Crist Cook

Sonic hedgehog signaling regulates the expression of insulin-like growth factor binding protein-6 during fetal prostate development.

At the onset of ductal morphogenesis in the developing prostate, Shh expression condenses at evaginations of urogenital sinus epithelium and activates Gli transcription factors in the adjacent mesenchyme. Abrogation of Hedgehog signaling disrupts proper prostatic budding, ductal growth, and branching. We now show that Hedgehog signaling regulates the expression of insulin‐like growth factor binding protein‐6 (Igfbp‐6) in the developing mouse prostate. Igfbp‐6 is a secreted factor that specifically binds insulin‐like growth factor‐II (IGF‐II), prevents its binding to the IGF‐I receptor, and is thought to regulate the activity of IGF‐II in growth and differentiation. Igfbp‐6 is expressed in both the developing and adult prostate. In the urogenital sinus, Igfbp‐6 mRNA colocalized with Ptc1 and Gli1 mRNA in the mesenchyme, while Igfbp‐6 protein was found in both the mesenchymal and epithelial layers. Exogenous Shh peptide induced expression of Igfbp‐6 in the developing prostate while the chemical inhibitor of Hedgehog signaling, cyclopamine, reduced its expression. These studies show that Igfbp‐6 is an actual target of Shh signaling in the urogenital sinus and provide the first evidence for a linkage between the Hedgehog and IGF signaling pathways in prostate development. Developmental Dynamics 233:829–836, 2005.

Muscle fiber-type changes induced by botulinum toxin injection in the rat larynx.

This study examined muscle fiber-type alterations after single or multiple botulinum toxin (BT) injections to better understand possible morphologic changes induced by therapeutic BT injections in patients with spasmodic dysphonia. Muscle fiber staining was accomplished in rat intrinsic laryngeal muscles with antibodies to specific myosin heavy chains. Results indicated that the typical baseline distributions of type II muscle fibers (ie, types IIa, IIb, IIx, and IIL) were altered by BT injection, while no change was observed in type I fibers. Embryonic fibers were observed only along the needle insertion site at 7 days post BT injection. Although inferences from these animal data to human neuromuscular function must be made with caution, our findings provide insight into the possible cellular and molecular changes characterizing BT-injected muscles.

The nuclear/mitotic apparatus protein NuMA is a component of the somatodendritic microtubule arrays of the neuron

Neurons are terminally post-mitotic cells that utilize their microrubule arrays for the growth and maintenance of axons and dendrites rather than for the formation of mitotic spindles. Recent studies from our laboratory suggest that the mechanisms that organize the axonal and dendritic microtubule arrays may be variations on the same mechanisms that organize the mitotic spindle in dividing cells. In particular, we have identified molecular motor proteins that serve analogous functions in the establishment of these seemingly very different microtubule arrays. In the present study, we have sought to determine whether a non-motor protein termed NuMA is also a component of both systems. NuMA is a ~230 kDa structural protein that is present exclusively in the nucleus during interphase. During mitosis, NuMA forms aggregates that interact with microtubules and certain motor proteins. As a result of these interactions, NuMA is thought to draw together the minus-ends of microtubules, thereby helping to organize them into a bipolar spindle. In contrast to mitotic cells, post-mitotic neurons display NuMA both in the nucleus and in the cytoplasm. NuMA appears as multiple small particles within the somatodendritic compartment of the neuron, where its levels increase during early dendritic differentation. A partial but not complete colocalization with minus-ends of microtubules is suggested by the distribution of the particles during development and during drug treatments that alter the microtubule array. These observations provide an initial set of clues regarding a potentially important function of NuMA in the organization of microtubules within the somatodendritic compartment of the neuron.

Increased acute and chronic mitotic activity in rat laryngeal muscles after botulinum toxin injection

Objectives: To characterize the acute and chronic cellular effects of botulinum toxin (BT) injection into rat laryngeal muscles. A complete characterization of these effects is important because patients with focal dystonias of the head and neck are commonly treated with BT injection. Further, potential muscular changes in the larynx must be carefully delineated owing to the critical phonatory and airway protective functions of these muscles. Study Design: The acute and chronic cellular effects of BT injection were studied using 5′‐bromo 2′‐deoxyuridine (BrdU) following single and repeated BT injection into rat laryngeal muscles. BrdU is incorporated into mitotically active nuclei such that changes in cell proliferative behavior following BT injection can be monitored. Results: Increased mitotic activity was detected in the tissue samples studied following BT injection. Differences in the times of the peak distribution of BrdU‐labeled cells in each laryngeal muscle were observed. This may be related to the diffusion effects of BT. Prolonged muscle fiber changes, including splitting, were also observed as the result of repeated BT injection. Conclusions: The results of this study suggest that BT may induce a proliferative response in muscle tissue.

Acute and chronic mitofic activity in rat laryngeal muscles after botulinum toxin injection

recording analysis were performed off-line. The EMG of laryngeal muscle groups demonstrated three categories of activation as they relate to AbdSD speech breaks: delayed activation, premature activation, and sustained activation. Each of these categories, as applied to the laryngeal muscle groups studied, demonstrated subject-unique and intrasubject-consistent coordination and tone modulation. Although the number of subjects studied is small, this study demonstrated how the AbdSD disorder is complex and not a simple overactivation of the posterior cricoarytenoid muscle. Individuals with AbdSD are dissimilar in the expression of this disorder. Effective BoTox therapy for relief of symptomatic AbdSD speech needs to be tailored to the specific hyperactive laryngeal muscle group as dictated by laryngeal EMG.

Muscle fiber-type changes induced by single and repeated botulinum toxin injections in rat larynges

ports have indicated that some patients develop antibodies to BoTox type A such that the injections no longer provide relief of their symptoms. BoTox type F may offer an alternative therapy for those individuals who are immunoresistant to type A. This study proposed to investigate the characteristics of neuromuscular blockade, time course of effect and recovery, and dose-response characteristics of BoTox type F. Eighteen male Sprague-Dawley rats were implanted with a stimulus electrode cuff around the sciatic nerve with recording electrodes placed in the Achilles tendon, the gastrocnemius muscle, and the tibial protuberance. The electrode leads were tunneled subcutaneously to a plug between the scapulae, from which connections to peripheral stimulating and recording equipment were made. This implanted system allowed direct stimulation of the sciatic nerve and recording of EMG activity from the muscle injected with BoTox type F or placebo. After the animals were allowed 1 week to recover from implant surgery, evoked potentials were recorded three times a week for at least 1 month to determine interest variability. Any animal demonstrating greater than 10% variability in recordings in the 2 weeks before injection was replaced. Implanted animals were divided into six groups. The gastrocnemius muscle was injected with a minimal (0.625 unit), very low (1.25 units), low (2.5 units), moderate (5.0 units), or high (10.0 units) dose of BoTox type F. The remaining three animals were injected with an equal volume of saline placebo. After injection, evoked potentials were recorded every 4 hours for the first 3 days and triweekly thereafter until the EMG values recovered maximally and were stable for 1 month. All data were obtained in the awake animal, restrained in a testing chamber, to prevent gross movement from influencing EMG recordings. This study characterized the biologic activity of BoTox type F in a chronically implanted rat model. Evoked EMG data from the experimental animals found that the maximal neuromuscular blockade with type F occurred within 72 hours. Recovery of evoked potentials to preinjection baseline levels was observed within 1 month for all animals. Doserelated differences in blockade and time course for recovery were studied. Evoked potentials from the placebo animals demonstrated no significant change over time. The feasibility of using BoTox type F as a clinical alternative to type A is discussed.