bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic resonance imaging of the hippocampal formation and mammillary nuclei distinguish medial temporal lobe and diencephalic amnesia
Authors: Squire LR , Amaral DG , Press GA
Published: March 2018

Studies of circumscribed amnesia have been a useful source of information about the organization of human memory functions. In an effort to obtain neuroanatomical information about the patients being studied, we have used 2 high-resolution protocols for imaging the human brain with magnetic resonance (MR). One provides images of the hippocampus, permitting visualization of the hippocampal formation in considerable detail. The second provides images of the mammillary nuclei. Four amnesic patients with alcoholic Korsakoff's syndrome had abnormally small mammillary nuclei that were barely detectable by MR in most cases. The temporal lobe, hippocampal formation, and parahippocampal gyrus were of normal size. In a second group of 4 (non- Korsakoff) amnesic patients, the opposite findings were obtained. The hippocampal formation was markedly reduced in size in the absence of a detectable change in the size of the temporal lobe. By contrast, the mammillary nuclei, though somewhat reduced in volume, were considerably larger than in the patients with Korsakoff's syndrome. The anatomical findings for individual patients generally corresponded to the severity of their memory impairment. The results show that neuroimaging techniques can distinguish between patients with diencephalic and medial temporal lobe amnesia. These techniques can therefore provide useful information about the crucial issue of patient classification, and they set the stage for exploring possible quantitative and qualitative differences between patients.
Interactions between adjacent ganglia bring about the bilaterally alternating differentiation of RAS and CAS neurons in the leech nerve cord
Authors: Blair SS , Martindale MQ , Shankland M
Published: March 2018

Antibodies to small cardioactive peptide (SCP) label a segmentally iterated subset of cells in the leech nerve cord, including the previously identified alternating SCP (AS) neurons. Unlike the majority of leech neurons, these cells are asymmetrically distributed in the adult nerve cord. Moreover, each AS neuron shows a strong tendency to lie on alternate right and left sides in successive ganglia. Previous work has shown that these unpaired neurons arise from bilaterally paired embryonic homologues, only 1 of which takes on the mature immunoreactive phenotype. The 2 AS homologues within a ganglion compete for this fate, in that either the right or the left homologue will become a mature AS neuron with a high degree of reliability if its contralateral homologue is ablated during embryogenesis. In this paper, we demonstrate the existence of interactions between neurons in adjacent ganglia that could account for the alternation of sides observed during normal development. The unilateral ablation of a single AS homologue neuron forced its contralateral homologue to take on the mature AS fate, and this consistently biased the side of AS development in adjacent, unlesioned ganglia both anterior and posterior to the lesion. One of the AS neurons, the caudal alternating SCP (CAS) cell, was injected with Lucifer yellow in adult nerve cords and was shown to have a large primary axon that extends into more anterior ganglia, as well as other, finer axons that are variable in number and arrangement. If the interganglionic interaction of AS neuron homologues is mediated by their primary axons, signals of developmental import must be transmitted both anterogradely and retrogradely along the axon's length. The present results indicate that the development of individual AS neurons is influenced by homologous cells located in the same and neighboring ganglia and suggest that the final, multisegmental patterning of the AS neuron distribution is not predetermined, but rather, arises as an emergent property of the cell interactions that occur during nervous system differentiation.
A circuit for detection of interaural time differences in the brain stem of the barn owl
Authors: Carr CE , Konishi M
Published: March 2018

Detection of interaural time differences underlies azimuthal sound localization in the barn owl Tyto alba. Axons of the cochlear nucleus magnocellularis, and their targets in the binaural nucleus laminaris, form the circuit responsible for encoding these interaural time differences. The nucleus laminaris receives bilateral inputs from the cochlear nucleus magnocellularis such that axons from the ipsilateral cochlear nucleus enter the nucleus laminaris dorsally, while contralateral axons enter from the ventral side. This interdigitating projection to the nucleus laminaris is tonotopic, and the afferents are both sharply tuned and matched in frequency to the neighboring afferents. Recordings of phase-locked spikes in the afferents show an orderly change in the arrival time of the spikes as a function of distance from the point of their entry into the nucleus laminaris. The same range of conduction time (160 mu sec) was found over the 700-mu m depth of the nucleus laminaris for all frequencies examined (4-7.5 kHz) and corresponds to the range of interaural time differences available to the barn owl. The estimated conduction velocity in the axons is low (3-5 m/sec) and may be regulated by short internodal distances (60 mu m) within the nucleus laminaris. Neurons of the nucleus laminaris have large somata and very short dendrites. These cells are frequency selective and phase-lock to both monaural and binaural stimuli. The arrival time of phase-locked spikes in many of these neurons differs between the ipsilateral and contralateral inputs. When this disparity is nullified by imposition of an appropriate interaural time difference, the neurons respond maximally. The number of spikes elicited in response to a favorable interaural time difference is roughly double that elicited by a monaural stimulus. Spike counts for unfavorable interaural time differences fall well below monaural response levels. These findings indicate that the magnocellular afferents work as delay lines, and the laminaris neurons work as co- incidence detectors. The orderly distribution of conduction times, the predictability of favorable interaural time differences from monaural phase responses, and the pattern of the anatomical projection from the nucleus laminaris to the central nucleus of the inferior colliculus suggest that interaural time differences and their phase equivalents are mapped in each frequency band along the dorsoventral axis of the nucleus laminaris.
Opsin synthesis and mRNA levels in dystrophic retinas devoid of outer segments in retinal degeneration slow (rds) mice
Authors: Agarwal N , Nir I , Papermaster DS
Published: March 2018

Opsin gene regulation, as a function of outer segment structure, was studied in normal and mutant retinal degeneration slow (rds) mice. We investigated the level of expression of the opsin gene in the rds mutant to determine if the reduced opsin content observed in this mutation (around 3% of normal) is a consequence of lowered expression of its gene. Normal BALB/c and rds mice were analyzed for levels of opsin mRNA and opsin content by Northern and immunoblot analysis, respectively. The rate of opsin synthesis in isolated retinas was measured by 35S-methionine incorporation in vitro, followed by analysis of the radiolabeled opsin by SDS-gel electrophoresis and autoradiography. Photoreceptor cell loss at various stages of degeneration was determined by quantitation of surviving photoreceptor nuclei. Opsin was localized in the mutant photoreceptors by immunoelectron microscopy of LR gold-embedded retinas using anti-opsin and antibody gold conjugates. The results indicate that 11- and 30-d- old mutant mice have considerable levels of opsin mRNA (60–70% of normal) and opsin synthetic rates (76–92% of normal), after the data from mutant mice are corrected for photoreceptor cell loss. We conclude, therefore, that the very low level of opsin observed in rds mice (approximately 3%) is not a result of greatly reduced expression of the opsin gene. Rather, continuous turnover of newly synthesized opsin as a result of its failure to become sequestered into an intact outer segment appears to account for the low levels of opsin in the rds mutant.
Selective short- and long-term effects of serotonin, small cardioactive peptide, and tetanic stimulation on sensorimotor synapses of Aplysia in culture
Authors: Schacher S , Montarolo P , Kandel ER
Published: March 2018

Synapses between the sensory and motor cells of Aplysia can be enhanced by heterosynaptic or homosynaptic stimulation. We have used the isolated sensorimotor synapse of Aplysia in cell culture to explore short- and long-term heterosynaptic facilitation produced by 2 facilitatory transmitters and compared these to homosynaptic facilitation produced by posttetanic potentiation. We found that brief application of 5-HT or small cardioactive peptide (SCP) evokes comparable short-lasting enhancement of nondepressed sensorimotor synapses. The effect evoked by SCP diverges from that of 5-HT when the sensorimotor synapse is first depressed by low-frequency homosynaptic stimulation. Whereas 5-HT facilitates sensorimotor synapses whether or not they are depressed, SCP has little or no effect on synapses that have been depressed by more than 75%. The 2 transmitters also differ in producing long-term facilitation. Whereas repeated applications of 5-HT evoke long-term facilitation of the synapses, SCP applications do not. To determine whether these failures to facilitate could be overcome by increasing levels of cAMP, we applied SCP in the presence of phosphodiesterase inhibitors, which resulted in SCP evoking both short- and long-term changes comparable to that of 5-HT. Homosynaptic facilitation by post-tetanic potentiation differed from heterosynaptic facilitation in that tetanic stimulation failed to evoke long-lasting changes in the synapse. These results support recent findings that 5-HT is a critical neuromodulator in behavioral sensitization and dishabituation and suggest that critical levels of cAMP may be required for long- and short-term facilitation of depressed synapses.(ABSTRACT TRUNCATED AT 250 WORDS)
Projection subtypes of rat neostriatal matrix cells revealed by intracellular injection of biocytin
Authors: Kawaguchi Y , Wilson CJ , Emson PC
Published: March 2018

Individual neostriatal-matrix spiny neurons were stained intracellularly with biocytin after intracellular recording in vivo, and their axons were traced into the globus pallidus (GP), entopeduncular nucleus (EP), and/or substantia nigra (SN). The locations of the neurons within the matrix compartment of the neostriatum (NS) were established by immunocytochemical counterstaining of sections containing the cell bodies using antibodies for calbindin- D28K. This allowed nearly complete visualization of the axonal projections of single NS neurons. On the basis of their intrastriatal axonal arborizations, matrix spiny neurons could be divided into 2 types. One type, which was the more common, had local axonal arborizations restricted to the region of the dendritic field, often with axon collaterals arborizing within the dendritic field of the cells of origin. A second, less common, cell type in the matrix had local axon collaterals distributed widely in the NS. Among matrix neurons with restricted local collateral fields, 3 subtypes could be distinguished on the basis of their efferent axonal projections. Type I cells projected only to the GP. Type IIa cells projected to the GP, EP, and SN pars reticulata. Type IIb cells projected to the GP and SN but not to the EP. The shapes and densities of the GP arborizations varied in the 3 cell types, with the cells projecting only to the GP (type I) projecting more heavily and filling a larger volume there than type II cells. The dendrites and intrastriatal axon collaterals of 3 subtypes were similar in morphology. The class of matrix spiny neurons with intrastriatal axon collaterals distributed widely in the NS were observed to project to the GP. Projections beyond the GP were not identified for this cell type, but could not be ruled out. Somatodendritic morphologies of neurons did not differ according to the projection site. These results demonstrate that NS matrix spiny cells are more heterogeneous in their efferent projection patterns than previously suspected on the basis of retrograde axonal tracing and immunocytochemical studies. As predicted by those previous studies, there is a class of matrix neurons that projects only to the GP. Presumably, these cells contain enkephalin. Cells projecting to the SN and EP, and so presumably containing substance P, give off a small projection to the GP, as well, and differ in their collateralization patterns within the 3 major target nuclei.
Amygdalar interaction with the mediodorsal nucleus of the thalamus and the ventromedial prefrontal cortex in stimulus-reward associative learning in the monkey
Authors: Gaffan D , Murray EA
Published: March 2018

Cynomolgus monkeys (Macaca fascicularis) were assessed for their ability to associate visual stimuli with food reward. They learned a series of new 2-choice visual discriminations between colored patterns displayed on a monitor screen. The feedback for correct choice was the delivery of food. In order to promote associative learning between the visual stimuli and the incentive value of the food reward, reward delivery was not accompanied by any distinctive visual feedback on the display screen. The rate of learning new problems was assessed before and after surgery in a total of 16 monkeys. Three groups of 3 monkeys received bilaterally symmetrical ablations in either the amygdala, the mediodorsal nucleus of the thalamus, or the ventromedial prefrontal cortex. All these groups showed a severe postoperative learning impairment. Seven other animals were given a unilateral ablation in 1 of those 3 structures and a second unilateral ablation, in each case contralateral to and different from the first, in order to produce 2 groups in which a putative amygdalo-thalamo-prefrontal pathway had been disconnected by crossed unilateral lesions. One disconnection group had lesions in the amygdala and ventromedial prefrontal cortex; the other had lesions in the amygdala and the mediodorsal nucleus of the thalamus. The disconnection groups showed a significant impairment, but the effect of the disconnection surgeries was significantly milder than the effect of any of the 3 bilaterally symmetrical lesions. Therefore, symmetrical bilateral lesions in either the amygdala, the mediodorsal nucleus, or the ventromedial prefrontal cortex produce similar impairments in the present task, implying that these structures are functionally related to each other; but the relatively mild effect of disconnecting these structures from each other argues against the hypothesis that they are serial stages in a single, tightly linked functional pathway.
How well do response changes of striate neurons signal differences in orientation: a study in the discriminating monkey
Authors: Vogels R , Orban GA
Published: March 2018

Just-noticeable differences (JNDs) in orientation were measured in 2 monkeys using a temporal same-different task, with stationary rectangular gratings as stimuli, and compared to those of humans tested in the same setup. The JNDs of one monkey (1.5 degree) were similar to those of humans; those of the other monkey were larger (5.8 degrees). We recorded from V1 neurons in these monkeys while they were performing the orientation discrimination with the same stimuli and under the same conditions as used in the behavioral testing. In order to determine how small a difference in orientation the V1 neurons can, in these conditions, signal reliably by small changes in firing rate, we performed 2 different receiver-operating characteristic (ROC) analyses. One ROC analysis was performed on the number of spikes evoked by the first of the 2 stimulus presentations as a function of the orientation of this stimulus. Neural JNDs derived from the neurometric curve were obtained in this way for 50 cells. In the second ROC analysis, the difference in the number of spikes evoked by the 2 stimuli presented in succession during 1 trial was analyzed as a function of orientation difference between the 2 stimuli. Neural JNDs were obtained by this procedure for 21 cells. These 2 complementary ROC analyses yielded very similar results. Also, the results were similar for the 2 monkeys. A minor fraction of V1 cells can reliably signal difference in orientation as small as 2.5 degrees, but none could signal differences smaller than 2 degrees. Our results also showed that the neural JND obtained by the ROC analysis depends on the duration of the interval during which spikes are counted. In these experiments, this duration could be chosen rather precisely, because the reaction times of the 2 monkeys were measured. Also, our results showed that the neural JND depends on the point of the tuning curve at which the measurement is made and is smallest when this is done on the steepest part of the tuning curve. Finally, our results show that the discriminative capacity of V1 neurons does not depend so much on each of the tuning characteristics--bandwidth, response strength, and variability--as on the combination of these factors.
Inhibition of agrin-induced acetylcholine-receptor aggregation by heparin, heparan sulfate, and other polyanions
Authors: Wallace BG
Published: March 2018

Heparin and heparan sulfate have been shown to block nerve-induced acetylcholine-receptor (AChR) aggregation at developing neuromuscular junctions. We found that heparin, heparan sulfate, and a wide variety of other polyanions also inhibited agrin-induced AChR aggregation. The more highly charged the polyanion, the more potent it was as an inhibitor. Inhibition of agrin-induced AChR aggregation was due, at least in part, to the formation of a complex between the polyanion and agrin that was inactive. These findings are consistent with the hypothesis that nerve-induced aggregation of AChRs is mediated by the release of agrin, or a closely related protein, from axon terminals and suggest that a polyanion, such as a sulfated proteoglycan, may be involved in the interaction of agrin with its receptor on the myotube surface.
Membrane properties and response to opioids of identified dopamine neurons in the guinea pig hypothalamus
Authors: Loose MD , Ronnekleiv OK , Kelly MJ
Published: March 2018

The electrophysiological properties and opioid responsiveness of the dopamine-containing neurons in the arcuate nucleus of the guinea pig hypothalamus were examined. Dopamine-containing neurons, identified immunocytochemically by the presence of tyrosine hydroxylase, had a mean length-to-width profile of 14.9 +/- 4.4 x 11.5 +/- 3.1 microns (N = 14). The Na+ action potential of these neurons was of short duration, and induction of repetitive firing (20-50 Hz) caused an afterhyperpolarization of 6-9 mV in amplitude, with a decay half-time of approximately 1.5 sec. Dopamine-containing cells exhibited a low threshold spike, which induced 1-4 Na+ action potentials. This potential had a threshold close to -65 mV, could not be induced without prior hyperpolarization and was not sensitive to TTX. Dopamine- containing neurons also exhibited a time- and voltage-dependent inward current at potentials negative to -70 mV, and Cs+ blocked this conductance. The mu-opioid agonist Tyr-D-Ala-Gly-mePhe-Gly-ol hyperpolarized (14 +/- 3 mV) dopamine neurons via induction of an outward current (93 +/- 44 pA near the resting membrane potential) which had a reversal potential similar to that expected for a selective potassium conductance. TTX (1 microM) did not block the opioid effects. These results show that dopamine neurons of the arcuate nucleus differ in their intrinsic conductances and their responsiveness to opioids from other CNS dopaminergic neurons. Furthermore, opioid activation of a potassium conductance resulted in a direct hyperpolarization of dopamine neurons of the arcuate nucleus, and we suggest that this mechanism may underlie the effects of opioids on dopamine-mediated prolactin release.
Circadian timekeeping in BALB/c and C57BL/6 inbred mouse strains
Authors: Schwartz WJ , Zimmerman P
Published: March 2018

Circadian rhythms of locomotion (wheel-running activity) in 12 inbred mouse strains were recorded for interstrain differences in tau DD, the endogenous (free-running) period of the circadian pacemaker measured in constant environmental darkness. The results indicate that 1 or more genetic loci influence the value of tau DD, and a large (50 min) difference in mean tau DD between 2 of the strains, BALB/cByJ and C57BL/6J, allowed further characterization of the origins and inheritance of the polymorphic expression of this circadian pacemaker property. The interstrain difference in mean tau DD was associated with an interstrain difference in light-induced shifts of the phase of the free-running locomotor rhythm; the BALB/c strain (with the shorter mean tau DD) displayed relatively fewer advance phase shifts. Neither the history of previous light exposure, albinism, nor elevated circulating testosterone levels could account for the interstrain difference in mean tau DD. The value of tau DD based on the circadian rhythm of drinking activity (with the running wheel removed) was longer than that based on locomotion; this discrepancy was significantly greater and more variable in BALB/c than in C57BL/6 mice, though the interstrain difference in mean tau DD could not be attributed entirely to this effect. Reciprocal F1 hybrids of BALB/c x C57BL/6 matings revealed dominance of the C57BL/6 genotype, no sex linkage, and a significant (but small) maternal effect. Examination of CXB recombinant inbred strains provided no support for the hypothesis of monogenic inheritance. Further study of inherited differences in the BALB/c and C57BL/6 strains may be a useful noninvasive experimental approach for investigation of the neurobiological substrates of circadian rhythmicity.
Brain IL-1-induced immunosuppression occurs through activation of both pituitary-adrenal axis and sympathetic nervous system by corticotropin- releasing factor
Authors: Sundar SK , Cierpial MA , Kilts C , Ritchie JC , Weiss JM
Published: March 2018

Intracerebroventricular infusion of femtomolar quantities of interleukin-1 (IL-1) or stimulated release of endogenous IL-1 in the brain suppresses various cellular immune responses, decreasing natural killer cell (NK) activity, response to mitogen, and interleukin-2 production of splenic and blood lymphocytes (an effect hereafter called “brain IL-1-induced immunosuppression”). The present study examines mechanisms by which IL-1 produces this effect. First, because IL-1 in the brain activates the pituitary-adrenal axis by stimulating release of corticotropin-releasing factor (CRF), the role of CRF was investigated. To block CRF, affinity-purified antibody to CRF was infused into the lateral ventricle 30 min before introduction of IL-1. When this was done, suppression of cellular immune responses that normally follow IL-1 infusion was completely prevented. Infusion with an equal quantity of non-CRF IgG prior to IL-1 was without effect. Second, the role of sympathetic nervous activity was examined. To block neural transmission at sympathetic ganglia, chlorisondamine (3.0 mg/kg) was injected intraperitoneally 60 min before IL-1 infusion. When this was done, suppression of immune responses by IL-1 was partially blocked. These results indicate that IL-1 in the brain suppresses various cellular immune responses by activating both the pituitary- adrenal axis and the sympathetic nervous system, and that these systems are both activated through the influence of IL-1 on CRF.
Multiple signal transduction mechanisms leading to the secretion of 5- hydroxytryptamine by MTC cells, a neurectodermally derived cell line
Authors: Tamir H , Liu KP , Hsiung SC , Adlersberg M , Nunez EA , Gershon MD
Published: March 2018

Parafollicular (PF) cells of the thyroid gland are neural crest derivatives. These cells remain plastic even in adult animals and can be induced to exhibit neural properties when exposed to NGF in vitro. A human cell line derived from PF cells, medullary thyroid carcinoma (MTC), has previously been shown to synthesize and store 5-HT, a serotonin-binding protein (SBP), and several neuropeptides; moreover, when grown in impoverished media, MTC cells display neural properties. The purpose of the current study was to utilize MTC cells as a neurally relevant model system to investigate factors involved in mediating 5-HT secretion. Electron microscopic immunocytochemistry revealed that secretory vesicles of MTC cells costore immunoreactive 5-HT with SBP and calcitonin. The cAMP derivative, N6-2′-O-dibutyryl-adenosine 3′,5′- cyclic monophosphate (dibutyryl-cAMP; 1.0 mM) increased the concentration of 5-HT in MTC cells and almost doubled the rate of synthesis of 5-HT from L-tryptophan. Dibutyryl-cAMP also significantly increased the secretion of 5-HT. Cycloheximide (20 micrograms/ml) and anisomycin (20 microM) inhibited the dibutyryl-cAMP-induced increase of 5-HT release, suggesting that this action of dibutyryl-cAMP requires protein synthesis. Cholera toxin (1.0 microgram/ml) and forskolin (0.05 mM) in the presence of the phosphodiesterase inhibitor 3-isobutyl-1- methylxanthine (1.0 mM) both increased 5-HT biosynthesis and secretion. Attempts were made to identify a ligand that stimulates cAMP-mediated secretion of 5-HT. Both thyroid-stimulating hormone (TSH: 50 mU/ml) and elevated [Ca2+]e (7.0 mM), each of which acts as a secretogogue for PF cells, stimulated the secretion of 5-HT. The effect of TSH was Ca2(+)- dependent. Immunocytochemistry with monoclonal antibodies to the TSH receptor confirmed that these receptors are present on MTC cells. Neither TSH nor elevated [Ca2+]e elevated cAMP levels. Measurements of Fura-2 fluorescence, however, indicated that both TSH and elevated [Ca2+]e increased cytosolic calcium ([Ca2+]i), as did elevation of [K+]e. It is concluded that exocytosis can be triggered in MTC cells by multiple signal transduction mechanisms. Either cAMP or elevated [Ca2+]i can stimulate secretion; however, a secretogogue that increases cAMP has yet to be identified.
Dynorphin A-(1-17) induces alterations in free fatty acids, excitatory amino acids, and motor function through an opiate-receptor-mediated mechanism
Authors: Bakshi R , Newman AH , Faden AI
Published: March 2018

The endogenous opioid dynorphin A-(1-17) (Dyn A) has been implicated as a mediator of tissue damage after traumatic spinal cord injury (TSCI) and causes hindlimb paralysis when administered intrathecally. Motor impairment following intrathecal Dyn A is attenuated by antagonists of excitatory amino acids (EAAs); whether opioid receptors mediate such injury has been questioned. TSCI causes various biochemical changes associated with secondary tissue damage, including alterations in tissue amio acids, phospholipids, and fatty acids. Such changes reflect injury severity and correlate with motor dysfunction. The present studies examined whether dynorphin administration causes similar biochemical alterations and whether effects of Dyn A can be modified by treatment with opioid-receptor antagonists. At 24 hr after intrathecal Dyn A, there were significant declines in tissue levels of glutamate, aspartate, and glycine. Increases in total free fatty acids were found at 2 and 24 hr, reflecting changes in both saturated and unsaturated components, which were associated with significant decreases in tissue cholesterol and phospholipid phosphorus at the earlier time point. Each of these neurochemical changes, as well as corresponding motor deficits, were limited by pretreatment with the opioid antagonist nalmefene. In separate experiments, both nalmefene and the selective kappa-opioid antagonist nor-binaltorphimine (nor-BNI) limited dynorphin- induced motor dysfunction; effects of nor-BNI were dose related, and those of nalmefene were stereospecific. Therefore, behavioral and neurochemical consequences of Dyn A administration are mediated in part through opiate receptors, most likely kappa-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
The formation of terminal fields in the absence of competitive interactions among primary motoneurons in the zebrafish
Authors: Liu DW , Westerfield M
Published: March 2018

To make specific synaptic connections, projection neurons extend neurites to regions containing appropriate targets, then form synapses with the correct type and number of target cells. To investigate the mechanisms controlling this process, we have studied the formation of motoneuronal terminal fields in live zebrafish embryos. The primary motoneurons of the zebrafish are identifiable as individuals and innervate neighboring but mutually exclusive territories. To study the first week of their development, which includes embryonic and early larval stages, we labeled identified motoneurons with fluorescent dyes and made sequential observations of the axonal branches of individual neurons. We assessed the roles of competitive interactions and synapse elimination in the formation of specific synapses by identified neurons that innervate neighboring territories. Our results demonstrate that primary motoneurons establish their cell-specific terminal fields primarily by directed outgrowth of branches and formation of neuromuscular junctions almost exclusively on appropriate muscle fibers, rather than by overproduction and selective elimination of inappropriate branches. Retraction of the few branches that are inappropriately placed, though correlated in time with the ingrowth of branches from appropriate motoneurons, occurs independently of the influences of these other cells and when neuromuscular transmission is blocked. We suggest that, similar to the way in which they pioneer peripheral nerve pathways, primary motoneurons establish their cell- specific terminal fields using mechanisms that operate independently of activity and competition. The target or substrate interactions that are likely to instruct directed growth-cone navigation may be similar to the interactions that determine the locations of territorial borders and that instruct the retraction of misplaced branches.
Kainic acid on neostriatal neurons intracellularly recorded in vitro: electrophysiological evidence for differential neuronal sensitivity
Authors: Calabresi P , De Murtas M , Mercuri NB , Bernardi G
Published: March 2018

The electrophysiological effects produced by different concentrations of kainic acid (KA) were studied by utilizing intracellular recordings from neostriatal slices. In most of the recorded cells (81%), concentrations of KA ranging between 10 and 300 nM produced reversible and dose-dependent membrane depolarizations. Higher concentrations of this agonist caused larger depolarizations and changes of the membrane properties of the recorded neurons not reversible during the time of recording. In a smaller percentage (19%) of the recorded cells, 10-100 nM KA did not produce significant membrane depolarizations; in these neurons, the depolarizations produced by higher concentrations of KA were small and reversible. The 2 populations of neurons showed similar electrophysiological properties and did not reveal differential sensitivity to quisqualic acid (QUIS; 10-30 microM) or to NMDA (10-30 microM). Tetrodotoxin (TTX; 1 microM) did not reduce the depolarizations produced by KA and by NMDA. Low-calcium, cobalt- containing solutions abolished the effects produced by NMDA, but not the KA-induced depolarizations. Kynurenic acid (500 microM) significantly antagonized the depolarizations produced by KA and reduced the changes of the membrane properties caused by high doses of this agonist. In several neurons, KA induced bicuculline-sensitive synaptic depolarizing potentials. Our findings suggest the presence of 2 subpopulations of neostriatal neurons showing differential postsynaptic sensitivity to KA. The differential sensitivity of neostriatal neurons to KA might influence the responses of these cells to glutamatergic cortical inputs and the degenerative changes observed in neostriatal neurons in some pathological conditions.
Cell interactions regulate dendritic morphology and responses to neurotransmitters in embryonic chick sympathetic preganglionic neurons in vitro
Authors: Clendening B , Hume RI
Published: March 2018

The influence of non-neuronal cells and interneurons on the morphological development of chick sympathetic preganglionic neurons (SPNs) and on the responsiveness of these neurons to the neurotransmitters GABA, glycine, and glutamate was studied. SPNs were retrogradely labeled with the fluorescent dyes dil and diO, then separated from spinal-cord non-neuronal cells and interneurons by fluorescence-activated cell sorting. SPNs were grown in culture, either alone or in coculture with non-neuronal cells alone, with interneurons alone, or with both of these cell types (control cultures). The responsiveness of SPNs to neurotransmitters was assessed by whole-cell recording, while cell morphology was assessed after intracellular staining with 6-carboxyfluorescein. Cell size and morphology were affected by non-neuronal cells. In the absence of non-neuronal cells, SPNs had smaller cell bodies and fewer major processes, whether or not interneurons were present. In contrast, responses to the 3 neurotransmitters were affected by both non-neuronal cells and interneurons, but in ways that differed slightly for each transmitter. In the absence of both non-neuronal cells and interneurons, responses to all 3 transmitters were much smaller than in control cultures, with responses to glutamate most profoundly affected. The addition of either non-neuronal cells or interneurons slightly increased the amplitude of SPN responses to glutamate, but the level of responsiveness with either cell type alone was much lower than for SPNs grown in the presence of both cell types. The addition of interneurons also slightly increased the responsiveness of SPNs to GABA, but non-neuronal cells alone had no significant effect on the responses of SPNs to GABA. Finally, the glycine responsiveness of SPNs was raised to control levels when either non-neuronal cells or interneurons were added. These experiments demonstrate that, though interneurons can have a significant inductive effect on the responses of SPNs to neurotransmitters, not all of the changes in neurotransmitter responsiveness can be related to the formation of functional synapses.
Continuous repetitive stimuli are more effective than bursts for evoking LHRH release in bullfrog sympathetic ganglia
Authors: Peng YY , Horn JP
Published: March 2018

Effects of different patterns of presynaptic stimulation upon release of leuteinizing hormone releasing hormone (LHRH) were studied by monitoring LHRH-induced slow currents from individual postsynaptic neurons in bullfrog sympathetic ganglia. LHRH-mediated synaptic currents in ganglionic B and C neurons were recorded by a single- electrode voltage-clamp technique. Using continuous stimulation, release increased with frequency between 2 and 20 Hz, then declined. Though bursts of stimuli always evoked more release than continuous stimuli of the same average frequency, they were invariably less effective than continuous stimulation at the intraburstal frequency. This demonstrates that frequency, not bursting structure, governs peptide release. The dependence of release upon stimulus frequency was altered when extracellular Ca2+ concentration was changed, implying that release does not depend intrinsically upon stimulation frequency, but simply on the availability of Ca2+.
Neurochemical characterization of excitotoxin lesions in the cerebral cortex
Authors: Beal MF , Swartz KJ , Finn SF , Mazurek MF , Kowall NW
Published: March 2018

Neuronal degeneration that occurs in both ischemia and degenerative neurologic illnesses may involve excitotoxic mechanisms. In the present study, we examined whether cortical lesions with agonists acting at subtypes of glutamate receptors result in selective patterns of neuronal death. Injections of quinolinic acid, NMDA, homocysteic acid, kainic acid (KA), and alpha-amino-3-hydroxy-5-methylisoxazole-4- proprionic acid (AMPA) were made at 2 sites in the dorsolateral frontoparietal cortex in rats. After 1 week, the cerebral cortex was either dissected for neurochemical studies, or animals were perfused for histologic evaluation. Concentrations of somatostatin (SS), neuropeptide Y (NPY), substance P (SP), cholecystokinin (CCK), and vasoactive intestinal polypeptide (VIP) were measured by radioimmunoassay, while amino acids and catecholamines were measured by high-performance liquid chromatography (HPLC) with electrochemical detection. NMDA agonists (quinolinic acid, homocysteic acid, and NMDA itself) resulted in dose-dependent reductions in glutamate and GABA, while SS, NPY, SP, CCK, and VIP were either unchanged or significantly increased in concentration. KA and AMPA at doses that resulted in comparable GABA depletions caused significant reductions in SS concentrations. Markers of cortical afferents were spared. All excitotoxins resulted in dose-dependent marked increases in uric acid concentrations. Histologic examination verified that lesions with NMDA agonists produced relative sparing of NADPH-diaphorase, SS, VIP, and CCK neurons. These results show that NMDA excitotoxin lesions result in a pattern of selective neuronal damage in the cerebral cortex that is similar to that which occurs in both ischemia and Huntington's disease.
The nasotemporal division of retinal ganglion cells with crossed and uncrossed projections in the fetal rhesus monkey
Authors: Chalupa LM , Lia B
Published: March 2018

The development of the partial decussation pattern in the primate retina was studied in fetal rhesus monkeys of known gestational ages. Retinal ganglion cells with either crossed or uncrossed projections were identified by labeling with HRP following unilateral injections of this tracer into the optic tract. At all fetal ages, very few cells (less than 0.5% of the total ganglion cell population) were found to project to the inappropriate hemisphere. The nasotemporal overlap zone, defined as the retinal region along the vertical meridian containing cells with either crossed or uncrossed projections, also appeared equivalent to that described for the adult animal. A temporal offset in the decussation pattern of large ganglion cells, similar to that of the mature retina, could be recognized as early as 50 d before birth. These results indicate that an adultlike retinal decussation pattern is evident in the fetal primate at a stage when projections from the 2 eyes are completely intermingled within retinorecipient nuclei, and prior to the onset of retinal ganglion cell loss. Moreover, the primate visual system exhibits a degree of precision in the specification of the nasotemporal division unrivaled among the mammalian species studied to date. The developmental specificity evident in the decussation pattern of the fetal rhesus monkey appears to reflect the specialized organization of this primate's retina for binocular focal vision.
Histochemical and immunocytochemical compartments of the thalamic VPM nucleus in monkeys and their relationship to the representational map
Authors: Rausell E , Jones EG
Published: March 2018

The ventral posteromedial nucleus (VPM) of the monkey thalamus was investigated with correlative anatomical and physiological techniques. On the basis of staining for cytochrome oxidase (CO), VPM is divided into a lightly stained, background matrix domain and an intensely stained rod domain. The latter consists of elongated rods of large, medium, and small cells, 500 microns wide on average and extending anteroposteriorly, many of them through the full extent of the nucleus. The matrix, consisting of small cells, penetrates between the rods and expands at the dorsomedial, ventrolateral, and posterior aspects of VPM. Multiunit mapping reveals that VPM contains a dorsally situated representation of the contralateral side of the head, face, eye, and interior of the mouth and a medially situated representation of the ipsilateral side of the lips and interior of the mouth, and that the same small region is represented in the same relative position through the full anteroposterior extent of the nucleus. Earlier work had shown that single CO rods contain the representation of the same portion of the periphery throughout their length. The present study suggests that rods in equivalent positions may represent the same portion of the periphery from animal to animal. The cells of the rod and matrix domains show different patterns of immunoreactivity. Virtually all of the large- and medium-sized rod cells are immunoreactive for the calcium-binding protein parvalbumin, and many are stained by the monoclonal antibody CAT 301. Small GABA-immunoreactive cells and terminal-like puncta are highly concentrated in the rods but are dispersed in the matrix. In the matrix, all non-GABA cells are small, immunoreactive for 28-kDa calbindin, and not stained by CAT 301. They appear to form part of a wider system of calbindin-positive cells that extends into adjacent nuclei. The CO rods are indicative of the modularity of the lemniscal component of the trigeminal part of the somatic sensory system at thalamic levels. Thalamocortical relay neurons in this compartment of VPM express a calcium-binding protein and a surface proteoglycan that distinguishes them from relay neurons in the matrix compartment of the nucleus. In the following paper (Rausell and Jones, 1991), the rod and matrix compartments are shown also to have different patterns of input and output connections.
The regulation of synaptogenesis during normal development and following activity blockade
Authors: Dahm LM , Landmesser LT
Published: March 2018

The mature neuromuscular junction is characterized by the tight spatial colocalization of synaptic vesicles and acetylcholine receptor (AChR) clusters. Although a large body of work exists on the interactions between motoneurons and myotubes leading to synaptogenesis in tissue culture, how the neuromuscular junction acquires its highly specialized structure in vivo is not well understood, particularly during the earliest period of synaptogenesis. In this study, the development of the neuromuscular synapse in chick hindlimb muscles was examined and quantified by simultaneously labeling the pre- and postsynaptic elements from the time the main nerve trunks leave the lumbosacral plexus region to enter the developing limb (St 24) through the end of the motoneuron cell death period (St 36). Based on these results, synaptogenesis can be divided into several distinct stages that are intimately connected to the innervation sequence described in a previous paper (Dahm and Landmesser, 1988). Briefly, as large nerve trunks approach the developing muscles and the first AChR clusters are induced to form on nearby myotubes, none of these initial receptor clusters are in direct contact with a nerve profile. The first appearance of nerve-contacted clusters (synapses) is coincident with the growth of large, unbranched nerve trunks into the muscles. The next step is initiated by the formation of small nerve side branches that grow out from the larger intramuscular nerve trunks to bring most axons and myotubes into contact for the first time. As side branches form, synapses appear around them, and non-nerve-contacted receptor clusters disappear from around the main intramuscular nerve trunks. The next step in synaptogenesis is the restriction of synaptic vesicle antigen to sites of synaptic contact. These early stages of synaptogenesis are also characterized by the growth of the presynaptic terminal to match the length of the postsynaptic receptor cluster. This study showed that AChR cluster formation during early in vivo neuromuscular development does not require close anatomical nerve contact, but that the presence of the nerves is necessary for AChR clusters to form. This suggests that the nerves normally induce AChR clustering via the release of a diffusible substance, a suggestion substantiated by the observation that AChR clusters do not form on aneural myotubes in vivo. In order to assess the role of synapse formation in the regulation of motoneuron number, synaptogenesis was quantitatively examined after chronic neuromuscular blockade, which prevents motoneuron cell death.(ABSTRACT TRUNCATED AT 400 WORDS)
Peptide cotransmitter potentiates calcium channel activity in crayfish skeletal muscle
Authors: Bishop CA , Krouse ME , Wine JJ
Published: March 2018

The activity of 2 types of Ca2+ channels (38 and 14 pS in 137 mM Ba2+) in the plasma membrane of the crayfish tonic flexor muscle is modulated by the peptide proctolin. This peptide serves as a cotransmitter in 3 of the 5 excitatory tonic flexor motoneurons and greatly enhances tension after depolarization by the conventional neurotransmitter. Proctolin alone has no effect on these channels, but renders them capable of sustained activity following depolarization. After depolarization induces activity, 5 x 10(-9) M proctolin increases the open probability of the larger channel up to 50-fold due to a marked decrease in the mean channel closed time. There is also at least a 4- fold increase in the percentage of patches with active channels for the large channel and a 2-fold increase for the small channel. Proctolin modulation appears to occur via an intracellular messenger, possibly cAMP. The peptide's effect on channel activity is dose dependent in a manner that parallels its effect on tension. These results indicate that the activation of these channels and the resulting influx of Ca2+ into the muscle fiber play a role in the potentiation of tension in this muscle.
Developmental expression of REGA-1, a regionally expressed glial antigen in the central nervous system of grasshopper embryos
Authors: Carpenter EM , Bastiani MJ
Published: March 2018

Glial cells are a large component of the developing nervous system, appearing before the onset of axon outgrowth in a variety of developing systems. Their time of appearance and their location in conjunction with developing axon pathways may allow them to define the position of axon pathways. Specific glial cells may be utilized as guideposts by growing axons, allowing them to recognize the appropriate pathway, or conversely, glial cells may inhibit axons from growing along an inappropriate pathway. The 7F7 monoclonal antibody labels a subset of glial cells in grasshopper embryos that may play a role in defining the location of selected axonal pathways. This antibody recognizes the REGA- 1 molecule, a cell-surface antigen with a molecular weight of 60 kDa, which is regionally expressed on developing glial cells. REGA-1 is expressed around the edges of clusters of glial cells and on lamellae extending from glial cells to line the edges of some axonal pathways. REGA-1 expression is first seen in the neuroblast sheet, surrounding neuroblast 4–1. Slightly later in development, 2 glial cells extend processes that express REGA-1 and demarcate the caudal edge of the anterior commissure. As the animal matures, cell processes expressing REGA-1 line the edges of the longitudinal connective, then expand to surround the central neuropil of the segmental ganglia. REGA-1 expression is also seen in conjunction with axons leaving the segmental ganglia via the segmental nerves and the intersegmental connectives. REGA-1 expression is limited to a subset of glial cells; some known glial cells such as the segment boundary cell do not express REGA-1. Glial cell processes expressing REGA-1 are seen only in association with axons, which suggests that these processes may act as borders or guard rails confining axons to the appropriate regions of the developing CNS. Axons navigating a path through the CNS may be prohibited from growing into inappropriate regions based on their inability to cross the boundaries established by glial cells expressing REGA-1.