bluuebunny/crossref_metadata_2025 huggingface dataset:
The "motion-blind" patient: low-level spatial and temporal filters
Authors: Hess RH , Baker CL , Zihl J
Published: March 2018

The “motion-blind” patient previously described by Zihl et al. (1983) was investigated using standard psychophysical procedures with stimuli whose spatial and temporal properties could be separately manipulated. Detection experiments for sinewave grating stimuli of varying spatial and temporal frequency showed sensitivity in this patient to be only slightly impaired. Temporal integration for stimuli of varying spatiotemporal frequency exhibited the expected space-time covariation seen in normal vision. An examination of the suprathreshold discriminative capacity of this patient was undertaken for spatial frequency, contrast, and temporal frequency. Although all of these discriminative functions were impaired, those concerning temporal frequency or velocity were dramatically reduced. No similar loss was seen for spatial frequency discrimination for moving or temporally varying stimuli. No measurable temporal frequency discrimination was present above 6 Hz and no velocity discrimination above 6 degrees/sec. Experiments involving the direction discrimination of suprathreshold drifting gratings of arrays of random dots revealed an inability to perceive direction of movement above a velocity of about 6 degrees/sec. Contrast thresholds contingent on direction of motion of a drifting grating also showed a much greater deficit than simple detection. Apparent motion using 2-flash random dot kinematograms revealed that the residual motion vision of this patient corresponded to the “short- range” motion process of normal vision. This process originally defined by Braddick (1974) operates over restricted space and time intervals. Apparent motion could only be supported by a narrow range of intermediate spatial displacements. These results suggest that this patient does exhibit some residual motion perception, probably corresponding to a severely impaired “short-range” mechanism. The patient's relatively intact ability to perform simple types of discrimination but severe impairment of performance at making judgments relevant to the nature of motion of the same stimuli suggests that while the components necessary for the analysis of motion are intact their more global associations have been disrupted. This implicates an extrastriate locus of the brain damage. Alternative explanations for the nature of the deficit are discussed.
A circumscribed projection from the nucleus of the solitary tract to the nucleus ambiguus in the rat: anatomical evidence for somatostatin- 28-immunoreactive interneurons subserving reflex control of esophageal motility
Authors: Cunningham ET , Sawchenko PE
Published: March 2018

Axonal transport and immunohistochemical methods were used to investigate the anatomical and biochemical organization of projections from the nucleus of the solitary tract (NTS) to the rostral, esophageal, part of the nucleus ambiguus (NA) in the rat. Discrete iontophoretic deposits of a retrogradely transported tracer, fluorogold, placed in the rostral NA labeled a column of cells within the NTS, termed the central part of the NTS (after Ross et al., 1985), situated just medial to the solitary tract and extending from about 300 to 1000 microns rostral to the obex. Iontophoretic deposits of the anterogradely transported tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L), placed in the central part of the NTS gave rise to dense and topographically restricted projections to the rostral NA. More caudal and ventral aspects of the NA did not receive prominent inputs from the central part of the NTS, and deposits that spared the central part of the NTS gave rise to only sparse projections to the rostral NA. Antisera against somatostatin-28 (SS-28) stained cell bodies within the central part of the NTS. In addition, a double-labeling procedure, capable of colocalizing anterogradely transported PHA-L and endogenous peptides to individual fibers and/or terminals, demonstrated an appreciable number of SS-28-immunoreactive terminals within the rostral NA that arose from the NTS. Correspondingly, unilateral lesions that involved the central part of the NTS resulted in a marked depletion of SS-28 immunoreactivity in the ipsilateral rostral NA. These data provide evidence for a discrete, partly somatostatinergic, projection from the central part of the NTS to the rostral NA. Anatomical and physiological studies implicating the central part of the NTS and the rostral NA in esophageal function suggest this pathway to be involved in the reflex control of esophageal motility.
Ultrastructural basis for interactions between central opioids and catecholamines. I. Rostral ventrolateral medulla
Authors: Milner TA , Pickel VM , Reis DJ
Published: March 2018

Opioids and some alpha 2-adrenergic agonists are both known for their potent hypotensive actions following local application to the rostral ventrolateral medulla (RVL), in particular the region containing the C1 adrenergic neurons. We sought to determine whether coexistence and/or synaptic interactions might account for the commonality of cardiovascular responses to opioids and catecholamines in the RVL. Dual light and electron microscopic (EM) immunoperoxidase labeling of a rat monoclonal antibody against the opioid peptide Leucine5 (Leu5)- enkephalin and immunoautoradiographic localization of a rabbit antiserum against the catecholamine synthesizing enzyme tyrosine hydroxylase (TH) were examined in single sections through the RVL of adult colchicine-pretreated rats. Cross-reactivity of the enkephalin antibody was most intense with Leu5-enkephalin. Methionine5-enkephalin as well as dynorphin A, but not beta-endorphin, were also recognized by the antisera. By light microscopy, the Leu5-enkephalin-like immunoreactivity (LE-LI) was identified by peroxidase reaction product in perikarya and processes. Most of the perikarya containing LE-LI were located dorsolaterally or ventromedially to those showing immunoautoradiographic labeling for TH. However, a few perikarya appeared to contain both LE-LI and TH-immunoreactivity (TH-I) which were difficult to differentiate by light microscopy. By EM, perikarya and dendrites immunoreactive for LE, TH, and both LE and TH were readily distinguishable. Perikarya and dendrites immunoautoradiographically labeled for TH alone were more numerous than those containing LE-LI or TH-I and LE-LI. Axon terminals also were immunolabeled either for one or both reaction products. However, the TH- labeled neurons constituted one of the primary (42% from a total of 118) targets of terminals containing LE-LI. Additionally, some of these terminals containing LE-LI shared a common target with TH-labeled terminals. These common target neurons contained either TH-I or TH-I and LE-LI. In most cases, the identified junctions were symmetric and the terminals with LE-LI (0.4–1.2 microns in diameter) contained either (1) a few small clear vesicles (scv's) and numerous intensely immunoreactive large (100–150 nm) dense-core vesicles (dcv's); or (2) many scv's and from 0–6 dcv's of a somewhat smaller (80–120 nm) diameter. The latter type of terminal was more consistently dually labeled for TH. The remaining terminals containing LE-LI formed synaptic junctions with unlabeled perikarya or dendrites (32%), were in apposition to other unlabeled as well as TH or LE- and TH-containing terminals (4%) or were without recognizable specializations within the plane of section (22%).(ABSTRACT TRUNCATED AT 400 WORDS)
Segregation and overlap of callosal and association neurons in frontal and parietal cortices of primates: a spectral and coherency analysis
Authors: Johnson PB , Angelucci A , Ziparo RM , Minciacchi D , Bentivoglio M , Caminiti R
Published: March 2018

The spatial relations between selected classes of association and callosal neurons were studied in the frontal and parietal lobes of the macaque monkey using retrogradely transported fluorescent dyes. Fast blue and nuclear yellow were injected in the left frontal (areas 4 and 6) and right posterior parietal (area 5) cortices, respectively. These injections led to the retrograde labeling, in the right frontal cortex, of callosal neurons projecting homotopically and association neurons projecting to ipsilateral area 5; in the left superior parietal lobule, of callosal neurons projecting to contralateral area 5 and association neurons projecting to the ipsilateral frontal lobe. In both frontal and parietal cortices, callosal and association neurons were located in layers III and V-VI; a few neurons were also found in layer II. The contribution of layers V-VI to the callosum was significantly higher in areas 4 and 6 than in area 5. Only a small number of neurons (less than 1%) were double labeled. Spectral analyses were used to characterize the spatial periodicities of the distributions of callosal and association neurons. In areas 4, 6, and 5, both association and callosal spectra were dominated by a strong elevation in the range of low spatial frequencies, corresponding to periodicities in cell density with a peak-to-peak distance of about 8 mm. This indicated an arrangement of these corticocortical cells in the form of bands. The latter displayed various shapes and orientations and were composed of more discrete assemblies of cell clusters of about 400–1000 microns width. Their presence was revealed in the power spectra by a small elevation in the range of high spatial frequencies. The coherency analysis assessed the degree of linear relationships for each spatial frequency, and therefore the degree of similarity, between callosal and association cell distributions, together with their phase relations. Little coherency was found in areas 4 and 6 between bands of callosal and association neurons, which suggests that the 2 cell populations are differently and independently distributed in the tangential domain, with no simple phase relations. The overall mean coherency was higher in area 5 than in the frontal cortex: callosal and association bands were more similar in shape, with more extensive zones of overlap. These data indicate that callosal and association neurons share common principles of spatial organization despite the great regional variability of their interrelations in the tangential cortical domain.(ABSTRACT TRUNCATED AT 400 WORDS)
Functional anatomy of the second visual area (V2) in the macaque
Authors: Tootell RB , Hamilton SL
Published: March 2018

To study the functional organization of secondary visual cortex (V2) in the primate, 14C-2-deoxy-d-glucose (DG) was injected while macaque monkeys were shown specific visual stimuli. Wherever possible, patterns of DG uptake were compared with the position of dark and light cytochrome oxidase (cytox) stripes (Tootell et al., 1983). Often, the DG effects of 2 different stimuli were compared in the same hemisphere to eliminate ambiguities inherent in between-animal comparisons. Data were obtained from a large number of animals in conjunction with related DG studies in area V1 (primary visual or striate cortex). The following conclusions were reached: (1) in some macaque monkeys, dark cytox stripes were faint or absent. Although this could conceivably be due to poor staining technique, some evidence suggests that the lack of enzyme stripe pattern is real. In all animals, including those that showed poor or no cytox staining evidence for stripes, the functional architecture revealed by the DG was consistently present and robust. (2) Uniform gray stimuli produce a relatively uniform pattern and minimal stimulus-related DG uptake. (3) Eye movements per se produce some uptake in the V2 stripes. (4) Very generalized visual stimulation conditions (e.g., binocular stimulation with a grating of varied orientation and varied spatial frequency) produced a pattern of uptake that is greatest in both sets of dark cytox stripes and lighter in the light cytochrome stripes. (5) In both the DG and cytox results, the V2 “stripes” are more accurately described as stripe-shaped collections of patches. (6) In almost all cases, DG patterns were columnar in shape, extending from white matter to cortical surface. The boundaries of the columns were most sharply defined, and the contrast was highest, in layers 3B/4, becoming slightly more blurry and lower in contrast in other layers. Laminar differences between DG patterns in V2 were almost negligible, compared with the profound laminar differences in macaque V1. (7) There is no DG evidence for, and much against, the possibility of an ocular dominance architecture in V2. (8) There are orientation columns in macaque V2. DG-labeled orientation columns are spaced further apart than those in V1, by a factor of about 1.6, but the columns are not correspondingly wider. (9) Spatially diffuse variations in color produce high uptake confined, at least largely, to the thin cytox stripes. (10) There is evidence for spatially antagonistic color surrounds in color cells in the thin stripes.(ABSTRACT TRUNCATED AT 400 WORDS)
Endogenous activation of glycine and NMDA receptors in lamprey spinal cord during fictive locomotion
Authors: Alford S , Williams TL
Published: March 2018

Strychnine is shown to abolish left-right alternation in fictive locomotion induced by sensory stimulation. Robust rhythmic activity, characterized by left-right coactivation at each segmental level, is seen in the presence of strychnine at all doses used (0.5–20 microM). The proportion of the cycle occupied by the ventral root bursts and the rostral-caudal coordination is similar to that seen in the absence of strychnine. Furthermore, the rhythm is abolished by cis-2,3-piperidine dicarboxylic acid (PDA), 2-amino-5-phosphonovalerate (APV), or the removal of Mg2+ from the perfusate, as in the absence of strychnine. Voltage clamp was applied to ventral horn neurons during stimulation in the presence of strychnine, with holding potentials negative to the plateau potential associated with a ventral root burst but positive to the potential in the interburst. Inward current was seen during the ventral root burst, but no outward current was seen at burst termination or during the interburst. The results indicate that in fictive locomotion induced by endogenous release of NMDA receptor agonists, left-right alternation is dependent on glycinergic transmission. Furthermore, evidence is provided that in the absence of glycinergic transmission, burst termination may depend on NMDA receptor- linked voltage-sensitive processes.
Differential ascending projections to aural regions in the 60 kHz contour of the mustache bat's inferior colliculus
Authors: Ross LS , Pollak GD
Published: March 2018

The inferior colliculus of the mustache bat is similar in many respects to the inferior colliculus of more commonly studied mammals. However, the isofrequency contour devoted to processing 60 kHz, the dorsoposterior division (DPD) is greatly expanded, encompassing an area approximately equal to one-third of the central nucleus. Of particular significance is that monaural and binaural neurons are segregated in the DPD into 4 spatially distinct aural regions. In this study we exploit the great enlargement of the 60 kHz region in the central nucleus of the inferior colliculus (ICc) of the mustache bat to determine the source of ascending projections to the 4 different aural regions of the DPD. Small iontophoretic deposits of HRP were made within each of the physiologically defined aural regions, and the locations and numbers of retrogradely labeled cells in the auditory brainstem nuclei were determined. Two major features of collicular organization were found. The first is that each aural region receives a unique set of projections from a subset of lower auditory nuclei and thus is distinguished both by its neural response properties and by the pattern of ascending projections it receives. The dorsomedial EE region receives inputs primarily from the ipsilateral intermediate nucleus of the lateral lemniscus (INLL) and ventral nucleus of the lateral lemniscus (VNLL), and the contralateral ICc. In contrast, the ventrolateral EE region receives projections from the ipsilateral medial superior olivary nucleus (MSO), VNLL, and INLL. The inputs to the EI region originate primarily from the dorsal nucleus of the lateral lemniscus (DNLL) and lateral superior olivary nucleus (LSO) bilaterally and from the ipsilateral INLL. The afferents to the EO region include the contralateral cochlear nucleus, the ipsilateral VNLL and INLL and MSO. The second major organizational feature is that the binaural nuclei of the brain-stem project upon the DPD in a more restricted manner than do some of the lower monaural nuclei, such as the VNLL and INLL, which project in a more widespread manner. The unique set of projections terminating in each aural region of the DPD suggests that the neurons should have substantially different properties, even when neurons in different regions are of the same general aural type. Moreover, the elucidation of the micro-organization of the DPD provides insights into the different ways that binaural properties of DPD neurons are created by the convergence of inputs from particular subsets of lower auditory nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)
A hyperpolarization-activated inward current in heart interneurons of the medicinal leech
Authors: Angstadt JD , Calabrese RL
Published: March 2018

Heart interneurons (HN cells) in isolated ganglia of the medicinal leech were voltage-clamped with single microelectrodes. Hyperpolarizing voltage steps elicited a slow inward current (Ih), which underlies the characteristic depolarizing response of HN cells to injection of prolonged hyperpolarizing current pulses (Arbas and Calabrese, 1987a). The conductance underlying Ih begins to activate near -mV and is fully activated between -70 and -80 mV. The activation kinetics of Ih are slow and voltage dependent. The activation time constant (tau h) ranges from approximately 2 sec at -60 mV to near 700 msec at -100 mV. Ih persists in low Ca2+ (0.1 mM), 5 mM Mn2+ saline and exhibits a reversal potential of -21 +/- 5 mV. The reversal potential is shifted by altering [Na+]o or [K+]o but is unaffected by changes in [Cl-]o. Ih is blocked by extracellular Cs+ (1–5 mM) but not Ba2+ (5 mM) or TEA (25 mM). Low concentrations of Cs+ (100–200 microM) cause a partial block that exhibits strong voltage dependence. Temperature changes were also shown to affect Ih. Both the rate of activation and the steady-state amplitude of Ih are enhanced by temperature increases. HN cells are interconnected by inhibitory chemical synapses, and their normal electrical activity consists of bursts of action potentials separated by periods of inhibition. During the inhibitory phase of rhythmic bursting activity, HN cells hyperpolarize to a voltage range where Ih is activated. Block of Ih with extracellular Cs+ (4 mM) disrupted the normal bursting activity of HN cells. These results are consistent with the hypothesis that Ih contributes to escape from inhibitory inputs during normal bursting activity.
Induction of active zones at ectopic neuromuscular junctions in the frog
Authors: Ko CP , Folsom DB
Published: March 2018

To examine de novo differentiation of the active zone, ectopic neuromuscular junctions were studied in adult frog muscles. Ectopic junctions induced by excising the original endplate region and implanting the nerve to an endplate-free site were examined by light and electron microscopy 4 weeks-1 year after operations. The earliest time point at which ectopic junction formation was detected with freeze fracture was 6 weeks postoperation, when clusters of active zone particles were observed scattered across the nerve ending. Subsequently, short active zones (6–10 weeks postoperation, length mean = 0.36 +/- 0.24 microns) composed of the characteristic 2 double rows of particles are detected. Before junctional folds are observed with freeze fracture, many active zones are parallel to each other and to the long axis of the nerve. The average angle 6–10 weeks postoperation is 27 degrees +/- 23 degrees. Even during these early stages of formation, active zones are functional. As time passes, active zones attain a more typical, perpendicular orientation (12–18 weeks postoperation, mean = 62 degrees +/- 24 degrees) and also increase in length (mean = 0.69 +/- 0.45 microns). However, even after 1 year, the orientation (angle, mean = 70 degrees +/- 22 degrees) and the length (mean = 0.78 +/- 0.63 microns) of active zones at ectopic junctions are still not well correlated with active zones at normal junctions (normal active zone angle mean = 85 degrees +/- 5 degrees, length mean = 1.00 +/- 0.57 microns).(ABSTRACT TRUNCATED AT 250 WORDS)
GABAergic neurons in the rat hippocampal formation: ultrastructure and synaptic relationships with catecholaminergic terminals
Authors: Milner TA , Bacon CE
Published: March 2018

Numerous studies indicate that gamma-aminobutyric acid (GABA) can either hyperpolarize or depolarize hippocampal pyramidal and granule cells. While the inhibitory action of GABA may occur directly on these cells, the excitatory action may be mediated by interactions of GABAergic neurons with each other or with catecholaminergic afferents. We sought to examine the cellular basis for these interactions and their relative frequency. Thus, the ultrastructural morphology of GABAergic neurons and their relation to terminals exhibiting immunoreactivity for the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) were examined in the rat hippocampal formation using combined immunoautoradiographic and peroxidase-antiperoxidase labeling methods. By light microscopy, GABAergic perikarya and processes codistributed most noticeably with TH-containing processes in the hilus of the dentate gyrus (DG) and in strata lucidum, radiatum, and lacunosum-moleculare of the CA3 region of the hippocampus. Thus, these regions were examined further by electron microscopy. In the ultrastructural analysis, GABA-like immunoreactivity (GABA-LI) was detected in neuronal perikarya, dendrites, axons, and axon terminals. The GABA-containing perikarya were large, ovoid (20–40 microns in diameter), and contained abundant cytoplasm and an indented nucleus with one nucleolus. Synaptic junctions on the perikarya and dendrites with GABA-LI were both symmetric and asymmetric. Approximately equal numbers of TH-labeled terminals (19% of 133 in DG; 39% of 26 in CA3) and GABA-containing terminals (19% DG, 15% CA3) formed synapses with GABA-labeled perikarya. The remainder of the presynaptic terminals (62% DG, 46% CA3) were unlabeled, i.e., contained unidentified transmitters. Terminals with GABA-LI (0.5–1.6 microns) contained numerous small clear vesicles and from 0 to 2 large dense-core vesicles. The types of associations formed by terminals with GABA-LI were remarkably similar in the DG and hippocampus proper despite differences in intrinsic cell type and function. Terminals with GABA-LI formed associations with unlabeled perikarya and dendrites (24% of 151 in DG, 25% of 75 in CA3) and synapses with GABA-containing perikarya and dendrites (18% DG, 5% CA3). Additionally, GABAergic terminals converged upon the same perikarya or dendrite as a TH-containing terminal (15% DG, 21% CA3) and were in direct apposition to TH-labeled terminals (19% DG, 20% CA3). The remaining GABAergic terminals (24% DG, 28% CA3) were without any apparent synaptic relations. In both the DG and CA3, the junctions formed by GABAergic terminals were symmetric. Terminals showing colocalization of GABA-LI and TH-I were also detected although rarely.(ABSTRACT TRUNCATED AT 400 WORDS)
Evidence for a novel mechanism of binding and release of stimuli in the primate taste bud
Authors: Farbman AI , Hellekant G
Published: March 2018

In previous work, we showed that thaumatin, an intensely sweet protein, binds to certain formed elements in taste pores of Rhesus monkey foliate papillae, namely, microvilli and small vesicles shed from microvilli, in addition to amorphous secretions (Farbman et al., 1987). We suggested that the taste bud responds to a thaumatin stimulus by shedding the small vesicles containing fragments of microvillar membrane bearing the stimulus-binding site complex. To examine this hypothesis further, we used electron microscopy to examine taste pores of both vallate and foliate papillae from Rhesus monkeys before or after stimulation with thaumatin or sucrose. We also recorded the neural activity from the glossopharyngeal nerve during stimulation with thaumatin, sucrose, citric acid, and NaCl. The results indicate (1) with no stimulation, vesicles are found in pores of foliate papilla taste buds much more frequently than in pores of vallate papilla buds, (2) in both types of papillae, stimulation with sucrose has no apparent effect on the number of pores containing vesicles, (3) stimulation with thaumatin elicits release of vesicles into pores of both foliate and vallate buds, (4) repeated stimulation of taste buds with thaumatin results in a declining neural response, not seen after repeated stimulation with sucrose, citric acid, or NaCl, and (5) stimulation with thaumatin suppresses the neural response to sucrose, but the reverse does not occur. The combined morphological and physiological data support our original hypothesis that, in response to thaumatin stimulation, binding sites on taste microvillar membranes may be shed as a stimulus-receptor complex into the pore. Alternatively, the binding sites may in some way be altered by the shedding of part of the membrane. The data suggest further that the binding site for sucrose may be close to that for thaumatin because it too is lost or altered after thaumatin stimulation. The reduced neural response after repeated thaumatin stimulation indicates that cells may have suffered a net loss of functional receptors or at least a loss in functional capacity of the receptors. The data indicate that the cellular mechanism for handling the protein sweetener, thaumatin, is strikingly different from the adsorption-desorption response to saccharide sweeteners.
A comparison of neuronal growth cone and cell body membrane: electrophysiological and ultrastructural properties
Authors: Guthrie PB , Lee RE , Kater SB
Published: March 2018

This study investigated a broad set of general electrophysiological and ultrastructural features of growth cone and cell body membrane of individual neurons where membrane from different regions of the same neuron can be directly compared. Growth cones were surgically isolated from identified adult Helisoma neurons in culture and compared with the cell body using whole-cell patch-clamp recording techniques. All isolated growth cones generated overshooting regenerative action potentials. Five neurons (buccal neurons B4, B5, and B19; pedal neurons P1 and P5) were selected that displayed distinctive action potential waveforms. In all cases, the growth cone action potential was indistinguishable from the cell body action potential and different from growth cones from other identified neurons. Two of these neurons (B5 and B19) were studied further using voltage-clamp procedures; growth cones and cell bodies again revealed major similarities within one neuron type and differences between neuron types. The only suggested difference between the growth cone and cell body was an apparent reduction in the magnitude of the A-current in the growth cone. Peak inward and outward current densities, as with other electrophysiological features, were different between neuron types, but were, again, similar between the growth cone and the cell body of the same neuron. Freeze-fracture analysis of intramembraneous particles (IMPs) was also performed on identified regions of the same neuron in culture. Both the density and the size distribution of IMPs were the same in growth cone, cell body, and neurite membranes. In these general electrophysiological and ultrastructural characteristics, therefore, growth cone membranes appear to retain the identity of the parent neuron cell body membrane.
Axonal transport and distribution of endogenous calcitonin gene-related peptide in rat peripheral nerve
Authors: Kashihara Y , Sakaguchi M , Kuno M
Published: March 2018

Calcitonin gene-related peptide (CGRP) has been found in both sensory and motor neurons. It has been suggested that CGRP is transported from neuron cell bodies to their terminals, where it may act as an anterograde trophic factor. However, it is not known how fast CGRP is transported or whether CGRP found in the innervated target organ indeed originated in neural tissues. We have quantified endogenous CGRP in the rat peripheral nerve by a newly developed enzyme immunoassay. The CGRP immunoreactive material obtained from neural tissues coincided with synthetic rat CGRP in fractional distributions separated by gel filtration. After ligation of the sciatic nerve, tissue CGRP accumulated in the segment central to the ligature. The rate of anterograde transport of CGRP was about 1 mm/hr in both sensory and motor fibers. In the sciatic nerve, only a small fraction of CGRP measured was found to originate from the motor nerve fibers. This may be due in part to the disproportionately large number of sensory fibers in the sciatic nerve and in part to the possible presence of CGRP in sympathetic nerve fibers. The CGRP content in the dorsal root fibers was significantly lower than that in the peripheral processes of the sensory neurons. The CGRP content in the hind leg muscle was much higher than that expected from the amount of CGRP per nerve fiber in the sciatic nerve. Most CGRP in muscle disappeared following denervation. It is concluded that CGRP highly concentrated in nerve terminals is supplied by axonal transport from the neuron cell bodies.
Quantified distribution of the noradrenaline innervation in the hippocampus of adult rat
Authors: Oleskevich S , Descarries L , Lacaille JC
Published: March 2018

A recently developed radioautographic technique, based on the uptake labeling of monoamine terminals (axonal varicosities) in vitro, was used to quantify the noradrenaline (NA) innervation in adult rat hippocampus. After incubation of brain slices with 1 microM 3H-NA, the NA varicosities were visualized as small aggregates of silver grains, in light microscope radioautographs prepared at 3 equidistant horizontal levels across the ventral 2/3 of the hippocampus. Using a computer-assisted image analyzer, counts were obtained from the subiculum (SUB), 3 sectors of Ammon's horn (CA1, CA3-a, CA3-b) and 3 sectors of the dentate gyrus (DG-medial blade, crest, and lateral blade), every lamina being sampled in each region. After a double correction for duration of radioautographic exposure and section thickness, and following measurement of varicosity diameter in electron microscope radioautographs, it was possible to express these results in number of terminals per volumetric unit of tissue. It was thus found that the overall density of hippocampal NA innervation averages 2.1 million varicosities/mm3 of tissue, a value almost twice as high as that in cerebral cortex. This innervation is 20% denser ventrally than dorsally and is heterogeneous both in terms of regional and laminar distribution. SUB and DG are more strongly innervated than Ammon's horn, wherein CA1 has the lowest overall density. In SUB and CA1, there is a clear predilection of NA varicosities for the stratum moleculare. In CA3, there is a narrow band of even stronger innervation in the stratum radiatum, near the apical border of the stratum pyramidale, contrasting with a 3 times lower density in this cell layer and the stratum oriens. In DG, the NA innervation is again the weakest in the cell body layer (granule) and exhibits an almost 3-fold greater density in the polymorph layer, the highest of all hippocampus. These figures allow for numerous correlations with other quantitative parameters-- cytological, biochemical, and pharmacological--of NA function in the hippocampus. They also provide a strong basis for elucidating, at a cellular level, the action of NA in this part of the brain.
Sexual maturity-dependent changes in neuronal morphology in the prepacemaker nucleus of adult weakly electric knifefish, Eigenmannia
Authors: Zupanc GK , Heiligenberg W
Published: March 2018

Knifefish of the genus Eigenmannia (Gymnotiformes, Teleostei) are seasonal breeders that spawn only during the tropical rainy season. Both sexes modulate their otherwise constant wave-like electric organ discharges (EODs) in the context of courtship and aggressive behavior by “chirps,” abrupt frequency modulations with brief interruptions. Play-backs of recordings of male courtship chirps can induce spawning in gravid females (Hagedorn and Heiligenberg, 1985). The EOD, produced by a specialized electric organ, is under the control of a pacemaker nucleus (Pn) in the medulla oblongata. Injections of HRP into the Pn label only a small cluster of cells bilaterally at the boundary of diencephalon and mesencephalon, constituting the prepacemaker nucleus, PPn (Heiligenberg et al., 1981). Microstimulation experiments have shown that chirp-like EOD modulations can be elicited from a subnucleus of the PPn, the PPn-C (Kawasaki and Heiligenberg, 1988; Kawasaki et al., 1988). By retrograde HRP labeling, we investigated the dependence of the PPn's morphology upon the sexual maturity of the fish. The most prominent effect was that, during the breeding season, females developed an abundance of “varicosities,” swellings 1–4 microns in diameter in distal regions of dendrites at a density of approximately 1/10 microns. In contrast to mature females, immature females had none or only a few varicosities. Such a clear correlation between the abundance of varicosities and relative gonadal weight was not found in males, most likely because testicular and dendritic development are not strictly synchronized. After the onset of the simulated dry season, however, relative gonadal weight, as well as the number of varicosities, was reduced drastically in both sexes. This reduction in the number of varicosities is accompanied by a decrease in their diameter. Varicosities may represent growing buds or regions of synaptic input from afferent areas or both. Reconstruction of individual PPn-C neurons showed maturity-dependent changes in the pattern of dendritic proliferation in females. Such dynamic changes in the structure of neurons might subserve seasonal modifications in an animal's propensity to execute specific behaviors.
Vasopressin receptors of the vasopressor (V1) type in the nucleus of the solitary tract of the rat mediate direct neuronal excitation
Authors: Raggenbass M , Tribollet E , Dubois-Dauphin M , Dreifuss JJ
Published: March 2018

The existence of vasopressin-sensitive neurons in the nucleus of the solitary tract of the rat and the presence in this brain area of vasopressin binding sites were investigated using extracellular single- unit recordings from brain-stem slices and light microscopic autoradiography. About 45% of the recorded neurons responded to vasopressin at 5–2000 nM by a reversible, concentration-dependent increase in firing rate. The action of vasopressin was direct, was suppressed by a vasopressor antagonist, and was mimicked by a vasopressor agonist. Oxytocin was 10–100 times less efficient than vasopressin and a specific antidiuretic agonist was without effect. Using light microscopic autoradiography and 3H-arginine vasopressin as a ligand, high-affinity vasopressin binding sites were found distributed over the whole rostrocaudal extent of the nucleus of the solitary tract. Binding was displaced by unlabeled vasopressor agonist but not by unlabeled antidiuretic agonist. Thus, the nucleus of the solitary tract contains V1-type vasopressin receptors which are, at least in part, located on neuronal membranes and whose activation generates bioelectrical signals. Solitary tract vasopressin-sensitive neurons may be the target of a vasopressinergic innervation originating in the hypothalamic paraventricular nucleus and could be involved in the central regulation of cardiovascular functions.
A role for cGMP during tetanus toxin blockade of acetylcholine release in the rat pheochromocytoma (PC12) cell line
Authors: Sandberg K , Berry CJ , Eugster E , Rogers TB
Published: March 2018

In order to identify the specific molecular mechanisms involved in neurosecretion, we investigated the mechanism of action of tetanus toxin, a potent presynaptic neurotoxin, in the rat adrenal pheochromocytoma PC12 cell line. It has recently been reported that tetanus toxin is a potent inhibitor of the release of depolarization- evoked 3H-acetylcholine (ACh) from nerve growth factor-differentiated PC12 cells (Sandberg et al., 1989a). In PC12 cells, as in many neural tissue preparations, cGMP accumulation in intact cells increased 6- to 17-fold when stimulated with veratridine (200 microM), carbachol (1 mM), Ba2+ (2 mM), or K+ (30 mM). Preincubation of the cells with tetanus toxin inhibits this accumulation by greater than 95%. The toxin dose-inhibition curves for 3H-ACh release and cGMP accumulation are similar, with half-maximal doses of tetanus toxin seen at approximately 5 nM. The time courses for the development of the effects of tetanus on 3H-ACh release and on cGMP accumulation were also similar. Protocols which elevated intracellular cGMP levels reversed the action of the toxin. For example, evoked ACh release was restored in intoxicated PC12 cells by a 15 min exposure to 100 microM 8-bromo-cGMP. The half-maximal dose was observed at 50 microM nucleotide. Examination of the nucleotide specificity revealed that only cyclic guanine analogs were effective in reversing the effects of tetanus toxin. These results suggested that the inhibition of depolarization-evoked cGMP accumulation is causally related to the action of tetanus toxin on neurosecretion.(ABSTRACT TRUNCATED AT 250 WORDS)
Norepinephrine and learning-induced plasticity in infant rat olfactory system
Authors: Sullivan RM , Wilson DA , Leon M
Published: March 2018

Postnatal olfactory learning produces both a conditioned behavioral response and a modified olfactory bulb neural response to the learned odor. The present report describes the role of norepinephrine (NE) on both of these learned responses in neonatal rat pups. Pups received olfactory classical conditioning training from postnatal days (PN) 1– 18. Training consisted of 18 trials with an intertrial interval of 24 hr. For the experimental group, a trial consisted of a pairing of unconditioned stimulus (UCS, stroking/tactile stimulation) and the conditioned stimulus (CS, odor). Control groups received either only the CS (Odor only) or only the UCS (Stroke only). Within each training condition, pups were injected with either the NE beta-receptor agonist isoproterenol (1, 20, or 4 mg/kg), the NE beta-receptor antagonist propranolol (10, 20, 40 mg/kg), or saline 30 min prior to training. On day 20, pups received one of the following tests: (1) behavioral conditioned responding, (2) injection with 14C-2-deoxyglucose (2-DG) and exposed to the CS odor, or (3) tested for olfactory bulb mitral/tufted cell single-unit responses to the CS odor. The results indicated that training with either: (1) Odor-Stroke-Saline, (2) Odor- Stroke-Isoproterenol-Propranolol, or (3) Odor only-Isoproterenol (2 mg/kg) was sufficient to produce a learned behavioral odor preference, enhanced uptake of 14C-2-DG in the odor-specific foci within the bulb, and a modified output signal from the bulb as measured by single-cell recordings of mitral/tufted cells. Moreover, propranolol injected prior to Odor-Stroke training blocked the acquisition of both the learned behavior and olfactory bulb responses. Thus, NE is sufficient and may be necessary for the acquisition of both learned olfactory behavior and olfactory bulb responses.
Nonlinearity and facilitation in phosphoinositide signaling studied by the use of caged inositol trisphosphate in Xenopus oocytes
Authors: Parker I , Miledi R
Published: March 2018

The phosphoinositide signaling pathway, which mediates neurotransmitter responses, was studied in Xenopus oocytes by recording membrane currents evoked using lightflash photolysis of caged inositol trisphosphate (caged IP3) to produce rapid and reproducible transients in intracellular IP3 levels. Photolysis of caged IP3 evoked currents which were carried largely by chloride ions and depended upon intracellular, but not extracellular, calcium. A given light flash evoked larger responses when the amount of caged IP3 loaded into the oocyte was increased, and illumination of the vegetal hemisphere gave larger responses than the animal. Long (10 sec) light exposures produced oscillatory currents, resembling responses to serotonin and other agonists, which became larger, more transient, and of shorter latency as the light intensity was increased. Brief (ca. 100 msec) flashes evoked a single “spike” of current. The caged IP3 response showed a threshold, in that light flashes had to be greater than a certain intensity and duration before currents could be detected. Associated with this, sub- and suprathreshold light flashes caused a long-lasting (seconds or minutes) potentiation of responses to subsequent test flashes. The lightflash response was also potentiated by a preceding intracellular injection of IP3 and by extracellular application of an agonist thought to induce IP3 liberation. However, intracellular injections of calcium depressed the response. We conclude that the liberation of calcium from intracellular stores varies nonlinearly with the intracellular level of IP3. This phenomenon may explain earlier observations, including the long latency of currents evoked by low doses of agonists such as acetylcholine and serotonin, and the nonlinear facilitation seen between these agonists. Further, it suggests a mechanism for “chemical integration,” which may be important in the functioning of neurons and other cells which use IP3 as an intracellular messenger.
Innervation of the kidney of Aplysia by L10, the LUQ cells, and an identified peripheral motoneuron
Authors: Koester J , Alevizos A
Published: March 2018

The purpose of this study was to begin to describe the neural circuit within the abdominal ganglion that modulates renal functioning in Aplysia. We found that the previously described cholinergic neuron L10 and peptidergic left upper quadrant (LUQ) neurons have important roles in the control of the kidney. Cell L10 and a subset of the LUQ cells branch extensively within the kidney and send major processes to the renal pore, a sphincter that controls the efflux of urine. The renal pore has circular (closer) and radial (opener) muscle fibers that act as antagonists. Embedded within the wall of the renal pore is a newly identified peripheral neuron, RPO, which is a renal pore opener motoneuron. L10 activity causes opening of the renal pore by directly exciting pore opener muscle, inhibiting closer muscle, and exciting RPO. When RPO is active, it generates synchronous, discrete twitches in the opener muscle fibers. The action potentials recorded in RPO exhibit pronounced broadening at physiological rates of firing. LUQ cells that project to the renal pore cause it to close, and they antagonize the opening generated by an L10 burst. The pore closing caused by the LUQ cells is mediated in part by heterosynaptic inhibition of the L10 to RPO excitatory connection. The previously described central inhibitory connections from L10 to the LUQ cells ensure that these 2 classes of antagonists fire out of phase with each other. Our data, along with those from earlier studies demonstrating that L10 plays an important role in controlling the circulatory system, suggest that L10 and the LUQ cells modulate various aspects of renal function in Aplysia, including filtration and micturition.
Hypothalamic expression of a novel gene product, VGF: immunocytochemical analysis
Authors: van den Pol AN , Decavel C , Levi A , Paterson B
Published: March 2018

VGF is the designation for a new 712 amino acid protein, regulated by nerve growth factor (NGF) in PC12 cells, that has not been previously described in the CNS. Northern blot analysis with a nick-translated VGF cDNA probe revealed a single band of mRNA in the brain with a molecular weight identical to that found in PC12 cells. The current paper presents a series of immunocytochemical studies of VGF expression with a focus on the hypothalamus. Two different antisera were raised against nonoverlapping amino acid sequences of a bacterial-expressed protein from the VGF gene cloned from PC12 cells. VGF immunoreactivity is strongly expressed in the rat suprachiasmatic nucleus (SCN), particularly in the dorsomedial part of the nucleus. The administration of colchicine to block axonal transport facilitates detection of the VGF immunoreactivity also in the ventrolateral suprachiasmatic nucleus. This protein appears to be the first one of limited neuronal distribution which is found in both dorsomedial SCN and ventrolateral SCN. Immunostaining of serial 1 micron SCN sections reveals co- localization of VGF in cells which also contain vasopressin or vasoactive intestinal polypeptide. Weaker immunoreactivity is also found in the magnocellular paraventricular and supraoptic nuclei, where the VGF immunoreactivity co-localizes with oxytocin or vasopressin. Mutant Brattleboro rats which do not express vasopressin showed strong VGF immunoreactivity both in the dorsomedial SCN and in cells of the magnocellular neuronal systems, including cells which normally express vasopressin. When axonal transport of the protein is blocked by colchicine, VGF-immunoreactive cells in the hypothalamic arcuate, parvocellular paraventricular, and tuberomammillary nuclei can also be detected, in addition to weakly immunoreactive scattered cells in the hippocampus, amygdala, thalamus, and cortex. VGF immunoreactivity is strong in the axonal projections of SCN and weak in the axons of the paraventricular and supraoptic nuclei. With ultrastructural studies, VGF immunoreactivity is found in presynaptic boutons in the SCN and in axons in the neurohypophysis. Weak axonal staining is present in some regions of the hypothalamus and in the external and internal zones of the median eminence. Immunoreactivity is absent from the intermediate lobe of the hypophysis. In neonatal rats strong VGF immunoreactivity is found throughout the SCN at postnatal day 4 but not in the adjacent hypothalamus. VGF immunoreactivity is also seen in other areas of the brain in neonatal rats, including the lateral geniculate nucleus; while the staining in the dorsal lateral geniculate disappears in the adult, that in the intergeniculate leaflet, a visual center which projects to the SCN, remains.(ABSTRACT TRUNCATED AT 400 WORDS)