Response characteristics of neurons in the cat vestibular nuclei during slow and constant velocity off-vertical axes rotations in the clockwise and counterclockwise rotations

The responses to slow constant velocity rotations in the clockwise (CW) and counterclockwise (CCW) directions about an axis tilted 10 degrees from the earth's vertical were studied in static tilt-sensitive neurons in the vestibular nuclei of decerebrate cats. Each unit responded to any 360 degrees unidirectional rotation with a position-dependent discharge maximum. The location of the maximum, obtained by rotation in one direction, differed from that obtained by an oppositely directed rotation (phase difference). In about 80% of the units such phase difference (up to 160 degrees in second-order neurons) in response to oppositely directed rotations was unaffected by different amplitudes of head displacement (5-25 degrees). Units were thus classified into two groups depending on the location of the CW discharge maximum relative to the CCW counterpart. The direction of rotation had no influence on the response gains of these units.     

Ultrastructural basis for interactions between central opioids and catecholamines. II. Nuclei of the solitary tracts

Interactions between central opioids and catecholamines are thought to underlie the ability of adrenergic agonists both to lower blood pressure and alleviate certain symptoms of opiate withdrawal. We examined the cellular substrate for interactions between neurons containing enkephalin-like opioid peptides and catecholamines in cardiovascular portions of the medial nuclei of the solitary tracts (m-NTS) of adult rats. Single sections were dually labeled using a double-bridged peroxidase method for the localization of a monoclonal leucine (Leu5)-enkephalin-antibody and immunoautoradiography for the localization of polyclonal antibodies against the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). Light microscopy revealed a few perikarya and numerous varicosities containing Leu5-enkephalin-like immunoreactivity (LE-LI). These were distributed among TH-labeled perikarya and processes throughout the rostrocaudal NTS. Electron microscopy of the m-NTS at the level of the area postrema further established the single as well as dual localization of TH and LE-LI in individual perikarya, dendrites, and axon terminals. Silver grains indicative of TH-labeling were usually distributed throughout the cytoplasm, whereas the peroxidase reaction product for LE-LI was localized principally to large (80-150 nm), dense-core vesicles. Immunoautoradiographic labeling for TH was detected in 118 terminals within a series of sections containing 183 terminals with LE-LI. Of these, 26% of the TH-labeled terminals and 32% of the enkephalin-containing terminals formed symmetric synapses with unlabeled dendrites, while only 7% of each type formed symmetric synapses with TH-labeled dendrites. In favorable planes of sections, the unlabeled as well as TH-labeled dendrites received convergent input from both types of terminals. A few of the remaining terminals that contained either TH or LE-LI formed asymmetric junctions with unlabeled distal dendrites; the others were without recognizable synaptic specializations within the plane of section. Approximately 20% of the TH-labeled terminals and 6% of the terminals containing LE-LI were dually labeled for both antibodies. These were invested with astrocytic processes characterized by bundles of intermediate filaments. We conclude that within cardiovascular portions of the m-NTS, opioid peptides and catecholamines contained within the same or separate terminals modulate the activity of target neurons through direct symmetric, probably inhibitory, synaptic junctions and may additionally modulate the activity of neighboring astrocytes through exocytotic release from large dense-core vesicles.(ABSTRACT TRUNCATED AT 400 WORDS)     

Comparison of reorganization of the somatosensory system in rats that sustained forelimb removal as neonates and as adults

Studies of sensory pathways in several species indicate that the extent and form of reorganization resulting from deafferentation early in life vs. adulthood are not the same. The reasons for such differences are not well understood. To gain further insight into age-dependent mechanisms of reorganization, this study compared the consequences of neonatal vs. adult forelimb amputation in rats at multiple levels of the sensory pathway, including primary somatosensory cortex, brainstem, and dorsal root ganglia. At the cortical level, the average area of the functional forelimb-stump representation from rats amputated as adults was significantly smaller (P < 0.05) than that of neonatally amputated rats (4.3 +/- 1.3 mm(2) vs. 6.6 +/- 1.5 mm(2), respectively). At the brainstem level, neonatally amputated rat cuneate neurons possessed the following responsivities: 20% stump responsive, 40% responsive to both stump and hindlimb, 30% responsive to another body region, and 10% unresponsive. In contrast, cuneate neurons of adult amputated rats were 70% stump responsive, 2% responsive to both stump and hindlimb, and 30% unresponsive. A significantly (P < 0.001) greater percentage of the C(6)-C(8) dorsal root ganglia neurons of adult amputated rats were unresponsive to peripheral stimulation vs. neurons from neonatally amputated rats (48% vs. 16%, respectively). These results indicate that the reorganization that occurs in response to forelimb amputation at birth vs. adulthood is distinctly different at each of these levels of the dorsal column-medial lemniscal pathway. Possible mechanisms to account for these differences are considered.     

Temporal response of brachial artery dilation after occlusion and nitroglycerin

This study shows that a set time after cuff deflation or after nitroglycerin administration may not be suitable to capture peak, brachial artery dilatory responses in assessing endothelial dysfunction. Automated, continuous monitoring methods are required to simplify identification of peak responses and to standardize reporting.     

Temporally structured metapopulation dynamics and persistence of influenza A H3N2 virus in humans

Populations of seasonal influenza virus experience strong annual bottlenecks that pose a considerable extinction risk. It has been suggested that an influenza source population located in tropical Southeast or East Asia seeds annual temperate epidemics. Here we investigate the seasonal dynamics and migration patterns of influenza A H3N2 virus by analysis of virus samples obtained from 2003 to 2006 from Australia, Europe, Japan, New York, New Zealand, Southeast Asia, and newly sequenced viruses from Hong Kong. In contrast to annual temperate epidemics, relatively low levels of relative genetic diversity and no seasonal fluctuations characterized virus populations in tropical Southeast Asia and Hong Kong. Bayesian phylogeographic analysis using discrete temporal and spatial characters reveal high rates of viral migration between urban centers tested. Although the virus population that migrated between Southeast Asia and Hong Kong persisted through time, this was dependent on virus input from temperate regions and these tropical regions did not maintain a source for annual H3N2 influenza epidemics. We further show that multiple lineages may seed annual influenza epidemics, and that each region may function as a potential source population. We therefore propose that the global persistence of H3N2 influenza A virus is the result of a migrating metapopulation in which multiple different localities may seed seasonal epidemics in temperate regions in a given year. Such complex global migration dynamics may confound control efforts and contribute to the emergence and spread of antigenic variants and drug-resistant viruses.