的...

Cortical potentials evoked by stimulation of the contralateral tooth-pulp were recorded epidurally from the SI cortex of rabbits anesthetized with urethane and chloralose. It was found that nociceptive components of the evoked potential consisted of P1 and P2 wavelets with a relative stable peak latency of 22.5 +/- 1.2 ms and 66.1 +/- 1.9 ms respectively. Higher intensity of tooth pulp stimulation was required for appearance of P2 than P1. Diazepam, a non-analgesic sedative, reduced P1 but not P2 amplitude. On the contrary, dolantin, an analgesic, suppressed P2 but showed no significant influence on P1. The results suggest that P2, but not P1 might be related to pain. The effects of l-tetrahydropalmatine (1-THP) and electroacupuncture on P2 were observed on 12 animals. The results showed that both iv l-THP 8mg/kg and electroacupuncture brought forth a decrease in P2 amplitude by 40.3 +/- 14% and 59.3 +/- 10% respectively, while electroacupuncture combined with l-THP produce a further decrease in P2 amplitude by 92.8 +/- 7%. Furthermore, the inhibitory periods of P2 amplitude were significantly prolonged after electroacupuncture combined with l-THP. The results indicated that l-THP enhanced the suppression of P2 by electroacupuncture.     

A refined linkage map for DNA markers around the pericentromeric region of chromosome 10

A refined genetic linkage map for the pericentromeric region of human chromosome 10 has been constructed from data on 12 distinct polymorphic DNA loci as well as the locus for multiple endocrine neoplasia type 2A (MEN 2A), a dominantly inherited cancer syndrome. The map extends from D10S24 (at 10p13-p12.2) to D10S3 (at 10q21-q23) and is about 70 cM long. Overall, higher female than male recombination frequencies were observed for this region, with the most remarkable female excess in the immediate vicinity of the centromere, as previously reported. Most of the DNA markers in this map are highly informative for linkage and the majority of the interlocus intervals are no more than 6 cM apart. Thus this map should provide a fine framework for future efforts in more detailed mapping studies around the centromeric area. A set of ordered cross-overs identified in this work is a valuable resource for rapidly and accurately localizing new DNA clones isolated from the pericentromeric region.     

Hormonal regulation of gonadotropin-releasing hormone receptors and messenger RNA activity in ovine pituitary culture

Previous studies demonstrate that gonadotroph responsiveness to GnRH, GnRH binding, and the apparent number of GnRH receptors are all increased by 17 beta-estradiol (E) or inhibin (IN) in ovine pituitary cultures. Progesterone (P) attenuates these effects. To explore differences between the effects of IN and E on GnRH binding, a detailed time-course study was performed. The results indicate that after 48 h, IN had a greater effect on binding of a GnRH agonist (5-fold increase) than E (3-fold increase), but was slower to act initially. A combined treatment of IN and E gave a partially additive effect at 48 h (6.5-fold increase). The mechanism of receptor regulation in this system is not known, but could involve synthesis, recycling, or modification of GnRH receptors. To investigate the contribution of altered receptor biosynthesis to the regulation of receptor levels, a functional Xenopus oocyte-based assay for GnRH receptor mRNA activity was employed. After 48 h of treatment, IN or E each led to a 7- to 8-fold increase in GnRH receptor mRNA activity. Treatment with both hormones led to a 19-fold increase. The increase in mRNA activity induced by either hormone was greatly attenuated by P. Modulation of GnRH receptor mRNA levels suggests that IN, E, and P regulate responsiveness to GnRH in the ovine pituitary at least in part by altering de novo synthesis of GnRH receptors. The differing time courses of action, as assayed by GnRH binding, and the additivity of effects at the mRNA level suggest that IN and E alter mRNA levels via different mechanisms.     

DXS28 (C7) maps centromeric to DXS68 (L1-4) and DXS67 (B24) by deletion analysis

Complex glycerol kinase deficiency (CGKD) is a contiguous gene syndrome consisting of glycerol kinase deficiency together with Duchenne muscular dystrophy (DMD), congenital adrenal hypoplasia, and/or Aland Island eye disease. Deletion mapping of genomic DNA from patients with CGKD was carried out and allowed definitive ordering of loci DXS28 (C7), DXS68 (L1-4), and DXS67 (B24). Most reports have placed DXS68 centromeric to DXS28 and DXS67 on the basis of the initial mapping of the Iowa patient 3, but others have presented evidence consistent with the placement of DXS28 telomeric to DXS68 and DXS67. Through the use of DNA from CGKD patients with a variety of genomic deletions, this controversy is resolved and the order Xcen...DMD-DXS28-DXS68-DXS67...pter is definitively demonstrated.     

Sex determination in the dioecious Melandrium

Summary Melandrium album (2n=24), a dioecious species with heteromorphic sex chromosomes (XY, males and XX, females), has a strong genetic commitment for sex determination. We report here a procedure for obtaining haploid plants from cultured anthers and show that genotype, pollen stage, cold treatment and certain culture media components are essential for a reproducible yield of embryos. Our procedure increased the number of responsive anthers and not the number of responsive microspores per anther. Most likely, our experimental system allows the recovery of competent microspores, and this on a medium containing either an auxin or a cytokinin. All of the 36 anther-derived plants tested expressed a female phenotypic sex instead of the theoretical one male one female ratio. When analysed cytologically, the plants exhibited the corresponding female genetic sex (one or two X chromosomes).     

Corrected sequence of the mannitol (mtl) operon in Escherichia coli

The previously published sequences of the operator-promoter region of the mannitol operon of Escherichia coli and of the mtlD gene have been found to contain a number of errors. The major conclusions reported previously were correct, but additionally it is now clear that a C-terminal portion of mannitol-1-phosphate dehydrogenase (the mtlD gene product) exhibits significant sequence identity with an amino-terminal region of human liver fructose-6-phosphate-2-kinase:fructose-2,6-bisphosphatase.     

Regulation of bacterial physiological processes by three types of protein phosphorylating systems

A single type of protein-phosphorylating system, the ATP-dependent protein kinases, is employed in the regulation of a variety of cellular physiological processes in eukaryotes. By contrast, recent work with bacteria has revealed that three types of protein-phosphorylating systems are involved in regulation: (1) the classical protein kinases, (2) the newly discovered sensor-kinase/response-regulator systems, and (3) the multifaceted phosphoenolpyruvate-dependent phosphotransferase system. Physiological and mechanistic aspects of these three evolutionarily distinct systems are discussed.