Coordination of distinct but interacting rhythmic motor programs by a modulatory projection neuron using different co-transmitters in different ganglia.

While many neurons are known to contain multiple neurotransmitters, the specific roles played by each co-transmitter within a neuron are often poorly understood. Here, we investigated the roles of the co-transmitters of the pyloric suppressor (PS) neurons, which are located in the stomatogastric nervous system (STNS) of the lobster Homarus americanus. The PS neurons are known to contain histamine; using RT-PCR, we identified a second co-transmitter as the FMRFamide-like peptide crustacean myosuppressin (Crust-MS). The modulatory effects of Crust-MS application on the gastric mill and pyloric patterns, generated in the stomatogastric ganglion (STG), closely resembled those recorded following extracellular PS neuron stimulation. To determine whether histamine plays a role in mediating the effects of the PS neurons in the STG, we bath-applied histamine receptor antagonists to the ganglion. In the presence of the antagonists, the histamine response was blocked, but Crust-MS application and PS stimulation continued to modulate the gastric and pyloric patterns, suggesting that PS effects in the STG are mediated largely by Crust-MS. PS neuron stimulation also excited the oesophageal rhythm, produced in the commissural ganglia (CoGs) of the STNS. Application of histamine, but not Crust-MS, to the CoGs mimicked this effect. Histamine receptor antagonists blocked the ability of both histamine and PS stimulation to excite the oesophageal rhythm, providing strong evidence that the PS neurons use histamine in the CoGs to exert their effects. Overall, our data suggest that the PS neurons differentially utilize their co-transmitters in spatially distinct locations to coordinate the activity of three independent networks.

Predicting the location of human perirhinal cortex, Brodmann's area 35, from MRI.

The perirhinal cortex (Brodmann's area 35) is a multimodal area that is important for normal memory function. Specifically, perirhinal cortex is involved in the detection of novel objects and manifests neurofibrillary tangles in Alzheimer's disease very early in disease progression. We scanned ex vivo brain hemispheres at standard resolution (1 mm × 1 mm × 1 mm) to construct pial/white matter surfaces in FreeSurfer and scanned again at high resolution (120 µm × 120 µm × 120 µm) to determine cortical architectural boundaries. After labeling perirhinal area 35 in the high resolution images, we mapped the high resolution labels to the surface models to localize area 35 in fourteen cases. We validated the area boundaries determined using histological Nissl staining. To test the accuracy of the probabilistic mapping, we measured the Hausdorff distance between the predicted and true labels and found that the median Hausdorff distance was 4.0mm for the left hemispheres (n=7) and 3.2mm for the right hemispheres (n=7) across subjects. To show the utility of perirhinal localization, we mapped our labels to a subset of the Alzheimer's Disease Neuroimaging Initiative dataset and found decreased cortical thickness measures in mild cognitive impairment and Alzheimer's disease compared to controls in the predicted perirhinal area 35. Our ex vivo probabilistic mapping of the perirhinal cortex provides histologically validated, automated and accurate labeling of architectonic regions in the medial temporal lobe, and facilitates the analysis of atrophic changes in a large dataset for earlier detection and diagnosis.

Entorhinal verrucae geometry is coincident and correlates with Alzheimer's lesions: a combined neuropathology and high-resolution ex vivo MRI analysis.

Entorhinal cortex displays a distinctive organization in layer II and forms small elevations on its surface called entorhinal verrucae. In Alzheimer's disease, the verrucae disappear due to neurofibrillary tangle formation and neuronal death. Isosurface models were reconstructed from high-resolution ex vivo MRI volumes scanned at 7.0 T and individual verruca were measured quantitatively for height, width, volume, and surface area on control and mild Alzheimer's cases. Mean verruca height was 0.13 ± 0.04 mm for our cognitively normal (controls) sample set whereas for mild AD samples mean height was 0.11 mm ± 0.05 mm (p < 0.001) in entorhinal cortex (n = 10 cases). These quantitative methods were validated by a significant correlation of verrucae height and volume with qualitative verrucae ratings (n = 36 cases). Entorhinal surfaces were significantly different from other cortical heights such as, cingulate, frontal, occipital, parietal and temporal cortices. Colocalization of verrucae with entorhinal islands was confirmed in ex vivo MRI and, moreover, verrucae ratings were negatively correlated to Braak and Braak pathological stage. This study characterizes novel methods to measure individual entorhinal verruca size, and shows that verrucae size correlates to Alzheimer's pathology. Taken together, these results suggest that verrucae may have the potential to serve as an early and specific morphological marker for mild cognitive impairment and Alzheimer's disease.

Direct visualization of the perforant pathway in the human brain with ex vivo diffusion tensor imaging.

Ex vivo magnetic resonance imaging yields high resolution images that reveal detailed cerebral anatomy and explicit cytoarchitecture in the cerebral cortex, subcortical structures, and white matter in the human brain. Our data illustrate neuroanatomical correlates of limbic circuitry with high resolution images at high field. In this report, we have studied ex vivo medial temporal lobe samples in high resolution structural MRI and high resolution diffusion MRI. Structural and diffusion MRIs were registered to each other and to histological sections stained for myelin for validation of the perforant pathway. We demonstrate probability maps and fiber tracking from diffusion tensor data that allows the direct visualization of the perforant pathway. Although it is not possible to validate the DTI data with invasive measures, results described here provide an additional line of evidence of the perforant pathway trajectory in the human brain and that the perforant pathway may cross the hippocampal sulcus.

SIFamide peptides in clawed lobsters and freshwater crayfish (Crustacea, Decapoda, Astacidea): a combined molecular, mass spectrometric and electrophysiological investigation.

Recently, we identified the peptide VYRKPPFNGSIFamide (Val(1)-SIFamide) in the stomatogastric nervous system (STNS) of the American lobster Homarus americanus using matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry (MALDI-FTMS). Given that H. americanus is the only species thus far shown to possess this peptide, and that a second SIFamide isoform, Gly(1)-SIFamide, is broadly conserved in other decapods, including another astacidean, the crayfish Procambarus clarkii, we became interested both in confirming our identification of Val(1)-SIFamide via molecular methods and in determining the extent to which this isoform is conserved within other members of the infraorder Astacidea. Here, we present the identification and characterization of an H. americanus prepro-SIFamide cDNA that encodes the Val(1) isoform. Moreover, we demonstrate via MALDI-FTMS the presence of Val(1)-SIFamide in a second Homarus species, Homarus gammarus. In contrast, only the Gly(1) isoform was detected in the other astacideans investigated, including the lobster Nephrops norvegicus, a member of the same family as Homarus, and the crayfish Cherax quadricarinatus, P. clarkii and Pacifastacus leniusculus, which represent members of each of the extant families of freshwater astacideans. These results suggest that Val(1)-SIFamide may be a genus (Homarus)-specific isoform. Interestingly, both Val(1)- and Gly(1)-SIFamide possess an internal dibasic site, Arg(3)-Lys(4), raising the possibility of the ubiquitously conserved isoform PPFNGSIFamide. However, this octapeptide was not detected via MALDI-FTMS in any of the investigated species, and when applied to the isolated STNS of H. americanus possessed little bioactivity relative to the full-length Val(1) isoform. Thus, it appears that the dodeca-variants Val(1)- and Gly(1)-SIFamide are the sole bioactive isoforms of this peptide family in clawed lobsters and freshwater crayfish.