Interstitial 3-Methoxytyramine Reflects Striatal Dopamine Release: An In Vivo Microdialysis Study

Previous ex vivo studies have provided indirect evidence that the dopamine (DA) metabolite 3-methoxytyramine (3-MT) may be a useful index of DA release in vivo. In the present study, in vivo microdialysis was utilized to assess directly the relationship between extracellular DA and 3-MT in the striatum of rats following a variety of pharmacological manipulations. Apomorphine, a DA receptor agonist, produced a rapid, transient decrease in both DA and 3-MT. Conversely, the DA receptor antagonist haloperidol produced a concomitant increase in extracellular DA and 3-MT. Increases in DA and 3-MT were also noted following the administration of the DA uptake inhibitor, bupropion. Local application of tetrodotoxin resulted in the complete elimination of measurable amounts of DA and 3-MT in the dialysate, gamma-Butyrolactone also greatly decreased DA and 3-MT. Finally, d-amphetamine produced a large increase in DA and 3-MT in animals that had been treated previously with gamma-butyrolactone. The Pearson correlation coefficients for DA and 3-MT following these manipulations ranged from 0.87 to 0.97. These data indicate that interstitial 3-MT is an accurate index of DA release. However, when compared with previous ex vivo findings, the present results also suggest that changes in tissue concentrations of 3-MT may not reliably reflect DA release following certain pharmacological manipulations.     

Increased Axonal Ribosome Numbers Is an Early Event in the Pathogenesis of Amyotrophic Lateral Sclerosis

Myelinating glia cells support axon survival and functions through mechanisms independent of myelination, and their dysfunction leads to axonal degeneration in several diseases. In amyotrophic lateral sclerosis (ALS), spinal motor neurons undergo retrograde degeneration, and slowing of axonal transport is an early event that in ALS mutant mice occurs well before motor neuron degeneration. Interestingly, in familial forms of ALS, Schwann cells have been proposed to slow disease progression. We demonstrated previously that Schwann cells transfer polyribosomes to diseased and regenerating axons, a possible rescue mechanism for disease-induced reductions in axonal proteins. Here, we investigated whether elevated levels of axonal ribosomes are also found in ALS, by analysis of a superoxide dismutase 1 (SOD1)^G93A mouse model for human familial ALS and a patient suffering from sporadic ALS. In both cases, we found that the disorder was associated with an increase in the population of axonal ribosomes in myelinated axons. Importantly, in SOD1^G93A mice, the appearance of axonal ribosomes preceded the manifestation of behavioral symptoms, indicating that upregulation of axonal ribosomes occurs early in the pathogenesis of ALS. In line with our previous studies, electron microscopy analysis showed that Schwann cells might serve as a source of axonal ribosomes in the disease-compromised axons. The early appearance of axonal ribosomes indicates an involvement of Schwann cells early in ALS neuropathology, and may serve as an early marker for disease-affected axons, not only in ALS, but also for other central and peripheral neurodegenerative disorders.     

Sawfishes and Other Elasmobranch Assemblages from the Mio-Pliocene of the South Caribbean (Urumaco Sequence,Northwestern Venezuela)

The Urumaco stratigraphic sequence, western Venezuela, preserves a variety of paleoenvironments that include terrestrial, riverine, lacustrine and marine facies. A wide range of fossil vertebrates associated with these facies supports the hypothesis of an estuary in that geographic area connected with a hydrographic system that flowed from western Amazonia up to the Proto-Caribbean Sea during the Miocene. Here the elasmobranch assemblages of the middle Miocene to middle Pliocene section of the Urumaco sequence (Socorro, Urumaco and Codore formations) are described. Based on new findings, we document at least 21 taxa of the Lamniformes, Carcharhiniformes, Myliobatiformes and Rajiformes, and describe a new carcharhiniform species (†Carcharhinus caquetius sp. nov.). Moreover, the Urumaco Formation has a high number of well-preserved fossil Pristis rostra, for which we provide a detailed taxonomic revision, and referral in the context of the global Miocene record of Pristis as well as extant species. Using the habitat preference of the living representatives, we hypothesize that the fossil chondrichthyan assemblages from the Urumaco sequence are evidence for marine shallow waters and estuarine habitats.     

Invariant chain transmembrane domain trimerization: a step in MHC class II assembly

The transmembrane (TM) domain of the major histocompatibility complex (MHC) class II-associated invariant chain (Ii) has long been implicated in both correct folding and function of the MHC class II complex. To function correctly, Ii must form a trimer, and the TM domain is one of the domains thought to stabilize the trimeric state. Specific mutations in the TM domain have been shown previously to disrupt MHC class II functions such as mature complex formation and antigen presentation, possibly due to disruption of Ii TM helix-helix interactions. Although this hypothesis has been reported several times in the literature, thus far no experimental measurements have been made to explore the relationship between TM domain structure and TM mutations that affect Ii function. We have applied biophysical and computational methods to study the folding and assembly of the Ii TM domain in isolation and find that the TM domain strongly self-associates. According to analytical ultracentrifugation analyses, the primary oligomeric state for this TM domain is a strongly associated trimer with a dissociation constant of approximately 120 nM in DPC micelles. We have also examined the effect of functionally important mutations of glutamine and threonine residues in the TM domain on its structure, providing results that now link the disruption of TM helix interactions to previously reported losses of Ii function.