bluuebunny/crossref_metadata_2025 huggingface dataset:
Topography of NPY-, somatostatin-, and VIP-immunoreactive, neuronal subpopulations in the guinea pig celiac-superior mesenteric ganglion and their projection to the pylorus
Authors: Lindh B , Hokfelt T , Elfvin LG , Terenius L , Fahrenkrug J , Elde R , Goldstein M
Published: March 2018

The topography of the peptidergic neuronal subpopulations in the guinea pig celiac-superior mesenteric ganglion was studied analyzing the distribution of immunoreactivity to neuropeptide Y (NPY), somatostatin (SOM), and vasoactive intestinal polypeptide (VIP)/polypeptide HI (PHI). For comparison, the ganglion was also studied using antisera against the 2 catecholamine-synthesizing enzymes tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH). Approximately 65% of the neuronal cell bodies contained NPY-like immunoreactivity (NPY-LI), whereas 25% of the principal ganglion cells contained SOM-like immunoreactivity (SOM-LI). Though occasional cells were found to contain both NPY-LI and SOM-LI, these peptides had a complementary distribution in the ganglion, with NPY cells in the celiac poles and SOM cells in the superior mesenteric pole. The vast majority of both the NPY- and SOM-positive cells also contained TH-like immunoreactivity (TH-LI), confirming their catecholaminergic, presumably noradrenergic, nature. Some noradrenergic neurons seemed to lack NPY- and SOM-LI. Small numbers of VIP/PHI-containing cell bodies were found in areas where the NPY-immunoreactive neurons predominated. Many of the VIP/PHI- positive cells contained NPY-LI and occasionally also TH-LI. The immunohistochemical markers were also observed in fibers. Thus, a comparatively weak NPY-LI was seen in smooth fibers, probably representing axons and axon bundles. SOM-LI was seen in a similar type of fiber but also in more strongly fluorescent fibers with a varicose appearance. The latter fibers were observed only in the SOM-dominated part of the ganglion, often surrounding the ganglion cells. Varicose fibers with a similar distribution containing DBH-like immunoreactivity (DBH-LI) were also seen. In addition, DBH- and TH-LI were seen in smooth axonlike processes. VIP-positive fibers exhibited a very dense fiber network, almost exclusively related to the SOM cell-dominated part of the ganglion. The projection of the postganglionic sympathetic neurons was studied with special reference to the pylorus using a combination of retrograde axonal tracing and indirect immunofluorescence techniques. Seventy-two hours after injection of the fluorescent tracer Fast Blue into the pyloric sphincter, labeled neurons were found in the ganglion. By comparing the Fast Blue-labeled cells with the immunoreactive cell bodies, neurons containing both dye and NPY- or SOM-LI were observed. In elution-restaining experiments, it was established that the majority of these cells were also immunoreactive to TH, indicating that they produce noradrenaline.(ABSTRACT TRUNCATED AT 400 WORDS)
Modulatory synaptic actions of an identified histaminergic neuron on the serotonergic metacerebral cell of Aplysia
Authors: Weiss KR , Shapiro E , Kupfermann I
Published: March 2018

Possible sources of excitatory synaptic input to the serotonergic metacerebral cell (MCC) were determined by stimulating various neurons in the cerebral ganglion. Firing of the previously identified histaminergic neuron C2 was found to produce synaptic input to the MCC. The synaptic input consists of fast excitatory-inhibitory synaptic potentials on a background of a slow EPSP. The slow EPSP appears to be monosynaptic and chemically mediated since it persists in a solution of high divalent cations; broadening of the presynaptic spike enhances the EPSP; the size of the EPSP is a function of the Mg2+ and Ca2+ concentrations of the bathing solution; and the EPSP can be mimicked by application of histamine to the MCC. The slow EPSP, in addition to firing the MCC, can increase the excitability of the cell, even under conditions in which C2 is fired at a rate too slow to produce a measurable EPSP when the MCC is at rest potential. This property appears to be due to the fact that the slow EPSP results from an apparent decrease of membrane conductance so that the size of the EPSP increases markedly as the cell is depolarized, and the EPSP appears to be highly voltage-dependent so that it is small or absent close to the rest potential of the MCC. When the MCC is voltage-clamped, application of histamine to the bath results in an inward current that disappears when the MCC is hyperpolarized. The potential at which the histamine- induced current reverses or disappears is dependent on the concentration of external potassium, suggesting that, at least in part, the slow EPSP is due to a decrease of potassium conductance. The data on C2 are consistent with its being an element of the neuronal system that mediates a state of food arousal in Aplysia.
Insect cardioactive peptides: cardioacceleratory peptide (CAP) activity is blocked in vivo and in vitro with a monoclonal antibody
Authors: Tublitz NJ , Evans PD
Published: March 2018

We demonstrate here that a specific monoclonal antibody can be utilized as a physiological tool to analyze neuropeptide function. Two cardioacceleratory peptides (CAPs) have been recently isolated from the CNS of the tobacco hawkmoth, Manduca sexta (Tublitz and Truman, 1985a), and it has been suggested that they act as cardioregulatory neurohormones during adult emergence and wing inflation (Tublitz and Truman, 1985b). Evidence is presented here indicating that a monoclonal antibody, 6C5, selectively and specifically precipitated the biological activities of both CAPs. In vivo injections of 6C5 markedly reduced CAP hemolymph titers in newly emerged adults. The 6C5 treatment also blocked the primary physiological effect of the CAPs, the increase in cardiac activity seen during adult wing expansion. In addition, removal of the postemergence CAP pulse with 6C5 prolonged the duration of wing- inflation behavior. Thus, by neutralizing CAP hemolymph activity with a CAP-specific antibody, we have shown that the CAPs are involved in cardioregulation in newly emerged moths.
The selective inhibition of growth cone extension by specific neurites in culture
Authors: Kapfhammer JP , Grunewald BE , Raper JA
Published: March 2018

We have found that neurites from embryonic chick retinal and sympathetic explants do not mix in culture, while retinal neurites mix with retinal neurites, and sympathetic neurites mix with sympathetic neurites. These results confirm those obtained with embryonic rat tissues by Bray et al. (1980). We have also used video time-lapse techniques to examine the behavior of individual retinal and sympathetic growth cones as they attempt to cross retinal and sympathetic neurites. We have found that retinal growth cones cross retinal neurites without delay, retinal growth cones usually retract from sympathetic neurites but often cross them on a second advance, sympathetic growth cones repeatedly retract from retinal neurites, rarely managing to cross them at all, and sympathetic growth cones cross sympathetic neurites but are sometimes delayed. Our results indicate that retinal and sympathetic growth cones can distinguish between specific labels associated with retinal and sympathetic neurites. They also suggest that active avoidance could play an important role in growth cone navigation.
Survival of motoneurons in the brachial lateral motor column of limbless mutant chick embryos depends on the periphery
Authors: Lanser ME , Carrington JL , Fallon JF
Published: March 2018

Motoneuron survival in the embryonic spinal cord is influenced by the presence or absence of the developing limb bud. We have recently begun a reexamination of the relationship between limb absence and motoneuron survival in a nonsurgical limb deletion model, the limbless mutant chick embryo. As in surgically limb-deleted normal embryos, only 10% of the motoneurons that are initially produced in the limbless mutant lateral motor column (LMC) survive the embryonic period (Lanser and Fallon, 1984). We now report that, when supplied with a normal periphery (i.e., a normal limb bud), more than 40% of the motoneurons initially produced in the limbless LMC survive the embryonic period. Motoneuron cell counts in one-winged limbless embryos reveal that over 3.5 times as many motoneurons survive the cell death period in the LMC on the side with the limb than on the opposite, limbless side. This demonstrates the dependence of embryonic LMC motoneurons on the developing limb for survival and indicates that the limbless mutant is an appropriate model for studying the death and survival of LMC motoneurons during development. Using the limbless mutant to study LMC motoneuron survival eliminates the complication of possible direct surgical effects on motoneuron death. In addition, we found that a substantial effect of the wing on rescuing LMC motoneurons was exerted prior to the 6th day of embryonic development. Normally, little cell loss occurs in the brachial LMC during this time. Accordingly, motoneuron death in the limb-deprived brachial LMC, whether in surgically limb-deleted normal embryos or in genetically limbless embryos, is accelerated with respect to cell death in the normal brachial LMC.
Elevated synthesis of an axonally transported protein correlates with axon outgrowth in normal and injured pyramidal tracts
Authors: Kalil K , Skene JH
Published: March 2018

Axons of the adult mammalian CNS typically fail to regenerate after injury. Among the hypotheses to account for this failure is the proposition that certain axonal proteins necessary for axon growth are expressed in much greater abundance in developing than in mature neurons, and that these proteins are not reinduced after injury to mature axons (Skene and Willard, 1981b). In the present experiments, we have found that hamster pyramidal tract neurons synthesize an acidic, 43K protein that is transported into growing axons during the first 2 weeks of postnatal development, and then declines at least an order of magnitude by the fourth postnatal week. The decline in synthesis of the 43K protein coincides with the cessation of pyramidal tract axon elongation. This protein resembles a “growth-associated protein,” GAP- 43, which is induced during regeneration of CNS axons in lower vertebrates. The 43K protein in hamster pyramidal tract neurons is not reinduced after axotomy in adult animals, which correlates with the failure of the injured axons to regenerate. Injury to neonatal pyramidal tract axons does not reverse or delay the decline in 43K protein synthesis. This is consistent with previous findings (Kalil and Reh, 1982) that pyramidal tract axons regrow for only a brief period after neonatal injury. Taken together, these results lend support to the hypothesis that synthesis of GAP-43 is important for axon growth in development and regeneration.
Immunocytochemical localization of protein kinase C in identified neuronal compartments of rat brain
Authors: Wood JG , Girard PR , Mazzei GJ , Kuo JF
Published: March 2018

Polyclonal antisera to the phospholipid/Ca2+-dependent protein kinase have been used to study the distribution of the enzyme in identified neurons of several brain regions. The results indicated that the enzyme was concentrated in synaptic terminals of mossy fibers, Golgi II neurons and Purkinje neurons in the cerebellum, and in granule cell terminals in the hippocampus. These synapses have different physiological properties and utilize different neurotransmitters. Electron microscopic results indicated that the enzyme was concentrated in presynaptic terminals. Thus, the protein kinase may play a broad role in Ca2+-related events of the presynaptic terminal during neurotransmission. Light- and electron-microscopic immunocytochemical analysis also indicated that the enzyme was inside the nucleus concentrated in a region adjacent to the inner nuclear membrane, where it may play a role in the regulation of neuronal function.
Detection and characterization of beta-adrenergic receptors and adenylate cyclase in coated vesicles isolated from bovine brain
Authors: Chuang DM , Dillon-Carter O , Spain JW , Laskowski MB , Roth BL , Coscia CJ
Published: March 2018

To assess whether internalization of beta-adrenergic receptor occurs in the CNS, we have isolated clathrin-coated vesicles from bovine forebrain and examined them for the presence of beta-adrenergic receptor binding and adenylate cyclase activities. A coated vesicle enriched preparation isolated by successive D2O-Ficoll density gradient centrifugations was applied to a glass bead permeation column to achieve further purification. Two major peaks of protein were eluted from the column and monitored by electron microscopy and SDS-PAGE. Peak II contained almost exclusively coated vesicles (98%), whereas peak I, which appeared in the void volume, contained larger smooth vesicles and few coated vesicles. beta-Adrenergic receptor binding to peaks I and II was measured with 125I-cyanopindolol (CYP) as ligand in Sepharose 4B column assays. 125I-CYP was found to bind specifically and saturably to both peaks I and II with a Bmax of 28 +/- 4 and 32 +/- 3 fmol/mg protein, respectively. 3H-CGP 12177, a hydrophilic beta-adrenergic receptor ligand, did not label receptors present in peak II, but it specifically bound to synaptic plasma membranes (SPM) prepared from bovine hippocampus and, to a lesser extent, to peak I. These results suggest that receptors present in coated vesicles are cryptic in nature. In the displacement of 125I-CYP binding by (-)-isoproterenol, addition of 50 microM GppNHp caused a significant “right shift” with SPM and peak I but not the peak II preparation. Adenylate cyclase activities could also be detected in both peaks I and II (specific activities, 21 +/- 0.6 and 24 +/- 0.5 pmol cAMP/mg protein/min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
Tyrosine hydroxylase in the rat parabrachial region: ultrastructural localization and extrinsic sources of immunoreactivity
Authors: Milner TA , Joh TH , Pickel VM
Published: March 2018

We sought to determine the ultrastructural localization and the extrinsic sources of the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH), in the lateral parabrachial region (PBR) of adult male rats. In the first portion of the study, a rabbit antiserum to TH was immunocytochemically localized in coronal sections through the lateral PBR from acrolein-fixed brains using the peroxidase- antiperoxidase method. Electron-microscopic analysis revealed that perikarya and dendrites with peroxidase immunoreactivity for TH constituted only 17% of the total labeled profiles. Afferents to the TH- labeled perikarya and dendrites usually failed to exhibit immunoreactivity and were thus considered noncatecholaminergic. Somatic synapses were most commonly detected on small immunoreactive perikarya in the central lateral nucleus of the PBR. Other labeled perikarya located in the dorsal lateral or ventral lateral nuclei received few somatic synapses and were morphologically distinct in terms of their larger size, infolded nuclear membrane, and abundance of cytoplasmic organelles. Axons and axon terminals with peroxidase immunoreactivity constituted the remaining labeled profiles in the lateral PBR. These terminals primarily formed symmetric synapses with unlabeled and a few labeled dendrites. The labeled axon terminals were categorized into 2 types: Type I was small (0.3–0.6 micron), contained many small clear vesicles, and exhibited few well-defined synaptic densities. The second type was large (0.8–1.4 micron), contained both small clear and large dense core vesicles, and exhibited well-defined synaptic densities. The 2 types of terminals were morphologically similar to dopaminergic terminals. The location of catecholaminergic neurons contributing to the TH-labeled terminals was determined by combining peroxidase- antiperoxidase immunocytochemistry for TH with retrograde transport of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP). The tracer was unilaterally injected into the PBR of anesthetized adult rats. Immunocytochemical labeling for TH was seen as a brown reaction product within neurons in known catecholaminergic cell groups. A black granular reaction product formed by a cobalt-intensified and diaminobenzidine-stabilized tetramethyl benzidine reaction for WGA-HRP was evident within many TH-labeled and unlabeled neurons.(ABSTRACT TRUNCATED AT 400 WORDS)
A structure-activity study on the sucrose taste antagonist methyl 4,6- dichloro-4,6-dideoxy-alpha-D-galactopyranoside
Authors: Vlahopoulos V , Jakinovich W
Published: March 2018

In order to assess the effect of the antagonist methyl 4,6-dichloro-4,6- dideoxy-alpha-D-galactopyranoside (MAD-diCl-Gal) upon the gerbil's chorda tympani sucrose taste response, we tested several concentrations of this compound, as well as single concentrations of closely related derivatives, and found that MAD-diCl-Gal was the most potent inhibitor tested. It appears that the inhibition mechanism is very specific. For example, we have found that 2 chlorine atoms at the C-4 and C-6 positions on the glucopyranoside ring are required for inhibition. In addition, with regard to the orientation of the chlorine atoms, the galacto derivative seems to be more potent than the gluco derivative. We have also found that the methyl glycoside is more potent than the free sugar. With regard to the orientation of the methyl group, MAD- diCl-Gal is more potent than its beta-anomer. (Because of this discovery of the methyl group enhancement and orientation effect, we shall discontinue using the acronym diCl-Gal and replace it with the more specific MAD-diCl-Gal.) Of particular significance is the fact that there appears to be a structure-activity relationship between the most active stimulants and inhibitors in that the requirement for an axial orientation at C-1 and the enhancement by the methyl group at that position are the same in both cases. These results suggest that both the stimulator and the antagonist are acting at the same receptor site.(ABSTRACT TRUNCATED AT 250 WORDS)
Weaver mouse cerebellar granule neurons fail to migrate on wild-type astroglial processes in vitro
Authors: Hatten ME , Liem RK , Mason CA
Published: March 2018

To study the regulation of glial-guided neuronal migration, we have analyzed the behavior of cerebellar granule neurons purified from the homozygous weaver (wv/wv) B6CBA-w mouse, an autosomal recessive genetic mutation that suffers a failure of granule cell migration along Bergmann glial processes (Rakic and Sidman, 1973a, b; Rezai and Yoon, 1972), on the processes of astroglia purified from homozygous normal B6CBA-Aw-J-wv (+/+) mouse cerebella. When co-cultured with normal astroglia, weaver granule neurons failed to form neuron-glia contacts characteristic of migrating neurons and impaired normal astroglial morphological differentiation. Normal astroglial cells co-cultured with weaver granule cells had enlarged cell somata with stunted processes and enlarged endfeet compared to normal astroglia co-cultured with normal granule cells. In contrast, normal neurons associated with weaver astroglia, forming tight appositions seen for migrating neurons in vivo, and enhanced weaver astroglial morphological differentiation. Weaver astroglia co-cultured with normal granule cells contained a more normal complement of glial filaments and had a smaller perikaryon with longer, more tapered processes than their counterparts co-cultured with weaver neurons. These results suggest, in agreement with the study of Goldowitz and Mullen (1982) on heterozygous mutant chimeras, that the granule neuron is a primary site of action of the weaver gene, and further support our previous findings that neuron-glia interactions regulate astroglial morphological differentiation (Hatten, 1985).
Retardation of associative learning in the rabbit by an adenosine analog as measured by classical conditioning of the nictitating membrane response
Authors: Winsky L , Harvey JA
Published: March 2018

A series of 5 experiments examined the effects of the adenosine agonist, N6-(L-phenylisopropyl) adenosine (L-PIA) and its isomer, D- PIA, on the acquisition of conditioned responses in the rabbit. Extension of the nictitating membrane was classically conditioned to a tone and light stimulus presented for 800 msec before delivery of a 100 msec shock--the unconditioned stimulus--to the skin over the paraorbital region of the head. L-PIA (5.0 mumol/kg) retarded the rate of acquisition of conditioned responses to both the tone- and light- conditioned stimuli, while D-PIA, at doses of 5.0 and 10.0 mumol/kg, had no significant effect. Control experiments employing the explicitly unpaired presentations of tone, light, and shock stimuli indicated that the retarded acquisition of conditioned responses produced by L-PIA was due to an action on associative learning. L-PIA had no effect on the threshold of the shock's eliciting of the unconditioned response nor on the amplitude of the elicited response, but produced a large and significant reduction in the ability of the tone-conditioned stimulus to evoke conditioned responses. It was concluded that L-PIA blocked the rate of associative learning by decreasing the excitatory properties of conditioned stimuli. These effects of L-PIA suggest that endogenous adenosine may act to modulate the rate of associative learning.
Distribution of adenosine deaminase activity in rat brain and spinal cord
Authors: Geiger JD , Nagy JI
Published: March 2018

The activity of adenosine deaminase (ADA) was measured in 62 discrete regions of the CNS, and in some autonomic and sensory ganglia, peripheral nerves, and peripheral tissues of the rat using an automated high-pressure liquid chromatography (HPLC) method. The formation of inosine and hypoxanthine as a measure of ADA activity in homogenates of brain was optimal at pH 7.0, linear for up to 60 min at 37 degrees C using 500 microM adenosine as substrate, and linear with protein concentrations ranging from 0.05 to 0.8 mg. The Km and Vmax values for ADA activity in homogenates of whole brain were 47 microM and 107 nmol/mg protein/30 min, respectively. Among the CNS regions examined, the highest activity was found in posterior hypothalamic magnocellular nuclei and the lowest in hippocampus. In general, spinal cord contained relatively low levels of ADA activity, with that in dorsal cord approximately 40% higher than ventral cord. In the periphery, parasympathetic ganglia contained higher levels of ADA than sensory ganglia and brain. Most peripheral tissues--including adrenal gland, lung, liver, and anterior and posterior pituitary--exhibited activity comparable to levels in the posterior hypothalamus. ADA activity in thymus was about 10 times higher than any other tissue examined. The uneven distribution of ADA activity in the rat CNS corresponds well with the immunohistochemical localization of this enzyme in discrete neural systems of this species. Structures that contain high ADA activity exhibit intense ADA immunostaining of neuronal perikarya and/or fibers.
Serotonin and cyclic GMP both induce an increase of the calcium current in the same identified molluscan neurons
Authors: Paupardin-Tritsch D , Hammond C , Gerschenfeld HM
Published: March 2018

Serotonin (5-HT) has previously been shown to evoke an increase in the duration of the Ca2+-dependent spike of molluscan neurons by decreasing the S current (Klein et al., 1982), a K+ current controlled by cAMP. However, in a group of identified ventral neurons of the snail Helix aspersa in which 5-HT (1–10 microM) also prolonged the duration of the Ca2+-dependent action potential, no 5-HT-induced depression of S current or of any other outward current was observed. Instead, 5-HT was found to evoke the prolongation of the somatic spike by inducing an increase in Ca2+ membrane conductance. This 5-HT-induced increase of Ca2+-current was mimicked neither by the intracellular injection of cAMP nor by the extracellular application of forskolin (20 microM). In contrast, it was mimicked by the intracellular injection of cGMP and by the extracellular application of 100 nM zaprinast, a cGMP- phosphodiesterase inhibitor. The extracellular application of phorbol ester TPA (100 nM), an activator of protein kinase C, was also found to increase the Ca2+ current in the identified snail ventral neurons, but this enhancing effect had a different time course from that induced by 5-HT. These results indicate that there is a second mechanism for prolonging the Ca2+ spike of molluscan neurons, consisting of an increase in Ca2+ current, in which cGMP may play a role as second messenger.
Gangliogenesis in leech embryos: migration of neural precursor cells
Authors: Torrence SA , Stuart DK
Published: March 2018

In the metameric CNS of leeches, identified neurons occupy highly stereotyped positions in each segmental ganglion. Although many of the neural precursor cells arise near their definitive positions, some arise outside the prospective domain of the segmental ganglia and thus must migrate into the CNS. Here, we report the results of an analysis of the role of cell migration in gangliogenesis in the leech Theromyzon rude. Segmental ganglia of the ventral nerve cord arise as laterally thickened sheets of tissue lying astride the ventral midline. Particular identified circular and longitudinal muscle fibers, visualized by indirect immunofluorescence using a monoclonal antibody against leech muscle, outline the presumptive ganglionic territories even before the ganglionic rudiments become morphologically distinct and serve as anatomical landmarks to which the cell movements are related. Cell lineage tracers microinjected into precursor blastomeres are used to visualize migratory cells. Small groups of neural precursor cells that arise outside the prospective ganglionic territories migrate with stereotyped timing along stereotyped pathways to reach their definitive positions, and each group of migratory cells gives rise to a stereotyped subset of the cells in a ganglion. No segmental or regional differences are observed in any aspect of cell migration studied here, supporting the view that segmental differences in the architecture of the leech CNS arise only after the initial condensation of the ganglionic rudiments.
Processing by local interneurons of mechanosensory signals involved in a leg reflex of the locust
Authors: Burrows M , Pfluger HJ
Published: March 2018

At the distal end of the tibia of a locust hind leg are 2 pairs of movable spurs that can be moved by contact with external objects--as, for example, when the body sways from side to side and loads one leg unevenly or when the foot is placed on rough ground--but not by direct muscular action. Movements imposed on a spur evoke phasic bursts of spikes in the axon of a single receptor cell at its base. If the displacement is maintained, however, the response adapts within a few seconds. The afferents from these spur receptors excite particular spiking local interneurons with cell bodies at the ventral midline of the metathoracic ganglion. Each afferent spike is consistently followed at a constant latency by a depolarizing potential in one of these interneurons. The potential can evoke a spike, and its amplitude is enhanced by a hyperpolarization applied to the interneuron. The central delay to this chemically mediated EPSP, which also includes conduction time to synaptic sites, probably indicates a direct connection. Some spiking local interneurons are excited by the 2 anterior spurs but are unaffected by the 2 posterior ones, while others receive the converse pattern of inputs. The receptive fields of these interneurons also include regions on either the anterior or posterior surfaces of the tibia with excitatory inputs from hair afferents. A reliable inhibitory reflex effect on the single levator tarsi is evoked by movement of any of the 4 spurs. The inhibitory potentials are not caused directly by the sensory afferents but involve the spiking local interneurons upon which the afferents synapse. The receptive field of this motor neuron therefore results from the convergence of inputs from a few interneurons. Motor neurons of other tarsal muscles are unaffected by movement of the spurs, but those of some more proximal muscles may be excited. These reflex effects should enhance the traction of the tarsus with the ground.
In vivo electrophysiological evidence for the regulatory role of autoreceptors on serotonergic terminals
Authors: Chaput Y , Blier P , de Montigny C
Published: March 2018

The present in vivo studies were undertaken to evaluate electrophysiologically the modulatory role of the terminal 5-HT autoreceptor on 5-HT neurotransmission. In a first series of experiments, the effect of the electrical activation of the ascending 5- HT pathway on the firing activity of CA3 hippocampal pyramidal neurons was measured before and after the intravenous administration of methiothepin, a terminal 5-HT autoreceptor antagonist. Methiothepin significantly increased the duration of the suppression of firing activity of these neurons by the electrical stimulation of the 5-HT pathway, without modifying their responsiveness to microiontophoretically applied 5-HT. This suggests that endogenously released 5-HT activates the 5-HT terminal autoreceptor and that methiothepin enhances the efficacy of 5-HT synaptic transmission by blocking this activation. In a second series of experiments, further evidence for the activation of terminal 5-HT autoreceptors by 5-HT released by the electrical stimulation was sought by assessing the effectiveness of 2 series of stimulations of the ascending 5-HT pathway delivered at different frequencies while recording the same postsynaptic neuron. Increasing the frequency of stimulation (from 0.8 to 5 Hz) significantly reduced the duration of suppression of firing activity of the postsynaptic neurons. This difference between the 0.8 and 5 Hz stimulations was decreased by intravenous methiothepin, suggesting that the reduced effectiveness of the stimulations delivered at the higher frequency is attributable to a greater activation of the terminal 5-HT autoreceptor. These results provide direct electrophysiological evidence for the modulatory role of the 5-HT terminal autoreceptor on 5-HT neurotransmission.
Transmembrane topology and subcellular distribution of the benzodiazepine receptor
Authors: Czajkowski C , Farb DH
Published: March 2018

The distribution and transmembrane topology of benzodiazepine receptors were investigated in situ using intact and saponin-treated neurons of brain cell cultures. Reversible ligand binding and photoaffinity labeling, using 3H-flunitrazepam as a probe, were employed in conjunction with trypsin-induced exhaustive proteolysis and competition binding using a novel benzodiazepine (Ro7–0213) that contains a quaternary ammonium moiety bearing a full positive charge. About 80% of the benzodiazepine receptors, with apparent subunit molecular weights of 48,000 and 51,000, are located in the surface membrane and contain one or more trypsin-sensitive sites exposed at the extracellular surface. The ligand recognition sites of the surface receptors are orientated toward the extracellular space and are sensitive to both competition by Ro7–0213 and trypsin attack. Approximately 20% of the receptors are intracellular or sequestered and are insensitive to both trypsin and competition by Ro7–0213 in intact cells. Strikingly, all of the 3H-flunitrazepam photolabeled sites inaccessible to competition by Ro7–0213 are also resistant to extracellular trypsin, but are sensitive to trypsin and Ro7–0213 in saponin-treated cells. This result provides strong evidence for protected receptors. Surface receptors are differentially sensitive to trypsin-induced inactivation such that 57% (of total) are inactivated, while 24% (of total) are cleaved but, surprisingly, retain the capacity to bind 3H-flunitrazepam. The observation that the ability of the receptor fragment to bind ligand is unaltered demonstrates that the integrity of the benzodiazepine binding site is not contingent upon the presence of about half of the intact polypeptide chain.(ABSTRACT TRUNCATED AT 250 WORDS)
Cell death of lumbosacral motoneurons in chick, quail, and chick-quail chimera embryos: a test of the quantitative matching hypothesis of neuronal cell death
Authors: Tanaka H , Landmesser LT
Published: March 2018

The quantitative matching hypothesis of neuronal cell death was tested for the chick hindlimb by determining the relationship between myotube number at the onset of motoneuron cell death and the number of motoneurons that survive in chicks, quail, and chick-quail chimeras. Hindlimb buds, which differ in size between the 2 species, were exchanged at stages 16 1/2–19, myosin ATPase-stained myotubes in selected thigh muscles were counted during the cell death period (stages 30–34), and lumbosacral motoneurons were counted following the cell death period (stage 38). No quail motoneurons were rescued when quail cords innervated chick limbs. When chick cords innervated quail limbs, the number of surviving motoneurons was significantly decreased but not to quail values. We consider that this occurred because chicks develop more slowly than quail, and we found that transplanted chick limbs were developmentally younger than the contralateral quail limb at the onset of motoneuron cell death and contained fewer myotubes. Similarly, transplanted quail limbs contained more myotubes at the onset of cell death than normal stage 30 quail limbs. An excellent correlation was obtained during normal development of both species between the number of myotube clusters at the onset of cell death and the number of surviving motoneurons. This correlation was also observed for chick-quail chimeras, and when the data points were plotted for control chick, control quail, chick host-quail limb, and quail host- chick limb, the correlation coefficient was 0.996. This strongly suggests that some parameter closely related to myotube number limits the number of motoneurons that will survive. A proposal consistent with our observations is that motoneuron survival is dependent on the uptake of a myotube-derived trophic factor that can only be taken up at synaptic sites and that the number of such sites is limited and directly related to myotube number. In conclusion, our observations strongly support a quantitative-matching component in the process of neuronal cell death. However, since we were unable to rescue any neurons, we cannot exclude the possibility that some proportion of neurons normally dies for reasons other than peripheral competition.
Intracellular fluoride alters the kinetic properties of calcium currents facilitating the investigation of synaptic events in hippocampal neurons
Authors: Kay AR , Miles R , Wong RK
Published: March 2018

We have attempted to suppress voltage-dependent conductances in hippocampal neurons by introducing various intracellular agents. Voltage-clamp studies were carried out using acutely dissociated hippocampal neurons from adult guinea pigs. Synaptic events were examined using intracellular recordings in the slice preparation. Sodium conductance was suppressed when the quaternary lidocaine derivative QX 314 was introduced intracellularly. Potassium conductances were blocked by intracellular cesium or Tris. We also found that the anion fluoride could affect calcium conductance by an intracellular action. When anions other than fluoride were used for intracellular recordings, the voltage-dependent calcium current inactivated slowly and showed persistent activation at membrane potentials between -40 and -10 mV. In contrast, when fluoride was present intracellularly, the inactivation kinetics of the calcium current were accelerated and the persistent component of the current was largely suppressed. Intracellular recordings in the hippocampal slice showed that when electrodes contained cesium, QX 314, and fluoride, the spiking and nonlinear responses of the neuronal membrane to depolarization were blocked. In these conditions the time course and voltage-dependence of EPSPs could be examined in detail without complications due to voltage-dependent currents of the postsynaptic cell.
3H-3-N-methylspiperone labels D2 dopamine receptors in basal ganglia and S2 serotonin receptors in cerebral cortex
Authors: Lyon RA , Titeler M , Frost JJ , Whitehouse PJ , Wong DF , Wagner HN , Dannals RF , Links JM , Kuhar MJ
Published: March 2018

Detailed studies of the properties of 3H-3-N-methylspiperone (NMSP) binding in rat and human brain homogenates were performed at 37 degrees C. In homogenates of rat striatum and frontal cortex and human caudate and frontal cortex tissues, the specific binding was found to be saturable. Rat caudate contained 33.2 pmol/gm wet-weight tissue and displayed an equilibrium dissociation constant (Kd) of 8.7 X 10(-11) M; rat frontal cortex contained 18.5 pmol/gm wet-weight tissue and displayed a Kd of 1.5 X 10(-10) M. Human caudate contained 8.96 pmol/gm wet-weight tissue and displayed a Kd of 1.1 X 10(-10) M; human frontal cortex possessed 9.8 pmol/gm wet-weight tissue and a Kd of 4.4 X 10(- 10) M. Kinetic studies revealed a very rapid rate of association in all the tissues studied. The rate of dissociation was relatively slow in all 4 tissue preparations; the dissociation rate was somewhat slower in rat striatum and human caudate relative to rat and human frontal cortex. This was consistent with the somewhat higher affinity, relative to frontal cortex, displayed by 3H-NMSP in rat striatal and human caudate tissue. The pharmacological properties of the specific binding in rat striatal and human caudate tissues were very similar and indicated the presence of brain D2 dopamine receptors. In rat and human frontal cortex tissue homogenates, the pharmacological characteristics of the specific binding indicated the presence of 5-HT2 receptors.
Membrane currents in identified lactotrophs of rat anterior pituitary
Authors: Lingle CJ , Sombati S , Freeman ME
Published: March 2018

Qualitative features of the primary inward and outward current components of identified lactotrophs of the rat anterior pituitary were examined. Identification of lactotrophs in heterogeneous dissociated anterior pituitary cultures was accomplished by application of the reverse hemolytic plaque assay. Currents in lactotrophs were subsequently examined using whole-cell or patch recording techniques. Two components of inward calcium current were observed: a transient component and a sustained component. The transient component activated at voltages as negative as -50 mV and was the major contributor to total lactotroph calcium current. The sustained component activated at voltages above about -10 mV. The 2 currents could be qualitatively separated by differences in inactivation properties and in sensitivity to cadmium. At least 3 components of outward current were distinguished. Either 30 mM TEA or 0 calcium eliminated a major portion of sustained outward current. This is likely to represent primarily calcium- and voltage-activated potassium current. The remaining current could be further differentiated into a transient current component that could be inactivated with conditioning potentials above -60 mV. A slowly activating and deactivating potassium current remained following inactivation of the transient current. Although the time course of the transient current is reminiscent of “A” current, activation of this current required potentials above -30 mV. Candidates for the single- channel currents that underlie the whole-cell outward currents were observed in cell-attached recordings. When combined with patch-clamp electrophysiological methods, the reverse hemolytic plaque assay promises to be a powerful technique for the electrophysiological characterization of specific cell subtypes in heterogeneous dissociated cell populations.
Preserved motor learning in Alzheimer's disease: implications for anatomy and behavior
Authors: Eslinger PJ , Damasio AR
Published: March 2018

Learning and retention of 3 types of information were examined in patients with Alzheimer's disease (AD) and in normal controls. While patients were unable to learn series of frequent words and unfamiliar faces, they improved significantly in a motor skill, showing a learning curve similar to controls. Furthermore, no significant loss of the motor skill was evident in a 20 min delay trial. Such dissociation in learning has not been noted previously in AD, although it has been noted in amnesias caused by other disease processes. The results support the existence of two, relatively independent, learning systems related to “declarative” knowledge and “procedural” knowledge. Judging from the pathologic correlates of these amnesias, the declarative knowledge system appears to be associated with corticotemporo/limbic structures, while the procedural system is likely to depend on corticocerebellar/striatal structures. The data also offer additional cognitive correlates for the selective damage to neural systems recently identified in AD.
Primary culture of identified neurons from the visual cortex of postnatal rats
Authors: Huettner JE , Baughman RW
Published: March 2018

We have examined the properties of neurons from the visual cortex of postnatal Long Evans rats in dissociated cell culture. Visual cortex from rat pups 1–15 d old was subjected to enzymatic and mechanical dissociation to yield a suspension of single cells. Neurons plated onto collagen or a feeder layer of astrocytes rapidly extended processes and survived for 4–10 weeks. Antisera to glutamic acid decarboxylase, choline acetyltransferase, and vasoactive intestinal polypeptide stained 22 +/- 2, 2.3 +/- 0.3, and 2.4 +/- 0.2% of all neurons, respectively, suggesting that different neuronal classes survived roughly in proportion to their number in vivo. In order to study a particular identified class of cortical neurons, we prelabeled cells in vivo by retrograde transport of a fluorescent tracer. Neurons in layer V of visual cortex that project to the superior colliculus were labeled after injecting fluorescent latex microspheres into the colliculus. Retrogradely labeled neurons were readily identified immediately after dissociation and throughout the period in vitro. After 2 weeks in culture, labeled cells exhibited many ultrastructural features characteristic of pyramidal neurons in vivo. Intracellular recording techniques were used to evaluate the response properties of labeled layer V neurons, as well as other, unlabeled neurons, to excitatory amino acid agonists and antagonists. Glutamate and aspartate--as well as the synthetic agonists N-methyl-D-aspartate (NMDA), kainate, and quisqualate--excited every cortical neuron tested. The antagonist 2- amino-5-phosphonovaleric acid had no effect on responses to quisqualate and kainate but completely blocked depolarizations due to NMDA and aspartate and reduced depolarizations elicited by low concentrations of glutamate. Kynurenic acid, piperidine dicarboxylic acid, and gamma-D- glutamylglycine antagonized responses to all 5 of the agonists. These results provide evidence that corticocollicular neurons in culture express both NMDA-type and non-NMDA receptors for excitatory amino acids.
Pharmacological properties of immuno-isolated neuronal nicotinic receptors
Authors: Whiting P , Lindstrom J
Published: March 2018

Recently we immunoaffinity-purified an ACh receptor from chicken brain using a monoclonal antibody raised against receptors from fish electric organ (Whiting and Lindstrom, 1986). This neuronal receptor could be affinity-labeled with 3H-bromoacetylcholine, and antisera to it specifically blocked ACh-induced depolarization of chicken ciliary ganglion cells. Here we show that this neuronal ACh receptor binds 3H- nicotine with high affinity (KD = 6.61 +/- 0.13 nM). 3H-Nicotine binding was blocked by various nicotinic cholinergic ligands but not by alpha-bungarotoxin or the muscarinic antagonist atropine. Binding was also blocked by affinity labeling the receptor with bromoacetylcholine (after reduction by dithiothreitol). Additionally, we were able to use rat antisera raised against the chicken brain receptor to isolate a component from detergent extracts of rat brain that also bound 3H- nicotine with high affinity (KD = 1.5 nM). The pharmacology of this putative ACh receptor from rat brain was almost identical to the receptor from chicken brain, and its regional distribution was in good agreement with that of 3H-nicotine binding to rodent brain membranes reported by other workers. Thus, by analogy to the receptor we have purified and characterized from chicken brain, this nicotine-binding component from rat brain is probably a functional mammalian neuronal nicotinic ACh receptor.
Kinematics and end-point control of arm movements are modified by unexpected changes in viscous loading
Authors: Sanes JN
Published: March 2018

These experiments were undertaken to evaluate whether the kinematics and end-point control of learned movements were affected by changes in dynamic loads or were determined largely by centrally specified motor programs. Human subjects performed flexion movements about the wrist in a discrete visual tracking task for a range of movement sizes. For some movements, viscosity was increased at movement onset. When the viscous load opposed movement unexpectedly, subjects initially overshot the intended target for all movement sizes, but only for the smaller movements did the overshoot persist. Unexpected introduction of heavier loads was more effective in inducing these behavioral changes; the lightest loads did not alter end-point positioning. When subjects had visual guidance about performance when load changes occurred, the effect of the unexpected occurrences of viscous loads was diminished, suggesting that subjects rapidly adjusted their movement strategy, depending on task demands and performance. The movement responses were mediated by short-latency and long-duration muscle responses triggered by the change in viscous loading. Although the triggered muscle responses were larger when the loads were encountered during performance of large, in comparison to small, movements, smaller muscle responses affected small movements more than large triggered responses did large movements. This suggests that triggered muscle responses are compensatory in certain movement situations but disruptive in others. In addition, these findings demonstrated that dynamic loads especially affect the kinematics and end-point control of smaller movements, suggesting that kinesthetic inputs and central motor commands interact so subjects may achieve accurate positioning for certain classes of movements.
Competition regulates the efficacy of an identified synapse in crickets
Authors: Shepherd D , Murphey RK
Published: March 2018

The efficacy of the synaptic contact between an identified sensory neuron and an identified interneuron in crickets is increased when neighboring afferent synapses are removed early in postembryonic life. The physiological changes are correlated with changes in the structure of the presynaptic neuron's axonal arborizations: When neighboring axons are destroyed, there is a shift of the remaining axonal arbors into deafferented regions and an increase in the number of putative contacts with the postsynaptic neuron. Changes in the structure of the presynaptic neuron also directly affect the probability of formation of this synaptic connection. The connection was found in 67% of the control specimens, but it was present in 100% of the partially deafferented specimens. The results demonstrate that interactions between growing sensory neurons can influence both the probability of synapse formation and the strength of those connections. This is the first case in which the effects of competition on the structure of a single, identified, presynaptic neuron can be directly related to its synaptic efficacy.