bluuebunny/crossref_metadata_2025 huggingface dataset:
Concentration-dependent effects of neostigmine on the endplate acetylcholine receptor channel complex
Authors: Fiekers JF
Published: March 2018

The concentration-dependent actions of neostigmine, a carbamate anticholinesterase agent, were studied on the acetylcholine receptor channel complex in voltage-clamped twitch fibers of costocutaneous muscles of garter snakes. Low concentrations of neostigmine (10(-6) or 10(-5) M) increased miniature endplate current (MEPC) amplitude and the time constant of MEPC decay without changing the relationship between the MEPC decay time constant and membrane potential. Acetylcholine- or carbachol-induced endplate current fluctuation spectra were well fitted by a single Lorentzian curve with a characteristic frequency and single- channel conductance unaltered by low concentrations of neostigmine. Concentrations of neostigmine greater than 5 X 10(-5) M decreased MEPC amplitude and split the decay of MEPCs into two components, one faster and one slower than the control rate. These effects were both voltage and concentration dependent. Spectra of current fluctuations recorded in concentrations greater than or equal to 5 X 10(-5) M neostigmine required two time constants, one faster and one slower than the control. Two component spectra were also obtained with carbachol- induced current fluctuation spectra, indicating that these effects of neostigmine were direct and not a consequence of acetylcholinesterase inhibition. Similar results were also obtained in muscles pretreated with collagenase to remove junctional acetylcholinesterase. The fast and slow time constants obtained from current fluctuation spectra decreased and increased, respectively, with either increases in the concentration of neostigmine or membrane hyperpolarization when analyzed in the same fiber. The effects of neostigmine on channel lifetime were reversible with washing. These results indicate that the effects of neostigmine are concentration dependent. Concentrations greater than 2.5 X 10(-5) M exhibit direct effects on the endplate receptor channel complex which are unrelated to acetylcholinesterase inhibition. These actions include: a prolongation of the gating kinetics of the endplate receptor channel complex, the production of an altered state of the receptor channel complex evidenced by a high frequency component to current fluctuation spectra, and a direct action to block the acetylcholine receptor.
Long-term enhancement produced by activity-dependent modulation of Aplysia sensory neurons
Authors: Walters ET , Byrne JH
Published: March 2018

We have investigated long-lasting enhancement of signaling effectiveness in the tail sensory neurons of Aplysia using both intracellular and extracellular stimulation. The pairing of high frequency homosynaptic activation with heterosynaptic modulation produced significantly greater enhancement of monosynaptic connections to identified motor neurons than did homosynaptic activity, heterosynaptic modulation, or test stimuli alone. Enhancement of the monosynaptic excitatory postsynaptic potential produced by pairing persisted for at least 4 hr, and the kinetics of decay of this potentiation indicated a time constant of about 5 hr. Although unpaired stimulation produced much weaker enhancement, both homosynaptic activity and heterosynaptic modulation alone produced enhancement lasting more than 90 min. The results are consistent with the possibility that intrinsic electrical activity can amplify the modulatory effects of a paired extrinsic chemical signal to produce long-term changes in synaptic strength. Paired stimulation also produced a relative enhancement of the excitability of the sensory neuron soma as judged by changes in action potential threshold. The lack of generalized changes in the postsynaptic cell and the observation of pairing-induced long-term changes in action potential threshold in the presynaptic cell soma suggest that long-term enhancement produced by pairing has a presynaptic locus in this system. Since pairing-specific enhancement can encode associations between sensory and motivational events in these cells, this form of plasticity may function as a form of associative memory. Similarities between long- term paired enhancement in this system and associative long-term potentiation in other systems suggest that activity-dependent neuromodulation might be involved in cellular memory in other systems as well.
A regional analysis of alpha-spectrin in the isolated Mauthner neuron and in isolated axons of the goldfish and rabbit
Authors: Koenig E , Repasky E
Published: March 2018

Isolated dendrites, somata, and desheathed axons of the goldfish Mauthner neuron (M-cell), in addition to other isolated myelin sheath- free axons of the goldfish spinal cord and of rabbit lumbar ventral roots, were shown by immunochemical and immunofluorescence techniques to contain alpha-spectrin (fodrin). alpha-Spectrin appeared to be organized as a randomly distributed reticular network, localized to the surface of isolated neuronal cellular structures. In addition, alpha- spectrin was also distributed nonrandomly at specialized cellular sites. These sites included synaptic junctions and morphologically differentiated nodes of Ranvier (i.e., rabbit axons, but not goldfish axons). At the latter sites, it is possible to demonstrate that alpha- spectrin is co-localized with F-actin, as indicated by a striking correspondence of fluorescent images due to double labeling, using the indirect immunofluorescence technique with alpha-spectrin antiserum, and direct binding of F-actin by rhodamine-conjugated palloidin. However, the spectrin-actin network at synaptic junctions appears to be distributed over the entire area of junctional contact and is not just restricted to postsynaptic densities. The possibility of a duality of roles of spectrin in membrane-related motile and anchorage functions is discussed.
Rapid mobility of motile varicosities and inclusions containing alpha- spectrin, actin, and calmodulin in regenerating axons in vitro
Authors: Koenig E , Kinsman S , Repasky E , Sultz L
Published: March 2018

Time-lapse video recording was used to investigate the bidirectional movements of motile varicosities and intervening phase-dense (IPD) inclusions associated with axons of goldfish retinal ganglion cells regenerating in vitro. In addition, analyses of fine structure and immunocytochemical distributions of alpha-spectrin (fodrin), actin, and calmodulin in axonal fields were undertaken. Varicosities and IPD inclusions undergo saltations in a random manner at mean rates of 0.218 and 3.33 micron/sec, respectively. Experiments involving calcium antagonists or depletion of internal calcium stores resulted in an arrest of all intra-axonal movement, indicating that saltations of the two mobile structures are dependent on intra-axonal calcium. The predominant structure in varicosities is a large aggregation of an anastomosing, tubular, smooth endoplasmic reticulum embedded in an amorphous matrix, suggesting a form of “packaged” cytomembranes undergoing bulk transport. IPD inclusions, presumably carrying membranes, appear to shuttle between varicosities and growth cones during axon elongation, and between growth cones and varicosities during axon retraction. alpha-Spectrin, actin, and calmodulin were shown by immunocytochemistry to be preferentially distributed to varicosities and IPD inclusions. The co-transport of spectrin, actin, and calmodulin with cytomembranes undergoing rapid saltations departs from reported results of radioactive labeling experiments insofar as spectrin, actin, and calmodulin are not normally associated with rapidly transported membrane components in the latter studies. Possible reasons for the discrepancy are discussed. Our results suggest that spectrin and actin may play a role in the packaging and axoplasmic transport of cytomembranes concerned with plasmalemma recycling.
A postnatal change in the immunological properties of the acetylcholine receptor at rat muscle endplates
Authors: Hall ZW , Gorin PD , Silberstein L , Bennett C
Published: March 2018

We have used a myasthenic serum that in adult rat muscle is specific for acetylcholine receptors (AChRs) in the extra-junctional membrane to characterize the AChRs at developing endplates. Immunocytochemical experiments show that AChRs at endplates in the rat diaphragm bind the myasthenic antibodies during the first week after birth but lose their reactivity during the second and third postnatal weeks. AChRs at endplates in adult rat diaphragm do not bind the antibodies even after denervation; in contrast, AChRs at endplates in an adult chicken muscle (anterior latissimus dorsi) are recognized by the antibodies. The loss of immunological reactivity thus may be correlated with a change in the channel properties of the AChR and with the appearance of synaptic folds, two postnatal developmental changes that occur at the endplates of rats, but not of chickens.
The topography of ganglion cell production in the cat's retina
Authors: Walsh C , Polley EH
Published: March 2018

The ganglion cells of the cat's retina form several classes distinguishable in terms of soma size, axon diameter, dendritic morphology, physiological properties, and central connections. Labeling with [3H]thymidine shows that the ganglion cells which survive in the adult are produced as several temporally shifted, overlapping waves: medium-sized cells are produced before large cells, whereas the smallest ganglion cells are produced throughout the period of ganglion cell generation (Walsh, C., E. H. Polley, T. L. Hickey, and R. W. Guillery (1983) Nature 302: 611–614). Large cells and medium-sized cells show the same distinctive pattern of production, forming rough spirals around the area centralis. The oldest cells tend to lie superior and nasal to the area centralis, whereas cells in the inferior nasal retina and inferior temporal retina are, in general, progressively younger. Within each retinal quadrant, cells nearer the area centralis tend to be older than cells in the periphery, but there is substantial overlap. The retinal raphe divides the superior temporal quadrant into two zones with different patterns of cell addition. Superior temporal retina near the vertical meridian adds cells only slightly later than superior nasal retina, whereas superior temporal retina near the horizontal meridian adds cells very late, contemporaneously with inferior temporal retina. The broader wave of production of smaller ganglion cells seems to follow this same spiral pattern at its beginning and end. The presence of the area centralis as a nodal point about which ganglion cell production in the retinal quadrants pivots suggests that the area centralis is already an important retinal landmark even at the earliest stages of retinal development. This sequence of ganglion cell production differs markedly from that seen in the retinae of nonmammalian vertebrates, where new ganglion cells are added as concentric rings to the retinal periphery, and also bears no simple relationship to the cat's retinal decussation line. However, it can be related in a straightforward manner to the organization of axons in the cat's optic tract, suggesting that the fiber order in the tract represents a grouping of fibers by age.
Characterization of the prodynorphin and proenkephalin neuropeptide systems in rat hippocampus
Authors: Chavkin C , Shoemaker WJ , McGinty JF , Bayon A , Bloom FE
Published: March 2018

Opioid peptides derived from prodynorphin were localized immunocytochemically to dentate granule cells and mossy fibers of the rat hippocampus with antisera against dynorphin A(1–17) and dynorphin B. Extracts of microdissected hippocampal regions were resolved by reverse phase and molecular exclusion chromatography to identify the molecular forms of the dynorphin A immunoreactivity and to quantify regional contents. Results demonstrated that the relative concentration of dynorphin A within each dissected region of hippocampus agreed well with the distribution of dynorphin A detected by immunocytochemical methods. Immunostaining of proenkephalin-derived opioid peptides, [Leu5]enkephalin and bovine adrenal medullary peptide-22P, was concentrated in cell bodies of the entorhinal cortex, nerve fibers in the perforant pathway, and terminals in the outer molecular layer of the dentate gyrus. Light immunostaining of granule cells and mossy fibers with these antisera was also found. The relative concentration of [Leu5]enkephalin immunoreactivity in each microdissected region of the hippocampus also agreed well with the distribution of [Leu5]enkephalin immunostaining. Chromatography of hippocampal regional extracts demonstrated that the immunoreactivity measured was due to the presence of authentic [Leu5]enkephalin. The probable neurotransmitter function of both [Leu5]enkephalin and dynorphin A was shown by their calcium-dependent release after in vitro depolarization of hippocampal tissue. The reported presence of beta-endorphin in hippocampus was not verified. Comparison of the hippocampal distribution and content of prodynorphin and proenkephalin-derived opioids suggests that separate populations of neurons containing these two peptide families form distinct neurotransmitter systems of roughly equal concentration.
Deficits in visual motion processing following ibotenic acid lesions of the middle temporal visual area of the macaque monkey
Authors: Newsome WT , Wurtz RH , Dursteler MR , Mikami A
Published: March 2018

Physiological experiments have produced evidence that the middle temporal visual area (MT) of the monkey is selectively involved in the analysis of visual motion. We tested this hypothesis by studying the effects of small chemical lesions of MT on eye movements made in response to moving as opposed to stationary visual targets. We observed two deficits for eye movements made to moving targets: a monkey's ability to match the speed of his smooth pursuit eye movements to the speed of the moving target was impaired, and a monkey's ability to adjust the amplitude of a saccadic eye movement to compensate for target motion was impaired. In contrast, saccades to stationary targets were unaffected by the MT lesions, suggesting that monkeys with MT lesions had more difficulty responding to moving than to stationary stimuli. These results provide the first behavioral evidence that neural processing in MT contributes to the cortical analysis of visual motion.
Lesions in nucleus basalis magnocellularis and medial septal area of rats produce qualitatively similar memory impairments
Authors: Hepler DJ , Olton DS , Wenk GL , Coyle JT
Published: March 2018

The functional contribution of nucleus basalis magnocellularis (NBM) and the medial septal area (MSA) to memory was evaluated in two different spatial discriminations. Preoperatively, rats were trained to a criterion level of performance in a simultaneous left/right discrimination on the stem of a T-maze (a trial-independent memory) and a discrete-trial, rewarded alternation discrimination on the arms of the T-maze (a trial-dependent memory). Bilateral lesions were made by injecting ibotenic acid (IBO) into the NBM, MSA, both NBM and MSA, or dorsal globus pallidus (DGP), and by radiofrequency current (RF) in the NBM and MSA. Control rats received operations in which either no current was passed or no neurotoxin was injected. Lesions in the NBM, MSA, or both the NBM and MSA produced a similar pattern of behavioral changes relative to the performance of controls; postoperative reacquisition of the arm discrimination was initially impaired but showed recovery to normal levels, whereas postoperative reacquisition and reversal of the stem discrimination was not impaired (except following the combined NBM and MSA lesion). Lesions of the DGP had no effect on choice accuracy in any discrimination. When the discrimination on the arms was made more difficult by increasing the delay interval during which the information had to be remembered, rats with combined NBM and MSA lesions were again impaired relative to controls and showed no signs of recovery of function. These results provide information about the behavioral functions of the basal forebrain cholinergic system and suggest that pathological changes in certain components of this system can cause disorders of memory.
Development of the ipsilateral retinothalamic projection in the frog Xenopus laevis. I. Retinal distribution of ipsilaterally projecting cells in normal and experimentally manipulated frogs
Authors: Hoskins SG , Grobstein P
Published: March 2018

The distribution of ipsilaterally and contralaterally projecting cells within the retina in Xenopus laevis was studied by injection of horseradish peroxidase into the thalamus on one side of the brain and subsequent determination of the locations of retrogradely labeled cells in both retinas. In normal animals, contralaterally projecting cells were found throughout the retina. Ipsilaterally projecting cells, in contrast, were most frequent in temporoventral retina and largely absent from dorsonasal retina as well as from a region surrounding the nerve head. A similarly restricted distribution of ipsilaterally projecting cells was observed in retinas of animals after regeneration of one optic nerve as well as in animals from which one eye was removed prior to the time when the ipsilateral projection first develops. The restricted distribution of ipsilaterally projecting cells in normal animals raises the possibility that these cells may be produced relatively late in development. This hypothesis is explored in the following paper (Hoskins, S.G., and P. Grobstein (1985) J. Neurosci. 5: 920–929). The fact that similar distributions were seen in normal and experimental animals implies that organization of the ipsilateral retinothalamic projection in X. laevis is not critically dependent either on particular patterns of axonal organization which may be present during normal development or on interactions among fibers from the two eyes.
Development of the ipsilateral retinothalamic projection in the frog Xenopus laevis. III. The role of thyroxine
Authors: Hoskins SG , Grobstein P
Published: March 2018

The ipsilateral retinothalamic projection in Xenopus laevis normally first appears at about stage 54, at a time when a number of other changes known to be dependent on a rise in circulating levels of thyroxine begin to occur. We have investigated the role of thyroxine in the development of the ipsilateral retinothalamic projection by studying retinal projections and patterns of retinal histogenesis in tadpoles whose ability to produce thyroxine was blocked by treatment with propylthiouracil (PTU), and in similar tadpoles in which thyroxine was restored by injection of small amounts of thyroxine into one eye. PTU-reared tadpoles continue to grow and to add neurons to the retina in a symmetric pattern like that of normal tadpoles at early developmental stages. The PTU-reared tadpoles remained by external criteria at stage 54. Like normal stage 54 tadpoles, the PTU-reared tadpoles either lacked an ipsilateral projection entirely or had an extremely sparse projection. Injection of thyroxine into one eye of PTU- reared tadpoles resulted in the production of substantial ipsilateral projections from the treated eyes as well as shifts to the asymmetric pattern of retinal cell addition which normally begins after stage 54. Such changes were much more prominent in hormone-treated than in untreated eyes, suggesting that they are caused by local action of thyroxine on the treated eyes. With low doses, thyroxine-induced effects on the development of the ipsilateral projection and on retinal histogenesis were restricted to the treated eye. These results suggest that the presence of thyroxine in one eye alone is sufficient to cause the development of the ipsilateral projection.
Gating kinetics of nonjunctional acetylcholine receptor channels in developing Xenopus muscle
Authors: Kullberg R , Kasprzak H
Published: March 2018

The development of nonjunctional acetylcholine (ACh) receptor gating kinetics was studied in myotomal muscle of Xenopus laevis by spectral analysis of ACh-induced noise. The results are consistent with the idea that there is a developmental shift in relative numbers of receptors with fast and slow gating kinetics. For about the first 20 hr following the onset of ACh sensitivity, the majority of channel openings contributing to the ACh noise were slow, having an apparent mean open time of about 3 msec. Shortly before the time of hatching, there began to appear a significant contribution to the noise from channels having a mean open time of less than 1 msec. The relative amount of fast channel activity increased during the 2 days following hatching, and by the age of maturity of the myotomal synapse, most of the ACh noise arose from fast channel activity. A comparison of nonjunctional kinetics with synaptic currents at maturity suggests that the control of channel gating time is similar at junctional and nonjunctional regions.
The distribution of a peptide neurotransmitter in the postembryonic grasshopper central nervous system
Authors: Keshishian H , O'Shea M
Published: March 2018

Proctolin is a peptide neurotransmitter, discovered in the visceral muscles of the cockroach. The peptide has recently been identified in the nervous systems of many invertebrates. Using reverse phase high pressure liquid chromatography together with a sensitive bioassay, we analyzed the distribution of proctolin in the central nervous system of the grasshopper Schistocerca nitens. We also used immunocytochemistry to identify about 70 diverse proctolin-staining neurons in the postembryonic ventral nerve cord. Proctolin immunoreactivity is rare, being found in only about 0.6% of the ganglionic neurons. Among the cells we stained for proctolin were thoracic skeletal motoneurons, a cluster of efferents to the intrinsic muscles of the hindgut, and both inter- and intraganglionic thoracic interneurons, as well as several interspecies homologues to proctolin-staining neurons in the cockroach. The map of proctolin expression within the central nervous system is not extensively altered during postembryonic life. It is the product of embryonic development, which is the subject of the following paper (Keshishian, H., and M. O'Shea (1985) J. Neurosci. 5: 1005–1015).
Localization of type I benzodiazepine receptors to postsynaptic densities in bovine brain
Authors: Trifiletti RR , Snyder SH
Published: March 2018

The subcellular localization of central-type benzodiazepine receptors in bovine cerebral cortex, cerebellum, hippocampus, and corpus striatum has been studied. In all regions except for the corpus striatum, benzodiazepine receptors are most highly enriched in purified postsynaptic densities (PSDs) prepared by Triton X-100/hypotonic lysis of purified synaptosomal plasma membranes. Benzodiazepine receptor enrichment in PSDs varies regionally, following the order cerebellum (approximately 8.5-fold enriched relative to crude P2 membranes) greater than cerebral cortex greater than hippocampus greater than striatum (no significant enrichment); the percentage of putative type I benzodiazepine receptors in each of these brain regions follows the same rank order. In cerebral cortex, analysis of displacement of the benzodiazepine antagonist [3H]Ro-15–1788 by the type I-selective drug CL-218,872 reveals that PSDs contain type I benzodiazepine receptors exclusively; other subcellular fractions contain mixtures of type I and type II benzodiazepine receptors. Benzodiazepine receptors in PSDs resist further extraction with detergent but can be solubilized with detergent containing greater than or equal to 0.2 M NaCl. The enrichment of detergent-resistant/detergent-plus-salt extractable type I benzodiazepine receptors in PSDs might account in part for the differential solubilization of type I and type II benzodiazepine receptors from crude brain membranes previously reported. The benzodiazepine-binding protein in cerebral cortical PSDs was identified by photoaffinity labeling with [3H]flunitrazepam followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography. The PSD benzodiazepine-binding protein is identical in molecular weight to the binding protein from whole brain; partial tryptic and alpha-chymotryptic fingerprints are also very similar in PSDs and whole brain.
Nerve growth factor treatment enhances nicotine-stimulated dopamine release and increases in cyclic adenosine 3':5'-monophosphate levels in PC12 cell cultures
Authors: Baizer L , Weiner N
Published: March 2018

In order to examine the relationship between cyclic AMP (cAMP) levels and evoked neurotransmitter release, experiments have been performed with cultures of clonal rat PC12 pheochromocytoma cells. Stimulation of the release of endogenous dopamine by nicotine in these cultures is calcium-dependent and blocked by d-tubocurarine, a specific nicotinic cholinergic antagonist. Similarly, nicotine causes increases in cAMP levels in PC12 cell cultures that are calcium-dependent and blocked by d-tubocurarine. Cultures treated for 6 days or longer with 2 X 10(-9) M nerve growth factor (NGF) release a 3- to 4-fold greater amount of dopamine than do control cultures in response to a maximal concentration of nicotine. Correspondingly, nicotine causes a 3-fold greater increase in cAMP levels in the NGF-treated cultures than in the controls. These results suggest that stimulation of the nicotinic cholinergic receptor in PC12 cells results in some manner in the activation of adenylate cyclase and further support the notion that cAMP is involved in the process of neurotransmitter release.
Pharmacological and ionic characterizations of the muscarinic receptors modulating [3H]acetylcholine release from rat cortical synaptosomes
Authors: Meyer EM , Otero DH
Published: March 2018

The muscarinic receptors that modulate acetylcholine release from rat cortical synaptosomes were characterized with respect to sensitivity to drugs that act selectively at M1 or M2 receptor subtypes, as well as to changes in ionic strength and membrane potential. The modulatory receptors appear to be of the M2 type, since they are activated by carbachol, acetylcholine, methacholine, oxotremorine, and bethanechol, but not by pilocarpine, and are blocked by atropine, scopolamine, and gallamine (at high concentrations), but not by pirenzepine or dicyclomine. The ED50S for carbachol, acetylcholine, and oxotremorine are less than 10 microM, suggesting that the high affinity state of the receptor is functional. High ionic strength induced by raising the NaCl concentration has no effect on agonist (oxotremorine) potency, but increases the efficacy of this compound, which disagrees with receptor- binding studies. On the other hand, depolarization with either KCl or with veratridine (20 microM) reduces agonist potencies by approximately an order of magnitude, suggesting a potential mechanism for receptor regulation.
Glutamic acid decarboxylase in the striate cortex of normal and monocularly deprived kittens
Authors: Bear MF , Schmechel DE , Ebner FF
Published: March 2018

Degeneration of the thalamic fibers in the visual cortex of turtles leads to an increase in the numerical density of cortical synapses with flattened vesicles and symmetrical membrane differentiations (Smith, L. M., and F. F. Ebner (1980) Soc. Neurosci. Abstr. 6: 328). This change correlates with an increase in the cortical activity of glutamic acid decarboxylase (GAD), the synthetic enzyme for gamma-aminobutyric acid (GABA). These data are consistent with the hypothesis that removal of thalamic input activity is the stimulus for cortical GABAergic neurons to form new synapses. Pharmacological evidence suggests that even simple environmental deprivation may induce a similar increase in the numerical density of GABAergic synapses in kitten striate cortex (Duffy, F. H., S. R., Snodgrass, J. L. Burchfiel, and J. L. Conway (1976) Nature 260: 256–257). We have examined this possibility in monocularly deprived kittens using methods to localize and measure GAD. GAD in kitten striate cortex was localized using immunocytochemistry. GAD-positive cells were found in all layers and were uniformly distributed in layers II to VI. Immunoreactivity associated with axon terminals (puncta), in contrast, was laminated with a distinct band in layer IV. Monocular deprivation (MD), by either unilateral enucleation or lid closure, had no detectable effect on the distribution of GAD in striate cortex. The band of layer IV puncta remained uniform even under conditions that produced alterations in layer IV cytochrome oxidase activity. We measured GAD activity in homogenates of striate cortex to address the possibility that MD causes an absolute change in the density of GABAergic synapses. Again, however, GAD activity in the binocular and monocular segments of striate cortex was found to be unaffected by early enucleation. These data suggest two conclusions: first, that the numerical density of GABAergic synapses in visual cortex is not regulated directly by thalamic activity, and second, that changes in GABAergic synapse density do not account for the ocular dominance shift observed in kitten striate cortex after MD.
Peptidergic neurons of Aplysia lose their response to cyclic adenosine 3':5'-monophosphate during a prolonged refractory period
Authors: Kauer JA , Kaczmarek LK
Published: March 2018

Although the peptidergic bag cell neurons of Aplysia are ordinarily silent, they respond to brief electrical stimulation by producing an afterdischarge of about 30 min duration. This afterdischarge is followed by a refractory period lasting many hours during which electrical stimulation either fails to initiate afterdischarges or produces discharges of much shorter duration. Previous work has demonstrated that cyclic AMP plays a role in the genesis of afterdischarge, both in intact bag cell clusters and in isolated cultured bag cells. We have now examined the hypothesis that in the refractory period either the synthesis of cyclic AMP or the response to cyclic AMP is attenuated. Direct measurements of cyclic AMP showed that cyclic AMP levels in the bag cell neurons are elevated to a similar extent after stimulation in refractory and nonrefractory clusters of neurons. We have found, however, that the response to cyclic AMP is altered during the refractory period. The electrophysiological responses of bag cell neurons were first examined in intact clusters of cells within the abdominal ganglion. Cyclic AMP levels were elevated using the adenylate cyclase activator, forskolin, in the presence of theophylline (FT). The duration of a first bag cell afterdischarge could be greatly increased if FT was added before stimulation. The duration of a stimulated second bag cell afterdischarge could also be significantly increased if FT was added within a brief period following the end of the first afterdischarge. Furthermore, at these times the addition of FT often resulted in the onset of spontaneous afterdischarges.
Cholecystokinin-induced excitation in the substantia nigra: evidence for peripheral and central components
Authors: Hommer DW , Palkovits M , Crawley JN , Paul SM , Skirboll LR
Published: March 2018

Cholecystokinin (CCK), one of the most common brain peptides, coexists with dopamine (DA) in neurons of the medial substantia nigra (SN). CCK has been shown to excite these neurons following either direct iontophoretic or systemic administration suggesting that peripherally administered CCK may cross the blood brain barrier to act directly on nigral DA cells. However, biochemical evidence suggests that CCK does not cross the blood brain barrier, and several studies have shown that the behavioral and the satiety-inducing effects of peripherally administered CCK are abolished by vagotomy. In order to test for vagal mediation of the nigral response to systemically administered CCK, we examined the effects of a series of lesions to the vagal pathways on CCK-induced excitation in the SN. Neither acute thoracic nor chronic subdiaphragmatic vagotomies had any effect on the excitatory response of nigral DA neurons to systemically administered CCK. High cervical spinal cord transections were similarly without effect. In contrast, lesions of either vagal fibers in the medulla or of the efferent pathways from the nucleus tractus solitarii, the primary sensory nucleus of the vagus, produced significant attenuations of the nigral effects of systemically administered CCK. However, neither lesion blocked effects of CCK completely. We suggest that peripherally administered CCK has two components to its excitatory action in the SN; a component probably mediated through CCK receptors in the nucleus tractus solitarii and a direct action on DA neurons.
Recurrent inhibition of cat phrenic motoneurons
Authors: Lipski J , Fyffe RE , Jodkowski J
Published: March 2018

These experiments were performed to re-examine the presence of a recurrent inhibitory pathway to phrenic motoneurons in cats. Following intracellular staining of 49 phrenic motoneurons with horseradish peroxidase, initial axon collaterals were demonstrated in six axons (12%). Intracellular recording and averaging of the synaptic responses evoked by stimulation of the phrenic roots with an intensity subthreshold for axons of the examined motoneurons revealed (in spinalized cats with dorsal roots cut) inhibitory postsynaptic potentials (i.p.s.p.s) in 11/28 (40%) motoneurons (amplitude, 115 +/- 69 (SD) microV; latency, 3.0 +/- 0.6 msec; duration from 12 to 25 msec). In the vicinity of the phrenic nucleus, Renshaw-like units were extracellularly recorded, which fired high-frequency bursts of action potentials following the stimulation of the phrenic roots (burst duration, 8 to 21 msec). Antidromic activation of the C5 phrenic root reduced the firing probability of fibers in the C6 root. The duration of the reduced firing probability corresponded to the duration of both the i.p.s.p.s and the Renshaw units' firing period. It is concluded that Renshaw inhibition is present in phrenic motoneurons. The inhibitory effects of this recurrent pathway may be greater than judged from the small amplitude of the i.p.s.p.s recorded in individual motoneurons, particularly when the whole phrenic pool is activated and when motoneurons are near threshold. It is suggested that one of the functions of the pathway is to control phrenic motoneurons supplying the dorsal part of the diaphragm through the C6 root when the more ventral part of the diaphragm is strongly activated.
Spinalization unmasks clonidine's alpha 1-adrenergic mediated excitation of the flexor reflex in rats
Authors: Kehne JH , Gallager DW , Davis M
Published: March 2018

Clonidine exerts alpha 2-adrenergic mediated depressant effects on most behaviors measured in a normal animal. However, in the spinal- transected (spinalized) animal, clonidine apparently facilitates the flexor reflex through a stimulation of spinal alpha 1-adrenoceptors. The purpose of the present study was to determine if spinalization per se causes the shift in clonidine's profile from an alpha 2- to an alpha 1-adrenergic agonist. The hindlimb flexor reflex was elicited by electrical pulses delivered through electrodes implanted subcutaneously in the hindpaw and was measured with a force transducer and polygraph. In contrast to an alpha 2-adrenergic mediated inhibition of the flexor reflex in intact rats, clonidine produced an alpha 1-adrenergic mediated increase in flexor reflex amplitude in spinalized rats. Because decerebration did not alter the depression due to clonidine, and intraventricular (but not intrathecal) administration of oxymetazoline mimicked the effect of clonidine, the depressant effects of alpha 2-adrenergic agonists are mediated through alpha 2-adrenergic receptors localized in the brainstem. Alternate methods for inducing a functional spinal transection (spinal block with intrathecal procaine; spinal ligation) indicated that the shift in clonidine's effect from inhibition of the flexor reflex to excitation occurred immediately following spinalization. Spinal ligation did not produce alpha 1- adrenergic supersensitivity at 15 min or 2 hr after transection, as measured by alterations in [3H]prazosin receptor binding or behavioral responses to clonidine. Thus, the shift in clonidine's effects from alpha 2-adrenergic mediated inhibition of the flexor reflex in intact rats to alpha 1-adrenergic mediated excitation in spinalized rats results because spinal transection unmasks clonidine's alpha 1- adrenergic stimulatory effect. Other conditions under which clonidine exerts alpha 1-adrenoceptor mediated excitatory effects on behavior are discussed.
Distribution of neuropeptide Y-like immunoreactivity and its relationship to FMRF-amide-like immunoreactivity in the sixth lumbar and first sacral spinal cord segments of the rat
Authors: Sasek CA , Elde RP
Published: March 2018

The present study was aimed at describing the distribution of neuropeptide Y (NPY)-like immunoreactivity in the sixth lumbar (L6) and first sacral segments (S1) of the rat spinal cord, comparing this distribution to that of FMRF-amide-like immunoreactivity and determining whether NPY- and FMRF-amide-like immunoreactivities are present in the same neurons in the dorsal gray commissure (DGC) in L6 and S1 of the rat spinal cord. For distribution studies tissue from colchicine-treated animals was processed according to the peroxidase- antiperoxidase technique using anti-NPY as the primary antiserum. For co-localization studies serial 5-micron sections were processed for immunofluorescence. Adjacent sections were incubated with either anti- NPY or anti-FMRF-amide as the primary antiserum. The number of immunoreactive cells per section was counted and each section was photographed. The sections were then restained with the other antiserum (i.e., tissue first stained with anti-NPY was stained with anti-FMRF- amide and vice versa), the number of cells per section was recounted, and the sections were rephotographed. NPY-like immunoreactive cells and fibers were identified in the DGC, sacral parasympathetic nucleus, substantia gelatinosa, marginal zone, nucleus proprius, and ventral horn. Every cell in the DGC that contained NPY-like immunoreactivity was found also to contain FMRF-amide-like immunoreactivity, and the distribution of NPY-like immunoreactive fibers was found to be similar, although denser than FMRF-amide-like immunoreactive fibers. The distribution of NPY-like immunoreactivity in L6 and S1 of the rat spinal cord suggests that an NPY-like peptide may be involved in regulation of pelvic viscera, processing of primary afferent information, and motor regulation of pelvic muscles. The presence of NPY- and FMRF-amide-like immunoreactivities in the same neurons in the DGC together with the lack of bona fide FMRF-amide in the rat central nervous system, the presence of NPY in the rat central nervous system, and the cross-reactivity of anti-FMRF-amide with NPY support the hypothesis that the FMRF-amide antiserum recognizes an NPY-like peptide in the rat spinal cord.
Biochemical and immunocytological localization of molluscan small cardioactive peptides in the nervous system of Aplysia californica
Authors: Lloyd PE , Mahon AC , Kupfermann I , Cohen JL , Scheller RH , Weiss KR
Published: March 2018

High pressure liquid chromatography (HPLC) followed by bioassay on isolated snail hearts were used to locate two related peptides, termed small cardioactive peptides A and B (SCPA and SCPB) in each of the central ganglia of Aplysia. The peptides are most concentrated in the buccal ganglia, the ganglia involved in the control of feeding movements. Immunocytology with antisera raised to conjugated SCPB stained three groups of neurons in the buccal ganglia. One group consisted of relatively small neurons that were tightly clustered. The second group was comprised of larger neurons that were more scattered. The third group was made up of several neurons including the two largest in the ganglia, identified cells B1 and B2. B1 and B2 and other neurons in this group innervate the gut by way of the esophageal nerve. HPLC-bioassay of single, individually dissected B1 or B2 neurons demonstrated that the two peptides are present in a single cell. For B2, but not B1, choline injected into the cell body was converted to the conventional transmitter, acetylcholine. This indicates that, in addition to the two peptides, B2 also contains choline acetyltransferase, and raises the possibility that acetylcholine and the SCPs may act as co-transmitters in B2. Strong immunocytological staining of fibers and varicosities was observed in the neuropilar region of the cerebral, pleural, pedal, and abdominal ganglia. In addition to the buccal ganglia, immunoreactive neurons were observed in all of the other central ganglia. The high concentration of the SCPs and the relatively large number of immunoreactive neurons in the buccal ganglion suggest a particularly important role of these peptides specifically in feeding behavior. However, the widespread occurrence of the SCPs in fibers and neuronal cell bodies throughout the nervous system suggests that these peptides also may have additional behavioral functions in Aplysia.
DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine) depletes noradrenaline in kitten visual cortex without altering the effects of monocular deprivation
Authors: Daw NW , Videen TO , Parkinson D , Rader RK
Published: March 2018

Kittens were given N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) to deplete cortical noradrenaline (NA) in order to test whether this would affect the results of monocular deprivation. Seven kittens that received DSP-4 systemically had cortical NA depleted by 25 to 98%, and six kittens that received DSP-4 in the lateral ventricle had cortical NA depleted by 72 to 92%. In all of these kittens, suturing shut the eyelids of one eye for 1 to 2 weeks produced a visual cortex in which most neurons responded only or most strongly to the eye that remained open. These results are considered together with previous results from our laboratory on monocular deprivation and NA depletion. There is little difference between the ocular dominance histograms of depleted and undepleted animals and little correlation between the extent of the ocular dominance shift and the extent of NA depletion. We conclude that depletion of cortical NA by itself does not prevent the cortical effects of monocular deprivation and that, where such an effect has been found, it may be due to some other factor.
Dendritic transport. I. Colchicine stimulates the transport of lysosomal enzymes from cell bodies to dendrites
Authors: Gorenstein C , Bundman MC , Lew PJ , Olds JL , Ribak CE
Published: March 2018

Injection of colchicine into the lateral cerebral ventricle of the rat was found to induce a paradoxical translocation of two lysosomal enzymes, dipeptidyl peptidase II (Dpp II) and acid phosphatase, from the soma of neurons to the dendrites. Following a single injection of colchicine, neuronal somata, which normally contain the bulk of these lysosomal enzymatic activities, become depleted of these enzymes, whereas dendrites become abnormally enriched. All neurons which contained these enzymes, except those of the mesencephalic nucleus of the trigeminal nerve, displayed this phenomenon. Lysosomal enzyme translocation into dendrites was observed in the mitral cell layer within 1 hr after a colchicine injection and could be induced in most neuronal populations by injections of colchicine as low as 25 micrograms. Five days after a 100-micrograms colchicine injection, a normal pattern of enzyme distribution was observed, indicating that the effect of colchicine was reversible. Enzyme translocation was not accompanied by gross changes in cell morphology, nor did it result in the specific loss of neuronal cell bodies which contained these enzymes. The results indicate that colchicine, under conditions known to inhibit axoplasmic transport, stimulates the transport of lysosomal enzymes from the cell body to the dendrites.
Specificity of early motoneuron growth cone outgrowth in the chick embryo
Authors: Tosney KW , Landmesser LT
Published: March 2018

During development, chick lumbosacral motoneurons have been reported to form precise topographic projections within the limb from the time of initial outgrowth. This observation implies, first, that motoneurons select the appropriate muscle nerve pathway and, second, that they restrict their ramification within the primary uncleaved muscle masses to appropriate regions. Several reports based on electrophysiology and orthograde horseradish peroxidase (HRP) labeling have shown muscle nerve pathway selection to be fairly precise. However, studies based on retrograde labeling with HRP have produced conflicting reports on the extent to which vertebrate motoneurons make projection errors. Since it is difficult to distinguish between true projection errors and HRP leakage when using retrograde labeling, we decided to assess the distribution of labeled growth cones in 25-micron serial plastic sections, following orthograde labeling of identifiable subpopulations of motoneurons during the period of initial axon outgrowth. Examination of a large number of muscle nerves revealed no segmentally inappropriate axons, confirming earlier reports that muscle nerve pathway selection is very accurate. In addition, we observed that growth cones take widely divergent trajectories into the same muscle nerve, suggesting that growth cones are responding independently to some specific environmental cue rather than being passively channeled at this point. The distribution of labeled growth cones within the muscle masses provided direct evidence that motoneurons did not at any time project to obviously inappropriate muscle regions.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of neurotransmitter action: control of the gamma- aminobutyric acid response through the benzodiazepine receptor
Authors: Chan CY , Farb DH
Published: March 2018

The ability of several homologous benzodiazepine and heterologous nonbenzodiazepine ligands to alter the conductance increase induced in spinal cord neurons by gamma-aminobutyric acid (GABA) was determined. Complete dose-response curves were carried out on individual neurons, reducing error introduced by cell-to-cell variability. The efficacies of modulation differ for “classical” benzodiazepines and novel nonbenzodiazepine drugs in a manner consistent with a model of control of GABA receptor action through a common receptor. There was no apparent correlation between efficacy and potency. CL 218,872, a triazolopyridazine, gave the lowest efficacy of the tranquilizers tested. Ro 15–1788 (an imidazobenzodiazepine) potentiated g GABA with high potency and low efficacy, consistent with an action as a partial agonist and an “antagonist” of classical benzodiazepine action. In order of increasing efficacy, Ro 15–1788, CL 218,872, and flurazepam are partial agonists, whereas clonazepam, chlordiazepoxide, diazepam, and flunitrazepam are full agonists. The beta-carboline drugs methyl- beta-carboline-3-carboxylate (beta-CCM) and methyl-6,7-dimethoxy-4- ethyl-beta-carboline-3-carboxylate (DMCM) are “anxiogenics” and convulsants that were found to exert through the benzodiazepine receptor-inhibitory and apparently insurmountable control of g GABA . beta-CCM and DMCM display large negative efficacies and act like effectors at a site distinct from the picrotoxin-sensitive chloride ionophore and coincident with the benzodiazepine site. The actions of these different benzodiazepine receptor ligands in vivo range from anxiolytic and anticonvulsant to anxiogenic and convulsant. Efficacy rather than potency almost certainly determines the qualitative nature of the pharmacological actions of these drugs.