Disruption of Lateral Efferent Pathways: Functional Changes in Auditory Evoked Responses

The functional consequences of selectively lesioning the lateral olivocochlear efferent system in guinea pigs were studied. The lateral superior olive (LSO) contains the cell bodies of lateral olivocochlear neurons. Melittin, a cytotoxic chemical, was injected into the brain stem using stereotaxic coordinates and near-field evoked potentials to target the LSO. Brain stem histology revealed discrete damage to the LSO following the injections. Functional consequences of this damage were reflected in depressed amplitude of the compound action potential of the eighth nerve (CAP) following the lesion. Threshold sensitivity and N1 latencies were relatively unchanged. Onset adaptation of the cubic distortion product otoacoustic emission (DPOAE) was evident, suggesting a reasonably intact medial efferent system. The present results provide the first report of functional changes induced by isolated manipulation of the lateral efferent pathway. They also confirm the suggestion that changes in single-unit auditory nerve activity after cutting the olivocochlear bundle are probably a consequence of disrupting the more lateral of the two olivocochlear efferent pathways.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41379/1/10162_2002_Article_3018.pd

Suppressor of Fused Regulates Gli Activity through a Dual Binding Mechanism

The Hedgehog pathway drives proliferation and differentiation by activating the Gli/Ci family of zinc finger transcription factors. Gli/Ci proteins form Hedgehog signaling complexes with other signaling components, including the kinesin-like protein Costal-2, the serine-threonine kinase Fused, and Suppressor of Fused [Su(fu)]. In these complexes Gli/Ci proteins are regulated by cytoplasmic sequestration, phosphorylation, and proteolysis. Here we characterize structural and functional determinants of Su(fu) required for Gli regulation and show that Su(fu) contains at least two distinct domains: a highly conserved carboxy-terminal region required for binding to the amino-terminal ends of the Gli proteins and a unique amino-terminal domain that binds the carboxy-terminal tail of Gli1. While each domain is capable of binding to different Gli1 regions independently, interactions between Su(fu) and Gli1 at both sites are required for cytoplasmic tethering and repression of Gli1. Furthermore, we have solved the crystal structure of the amino-terminal domain of human Su(fu)(27-268) at 2.65 Å resolution. This domain forms a concave pocket with a prominent acidic patch. Mutation at Asp(159) in the acidic patch disrupts Gli1 tethering and repression while not strongly disrupting binding, indicating that the amino-terminal domain of Su(fu) likely impacts Gli binding through a mechanism distinct from that for tethering and repression. These studies provide a structural basis for understanding the function of Su(fu)

ICG-mediated photodisruption of the inner limiting membrane enhances retinal drug delivery

Many groundbreaking therapies for the treatment of blindness require delivery of biologics or cells to the inner retina by intravitreal injection. Unfortunately, the advancement of these therapies is greatly hampered by de-livery difficulties where obstruction of the therapeutics at the inner limiting membrane (ILM) represents the dominant bottleneck. In this proof-of-principle study, we explore an innovative light-based approach to locally ablate the ILM in a minimally invasive and highly controlled manner, thus making the ILM more permeable for therapeutics. More specifically, we demonstrate that pulsed laser irradiation of ILM-bound indocyanine green (ICG), a clinically applied ILM dye, results in the formation of vapor nanobubbles which can disrupt the bovine ILM as well as the extraordinary thick human ILM. We have observed that this photodisruption allows for highly successful retinal delivery of model nanoparticles which are otherwise blocked by the intact ILM. Strikingly, this treatment is furthermore able of enhancing the efficacy of mRNA-loaded lipid nanoparticles within the bovine retina by a factor of 5. In conclusion, this study provides evidence for a light-based approach to overcome the ILM which has the potential to improve the efficacy of all retinal therapies hampered by this delivery barrier