Distribution of calcium-binding proteins,parvalbumin and calbindin,in the midbrain auditory center (MLd) of a pigeon

Immunohistochemical distribution of calcium-binding proteins, parvalbumin (PV) and calbindin (CB), has been studied in the mesencephalic auditory center (MLd) of pigeon (Columba livia). In the central region of the MLd (core, ICC), an overlap in distribution of the PVand CB-immunopositive (ip) neurons and neuropil has been observed, with different patterns in the central and peripheral parts. In the peripheral region of the MLd (belt, ICS, and ICX), both neurons and neuropil contained only CB. A selective CB chemospecificity of the belt, ICS, and ICX is an evolutionary conserved feature characteristic of all avian species. Interspecies differences in the distribution of PV and CB immunoreactivity in the ICC are a result of adaptive functional specialization, which provides specific processing of different aspects of the auditory information.     

Termination of the afferent fiber in the spinal cord of the turtle Testudo horsfieldi and three-dimensional reconstruction of the sensory-motoneuron connection

Horseradish peroxidase (HRP) tracing methods and subsequent computer reconstruction were used to study the structural organization of sensory-motoneuron connections in turtles. HRP was applied through suction electrodes to thin dorsal and ventral root filaments of superfused isolated lumbar spinal cord of the turtle Testudo horsfieldi. Single motoneurons were labeled ionophoretically with intracellular glass microelectrodes. Labeled elements were examined under a light microscope. The Eutectic neuron tracing system and its associated program were used for three-dimensional reconstructions and morphometry. The distribution of afferent fibers of the dorsal root and their terminations were presented in a new scheme in which new zones, in addition to those that were already well known, were shown, including the following: in the Lissauer zone, motor nuclei, and ventrolateral funiculus, as well as in the contralateral medial gray matter (laminae IV–V). Unlike in frogs, the motoneuron dendritic field in turtles was restricted to an ellipsoid space with a short axis in the rostrocaudal direction (300–500 µm). The afferent fibers of the dorsal root connected to motoneurons produced very short branches in a restricted rostrocaudal direction (50–70 μm). One fiber collateral of the dorsal root had about 80 synapse-like enlargements (approximately tenfold fewer than in frogs). Putative sensory-motoneuron contacts were found on the I–VII-order dendritic segments of the dorsal and ventro-medial dendritic trees. It was shown that, in turtles, only one first-order collateral of the dorsal root fiber participated in the sensory-motoneuron connection with a small number (about 4) of putative contacts, which is also one order less than in frogs. It is likely that the simplification of the synapse structure in turtles is compensated by a higher efficiency of the signal transmission comparable to that in mammals.     

Involvement of 5-HT1 and 5-HT5A Receptors in Modulation of Synaptic Transmission and Intrinsic Membrane Properties of Spinal Motoneurons of the Frog (Rana ridibunda)

Journal of Evolutionary Biochemistry and Physiology - The endogenous monoamine serotonin (5-HT) is involved in the modulation of motor output in vertebrates by interacting with different types of...     

Effects of Serotonin on Primary Afferents in the Frog Spinal Cord

We studied, on isolated preparations of the frog spinal cord, the effects of serotonin in different concentrations on the amplitude-temporal parameters of action potentials (AP) in primary afferent fibers, on the potentials reflecting depolarization of primary afferents (DPA), and on the properties of the membrane of these fibers. It was demonstrated that in a part of the dorsal root afferent fibers serotonin caused a drop in the AP amplitude (by 15-20%) and an increase in the AP duration (by 8-13%). Serotonin also significantly (by 70-90%) decreased the amplitude of DPA induced by stimulation of a neighboring dorsal root and noticeably reduced the input membrane resistance of afferent fibers. Serotonin-induced modulation of the AP parameters in the afferents and suppression of DPA under the influence of this amine are postulated as possible factors involved in the central control of afferentation.     

Collaterals and Bifurcations of Axons of Spinal Cord Motoneurons of the Lamprey <Emphasis Type="Italic">Lampetra fluviatilis</Emphasis>

Structure of central projections of the motoneuron axons of the spinal cord of the lamprey Lampetra fluviatilis was studied using labeling with horseradish peroxidase in vitro. Axons of the lamprey spinal cord motoneurons were found to have collaterals terminating in ventral columns of the white matter, in which they establish contacts with dendrites of adjacent motoneurons, which can be considered as a substrate of the intermotoneuron interaction. Some axons of motoneurons give bifurcations to two equal branches connected with two neighboring ventral roots, which seems to facilitate propagation of rhythmic activity of locomotor generator in the rostro caudal direction for providing continuous wave of contraction of myotome muscles in the course of undulating movement.     

Effects of GABA and Glycine on Postsynaptic Potentials of Motoneurons of the Frog <Emphasis Type="Italic">Rana ridibunda</Emphasis>

On a preparation of isolated spinal cord of the frog Rana ridibunda, using intracellular recording from lumbar motoneurons, there were compared effects of GABA and Gly on membrane potentials, membrane resistance, and EPSP evoked by activation of dorsal root fibers or of brainstem reticular formation. All parameters were compared in the same cell. At the same concentration (10 mM), Gly evoked membrane depolarization by 20–50% greater than GABA. Response of application of a mixture of GABA and Gly was by 20% lower than the arithmetic sum of responses to the GABA application and the Gly application. The late components and the semiwidth both of complex and of simpler DR and RF EPSP decreased significantly (to 95%) on the background of application of GABA and Gly. The late components of the both EPSP were inhibited stronger by GABA than by Gly. The early mono- and disynaptic EPSP components were inhibited to the essentially lesser degree than the late components. Gly always inhibited the early DR EPSP more markedly than GABA did. In the greater part of motoneurons the early RF EPSP were stronger inhibited by Gly, in their smaller part, by GABA. In many motoneurons the early components did not decrease at all. The motoneuron membrane resistance decreased under effect of GABA and Gly to the approximately equal extent (by 10–30%). Not in all neurons there was revealed the correspondence between a decrease of the membrane resistance (R_M) and a decrease of the early EPSP components. Based on the obtained data, it is suggested that the inhibitory influences in frogs is mediated by both Gly- and GABA-receptors. On the membrane of motoneuron the inhibition is mediated to the relatively greater degree by Gly-receptors, whereas on the membrane of interneurons, by GABA-receptors. During inhibition of DR EPSP the predominance of Gly-receptors is observed in the greater number of motoneurons than during inhibition of RF EPSP. Between individual motoneurons there are significant quantitative differences of all parameters.