Biomedical subjects

D L Polk

Publications and source records attributed to D L Polk.

3 recordsLinked to original sources

PubMed1997

Delta-1 is a regulator of neurogenesis in the vertebrate retina.

In the retina, cell fate determination is thought to be regulated by a series of local cell-cell interactions. Evidence suggests that retinal precursors utilize Notch-mediated intercellular signaling to regulate their fates. However, the identity of the endogenous ligand and its role in the Notch-signaling pathway is not well understood. We have identified C-Delta-1 as the putative endogenous ligand for Notch, in the developing chick retina. C-Delta-1 is coexpressed spatially and temporally with C-Notch-1 and their expression is associated with the temporal aspects of cell birth in the developing retina. This suggests that Delta-Notch signaling is utilized to maintain progenitors in an uncommitted state and that a subtle fluctuation in this signaling helps to sort out competent cells during successive cell-fate determination. We have tested the latter possibility in the specification of the ganglion cells. In early stages of retinal development when ganglion cells are the predominant cells born, decreasing C-Delta-1 expression with antisense oligonucleotides increases the proportion of RA4 antigen-expressing ganglion cells which are recruited predominantly in the periphery. Conversely, use of exogenous Drosophila Delta leads to a decrease in the RA4 antigen-expressing ganglion cells. Our results suggest that C-Delta-1 activation of the Notch pathway regulates the specification of retinal neurons in general and of ganglion cells in particular.

Animals↗

PubMed1994

Percutaneous discectomy.

1. In patients with symptomatic lumbar disc herniations contained within the interspace, the percutaneous automated discectomy is a reasonable option to open operative procedures. The results appear to be comparable in either case. 2. The procedure is done under local anesthesia, thus avoiding a general anesthetic, and has a shorter and less painful postoperative recovery period. 3. The complications and morbidity from the percutaneous technique appear to be significantly less than the open surgical techniques. 4. Proper selection of surgical candidates is extremely important in any surgical approach to the treatment of lumbar degenerative disc disease. Patients who have had a prior lumbar surgery (or "redo" cases) do not appear to do well with percutaneous discectomy. 5. As demonstrated in many other studies, the workers' compensation/liability patients did not fare as well as "standard" patients. 6. Since the original study, we have performed an additional 50 automated percutaneous discectomies and 52 laser discectomies (totaling 212 cases in all). 7. Although the sample size is small, and our experience is limited, patients treated with laser discectomy appear to be experiencing a higher percentage of favorable results than patients treated with automated percutaneous discectomy.

Diskectomy, Percutaneous↗

PubMedDate not supplied

Effects of sodium salicylate, aminopyrine and chlorpromazine on behavioral temperature regulation.

To characterize drug actions on thermoregulatory processes it is necessary to know whether compounds which alter body temperature also cause changes in thermoregulatory motivation. In the present experiments the effects of sodium salicylate, aminopyrine and chlorpromazine (CPZ) on rectal temperature (Tre) and behavior were measured in rats trained to escape heat and obtain cooling. All three drugs produced hypothermia in a 23 degree C environment but the effects upon behavior suggest that the compounds have different actions. Sodium salicylate (60-300 mg/kg) increased the amount of time spent responding to escape heat and obtain cooling so that Tre was held below control levels. Aminopyrine (12.5-75 mg/kg) did not alter thermoregulatory motivation even though it caused marked hypothemia. The time spent responding decreased after CPZ (2 and 3 mg/kg) so that drug-induced hypothermias were compensated. The results suggest that sodium salicylate influences the central mechanisms of physiological and behavioral temperature control whereas CPZ affects either peripheral thermoeffectors or central effector pathways without disrupting thermoregulatory motivation. Aminopyrine is presumed to act on central temperature controls to lower body temperature and, at the same time, to reduce the significance of the low body temperature to behavior.

Aminopyrine↗