bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuronal circuit reorganization in mammalian agranular cerebellar cortex
Authors: Llinás R. , Hillman D. E. , Precht W.
Published: January 2005

Morphological and electrophysiological studies of the agranular cerebellar cortex of ferret after infection with panleukopenia virus have led to the following conclusions:

At light microscopic level this agranular cerebellar cortex is shown to be totally disorganized when compared to its normal lamination.

From an ultrastructural point of view, Purkinje cells are present throughout the thickness of the cerebellar cortex, demonstrating dendritic branches studded with unwed spines.

Purkinje cells receive four different types of inputs‐climbing fibers, mossy fibers, stellate cell terminals, and Purkinje cell axon collateral terminals. The mossy fiber contacts which are generally not present in mammals are made in some cases to elongated, “dolichoderic” spines.

Stellate, basket, and Golgi cell interneurons are present, and receive inputs from mossy and climbing fiber terminals, and probably from axon collaterals of Purkinje cells. The mossy fiber input to these neurons represents a true reorganization of the cerebellar circuit, since it has never been observed in any other vertebrate.

Stellate and basket cells terminate in contact with dendrites and somata from Purkinje cells, while the Golgi cell terminals seem to be restricted to somata and dendrites of other Golgi cells.

Electrophysiologically, Purkinje cells can show normal excitability following antidromic invasion, and may be activated by the mossy and climbing fiber afferent systems. Intra‐and extracellular recording from Purkinje cells demonstrates that the mossy fiber afferent system activates Purkinje cells with a latency of approximately 1 msec and its excitatory action is graded with relation to the amplitude of the white matter stimulation. Following an initial excitation, this input generates a longlasting inhibition (50 msec), which is attributed to mossy and climbing fiber activation of inhibitory interneurons.

Climbing fiber activation generates the typical all‐or‐none burst response in Purkinje cells extracellularly. Intracellularly, large unitary EPSPs characteristic of this form of activation may be recorded with a latency of 1.5 to 3 msec. This large unitary EPSP seems to behave in the usual one‐to‐one relation (one climbing fiber to one Purkinje cell).

Double climbing fiber activation reveals that a conditioning white matter stimulation produces a total inhibition of a climbing fiber burst at 15 msec interval, which indicates a rather strong inhibitory action on Purkinje cells following this form of activation.

Climbing fiber activation is followed in most cases by a so‐called climbing fiber reflex, suggesting that the inferior olive in this agranular condition is functioning in a normal manner.

Finally, some of the neurobiological implications of these findings are considered in the discussion.
Neuronal basis of behavior in Tritonia. II. Relationship of muscular contraction to nerve impulse pattern
Authors: Hoyle G. , Willows A. O. D.
Published: January 2005

Recordings were made of the movements elicited in the body of Tritonia diomedia by direct intracellular stimulation of identified brain neurons, which have a motor command function. It was shown that the latency of a movement response decreases as the frequency of stimulation is increased in the range 1 Hz to 20 Hz. Over the same range, the speed of the response increases. The extent, and also the speed, of a movement are proportional to the total number of stimuli, but response speeds and magnitudes vary greatly at different times. The minimum latency, after deduction of conduction time, is 160 ms at 11 °C.

It is concluded that the identified brain cells, which cause discrete movements, do so indirectly, by activating a peripheral nerve net which in turn excites the muscle fibers. The nerve net is the site of independent excitatory, inhibitory, and local reflex action.
Five classes of visual interneurons in the optic nerve of the hermit crab
Authors: Glantz Raymon M.
Published: January 2005

Response characteristics and trigger features are described for five operational classes of visual interneurons in the optic nerve of the hermit crab. The units were initially segregated on the basis of response sign (“on”, “off”, “on‐off”) and duration (phasic, tonic). Tonic “on” and tonic “off” units were observed to be indistinguishable from the previously described sustaining and dimming fibers of other decapod crustacea. Phasic “off” units closely resemble either jittery motion or novelty detectors also previously documented. Phasic “on” units are characterized by an excitable antagonistic surround, a slow rate of habituation, and a sustained low level discharge during periods of increasing luminous flux at any point within their receptive fields. Highly sensitive to moving contours, they occasionally revealed a directional preference. The phasic “on” units are also capable of following brief stimuli at rates of up to 20/sec. Phasic “on‐off” units were characterized by coextensive receptive fields for “on” and “off” responses and movement sensitivity independent of contrast.
Restorative effects of cyclic AMP on complex bioelectric activities of cultured fetal rodent CNS tissues after acute CA++‐deprivation
Authors: Crain Stanley M. , Pollack Emanuel D.
Published: January 2005

Explants of fetal mouse spinal cord and cerebral cortex generate organotypic slow‐wave and repetitive‐spike discharges in vitro which can be abolished by agents which reduce the concentration of Ca++ available to the tissue. Synaptically mediated discharges are rapidly blocked in Ca++‐free balanced salt solution (BSS), or in regular BSS after addition of 10−3 M EGTA, 5–10 × 10−3 M Mg++, or 10−4 M xylocaine, but simple spike potentials can still propagate. When low concentrations of cyclic AMP or dibutyryl cyclic AMP (2 × 10−6 M) are added to the Ca ++‐free BSS or Ca++‐antagonist‐BSS, a temporary (1–20 min) restoration of characteristic complex bioelectric activities occurs (or the onset of depression is delayed if cyclic AMP is initially added). Phosphodiesterase inhibitors, e.g. 10−3 M caffeine, are also effective in restoring these blockades, whereas 5′AMP and ATP are not. Application of 10−6 M cyclic AMP or 10−3 M caffeine in regular BSS greatly enhances excitability of some CNS explants, resembling convulsive effects observed in CNS in situ.

The data suggest that cyclic AMP can mobilize Ca++ from membranebound Ca pools within neurons in CNS explants so as to permit Ca++‐dependent release of neurotransmitter during Ca++ deficits. Thus, it may also be that under normal conditions, cyclic AMP can regulate the availability of Ca++ for synaptic transmission in the central nervous system, thereby modulating the efficacy of synaptic functions.
Effects of axonal injury on norepinephrine, tyrosine hydroxylase and monoamine oxidase levels in sympathetic ganglia
Authors: Cheah T. B. , Geffen L. B.
Published: January 2005

A combined morphological and biochemical study was made of the responses of lumbar sympathetic ganglion cells to ligation of their axons in the sciatic nerve of the rat. There was a progressive accumulation of norepinephrine proximal to the ligature for the first few days without detectable changes in the ganglion cells. However, three days after ligation there was a decrease in the axoplasmic accumulation of norepinephrine, accompanied by pronounced falls in ganglion norepinephrine, tyrosine hydroxylase, and monoamine oxidase. These changes, that coincided with the development of signs of chromatolysis in the light and electron microscope, were fully developed one week after ligation and by one month were almost reversed. Proteolysis and death of chromatolytic cells may have made some contribution to the observed changes, but there were no significant changes in the soluble protein content of the lumbar ganglia, presumably because of the counter‐balancing increase in protein synthesis known to occur during chromatolysis and regeneration. It is suggested that axotomy caused a reordering of the priorities of protein synthesis in sympathetic neurones to favor the production of proteins necessary for regenerative rather than transmitter functions.
Dopaminergic neurons in explants of substantia nigra in culture
Authors: Coyle Joseph T. , Jacobowitz David , Klein David , Axelrod Julius
Published: January 2005

Explants of substantia nigra and corpus striatum obtained from newborn rats were maintained in tissue culture for up to six days. Explants of substantia nigra exhibited a net increase in the ability to take up H3‐dopamine, a process associated with the dopaminergic neurons; in contrast, the explants of corpus striatum showed a rapid loss in this ability to accumulate H3‐dopamine. After three days in culture, the specific activity of tyrosine hydroxylase and monoamine oxidase had decreased 50% in explants of substantia nigra. A medium including fetal calf serum and chick embryo extracts was necessary for the increase in H3‐dopamine uptake, and nerve growth factor had an inhibitory effect. Histofluorescent examination of nigral explants cultured for three days indicated morphologically normal dopaminergic neurons.
Intracortical impedance changes during spreading depression
Authors: Hoffman Clifford J. , Clark Francis J. , Ochs Sidney
Published: January 2005

Specific impedance at various depths in the cerebral cortex of the rat was measured using a newly developed thin film coaxial microelectrode. This novel electrode has the advantage of measuring specific impedance of extremely small volumes of tissue, and thus of making highly localized measurements.

The resting level of cortical impedance in the rat was found to be stable, but to vary for different sites and animals from 200–700 ohm‐cm. During spreading depression, loop‐shaped impedance loci were consistently observed in the complex impedance plane with peak magnitude 2–3 times resting level. These unusual loop‐shaped loci are thought to represent distinct process differences during development and recovery phases of spreading depression.

This preliminary investigation has demonstrated the feasibility of a technique for making highly localized impedance measurements in nervous tissue. Such measurements are useful for in vivo studies of such tissue parameters as extracellular space.
Control of habituation of the withdrawal reflex by the gill ganglion in Aplysia
Authors: Peretz Bertram , Moller Robert
Published: January 2005

The regions of the gill neural plexus responsible for habituation of the withdrawal reflex were studied using surgical and electrophysiological techniques. Waterdrops were applied to the gill pinnule, and testing for habituation was carried out in each preparation before and after ganglionectomy of the large ganglion in the gill and pinnule isolation. Three parameters of habituation, response decrement, spontaneous recovery, and dishabituation, were used to evaluate the function of the ganglion and the plexus in the pinnule in habituation of the reflex. Disruption of response decrement, of spontaneous recovery, and of dishabituation were caused by either isolating the stimulated pinnule from the gill ganglion by severing the branchial nerve, or by extirpating the gill ganglion. We conclude that: (a) the gill ganglion is necessary for the withdrawal reflex to exhibit the three parameters which characterize hibituation; and (b) the plexus in the pinnule mediates the withdrawal reflex. Extracellular recordings from the pinnule showed that sensory adaptation cannot be contributing to habituation of the reflex since the apparent sensory activity evoked by waterdrops in the pinnule was unaltered by repeated stimulation. In gill ganglion neurons, biphasic potentials were evoked by waterdrops and consisted of an initial depolarization followed by a longer lasting hyperpolarization whose duration was increased with repeated stimulation. In three spontaneously active neurons the rate of activity decreased with repeated stimulation. It is felt that the decreased rate is brought about by potentiation of the hyperpolarization. The rate of spike activity is considered to control the reflex amplitude since the increased rate with intracellular stimulation, in one neuron, resulted in an increased amplitude and since the absence of spontaneous discharge, after ganglionectomy, resulted in a reduced amplitude. A neural network mediating habituation of the withdrawal reflex is proposed.
Specific protein metabolism in identifiable neurons of Aplysia californica
Authors: Gainer Harold , Wollberg Zvi
Published: January 2005

The patterns of protein metabolism of identified cholinergic (R2, L10, and L11) and neurosecretory (R3–13, R14, and Bag cells) cells were analyzed with the use of SDS‐polyacrylamide gel electrophoresis and isoelectric focusing. L11 was unique amongst the three cholinergic neurons in its relatively high rate of incorporation of labeled leucine into proteins at 12,000 daltons. All the neurosecretory cells incorporated relatively large quantities of 3H‐leucine into small proteins (<12,000 daltons), which were concentrated in putative neurosecretory granule fractions of these cells. R3–13 and R14 synthesized a distinct basic protein which appeared specifically in the branchial nerve which contains the axons of these cells. The combination of these two analytical electrophoretic techniques allowed for the characterization of protein specificity in single nerve cells.
Comparative effects of nerve growth factor and ganglionic nonneuronal cells on purified mouse ganglionic neurons in culture
Authors: Varon Silvio , Raiborn Charles , Burnham Patricia
Published: January 2005

Purified neuronal fractions from dissociated mouse dorsal root ganglia were cultured in the presence of variable amounts of homologous ganglionic nonneuronal cells, and with or without addition of variable amounts of exogenous Nerve Growth Factor in the culture medium. The ability of the nonneurons to support long‐term neuronal survival in the absence of exogenous Nerve Growth Factor increased linearly with their numbers and maximal neuronal performance was achieved with a 4:1 ratio of non‐neurons to neurons; however, neuronal attachment was elicited maximally as soon as that ratio reached or slightly exceeded a value of one. Besides this Nerve Growth Factor‐like function, the nonneurons were also involved in determining whether and to what extent the factor was capable of supporting neuronal performance. In the absence of non‐neurons, even high concentrations of the factor failed to elicit neuronal attachment. As more nonneuronal cells were made available, Nerve Growth Factor progressively raised neuronal performance and did so at sharply declining requirement levels: with 12,000 nonneurons/dish maximal performance required only 10−2 biological unit/ml of the factor. Further increases of the nonneurons reduced the scope of a neuronal response to Nerve Growth Factor between the maximal performance of the culture system and the increasing performance elicited without the factor. The results indicate that, given a minimal level of nonneurons, the performance in culture of these ganglionic neurons could be promoted in very similar patterns by either increasing the exogenous Nerve Growth Factor in the medium or increasing the ganglionic nonneurons on the culture floors, with an approximate and fixed ratio of 10−7 biological unit per nonneuron. Possibilities are discussed of a common mechanism underlying the supportive properties of the two agents.
Incorporation of [14C] ethanolamine and [3H] Methionine into phospholipids of rat brain and liver in vivo and in vitro
Authors: Morganstern Roberta D. , Abdel‐Latif Ata A.
Published: January 2005

Comparative studies were undertaken on the in vivo and in vitro incorporation of [14C] ethanolamine, [3H] methionine and [14C] S‐adenosyl‐methionine into phosphatidylethanolamine (PhE) and phosphatidylcholine (PhC) of rat liver and brain. It was observed that brain can synthesize de novo PhC from PhE via the transmethylation pathway, however synthesis rates were (1) markedly lower than those of liver and (2) decreased significantly with age. In the choline‐containing lipids more than 95% of the radioactivity was found in PhC. Studies on the localization of the radioactivity in PhC following the intracranial injection of [3H] methionine or [14C] ethanolamine revealed that both precursors are incorporated almost exclusively into the choline moiety of this phospholipid. There was significant labeling of PhC only when the precursors were administered intracranially and much less incorporation was observed with the systemic routes. Thus following the intravenous administration of [14C] ethanolamine, the specific radioactivities of liver PhE and PhC were up to 75 times as high as those of brain and 4 to 5 times as high in the organs of the 20‐day old as those of the adult. In contrast, when this precursor was administered intracranially the specific radioactivities of both phospholipids in liver were only twice as high as those of brain. Although the short‐and long‐term time‐course studies on the in vivo incorporation of [14C] ethanolamine and [3H] methionine into PhC of both organs could suggest a precursor‐product relationship between the biosynthesis of this phospholipid in liver and brain, this apparent relationship could also be due to the high turnover of PhE in liver, with half‐life of 2.87 hr, and its low turnover in brain, with half‐life of 10.7 days. The present findings on the low rate of formation of PhC from PhE in brain coupled with the fact that this conversion declines sharply with age, especially when the isotopes are administered systemically, could explain the observation of previous investigators that the brain cannot synthesize its own choline and thus it must derive its choline from exogenous sources such as lipid‐choline. It was concluded that the brain can synthesize its own choline; however it remains also dependent on liver and dietary choline which are probably transported into the brain as free choline.
Habituation of mechanoreceptive interneurons in the crayfish
Authors: Aréchiga H. , Barrera‐Mera B. , Fuentes‐Pardo B.
Published: January 2005

The effect of repetition of sensory stimuli was studied on the responses of mechanoreceptive interneurons in the optic tract of the crayfish (Procambarus bouvieri (Ortmann)). The number of spikes recorded from a given unit gradually decreased during a train of stimuli. The decrease showed a negative exponential time course, with a curvature dependent upon the frequency of stimulation, the intensity of stimuli, and the hour of the day. Habituation is selective for the intensity and rate of stimulation, and the particular spot of receptive field stimulated. Locomotor excitation results in a dimminution of the rate of decay. The effect of a single train of stimuli when leading to pronounced habituation may persist for periods longer than 24 hr.
Differences in some properties of newborn and adult brain glutamate decarboxylase
Authors: Tapia Ricardo , Meza‐Ruíz Graciela
Published: January 2005

Some properties of glutamate decarboxylase (EC 4.1.1.15) activity in brain of newborn and adult mouse were studied comparatively. It was found that glutamate decarboxylase of the newborn brain was strongly inactivated by homogenization in hypotonic medium, centrifugation of isotonic sucrose homogenates, preincubation at 37°C or the addition of Triton‐X‐100, whereas the adult brain enzyme was practically unaffected by any of these conditions. It was also found that the newborn glutamate decarboxylase was less activated by pyridoxal 5′‐phosphate and less inhibited by pyridoxal 5′‐phosphate oxime‐O‐acetic acid, than the adult enzyme. These differences do not exist for brain dihydroxyphenylalanine decarboxylase (EC 4.1.1.26) and are not due to the release of inhibitors from the newborn brain. On the basis of the results obtained it is postulated that two forms of glutamate decarboxylase exist in brain: a newborn form, which is unstable and has high affinity for pyridoxal 5′‐phosphate, and an adult form, which is much more stable and has low affinity for pyridoxal 5′‐phosphate. The possible implications of these findings in the establishment of the σ‐aminobutyric acid dependent synaptic inhibitory mechanisms during development are discussed.
A quantitative analysis of isotope concentration profiles and rapid transport velocities in the C‐fibers of the garfish olfactory nerve
Authors: Gross Guenter W. , Beidler Lloyd M.
Published: January 2005

In the olfactory nerve of the long‐nosed garfish (Lepisosteus osseus), unusually well‐defined isotope concentration distributions can be established with the rapid transport process. Transport velocities of two profile loci can be accurately described and a quantitative profile analysis is possible after profile normalization. Results from such studies indicate that: (1) peak amplitudes decrease exponentially as a function of distance from the olfactory mucosa according to the equation p = 2130 exp (– 0.109x); (2) the wavefront base and the peak apex loci move at rates of 221 ± 2 and 201 ± 4 mm/day, respectively (at 23°C), revealing a peak dispersion or broadening during transport; (3) the broadening is asymmetric with material shifting to the rear of the peak; (4) plateau regions are established behind the peak with material deposited by the peak; (5) only 20% of the total radioactivity in a cut nerve reaches the nerve terminals in the rapid transport peak while 80% is deposited along the axon; (6) profile areas from cut nerves decrease and lose 15% of their activity in 20 hr, while intact nerve profiles increase 10% in 16 hr due to continued somal contribution to the profile; (7) the displacement of the wavefront base (WFB) and peak apex (PA) profile loci can be described by the functions

(8) transport velocities are linear functions of temperature between 10 and 25°C and increase 370% in that range. A linear extrapolation of the WFB and PA functions to 37°C yields 410 and 377 mm/day, respectively.
Effect of aromatic acids on protein synthesis in subcellular preparations from the rat brain
Authors: Lähdesmäki P. , Oja S. S.
Published: January 2005

The incorporation of [3H]phenylalanine, [3H]tyrosine, and [3H]tryptophan into protein and amino acyl–tRNA was studied in cell‐free preparations from rat brain. Tyrosine and tryptophan inhibited the incorporation of phenylalanine into protein, and tyrosine inhibited the incorporation of phenylalanine and tryptophan into amino acyl–tRNAs. In most cases, homogentisate, phenylpyruvate, and phenyllactate inhibited the incorporation of phenylalanine, tyrosine, and tryptophan into protein and amino acyl–tRNAs, and the incorporation of phenylalanine into polyphenylalanine. All other protein amino acids, and phenylacetate, salicylate, and benzoate were wholly ineffectual. The results suggest that the formation of amino acyl–tRNAs may have been the step which was affected most by the inhibitors. The incorporation data at different concentrations of the aromatic amino acids were fitted to the simple Michaelis equation. Homogentisate and phenylpyruvate generally tended to reduce both Km and V in the incorporation of aromatic amino acids into protein and amino acyl‐tRNAs, even if V decreased more than Km.
Neuromuscular junctions in the buccal mass of Aplysia: Fine structure and electrophysiology of excitatory transmission
Authors: Orkand P. M. , Orkand R. K.
Published: January 2005

The lower extrinsic protractor muscle in the buccal mass of Aplysia consists of bundles of muscle fibers 4–12 m̈ in diameter, containing thick and thin filaments that are not arranged in a transversely striated pattern. Individual fibers come close to one another and form specialized junctional regions. Electrophysiological evidence indicates that the muscle fibers form an electrical syncytium. Muscle bundles are innervated by more than one excitatory axon at a number of points along their length. The presynaptic terminals contain spherical electron‐lucent vesicles and a few larger electron‐dense vesicles. There are no obvious structural postsynaptic specializations. Graded contraction can result from summation of excitatory junctional potentials in separate axons or from summation and facilitation of junctional potentials from a single axon. The buildup of facilitation during a train of stimuli results from the linear summation of facilitation remaining from preceding impulses.
Isolation from bovine brain of a fraction containing capillaries and a fraction containing membrane fragments of the choroid plexus
Authors: Sessa Grazia , Orlowski Marian , Green Jack Peter
Published: January 2005

Combined differential and density gradient centrifugation was used for the isolation of a capillary‐rich fraction from the cerebral cortex and a brush border containing fraction from the bovine choroid plexus.

The activities of γ‐glutamyl transpeptidase and several other marker enzymes were monitored during the fractionation procedure. Electron microscopic examination showed a membrane‐rich fraction in the choroid plexus high in γ‐glutamyl transpeptidase and 5'‐nucleotidase activities. From the brain cortex, a capillary‐rich fraction was obtained which was high in γ‐glutamyl transpeptidase and alkaline phosphatase activities. A histochemical examination showed γ‐glutamyl transpeptidase activity localized in the capillary walls.
Ionic mechanism of 5‐hydroxytryptamine induced hyperpolarization and inhibitory junctional potential in body wall muscle cells of Hirudo medicinalis
Authors: Sawada Masashi , Coggeshall Richard E.
Published: January 2005

Five‐hydroxy tryptamine (5‐HT) causes a hyperpolarization and increased conductance of the leech body wall muscle cell membrane. If 5‐HT is applied in the absence of the Cl−ion, the response appears as a depolarization, whereas if 5‐HT is applied in the absence of the K+ion, the response is a hyperpolarization. In both cases, the conductance of the muscle cell membrane is increased. Stimulation of the peripheral nerve to the body wall muscle produces a complex junctional potential in muscle cells. Exposing the muscle to d‐tubocurarine (d‐TC) eliminates the excitatory component (EJP) of the complex potential. The inhibitory potential (IJP) that remains has an equilibrium potential at approximately 65 m V. Furthermore, this IJP appears as a depolarization when the nerve is stimulated in the presence of d‐TC and low CL−, whereas this is not the case if the nerve is stimulated in the presence of d‐TC and low K+. The drugs BOL‐148 and cyproheptadine block the IJP's in the body wall muscle. These data are interpreted as indicating that 5'HT acts on leech body wall muscle cells by increasing the conductance to the Cl−ion and that the IJP's caused by nerve stimulation are probably the result of 5‐HT release at nerve terminals.

As a final point, it has been shown that the inhibition by 5‐HT of the spontaneous EJP's that occur on the leech body wall muscle results from an inhibition of central neurons and not from any direct effect on the muscle cell or on peripheral synapses.
Effects of different ions on resting polarization and on the mass receptor potential of carotid body chemosensors
Authors: Eyzaguirre C. , Nishi K.
Published: January 2005

The carotid body and its own nerve were removed from cats anesthetized with sodium pentobarbital and placed in an air gap system; the carotid body was bathed in modified Locke's solution equilibrated with 50% O2 in N2, pH 7.43 at 35°C. The sensory discharges, changes in “resting” receptor polarization and the mass receptor potential evoked by ACh or NaCN were recorded with nonpolarizable electrodes placed across the gap.

Receptor potentials and sensory discharges evoked by ACh showed an appreciable increase in amplitude and frequency when the preparation was bathed in eserinized Locke. Eserine did not change appreciably the responses evoked by NaCN. Excessive depolarization elicited by either ACh or NaCN was accompanied by sensory discharge block.

Removal of K+ ions from the bathing solution induced receptor hyperpolarization and an increase in the amplitude of the evoked receptor potentials. An increase of K+ concentration had the opposite effect.

Reduction of Na+ or NaCl to one half, or total removal of this salt, induced an initial reduction and later disappearance of the sensory discharges, some receptor hyperpolarization and a reduction in the amplitude of the evoked receptor potentials.

Reduction or removal of Ca++ produced receptor depolarization, a marked depression of the evoked receptor potentials, an increase in the frequency of the sensory discharges and a reduction in the amplitude of the nerve action potentials.

High Ca++ or Mg++ had little or no effect on action potential amplitude or resting polarization, but decreased sensory discharge frequency and the evoked receptor potentials.

Total or partial replacement of Ca++ with Mg++ induced complex effects: (1) receptor depolarization which occurred in low Ca++, was prevented by addition of Mg++ ions; (2) the amplitude of the evoked receptor potentials was depressed; (3) the nerve discharge frequency was reduced as it was in high Mg++ solutions; and (4) the amplitude of the nerve action potentials was reduced as it was in low Ca++ solutions.

Temperature had a marked effect on the chemoreceptors since a t high temperatures the receptors were depolarized and the discharge frequency increased. The baseline discharge and responses evoked by ACh or NaCN were depressed at low temperatures.

The results are discussed in terms of possible receptor mechanisms influenced by the different ions.
Muscle insensitivity to tetrodotoxin: Induction by α‐bungarotoxin and removal by submechanical threshold stimulation
Authors: Gruener Raphael , Baumbach Neal
Published: January 2005

Intramuscular injection of alpha‐bungarotoxin (αBGT) into rat extensor digitorum longus muscles produced pharmacological blockade of neuromuscular transmission and resulted in denervation‐like changes (Berg, D. and Hall, Z. (1975), J. Physiol. (London) 244:659–676). More than 80% of fibers from αBGT‐injected muscles produced action potentials (ap's) in the presence of tetrodotoxin (TTX, 1 × 10−6 M). Chronic electrical stimulation of these muscles, below the level necessary to elicit a contraction, resulted in a marked return toward normal of sarcolemmal sensitivity to TTX. After 4 days of submechanical threshold stimulation, less than 45% of αBGT‐injected fibers produced ap' in the presence of TTX, whereas more than 80% of unstimulated fibers from contralateral control muscles exhibited resistance to TTX. These findings indicate that in addition to sarcolemmal sensitivity to acetylcholine, sensitivity of the sodium conductance mechanism to TTX is also directly influenced by muscle activity independent of contraction.
Intracellular calcium and extra‐retinal photoreception in Aplysia giant neurons
Authors: Brown A. M. , Brodwick M. S. , Eaton D. C.
Published: January 2005

The early or “instantaneous” current‐voltage relationship for the light‐activated potassium current in Aplysia giant neurons was linear during the first second of illumination. However, the light current was greatly reduced or abolished by prolonged hyperpolarization. It was also greatly reduced by the injection of calcium EGTA buffers having calcium activities of 5.6 × 10−8 M and simulated by injecting buffers with calcium activities of 2.8–5.6 × 10−7 M. Removal of calcium from the extracellular fluid had no effect. Both the light‐and calcium‐activated outward potassium currents were reduced by tetra‐ethylammonium (TEA) ions. The light current was not affected by substituting rubidium for potassium nor by substituting either lithium or Tris for sodium. The calcium‐activated potassium current persisted when the neuron was cooled to 5°C. However, the light response could no longer be elicited. Light hyperpolarizes Aplysia neurons probably by increasing intracellular calcium activity two‐to six‐fold which activates a membrane potassium conductance. Calcium levels appear to be restored within the cell and are energy dependent. The light‐activated release of calcium is inhibited by cooling. The body wall of Aplysia transmits enough visible or 500‐nm light to hyperpolarize some Aplysia giant neurons under ambient conditions. These neurons may be involved in the extraretinal light entrainment that occurs in Aplysia.
Neurotrophic control of cyclic nucleotide levels during muscle differentiation in cell culture
Authors: Festoff B. W. , Oh T. H.
Published: January 2005

The effects of chick brain–spinal cord extract on morphological development and cyclic nucleotide levels of cultured chick embryo skeletal muscle cells were determined. It had previously been shown that the extract stimulated morphological differentation, protein synthesis, and cholinesterase activity of muscle cells. Myoblasts fused earlier and an increase in number as well as diameter of myotubes were seen in the extract treated cultures. Cyclic nucleotides levels were higher (almost twice the controls for both adenosine 3′, 5′ ‐cyclic monophosphate and guanosine 3′, 5′ ‐cyclic monophosphate) and preceded their occurence in the control cultures. It was suggested that factor(s) in the extract interact with membrane receptor(s) to alter nucleotide levels which, in turn, allow the effects to be expressed.
Effect of curare on responses to different putative neurotransmitters in Aplysia neurons
Authors: Carpenter D. O. , Swann J. W. , Yarowsky P. J.
Published: January 2005

We have studied the effects of curare on responses resulting from iontophoretic application of several putative neurotransmitters onto Aplysia neurons. These neurons have specific receptors for acetylcholine (ACh), dopamine, octopamine, phenylethanolamine, histamine, γ‐aminobutyric acid (GABA), aspartic acid, and glutamic acid. Each of these substances may on different specific neurons elicit at least three types of response, caused by a fast depolarizing Na+, a fast hyperpolarizing Cl−, or a slow hyperpolarizing K+ conductance increase. All responses resulting from either Na+ or Cl− conductance increases, irrespective of which putative transmitter activated the response, were sensitive to curare. Most were totally blocked by ≤ 10−4 M curare. GABA responses were less sensitive and were often only depressed by 10−3 M curare. K+ conductance responses, irrespective of the transmitter, were not curare sensitive. These results are consistent with a model of receptor organization in which one neurotransmitter receptor may be associated with any of at least three ionophores, mediating conductance increase responses to Na+, Cl−, and K+, respectively. In Aplysia nervous tissue, curare appears not to be a specific antagonist for the nicotinic ACh receptor, but rather to be a specific blocking agent for a class of receptor‐activated Na+ and Cl− responses.
Similar polypeptide composition of fast‐transported proteins in rat motor and sensory axons
Authors: Bisby M. A.
Published: January 2005

SDS‐polyacrylamide gel electrophoresis was used to characterize labeled proteins transported in rat motor and sensory axons after application of 3H‐leucine to the neuron cell bodies. Two types of experiments were performed: first, transported protein accumulating proximal to a ligature placed on the sciatic nerve was analyzed; second, the segment of sciatic nerve nearest to the “lwavecrest” of transported protein travelling down the nerve was analyzed. In both cases, no significant differences in peak position or amplitude were found in gels containing labeled proteins from motor or sensory axons. This may mean that the majority of fast‐transported protein is involved in an axonal function common to the two types of neuron.
Excitatory effects of cholinergic, adrenergic and glutaminergic agonists on a buccal muscle of Aplysia
Authors: Taraskevich P. S. , Gibbs D. , Schmued L. , Orkand R. K.
Published: January 2005

The anterior extrinsic protractors in the buccal mass of Aplysia are symmetrical sheets of branching bundles of muscle fibers which form an electrical syncytium. The addition of potassium or cholinergic, adrenergic, and glutaminergic agonists to the sea water bathing medium produces contracture of the muscle.

Strychnine and cholinergic or adrenergic antagonists all block contractures produced by cholinergic and adrenergic agonists but not those produced by potassium or glutamate.

Iontophoretic application through microelectrodes of acetylcholine or dopamine anywhere on the muscle surface produced a graded depolarization of the membrane. By contrast, glutamate produces depolarization only at discrete membrane sites. Endogeneous contractions often appeared spontaneously or could be induced by drug exposure. ATP inhibits endogeneous contractions.
A prolonged, voltage‐dependent calcium permeability revealed by tetraethylammonium in the soma and axon of Aplysia giant neuron
Authors: Horn Richard , Miller Jeffrey J.
Published: January 2005

The soma but not the axon of the giant neuron, R2, of Aplysia can generate an all‐or‐none Ca spike in Na‐free or TTX‐containing medium (Junge and Miller, 1974). Extracellular axonal recordings made at several distances from the soma provide evidence that the transition in ability to fire a spike in Na‐free medium occurs within the first 250 μm of the axon. Application of 25 mM TEA‐Br to the bathing medium causes a more than tenfold increase in the duration of the somatic action potential. The duration of the axonal action potential in TEA decreases with distance from the soma. At distances greater than 3 mm from the soma this concentration of TEA causes little or no increase in the duration of the axon spike. The effect of 25 mM TEA on both the soma and proximal axon is blocked reversibly by 30 mM CoCl2 or 1 mM CdCl2. The duration of the somatic action potential in TEA increases with an increase in Ca concentration of the bath. At a constant concentration of Na, the voltage level of the somatic plateau increases with Ca concentration in the manner predicted for a Ca electrode. In the presence of 11 mM Ca2+ the potential of the plateau is relatively insensitive to Na concentration. The TEA plateau in R2 reveals a prolonged voltage‐dependent permeability to Ca. The duration of the plateau may indicate the degree of Ca activation during a spike.
The role of the electrosensory system in postural control of the weakly electric fish Eigenmannia virescens
Authors: Feng Albert S.
Published: January 2005

The role of the electrosensory inputs in postural control was examined in the weakly electric fish Eigenmannia virescens. These fish exhibit tonic postural tilt in response to a tilted plexiglas substrate in both transverse and longitudinal planes (rolling and head‐up pitching responses, respectively), but not to electrically “transparent” agar substrate. The fish's pitching and rolling responses were abolished when the electrosensory inputs from the trunk were bilaterally eliminated even though the fish's visual and mechanosensory lateral‐line systems remained intact. Unilateral lesion abolished the rolling response but not the pitching response. These results demonstrate the functional role of the electrosensory system in postural control, in addition to its known role in social communication and in object location, and the underlying neuronal mechanism is discussed.
Hypothermic decrease in microtubule density and birefringence in unmyelinated axons
Authors: Rome‐Talbot D. , Andre D. , Chalazonitis N.
Published: January 2005

The density of microtubules, T.D. (number of tubules/unit area) is highest in small crab nerve axons. After cooling of the nerve at 0°C, the tubule density tends to zero (T.D. 2% of the normothermic value). Once the cooled nerves are returned in normothermia, the reconstitution of the microtubules is evidenced (T.D. = 90% of the initial normothermic value). Therefore cooling “depolymerizes” the tubules, whereas rewarming leads to their “repolymerization.” These results definitely improve the interpretation of the birefringence decrease by cooling: as tubules and filaments contribute to the positive fraction of the total positive birefringence, their depolymerization by cooling explains to a large extent the decrease in total birefringence.
A difference between the proteins conveyed in the fast component of axonal transport in guinea pig hypoglossal and vagus motor neurons
Authors: Black Mark M. , Lasek Raymond J.
Published: January 2005

We compared the proteins transported in the fast component of guinea pig hypoglossal motor neurons with those of guinea pig vagus (preganglionic parasympathetic) neurons. The fast component proteins of hypoglossal and vagus neurons were radioactively labeled by injecting 3H‐amino acids into the hypoglossal and vagus motor nuclei. The radioactive fast component proteins obtained from each system were then compared with each other by SDS‐polyacrylamide slab gel electrophoresis and fluorography. These analyses revealed at least twenty polypeptides which appear common to the fast component of each neuronal system. In addition, we identified one difference between the proteins comprising the fast component of these neuronal systems. A polypeptide, molecular weight 50,000 daltons, present in the fast component of vagus neurons was not detected in the fast component of hypoglossal motor neurons. These observations are discussed with regard to the similarities and differences between these neuronal systems.
Some observations on habituation of the flexor reflex in the rat: The influence of strychnine, bicuculline, spinal transection, and decerebration
Authors: MacDonald J. F. , Pearson J. A.
Published: January 2005

The involvement of inhibition in habituation of the flexor reflex was investigated in intact, spinal, and decerebrate rats. Strychnine and bicuculline were administered in order to determine the contribution of certain forms of central inhibition to the development of habituation. Both strychnine and bicuculline reduced habituation in the intact rat but did not do so in the spinal preparation. Strychnine, in fact, caused a facilitation of habituation in the spinal rat. The impairment of habituation by strychnine was related to the intensity of stimulation used to elicit the reflex. Thus, the effect of strychnine was only demonstrable when relatively high intensities were used. Flexor reflex habituation was shown to be more pronounced in the decerebrate than in the spinal preparation. This difference could be demonstrated only when stimuli of high intensity were given. It is concluded that, in the absence of supraspinal influences, habituation of the flexor reflex does not require inhibitory mechanisms. However, inhibition may play a role in habituation of the component of the reflex that utilizes descending influences.
Motor innervation of the pharynx levator muscle of the snail, Helix pomatia: Physiological and histological properties
Authors: Peters M.
Published: January 2005

(1) Motor innervation of the pharynx levator muscle of Helix pomatia was investigated with intracellular recording and axonal iontophoresis of cobalt chloride.

Muscle fibers respond to direct electrical stimulation of the muscle with active graded responses or non‐overshooting spike potentials.

Each fiber is innervated via the external and internal lip nerves by several (mostly 3) excitatory nerve fibers each. Two types of EPSPs can be distinguished according to amplitude, duration, and facilitation.

Axonal CoCl2‐staining via an external lip nerve branch revealed many nerve fibers entering the muscle and branching there into a rich network of blebbed fibers of various diameters.
The structure and function of serially homologous leg motor neurons in the locust. II. Physiology
Authors: Wilson John A.
Published: January 2005

Simultaneous intracellular recordings were made from pairs of motor neurons in the pro‐ or mesothoracic ganglion of the locust. Though central connections were sought between pairs of motor neurons, none were found. This is in sharp contrast to the findings that flexor and extensor tibiae neurons in the metathoracic ganglion make certain connections between themselves (Hoyle and Burrows, 1973; Heitler and Burrows, 1977a). As the previously mentioned authors believed that the metathoracic flexor‐extensor connections were used as part of the motor program for jumping and kicking, the present results strongly support their hypothesis.

Common PSPs have been found in a variety of pairs of motor neurons. Of note are common PSPs of the same sign to antagonists. Different innervation patterns have been found for the flexor and extensor muscles.

It is proposed that serially homologous motor neurons serving similar functions are, to a first approximation, similar in the locust. Serially homologous motor neurons serving different functions will, in most cases, have altered structures and/or functions.
Catecholamine‐rich cells and varicosities in bovine splenic nerve, vesicle contents and evidence for exocytosis
Authors: Thureson‐Klein Åsa , Klein Richard L. , Johansson Olie
Published: January 2005

The bovine splenic nerve trunk contins mast cells, ganglion cells, small intensely flurescent (SIF) cells, and varicosities which exhibit a brilliant fluorescence characteristic for noradrenaline (NA) and dopamine (DA) after formaldehyde exposure. All these catecholamine‐rich structure could contribute particles to isolated nerve vesicle fractions. Mast cells are recognized ultrastructurally by their large (300–800nm) dense granules. SIF cells may be represented by cells and processes containing dense cored vesicles (120–140 nm) which are larger than the typical vesicles in axons and terminals. Terminal‐like areas with typical large dense cored vesicles (LDV, 75 nm) and small dense cored vesicles (SDV, 45–55 nm) probably correspond to the fluorescent varicosities. The LDV constitute about 40% of all vesicle in terminal‐like areas and terminals. Their staining properties indicate the presence of protein, phospholipids, and ATP. Tyramine depletes NA without loss of matrix density. The LDV can fuse with the terminal membrane, and released material outside omega profiles is interpreted to depict exocytosis. Large and small vesicles are easily distinguished from the very large mast cell granules and the moderately dense Schwann cell vesicles. Neither appear to contaminate the LDV fractions but the latter may contain a small population of SIF cell vesicles. Golgi vesicles from the Schwann cells mainly occur in the lighter zones of the gradient.
Primitive nervous system: Electrophysiology of inhibitory events in flatworm nerve cords
Authors: Koopowitz Harold , Keenan Larry , Bernardo Kerry
Published: January 2005

Evoked potentials from the major longitudinal nerve cords of Notoplana acticola are potentiated if the preparation is decerebrated or if certain nerves in the ventral submuscular plexus are severed. Concomitant with an increase in amplitude of the response (in some preparations over fourfold) is a decrease in latency of the response and a decrease in the threshold stimulus intensity needed to evoke activity. Evoked activity can also be depressed with moderate increases in stimulus intensity and is induced some distance from the recording site. The depressant effects can be lifted if the brain is bisected, if the contralateral nerve VI is severed close to the brain, and if the commissures between the two nerves VI are cut. The depressant effects of nerves V and VI are additive. Depression and the subsequent lifting of the inhibition occur in Ringer baths containing either normal sea water or equal mixtures of sea water and isotonic MgCl2. The possibility of inhibitory synapses immune to high concentrations of magnesium ions is discussed.