Neural correlates of novelty detection in pulse-type weakly electric fish

Evoked potentials (EPs) and single unit recordings from various electrosensory-processing regions of several pulse-type gymnotiform species were made to investigate neural activity patterns that could be associated with novelty detection. Whereas the electrosensory afferents and cells in the ELL exhibited only minor changes in response size as stimuli were presented less frequently (novel stimuli), most units studied in the torus semicircularis (TS) showed very strong, increased responsiveness to stimuli presented less frequently relative to stimuli presented persistently (at every EOD event. The responses of the TS were graded with respect to stimulus frequency. The discrimination between novel and persistent stimuli by the TS occurred with stimuli presented transversely or longitudinally with respect to the fish's long axis, and regardless of the timing of the stimulus with respect to the fish's pacemaker-related signal (PS). When electrosensory novelties were presented persistently the responses of the TS rapidly habituated. This may indicate that activity in this region of the TS is novelty related. This novelty-related activity in the TS can be correlated with certain aspects of the fish's behavior, i.e., EOD interval length during a behavioral novelty response. However, TS activity may continue to indicate the occurrence of electrosensory novelties after the behavior has habituated. It is suggested that the novelty-related activity of the TS of these fish is necessary, but not sufficient, for the production of electrosensory novelty-induced behavioral responses. Lesions of the region of the TS containing the rapidly-habituating neurons abolished the electrosensory novelty response, but not that resulting from visual and auditory stimulation.     

Immunocytochemistry and laser capture microdissection for real-time quantitative PCR identify hindbrain neurons activated by interaction between leptin and cholecystokinin.

Current evidence suggests that leptin reduces food intake in part by enhancing the hindbrain neuronal response to meal-related gastrointestinal signals, including cholecystokinin (CCK), but the phenotypes of the relevant cells are not known. To identify neurons that participate in this interaction in the rat nucleus of the solitary tract (NTS), we induced c-Fos gene expression in NTS neurons with leptin and CCK. We focused on NTS catecholamine neurons because these cells have been implicated in the feeding response to CCK. Hindbrain sections from rats that received CCK with or without leptin pretreatment were immunostained for c-Fos and tyrosine hydroxylase (TH) by a double immunofluorescence procedure. Leptin pretreatment increased the number of NTS cells expressing c-Fos-like immunoreactivity (cFLI) 3-fold relative to CCK alone, but the number of TH-positive cells with cFLI was increased 6-fold. Next, cells detected by immunofluorescence for TH were collected by laser capture microdissection and pooled for real-time quantitative PCR of c-Fos mRNA. Here, neither le0ptin nor CCK alone affected the relative amount of mRNA in the TH cell-enriched samples, but leptin plus CCK substantially increased c-Fos mRNA content. These histochemical findings identify hindbrain catecholamine cells as potential mediators of the interaction between leptin and CCK.     

MicroRNA loci support conspecificity of Gyrodactylus salaris and Gyrodactylus thymalli (Platyhelminthes: Monogenea)

The monogenean flatworm Gyrodactylus salaris is a serious threat to wild and farmed Atlantic salmon stocks in Norway. Morphologically, the closely related but harmless Gyrodactylus thymalli on grayling can hardly be distinguished from G. salaris. Until now, molecular approaches could not resolve unambiguously whether G. salaris and G. thymalli represent just one polytypic species, two polytypic species or a complex of more than two species. In the first known genome-wide analysis utilizing 37 conserved microRNA loci, the genetic differentiation of seven populations of G. salaris and G. thymalli was assessed. The concatenated alignment spanned 21,742 bp including 62 variable positions. A neighbor-joining cluster analysis did not support any host-based or mitochondrial haplotype-based grouping of strains. We conclude that a two species concept for G. salaris and G. thymalli does not reflect meaningful biological entities. Instead, G. salaris and G. thymalli are just one species comprising several pathogenic and non-pathogenic strains on various primary hosts. Following the International Code for Zoological Nomenclature, G. salaris Malmberg, 1957 is the valid species name with G. thymalli ?itňan, 1960 becoming the junior synonym. Accordingly, the range of G. salaris is significantly increased, given that formerly G. salaris-free countries such as e.g., Great Britain are now within the species’ natural range. The synonymization of G. salaris and G. thymalli implies severe challenges to current disease management routines, which assume that G. salaris and G. thymalli are readily distinguishable. Protocols for reliable identification of pathogenic and non-pathogenic strains of G. salaris need to be developed.     

A method for enumeration ot T and B lymphocytes in tissues.

A method for the identification of T and B lymphocytes in tissue specimens is described. A sonication technique results in viable relatively pure lymphocyte populations which are easily classified by their surface markers. This readily reproducible method can become a standard laboratory procedure in the evaluation of disease states which require such information related to the classification of lymphocyte cell origin.