bluuebunny/crossref_metadata_2025 huggingface dataset:
Different synaptic channel kinetics in sympathetic B and C neurons of the bullfrog
Authors: Marshall LM
Published: March 2018

Sympathetic ganglia of the frog contain two types of principal neurons, B and C cells, which are innervated by two distinct classes of cholinergic preganglionic axons, B and C fibers. This study examined and compared the kinetics of nicotinic ACh-gated channels that produce the fast excitatory postsynaptic currents (EPSCs) in B and C cells. Neurons were identified and voltage-clamped at -50 mV, 22 degrees C. The EPSC decayed as a single exponential for both cell types, but the decay time constants differed considerably; 10.2 +/- 2.3 msec (mean +/- SD) for C cells and 5.5 +/- 1.1 msec for B cells. Analysis of ACh- induced membrane current fluctuations revealed spectra that fit single- Lorentzian functions and gave estimates of the mean channel open time of 9.8 +/- 2.0 msec and 5.2 +/- 0.9 msec for C and B cells, respectively. Thus, the clear difference in EPSC decay rate for these two types of ganglion cells is most likely due to the differences in the mean lifetimes of their synaptic channels.
Excitatory action of ATP on embryonic chick muscle
Authors: Hume RI , Honig MG
Published: March 2018

It has been suggested that ATP might play a role in synaptic transmission at developing vertebrate neuromuscular junctions. To increase our understanding of the events underlying synapse formation, we have used intracellular recording and patch clamp recording to examine the response of chick myoblasts and myotubes to to ATP and other nucleotides, ATP, applied at micromolar concentrations, has a potent depolarizing action on chick myoblasts and myotubes. The ATP depolarization declines during prolonged application of ATP and shows no recovery for at least 20 min after the removal of ATP. The physiological event that underlies the ATP response has a reversal potential near O mV and is due to a conductance increase. However, contrary to our expectation, in a series of nearly 200 cell-attached and outside-out patch recordings, we did not detect single-channel currents that were related to ATP. The myotube ATP receptor is pharmacologically distinct from putative ATP receptors in other systems. It is not activated by ADP, AMP, or adenosine. Furthermore, the nonhydrolyzable ATP analogs, AMP-PNP, alpha,beta-meATP, and beta,gamma-meATP (respectively, 5-adenylylimido diphosphate; alpha,beta- methylene adenosine 5′-triphosphate; and beta,gamma-methylene adenosine 5′-triphosphate), which are potent ATP agonists in other systems, have no depolarizing action on myotubes. The ATP receptor is also distinct from the nicotinic ACh receptor since responses to ATP are unaffected by the nicotinic antagonists d-tubocurarine and alpha-bungarotoxin. We therefore applied alpha-bungarotoxin to nerve-muscle co-cultures in the hope of uncovering an additional component of the postsynaptic potential, which might represent a synaptic action of ATP. Under these experimental conditions no evidence indicative of a postsynaptic action of ATP released from nerve terminals was observed.
Movements resembling orientation or avoidance elicited by electrical stimulation of the superior colliculus in rats
Authors: Sahibzada N , Dean P , Redgrave P
Published: March 2018

Some studies have reported that stimulation of the superior colliculus in rats produces orienting responses, as it does in a number of species. However, other studies have reported movements resembling avoidance and escape, which are not characteristic of collicular stimulation in other mammals. This apparent discrepancy was investigated by systematically recording the effects on head and body movements of electrical stimulation at a large number of sites throughout the superior colliculus (SC) and surrounding structures. It was found that the nature of the movements observed depended on the location of the stimulating electrode. Contralateral head and body movements resembling orienting and approach were obtained from sites in the intermediate and deep layers in rostral colliculus, the intermediate white layer and immediately surrounding tissue in central colliculus, and in all layers except deep white in caudal colliculus. At the remaining responsive sites, movements resembling avoidance and escape were obtained. The most common response was an ipsilateral cringelike movement of the body that developed into ipsilateral locomotion, followed by running and jumping as the current was increased. These movements were obtained from sites in the superficial and intermediate layers rostrally; from the intermediate gray and the medial superficial and deep layers in central colliculus; and from the deep layers and underlying tegmentum caudally. The distributions of sites, together with evidence from other studies, suggested the following conclusions: Within the superficial layers, avoidance responses were obtained from a region of the superior colliculus that appeared to represent the upper visual field, whereas orienting responses were obtained from a region apparently representing the lower visual field. Stimulation of the area containing the cells of origin of the predorsal bundle produced orientation and approach movements, whereas the avoidance and escape movements were probably mediated by parts of the ipsilateral descending pathway. The stimulation-induced avoidance and escape may reflect the importance of such responses to visual “events,” particularly in the upper part of the visual field, in animals, like rats, with many predators.
A model of chronic pain in the rat: response of multiple opioid systems to adjuvant-induced arthritis
Authors: Millan MJ , Millan MH , Czlonkowski A , Hollt V , Pilcher CW , Herz A , Colpaert FC
Published: March 2018

Chronic arthritic pain was induced by intradermally inoculating rats at the tail-base with Mycobacterium butyricum, which results in swelling, inflammation, and hyperalgesia of the joints. These symptoms peak at 3 weeks after inoculation and disappear by 10 weeks. The following changes were seen at 3 weeks. Immunoreactive dynorphin (ir-Dyn) and ir- alpha-neo-endorphin (alpha-NE) manifested comparable patterns of change. Their levels were increased in the anterior, but not neurointermediate, pituitary. The thalamus showed a rise in ir-Dyn and ir-alpha-NE, but no alterations were seen in other brain regions. In each case, cervical, thoracic, and lumbosacral sections of the spinal cord showed a rise in ir-Dyn and ir-alpha-NE: This was most pronounced in the lumbosacral region, where the magnitude of these shifts correlated with the intensity of arthritic symptoms. In addition, a moderate elevation in ir-methionine-enkephalin (ME) was seen in lumbosacral spinal cord. In brain, ir was not changed. The level of ir- beta-endorphin (beta-EP) was elevated both in the plasma and the anterior, but not the neurointermediate, pituitary. In addition, the content of messenger RNA encoding the beta-EP precursor, proopiomelanocortin (POMC), was enhanced in the anterior lobe. Thus, there was a selective activation of synthesis of beta-EP in, and its secretion from, the anterior lobe. In no brain tissue did levels of ir- beta-EP change. At 10 weeks postinoculation, the above changes were no longer apparent, indicating their reversibility.(ABSTRACT TRUNCATED AT 250 WORDS)
Evidence implicating descending fibers in self-stimulation of the medial forebrain bundle
Authors: Bielajew C , Shizgal P
Published: March 2018

The role of ascending and descending fibers in self-stimulation of the lateral hypothalamus and ventral tegmental area in the rat was assessed by noting whether anodal hyperpolarization of one of these sites could reduce the rewarding effect of stimulating the other site. Strength- duration curves were obtained by psychophysical means, with one of the depth electrodes serving as the cathode and the other as the anode. It was anticipated that at long pulse durations, conduction in some of the fibers stimulated at the cathode would be blocked at the anode. At shorter durations, the anodal hyperpolarization should have dissipated before the arrival of the action potentials triggered by the cathode. Thus, the predicted effect of the block was to bend the strength- duration curves obtained with two depth electrodes upward at long pulse durations, provided that the anode lay between the cathode and the efferent stages of the pathway responsible for the rewarding effect. To control for possible differences in the density of the reward substrate in the lateral hypothalamic and ventral tegmental areas, the strength- duration curves obtained with a given cathode and a depth anode were compared to curves obtained with the same cathode but with an anode consisting of a set of skull screws. It was expected that the concentrated current entering from the depth anode would much more effectively block conduction in the medial forebrain bundle than the diffuse current entering from the large, distant skull screws. The predicted change in the shape of the strength-duration curves was observed only when the ventral tegmental electrode served as the anode and the lateral hypothalamic electrode as the cathode. This is consistent with the notion that in at least some of the neurons responsible for the rewarding effect, action potentials elicited by the lateral hypothalamic electrode had to pass through the ventral tegmental area in order to reach the efferent stages of the reward pathway. In the simplest anatomical arrangement consonant with this view, the somata of these cells lie in the forebrain and give rise to descending axons. As a test of the hypothesis that anodal block was responsible for changing the shape of the strength-duration curve obtained with the ventral tegmental anode, a psychophysical version of the collision test was used to determine whether the tips of the lateral hypothalamic and ventral tegmental electrodes were indeed linked by a common set of reward-related fibers.(ABSTRACT TRUNCATED AT 400 WORDS)
Parallel antagonism of synaptic transmission and kainate/quisqualate responses in the hippocampus by piperazine-2,3-dicarboxylic acid analogs
Authors: Ganong AH , Jones AW , Watkins JC , Cotman CW
Published: March 2018

A new series of potent antagonists of excitatory neurotransmission in the rat hippocampus has been identified. These derivatives of piperazine-2,3-dicarboxylate (PzDA) include the most potent acidic amino acid antagonists yet described for Schaffer collateral- commissural EPSPs. These antagonists also effectively block excitatory synaptic responses recorded in the lateral and medial perforant pathways and in the mossy fiber pathway. The PzDA derivatives also block focal depolarizations produced by kainate, quisqualate, and N- methyl-D-aspartate. N-methyl-D-aspartate responses are more susceptible to inhibition by PzDA derivatives, although the spectrum of antagonism of N-methyl-D-aspartate and synaptic responses by PzDA derivatives is not parallel. However, the antagonism of kainate and quisqualate responses by PzDA derivatives shows the same rank order of potency as synaptic responses. These data indicate that synaptic receptors in the hippocampus have a pharmacologic profile similar to that of kainate or quisqualate receptors.
Pattern and motion vision in cats with selective loss of cortical directional selectivity
Authors: Pasternak T , Leinen LJ
Published: March 2018

Neurons in the visual cortex of cats reared in 8 Hz stroboscopic illumination show a profound loss of directional selectivity, but no detectable deficits in orientation selectivity, contrast sensitivity, and temporal frequency response, and only a slight reduction in spatial resolution. In the present study, spatial vision, temporal resolution, and a variety of motion detection and discrimination thresholds were examined behaviorally in such cats. These psychophysical measurements revealed nearly normal spatial and temporal vision, but severe abnormalities in visual discriminations based on differences in stimulus direction. Specifically, strobe-reared cats showed normal orientation discrimination and temporal frequency resolution, nearly normal contrast sensitivity at low spatial frequencies, and a slight reduction of sensitivity to high spatial frequencies. At high contrasts, the cats were able to discriminate opposite directions of motion over a wide range of visible speeds, and their performance was indistinguishable from that of normal cats. However, a comparison of contrast thresholds for detecting moving gratings and for discriminating their direction of motion revealed severe abnormalities in strobe-reared animals. At low spatial frequencies (0.28 cycles/deg), normal cats could discriminate the direction of grating motion at contrasts that were just barely visible, whereas the strobe-reared cats could detect the grating at contrasts similar to those required by normal cats, but required contrasts about 10 X the threshold to identify the direction of motion. Normal cats showed nearly identical contrast sensitivity for detecting and discriminating gratings of high spatial frequency at high temporal frequency (drift rates), but when the temporal frequency was low, their sensitivity for detection exceeded that for direction discrimination.(ABSTRACT TRUNCATED AT 250 WORDS)
PCPP-260, a Purkinje cell-specific cyclic AMP-regulated membrane phosphoprotein of Mr 260,000
Authors: Walaas SI , Nairn AC , Greengard P
Published: March 2018

The present study reports the existence of Purkinje cell-specific phosphoprotein, Mr 260,000 (PCPP-260), a neuronal membrane phosphoprotein, in cerebellar Purkinje cells. PCPP-260, which on sodium dodecyl sulfate-polyacrylamide gel electrophoresis has an apparent molecular mass of 260,000 Da, has been found to be phosphorylated in particulate preparations by endogenous or added exogenous cyclic AMP- dependent protein kinase, but not by cyclic GMP-dependent, calcium/calmodulin-dependent or calcium/phospholipid-dependent protein kinases. The protein has been found in high concentrations in all mammalian cerebella so far analyzed, including human cerebellum. One- and two-dimensional electrophoretic and peptide mapping analyses of proteins in other brain regions show that a closely related 265,000 Da phosphoprotein also exists, albeit in low concentrations, outside the cerebellum. Analysis of cerebella from mutant mice, deficient in either Purkinje cells or in granule cells, indicates that PCPP-260 within the cerebellum is restricted to Purkinje cells. Furthermore, subcellular fractionation of rat cerebella indicates that the protein is an integral membrane protein. The cAMP-regulated phosphorylation of PCPP- 260 is presumably involved in membrane functions important to Purkinje cells.
Retinal ganglion cells in goldfish: a qualitative classification into four morphological types, and a quantitative study of the development of one of them
Authors: Hitchcock PF , Easter SS
Published: March 2018

In this paper we describe the dendritic morphology of ganglion cells that have been retrogradely stained with HRP taken up by the cut optic nerve. This technique produces an extensive Golgi-like filling of the cells. From their appearance in the retinal whole-mount, they were classified as four types, according to the sizes of the soma and dendritic field, the thickness of the primary dendrites, and the density of the arbors. Each type was subdivided according to the level(s) of stratification of the dendrites within the inner and outer plexiform layer(s) to yield a total of 15 subtypes (four for three types, three for the other). The retina of the goldfish grows by a balloon-like expansion, and by the addition of new neurons, in annuli, at the margin. Therefore, a similar cell type may be examined at a variety of stages of development in the same retina, as well as in the retinae from fish of various ages. We have used a computer-assisted microscope to do so, quantitatively, for one large and easily identified subtype. In small fish (ca. 4 cm long), the number of dendritic branch points, the total dendritic length, and the dendritic field sizes of these cells are constant inside a central zone extending to 70–80% of the retinal radius. The magnitudes of all three numeric descriptors decrease closer to the margin. In large fish (ca. 14 cm long), the central zone extends to more than 90% of the retinal radius, and the same pattern holds. The area of the dendritic fields and the total dendritic lengths are both greater in the central zone of the large fish than in the small, but the number of branches is the same in both. This suggests that once a cell has achieved the “mature” number of dendritic branches, further growth is interstitial. A comparison of dendritic morphologies across the retina shows that the pattern of dendritic outgrowth in peripheral retina is initially directed parallel to the margin, and, later, toward the margin. This suggests that dendritic growth is impeded by the dendrites present in more central retina and proceeds preferentially where they are absent. Cells of the same age are at different distances from the optic disk in the small and large retinae. In some cases, they have quite different dendritic morphologies. This implies that dendritic development depends not only on the age and subtype of the cell, but on extrinsic factors as well.(ABSTRACT TRUNCATED AT 400 WORDS)
Phenylethanolamine N-methyltransferase-containing neurons in rat retina: immunohistochemistry, immunochemistry, and molecular biology
Authors: Park DH , Teitelman G , Evinger MJ , Woo JI , Ruggiero DA , Albert VR , Baetge EE , Pickel VM , Reis DJ , Joh TH
Published: March 2018

We sought to characterize in detail neurons in rat retina that contain phenylethanolamine N-methyltransferase (PNMT), the epinephrine biosynthetic enzyme. Cell bodies and processes of PNMT-containing neurons in retina were identified by immunohistochemistry. The coexistence of other catecholamine biosynthetic enzymes in the same cells was also investigated. Biochemical, molecular biological and immunochemical methods were applied to determine whether retinal PNMT is similar to the adrenal enzyme, since regulation of PNMT in retina and adrenal appears to be different. The results show that there are two types of PNMT-containing cells: those containing PNMT exclusively and those containing PNMT with two other catecholamine-synthesizing enzymes, tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC), but not dopamine beta-hydroxylase (DBH). PNMT- only cell bodies are localized in the inner nuclear layer (INL) and the ganglion cell layer (GCL). Their processes are observed in outer and inner strata of the inner plexiform layer (IPL). Only a small fraction of PNMT neurons in INL also contain TH and AADC. These cells send their processes to the adjacent stratum of the IPL. Antibodies to bovine adrenal DBH, however, fail to localize DBH in any rat retinal cells. Immunochemical titration shows that PNMT from both retina and adrenal gland has the same immunoreactivity. Furthermore, a PNMT-cDNA probe hybridizes equally with PNMT-mRNA isolated from both the retina and the adrenal gland. These results indicate that PNMT is identical in these tissues.
Involvement of serotonin in the excitation of phrenic motoneurons evoked by stimulation of the raphe obscurus
Authors: Holtman JR , Dick TE , Berger AJ
Published: March 2018

Short-latency averaged responses in the C5 phrenic nerves to electrical stimulation (2.5–80 microA; 5–80 Hz; 150 microseconds pulse duration) of raphe pallidus (RP) and raphe obscurus (RO) were investigated in anesthetized, paralyzed, and artificially ventilated cats. The responses to stimulation of RO were excitatory, whereas a mixture of inhibitory and excitatory responses of lesser magnitude were observed after stimulating in RP. The maximal response was obtained from the ventral part of RO and consisted of early and delayed excitatory responses that were of equal magnitude in both left and right C5 phrenic nerve roots. The mean latency for the early response was 2.5 +/- 0.1 msec and for the delayed response was 7.0 +/- 0.2 msec. Both responses were elicited during inspiratory phase stimulation, but only the delayed response was present during expiratory phase stimulation. The stimulus threshold of the early response was 5 microA; the delayed response was elicited at currents as small as 2.5 microA. Early and delayed responses were affected in different ways by increasing stimulus current and by increasing stimulus frequency. Intravenous administration of serotonin receptor antagonists methysergide (0.1–0.7 mg/kg), metergoline (33–244 micrograms/kg), and cinanserin (1.5–9.0 micrograms/kg) caused significant dose-related reductions in the magnitude of the delayed response, but did not significantly affect the early response. These data suggest that the early and delayed excitatory responses are mediated by different neuronal pathways. The early response does not involve serotonin release, while the later response is mediated at least in part by activation of a serotonergic pathway.(ABSTRACT TRUNCATED AT 250 WORDS)
Neuropeptide routing in the bag cells: kinetic differences in the appearance of newly labeled peptides in transport and secretion
Authors: Arch S , Linstedt A , Whitney G , Teal P , Smock T
Published: March 2018

The bag cell neurons of Aplysia synthesize and secrete several peptides. Some of these, in addition to the egg-laying hormone (ELH), are strongly implicated in the various alterations of central neuronal activity that accompany an electrical discharge of the bag cells. Thus, the secreted peptides appear to play a variety of roles in the animal's physiology. We have been interested in the intracellular mechanisms that precede peptide secretion from the bag cells because of the evidence that most, if not all, of these peptides are derived from a common precursor. Our objective has been to determine if presumed products of this precursor are processed coordinately following their synthesis. We have concentrated on two peptides (ELH and the acidic peptide, AP) because they are most easily identified in our analytical systems. On pulse-chase radiolabeling of the cells in vitro, we found that labeled AP appears before labeled ELH in axonal transport. This observation is not easily accounted for by the assumption, taken from studies of other peptide-secreting cells, that a precursor to both peptides is loaded into secretory granules before further processing ensues. Since the initial disproportion in the representation of the peptides in transport is no longer detectable at long chase times (18 and 24 hr), we examined the possibilities that ELH production is delayed relative to that of AP or that AP is degraded more rapidly than ELH. No evidence was found for either process. The disproportion between the newly labeled peptides in transport was evident on analysis of the medium bathing bag cells depolarized after 24 hr of chase.(ABSTRACT TRUNCATED AT 250 WORDS)
Noxiustoxin, a short-chain toxin from the Mexican scorpion Centruroides noxius, induces transmitter release by blocking K+ permeability
Authors: Sitges M , Possani LD , Bayon A
Published: March 2018

Noxiustoxin (NTX), a 39 amino acid peptide purified from the venom of the Mexican scorpion Centruroides noxius, has been shown to block voltage-dependent K+ currents in the squid giant axon (Possani et al., 1982; Carbone et al., 1982). Although several other drugs known as K+ channel blockers in the squid axon also act on isolated nerve terminals to produce an increase in transmitter release, these releasing effects have not been shown to be related to a decrease of K+ permeability in synaptosomes (Vizi et al., 1977; Tapia and Sitges, 1982). In this work we show that NTX increases 3H-GABA release from perfused mouse brain synaptosomes. This effect was not blocked by TTX. Ca2+ channel blockers (verapamil or Co2+) or the absence of external Ca2+ prevents the releasing effect of this toxin. NTX does not seem to induce transmitter release by directly increasing Ca2+ permeability: The K+ ionophore valinomycin completely inhibits the release induced by NTX, as well as that evoked by the K+ channel blocker 4-aminopyridine; in contrast, the release evoked by a Ca2+ ionophore is not blocked by valinomycin. These findings strongly suggest that the releasing effect of NTX is mediated by a decrease in K+ permeability. External Ca2+ is needed only in order to couple this stimulus with the release process. Consistent with this hypothesis, we present evidence that NTX blocks the efflux of 86Rb+ from synaptosomes. An extended comparison of the effect of 4- aminopyridine with that of NTX is also reported.
Hippocampal long-lasting potentiation produced by pairing single volleys and brief conditioning tetani evoked in separate afferents
Authors: Gustafsson B , Wigstrom H
Published: March 2018

Cooperative effects between afferents on the induction of long-lasting potentiation (LLP) of synaptic transmission were examined in the CA1 region of the hippocampal slice preparation. Synaptic activity was recorded extracellularly in the dendritic layer (stratum radiatum) as a field EPSP, and the amount of LLP produced was measured from the change in slope of the rising phase of this potential. Experiments were performed with the GABA antagonist picrotoxin in the bath solution in order to facilitate the induction of LLP. It is shown that under these conditions a test input evoked by single volleys (at 0.2 Hz) is potentiated when paired with brief tetani (2–15 impulses at 50 Hz) to a separate population of fibers in the stratum radiatum. For this potentiation to appear, the test input had to occur during the train or precede it by less than 40 msec. Maximal effects were observed with the test volley positioned in the early part of the tetanus, and were largely independent of train duration. The potentiation obtained in this manner reached a peak level after some 20 conjunction events, and its magnitude measured 10 min after conjunction was about half that which could be induced by homosynaptic tetanization. Prior homosynaptic potentiation occluded the potentiation induced by conjunction, suggesting an identity of their underlying mechanisms. A test input to the apical dendritic layer was potentiated also by inputs to the basal dendritic layer, although greater effects were observed with both inputs in the same dendritic layer. It is suggested that the conditioning effect is related to the postsynaptic depolarization created by the tetanus.(ABSTRACT TRUNCATED AT 250 WORDS)
Age-related fiber order in the ferret's optic nerve and optic chiasm
Authors: Walsh C
Published: March 2018

Although the mammalian optic tract shows a grouping of fibers by age, with newer fibers nearer the pial surface, the possible rules for fiber ordering in the mammalian optic nerve have not been well defined. In this study, preferential labeling of the older retinal fibers in the ferret, a close relative of the cat, shows that the age-related fiber order in the ferret's optic tract reflects a systematic sorting of fibers by age that occurs in the optic nerve, and that is maintained through the optic chiasm. The older retinofugal fibers, dispersed throughout the nerve near the retina, come to be limited to the perimeter of the nerve as it passes through the optic foramen, while newer fibers come to lie nearest the center of the nerve. These newest fibers approach the ventral surface of the brain nearer the optic chiasm. In the chiasm, as in the tract, the oldest fibers lie furthest from the pial surface of the brain, while newer fibers lie nearer the surface. The age-related fiber ordering in the ferret's optic nerve, with the newest fibers initially being furthest from the surface at the optic foramen, differs from age-related orderings seen in nonmammalian vertebrates, where the newest fibers are always nearest the surface. The changing patterns of fiber ordering along the ferret's optic nerve may relate to changes in the underlying glial structure of the developing nerve.
Enkephalin convertase: localization to specific neuronal pathways
Authors: Lynch DR , Strittmatter SM , Venable JC , Snyder SH
Published: March 2018

3H-Guanidinoethylmercaptosuccinic acid (GEMSA) selectively labels the carboxypeptidase B-like enzyme enkephalin convertase (EC) in rat brain tissue sections. We have used autoradiography with 3H-GEMSA to map membrane-bound EC in the rat forebrain and, in conjunction with lesioning techniques, to localize EC to specific neuronal pathways. The highest levels of EC are in the median eminence. High levels of EC also occur in the hypothalamic magnocellular nuclei, in several nuclei of the amygdala, the lateral septum, and the bed nuclei of the stria terminalis. Knife-cut lesions of the stria terminalis increase EC posterior to the lesion in the stria and deplete EC from the stria adjacent to the bed nucleus, suggesting that EC, like enkephalins, is axonally transported within the stria terminalis. Ibotenic acid lesions of the caudate nucleus destroy binding in the substantia nigra pars reticulata ipsilateral to the lesion, suggesting that nigral EC is associated with axons originating in the caudate nucleus. We have also mapped EC in detail in the hippocampus. EC levels are highest near pyramidal cells of CA 3–4 and the dentate gyrus granule cells. Quinolinic acid lesions destroy both the granule and pyramidal cells and destroy all of the 3H-GEMSA labeling except for a small amount in the molecular layer of the dentate gyrus. Selective destruction of CA 3– 4 pyramidal cells with kainic acid eliminates EC in the pyramidal cell region. Destruction of granule cells of the dentate gyrus with colchicine depletes binding in the dentate gyrus without any change in the area surrounding field CA 3–4. High levels of 3H-GEMSA binding are present in the hippocampus at least 3 d before birth. These observations suggest that in the hippocampus the majority of EC is associated with pyramidal cells, which have not been shown to contain enkephalins. 3H-GEMSA autoradiography of the trigeminal ganglion localizes EC to the sensory neurons and not to white matter tracts there. These studies demonstrate that while EC is contained in enkephalinergic pathways, it is also present in some neurons that do not contain enkephalins.
Vasopressin mRNA regulation in individual hypothalamic nuclei: a northern and in situ hybridization analysis
Authors: Sherman TG , McKelvy JF , Watson SJ
Published: March 2018

The present study examines the relative levels of vasopressin (AVP) mRNA within the paraventricular (PVN), supraoptic (SON), and suprachiasmatic (SCN) nuclei of the rat hypothalamus, and details the rates at which these levels change over the course of a 6 d salt- loading regimen. The quantitation of vasopressin mRNA was achieved by using three different procedures: (1) cell-free translation in rabbit reticulocyte lysate or (2) Northern analysis of poly(A)RNAs isolated from micro-punch dissected SON, PVN, and SCN, and (3) in situ hybridization histochemistry. The former involved the quantitative immunoprecipitation of the neurophysin precursors containing arginine8- vasopressin (AVP) or oxytocin, and the latter two techniques employed a radiolabeled synthetic oligodeoxynucleotide complementary to the 3′ region of the AVP mRNA. Both the cell-free studies and the Northern gel analyses detected a sevenfold increase of AVP mRNA in the SON, a fivefold increase in the PVN, and no significant change in the SCN following 6 d of salt-loading. After the initiation of salt-drinking, these increases were shown to occur between 24 and 48 hr in the SON and between 48 and 72 hr in the PVN. The in situ hybridization studies revealed the anatomically correct hybridization of either 32P- or 3H- labeled AVP oligonucleotide to magnocellular perikarya within both the SON and PVN. Autoradiographic grains could be shown to be confined to the cytoplasm of these cells, and could be co-localized with immunoreactivity directed against the carboxy terminus of the AVP percursor. Comparison of x-ray level autoradiograms of control and 6 day salt-loaded SON revealed up to a sevenfold increase in specific signal in the salt-loaded sections. It is concluded that the response of AVP mRNA to osmotic stimuli in the three hypothalamic nuclei is heterogeneous, and that this heterogeneity can be explained by separating AVP neurons into two systems: one responsible for eliciting the antidiuretic actions of AVP via plasma AVP levels, and the other involved in CNS activities not directly involved with antidiuresis.
Effects of interstimulus interval and contingency on classical conditioning of the Aplysia siphon withdrawal reflex
Authors: Hawkins RD , Carew TJ , Kandel ER
Published: March 2018

he siphon withdrawal reflex of Aplysia undergoes differential classical conditioning with cutaneous stimulation of the siphon or mantle shelf as the discriminative conditioned stimuli (CS+ and CS-) and shock to the tail as the unconditioned stimulus (US). The reflex has proved to be useful for analyzing the neural mechanisms of conditioning. To test the generality of this experimental system, we have begun to compare the properties of conditioning in Aplysia with those of conditioning in vertebrates. We first examined the effect of the interstimulus interval (ISI) by varying the time between presentation of the CS+ and the US in different groups of animals. Significant differential conditioning was obtained when the onset of the CS+ preceded the onset of the US by 0.5 sec, and marginal conditioning was obtained when the ISI was 1.0 sec. By contrast, no significant conditioning occurred when the CS+ preceded the US by 2, 5, or 10 sec, when the onsets of the stimuli were simultaneous, or when US onset preceded the CS+ by 0.5, 1.0, or 1.5 sec (backward conditioning). We next examined the effect of contingency by giving one group of animals normal differential conditioning, and a second group the same training but with additional USs inserted between the paired trials. Presentation of these additional USs reduced the degree to which the US was contingent on the CS+, but did not change the number of pairings. Animals receiving normal training again showed significant conditioning, whereas animals receiving additional USs showed no conditioning.(ABSTRACT TRUNCATED AT 250 WORDS)
The rat ventromedial thalamic nucleus and motor control: role of N- methyl-D-aspartate-mediated excitation, GABAergic inhibition, and muscarinic transmission
Authors: Klockgether T , Schwarz M , Turski L , Sontag KH
Published: March 2018

The rat ventromedial thalamic nucleus (VM) is a point of convergence of several pathways that are supposed to be involved in motor control. Cortical fibers terminating within this nucleus use an excitatory amino acid, possibly L-glutamate, as their transmitter. Excitatory amino acids are known to interact with N-methyl-D-aspartate (NMDA), kainate, and quisqualate receptors, the presence of which has been demonstrated within the thalamus, gamma-Amino-butyrate (GABA) has been identified as the transmitter of the basal ganglia afferents to the VM, whereas cerebellar afferents to the VM are supposed to release ACh acting on muscarinic receptors. The present study investigates the behavioral and motor consequences of local injections of drugs into the VM, which specifically interact with NMDA, GABA, and muscarine receptors. Both the NMDA antagonist (-)2-amino-7-phosphonoheptanoate [(-)AP7], and the GABA agonist muscimol, but not the muscarinic antagonist scopolamine, induced catalepsy and limb rigidity. Both the (-)AP7- and muscimol- induced catalepsy were antagonized by coadministration of NMDA and the GABA antagonist bicuculline. The (-)AP7-induced catalepsy was characterized as an akinetic-rigid syndrome, in which the ability to induce a phasic activation of a set of muscles is lost and replaced by exaggerated tonic muscular responses. NMDA, bicuculline, and the muscarinic agonist bethanechol induced an increase in locomotor activity. The present study provides evidence that an imbalance between NMDA-mediated excitation and GABAergic inhibition within the rat VM leads to disturbances of motility, whereas muscarinic transmission within this nucleus appears to be of minor importance.
Integration and spike initiation in neuronal terminals
Authors: Wang-Bennett LT , Glantz RM
Published: March 2018

Axoaxonal synapses impinge on the terminals of neurons and are thought to play a crucial role in the regulation of synaptic transmission. In the crayfish brain, the terminals of several identified interneurons exhibit both EPSPs and IPSPs in response to cephalic sensory stimulation. The terminal arbors extend into primary sensory neuropils near the terminals of primary afferent axons of the antennae and statocysts. The EPSPs arise monosynaptically from primary afferent stimulation and can elicit action potentials. Bidirectional conduction is routinely observed. Terminal IPSPs are transmitted via a polysynaptic pathway. Furthermore, two morphological classes of synaptic profiles impinge on the presynaptic terminals. These results indicate that the neuron terminal can function as a second, independent site of synaptic integration.
Autoradiographic localization of sigma receptor binding sites in guinea pig and rat central nervous system with (+)3H-3-(3-hydroxyphenyl)-N-(1- propyl)piperidine
Authors: Gundlach AL , Largent BL , Snyder SH
Published: March 2018

(+)3H-3-PPP [(+)3H-3-(3-Hydroxyphenyl)-N-(1-propyl)-piperidine] binds with high affinity to brain membranes with a pharmacological profile consistent with that of sigma receptors. The distribution of (+)3H-3- PPP binding sites in brain and spinal cord of both guinea pig and rat has been determined by in vitro autoradiography with binding densities quantitated by computer-assisted densitometry. (+)3H-3-PPP binding to slide-mounted brain sections is saturable and displays high affinity and a pharmacological specificity very similar to sites labeled in homogenates. (+)3H-3-PPP binding sites are heterogeneously distributed. Highest concentrations of binding sites occur in spinal cord, particularly the ventral horn and dorsal root ganglia; the pons- medulla, associated with the cranial nerve and pontine nuclei and throughout the brain stem reticular formation; the cerebellum, over the Purkinje cell layer; the midbrain, particularly the central gray and red nucleus; and hippocampus, over the pyramidal cell layer. Lowest levels are seen in the basal ganglia and parts of the thalamus, while all other areas, including hypothalamus and cerebral cortex, exhibit moderate grain densities. Quinolinic acid-induced lesions of the hippocampus indicate that (+)3H-3-PPP labels hippocampal pyramidal cells and granule cells in the dentate gyrus. Intrastriatal injection of ibotenic acid dramatically reduces (+)3H-3-PPP binding in this area, while injection of 6-hydroxydopamine produces a relatively slight decrease. The distribution of (+)3H-3-PPP binding sites does not correlate with the receptor distribution of any recognized neurotransmitter or neuropeptide, including dopamine. However, there is a notable similarity between the distribution of (+)3H-3-PPP sites and high-affinity binding sites for psychotomimetic opioids, such as the benzomorphan (+)SKF 10,047.
Pioneer growth cone steering along a series of neuronal and non- neuronal cues of different affinities
Authors: Caudy M , Bentley D
Published: March 2018

We have analyzed the morphology of over 5000 Ti1 pioneer growth cones labeled with anti-HRP, which reveals the disposition of axons, growth cone branches, and filopodia. Ti1 axon pathways typically consist of a sequence of 7 characteristically oriented segments, with a single, distinct reorientation point between each segment. Growth cones exhibit the same orientations and reorientations in a given region as do axon segments at later stages. The single, distinct reorientations suggest that growth cones make discrete switches between guidance cues as they grow. Ti1 growth cones are guided by various types of cues. A set of 3 immature identified neurons serves as nonadjacent guidepost cells and lies at the proximal end of 3 of the axon segments. To form another segment, growth cones reorient along a limb segment boundary within the epithelium. Growth cones also respond consistently to, and orient toward, a specific mesodermal cell, which may be a muscle pioneer. Thus, growth cones respond to at least 3 different types of cells in the leg. Ti1 growth cones exhibit a hierarchy of affinity for these cues. Guidepost neurons are the dominant cues in that contact with them reorients growth cones from guidance by the other types of cues. Growth cone branches are exclusively oriented to specific cues. Growth cones reorient by extending a branch directly to the cue of highest affinity and by withdrawing any branches that are extended to a cue of lesser affinity. A single filopodium in direct contact with a guidepost neuron can reorient a growth cone that still has multiple filopodia or even prominent branches specifically oriented to a previous cue of lesser affinity. These observations suggest that growth cone steering may not result simply from passive adhesion and filopodial traction, but may involve more active processes.
Stimulation-produced spinal inhibition from the midbrain in the rat is mediated by an excitatory amino acid neurotransmitter in the medial medulla
Authors: Aimone LD , Gebhart GF
Published: March 2018

It has been previously established that a bulbar relay plays an important role in descending inhibition of spinal dorsal horn nociceptive neurons and nociceptive reflexes produced by stimulation in the midbrain periaqueductal gray (PAG). In the present study, selected receptor antagonists were microinjected into the medial medullary nucleus raphe magnus (NRM) to determine whether descending inhibition of the tail flick (TF) reflex in the rat produced by focal electrical stimulation in the midbrain PAG was mediated by serotonin, opioid, or glutamate receptors on bulbospinal neurons in the NRM. It was determined in initial experiments that the serotonin receptor antagonist methysergide, the opioid receptor antagonist naloxone, the local anesthetic lidocaine, and the glutamate receptor antagonists gamma-D-glutamylglycine (DGG) and DL-2-amino-5-phosphonovalerate (APV) microinjected into the medulla all significantly increased the threshold of focal electrical stimulation in the medulla required to inhibit the TF reflex. The antinociceptive efficacy of agonists at opioid, serotonin, and glutamate receptors was also tested in other experiments. The microinjection of morphine (2.5–10 micrograms) into the NRM increased significantly TF latencies in a dose-dependent manner in rats in the awake or lightly anesthetized state; morphine was more potent in awake rats. Inhibition of the TF reflex produced by the microinjection of morphine was reversed by a subsequent microinjection of naloxone into the same site in the medulla. The microinjection of serotonin (5 and 10 micrograms), however, did not affect the latency of the TF reflex in either awake or lightly anesthetized rats. Glutamate (100 microM, 0.5 microliter) microinjected into the rostral ventral medulla produced an inhibition of the TF reflex of short duration that could be blocked or attenuated significantly by the glutamate receptor antagonists DGG or APV microinjected into the same site. In subsequent experiments, a nonspecific functional block was introduced adjacent to the NRM bilaterally in the medullary reticular formations (MRFs) by the microinjection of the local anesthetic lidocaine; receptor antagonists were then microinjected into the NRM and their effect on the threshold of focal electrical stimulation in the PAG to inhibit the TF reflex determined. No increase was seen in stimulation thresholds in the PAG following the microinjection of either methysergide or naloxone into the NRM. Following the microinjection of lidocaine, DGG or APV into the NRM, the stimulation threshold in the PAG for inhibition of the TF reflex was increased significantly.(ABSTRACT TRUNCATED AT 400 WORDS)
Determinants of directional specificity in the regeneration of lamprey spinal axons
Authors: Mackler SA , Yin HS , Selzer ME
Published: March 2018

The projection patterns of regenerating spinal axons in the larval sea lamprey (Petromyzon marinus) were determined by intracellular injection of HRP. Four hundred and eighty-six of 562 stained axons and axon-like neurites (87%) arising from Muller and Mauthner axons, giant interneurons, and dorsal cells terminated in an orientation similar to that of their counterpart control cells. Therefore, lamprey spinal axons regenerate selectively along their normal projection paths. During the first 4 weeks of recovery, i.e., before any had regenerated beyond the transection site, 91 of 114 axons and long neurites (80%) projected in the proper direction. Thus, the correctness of the final projection patterns did not result from selective retraction of randomly directed long neurites. When the cords were doubly transected 1 cm apart, orientation of regenerating neurites remained normal both within the 1 cm island and in the adjacent spinal cord. This suggests that the directional specificity of axonal regeneration was determined neither by the location of the scar nor by the availability of channels formed by the degenerating fibers. Finally, removing 1 cm of spinal cord eliminated potential synaptic targets for regenerating axons on either side of the lesion, but did not affect the direction of axonal growth. These findings are consistent with the hypothesis that the regeneration of lamprey spinal axons is guided by local chemical cues that persist long after the pathways are formed early in development.
Characteristics and distribution of high- and low-affinity alpha bungarotoxin binding sites in the rat hypothalamus
Authors: Meeker RB , Michels KM , Libber MT , Hayward JN
Published: March 2018

When binding of 125I-alpha bungarotoxin (125I-alpha BTX) to hypothalamic membranes is observed over a wide range of concentrations, 3 binding sites can be identified, with estimated equilibrium dissociation constants (Kds) of 4.1 X 10(-11) M, 6.2 X 10(-10) M, and 9.1 X 10(-7) M for high-, low-, and very-low-affinity interactions, respectively. The densities of the high- and low-affinity sites were similar at 14–21 fmol/mg protein, whereas the very-low-affinity site had approximately 1000 X greater capacity. Association and dissociation kinetics predicted a biphasic binding reaction, with association rate constants of 1.38 X 10(8) M-1 min-1 and 7.53 X 10(7) M-1 min-1 and dissociation rate constants of 5.23 X 10(-3) min-1 and 1.80 X 10(-3) min-1. The presence of Na+ inhibited the binding of 125I-alpha BTX with a half-maximally effective concentration of 22 mM. This decrease in binding was associated with the observation of a single binding site with a Kd of 4.3 X 10(-10) M and a density of 12.1 fmol/mg protein. In competition binding experiments, alpha BTX, curare, nicotine, and quinacrine were the most potent competitors. Acetylcholine competed with 125I-alpha BTX binding at 2 sites with estimated affinities of 3.6 X 10(-8) and 7.4 X 10(-5) M. In the rostral hypothalamus, high-affinity binding of 125I-alpha BTX was localized to the region of the supraoptic nucleus, paraventricular nucleus, suprachiasmatic nucleus, and the nucleus circularis complex. Within magnocellular regions, binding was closely associated with neurophysin-immunoreactive neurons and processes, while in the region of the suprachiasmatic nucleus, the binding was in a perinuclear region surrounding parvocellular neurophysin-immunoreactive neurons.