bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitatory amino acid-stimulated uptake of 22Na+ in primary astrocyte cultures
Authors: Kimelberg HK , Pang S , Treble DH
Published: March 2018

In this study we have found that L-glutamic acid, as well as being taken up by a Na+-dependent mechanism, will stimulate the uptake of 22Na+ by primary astrocyte cultures from rat brain in the presence of ouabain. By simultaneously measuring the uptake of 22Na+ and L-3H- glutamate a stoichiometry of 2–3 Na+ per glutamate was measured, implying electrogenic uptake. Increasing the medium K+ concentration to depolarize the cells inhibited L-3H-glutamate uptake, while calculations of the energetics of the observed L-3H-glutamate accumulation also supported an electrogenic mechanism of at least 2 Na+:1 glutamate. In contrast, kinetic analysis of the Na+ dependence of L-3H-glutamate uptake indicated a stoichiometry of Na+ to glutamate of 1:1, but further analysis showed that the stoichiometry cannot be resolved by purely kinetic studies. Studies with glutamate analogs, however, showed that kainic acid was a very effective stimulant of 22Na+ uptake, but 3H-kainic acid showed no Na+ -dependent uptake. Furthermore, while L-3H-glutamate uptake was very sensitive to lowered temperatures, glutamate-stimulated 22Na+ uptake was relatively insensitive. These results indicate that glutamate-stimulated uptake of 22Na+ in primary astrocytes cultures cannot be explained solely by cotransport of Na+ with glutamate, and they suggest that direct kainic acid-type receptor induced stimulation of Na+ uptake also occurs. Since both receptor and uptake effects involve transport of Na+, accurate measurements of the Na+ :glutamate stoichiometry for uptake can only be done using completely specific inhibitors of these 2 systems.
Roles for mitotic history in the generation and degeneration of hippocampal neuroarchitecture
Authors: Mattson MP , Guthrie PB , Hayes BC , Kater SB
Published: March 2018

The mechanisms regulating the highly ordered neuroarchitecture of the mammalian brain are largely unknown. The present study took advantage of hippocampal pyramidal-like neurons that arose from a common progenitor cell in cell culture (sister neurons) to ascertain the contribution of intrinsic factors to both the generation and degeneration of neuroarchitecture. Sister neurons were similar in overall cell form and dendritic numbers and lengths. Control non-sister neurons that grew in contact did not generate similar morphologies, indicating that the similarity of sister cells did not result from influences of the local microenvironment or cell interactions. These results suggest that intrinsic factors related to mitotic history play a role in the generation of neuroarchitecture. Since particular groups of hippocampal neurons are sensitive to glutamate neurotoxicity in situ and are vulnerable in neurodegenerative disorders, it was of interest to test glutamate sensitivity in the neuronal population and in mitotic sister neurons. A subpopulation of pyramidal neurons was sensitive to glutamate neurotoxicity. A striking finding was that sister neurons were invariably either both sensitive or both resistant to glutamate, while non-sister neurons often showed different responses to glutamate. Pharmacological studies indicated that glutamate neurotoxicity was mediated by kainate/quisqualate type receptors by a mechanism involving calcium influx through membrane channels. Fura-2 measurements of intracellular calcium revealed that sister neurons had similar rest levels of calcium and, strikingly, glutamate caused a dramatic increase in intracellular calcium levels only in neurons which subsequently degenerated. Apparently, intrinsic differences in sensitivity to glutamate lie at a point prior to calcium entry, probably at the level of glutamate receptors. Taken together, these results indicate that the mitotic history of a neuron can determine its presence and potential for connectivity as well as its susceptibility to neurodegeneration.
Two cell types in rat substantia nigra zona compacta distinguished by membrane properties and the actions of dopamine and opioids
Authors: Lacey MG , Mercuri NB , North RA
Published: March 2018

Intracellular recordings were made from 475 rat substantia nigra zona compacta neurons in vitro. The region from which recordings were made was rich in catecholamine fluorescence. Two groups of neuron, termed principal neurons (95% of the total) and secondary neurons (5% of the total) were clearly distinguishable according to one or more of the following 4 electrophysiological properties. Secondary neurons (23 cells) (1) fired spontaneous action potentials at frequencies greater than 10 Hz, or were quiescent (30%); (2) had action potentials less than 1 msec in duration; (3) did not show time-dependent inward rectification with step hyperpolarization; and (4) had slope conductances of about 4 nS (between -75 and -90 mV). In contrast, principal neurons (1) fired spontaneous action potentials in the range 1–8 Hz, or were quiescent (33%); (2) had action potentials greater than 1 msec in duration; (3) showed pronounced time-dependent inward rectification; and (4) had steady-state membrane slope conductances of around 22 nS (between -75 and -90 mV). Secondary cells were not affected by dopamine but were hyperpolarized by baclofen, GABA, and the mu opioid receptor agonist Tyr-D-Ala-Gly-MePhe-Gly-ol (DAGO). On the other hand, dopamine and baclofen inhibited firing and/or hyperpolarized all principal cells tested, but mu or delta opioid receptor agonists had no effect. The properties of these 2 cell types broadly correspond with those described by electrophysiological studies in vivo, in which case the majority, or principal, cells are believed to be dopaminergic.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of NGF on the survival of rat retinal ganglion cells following optic nerve section
Authors: Carmignoto G , Maffei L , Candeo P , Canella R , Comelli C
Published: March 2018

The ability of NGF (2.5S subunit) to support the survival of adult rat retinal ganglion cells (RGCs) and optic nerve fibers after intracranial section of the optic nerve was investigated. NGF was injected intraocularly at a dose of 3 micrograms/injection every 2.3 d from the day of axotomy to analysis. Control animals received cytochrome c injections. The survival of RGCs was analyzed in whole-mounted retinas after either cresyl violet staining or labeling with HRP applied to the proximal stump of the optic nerve. Survival times were 5 and 7 weeks. Diameter distribution and number of myelinated optic nerve fibers were assessed in ultrathin cross sections of the optic nerve. We found that RGCs surviving axotomy were much more numerous following NGF treatment compared with controls. Large-size cells were, in particular, preserved by NGF treatment. The quantitative ultrastructural studies indicated that the number of myelinated optic nerve fibers at 5 and 7 weeks postaxotomy was significantly greater in the NGF group with respect to the cytochrome c group. In agreement with the results obtained at the level of the RGCs, large-diameter axons were, in particular, preserved. We conclude that NGF injected intraocularly is effective in promoting the survival of RGCs and optic nerve fibers at least for a period as long as 7 weeks after intracranial section of the optic nerve.
Perceived roughness of a grating: correlation with responses of mechanoreceptive afferents innervating the monkey's fingerpad
Authors: Sathian K , Goodwin AW , John KT , Darian-Smith I
Published: March 2018

Human subjects scaled gratings of alternating grooves and ridges for perceived roughness. Roughness increased with an increase in groove width and decreased with an increase in ridge width, but the effect of groove width was much greater than the effect of ridge width. In corresponding neurophysiological experiments, the gratings were moved sinusoidally across the receptive fields of single mechano-receptive afferents innervating the fingerpads of anesthetized monkeys. The measure of response used was the mean cyclic discharge rate (averaged over one cycle of the sinusoid). Slowly adapting afferents (SAs), rapidly adapting afferents (RAs), and Pacinian afferents (PCs) all showed a marked increase in response when groove width increased. An increase in ridge width had no consistent effect on the responses of SAs or RAs but resulted in a small decrease in the response of PCs. The response to a smooth surface differed significantly from the responses to the finer gratings only for the RAs. An alternative measure of response (the number of impulses elicited by each spatial cycle of the grating) increased with an increase in ridge width for all 3 fiber types. Thus, the large effect of groove width on perceived roughness can be accounted for by the mean cyclic discharge rate in the active afferent fibers. The smaller effect of ridge width can be accounted for by the number of impulses per spatial cycle of the grating.
Agrin-induced specializations contain cytoplasmic, membrane, and extracellular matrix-associated components of the postsynaptic apparatus
Authors: Wallace BG
Published: March 2018

The aims of the studies reported here were to determine the extent to which the specializations induced by agrin on cultured chick myotubes resemble the postsynaptic apparatus and examine how these specializations form. We found that agrin induces the formation of specializations at which at least 6 components of the postsynaptic apparatus are concentrated: one cytoplasmic component [a 43 kDa acetylcholine receptor (AChR)-associated protein], 3 membrane components [AChRs and globular forms of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)], and 2 extracellular matrix-associated proteins (A12 asymmetric AChE and a heparan sulfate proteoglycan). The accumulation of AChE and BuChE into agrin-induced aggregates occurred in the absence of any change in the amount, rate of synthesis, accumulation, and release, or molecular forms of either enzyme. Thus, agrin affects primarily the distribution of these components of the postsynaptic apparatus and not their metabolism. Agrin-induced formation of AChR aggregates was not prevented by inhibition of protein synthesis, consistent with our previous results that agrin-induced accumulation of AChRs occurs by lateral migration. The accumulation of components of the extracellular matrix would seem less likely to occur by lateral migration and so might require release of newly synthesized proteins; indeed, formation of aggregates of heparan sulfate proteoglycan was prevented by inhibitors of protein synthesis. Thus, different components of the postsynaptic apparatus accumulate in agrin- induced specializations by different mechanisms.
Impulse blockade by intraocular tetrodotoxin during optic regeneration in goldfish: HRP-EM evidence that the formation of normal numbers of optic synapses and the elimination of exuberant optic fibers is activity independent
Authors: Hayes WP , Meyer RL
Published: March 2018

Optic fibers and synapses labeled with HRP were counted in the primary optic innervation layer of tectum after continuously blocking visual impulse activity with TTX during regeneration. Normal numbers of optic and nonoptic fibers and synapses were found at both 30 and 60 d, and key ultrastructural features of optic afferents such as fiber fasciculation, myelination, terminal clustering, synaptogenesis onto different classes of postsynaptic targets and general morphology were not notably affected by impulse blockade. These findings indicate that during regeneration the normal proliferation and elimination of optic fibers and the formation of normal numbers of optic synapses are not regulated by activity and are consistent with a pattern formation role for impulse activity rather than a trophic one.
A neuroglial cooperativity is required for the potentiation by 2- chloroadenosine of the muscarinic-sensitive phospholipase C in the striatum
Authors: el-Etr M , Cordier J , Glowinski J , Premont J
Published: March 2018

In rat striatal slices, 2-chloroadenosine, which had no direct effect on inositol phosphate formation, potentiated in a dose-dependent manner the accumulation of inositol phosphates induced either by carbamylcholine (10(-3) M) or by noradrenaline (10(-4) M). Experiments made on pure populations of striatal neurons or striatal glial cells in primary culture from mouse embryos indicated that 2-chloroadenosine potentiated the noradrenaline-elicited phosphoinositide breakdown in striatal glial cultures but did not modify the responses evoked either by noradrenaline or by carbamylcholine in striatal neuronal cultures. However, 2-chloroadenosine enhanced both the carbamylcholine and the noradrenaline-induced accumulation of inositol phosphates in neuroglial cocultures just as it did in rat striatal slices. The potentiation by 2- chloroadenosine of the carbamylcholine response, which is neuron specific, involved a cooperative effect between neurons and glial cells and, as shown by additional experiments, required a brief contact only between the 2 types of cells. The potentiating effect of 2- chloroadenosine was blocked completely by a nonselective A1, A2 adenosine antagonist isobutylmethylxanthine either on rat striatal slices or on mouse embryonic cocultures (noradrenaline and carbamylcholine responses) or on mouse embryonic glial cultures (noradrenaline response). These data indicate the involvement of an extracellular membrane-bound adenosine receptor, possibly of the A1 subtype since N6-cyclohexyladenosine, an A1 adenosine receptor agonist, was more efficient than 5′-N-ethylcarboxamide-adenosine, a rather selective A2 adenosine receptor agonist. We propose that 2- chloroadenosine acts through an adenosine receptor located on glial cells and induces the synthesis of a substance that improves the coupling between carbamylcholine or noradrenaline and phospholipase C located in glial cells or neurons.
Activation of GABAB receptors causes presynaptic inhibition at synapses between muscle spindle afferents and motoneurons in the spinal cord of bullfrogs
Authors: Peng YY , Frank E
Published: March 2018

Baclofen, a specific GABAB receptor agonist, was used to study the functional role of activation of GABAB receptors in synaptic transmission between muscle spindle afferents and motoneurons in the isolated spinal cord of bullfrogs. (+/-)-Baclofen (5 microM) reversibly reduced the amplitude of the excitatory postsynaptic potential (EPSP) evoked by simulation of various brachial muscle nerves and recorded extracellularly from the ventral root by 47% without shortening the falling phase of the EPSP. Neither the time course nor the amplitude of the action potentials in the sensory afferents was affected. Thus, baclofen caused synaptic inhibition without reducing either the potential change occurring in the muscle sensory afferents or the motoneuronal membrane resistance. Quantal analysis, performed using a deconvolution technique, of the monosynaptic EPSPs in brachial motoneurons evoked by activity in single triceps muscle spindle afferents showed that transmission at these synapses was quantal, and baclofen lowered the quantal content without altering the quantal size. Furthermore, quantal analysis of the electrical component of these unitary EPSPs showed that it did not fluctuate in amplitude, either in normal saline or with baclofen. The inhibition produced by activation of GABAB receptors is therefore presynaptic but is not likely to be caused by conduction failures in the sensory terminals.
Neurobehavioral deficit due to ischemic brain damage limited to half of the CA1 sector of the hippocampus
Authors: Auer RN , Jensen ML , Whishaw IQ
Published: March 2018

It is well known that ischemia causes neuronal necrosis in selectively vulnerable sectors of the hippocampus. Since the hippocampus is involved in spatial navigation, learning, and memory, selective deficits in these areas may arise from ischemic brain damage. The objective of this study was to test whether a minimal ischemic insult, producing selective neuronal necrosis restricted to only a portion of the CA1 pyramidal cells of the hippocampus, could produce a detectable spatial navigation deficit. Male Wistar rats received 9 min of forebrain ischemia induced by carotid clamping and hypotension or sham operation with exposure of the carotid arteries. The rats were allowed to recover and were tested on a simple place task, a place learning-set task, and a pattern discrimination task in swimming pools paradigms. Subsequently, the rats were perfusion-fixed and their entire brains subjected to quantitative histopathologic analysis. Although both ischemic and sham-operated groups learned the simple place task, the learning-set task revealed defects in spatial navigation, reflected as increased errors and latency in the performance of the ischemic rats. In the subsequent pattern discrimination task, the ischemic group was superior to the control group, which perseverated by attempting to use a place strategy to solve the discrimination. Quantitative neuropathology revealed neuronal necrosis in the ischemia group limited to 50% of the CA1 zone of the hippocampus. Extrahippocampal damage consisted of rare cortical neuronal necrosis in 2 of 6 animals.(ABSTRACT TRUNCATED AT 250 WORDS)
Hippocampal damage associated with prolonged and fatal stress in primates
Authors: Uno H , Tarara R , Else JG , Suleman MA , Sapolsky RM
Published: March 2018

Sustained exposure to glucocorticoids (GCs), adrenal hormones secreted during stress, can cause neural degeneration in the rat. This is particularly so in the hippocampus, a principal neural target site for GCs, in which GCs can exacerbate the rate of neuron death during normal aging, as well as the severity of neuronal damage after various neurological insults. Thus, stress can be a potent modulator of hippocampal degeneration in the rat. The present report suggests a similar association in the primate. Eight vervet monkeys, housed in a primate center in Kenya, that had died spontaneously from 1984 to 1986, were found at necropsy to have multiple gastric ulcers; a retrospective, neuropathological study was then done of this opportunistic population. Compared with controls euthanized for other research purposes, ulcerated monkeys had marked hippocampal degeneration that was apparent both quantitatively and qualitatively, and both ultrastructurally and on the light-microscopic level. Minimal damage occurred outside the hippocampus. Damage was unlikely to have been due to an agonal or post-mortem artifact. Instead, ulcerated monkeys appear to have been subject to sustained social stress, perhaps in the form of social subordinance in captive breeding groups: most came from social groups, had significantly high incidences of bite wounds at necropsy, and had hyperplastic adrenal cortices, indicative of sustained GC release. Moreover, the specific hippocampal cell fields damaged in ulcerated animals matched those damaged by GCs in the rodent hippocampus. Thus, this represents the first evidence suggesting that sustained stress, via GC hypersecretion, might be neurodegenerative in the primate.
MAP 1A and MAP 1B are structurally related microtubule associated proteins with distinct developmental patterns in the CNS
Authors: Schoenfeld TA , McKerracher L , Obar R , Vallee RB
Published: March 2018

Five high-molecular-weight microtubule-associated proteins (MAPs) were identified in brain tissue in previous work from this laboratory (Bloom et al., 1984). These proteins were termed MAP 1A, 1B, 1C, 2A, and 2B. The MAP 1's differed from the MAP 2's, and showed little evidence of interrelationship on the basis of immunological and biochemical comparison. We report here that MAP 1A and MAP 1B are, in fact, related at the level of subunit composition. Immunoprecipitation of the individual MAPs showed that both contained low-molecular-weight subunits of Mr 30,000 and Mr 19,000 (light chains 1 and 3). An additional subunit, light chain 2 (Mr 28,000), was primarily found in preparations of MAP 1A. The light chains co-sedimented with microtubules after chymotryptic digestion of the MAPs. This suggested an association of the light chains with the microtubule binding domains of the MAPs, which are identified here as distinct fragments of Mr 60,000 for MAP 1A and 120,000 for MAP 1B. A panel of monoclonal anti- MAP 1A and anti-MAP 1B antibodies, including one that reacts with a common phosphorylated epitope, was used to examine the distribution of these proteins in the developing rat brain and spinal cord. MAP 1B was found to be abundant in the newborn brain and to decrease with development, in contrast to MAP 1A which increased with development. By immunohistochemistry MAP 1B was found to be highly concentrated in developing axonal processes in the cerebellar molecular layer, the corticospinal tract, the mossy fibers in the hippocampus, and the olfactory nerve. Of particular interest, the mossy fiber and olfactory nerve staining persisted in the adult, indicating continued outgrowth of the mossy fibers as well as olfactory nerve axons. MAP 1A staining was, in contrast, weak or absent in developing axonal fibers but moderate in mature axons and intense in developing and mature dendritic processes. Our results indicate that MAP 1A and MAP 1B are structurally related components of the neuronal cytoskeleton with complementary patterns of expression.
In vivo visualization of pre- and postsynaptic changes during synapse elimination in reinnervated mouse muscle
Authors: Rich MM , Lichtman JW
Published: March 2018

Using a vital nerve terminal dye (4-Di-2-ASP) and fluorescently tagged alpha-bungarotoxin to stain postsynaptic acetylcholine (ACh) receptors, we viewed the same muscle fibers at multiple times in the sternomastoid muscle of living mice during the process of reinnervation following nerve crush. Soon after axons reenter the muscle, they precisely reoccupy the original endplate sites. However, in contrast to normal adult muscle, during the first several weeks of reinnervation, anatomical and physiological measures show that many of the endplate sites are innervated by more than one axon. Typically, one axon reinnervates the original endplate site by growing up the old Schwann cell tube while another originates as a sprout from a nearby endplate. Within 2 weeks after reinnervation nerve terminal staining shows that most of the sprouts have regressed and physiological evidence of multiple innervation has returned to the normal low level. By repeatedly observing the same endplates during the period of synapse elimination, we could directly view this phenomenon. At some endplates, nerve terminal boutons in one region of the endplate were eliminated at the same time a sprout entering that area regressed. These unoccupied sites seemed permanently eliminated as they are not subsequently occupied by sprouts from the axon remaining at the endplate. We were surprised to find that there is a corresponding permanent loss of ACh receptors within the muscle fiber membrane precisely underneath the eliminated nerve terminals. The decrease in receptors at sites of synapse elimination is due to both a selective loss of ACh receptors already incorporated into these sites and to a lack of insertion of new receptors at the same regions. These sites of pre- and postsynaptic loss, however, maintain cholinesterase staining in the basal lamina for long periods. Control experiments showed that endplates that were permanently denervated, incompletely reoccupied by reinnervating axons, or stained and viewed multiple times in normal muscle do not lose postsynaptic receptor regions. Interestingly, receptors appear to be eliminated before there is any obvious change in the staining of the overlying nerve terminal. Because of the lag between receptor and nerve terminal loss, we could predict which synaptic boutons would be eliminated by looking for lightly stained receptor regions. One interpretation of these data is that the removal or redistribution of relevant postsynaptic molecules by one innervating axon may instigate the elimination of competing terminals.
Differential loss of neuromuscular connections according to activity level and spinal position of neonatal rabbit soleus motor neurons
Authors: Callaway EM , Soha JM , Van Essen DC
Published: March 2018

We have tested whether the ability of synapses to compete for occupancy of endplates during neuromuscular synapse elimination is affected by differences in the spinal position or in the activity level of the parent motor neuron. To test the role of spinal position, the relative sizes of motor units for motor neurons from middle and extreme (rostral/caudal) positions in the rabbit soleus motor pool were determined at 3 postnatal ages: 4–5 d (“early” ages, when the soleus is heavily polyinnervated), 8–9 d (“intermediate”), and 11–s15 d (“late,” when the soleus has just reached singly innervated state). Average motor unit sizes from extreme ventral roots were similar to those from middle ventral roots in early-aged soleus muscles but were significantly smaller (by 18–27%) for both intermediate and late muscles. Thus, motor neurons from extreme positions evidently compete less effectively for retention of synapses than those from middle positions. To test the role of differential activity, inactive and active synapses were pitted directly against one another by implanting Silastic plugs laden with tetrodotoxin (TTX) into one of the spinal nerves containing a minority of the soleus motor axons. Differential activity was maintained during a period of extensive synapse loss, from the time of the implant at day 4 or 5 until the intermediate age (day 8– 9). Motor unit twitch tensions were subsequently measured to determine the relative number of synapses retained by individual active and inactive motor neurons. The inactivated motor units were on average significantly larger (by more than 50%) than the corresponding group from normal and control-implanted animals. The abnormally large size of inactivated motor units persisted in animals allowed to recover from the TTX block and examined after multiple innervation had disappeared. Hence, the effect of the TTX block cannot be attributed to a simple slowing of synapse elimination specifically among the inactive motor neurons. We conclude that complete presynaptic inactivity improves the chances of survival relative to that for normal activity during synapse elimination in the neonatal rabbit soleus muscle. This difference in competitive ability may contribute to the development of an important characteristic of adult muscles, the correlation between motor unit size and recruitment threshold.
Hippocampal neurons in the monkey with activity related to the place in which a stimulus is shown
Authors: Rolls ET , Miyashita Y , Cahusac PM , Kesner RP , Niki H , Feigenbaum JD , Bach L
Published: March 2018

In order to analyze the functions of the hippocampus in the primate, and to advance the understanding of amnesia, the activity of 994 single hippocampal neurons in the monkey was analyzed during the performance of a task known to be affected by hippocampal damage in which both an object, and its position in space, must be remembered. The serial multiple object-place memory task required a memory for the position on a video monitor in which a given object had appeared previously. It was found that 9.3% of neurons recorded in the hippocampus and hippocampal gyrus had spatial fields in this and related tasks, in that they responded whenever there was a stimulus in some but not in other positions on the screen. We found that 2.4% of the neurons responded to a combination of spatial information and information about the object seen, in that they responded more the first time a particular object was seen in any position. Six of these neurons were found that showed this combination even more clearly, in that, for example, they responded only to some positions and only if it was the first time that a particular stimulus had appeared there. It is concluded that there are neurons in the primate hippocampus which (1) respond to position in space and (2) in some cases combine information about stimuli and their position in space, responding to a stimulus only the first time it is seen in a position in space, for example. Thus, not only is spatial information processed by the primate hippocampus, but it can be combined with information about which stimuli have been seen before. The ability of the hippocampus to form such conjunctions may be an important property for its role in memory.
Synaptic ultrastructure of functionally and morphologically characterized neurons of the superficial spinal dorsal horn of cat
Authors: Rethelyi M , Light AR , Perl ER
Published: March 2018

Recordings of neuronal unitary discharges evoked by primary afferent input were made in the superficial part of the spinal cord's dorsal horn, the marginal zone and substantia gelatinosa (also known as laminae I and II), using fine micropipette electrodes filled with HRP. After physiological characterization with respect to primary afferent input, HRP was injected intracellularly iontophoretically into the recorded neuron. Following histochemical processing, the neurons so delineated were studied at the light and electron microscopic levels. No clear relationship between function and either general cellular configuration or synaptic ultrastructure appeared in these analyses, although the concentration of dendritic distribution could be related to the nature of primary afferent excitation. Nocireceptive cells had dendrites mostly branching and ending in lamina I and IIo, while the dendrites of innocuous mechanoreceptive cells arborized principally in lamina II and III. Glomerular synaptic complexes (large, complex arrays of axonic and dendritic profiles with synaptic interconnections) were found to contact a few neurons of both the nocireceptive and mechanoreceptive classes. All neurons received large numbers of simple axonic contacts (small axonic boutons with only 1 or 2 synaptic contacts with a single postsynaptic profile). A degree of specificity in the presynaptic articulations appeared to be reflected by the observations that (1) nocireceptive neurons were never found to receive synaptic contacts from boutons which resembled the known ultrastructure of peripheral innocuous mechanoreceptors, and (2) mechanoreceptive neurons were never seen to receive synaptic contacts from boutons which resembled the known ultrastructure of primary afferent nocireceptors. The axons of the labeled neurons of both nocireceptive and mechanoreceptive classes terminated in simple axonic synapses. All classes of neurons participated in dendrodendritic contacts; however, only some mechanoreceptive neurons had dendrites containing vesicles that were presynaptic to other profiles. No nocireceptive neurons, regardless of gross configuration, were found to have vesicles in their dendrites, but 3 nocireceptive neurons received synapses from presynaptic dendritic profiles.
Involvement of excitatory amino acids in neurotransmission of inspiratory drive to spinal respiratory motoneurons
Authors: McCrimmon DR , Smith JC , Feldman JL
Published: March 2018

The role of excitatory amino acids in the transmission of bulbospinal respiratory drive to spinal motoneurons was investigated in the in vitro and in vivo spinal cord of the rat. In vitro studies were performed with a preparation of neonatal rat brain stem and spinal cord that spontaneously generates rhythmic respiratory drive to spinal respiratory motoneurons. This in vitro system allowed examination of the effects of pharmacological agents on spinal motoneuron activity, without perturbing the activity of bulbospinal neurons transmitting the respiratory drive. The amplitude of spontaneous motor discharge in spinal ventral roots containing phrenic and intercostal motor axons was reduced in a dose-dependent manner by antagonists to excitatory amino acids acting at NMDA receptors [D,L-2-amino-5-phosphonovaleric acid (D,L-AP5)] and non-NMDA receptors [kynurenic acid, gamma-D- glutamylglycine, gamma-D-glutamyltaurine, and L- and D,L-2-amino-4- phosphonobutyric acid (L-AP4,D,L-AP4)]. The order of potency of the antagonists for complete block of the motor output was L-AP4 greater than D,L-AP4 greater than kynurenic acid greater than gamma-D- glutamylglycine greater than D,L-AP5 greater than or equal to gamma-D- glutamyltaurine. Amino acid uptake inhibitors augmented the spontaneous motoneuron activity, further confirming the involvement of endogenous excitatory amino acids in transmission of respiratory drive. The results obtained in vitro with AP4, kynurenic acid, and amino acid uptake inhibitors were confirmed in vivo by bathing segments of the rat spinal cord in situ with solutions containing antagonists and uptake inhibitors. The present results suggest that an important component of the neurotransmission of bulbospinal respiratory drive involves endogenous excitatory amino acids acting at AP4-sensitive sites and other non-NMDA (quisqualate/kainate) receptors. The bulbospinal-spinal respiratory motoneuron synapse may provide a convenient model synapse in the spinal cord for detailed analysis of mechanisms underlying excitatory amino acid-mediated synaptic transmission of motor drive.
Sexually dimorphic polypeptides in developing antennal sensory neurons of an insect
Authors: Kingan TG , Hildebrand JG
Published: March 2018

Many insects have sexually dimorphic antennae with sensilla peculiar to one sex specialized to detect sex pheromones released by the other sex. In the moth Manduca sexta, the axons of receptor cells in the male- specific sensilla as well as those common to both sexes terminate in the antennal lobes of the brain. We have used 2-dimensional electrophoresis (2DE) to study some of the proteins that are produced by sensory receptor cells in developing antennae and transported through their axons to the brain. Extracts of antennal nerves from mature male and female M. sexta yield nearly identical 2DE patterns of proteins after staining or fluorography. Gels prepared from antennal nerves of developing animals, however, exhibit a sexual dimorphism in the quantitative pattern of at least 2 classes of proteins. One class consists of four 49 kDa proteins of similar charge, designated 49a, 49b, 49c, and 49d in order of decreasing mobility on nonequilibrium pH gradient electrophoresis gels. The total amount and apparent rate of synthesis of 49b and 49d are ca. 4- to 7-fold greater in antennal nerves of developing males than in those of females. Protein 49c is comparably enriched in female antennal nerves, while 49a is enriched ca. 1.2-fold in females. The second class consists of a single polypeptide of 24 kDa, which is nearly undetectable in silver-stained gels but was shown to be ca. 9-fold enriched in males by fluorography. At the end of adult development, male and female moths have similar patterns of the 49 kDa polypeptides, and synthesis of the 24 kDa polypeptide is reduced to nearly undetectable levels. The patterns of sexual dimorphism thus appear to be associated with the growth and maturation of antennal sensory axons into the antennal lobes. Biosynthesis of the 24 kDa polypeptide was nearly undetectable in antennal lobes or fragments of antennal nerves incubated in vitro with radiolabeled methionine. The 49 and 24 kDa polypeptides appear to belong to separate classes of rapidly transported proteins. The 24 kDa polypeptide is among the most rapidly transported proteins; it is found exclusively in a particulate fraction and is associated with plasma membrane but apparently not mitochondria. The 49 kDa polypeptides are found in both the particulate and soluble fractions; the more basic 49a and 49b are enriched in the particulate fraction, while the more acidic 49c and 49d are enriched in the soluble fraction.
Ultrastructural demonstration of a gastric monosynaptic vagal circuit in the nucleus of the solitary tract in rat
Authors: Rinaman L , Card JP , Schwaber JS , Miselis RR
Published: March 2018

Previous light microscopic work in the rat has demonstrated that many dendrites of vagal gastric motoneurons extend beyond the cytoarchitectural boundaries of the dorsal motor nucleus of the vagus (DMV) into the nucleus of the solitary tract (NST), where they overlap with the central terminal field of vagal gastric primary sensory neurons (Shapiro and Miselis, 1985a). In the present ultrastructural study, the synaptic relationship of vagal afferent terminals and vagal motor neurons and dendrites was examined. Following injection of cholera toxin-HRP conjugate (CT-HRP) into the dorsal and ventral musculature of the stomach wall, centrally transported tracer was visualized using tetramethylbenzidine or diaminobenzidine histochemistry. Light microscopy confirmed the presence of retrogradely labeled gastric DMV neurons whose dendrites extended into the overlying NST. The subnucleus gelatinosus of the dorsomedial NST at a level just rostral to the obex contained the highest density of vagal motoneuronal dendrites coextensive with transganglionically labeled vagal sensory afferents. Ultrastructural analysis of several NST subfields at this rostrocaudal level revealed many asymmetric synaptic contacts between labeled sensory afferents and labeled motoneuronal dendrites in the subnucleus gelatinosus but not elsewhere. Following CT-HRP injection into the cervical vagus nerve in separate animals, vagovagal synaptic contacts were again observed only in the subnucleus gelatinosus, despite extensive afferent labeling in other NST subnuclei. The demonstration of a monosynaptic gastric vagovagal circuit provides the anatomical substrate for the relay of gastric interoceptive information directly to gastric vagal motoneurons, which may play a unique role in the central regulation of gastric motility and secretion.
Intracellular pH transients of mammalian astrocytes
Authors: Chesler M , Kraig RP
Published: March 2018

Intracellular pH (pHi) is an important physiologic variable that both reflects and influences cell function. Glial cells are known to alter their functional state in response to a variety of stimuli and accordingly may be expected to display corresponding shifts in pHi. We used fine-tipped, double-barreled, pH-sensitive microelectrodes to continuously monitor pHi in glial cells in vivo from rat frontal cortex. Cells were identified as glia by a high membrane potential and lack of injury discharge or synaptic potentials. Continuous, stable recordings of pHi from astrocytes were obtained for up to 80 min but typically lasted for approximately 10 min. Resting pHi was 7.04 +/- 0.02 with a membrane potential of 73 +/- 0.9 mV (mean +/- SEM; n = 51). With cortical stimulation, glia depolarized and became more alkaline by 0.05–0.40 pH (n = 50). During spreading depression (SD), glia shifted more alkaline by 0.11–0.78 pH (n = 26). After stimulation or SD, glia repolarized and pHi became more acidic than at resting levels. Superfusion of the cortical surface with 0.5–2 mM Ba2+ caused glia to hyperpolarize during stimulation and completely abolished the intracellular alkaline response. The predominant pH response of the interstitial space during stimulation or SD was a slow acidification. With superfusion of Ba2+ an early stimulus-evoked interstitial alkaline shift was revealed. The mechanism of the intracellular alkaline shift is likely to involve active extrusion of acid. However, internal consumption of protons cannot be excluded. The sensitivity of the response to Ba2+ suggests that it is triggered by membrane depolarization. These results suggest that glial pHi is normally modulated by the level of local neuronal activity.
Concomitant characterization of behavioral and striatal neurotransmitter response to amphetamine using in vivo microdialysis
Authors: Kuczenski R , Segal D
Published: March 2018

The temporal and dose-related behavioral and striatal monoamine response to amphetamine (AMPH) was examined using in vivo microdialysis in freely moving rats. Extracellular dopamine (DA), serotonin (5-HT), and their metabolites were monitored concomitant with detailed characterization of the locomotor and stereotypy profiles. Consistent with previous results, AMPH (0.5–5.0 mg/kg) induced a rapid dose- dependent increase in DA concentration and decrease in the concentrations of the DA metabolites, DOPAC and HVA. DA and its metabolites exhibited contrasting temporal and dose-related patterns, suggesting that the decline in DA metabolites is functionally dissociated from the AMPH-enhanced DA release. In addition, AMPH at doses of 2.0 mg/kg and greater significantly increased extracellular concentrations of 5-HT, which, in contrast to the changes in dopamine, persisted for only 20–40 min. Comparisons of concentrations of DA and 5- HT for individual animals revealed significant correlations both during baseline and drug response, suggesting a possible functional interdependence between dopaminergic and serotonergic activity in striatum. Dose-response comparisons revealed a significant relationship between AMPH-induced increases in behavioral perseveration and the magnitude and duration of the DA release. However, the temporal patterns of the neurotransmitter response and individual components of stereotypy were not parallel, suggesting that the presence of stereotypies is not associated simply with quantitative differences in striatal DA release. By contrast, some features of the behavioral response were significantly correlated with AMPH-induced changes in striatal 5-HT concentrations. Our results suggest that the behavioral response to AMPH may be influenced by the interaction between levels of DA and 5-HT release, as well as by the state of their respective receptors.
Structure-function studies on N-oxalyl-diamino-dicarboxylic acids and excitatory amino acid receptors: evidence that beta-L-ODAP is a selective non-NMDA agonist
Authors: Bridges RJ , Stevens DR , Kahle JS , Nunn PB , Kadri M , Cotman CW
Published: March 2018

Excitatory amino acids and their receptors play an important role in both normal synaptic transmission and excitotoxic-mediated neuronal death. In the present investigation we have prepared a series of glutamate analogs and examined the pharmacological specificity with which they interact with excitatory amino acid receptors. Included within this group of compounds is a potent excitotoxic amino acid, beta- N-oxalyl-L-alpha, beta-diaminopropionic acid (beta-L-ODAP). This excitotoxin is of particular interest because it has been identified as a major causative agent of human neurolathyrism, a disease characterized by permanent spastic paralysis. The site of action of beta-L-ODAP was delineated with both electrophysiological recordings in hippocampal slices and radioligand binding assays in synaptic plasma membranes. We report that beta-L-ODAP is a potent agonist at the non-N- methyl-D-aspartate (NMDA) type of excitatory amino acid receptor. beta- L-ODAP interacts most potently with the quisqualate class of non-NMDA receptors (IC50 = 1.3 microM), less potently with the kainate receptor (IC50 = 17 microM), and very weakly with NMDA receptors. The specificity of this binding was consistent with physiological experiments that demonstrated that beta-L-ODAP-induced depolarizations were potently blocked by the newly identified non-NMDA receptor antagonist, CNQX, but were not affected by the NMDA antagonist D-AP5. These results extend recent studies that have focused on the contribution of NMDA receptors to excitotoxicity and highlight the potential involvement of non-NMDA receptors in excitotoxic-mediated cell death.
A comparison of movement direction-related versus load direction- related activity in primate motor cortex, using a two-dimensional reaching task
Authors: Kalaska JF , Cohen DA , Hyde ML , Prud'homme M
Published: March 2018

Shoulder joint-related motor cortex cells show continuously graded changes in activity, centered on a preferred movement direction, during active arm movements in 8 directions away from a central starting position (Georgopoulos et al., 1982). We demonstrate here that many of these cells show similar large continuously graded changes in discharge when the monkey compensates for inertial loads which pull the arm in 8 different directions. These load-dependent discharge variations are typically unimodal, centered on one load direction called the cell's load axis, and are often sufficiently continuous, symmetric, and broad as to show a good fit to a sinusoidal curve. A vectorial representation of cell activity indicates that the pattern of load-dependent activity changes in the population forms a signal whose direction is appropriate to compensate for the loads. The responses of single cells to different combinations of movement and load direction are often complex. Nevertheless, the mean activity of the sample population under any condition of movement direction and load direction can be described reasonably well by a simple linear summation of the movement-related discharge without any loads, and the change in tonic activity of the population caused by the load, measured prior to movement. The strength of the load-dependent discharge variation differs among cells. Cells can be sorted into 2 phasic and 2 tonic groups that show differing degrees of sensitivity to loads. In particular, it was found that the greater the degree of cell discharge variation associated with different actively maintained limb postures, the greater the activity changes caused by loads. No similar correlation was found for the degree of discharge variation during movement. Preliminary evidence suggests that phasic and tonic cell groups may be spatially segregated in the motor cortex. These observations are consistent with the idea that there exists in the motor cortex activity encoding aspects of movement kinematics, as well as movement dynamics. These observations are in agreement with studies of more distal arm joints, showing that the activity of certain motor cortex cells varies with the patterns of muscle activity and output forces required to produce a movement. These experiments extend the description of the control of the direction of movement of a multiple degree-of-freedom joint into the spatial (direction) domain to a greater extent than previously achieved.
A monoclonal antibody, Py, distinguishes different classes of hippocampal neurons
Authors: Woodhams PL , Webb M , Atkinson DJ , Seeley PJ
Published: March 2018

A monoclonal antibody, Py, was produced by immunizing mice with a glycoprotein fraction isolated from 3-week-old rat hippocampus. Py antibodies gave strong immunocytochemical staining of the perikarya and dendrites of large neurons in many areas of the rat brain, including the cerebral cortex, hippocampus, cerebellum, brain stem, and olfactory bulb. Immunoelectron microscopy showed the antigen to be predominantly intracellular, although its presence on the neuronal cell surface was not excluded. The antibody gave differential staining of adult hippocampal neurons, large pyramids of field CA3 being strongly immunoreactive, while CA1 pyramids and the dentate granule cells were unstained. Some interneurons were positive in each of the hippocampal fields. In developing hippocampus, the Py antigen appeared by the middle of the first postnatal week, and the adult pattern of staining was achieved by the end of the second week. Immunoblotting showed the antigen to have a relative mobility of 146 kDa with an additional faint band at 166 kDa. Differential Py staining of neurons was seen in dissociated cultures of embryonic hippocampus and in subdissected hippocampal fragments transplanted into adult host brains. This antibody can therefore be used for identification of hippocampal neurons that have been removed from their normal anatomical context.