bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of learning and memory in Aplysia. III. Central neuronal correlates
Authors: Nolen TG , Marcus EA , Carew TJ
Published: March 2018

The defensive withdrawal reflex of the mantle organs of Aplysia californica has 2 major components, siphon withdrawal and gill withdrawal. In the previous paper of this series (Rankin and Carew, 1987), the development of 2 forms of nonassociative learning, habituation and dishabituation, was examined in the siphon withdrawal component of the reflex. In the present study we examined these same forms of learning in the gill withdrawal component of the reflex. The purpose of these experiments was 2-fold: to examine the development of learning in the other major component of the reflex; and to establish preparations in which it is possible to carry out a cellular analysis of the development of learning in the CNS. We first established that the gill withdrawal reflex in intact animals exhibited significant habituation in response to repeated tactile stimulation of the siphon and significant dishabituation in response to tail shock. We next determined the contribution of the CNS to the gill withdrawal reflex by surgically removing the abdominal ganglion from intact animals. Using the same stimulus intensity (4 mg) that produced habituation in the previous experiments, we found that the CNS accounted for approximately 95% of the reflex. Finally, we developed 2 preparations that allowed us to relate behavioral observations of learning directly to neural plasticity exhibited in the CNS. In a semi-intact preparation gill withdrawal was behaviorally measured as in the intact animal, but tactile stimulation of the siphon (to produce habituation) and shock to the tail (to produce dishabituation) were replaced by electrical stimulation of the siphon nerve and left connective, respectively. Stimulation parameters were matched to produce behavioral responses comparable with those in the intact animal. In an isolated CNS preparation the same nerve stimuli were used as in the semi-intact preparation, but the response measure used was the evoked neural discharge recorded in an efferent nerve innervating the gill. Both preparations exhibited response decrement and facilitation that was quantitatively as well as qualitatively similar to that observed in intact animals, indicating that 2 simple forms of learning exhibited by the gill withdrawal reflex in juvenile Aplysia can be localized to neural circuits within the abdominal ganglion.
In vivo biosynthesis of two subunit forms of dopamine beta-hydroxylase in rat brain
Authors: Sabban EL , Kuhn LJ , Levin BE
Published: March 2018

In vivo biosynthesis of the 2 subunit forms of dopamine beta- hydroxylase (DBH) was examined in the rat brain. 35S-methionine was injected into the noradrenergic neurons of the locus coeruleus (LC) using a stereotactic device. Several hours later, newly synthesized 35S- Met-labeled DBH was immunoprecipitated and quantitated. Both Mr = 77,000 (77K) and 73,000 (73K) subunit forms were present in near-equal proportions after 4 hr of labeling, and these were indistinguishable from those isolated from rat PC12 pheochromocytoma cells by electrophoretic mobility. Both forms sedimented with the vesicular subcellular fraction of LC homogenates, and a portion of the 73K form could be released by hypotonic lysis of these vesicles. The 77K form predominated in the first 30 min labeling period, while the 73K form appeared more slowly over the next several hours. By 16 hr, the 73K form comprised about 2/3 of the total 35S-Met-labeled DBH present. Inhibition of protein synthesis with puromycin 30 min after 35S-Met injection into the LC did not prevent the subsequent appearance of the 73K form, suggesting that this subunit form was the product of posttranslational modification of the 77K subunit form in a fashion similar to that seen in PC12 cells. Also, newly synthesized 35S-Met- labeled DBH that underwent axonal transport from the LC to the anterior hypothalamus was predominantly the 73K subunit form. A single injection of the catecholamine-depleting drug reserpine (10 mg/kg, i.p.) produced a 17-fold increase in the relative synthesis of DBH 2 d later without affecting the proportion of its 2 subunit forms.
Topographic mapping of motor pools onto skeletal muscles
Authors: Laskowski MB , Sanes JR
Published: March 2018

We have studied the segmental innervation of 2 rat skeletal muscles, the diaphragm and the serratus anterior. Both muscles are thin, flat, and composed of several sectors that form a clear rostrocaudal progression. Each is innervated through a single nerve, which is in turn supplied by motor neurons from several cervical spinal segments. Using intracellular recording, we found that in both cases, the rostrocaudal axis of the motor pool is systematically mapped onto the rostrocaudal axis of the muscle's surface. For the diaphragm, electrophysiological results were confirmed by immunohistochemical identification of denervated fibers following section of single ventral roots and by retrograde labeling of motoneurons following localized application of fluorescent dyes. In addition, an immunohistochemical method was used to study the arrangement of motor axons in the phrenic nerve, which supplies the diaphragm, and to show that contributions from individual ventral roots are compartmentalized within this nerve. We suggest that segmental ordering of axons in the nerve, axonal guidance at branch points in the nerve, and positional labels within the muscle may all contribute to the rostrocaudal mapping of motor pools onto muscle.
Evidence for two classes of nociceptive modulating neurons in the periaqueductal gray
Authors: Heinricher MM , Cheng ZF , Fields HL
Published: March 2018

The midbrain periaqueductal gray (PAG) and the rostral ventromedial medulla (RVM) are important links in a neuronal network that modulates nociceptive transmission. In the RVM, 2 classes of cells have been identified that show changes in activity at the time of the tail-flick response (TF) elicited by noxious heat (Fields et al., 1983a). We now report that neurons in the PAG region also show changes in activity related to TF. Extracellular recordings were made from the PAG and the ventrally adjacent tegmentum at sites from which it was possible to inhibit TF using stimulating currents of 10 microA or less. Cell activity, time of TF occurrence, and tail temperature were recorded during 5 repetitions of the heat stimulus. Periresponse and peristimulus histograms were plotted with reference to the TF and tail temperature, respectively. A significant number of neurons in the PAG region showed changes in activity that preceded the TF. “Midbrain On- cells” (13.6% of the sample) displayed an abrupt increase in firing just prior to the TF. “Midbrain Off-cells” (4.4%) paused just prior to the TF. The remaining neurons (241 of 294, or 82%) did not exhibit changes in firing prior to the TF. Thus, cells with changes in activity related to the TF are present in the PAG region as well as in the RVM. The PAG has a large projection to the RVM, and microinjection of morphine in the PAG increases activity of RVM Off-cells and decreases that of RVM On-cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Production, characterization, and immunohistochemical application of monoclonal antibodies to glutaminase purified from rat brain
Authors: Kaneko T , Urade Y , Watanabe Y , Mizuno N
Published: March 2018

Monoclonal antibodies were produced against phosphate-activated glutaminase (EC 3.5.1.2) as a marker for glutamatergic neurons: The enzyme was purified 1000-fold from rat brain mitochondria with a recovery of 27%. Upon SDS-PAGE the purified enzyme showed a single band up to 1.7 micrograms after the silver staining at molecular weight 62,000. Two monoclonal antibodies (IgMs) were produced; these absorbed more than 90% of glutaminase activity in rat brain homogenate. In immunoblotting after PAGE of the homogenate, the antibodies recognized only 1 protein band at the same position as that of the purified enzyme. Thus, the antibodies are specific and sufficient markers for glutaminase. Many neuronal cells in the rat brain were labeled immunohistochemically with these antibodies, but non-neuronal elements such as glial cells and vessels were not. Intense labeling was consistently observed in putative glutamatergic neurons such as pyramidal cells of layers V and VI in the cerebral neocortex. Intense staining was also seen in possible mossy fiber endings in the granular layer of the cerebellar cortex and in neurons giving off mossy fibers such as those in the pontine nuclei, pontine tegmental reticular nucleus of Bechterew, lateral reticular nucleus of the medulla oblongata, and external cuneate nucleus.
Glutamate neurotoxicity in cortical cell culture
Authors: Choi DW , Maulucci-Gedde M , Kriegstein AR
Published: March 2018

The central neurotoxicity of the excitatory amino acid neurotransmitter glutamate has been postulated to participate in the pathogenesis of the neuronal cell loss associated with several neurological disease states, but the complexity of the intact nervous system has impeded detailed analysis of the phenomenon. In the present study, glutamate neurotoxicity was studied with novel precision in dissociated cell cultures prepared from the fetal mouse neocortex. Brief exposure to glutamate was found to produce morphological changes in mature cortical neurons beginning as quickly as 90 sec after exposure, followed by widespread neuronal degeneration over the next hours. Quantitative dose- toxicity study suggested an ED50 of 50–100 microM for a 5 min exposure to glutamate. Immature cortical neurons and glia were not injured by such exposures to glutamate. Uptake processes probably do not limit GNT in culture, as the uptake inhibitor dihydrokainate did not potentiate GNT. Possibly reflecting the lack of uptake limitation, glutamate was found to be actually more potent than kainate as a neurotoxin in these cultures, a dramatic reversal of the in vivo potency rank order. Some neurons regularly survived brief glutamate exposure; these possibly glutamate-resistant neurons had electrophysiologic properties, including chemosensitivity to glutamate, that were grossly similar to those of the original population.
Ionic dependence of glutamate neurotoxicity
Authors: Choi DW
Published: March 2018

The cellular mechanisms by which excess exposure to the excitatory neurotransmitter glutamate can produce neuronal injury are unknown. More than a decade ago it was hypothesized that glutamate neurotoxicity (GNT) is a direct consequence of excessive neuronal excitation (“excitotoxicity” hypothesis); more recently, it has been hypothesized that a Ca influx triggered by glutamate exposure might mediate GNT (Ca hypothesis). A basic test to discriminate between these hypotheses would be to determine the dependence of GNT on the extracellular ionic environment. The excitotoxicity hypothesis predicts that GNT should depend critically on the presence of extracellular Na, since that ion appears to mediate glutamate neuroexcitation in the CNS; the Ca hypothesis predicts that GNT should depend critically on the presence of extracellular Ca. The focus of the present experiments was to determine the effects of several alterations in the extracellular ionic environment upon the serial morphologic changes that occur after mouse neocortical neurons in cell culture receive toxic exposure to glutamate. The results suggest that GNT in cortical neurons can be separated into 2 components distinguishable on the basis of differences in time course and ionic dependence. The first component, marked by neuronal swelling, occurs early, is dependent on extracellular Na and Cl, can be mimicked by high K, and is thus possibly “excitotoxic.” The second component, marked by gradual neuronal disintegration, occurs late, is dependent on extracellular Ca, can be mimicked by A23187, and is thus possibly mediated by a transmembrane influx of Ca. While either component alone is ultimately capable of producing irreversible neuronal injury, the Ca-dependent mechanism predominates at lower exposures to glutamate. Glutamate exposure likely leads to a Ca influx both through glutamate-activated cation channels and through voltage- dependent Ca channels activated by membrane depolarization. Addition of 20 mM Mg, however, did not substantially block GNT; this finding, together with the observation that GNT is largely preserved in sodium- free solution, supports the notion that the activation of voltage- dependent Ca channels may not be required for lethal Ca entry. The possibility that N-methyl-D-aspartate receptors may play a dominant role in mediating glutamate-induced lethal Ca influx is discussed.
Mechanisms controlling accurate changes in elbow torque in humans
Authors: Cordo PJ
Published: March 2018

This paper addresses a fundamental question of how motor commands specify target torque levels. Human subjects produced fast and accurate changes in torque with the isometric elbow joint. Visual stimuli were used to indicate target torque levels as well as to cue subjects to initiate their responses. During rapid changes in torque from one steady-state level to another, target torque was achieved through a sequence of approximations. During the first 200–250 msec of responses produced in the presence of visual feedback, 3 distinct control mechanisms were recruited to guide torque to the target level. The timing and accuracy of each control mechanism were evaluated. The first control mechanism was triggered by the visual stimulus and produced the initial rise in torque. Target torque predictability was found to strongly influence the accuracy of this control mechanism. The second control mechanism produced a corrective adjustment in torque within roughly the first 100 msec of responses. This mechanism incorporated target torque information provided by the stimulus into the response. The third control mechanism began 200–250 msec after response onset and produced corrective adjustments based on visual feedback of torque errors. The stability of the visual feedback mechanism was evaluated because of a long loop delay. Two strategies were used to control stability: low gain and information transfer between the visual feedback mechanism and the preceding (second) control mechanism.
Immunological probes reveal spatial and developmental diversity in insect neuroglia
Authors: Meyer MR , Reddy GR , Edwards JS
Published: March 2018

A set of monoclonal antibodies (MAbs) has been generated that recognizes distinct classes of neuroglia in the adult nervous system of the cricket Acheta domesticus corresponding to glial types distinguished by morphological criteria. These include antibodies that bind to the neuroglia of the ganglionic cortex, perineurium, neuropil, and glia associated with the glial lacunar system (interface) and fiber tracts. Another MAb specifically labels components of the neural lamella, a complex extracellular matrix secreted by underlying perineurial cells. Selected adult glial-specific MAbs recognize particular glial antigens expressed during embryonic development of Acheta. Immunohistochemical staining of frozen sections of late- (90– 95%) and intermediate- (50–55%) stage whole embryos reveals that the spatial distribution, degree of tissue restriction, or level of expression of some glial determinants changes as development proceeds. Labeling of certain neuroblasts in the embryonic CNS at 50–55% development by an antibody (MAb 3G6) that binds to neuropil glia in the adult CNS implies that at least 1 class of insect glia may be generated by these cells.
FMRFamide-like substances in the leech. III. Biochemical characterization and physiological effects
Authors: Li C , Calabrese RL
Published: March 2018

FMRFamide-like immunoreactivity has been previously localized to identified neurons in the CNS of the leech, Hirudo medicinalis (Kuhlman et al., 1985a). These leech antigens have been characterized biochemically by reverse-phase high-pressure liquid chromatography (HPLC) followed by radioimmunoassay (RIA). The majority of the FMRFamide-like immunoreactivity recovered by HPLC from extracts of leech nerve cords coelutes with authentic FMRFamide. We have tentatively identified this major leech peptide as authentic FMRFamide. Two neurons that control heartbeat in the leech, the HE motor and HA modulatory neurons, and their neural processes on the heart are FMRFamide-like immunoreactive (Kuhlman et al., 1985a). Single individually dissected HE and HA cells were analyzed by HPLC and RIA. Only 1 FMRFamide-like peptide was found in extracts of HA cells; this peptide was chromatographically indistinguishable from authentic FMRFamide. The FMRFamide-like peptide in HE cells could not be isolated by experimental procedures used. Most of the FMRFamide-like immunoreactivity contained within the neural processes on the heart also coeluted with authentic FMRFamide. HE motor neurons, which are believed to be cholinergic (Wallace, 1981a, b; Maranto and Calabrese, 1984a, b), were examined for their FMRFamide-like effects on the heart. The presence of curare in the bathing medium did not block the ability of FMRFamide to induce myogenic activity in heart muscle, suggesting that FMRFamide and ACh act at different receptor sites on the heart. Prolonged firing in HE cells in the presence of curare also induced myogenic activity in heart muscle. This FMRFamide-like action of the HE motor neurons may be normally masked by their cholinergic actions.
A steroid anesthetic prolongs inhibitory postsynaptic currents in cultured rat hippocampal neurons
Authors: Harrison NL , Vicini S , Barker JL
Published: March 2018

Whole-cell patch-clamp recordings were made from cultured rat hippocampal neurons to examine the effects of the steroidal general anesthetic alphaxalone (3 alpha-hydroxy 5 alpha-pregnane 11,20-dione) on responses to pharmacologically applied and physiologically released GABA. At low micromolar concentrations in the anesthetic range, alphaxalone potentiated Cl- conductance responses elicited by GABA and also prolonged evoked GABA-mediated postsynaptic potentials. Under voltage clamp at -40 mV, rapid outwardly directed synaptic currents were evoked that decayed with single exponential kinetics; mean decay time constant was 24 msec at room temperature. Alphaxalone prolonged the decay of these inhibitory postsynaptic currents by 5- to 8-fold, with no increase in peak amplitude or change in growth time. This substantial prolongation of GABA-mediated inhibitory synaptic conductance at clinically effective concentrations may contribute significantly to the anesthetic activity of alphaxalone.
Nerve fiber growth in culture on tissue substrata from central and peripheral nervous systems
Authors: Carbonetto S , Evans D , Cochard P
Published: March 2018

In adult mammals, injured neurons regenerate extensively within the PNS but poorly, if at all, within the CNS. We have studied the effect of substrata consisting of tissue sections from various nervous systems on nerve fiber growth in culture and correlated our results with the growth potential of these tissues in vivo. Ganglionic explants from embryonic chicks (9–12 d) fail to extend nerve fibers onto sections of adult rat optic nerve or spinal cord (CNS) but do so on sciatic nerve (PNS). Dissociated DRG neurons behave similarly whether in serum- containing or defined medium. Tissue substrata from nervous systems that support regeneration in vivo--i.e., goldfish optic nerve, embryonic rat spinal cord, degenerating sciatic nerve--also support fiber growth in culture. Within the same culture, neurons will grow onto sciatic nerve rather than neighboring optic nerve sections, suggesting that the responsible agent(s) is not soluble. In addition, neurons adhere more extensively to sciatic nerve substrata than to optic nerve. The occurrence of 3 molecules known to be involved in neuron-substratum adhesion and nerve fiber growth in vitro has been documented immunocytochemically in the tissue sections. One of these, laminin, is demonstrable in all tissues tested that supported nerve fiber growth. Immunoreactivities for fibronectin and heparan sulfate proteoglycan are found in only some of these tissues. None of these 3 molecules can be demonstrated in neural cells of normal adult rat CNS tissue. Our data suggest that these molecules may be important effectors of nerve regeneration in neural tissues.
Interruption of the connections of the mammillary bodies protects against generalized pentylenetetrazol seizures in guinea pigs
Authors: Mirski MA , Ferrendelli JA
Published: March 2018

Electrolytic lesions in the anterior and mid-diencephalon and ventral midbrain in guinea pigs were produced to examine the effects of interruption of the fornix (FX), mammillothalamic tracts (MT), and mammillary peduncles (MP), respectively, on the expression of pentylenetetrazol (PTZ) seizures. As a group, all mid-diencephalic lesioned animals had some degree of protection from the electroencephalographic and behavioral convulsant and lethal effects of the drug. Through a composite volume analysis of protected versus unprotected animals, as well as a retrospective comparison between MT and non-MT lesioned animals, it was demonstrated that small mid- diencephalic lesions incorporating only the MTs and their immediate vicinity were capable of completely preventing the convulsant and lethal effects of PTZ. Lesions of the FX and MP were also protective against PTZ seizures but to a lesser degree than the MT lesions. These results demonstrate that the major afferent and efferent connections of the mammillary bodies are involved in expressing PTZ seizure activity and suggest that the MT may be the major pathway mediating paroxysmal activity from brain stem to the thalamus.
Long-term potentiation in the hippocampus using depolarizing current pulses as the conditioning stimulus to single volley synaptic potentials
Authors: Gustafsson B , Wigstrom H , Abraham WC , Huang YY
Published: March 2018

The conditions responsible for the associative properties of long-term potentiation (LTP) were examined in the CA1 region of the hippocampal slice preparation. Intracellularly recorded EPSPs resulting from single- volley stimulation at low frequency (0.15–0.1 Hz) in the stratum radiatum or oriens were paired with depolarizing current pulses (50–100 msec) injected through the recording microelectrode. It is shown that these EPSPs, when paired with pulses of sufficient magnitude, become potentiated. This potentiation generally reached a peak after 20–30 pairing events and could outlast the conditioning period by more than 1 hr. It was specific to the paired input, was blocked by 2-amino-5- phosphonovalerate (APV) and was largely blocked by prior homosynaptic tetanization (and vice versa). In experiments performed with picrotoxin (PTX) in the bath, EPSPs were potentiated using 2–4 nA current pulses, with somewhat higher values in normal solution. The effective current pulses, in both normal and PTX solution, produced a repetitive spike discharge of 7–11 spikes (per 100 msec), and within this range, higher frequencies were associated with larger potentiations. However, since similar degrees of EPSP potentiation were observed following blockade of spike activity by intracellular QX-314, spike activity was not the primary conditioning factor. For the potentiation to appear, the EPSP had to occur together with the current pulse or precede it by less than about 100 msec. No potentiation was observed when the EPSP immediately succeeded the pulse. The results suggest that the cooperativity aspect of LTP is related to a need for sufficient postsynaptic depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)
Organization of a vertebrate cardiac ganglion: a correlated biochemical and histochemical study
Authors: Parsons RL , Neel DS , McKeon TW , Carraway RE
Published: March 2018

A correlated biochemical and histochemical study was undertaken to identify and quantify the presence of different biogenic amines and a substance P-like peptide within the parasympathetic cardiac ganglion of the mudpuppy (Necturus maculosus). Tissue extracts of the cardiac septum containing the parasympathetic cardiac ganglia from control animals were found, by high-pressure liquid chromatography, to contain significant amounts of norepinephrine (NE), epinephrine (E), dopamine (DA), and 5-HT. To allow neural elements of extraganglionic origin to degenerate, ganglia were explanted and maintained in organ culture for 8 d. Extracts from these explanted preparations had no detectable level of E, and NE was reduced, whereas DA and 5-HT levels were similar to those of control preparations. The results indicated that some of the neurons intrinsic to the cardiac septum contain DA and 5-HT and that most (greater than 70%) of the E and NE found in this tissue is of extrinsic origin. Histochemistry of control and explanted preparations showed 5-HT-immunoreactive and catecholamine-containing intrinsic neurons. A substance P-like peptide was identified by radioimmune assay in septal extracts. The peptide content diminished by one-third to one- fifth in preparations maintained in organ culture for 8–14 d, suggesting that a significant amount of the substance P-like peptide is derived from extraganglionic sources. Immunocytochemical studies demonstrated the presence of numerous long substance P-immunoreactive fibers coursing across the septum, branching over cardiac muscle fibers, and forming pericellular networks around individual parasympathetic ganglion cells and clusters of ganglion cells. In addition, numerous small intrinsic neurons exhibited immunoreactivity for substance P. Comparison of the substance P-staining patterns in control and explanted ganglia suggests that the majority of the long substance P-immunoreactive fibers innervating the mudpuppy cardiac ganglion cells are not parasympathetic preganglionic fibers. Rather, it is hypothesized that these fibers are processes of primary sensory fibers. The present observations indicate that the mudpuppy cardiac ganglion exhibits a complex organization similar to that of mammalian sympathetic and enteric ganglia.
Proteolytic processing of the Aplysia egg-laying hormone and R3-14 neuropeptide precursors
Authors: Newcomb R , Scheller RH
Published: March 2018

A number of animal behaviors are influenced by the actions of neuropeptides that arise from the processing of complex protein precursors. In this report we investigate the proteolytic processing of neuropeptide precursors expressed in the Aplysia californica bag cells, which govern egg-laying, and neurons R3–14, which mediate aspects of cardiac output. Peptides were purified by fractionation on 2 high- pressure liquid chromatography systems followed by determination of amino acid compositions. Most of these compositions are indicative of processing products derived from the egg-laying hormone (ELH) and R3–14 precursors by cleavage at basic residues. We characterized 9 peptides that arise from the ELH precursor by cleavage of the signal sequence, as well as 7 out of 8 dibasic residues and at least 1 single Arg residue. The peptides range in size from 5 to about 60 amino acids. The R3–14 neuropeptide precursor is cleaved at 2 internal dibasic residues in addition to the signal sequence, resulting in 3 peptides. Shortened forms of several peptides probably result from amino- and carboxy- terminal peptidase action. It is likely that the complex mixtures of neuropeptides arising from these single protein precursors are co- secreted.
Dissociated cingulate cortical neurons: morphology and muscarinic acetylcholine receptor binding properties
Authors: Vogt BA , Townes-Anderson E , Burns DL
Published: March 2018

Identifiable cortical neurons were obtained from area 29c of rat cingulate cortex using enzymatic and mechanical dissociation techniques. Dissociated neurons were either analyzed morphologically with the electron microscope or processed autoradiographically to evaluate the distribution of specific 3H-propylbenzilylcholine mustard (PrBCM) binding. Ultrastructurally, neurons appeared healthy and contained a full complement of cytoplasmic organelles. Membranes were intact and no presynaptic endings adhered to cell bodies or dendrites. Dendritic spines were not observed in these dissociations and serial sections of identified neurons indicated that all dendritic processes were smooth. Receptor binding studies were conducted on small and medium-to-large pyramidal neurons and multipolar cells. Specific binding of PrBCM was determined by calculating the mean number of grains/10 micron somal perimeter or dendritic length and subtracting mean values from a matched series of neurons that were coincubated in atropine. Specific binding was to somata and dendrites of all neurons. Nonspecific binding was an average of 33% of total binding. A 2 X 2 factorial analysis of variance comparing total and nonspecific binding for pairs of processes indicated that there were no regional differences in dendritic binding, either by cell type or by order of dendritic branching. Both somatic and dendritic PrBCM binding was antagonized by pirenzepine (PZ); however, PZ appeared to be more effective at secondary dendritic, rather than at somatic and primary apical dendritic sites. Thus, the IC50 values for somata and primary apical dendrites of small pyramids were 6 X 10(-7) and 9 X 10(-7) M PZ, respectively, while that for secondary basal dendrites of the same neurons was 5.8 X 10(-8) M. Morphological and pharmacological results together suggest that (1) muscarinic receptors are present on the smooth surfaces of all pyramidal and multipolar neurons; (2) many of the binding sites are high affinity, PZ-sensitive, M1 receptors; and (3) this binding is associated with the postsynaptic specialization of symmetric, cholinergic synapses.
Accuracy of reinnervation of rat internal intercostal muscles by their own segmental nerves
Authors: Hardman VJ , Brown MC
Published: March 2018

The positions of internal intercostal motoneurons within their motor pool were studied, following reinnervation of the intercostal muscles by their original nerves. Six to 9 weeks after proximal nerve section in 10-d-old and adult rats, 0.1 microliter injections of wheat germ agglutinin (WGA)-HRP were made in the distal part of the reinnervated internal intercostal muscle. The corresponding region of the contralateral control muscle was also injected. The positions of the retrogradely labeled motoneurons were mapped in 100 microns transverse sections of thoracic spinal cord that had been stained for HRP according to the method of Mesulam (1982). In normal rats, motoneurons innervating distal muscle fibers are found largely in the more dorsal part of the internal intercostal motoneuron pool (Hardman and Brown, 1985). In adult rats, regenerated motor axons did not show any selectivity; distal muscle fibers were innervated by motoneurons whose cell bodies were distributed throughout the internal intercostal pool. However, in rats operated on at 10 d of age, distal intercostal muscle fibers were reinnervated by motoneurons that were distributed mainly in the dorsal part of the motor pool. These results support the view that positional signals may be of importance in organizing the distribution of axon terminals within muscles during development.
Changes in local cerebral glucose utilization induced by the beta- carbolines FG 7142 and DMCM reveal brain structures involved in the control of anxiety and seizure activity
Authors: Ableitner A , Herz A
Published: March 2018

The brain regions that may be functionally involved in the control of anxiety and the development of seizures were examined using quantitative 1–14C-deoxyglucose autoradiography. For this purpose, beta- carbolines FG 7142 and DMCM were employed. They exert their effects via the benzodiazepine receptor, and whereas both possess anxiogenic properties, FG 7142 is a proconvulsant and DMCM a potent convulsant. The pattern of increases of local cerebral glucose utilization (LCGU) induced by FG 7142 was mainly restricted to limbic structures, such as the lateral septal nucleus, the anterior thalamic nuclei, and the mamillary nuclei. However, structures involved in motor regulation were also affected. A pronounced increase in LCGU was observed in the posterior part of the substantia nigra, pars reticulata. Further, the LCGU of the globus pallidus, the ventral thalamic nucleus, and the cerebellum was increased. DMCM likewise increased LCGU of the mamillary body and the lateral septal nucleus. In contrast to FG 7142, the hippocampal formation displayed an increase in LCGU, while LCGU of the anterior thalamic nuclei was unchanged. A pronounced increase in LCGU was seen in the substantia nigra, pars reticulata in addition to other structures functionally involved in central motor regulation. The specific benzodiazepine antagonist Ro 15–1788 antagonized the effects of both FG 7142 and DMCM. It is concluded that the beta-carbolines FG 7142 and DMCM produce selective effects upon LCGU that are mediated by benzodiazepine receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Background and bleaching equivalence in steady-state adaptation of vertebrate rods
Authors: Leibovic KN , Dowling JE , Kim YY
Published: March 2018

We have investigated background and bleaching adaptation in vertebrate rods by intracellular recording in the retina of Bufo marinus. Backgrounds and bleaching produce adaptation in photoreceptors and lead to a shift and a compression of the response operating range. Threshold elevation due to backgrounds follows the Rose-DeVries rule at low intensities and the Weber-Fechner rule at high intensities. Threshold elevation due to bleaching is linear almost up to 17% bleached pigment and exponential thereafter. An equivalence can be established between bleaching and backgrounds with respect to threshold elevation, on the one hand, and with respect to response compression, on the other. These equivalences are the same within experimental error. The equivalence, moreover, appears to extend to the complete response curve. These results have implications for psychophysics as well as for photoreceptor transduction.
Biochemical and immunocytological localization of the neuropeptides FMRFamide, SCPA, SCPB, to neurons involved in the regulation of feeding in Aplysia
Authors: Lloyd PE , Frankfurt M , Stevens P , Kupfermann I , Weiss KR
Published: March 2018

The localization of the neuropeptide FMRFamide in the buccal ganglia and buccal muscles of Aplysia was studied by immunocytology and high- pressure liquid chromatography (HPLC) combined with either a sensitive bioassay or 35S-methionine labeling. Immunocytology with an antiserum directed to FMRFamide stained a large number of fibers, varicosities, and neuronal somata. Two groups of stained neurons were of particular interest. One was the S cells, a group comprised of many small neurons, the majority of which were stained. HPLC of pooled labeled S cells confirmed that at least some of these neurons synthesize FMRFamide. The other group of stained neurons were in the ventral cluster, a group comprised of a small number of large neurons, many of which are motor neurons that innervate the buccal muscles involved in producing biting and swallowing movements. Several of the ventral neurons were previously shown to contain 2 other neuropeptides, the small cardioactive peptides SCPA and SCPB. These neurons are sufficiently large to permit HPLC analyses of the neuropeptides synthesized by individual neurons. This procedure confirmed that individual ventral neurons synthesized FMRFamide, or the SCPs, or all 3 peptides. The coexistence of FMRFamide and the SCPs in the same neuron was confirmed by simultaneous staining of sections from the buccal ganglia with a monoclonal antibody to the SCPs and an antiserum to FMRFamide. The coexistence of the 3 peptides in the same neuron was surprising in light of the observations that these peptides often have opposite biological activity. The ventral neurons are large and potentially identifiable as individuals. Thus, these neurons may be particularly useful for studying the physiological and behavioral roles of neuropeptides in generating complex behaviors.
Posttranslational modification of neurofilament proteins by phosphate during axoplasmic transport in retinal ganglion cell neurons
Authors: Nixon RA , Lewis SE , Marotta CA
Published: March 2018

The progressive modification of newly synthesized neurofilament proteins (NFPs) during axoplasmic transport in mouse retinal ganglion cell (RGC) neurons was studied after RGC perikarya were pulse-labeled with 32P-orthophosphate or radiolabeled amino acids. The 3 NFP subunits, H(igh), M(iddle), and L(ow), were among a group of axonally transported proteins that incorporated high levels of 32P. Covalent addition of phosphate slowed the electrophoretic mobility of H and M on SDS polyacrylamide gels and shifted the charge of all 3 subunits toward more acidic pH values, thereby providing an index of the phosphorylation state of this radiolabeled population of NFPs. NFPs were extensively phosphorylated before they entered axons at the optic nerve level, and continued to be modified during transport along RGC axons at the optic nerve and tract level. H and M exhibited charge shifts of 0.2–0.6 units toward a more acidic pH during axoplasmic transport. The charge modifications became more prominent when NFPs reached distal axonal levels, which may indicate regional differences in the activity of this modification process along axons. By contrast, the L subunit became more basic in charge, consistent with decreases in the phosphorylation state during transport. Additional observations (Nixon and Lewis, 1986) that a considerable proportion of phosphate groups initially added to L and M were later removed as neurofilaments advanced along RGC axons support the notion that the changing phosphorylation state of NFP subunits during axoplasmic transport reflects a dynamic equilibrium between phosphorylation and dephosphorylation events. Topographical remodeling of phosphate groups on NFPs during axoplasmic transport is proposed as a possible mechanism for coordinating interactions between neurofilaments and other constituents, as these elements are transported and integrated into the axonal cytoskeleton.
Down regulation of protein kinase C in neuronal cells: effects on neurotransmitter release
Authors: Matthies HJ , Palfrey HC , Hirning LD , Miller RJ
Published: March 2018

We investigated the effects of phorbol esters on protein kinase C (PKC) activity and on neurotransmitter release from cultured neuronal cells. Both differentiated and undifferentiated PC12 pheochromocytoma cells contained high levels of protein PKC. Under normal conditions all the enzyme activity was found in the cytoplasm. Addition of the phorbol esters phorbol 12-myristate-13-acetate (TPA) or phorbol 12,13- dibutyrate (PDBu) caused a rapid translocation of PKC from the cytoplasm to the particulate fraction. Continued culture of cells with these phorbol esters resulted in the decline of total PKC activity. After 10–20 hr of culture, both membrane and cytoplasmic PKC activity had declined to background levels. cAMP-dependent and Ca2+/calmodulin- dependent protein kinase activities were only slightly affected by chronic phorbol ester treatment. Addition of active phorbol esters to PC12 cells produced an enhancement of the depolarization-induced release of 3H-norepinephrine. Following chronic phorbol ester treatment, the ability of these substances to enhance evoked catecholamine release was lost. Furthermore, depolarizing stimuli released considerably less 3H-norepinephrine than in control untreated cells. Phorbol esters also enhanced depolarization-induced 3H- norepinephrine release from primary cultures of rat sympathetic neurons. Chronic treatment of these neurons with phorbol esters also resulted in the loss of their ability to enhance transmitter release and in a large reduction in the extent of depolarization-evoked transmitter release. Chronic phorbol ester treatment also resulted in the disappearance of PKC from sympathetic neurons, but had little effect on cAMP-dependent or Ca2+/calmodulin-dependent kinase activities. These results demonstrate that PKC-deficient neurons can be prepared. The data also demonstrate that depolarization-induced neurotransmitter release is mediated by both protein kinase C-dependent and independent pathways.
Local circuitry of identified projection neurons in cat visual cortex brain slices
Authors: Katz LC
Published: March 2018

The relationship between pyramidal cell morphology and efferent target was investigated in layer 6 of cat primary visual cortex (area 17). Layer 6 has 2 projections, one to the lateral geniculate nucleus (LGN) and another to the visual claustrum. The cells of origin of each projection were identified by retrograde transport of fluorescent latex microspheres. The labeled cells were visualized in brain slices prepared from area 17, using an epifluorescence compound microscope modified for intracellular recording. Individual retrogradely labeled cells were penetrated and intracellularly stained with Lucifer yellow to visualize the patterns of axons and dendrites associated with each projection. The neurons that give rise to the 2 projections had very different patterns of dendrites and local axonal collaterals, but the patterns within each group were highly stereotyped. The differences between their axonal collaterals were particularly dramatic. Claustrum projecting cells had fine, horizontally directed collaterals that arborized exclusively in layer 6 and lower layer 5. Most LGN projecting cells had virtually no horizontal arborization in layer 6. Instead, they sent widespread collaterals vertically, which arborized extensively in layer 4. The apical dendrites of the 2 groups also differed markedly. Claustrum projecting cells had apical dendrites reaching to layer 1, with branches in layer 5 only, while LGN projecting cells never had an apical dendrite reaching higher than layer 3, with side branches in layers 5 and 4. Therefore, each efferent target must receive inputs from neurons whose synaptic connections within area 17 are significantly different from those of neurons projecting to other targets. This further suggests that distinct visual response properties should be associated with each projection. In addition to the claustrum and LGN projecting cells, about 20% of layer 6 pyramidal neurons lacked an efferent axon. Morphologically, most resembled LGN projecting neurons, but a few had characteristics of claustrum projecting cells. These neurons may represent cells that either failed to make an efferent connection or cells that lost an efferent axon during development. Their frequency suggests that such intrinsic, presumably excitatory, neurons may play a significant role in cortical processing.
Morphological and physiological differentiation of Purkinje neurons in cultures of rat cerebellum
Authors: Gruol DL , Franklin CL
Published: March 2018

During ontogeny, vertebrate CNS neurons differentiate from relatively simple stem cells to complex units that express unique morphological and electrophysiological characteristics. We have examined several aspects of this developmental process in an identified CNS neuronal type, the Purkinje neuron (PN) of the cerebellum. Our approach has included the use of a tissue culture preparation and immunohistochemical and electrophysiological techniques. Using immunohistochemical techniques, we have identified immature PNs in culture and examined their morphological and synaptic development. These studies have shown that PNs undergo extensive morphological and synaptic development in culture, the morphological characteristics of the immature PNs in culture and the developmental sequence and time course are reflective of that described for PNs in vivo, synapse formation is initiated at an early stage of PN development in culture and proceeds concurrently with the morphological development, and the main period of synapse formation is associated with the main period of dendritic development, reflecting the preferential location of synaptic sites at the dendritic region of mature PN. Using electrophysiological techniques, we have examined the physiological development of PNs in culture and have correlated the stages in physiological, morphological, and synaptic development. Results from these studies show the following. Mature PNs in culture exhibit complex electrophysiological properties, including the ability to generate 2 types of spike events, simple and complex spikes, and endogenously generated activity. Expression of electrophysiological properties begins at an early stage in PN development, when the PNs consist of little more than a soma with a few fine perisomatic processes. The earliest physiological characteristics to be expressed by the PN include sensitivity to transmitters, the ability to respond to synaptic input, and the ability to generate simple spikes. Synaptic input produces spontaneous activity in young PNs, but the patterns of activity change during development as mechanisms underlying endogenously generated activity and complex spike generation are expressed, and synapse formation proceeds.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of early unilateral blur on the macaque's visual system. I. Behavioral observations
Authors: Kiorpes L , Boothe RG , Hendrickson AE , Movshon JA , Eggers HM , Gizzi MS
Published: March 2018

We raised 8 macaque monkeys with chronic atropinization of one eye throughout the first 6–10 months after birth. This rearing procedure produces retinal image blur, with the most pronounced contrast attenuation occurring at high spatial frequencies. Measurements of contrast sensitivity were made using behavioral methods in 6 monkeys and evoked potential methods in 2 monkeys. The results showed that this rearing procedure produced long-term deficits in the contrast sensitivity and spatial resolution of the atropinized eye, which were not due to residual losses in accommodative capacity. There was considerable interanimal variation in the magnitude of the effects on visual performance. Similar losses in visual performance are seen in some forms of human amblyopia. Rearing monkeys with chronic instillation of atropine therefore provides a nonhuman primate model for studying the underlying neural mechanisms of anisometropic amblyopia.
Dopamine D2 receptors in the rat brain: autoradiographic visualization using a high-affinity selective agonist ligand
Authors: Charuchinda C , Supavilai P , Karobath M , Palacios JM
Published: March 2018

The non-catechol, selective dopamine D2-agonist compound 3H-205–502 was used to localize dopamine D2 receptors by autoradiography after in vitro labeling of brain sections. The characteristics of the binding of this ligand to tissue sections were those expected from the labeling of dopamine D2 receptors. The binding of 3H-205–502 was inhibited selectively and stereospecifically by dopamine D2 agents but not by dopamine D1 compounds. The autoradiographic localization of 3H-205–502 binding sites showed high densities of dopamine D2 receptors in areas such as the glomerular layer of the olfactory bulb, the nucleus accumbens, caudate-putamen, olfactory tubercle, the lateral septum, and the islands of Calleja. Besides these dopamine-innervated areas the substantia nigra and the ventral tegmental area also showed important receptor densities. Other areas where dopamine D2 receptor binding was found were the stratum lacunosum-moleculare of the hippocampus, bands of labeling in the molecular layer of the 9th and 10th lobules of the cerebellum, and several components of the visual system. This distribution presents similarities and differences with previously reported distributions of dopamine D2 receptors visualized autoradiographically using 3H-labeled agonists and antagonists. In view of the high affinity, guanine nucleotide insensitivity, and dopamine D2 selectivity of this agonist ligand, it is suggested that dopamine D2 receptors exist in different states in different areas. 3H-205–502 appears to be a new and useful tool for the study of dopamine D2 receptors.