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Background: Feline models of neurologic diseases, such as lysosomal storage diseases, leukodystrophies, Parkinson's disease, stroke and NeuroAIDS, accurately recreate many aspects of human disease allowing for comparative study of neuropathology and the testing of novel therapeutics. Here we describe in vivo visualization of fine structures within the feline brain that were previously only visible post mortem., New Method: 3Tesla MR images were acquired using T1-weighted (T1w) 3D magnetization-prepared rapid gradient echo (MPRAGE) sequence (0.4mm isotropic resolution) and T2-weighted (T2w) turbo spin echo (TSE) images (0.3mm×0.3mm×1mm resolution). Anatomic structures were identified based on feline and canine histology., Results: T2w high resolution MR images with detailed structural identification are provided in transverse, sagittal and dorsal planes. T1w MR images are provided electronically in three dimensions for unrestricted spatial evaluation., Comparison With Existing Methods: Many areas of the feline brain previously unresolvable on MRI are clearly visible in three orientations, including the dentate, interpositus and fastigial cerebellar nuclei, cranial nerves, lateral geniculate nucleus, optic radiation, cochlea, caudal colliculus, temporal lobe, precuneus, spinocerebellar tract, vestibular nuclei, reticular formation, pyramids and rostral and middle cerebral arteries. Additionally, the feline brain is represented in three dimensions for the first time., Conclusions: These data establish normal appearance of detailed anatomical structures of the feline brain, which provide reference when evaluating neurologic disease or testing efficacy of novel therapeutics in animal models., (Published by Elsevier B.V.)

Cholinergic depletion in the medial septum (MS) is associated with impaired hippocampal-dependent learning and memory. Here we investigated whether long term potentiation (LTP) and synaptic currents, mediated by alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the CA1 hippocampal region, are affected following cholinergic lesions of the MS. Stereotaxic intra-medioseptal infusions of a selective immunotoxin, 192-saporin, against cholinergic neurons or sterile saline were made in adult rats. Four days after infusions, hippocampal slices were made and LTP, whole cell, and single channel (AMPA or NMDA receptor) currents were recorded. Results demonstrated impairment in the induction and expression of LTP in lesioned rats. Lesioned rats also showed decreases in synaptic currents from CA1 pyramidal cells and synaptosomal single channels of AMPA and NMDA receptors. Our results suggest that MS cholinergic afferents modulate LTP and glutamatergic currents in the CA1 region of the hippocampus, providing a potential synaptic mechanism for the learning and memory deficits observed in the rodent model of selective MS cholinergic lesioning.

Mammalian olfactory epithelium can withstand the external environment, undergo life-long regeneration, and respond to thousands of odorant stimuli, making it an attractive system for a variety of studies. Previously, we described a long-lived olfactory coculture of olfactory epithelium and bulb tissues and we present here the kinetic properties of that culture system. Neonatal mouse epithelial-bulbar explants were grown for periods as long as 121 days in vitro (DIV), nearly doubling the survival time of our previously longest lived cultures. Cultures at all ages responded to air-borne odorants. The youngest cultures (1-15 DIV) showed shorter half-rise and half-decay times than older cultures (21-121 DIV), and were more variable in their half-decay times. Zinc nanoparticles enhanced electro-olfactogram responses of both younger and older cultures and both groups were immunopositive for olfactory marker protein. The results show that our olfactory culture model can support mature, odorant-responsive olfactory receptor neurons that possess many of the response features of in situ olfactory receptor neurons., (Copyright © 2010 S. Karger AG, Basel.)

Zinc metal nanoparticles in picomolar concentrations strongly enhance odorant responses of olfactory sensory neurons. One- to 2-nm metallic particles contain 40-300 zinc metal atoms, which are not in an ionic state. We exposed rat olfactory epithelium to metal nanoparticles and measured odorant responses by electroolfactogram and whole-cell patch clamp. A small amount of zinc nanoparticles added to an odorant or an extracellular/intracellular particle perfusion strongly increases the odorant response in a dose-dependent manner. Zinc nanoparticles alone produce no odor effects. Copper, gold, or silver nanoparticles do not produce effects similar to those of zinc. If zinc nanoparticles are replaced by Zn(+2) ions in the same concentration range, we observed a reduction of the olfactory receptor neuron odorant response. Based on these observations, we hypothesize that zinc nanoparticles are closely located to the interface between the guanine nucleotide-binding protein and the receptor proteins and are involved in transferring signals in the initial events of olfaction. Our results suggest that zinc metal nanoparticles can be used to enhance and sustain the initial olfactory events.

The canine nasal airway is an impressively complex anatomical structure, having many functional roles. The complicated branching and intricate scrollwork of the nasal conchae provide large surface area for heat, moisture, and odorant transfer. Of the previous anatomical studies of the canine nasal airway, none have included a detailed rendering of the maxilloturbinate and ethmoidal regions of the nose. Here, we present a high-resolution view of the nasal airway of a large dog, using magnetic resonance imaging scans. Representative airway sections are shown, and a three-dimensional surface model of the airway is reconstructed from the image data. The resulting anatomic structure and detailed morphometric data of the airway provide insight into the functional nature of canine olfaction. A complex airway network is revealed, wherein the branched maxilloturbinate and ethmoturbinate scrolls appear structurally distinct. This is quantitatively confirmed by considering the fractal dimension of each airway, which shows that the maxilloturbinate airways are more highly contorted than the ethmoidal airways. Furthermore, surface areas of the maxilloturbinate and ethmoidal airways are shown to be much different, despite having analogous physiological functions. Functionally, the dorsal meatus of the canine nasal airway is shown to be a bypass for odorant-bearing inspired air around the complicated maxilloturbinate during sniffing for olfaction. Finally, nondimensional analysis is used to show that the airflow within both the maxilloturbinate and ethmoturbinate regions must be laminar. This work has direct relevance to biomimetic sniffer design, chemical trace detector development, intranasal drug delivery, and inhalation toxicology., (Copyright 2007 Wiley-Liss, Inc.)

Gross anatomy is time consuming to teach and to learn. Because the process of dissection takes up so much student time, assistance in the form of an in-lab instructional DVD program might improve student performance. The DVD could be viewed with a portable device by individual dissection groups at their tables. Groups could dissect at their own pace, with access to step-by-step demonstrations and answers to frequently asked anatomical questions. We created an instructional DVD program demonstrating dissection of the canine ventral neck and thoracic limb. The effect on student exam scores of using the DVD versus not using it was measured in a controlled, two-sample study using incoming first-year veterinary students as volunteers. Volunteers were told the study was of two different dissection methods; the DVD was not specifically mentioned until after the students were separated into two groups (Blue/DVD group and Orange/No DVD group), and then only to volunteers in the Blue group. Except for the DVD, the two groups had the same resources. The difference in scores on an exam given after a single dissection period did not differ sufficiently to conclude that DVD use raised the mean score; however, 73% of the DVD group scored 60% or higher, while only 38% of the No DVD group scored 60% or higher. The difference in mean scores overall was 2.3 points out of a possible 49, suggesting that the DVD helped students, especially those with lower scores, to earn two to three more points than they would have otherwise.

The first synapse in the olfactory pathway mediates a significant transfer of information given the restricted association of specific olfactory receptor neurons with specific glomeruli in the olfactory bulb. To understand better how this connection is made and what the functional capacities of the participating cells are, we created a long-lived culture system composed of olfactory epithelium and olfactory bulb tissues. Using the roller tube method of culturing, we grew epithelium-bulb cocultures, explanted from 1-4-day-old Swiss Webster mice, on Aclar for periods ranging from 18 hr to 68 days. The explants flattened so that in some areas the culture was only a few cells thick, making individual cells distinguishable. From 107 cultures studied, we identified the following cell types by expression of specific markers (oldest culture expressing marker, days in vitro, DIV): olfactory receptor neurons (neural cell adhesion molecule, 42 DIV); mature receptor neurons (olfactory marker protein, 28 DIV); postmitotic olfactory receptor neurons and olfactory bulb neurons (beta-tubulin, 68 DIV); astrocytes (glial fibrillary acidic protein, glutamate/aspartate transporter, 68 DIV); olfactory horizontal basal cells (cytokeratin, 22 DIV). Neuronal processes formed glomeruli in 2-4-week-old cultures. We also recorded electro-olfactography responses to puffs of vapor collected over an odorant mixture containing ethyl butyrate, eugenol, (+) carvone, and (-) carvone from cultures as old as 21 DIV. These features of our olfactory culture system make this model useful for studying properties of immature and mature olfactory receptor neurons, pathfinding strategies of receptor axons, and mechanisms of information transfer in the olfactory glomerulus., (Copyright 2004 Wiley-Liss, Inc.)

Synaptic nests are closely packed collections of synaptic endings. Nests may be deficient in the glial processes which usually separate terminals in the CNS and which transport much of the glutamate associated with high levels of excitatory activity. We hypothesized that nests might lack glial glutamate transporters, but possibly would conserve neuronal glutamate transporter. Although present throughout the brain, nests are especially numerous in the cochlear nucleus. We performed immunoelectron microscopy by preembedding peroxidase and immunogold methods and by postembedding immunogold to detect expression of the glutamate transporters GLAST, GLT-1, and EAAC1 in the mouse cochlear nucleus. Our results show that the glial transporters, GLAST and GLT-1, are absent in synaptic nests. This deficiency is not compensated by the neuronal transporter EAAC1, which is poorly represented in nests. Outside synaptic nests, all three glutamate transporters are strongly expressed in the cochlear nucleus. Thus, glutamate released outside nests should be quickly bound by transporters and removed from the extracellular glutamate pool. Glutamate released within synaptic nests may persist long enough to permit diffusion to extrajunctional targets in the nest, including presynaptic receptors. Consequently, synaptic nests may play a role in modulation of synaptic activity but also in excitotoxic mechanisms., (Copyright 2003 Wiley-Liss, Inc.)

The frog neuromuscular junction is sensitive to nitric oxide (NO), since exogenously applied NO reduces the release of transmitter b presynaptic terminals and the size of ATP-induced Caoffresponses in perisynaptic Schwann cells. This study aimed at determining whether an NO synthase (NOS) is present at the neuromuscular junction, notably in perisynaptic Schwann cells, the glial cells at this synapse. The NADPH-diaphorase (NADPH-d) histochemical technique revealed the presence of NOS in cell bodies and presumed processes of perisynaptic Schwann cells. Incubation with NOS inhibitors, NG-nitro-L-arginine methyl ester or NG-nitro-L-arginine-acetate abolished the NADPH-d staining. Moreover, L-arginine, the precursor of NO, impeded the blockade by NOS inhibitors, establishing the NOS specificity of NADPH-d staining in frog tissue. The pattern of labelling with a polyclonal antibody against the neuronal form of NOS was similar to the NADPH-d staining, also suggesting the presence of a neuronal NOS in perisynaptic Schwann cells. Using electron microscopy the NOS immunostaining was found at the membrane and occasionally in the cytoplasm of perisynaptic Schwann cells and was not detected in the nerve terminal or muscle. There was no enzymatic or immunocytochemical labelling of NOS 6 days after denervation. It is concluded that NOS is present in frog perisynaptic Schwann cells. The presence of this endogenous NOS suggests that NO may act as a diffusible glial messenger to modulate synaptic activity and synapse formation at the neuromuscular junction.

One of the most numerous neurons in the cochlear nucleus is the type I stellate cell. Previous attempts to understand the structural basis for its signal coding assumed that integration of synaptic potentials arising from axodendritic synapses should account for the generation of its response properties. However, the present study documents the importance of excitatory and inhibitory types of synapses on the soma and axon. Retrograde transport of cholera toxin B subunit, injected in the inferior colliculus of chinchillas, was used to label exclusively type I stellate cells in the anteroventral cochlear nucleus. The relative distribution of terminal types by vesicle morphology was pleomorphic > large spherical > flattened > smaller spherical. The somatic perimeter covered by endings ranged from almost none to nearly half. More flattened-vesicle terminals contacted somata in the high-frequency than in the low-frequency region. Eight of twenty axons received endings that contained large spherical vesicles and made asymmetric junctions; half of these extensively apposed the initial segment, forming a collar of presumed excitatory input. Thus, type I stellate cells are a heterogeneous group. Inhibitory synapses probably compose the majority of terminals. Some cells receive mostly inhibitory synapses near the presumed site of the spike generator, but others also have a prominent excitatory input. These findings call for a new look at the mechanisms for signal coding in stellate cells in the auditory system in particular and raise issues concerning the stochastic nature of information processing in sensory systems in general.