bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolic changes in deafferented central neurons of an insect, Acheta domesticus. II. Effects on cholinergic binding sites and acetylcholinesterase
Authors: Meyer MR , Reddy GR , Edwards JS
Published: March 2018

Following the finding that cercal deafferentation of developing giant interneurons in the terminal abdominal ganglion (TG) of the cricket Acheta domesticus reduces TG protein metabolism within target interneuron dendrites and somata (Meyer and Edwards, 1982), it is now shown that deafferentation alters the turnover of three macromolecules associated with cholinergic transmission in the cercal sensory-giant interneuron pathway. The labeled specific ligands 3H-quinuclidinyl benzilate and 125I-alpha-bungarotoxin were used to assay populations of putative TG muscarinic and nicotinic cholinergic receptors, respectively, in control and deafferented groups of ganglia. The AChE activity of TG was also determined by assay and histochemical methods. Long-term deafferentation sustained throughout postembryonic development markedly reduces the densities of both muscarinic and nicotinic binding sites in the TG; short-term deafferentation of adult TG also leads to characteristic alterations in the properties of all three cholinergic markers within several days. Rapid changes seen in adults thus correlate with ultrastructural data demonstrating loss of afferent terminals within hours of sensory appendage removal. We propose that peripheral innervation-dependent regulatory mechanisms operate in both the developing and adult insect nervous system. Such mechanisms may influence transsynaptically the synthesis and turnover of specific macromolecules, some of which may reside on the cell surface of insect central neurons that are part of the cercal sensory- giant interneuron system.
Cooperative regulation of neurotensin content in PC12 pheochromocytoma cell cultures: effects of nerve growth factor, dexamethasone, and activators of adenylate cyclase
Authors: Tischler AS , Lee YC , Costopoulos D , Slayton VW , Jason WJ , Bloom SR
Published: March 2018

Nerve growth factor, dexamethasone, and forskolin or cholera toxin (CT) act cooperatively to increase the content of neurotensin (NT) in PC12 pheochromocytoma cells. Relatively small increases in NT content occur in the presence of NGF alone or dexamethasone alone, but not of forskolin or CT alone. Increases of 10- to 100-fold occur in the presence of NGF plus dexamethasone or NGF plus forskolin, and up to 600- fold increases occur in the presence of all three agents. These increases are extremely stable and persist for at least 2 weeks after removal of dexamethasone or forskolin. The complex regulation of NT stores in PC12 cells might reflect mechanisms that regulate NT content of normal chromaffin cells and/or neurons during development or in adult life. A small amount of stored NT is released in response to stimulation with 52 mM K+. This release is blocked in the presence of 2 mM Co2+, suggesting that it occurs via Ca2+-mediated exocytosis.
Defective development of the thymus and immunological abnormalities in the neurological mouse mutation "staggerer"
Authors: Trenkner E , Hoffmann MK
Published: March 2018

The autosomal recessive mouse mutation “staggerer” (sg/sg), located on chromosome 9, has been recognized as a neurological mutant because of movement abnormalities and defective cerebellar development. We show here that the sg/sg mutation not only affects the development of the cerebellum, but also causes developmental and regulatory changes of the immune system: We observed, on gross inspection, a marked delay in the development of sg/sg thymus, generally enlarged lymph nodes, and undersized spleens. When immunized with SRBC, the sg/sg mouse generated, in normal proportions, helper T-cells in vivo and antibody- forming B-cells in vitro; however, a delay in terminating the response and a deficiency in generating suppressor cells was noted. This suggests the existence of a defect in regulatory feedback mechanisms. The marked delay in the growth of the thymus gland was associated with the prolonged existence of cell-surface carbohydrate patterns characteristic of immature thymocytes. The prolonged expression of embryonal cell-surface phenotypes was observed on the surface of cerebellum and thymus (and, to some extent, spleen) but not in cells from other organs.
The effects of brain stem transections on the neuronal networks responsible for rhythmical jaw muscle activity in the guinea pig
Authors: Chandler SH , Tal M
Published: March 2018

The purpose of this study was to determine the critical areas of brain stem necessary for the production of cortically induced rhythmical jaw muscle activity (RJMs) in the anesthetized guinea pig. It was found that longitudinal midline transections of the lower brain stem starting at the obex and extending to the rostral third of the inferior olivary nucleus (IO) were able to abolish rhythmical EMG activity in the jaw- opener muscle (digastric) on the same side (ipsilateral) as the cortical stimulus. Under these conditions, rhythmical activity in the contralateral digastric (DIG) EMG was not affected. Midline transections extending from the rostral superior colliculus to 500 microns rostral to the trigeminal motor nucleus had no effect on cortically evoked bilateral DIG rhythmical EMG activity. Serial transverse hemisections of the left side of the medulla, starting at the obex and extending to the rostral third of the IO, reduced the amplitude of the left DIG EMG without producing significant effects in the cycle characteristics [cycle duration (CD) or burst duration (BD)] of that muscle during stimulation of the contralateral (right) cortex. Hemisections more rostral to the IO completely abolished bilateral rhythmical DIG activity induced by stimulation of the cortex on the side opposite to the transection (right cortex). Under these conditions, stimulation of the cortex on the side ipsilateral to the left hemisection (left cortex) initiated rhythmical EMG activity with normal cycle characteristics in only the contralateral (right) DIG muscle. Transverse hemisections as little as 500 microns rostral to the trigeminal motor nucleus (Mot V), which spared the pyramidal tract, had no effect on RJMs induced by stimulation of either cortex. These data suggest that each ipsilateral cortex initiates activity in neuronal oscillatory networks located exclusively in the contralateral brain stem; bilateral rhythmical DIG activity is produced by neurons in the contralateral brain stem; each side of the lower brain stem is capable of producing rhythmical DIG activity independent of the integrity of the other side; and the location of the neuronal oscillators responsible for RJMs is between the rostral IO and the trigeminal motor nucleus.
The effect of periarcuate lesions in the monkey on the performance of symmetrically and asymmetrically reinforced visual and auditory go, no- go tasks
Authors: Petrides M
Published: March 2018

Monkeys with lesions restricted to the periarcuate region of the frontal cortex were impaired on go, no-go tasks in which, depending on the stimulus present on any given trial, they were rewarded either for pushing a manipulandum or for withholding this response for a given period of time. By contrast, these animals were able to learn at a normal rate go, no-go tasks in which they were rewarded if they responded in the presence of a “positive” stimulus, but not in the presence of a “negative” stimulus. In the latter situation, responding in the presence of the “negative” stimulus was extinguished through non- reward, whereas the tasks on which impairments were demonstrated required solution on the basis of a conditional rule: If stimulus A, respond, and if stimulus B, withhold responding, to receive reward. Because the 2 experimental situations were identical in every respect except for the one critical difference in the testing procedure, the present set of experiments provides a powerful demonstration of the involvement of the periarcuate cortex in conditional learning with exteroceptive stimuli.
Single-channel recordings of three K+-selective currents in cultured chick ciliary ganglion neurons
Authors: Gardner PI
Published: March 2018

Multiple distinct K+-selective channels may contribute to action potential repolarization and afterpotential generation in chick ciliary neurons. The channel types are difficult to distinguish by traditional voltage-clamp methods, primarily because of coactivation during depolarization. I have used the extracellular patch-clamp technique to resolve single-channel K+ currents in cultured chick ciliary ganglion (CG) neurons. Three unit currents selective for K+ ions were observed. The channels varied with respect to unit conductance, sensitivity to Ca2+ ions and voltage, and steady-state gating parameters. The first channel, GK1, was characterized by a unit conductance of 14 pico- Siemens (pS) under physiological recording conditions, gating that was relatively independent of membrane potential and intracellular Ca2+ ions, and single-component open-time distributions with time constants of approximately 9 msec. The second channel, GK2, was characterized by a unit conductance of 64 pS under physiological recording conditions and gating that was affected by membrane potential but was not dependent on the activity of intracellular Ca2+ ions. Open-time distributions indicated 2 open states, with open-time constants of 0.09 (61%) and 0.35 (39%) msec, at +40 mV membrane potential. The third channel, GKCa2+, was identified in isolated patch recordings in which the concentration of internal Ca2+ was 10(-7) M or greater, which was an absolute prerequisite for channel opening. GKCa2+ was characterized by a unit conductance of 193 pS in symmetrical 0.15 M KCl solutions, an open-state probability that was a function not only of [Ca2+]i, but also of membrane potential, and single-component open-time distribution with a time constant of 1.11 msec at -10 mV patch potential. These results suggest the presence of at least 3 distinct K+ channel populations in the membrane of cultured chick CG neurons.
Respiratory motoneuronal activity is altered by injections of picomoles of glutamate into cat brain stem
Authors: McCrimmon DR , Feldman JL , Speck DF
Published: March 2018

The local neural circuitry underlying the control of breathing was studied by injecting nanoliter volumes of excitatory amino acids into discrete regions of cat brain stem. Experiments were performed on chloralose-urethane anesthetized, vagotomized, paralyzed, and artificially ventilated cats. Phrenic, intercostal, and recurrent laryngeal nerve discharges were recorded. Multibarrel pipettes were used for recording and pressure ejection of drugs or a dye for marking recording and ejection sites. Ejected volumes were directly monitored for every injection. Injections, proximal to neurons discharging with a respiratory periodicity, of as little of 200 fmol of L-glutamate in 200 pl of saline elicited marked, site-specific increases or decreases in respiratory motoneuronal discharge. N-Methyl-D-aspartic acid and homocysteic acid elicited similar site-specific alterations in respiratory motor output, although some details of the response could differ qualitatively. Responses to all the excitatory agents used were attenuated by concurrent injection of kynurenic acid, DL-2-amino-4- phosphonobutyric acid, or glutamic acid diethyl ester. There was no change in spontaneous phrenic nerve discharge in response to injections of equivalent or larger volumes of saline or lidocaine. These results indicate a heterogeneity in the spatial organization of the brain-stem neural circuitry underlying respiratory control, which has not been described previously. This injection technique may provide a mechanism for probing the neural circuitry underlying other behaviors.
Sensory function and gating of histaminergic neuron C2 in Aplysia
Authors: Weiss KR , Chiel HJ , Kupfermann I
Published: March 2018

This paper explores the possible sensory function of the identified histaminergic neuron C2. Mechanical stimulation of a narrow region around the mouth of the animal (perioral zone) elicits brief depolarizing potentials in C2. Extracellular recordings from the peripheral axons of C2 indicate that the depolarizing potentials are due to action potentials that are conveyed from the periphery but do not invade the cell body, since they fail at a region with a low safety factor within the cerebral ganglion. These blocked axonal spikes (A- spikes) function as if they were excitatory synaptic inputs to C2, since the synaptic output of C2 does not occur unless the A-spikes succeed in evoking full action potentials in the soma (or an electrically close initial segment) of C2. Furthermore, like synaptic potentials, the A-spikes exhibit temporal and spatial summation, and facilitation. C2 receives both tonic and phasic inhibitory synaptic potentials, which can decrease the summation of A-spikes and thereby alter the frequency-filtering properties of C2 or block its synaptic output. Thus, C2 appears to be an unusual proprioceptive afferent that has a high degree of integrative function and may provide critical gating that is dependent on a variety of external and internal conditions.
Dopamine enhances terminal excitability of hippocampal-accumbens neurons via D2 receptor: role of dopamine in presynaptic inhibition
Authors: Yang CR , Mogenson GJ
Published: March 2018

The effects of dopamine on the axonal terminals of hippocampal-nucleus accumbens (HIPP-ACC) neurons were investigated in urethane-anesthetized rats using extracellular single-unit recording techniques. Antidromic responses recorded in the ventral subiculum of the hippocampus were evoked by stimulation of the medial accumbens. Baseline terminal excitability of these neurons, established by threshold stimulation of the accumbens, was markedly enhanced by conditioning stimulation (10 Hz) of the ventral tegmental area (VTA), the origin of the mesolimbic dopaminergic neurons. Iontophoretic application of sulpiride, a selective D2 antagonist, onto the HIPP-ACC terminals attenuated the increased terminal excitability of these neurons produced by conditioning VTA stimulation, while intraperitoneal injection of SCH23390, a selective D1 antagonist, failed to attenuate this effect. Iontophoretic application of dopamine or its selective D2 agonist, LY171555, onto the terminals of the HIPP-ACC neurons mimicked the prolonged enhancement of the terminal excitability produced by VTA stimulation, whereas SKF38393, a D1 agonist, had no effect. The effects of VTA stimulation, dopamine and LY171555 application were similar after the accumbens had been pretreated with ibotenic acid, suggesting a direct action of dopamine on the axonal terminals of HIPP-ACC neurons, and that changes in terminal excitability were not mediated via interneurons or feedback pathways from the accumbens to the hippocampus. Since iontophoretic application of potassium, a depolarizing agent, also enhanced the terminal excitability of the HIPP- ACC neurons, it appears that dopamine depolarized, via D2 receptors, the axonal terminals of HIPP-ACC neurons.(ABSTRACT TRUNCATED AT 250 WORDS)
Antagonism of the gerbil's sucrose taste response by p-nitrophenyl alpha-D-glucopyranoside and chloramphenicol
Authors: Vlahopoulos V , Jakinovich W
Published: March 2018

We have discovered that the gerbil's chorda tympani nerve response to sucrose is suppressed by p-nitrophenyl alpha-D-glucopyranoside (PNP- Glu) and chloramphenicol (CAP). Mixture experiments of PNP-Glu and CAP with sodium chloride, potassium chloride, hydrochloric acid, and sucrose gave rise to the following observations: Neither PNP-Glu nor CAP alone stimulates the gerbil's taste nerve; while the sucrose response is suppressed by these inhibitors, taste responses produced by sodium chloride, potassium chloride, and hydrochloric acid are unaffected by the presence of PNP-Glu or CAP; the antagonisms of PNP- Glu and CAP were surmounted by a high concentration of sucrose; CAP is a more potent antagonist (IC50 = 0.0013 M) than PNP-Glu (IC50 = 0.022 M), and both are more potent than methyl 4,6-dichloro-4,6-dideoxy-alpha- D-galactopyranoside (IC50 = 0.048 M); and sucrose antagonism occurs only when PNP-Glu and CAP are mixed with sucrose. It is short-lived and ceases when the mixtures are rinsed from the gerbil's tongue. Structure- activity studies provided the following information: The alpha anomer of PNP-Glu is a more potent inhibitor than its beta anomer; among the PNP-Glu derivatives tested (p-aminophenyl, p-nitrophenyl, and phenyl) only p-nitrophenyl inhibited; among the nitrophenyl galactosides, the para derivative was more potent than the ortho or meta; and p- nitrophenyl alpha-D-mannopyranoside and p-nitrophenyl alpha-D- galactoside are slightly more potent than PNP-Glu. On the basis of concentration experiments, we believe that the inhibitory mechanisms of PNP-Glu and CAP are different, which suggests the existence of at least 2 sucrose receptor sites.
Developmental potential of quail dorsal root ganglion cells analyzed in vitro and in vivo
Authors: Rohrer H , Acheson AL , Thibault J , Thoenen H
Published: March 2018

The cell types present in quail dorsal root ganglia during early development were identified using markers for neurons, glial cells, and fibroblasts (Rohrer et al., 1985). Using the quail-chick transplantation technique, the potential of quail dorsal root ganglion cells to differentiate to adrenergic chromaffin cells, as identified by tyrosine hydroxylase immunostaining, was analyzed. A population of undifferentiated cells, which is present in quail dorsal root ganglia at embryonic day 5, was separated from neurons and glial cells. We show that this population contains cells that differentiate to adrenergic chromaffin cells after back-transplantation into 2-d-old chick embryos. A large proportion of these undifferentiated cells also differentiates to neurons in vitro. Precursors for adrenal chromaffin cells and for neurons are present in dorsal root ganglia in significant numbers only during early development.
Evidence for GABA as a neurotransmitter in the leech
Authors: Cline HT
Published: March 2018

In the leech, Hirudo medicinalis, the inhibitory motor neurons to the longitudinal muscles in the body wall, cells 1 and 2, are linked via central inhibitory synapses to the excitatory motor neurons innervating the same muscles. Examination of these synapses showed that the inhibitors are GABAergic according to several electrophysiological and pharmacological criteria. Presynaptic release of neurotransmitter during passage of depolarizing current into the inhibitors, as well as direct application of GABA to the excitor cell bodies, hyperpolarizes the postsynaptic excitor. Moreover, both synaptic and extrasynaptic GABA receptors of the excitors are specifically blocked by the GABA antagonist bicuculline methiodide. The inhibitors, dissected from the ganglion and grown in culture, synthesize GABA when exposed to the GABA precursor glutamate, whereas the excitors do not synthesize detectable levels of GABA under these same conditions. The innervation and neurotransmitter sensitivity of the longitudinal muscles in the body wall of the glossiphoniid leeches Haementeria ghilianii and H. officinalis were examined in order to determine if the inhibitory neurotransmitter at the neuromuscular junction is GABA. Individual muscle fibers are innervated by both inhibitory and excitatory motor neurons in a manner such that the inhibitory and excitatory nerve terminals and neurotransmitter receptors are spatially and electrically separate. Intracellular recordings taken from the muscle fibers reveal a resting potential of about -70 mV. The amplitude of the spontaneous inhibitory junctional potentials (IJPs) falls to zero at a polarization of about -65 mV and reverses in sign at the normal resting potential.(ABSTRACT TRUNCATED AT 250 WORDS)
Sprouting of GABAergic synapses in the red nucleus after lesions of the nucleus interpositus in the cat
Authors: Katsumaru H , Murakami F , Wu JY , Tsukahara N
Published: March 2018

An immunocytochemical study using anti-GAD serum was performed to examine the plastic changes of GABAergic inhibitory synapses in the red nucleus (RN) after lesions of the nucleus interpositus (IP) of the cat. Light-microscopic analyses revealed that 20–175 d after the unilateral lesion of the IP, somatic profiles of large neurons in the magnocellular RN contralateral to the lesion were more densely covered with GAD-immunoreactive puncta than those in the ipsilateral RN. Electron-microscopic analyses demonstrated that the GAD-immunoreactive puncta observed with the light microscope were synaptic terminals and that the number of GAD-immunoreactive synaptic terminals per unit length of somatic membrane of RN neurons was increased on the deafferented side. The GAD-immunoreactive terminals on somata of RN neurons made symmetric synaptic contacts with somatic membranes on both the deafferented and control sides. The number of immunoreactive synapses on somata of RN neurons was markedly increased on the deafferented side following IP lesion, whereas that of the unlabeled asymmetric synapses was decreased. These observations indicate that new GABAergic synapses were formed on somata of RN neurons after deafferentation from the IP.
Cholecystokinin-dopamine coexistence: electrophysiological actions corresponding to cholecystokinin receptor subtype
Authors: Hommer DW , Stoner G , Crawley JN , Paul SM , Skirboll LR
Published: March 2018

Cholecystokinin (CCK)-like peptides when administered intravenously produce 2 distinct actions on the single-unit activity of mesencephalic dopamine (DA) neurons in the rat: an excitatory action and a potentiation of the inhibitory effects of DA agonists. The ability of several CCK fragments that have been shown to bind selectively to the peripheral and/or the central CCK-binding sites were examined for their ability to induce either excitation or a potentiation of DA. Only sulfated CCK-8 was able to induce excitation of mesencephalic DA neurons, but both sulfated and unsulfated CCK-8, as well as CCK-4, potentiated the inhibitory effects of the DA agonist apomorphine (APO). CCK-3 failed to potentiate APO-induced inhibition. Both of these effects appeared to be confined to cell bodies in regions of the ventral tegmental area and substantia nigra, zona compacta that have been reported to contain both DA and CCK. Thus, CCK-like peptides that have been shown to bind to the high-affinity CCK binding site in brain potentiated the effects of DA. In contrast, the ability of CCK-like peptides to induce neuronal excitation corresponds with their affinity for the peripheral-type CCK binding site.
Somatostatin, an inhibitor of ACTH secretion, decreases cytosolic free calcium and voltage-dependent calcium current in a pituitary cell line
Authors: Luini A , Lewis D , Guild S , Schofield G , Weight F
Published: March 2018

Somatostatin is a neurohormone peptide that inhibits a variety of secretory responses in different cell types. We have investigated the effects of somatostatin on calcium current and intracellular free calcium in AtT-20 cells, a pituitary tumor line in which the inhibitory actions of this peptide have been well characterized. At concentrations similar to those that inhibit adrenocorticotropic hormone (ACTH) release, somatostatin and its analogs reduced the levels of intracellular free calcium (as measured by the Quin-2 technique). Nifedipine and other blockers of voltage-dependent calcium channels also reduced cytosolic calcium levels. The effects of somatostatin and nifedipine were not additive, suggesting that somatostatin might inhibit calcium channels. Experiments using the whole-cell patch-clamp technique showed that somatostatin reduces voltage-dependent calcium current. The effects of somatostatin on cytosolic calcium and calcium current appear to be independent of its ability to reduce secretagogue- stimulated cAMP accumulation in these cells. We propose that the somatostatin-induced decrease in cytosolic calcium concentrations and the voltage-dependent calcium current are one of the mechanisms by which somatostatin suppresses ACTH release in AtT-20 cells.
Rapid axonal transport of the neural cell adhesion molecule
Authors: Garner JA , Watanabe M , Rutishauser U
Published: March 2018

The neural cell adhesion molecule (NCAM) is a cell-surface glycoprotein that mediates cell-cell interactions in the nervous system during development. In the present study, we demonstrate that NCAM is axonally transported in 3-d-old chick retinal ganglion cells and that it travels within the fast component of axonal transport (FC). Proteins were radiolabeled in retinal ganglion cell bodies after intraocular injection of 35S-methionine. The presence of radiolabeled NCAM in the optic nerves and contralateral tecta was detected by specific immunoadsorption to a monoclonal antibody. Major radioactive polypeptide bands at relative mobilities of approximately 200,000, 150,000, and 120,000 Mr (after SDS-PAGE) were recognized by the anti- NCAM antibody. These bands comigrated in 1-dimensional gels with components of purified NCAM from chick brain. The 2 largest NCAM polypeptides (at 200,000 and 150,000 Mr) were found to be transported in this system, while the 120,000 Mr form was apparently not transported. The ratio and electrophoretic profiles of the 2 transported forms of NCAM remained similar in the retina, optic nerve, chiasm, tract, and tectum, suggesting that there is no interconversion of the 2 major polypeptides. The fraction of NCAM in the 35S-labeled FC proteins appears to be at least an order of magnitude less than in the plasma membrane, suggesting that the turnover rate of NCAM at this age is slower than for other membrane proteins of the CNS.
Excitatory synaptic transmission between interneurons and motoneurons in chick spinal cord cell cultures
Authors: O'Brien RJ , Fischbach GD
Published: March 2018

We have examined the development of synaptic transmission between interneurons and motoneurons in spinal cord cell cultures. Unitary excitatory synaptic currents and complex bursts of excitatory currents develop rapidly: EPSCs (excitatory postsynaptic currents) were detected in 100% of the motoneurons by the 4th day after plating. Inhibitory synaptic currents develop more slowly: IPSCs (inhibitory postsynaptic currents) were detected in only 10% of the motoneurons on day 5 and 40% on day 8. During the 1st and 2nd days in vitro, 24% of the motoneurons tested were dye (Lucifer Yellow) coupled to nearby interneurons. The incidence of dye coupling declined during the first week in culture. No coupling was observed between motoneurons. Our data imply that both G1 and G2 receptors are activated at each synapse. The amplitude of spontaneous excitatory synaptic currents did not change when the motoneuron was hyperpolarized from -50 to -80 mV. This behavior is similar to that of currents induced by glutamate, an agonist that activates 2 types of receptors (G1 and G2) on motoneurons. In addition, a concentration of 2-amino-5-phosphonovaleric acid sufficient to inhibit all G1 receptors only partially inhibited the excitatory synaptic currents. Given the conductance of G1 and G2 channels and the ratio of channels activated during unitary EPSCs, we estimate that as few as 25 G1 channels and 5 G2 channels may mediate excitatory interaction between interneurons and motoneurons during the first week in culture.
Specific innervation of neurons in the paravertebral sympathetic ganglia of the chick
Authors: Yip JW
Published: March 2018

I have explored the chick sympathetic system as a model for the study of specific synapse formation by examining the pattern of ganglion cell innervation by preganglionic axons in 2 different ganglia. Using intracellular recording and HRP labeling techniques, the innervation of the 12th and 15th cervical ganglia (C12 and C15) was examined. Sympathetic ganglion cells of the chick are innervated in a stereotyped manner by preganglionic axons arising from different levels of the spinal cord. While each ganglion is innervated by preganglionic axons arising from several spinal cord segments, individual ganglion cells are innervated by only some of the spinal segments that supply each ganglion as a whole. The subset of spinal segments is always contiguous, with 1 segment providing the dominant innervation to the cell. Spinal segments adjacent to the dominant segment provide synaptic inputs that diminish as a function of distance from the dominant segment. This pattern of ganglion cell innervation in the chick is similar to that of the mammal, where re-innervation studies have suggested that ganglion cell innervation is selective. The similarity in the innervation of avian and mammalian sympathetic neurons suggests that the rules that underlie the specificity of synapse formation in the sympathetic system of the 2 species are the same. Because of the accessibility of the chick embryo for experimental manipulations during development, it is now possible to study the cellular basis that underlies the specificity of synapse formation in this relatively simple nervous system.
Coexistence of GABA receptors and GABA-modulin in primary cultures of rat cerebellar granule cells
Authors: Vaccarino FM , Alho H , Santi MR , Guidotti A
Published: March 2018

GABA-modulin (GM), a basic polypeptide purified from rat brain synaptosomes, which is an allosteric inhibitor of GABA recognition sites, has been detected in primary cultures of cerebellar interneurons enriched in granule cells by immunohistochemistry, using a specific antibody raised in rabbit injected with GM purified from rat brain synaptosomes. In these cultures, GM is expressed by the granule cells, which are postsynaptic to GABAergic interneurons, but not by glial cells. In rat cerebellar sections anti-GM antiserum intensely strains the granular cell layer and Purkinje cell dendrites and cell bodies. GM has been purified from the cerebellar granule cell cultures and appears to be identical under biochemical, immunological, and functional criteria to authentic GM purified from rat brain synaptosomes. Granule cell cultures devoid of GABAergic neurons contain the GABA/BZ/Cl- receptor complex; in fact, intact cell monolayers, incubated in physiological buffer at 25 degrees C, express 3H-muscimol and 3H- flunitrazepam binding sites, which are comparable to the sites detected in cell membrane preparations and which modulate each other reciprocally. It is concluded that GM might participate in the supramolecular organization of the GABA receptor complex, perhaps functioning as a modulator of this receptor protein.
The nerve growth factor-inducible large external (NILE) glycoprotein and neural cell adhesion molecule (N-CAM) have distinct patterns of expression in the developing rat central nervous system
Authors: Beasley L , Stallcup WB
Published: March 2018

The nerve growth factor-inducible large external (NILE) glycoprotein and the neural cell adhesion molecule (N-CAM) have both been implicated in the process of nerve fiber fasciculation. To evaluate the respective roles of the 2 molecules in fiber tract formation, we used immunohistochemical means to compare their distributions in the developing rat central nervous system. In the spinal cord, hindbrain, forebrain, retina, and cerebellum, N-CAM was present on undifferentiated cells in germinal zones as well as on differentiating cells and in nerve fiber tracts. In contrast, NILE was restricted to the developing fiber tracts in all these areas. No fiber tracts were found that were obviously lacking one or the other of the 2 molecules during the period of tract development. However, in all cases except that of the cerebellar molecular layer, nerve fiber tracts appeared to lose NILE and retain N-CAM after the major phases of tract development were completed. The fact that NILE is restricted to nerve fiber tracts during relatively short but crucial phases of tract development suggests that NILE plays a very specific role in the formation of fiber bundles. The more ubiquitous N-CAM molecule may have a more general role in neural histogenesis.
Fast axonally transported proteins in regenerating goldfish optic axons
Authors: Perry GW , Burmeister DW , Grafstein B
Published: March 2018

Fast axonal transport of protein was examined in regenerating goldfish optic axons after a lesion of either the optic tract or optic nerve, which revealed changes in the original intact optic axon segments or in the newly regenerated axon segments, respectively. In animals killed either 6 or 24 hr after injection of 3H-proline into the eye, labeling of total fast-transported protein in the original axon segments was increased by 2 d after the lesion, reached a peak of nearly 20 X normal at 2 weeks, and then declined to a level somewhat above normal at 12 weeks. When the labeling of individual transported proteins was examined by 2-dimensional gel electrophoresis, it was found that no new labeled proteins appeared during regeneration, but all proteins examined showed an increase in labeling. Among the various proteins, there was great variation in the magnitude and time course of the labeling increase. The largest increase, to nearly 200 X normal with 6 hr labeling, was seen in a protein with a molecular weight of 45 kDa and a pl of about 4.5, resembling a protein that has previously been designated a “growth-associated protein” (GAP-43; Skene and Willard, 1981a). The proteins showing increased labeling included a small fraction of cytoskeletal proteins (alpha-tubulin, beta-tubulin, and actin) that was apparently transported at a much faster rate than is usually expected of these constituents. In the new axon segments, the total protein labeling was increased by 1 week after the lesion, remained elevated at a nearly constant level of about 7 X normal from about 2 to 5 weeks, and then declined to levels somewhat above normal by 12 weeks. The 45 kDa protein again showed the largest increase, and became the single most prominently labeled constituent in the new axons. On the basis of the time course of labeling in both original and new axon segments during regeneration, the fast-transported proteins were tentatively separated into 5 classes that may represent groups of proteins that are coregulated during regeneration. They may conceivably correspond to different functional or structural entities within the neuron.
Numerical matching during cerebellar development: quantitative analysis of granule cell death in staggerer mouse chimeras
Authors: Herrup K , Sunter K
Published: March 2018

Cell death is a common yet puzzling feature of the development of many populations of neurons in the CNS. In the invertebrate phyla, such death is often preprogrammed; by contrast, in vertebrates, the best studied examples of histogenetic cell death are influenced by interactions among the neurons and their target. One attempt to explain this seemingly wasteful scheme of development has led to the hypothesis that this target-related cell death allows 2 populations of cells, which develop in isolation, to come into numerical and functional balance and hence to provide an epigenetic “buffer” mechanism to accommodate developmental variations. In the current study we have examined the extent to which the cell death observed in the cerebellar granule cell population serves to numerically match these neurons with their primary postsynaptic target, the Purkinje cell. Staggerer chimeras were made by aggregating 8-cell staggerer embryos with embryos of wild-type genotype. The cerebella of the resulting animals developed with widely varying numbers of normal (wild-type) Purkinje cell targets. Although staggerer Purkinje cells were present in the chimeric brains, these cells are intrinsically deficient in their normal developmental program (in the mutant, because of this deficiency, 100% of the granule cells die). Both granule cells and Purkinje cells were counted in chimeras and several wild-type mice. The results reveal that the number of granule cells present in these brains has a linear relationship with the number of Purkinje cells, and that the line connecting the points intersects the Y-axis close to the origin. These observations suggest that numerical matching is an important function of target-related cell death in the granule cell population.(ABSTRACT TRUNCATED AT 250 WORDS)
Brain spectrin(240/235) and brain spectrin(240/235E): differential expression during mouse brain development
Authors: Riederer BM , Zagon IS , Goodman SR
Published: March 2018

Mouse brain contains at least 2 distinct spectrin subtypes: brain spectrin(240/235) and brain spectrin(240/235E) (Riederer et al., 1986). In this study, we demonstrate that these subtypes are differentially expressed during mouse brain development. Brain spectrin(240/235) can be detected in fetal tissue and increases 2-fold during brain development. This subtype is enriched in the cortical cytoplasm of germinative neural cells and is also found in fibers resembling axons as early as fetal life. Brain spectrin(240/235E), which is specifically detected with antibodies to red blood cell spectrin, is below the limits of detection in fetal and neonatal brain but rapidly increases in concentration during the second postnatal week. Brain spectrin(240/235E) is confined to the cell body and dendrites of differentiating neurons and to glial cells but is not expressed in mitotic cells. This subtype is most prominent in granule cells of the cerebellum and dentate gyrus in the hippocampus.
Ca channels induced in Xenopus oocytes by rat brain mRNA
Authors: Leonard JP , Nargeot J , Snutch TP , Davidson N , Lester HA
Published: March 2018

RNA was isolated from brains of 16-d-old rats and poly(A) samples were injected into stage V and VI oocytes. After allowing 2–5 d for expression, most oocytes were exposed to medium in which the K had been replaced by Cs for 24 hr prior to recording. Ba currents were usually measured in Cl-free Ba-methanesulfonate saline. IBa in noninjected oocytes was often undetectable, but ranged up to 50 nA (22 +/- 4 nA, n = 21). In contrast, injected oocytes showed a peak IBa of 339 +/- 42 nA (n = 33). The threshold for activation of IBa was -40 mV, with peak currents at +10 to +20 mV. After a peak, currents decayed to a nearly steady level along a single-exponential time course (tau = 650 +/- 50 msec at +20 mV). The maintained current was 67 +/- 6% (n = 9) of the early peak amplitude. A prepulse duration of 5 sec was needed to examine the inactivation of barium currents in injected oocytes. The inward IBa could be observed in BaCl2 solutions at potentials positive to ECl and also in Na-free salines, indicating that neither Cl- nor Na+ was carrying the inward current. Although IBa displayed voltage- independent blockade by Cd (50% inhibition at 6 microM), the peptide Ca channel antagonist, omega-CgTX (1 microM), and the organic Ca channel- blocking agents (verapamil, compound W-7, and nifedipine) were uniformly ineffective. No effects were observed with the dihydropyridine antagonist nifedipine (even at 10 microM, or when cells were held at -40 mV) or agonist Bay K-8644. However, IBa was enhanced via activation of protein kinase C with 4-beta-phorbol dibutyrate (PBT2). In contrast, use of forskolin to activate protein kinase A did not alter IBa.(ABSTRACT TRUNCATED AT 250 WORDS)
Characterization of a novel 3H-5-hydroxytryptamine binding site subtype in bovine brain membranes
Authors: Heuring RE , Peroutka SJ
Published: March 2018

3H-5-Hydroxytryptamine (5-HT) binding sites were analyzed in bovine brain membranes. The addition of either the 5-HT1A-selective drug 8-OH- DPAT (100 nM) or the 5-HT1C-selective drug mesulergine (100 nM) to the assay resulted in a 5–10% decrease in specific 3H-5-HT binding. Scatchard analysis revealed that the simultaneous addition of both drugs decreased the Bmax of 3H-5-HT binding by 10–15% without affecting the KD value (1.8 +/- 0.3 nM). Competition studies using a series of pharmacologic agents revealed that the sites labeled by 3H-5-HT in bovine caudate in the presence of 100 nM 8-OH-DPAT and 100 nM mesulergine appear to be homogeneous. 5-HT1A selective agents such as 8- OH-DPAT, ipsapirone, and buspirone display micromolar affinities for these sites. RU 24969 and (-)pindolol are approximately 2 orders of magnitude less potent at these sites than at 5-HT1B sites which have been identified in rat brain. Agents displaying nanomolar potencies for 5-HT1C sites such as mianserin and mesulergine are 2–3 orders of magnitude less potent at the 3H-5-HT binding sites in bovine caudate. In addition, both 5-HT2- and 5-HT3-selective agents are essentially inactive at these binding sites. These 3H-5-HT sites display nanomolar affinity for 5-carboxyamidotryptamine, 5-methoxytryptamine, metergoline, and 5-HT. Apparent Ki values of 10–100 nM are obtained for d-LSD, RU 24969, methiothepin, tryptamine, methysergide, and yohimbine, whereas I-LSD and corynanthine are significantly less potent. In addition, these 3H-5-HT labeled sites are regulated by guanine nucleotides and calcium. Regional studies indicate that this class of sites is most dense in the basal ganglia but exists in all regions of bovine brain. These data therefore demonstrate the presence of a homogeneous class of 5-HT1 binding sites in bovine caudate that is pharmacologically distinct from previously defined 5-HT1A, 5-HT1B, 5- HT1C, 5-HT2, and 5-HT3 receptor subtypes. We therefore suggest that this class of sites be designated the 5-HT1D subtype of binding sites labeled by 3H-5-HT.
The somatotopic organization of the supplementary motor area: intracortical microstimulation mapping
Authors: Mitz AR , Wise SP
Published: March 2018

The somatotopic organization of the supplementary motor area (SMA) is commonly held to consist of a rostrocaudal sequence of orofacial, forelimb, and hindlimb representations. Recently, however, this somatotopy has been questioned. Studies of regional cerebral blood flow in humans and the movements evoked by intracortical electrical stimulation in cynomolgus monkeys have been unable to reveal evidence of distinct orofacial, forelimb, and hindlimb representations rostrocaudally situated along the medial cortex of the hemisphere. Partly on the basis of those results, it has been suggested that the SMA functions as a nontopographically organized “higher-order” motor center. The present study reexamines SMA organization by observing stimulation-evoked movements. The medial frontal cortex of 2 rhesus monkeys was mapped using a modified intracortical microstimulation technique. We observed a forelimb representation mainly on the medial surface of the hemisphere in both animals. Rostral or rostrolateral to the forelimb representation, depending on the individual, we evoked orofacial movements (including eye movements). Hindlimb movements were evoked from tissue overlapping, but largely caudal to, the forelimb representation. Thus, we conclude that there is a clear rostrocaudal progression of orofacial, forelimb, and hindlimb movement representations in the SMA.
The probabilistic nature of synaptic transmission at a mammalian excitatory central synapse
Authors: Walmsley B , Edwards FR , Tracey DJ
Published: March 2018

The synaptic connection between single group I afferents and dorsal spinocerebellar tract (DSCT) neurons in the cat spinal cord has been studied in an attempt to gain insight into the mechanisms of excitatory synaptic transmission in the mammalian CNS. Fluctuations in the amplitude of single group I fiber EPSPs in DSCT neurons were examined using a numerical deconvolution procedure to reduce the effects of contaminating noise. In general, it was found that single fiber EPSPs fluctuate in peak amplitude between discrete levels separated by equal or quantal increments. Many previous studies have proposed simple binomial statistics as a general model of quantal synaptic transmission. In the present study we show that simple binomial statistics do not describe the fluctuations in amplitude of single group I fiber EPSPs in DSCT neurons. It is suggested that nonuniformities in the probability of transmitter release from release site to release site explain the failure of the binomial model to describe the EPSP fluctuation pattern at this synapse. Nonuniform quantal transmission is proposed as a more adequate description of excitatory synaptic transmission in the mammalian CNS.
Parallel processing of proprioceptive signals by spiking local interneurons and motor neurons in the locust
Authors: Burrows M
Published: March 2018

The connections made by afferents from a proprioceptor at the femorotibial joint in a hind leg of a locust, the femoral chordotonal organ (FCO), were determined by making intracellular recordings from motor neurons and spiking local interneurons in the central nervous system and from afferent cell bodies in the periphery. Staining the central projections of the afferent neurons with dye introduced into their axons at the receptor, and the intracellular injection of dye into motor neurons and interneurons, shows that the branches of all 3 types of neuron overlap in specific regions of neuropile. Afferents excited by a movement of the receptor apodeme that is equivalent to an imposed extension of the femorotibial joint excite flexor tibiae motor neurons and some spiking local interneurons with cell bodies at the ventral midline of the metathoracic ganglion. The opposite movement excites extensor tibiae motor neurons and a different set of spiking local interneurons. Spikes in afferents that excite flexor motor neurons evoke depolarizing potentials that follow each spike with a consistent central latency of approximately 1.5 msec. The amplitude of the depolarizing potentials is dependent upon the membrane potential of the motor neuron. This evidence points to the connection being direct and to the potentials' being EPSPs. Simultaneous recordings from certain spiking local interneurons and certain flexor motor neurons show that they receive many synaptic potentials in common and are driven in a parallel fashion by movements of the receptor apodeme. Spikes of some afferents evoke EPSPs in both neurons with the same consistency and latency. An afferent can therefore synapse directly upon a motor neuron and a spiking local interneuron. Each afferent synapses on several motor neurons and possibly upon several interneurons. In turn, each motor neuron and each interneuron receives inputs from several afferents.
Expression of tyrosine hydroxylase in neurons of cultured cerebral cortex: evidence for phenotypic plasticity in neurons of the CNS
Authors: Iacovitti L , Lee J , Joh TH , Reis DJ
Published: March 2018

In vivo, neurons of the cerebral cortex of rat embryos did not stain with antibodies to the catecholamine (CA) biosynthetic enzyme tyrosine hydroxylase (TH) even when examined using a highly sensitive technique for radioimmunocytochemistry. However, when embryonic day (E) 13 cortex was grown 1 d in culture, several thousand cells expressed immunoreactive and catalytically active TH. All TH cells simultaneously labeled with the neuronal enzyme, neuronal specific enolase, indicating that the TH was exclusively localized in neurons. Moreover, all TH neurons were postmitotic since they did not incorporate 3H-thymidine. With time in culture, the number of TH cells selectively declined from nearly 3000 cells at 2 d to several cells at 14 d. Similarly, the number of neurons competent to express TH in culture declined with advancing age of the donor embryo. Thus, by E18, very few cortical neurons had the capacity to express TH. We conclude that during a critical period of development, postmitotic cerebral cortical neurons can express catecholamine traits in vitro but not in vivo. Thus, the neurotransmitter phenotype of certain classes of central neurons is not fixed but can be influenced by epigenetic factors found in their environment, thereby providing evidence of phenotypic plasticity in the central nervous system (CNS).