bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative immunohistochemical demonstration of peptide F‐ and other enkephalin‐containing neurons in the enteric nervous system of the rat
Authors: Wang Yen‐Nung , Wyatt Richard Jed
Published: December 2004

The immunohistochemical localization of peptide F and the related enkephalins met5‐enkephalin (met‐enk), leu5‐enkephalin (leu‐enk), met5‐enkephalin‐arg6‐Phe7(met‐enk‐arg‐phe); and met5‐enkephalin‐arg6‐gly7‐leg8 (met‐enk‐arg‐gly‐leu) was in vestigated by means of the indirect immunofluorescence technique in the enteric nervous system of the rat. Peptide F‐like immunoreactivity was widely distributed within neuronal structures throughout the gastrointestinal (GI) tract of the rat. Peptide F‐containing nerve cell bodies were meinly located in the myenteric plexus, and only rarely were seen in the submucosal plexus. Peptide F‐immunoreactive nerve fibers were principally present in the myenteric plexus and circular muscle layer; few were found in the submucosal plexus, longitudinal muscle layer, muscularis mucosa, and mucosa. No peptide F‐containing fibers were found associated with blood vessels in the gut. By comparing the distribution of immunoreactive peptide F with other related enkephalins met‐enk, leu‐enk, metenk‐arg‐phe, and met‐enk‐arg‐gly‐leu, we observed that there was a remarkable similarity in the distribution of peptide F and the other enkephalins in the GI tract. These data, combined with our previous studies, indicate that peptide F may coexist with other related enkephalins in the same neurons of the enteric nervous system. The results suggest that peptide F, a product of the proenkephalin A gene, may play a physiological role within the enteric nervous system.
Effects of a behaviorally active LHRH fragment and septal area stimulation on the activity of mediobasal hypothalamic neurons
Authors: Dudley Carol A. , Moss Robert L.
Published: December 2004

The effect of Ac‐LHRH5–10, An LHRH fragment capable of facilitating lordosis, and LHRH on the firing rate of mediobasal hypothalamic neurons receiving input from the septal area, (a site containing the majority of LHRH perikarya) was studied via conventional extracellular recording techniques. A multibarrelled glass electrode assembly was lowered through the dorsomedial and ventromedial hypothalamus to detect single units responsive to septal area stimulation, and to iontophoretically apply Ac‐LHRH5–10 and LHRH. Ovariectomized rats were primed with estradiol benzoate (EB; n = 21) or left untreated (n = 34) to determine if the neuronal responsiveness to septal area stimulation and/or to the two peptides was subject to estrogenic modulation.

Of the total number of 228 neurons recorded in the study, 51 units (22.4%) were orthodromically responsive to septal area stimulation. The orthodromic responses in EB‐primed animals (n = 20) were characterized by a short‐latency, short‐duration increase in membrane excitability. When spontaneous activity was sufficiently high, the excitatory response was followed by, or superimposed upon, an inhibitory response of longer duration. Similar orthodromic excitatory and inhibitory response characteristics were observed in 21 of the 31 neurons recorded in nonprimed animals. In the remaining ten neurons, however, the excitatory component was absent.

Iontophoretic application of both Ac‐LHRH5–10 and LHRH was found to produce predominantly an inhibitory effect on cell firing. Most neurons responded to the two peptides in a similar manner (i.e., inhibited by both peptides, excited by both peptides, or not effected by either peptide). However, 39.5% of the neurons exhibited a different response to the two agents. Responsiveness to Ac‐LHRH5–10, but not to LHRH, was enhanced by estrogen priming. Iontophoretically applied Ac‐LHRH5–10, was found to mimic the inhibitory component of the orthodromic response in 21 of the 30 neurons tested. The same was true for LHRH in 15 of the 27 neurons tested.

Taken together, these results indicate that the septal‐stimulation‐evoked inhibition of mediobasal hypothalamic neurons may be mediated by the LHRH fragment and/or LHRH and that this input is subject to estrogenic modulation. Furthermore, the results suggest that Ac‐LHRH5–10 may act to facilitate lordotic responding by inhibiting the firing rate of mediobasal hypothalamic neurons.
Specific antagonism of behavioral action of “uncommon” amino acids linked to motor‐system diseases
Authors: Ross Stephen M. , Spencer Peter S.
Published: December 2004

Beta‐N‐methylamino‐L‐alanine (BMAA) and beta‐N‐oxalylamino‐L‐alanine (BOAA) are chemically related amino acids present in the seeds of Cycas circinalis and Lathyrus sativus, respectively. Consumption of these seeds has been linked to Guam amyotrophic lateral sclerosis (BMAA) and lathyrism (BOAA; a form of primary lateral sclerosis). A single large dose of BOAA or BMAA causes seizures in newborn mice and postsynaptic neuronal edema and degeneration in CNS explants. We report that the acute neurotoxic actions of these amino acids are blocked selectively by specific glutamate‐receptor antagonists (administered intracerebroventricularly) (i.c.v.) prior to the amino acid. Administration of BOAA i.c.v. to neonatal mice (ED100 = 50 μg) elicits a spectrum of time‐dependent behavioral states including arm and leg rigidity, convulsions, and resting tremor. These are blocked in a dose‐dependent manner by cis‐2,3‐piperidine dicarboxylic acid (PDA), an antagonist of quisqualate (QA)‐preferring (A2) and kainate (KA)‐preferring (A3) glutamate receptors (ED50s; 2.8 μg, rigidity; 1.4 μg, convulsions; 2.4 μg, resting tremor). BMAA induces a transitory hyperexcitable state followed by a long‐lasting whole‐body shake/wobble (ED100 = 1,000 μg, i.c.v.). These responses are antagonized selectively and dose‐dependently by 2‐amino‐7‐phosphonoheptanoic acid (AP7), an N‐methyl‐D‐aspartate (NMDA) or A1 glutamate‐receptor antagonist (ED50 = 0.45 μg). Taken collectively, our data indicate that the acute neuronotoxic actions of BOAA and BMAA (or a metabolite) operate through different glutamate‐receptor species. BMAA likely exerts most of its action indirectly via the A1 glutamate receptor, while BOAA acts principally at the A2 and/or A3 receptor.
Release‐regulating GABAA receptors are present on noradrenergic nerve terminals in selective areas of the rat brain
Authors: Bonanno G. , Raiteri M.
Published: December 2004

The effects of γ‐aminobutyric acid (GABA) on the spontaneous release of [3H]‐norepinephrine ([3H]‐NE) were investigated by means of superfused synaptosomes prepared from different areas of the rat brain and prelabeled with [3H]‐NE. GABA increased in a concentration‐dependent way (1–300 μM) the release of [3H]‐NE in hippocampal synaptosomes. The effect of GABA was mimicked in part by muscimol. Similar effects were observed in cerebral cortex synaptosomes where GABA and muscimol were however less potent than in hippocampus. No effect could be observed in hypothalamic synaptosomes. Bicuculline antagonized the effect of muscimol and that of low concentrations of GABA (below 10 μM). Above 10 μM, the [3H]‐NE releasing effects of GABA became progressively less sensitive to bicuculline. (−)‐Baclofen did not affect the spontaneous release of [3H]‐NE. It is concluded that release‐regulating receptors of the GABAA subtype are present on NE nerve terminals in selective areas of the rat brain.
Sexual dimorphism in the synaptogenic effect of estradiol in prepuberal female rats
Authors: Rodriguez‐Sierra J. F. , Clough R. W.
Published: December 2004

A study has been made of the effects of estradiol benzoate (EB) on synaptogenic induction in the hypothalamic arcuate nucleus (ARC), medial preoptic area (MPOA), and medial septal area (MSA) of prepuberal male and female rats. Subcutaneous administration of EB to 25‐day‐old female rats induces accelerated synaptogenesis in the ARC concomitant with a precocious surge of plasma luteinizing hormone (LH) at 1600 h on day 27 of age. The synaptic area densities (No. synapses/unit area of tissue section) of the MPOA and MSA are not increased at 27 days of age in rats treated with EB on day 25 of age. The synaptic area densities of the ARC, MPOA, and MSA are significantly higher on day 31 compared to day 27. However, only the ARC exhibits a further increase of synaptic numbers in EB‐treated female rats. Similar estrogen treatment to prepuberal male rats induces neither an LH surge in plasma nor increased synaptogenesis in the ARC, MPOA, or MSA. Male 27‐day‐old rats of both estrogen‐treated and control groups exhibit a synaptic area density in the ARC similar to 27‐day‐old control female rats. These data indicate that the sexually dimorphic positive response to estrogen with LH secretion has an equally sexually dimorphic neuromorphological response in rats. In addition, the synaptogenic effect of EB in the prepuberal female rat ARC remains manifest for at least 6 days after estrogen treatment.
Induction of hippocampal long‐term potentiation in the absence of extracellular Ca2+
Authors: May P. B. Y. , Goh J. W. , Sastry B. R.
Published: December 2004

Extracellular Ca2+, synaptic transmission, and the activation of subsynaptic receptors are not required for the induction of long‐term potentiation of excitatory synaptic transmission at stratum radiatum‐‐CA1 neuron junctions as long as sufficient depolarizations of the presynaptic terminals and the postsynaptic neurons co‐occur.
Retinal neurons lack an acetylcholine receptor aggregating factor
Authors: Thompson Jeffrey M. , Rapoport Stanley I.
Published: December 2004

Spinal cord neurons form stable synapses on muscle cells in culture, whereas retinal neurons, an inappropriate presynaptic partner for muscle cells, form synapses that are transient. We have hypothesized that a trophic influence of neurons on muscle is involved in the stabilization of synapses. Because other neural tissues that form stable synapses on muscle cells contain factors that aggregate acetylcholine receptors (AChR) into clusters on the surface of muscle cells. It may be that these aggregation factors are necessary for stabilization of neuron‐muscle synapses. Therefore, we determined the AChR‐aggregating activity of retinal neurons. The results showed that cocultures of retinal neurons and muscle cells and retinal‐conditioned medium do not show increases in the number of AChR on muscle cells. Conversely, spinal cord‐muscle cocultures and spinal cord‐conditioned medium produce increases in the number of AChR clusters. These data, along with previous studies demonstrating that retinal neurons are unable to affect the electrical membrane properties of cultured muscle cells, whereas spinal cord neurons do elicit such changes, add support to the above hypothesis of a trophic influence of neurons in synapse stabilization.
Central and peripheral effects of iminodipropionitrile on catecholamine metabolism in rats
Authors: Cadet J. L. , Karoum F.
Published: December 2004

Chronic treatment with iminodipropionitrile (IDPN) causes a behavioral syndrome characterized by lateral and vertical neck dyskinesias, hyperactivity, random circling, and increased startle response (the “ECC syndrome”). The effects of the neurotoxin on norepinephrine (NE), dopamine (DA), and their metabolites were evaluated in the hypothalamus and the striatum of IDPN‐treated animals. Urinary excretion of the amines was also measured. There was no significant persistent change in central metabolism of dopamine. There was a transient increase in NE metabolism in the hypothalamus after the third injection of IDPN that lasted until the development of the syndrome at 7 days of drug treatment. Urinary excretion of NE and its metabolites was increased on the day that the syndrome developed. Urinary excretion of homovanillic acid was persistently decreased throughout and after cessation of drug treatment. There was no change in the excretion of either dopamine or dihydroxyphenyl acetic acid. The ratio of total NE/total DA excreted by IDPN‐treated rats was the inverse of that of control animals. These results suggest that persistent dyskinesias may be associated with a relative increase in facilitatory NE‐dependent mechanisms at the cortical, subcortical, or spinal cord level.
Organization of glutamate‐like immunoreactivity in the rat superficial dorsal horn: Light and electron microscopic observations
Authors: Miller Kenneth E. , Clements Jane R. , Larson Alice A. , Beitz Alvin J.
Published: December 2004

Glutamate has been shown to be a neurotransmitter in the central nervous system of vertebrates, and it has been hypothesized that glutamate is functional as a neurotransmitter in the spinal cord dorsal horn. A monoclonal antibody to fixativemodified glutamate was used in this study to examine the light microscopic and ultrastructural profiles of glutamate‐like immunoreactivity in the superficial dorsal horn of the rat spinal cord. Glutamate‐like immunoreactivity was observed in neurons, fibers, and terminals of both laminae I and II. Marginal zone immunoreactive neurons ranged from 10 to 30 μm in diameter and received many nonimmunoreactive somatic synapses. In substantia gelatinosa, immunoreactive neurons were observed in both inner and outer layers, ranged 5 to 10 μm in diameter, and received few nonimmunoreactive somatic synapses. Glutamate‐like immunoreactive dendrites were observed in both laminae and were contacted primarily by nonimmunoreactive synaptic terminals that generally contained small clear vesicles. Both myelinated and unmyelinated immunoreactive axons were observed in Lissauer's tract. Immunoreactive terminals contained small (40 nm) clear vesicles and generally formed simple synaptic contacts with nonimmunoreactive dendrites in laminae I and II. The results of this study corroborate the importance of glutamate as a neurotransmitter in spinal sensory mechanisms.
Muscarinic agonists modulate spontaneous and evoked unit discharge in auditory cortex of cat
Authors: McKenna Thomas M. , Ashe John H. , Hui Gabriel K. , Weinberger Norman M.
Published: December 2004

The present experiments studied the effects of cholinergic agonists and antagonists on the spontaneous and acoustic‐evoked discharge of auditory cortical neurons and examined whether these effects were mediated by muscarinic cholinergic receptors. A primary focus of this report is the analysis of specific effects of these agents on the spontaneous and tone‐evoked discharge and on different temporal components of the evoked discharge. Single neurons were recorded in the auditory cortex of chronically prepared, awake cats with multibarrel micropipette electrodes. The responses to acoustic stimuli were obtained before, during, and following continuous ejection of cholinergic agonist or antagonists by micropressure. The mean rate of discharge of the neurons was analyzed quantitatively for spontaneous discharge and for different peaks of the tone‐evoked PSTH corresponding to tone “on,” “through,” and “off” responses. Acetylcholine (ACh) and acetyl‐β‐methacholine (MCh) produced significant effects on spontaneous activity in 72% and 68% of neurons tested, respectively. Tone‐evoked responses were effected in 92% and 82% of cells tested, respectively. The ability of these agonists to modify spontaneous or evoked activity was dose‐dependent. Agonist effects on spontaneous and evoked activity were often different in the same cell; however, effects on spontaneous activity did predict effects on “through” responses. The most common effect of ACh or MCh on evoked activity was facilitation of the tone “on” responses. For neurons with multicomponent discharge patterns in response to tones, the agonists had nonuniform effects on different response components. However, the effects of ACh on the “on” and “off” responses covaried. Hence cholinergic agonists produce heterogenous, selective effects on different components of the responses of auditory cortical neurons rather than simple increases or decreases in discharge level. The effects of cholinergic agonists were modified in the presence of atropine. The effects of MCh were blocked by atropine in a higher proportion of cases than those of ACh.
Dendritic development and preferential growth into synaptogenic fields: A quantitative study of Golgi‐impregnated spinal motor neurons
Authors: Vaughn James E. , Barber Robert P. , Sims Terry J.
Published: December 2004

Branching patterns of dendrites may be modulated by the way in which dendritic growth cone filopodia come into initial synaptic relationships with afferent axons. This synaptotropic hypothesis of dendritic branching predicts that dendritic growth will be directed preferentially into regions containing numerous prospective presynaptic elements. The developing mouse spinal cord provides a natural experiment to test this prediction, because synapses are found exclusively within the marginal zones bordering the motor columns during the early (E11–14) period of synaptogenesis. During this time, therefore, most motor dendritic growth would be expected to be directed laterally or ventrally into the marginal zones, whereas internally directed growth should become more prevalent later, when synaptogenesis begins to take place within the intermediate zone, i.e., the motor columns proper. A computer‐assisted three dimensional reconstruction system has been used to test these expectations in Golgi preparations of developing mouse (C57BL/6J) spinal cords ranging in age from E13 through P1. Mean dendritic lengths and branch densities are significantly greater for marginal zone dendrites than for intermediate zone dendrites at early ages (E13–14), but there are no significant differences in these measures at later stages of development (PO,1). These findings are interpreted as meaning that motor dendritic growth is initially biased into the marginal zone by synaptogenic afferents and that this oreferential distribution is progressively lost as synapses develop within the intermediate zone to attract or to stabilize internally directed dendritic growth. Thus the findings of this study are consistent with predictions of the synaptotropic hypothesis of dendritic branching.
The ultrastructural localization of calcium‐activated protease “calpain” in rat brain
Authors: Perlmutter Lynn S. , Siman Robert , Gall Christine , Seubert Peter , Baudry Michel , Lynch Gary
Published: December 2004

Calpain I, a calcium‐activated neutral protease which degrades a number of cytoskeletal proteins, has been implicated in the rapid turnover of structural proteins that may participate in synaptic plasticity. In the present study, an antibody raised against purified erythrocyte calpain I was biochemically characterized and demonstrated to specifically bind the Mr=80,000 subunit of both rat erythrocyte and brain calpain I. This antibody was used to examine the cellular distribution of calpain I at the electron microscopic level in rat brain and spinal cord using the avidin‐biotin immunocytochemical technique. Reaction product was observed throughout neuronal perikarya, within both axonal and dendritic processes, and within spine heads and necks. Postsynaptic densities in both shaft and spine synapses were also immunoreactive. Glial cell bodies and processes were densely stained. In both neurons and glia, the reaction product was deposited along cytoskeletal elements. The localization of calpain I immunoreactivity to glial processes suggests this degradative enzyme may play a role in the glial hypertrophy and process retraction seen in brain. The presence of the enzyme in spines and postsynaptic densities is consistent with the hypothesis that it is involved in the turnover of synaptic cytoskeleton, thus providing a means through which transient physiological events effect lasting changes in the chemistry and morphology of spines.
A reevaluation of the mathematical models for simulating single‐channel and whole‐cell ionic currents
Authors: Millhauser Glenn L. , Oswald Robert E.
Published: December 2004

We have developed a technique that allows for the simulation of both single‐channel and whole cell ionic currents given any arbitrary first‐order kinetic scheme for the conformational states of an ion channel. The procedure is based on the solution of the master equation, which, in turn, is a general expression for a Markov process. The solution is expressed in terms of the eigenvalues and eigenvectors of the kinetic system and the system's deviation from equilibrium. Our derived expression provides a general recipe for the calculation of whole‐cell currents. By further manipulation of this expression, we show how conditional probabilities are derived that can be used for the simulation of single‐channel currents. We discuss computer implementation of the results so that complicated kinetic schemes can be solved numerically. Finally, we demonstrate the procedure by providing a worked example of a simple model of activation followed by inactivation.
Seizures induced by aminooxyacetic acid in mice: Pharmacolgical characteristics
Authors: Turski Waldemar A. , Dziki Marek , Urbanska Ewa , Calderazzo‐Filho Lineu S. , Cavalheiro Esper A.
Published: December 2004

Systemic (s.c.) administration of aminooxyacetic acid (AOAA) in mice triggered clonic convulsions with a CD50 (convulsive dose) of 68 mg/kg (range 54–86). AOAA also induced clonic covulsions in mice subjected to intracerebroventricular administration of the drug with a CD50 of 0.04 μmol (range 0.028–0.06). At the onset of convulsions induced by systemic AOAA (CD97; 150 mg/kg), the GAD activity in the frontal cortex and hippocampus was not affected. GABA mimetic drugs, progabide and gabaculine, had no effect on covulsions induced by AOAA. Convulsions induced by systemic administration of AOAA were blocked by diazepam, phenobarbital, and valproate. Ethosuximide, trimethadione, acetazolamide, diphenylhydantion, and carbamazepine remained ineffective. L‐Phenylisopropyladenosine was also found to protect mice against AOAA‐induced convulsions, whereas atropine and baclofen had no effect. The seizures induced by intracerebroventricular administration of AOAA (CD97; 0.1 μmol) were blocked by coadministration of preferential N‐methyl‐D‐aspartate antagonists, D‐(−)‐2‐aminophosphonoheptanoic (AP7), 3‐((±)‐2‐carboxypiperazinv4‐yl)‐propyl‐1‐phosphonic (CPP), and kynurenic acid (KYNA); preferential quisqualate/kainate antagonists, 6‐cyano‐7‐nitro‐quinoxaline‐2,3‐dione and γ‐D‐glutamylaminomethylsulphonic acid, remained inactive in the range of dosages sufficient to block seizures induced by quisqualic acid or kainic acid.

The antagonistic action of antiepileptic drugs effective against seizures induced by excitatory amino acids (diazepam and valproate), and drugs acting on excitatory amino acid receptors (AP7, CPP, and KYNA) upon seizures induced by AOAA suggests an involvement of excitatory neurotransmission in the covulsant action of the drug.
Effects of protein kinase C activators and inhibitors on membrane properties, synaptic responses, and cholinergic actions in CA1 subfield of rat hippocampus in situ an in vitro
Authors: Agopyan N. , Agopyan I.
Published: December 2004

Activation and inhibition of protein kinase C(PKC) has been reported to induce several effects in hippocampus in vitro. It has been also proposed that, in hippocampus, phorbol esters mimic the effects of acetylcholine. To test whether the actions produced by PKC activators and inhibitors in situ are comparable to those induced in vitro preparations, we studied in CA1 region of the hippocampus both in situ and in vitro, the responses produced by activation and inhibition of protein kinase C. Once the effects of various PKC activators and inhibitors were established their interaction with muscarinic agonists was studied. The main findings were as follows: (I) Extracellular studies in situ: (1)Phorbol diacetate (PDAc) enhanced the population spike and dendritic field amplitudes. Unlike ACh, it never induced disfacilitation or disinhibition. (2) The effects produced by mascarinic agonists were not occluded by prolonged PDAc applications. (3) Inhibition of PKC with H‐7 induced a strong excitation manifested by induction of multiple spikes and broadening of the dendritic field response. This excitation was associated with blockade of IPSPs, represented by positive waves, at a presynaptic site, which was antagonised by PDAc suggesting the involvement of PKC. (4) Sphingosine, a dual PKC/‐calciumcalmodulin‐dependent kinase inhibitor, did not reproduce H‐7‐induced responses. However, it did prevent the actions of muscarinic agonists. (II) Intracellular studies in vitro: (1) PDAc application by either iontophoresis or superfusion produced a (i) depolarization; (ii) increase in input resistance (RN); (iii) blockade of the anomalous rectification (“sag”)(iv) increase in the fast—but decrease in the slow—after hyperpolarization (AHP);and (v) reduction in excitability, measured by the repetitive firing evoked by depolarizing pulses. (2) During local (iontophoretic) applications of PDAc, the reversal shifted toward more positive values. (3) Iontophoresis of H‐7 caused a decrease in RN, hyperpolarization, and blockade of IPSPs. In conclusion, in the hippocampus, PKC can modulate the IPSPs, the anomalous rectification, and the membrane potential, but PKC is unlikely to be the major intracellular mediator of the excitatory actions of acetulcholine. The possible involvement of calcium‐calmodulinvdependent kinase is discussed.
Evidence that changes in spine neck resistance are not responsible for expression of LTP
Authors: Jung Min W. , Larson John , Lynch Gary
Published: December 2004

From modeling studies it is known that changes in spine neck resistance can influence the shape of the non‐linear curve relating synaptic current to synaptic conductance if the resistance of the neck approaches the synaptic input resistance. Such work also indicates that the effects of resistance will be much more pronounced for fast rather than slow synaptic currents. Accordingly, a reduction in neck resistance could produce an increase in the rapid responses generated by the quisqualate/AMPA class of glutamate receptors while only minimally affecting the slower NMDA receptor‐mediated responses and thus account for the pattern of changes known to be associated with long‐term potentiation (LTP). This hypothesis predicts that large reductions in synaptic conductance should have disproportionate effects on potentiated versus control responses. This was tested by using field potential recordings of synaptic currents in CA1 pyramidal cells in hippocampal slices in response to stimulation of Schaffer/commissural inputs that either received LTP‐inducing stimulation or did not. Two manipulations were used to systematically reduce synaptic conductances: reductions of extracellular Ca++ and partial blockade of postsynaptic receptors. Reductions jof synaptic field potentials by 40–75% by either method at control synapses were accompanied by equivalent reductions at priviously potentiated synapses. These results suggest that LTP expression is not due to a predicted by the curves relating synaptic current to synaptic conductance as would be predicted by the spine resistance hypotheses.
Regulation of spontaneous activity and oscillatory spike firing in rat midbrain dopamine neurons recorded in vitro
Authors: Grace Anthony A.
Published: December 2004

Intracellular recordings were obtained from identified dopamine (DA) neurons in rat midbrain slices maintained in vitro. DA neuron membranes exhibited pronounced instantaneous and time‐dependent anomalous rectification that showed evidence of maximal activation at average membrane potentials of −63 and −78 mV, respectively. Action potentials were followed by prominent afterhyperpolarizations (AHP) that consisted of two components. The fast component showed evidence of inactivation at −63 mV independent of the initial membrane potential, whereas the longer‐duration, later component increased in amplitude at hyperpolarized potentials. Unlike DA neurons recorded in vivo, there was no evidence of spike frequency adaptation or summation of AHPs with prolonged depolarization‐induced spike trains. Spontaneous spike discharge occurred via an endogenous pacemaker potential that was dependent on both TTX‐sensitive and cobalt‐sensitive processes. Hyperpolarizing prepulses could activate rebound pacemaker discharge, but this rebound activity was progressively blocked with larger‐amplitude hyperpolarizing prepulses.

DA neurons recorded in the ansthetized animal, freely moving animal, and in vitro preparations have been shown to exist in two states of activity: (1) spontaneously discharging action potentials or (2) hyperpolarized, quiescent, and non firing. Further‐more, although it is rare to find DA neurons in the untreated animal in transitional states of activity, quiescent neurons can be activated by stimuli that place a demand on the DA system. The evidence presented here is consistent with the hypothesis that the special combination of membrane properties of DA neurons contribute to the segregtion of their activity into active or inactive states.
Synaptic plasticity at crayfish neuromuscular junctions: Facilitation and augmentation
Authors: Bittner George D. , Baxter Douglas A.
Published: December 2004

Simultaneous intracellular recordings from presynaptic nerve terminals and postsynaptic muscle fibers were used to investigate the extent to which changes in presynaptic voltage may contribute to short‐term facilitation and augmentation of transmitter release at neuromuscular junctions of the crayfish (Procambarus simulans) opener muscle. Presynaptic nerve terminals have an average resting membrane potential of about–80 mV, single action potentials have an average foot‐to‐peak amplitude of about 98 mV, and single action potentials are followed by a depolarizing after potential (DAP) of about 10 mV. During stimulus trains of 9–16 impulses at 100 Hz, amplitudes of excitatory postsynaptic potentials (EPSPs) continuously facilitate up to 100‐fold. This dramatic facilitation is associated with oly slight increases in the peak voltage and duration of APs for first 2–4 pulses in such a stimulus train. Foot‐to‐peak total amplitude of APs usually decreases after the first pulse in a stimulus train. The data strongly suggest that short‐term facilitation is not due to changes in the amplitude or duration of APs invading the presynaptic terminal. Upon cessation of a longer stimulus train, the presnaptic terminal exh‐ibits a hyperpolarizing after potential (HAP) up to 16 mV in amplitude depending upon the frequency (10–100 Hz) and duration (1–10 sec) of the tetanic stimulation. This post‐tetanic HAP decays with a time constant of 10–20 sec, which is approximately equal to the third time constant of decay in EPSP amplitude (augmentation) following tetanic stimulation. Hence, presynaptic voltage changes and/or processes associated with these voltage changes (e.g., acumulation of ions, changes in ionic conductances, etc.) may be responsible for augmentation of EPSP amplitudes.
Competitive (AP7) and non‐competitive (MK‐801) NMDA receptor antagonists differentially alter glucose utilization in rat cortex
Authors: Clow Daniel W. , Lee Shay J. , Hammer Ronald P.
Published: December 2004

The effects of D, L‐2‐amino‐7‐phosphonoheptanoic acid (AP7), a competitive N‐methyl‐D‐aspartate (NMDA) receptor antagonist, and MK‐801, a non‐competitive NMDA receptor antagonist, on regional brain metabolism were studied in unanesthetized, freely moving rats by using the quantitative [14C]2‐deoxyglucose autoradiographic procedure. AP7 (338 or 901 mg/kg) produced a dose‐dependent decrease of metabolic activity throughout most of the regions studied including sensory, motor, and limbic cortices. In contrast, MK‐801 (0.1 or 1.0 mg/kg) resulted in a dose‐dependent decrease of metabolic activity in sensory cortices, and an increase in limbic regions such as the hippocampal stratum lacunosum moleculare and entorhinal cortex. MK‐801 also produced a biphasic response in agranular motor cortex, whereby the low dose increased while the high dose decreased labeling. In addition, MK‐801 produced heterogeneous effects on regional cerebral metabolism in sensory cortices. Metabolic activity decreased in layer IV relative to layer Va following MK‐801 treatment in primary somatosensory (SI) and visual (VI) cortices, suggesting a shift in activity from afferent fibers innervating layer IV to those innervating layer Va. MK‐801 administration also decreased metabolic activity in granular SI relative to dysgranular SI and in VI relative to secondary visual cortex (VII), thus providing a relative sparing of activity in dysgranular SI and VII. Thus, the non‐competitive NMDA receptor antagonist suppressed activity form extrinsic neocortical sources, enhancing relative intracortical activity and stimulating limbic regions while the competitive NMDA antagonist depressed metabolic activity in all cortical regions. These selective laminar and regional changes in metabolic activity may be due to an enhanced susceptibility of certain cortical circuits to non‐competitive NMDA receptor antagonists.
Bursting response to current‐evoked depolarization in rat ca1 pyramidal neurons is correlated with lucifer yellow dye coupling but not with the presence of calbindin‐D28k
Authors: Baimbridge Kenneth G. , Peet Martin J. , McLennan Hugh , Church John
Published: December 2004

Calbindin‐D28k (CaBP) immunohistochemistry has been combined with electrophysiological recording and Lucifer Yellow (LY) Cell identification in the CA1 region of the rat hippocampal formation. CaBP is shown to be contained within a distinct sub‐population of CA1 pyramidal cells which is equivalent to the superficial layer described by Lorente de Nó (1934). The neurogenesis of these CaBP‐Positive neurons occurs 1–2 days later than the CaBP‐negative neurons in the deep pyramidal cell layer, as shown by 3H‐thymidine autoradiography. No correlation could be found between the presence or absence of CaBP and the type of electrophysiological response to current‐evoked depolarizing pulses. The latter could be separated into bursting or non‐bursting types and the bursting‐type response was nearly always found to be associated with the presence of LY dye coupling. Furthermore, when dye coupling involved three neurons, a characteristic pattern was observed which may represent the coupling of phenotypically identical neurons into distinct functional units within the CA1 pyramidal cell layer. In this particular casse the three neurons were all likely to be CaBP‐positive.
Neurophysiological maturation of cat caudate neurons: Evidence from in vitro studies
Authors: Cepeda Carlos , Walsh John P. , Buchwald Nathaniel A. , Levine Michael S.
Published: December 2004

The membrane properties and synaptic physiology of developing cat caudate (Cd) nucleus neurons were studied in in vitro slice preparations. Recordings were obtained from 98 cells in kittens from fetal day (F) 56 to postnatal day (P) 90. With increasing age, the following maturational changes occurred; resting membrane potentials became more negative, action potential rise times decreased, action potential amplitudes increased, and action potential durations and input resistances decreased. The frequency of occurrence of afterhyperpolarizations and of of anomalous rectification increased with age. The primary response to local extracellular stimulation was depolarization usually accompanied by an action potential. Evoked hyperpolarizing responses were seen after P28 but only occurred if the membrane was depolarized by intracellular current injection. Cells identified by intracellular injection of Lucifer yellow were primarily medium‐sized spiny neurons although it was not always possible to determine the cell type in slices from animals < P5. Somatic diameter, dendritic length, and spine density increased with age. Dye‐coupling occurred in slices < P20. Its frequency decreased with age. These results show that Cd neurons undergo significant maturation during late pernatal and early postnatal periods. In contrast, substantia nigra neurons mature more rapidly and should be capable of influencing the less mature Cd neurons during development (Walsh et al., Synapse, 7:291–300, 1991).
Modulation of Mg2+‐dependent [3H]TCP binding by L‐glutamate, glycine, and guanine nucleotides in rat cerebral cortex
Authors: Hori Takafumi , Yamamoto Toshifumi , Hatta Kotaro , Moroji Takashi
Published: December 2004

Biochemical and electrophysiological studies have demonstrated that phencyclidine (PCP) recognition site exists in the ion channel of the N‐methyl‐D‐aspartate (NMDA) receptor in ion channel complex. Using an extensively washed rat cortical membrane preparation, the effects of Mg2+ and guanylylimidodiphosphate (GppNHp) were examined on the binding of [3H]‐N‐[1‐(2‐thienyl)cyclohexyl]‐3, 4‐piperidine ([3H]TCP). Low concentrations of Mg2+ (EC50 = 11μM) stimulated [3H]TCP binding under the basal condition and high concentrations of Mg2+ (IC50 = 1 mM) inhibited it. In the presence of 10 μM L‐glutamate and 10 μM glycine, their EC50 values for Mg2+ enhancement of [3H]TCP binding were markedly reduced (to 1.9 μM or 8.4 μM), respectively. By contrast, the IC50 values for Mg2+ inhibition of [3H]TCP binding were reduced in the presence of L‐glutamate, but not glycine. Furthermore, a stimulatory effect of Mg2+ on [3H]TCP binding was additional to the [3H]TCP binding stimulated by a maximally effective concentration of L‐glutamate (10 μM) or glycine (10 μM). In the kinetic study, 300 μM Mg2+ produced an increase in the rates of both association and dissociation of [3H]TCP. Similar results were obtained with L‐glutamate (10 μM) and glycine (10 μM); 10 mM Mg2+ also caused an acceleration of the association rate but strongly decreased [3H]TCP binding at equilibrium. Compared with [3H]TCP binding under the basal condition, K+ (10 mM) alone decreased the maximal binding without producing any change in the association rate; 10 mM K+ also significantly decreased Mg2+ ‐stimulated [3H]TCP binding but caused no change no change in the acceleration of the association rate caused by Mg2+. At 100 μM, GppNHp resulted in a rightward shift in the Mg2+ dose–response curve of [3H]TCP binding to a high affinity site for Mg2+ under the basal condition and in the presence of glycine. The observations presented here strongly suggest that a Mg2+ recognition site with high affinity (a high affinity Mg2+ site) is distinct not only from the L‐glutamate and glycine binding sites but also from the Mg2+ recognition site with low affinity located in the ion channel and that the high affinity Mg2+ site may be associated with a GTP binding site.
Correlation of 125I‐LSD autoradiographic labeling with serotonin voltage clamp responses in Aplysia neurons
Authors: Evans Martyn L. , Kadan Michael J. , Hartig Paul R. , Carpenter David O.
Published: December 2004

Autoradiographic receptor binding studies using 125I‐LSD (2‐[125I]lysergic acid diethyamide) revealed intense labelling on the soma of a symmetrically located pair of cells in the abdominal ganglion of Aplysia californica. This binding was blocked by micromolar concentrations of serotonin and lower concentrations of the serotonergic antagonists, cyproheptadine and mianserin (Kadan and Hartig, 1988). Electrophysiological investigation of responses to serotonin of neurons in the left upper quadrant, where one of the labeled neurons is located, revealed a range of serotonin responses. Cells L3 and L6 have a K+ conductance increase in response to serotonin that is not blocked by cyproheptadine or mianserin. Cells L2 and L4 have a biphasic response to serotonin: a Na+ conductance increase, which can be blocked by cyproheptadine and mianserin, followed by a voltage dependent Ca2+ conductance which is blocked by Cs2+ but not the serotonergic antagonists. Cell L1, and its symmetrical pair, R1, have in addition to the Na+ and Ca2+ responses observed in L2 and L4, a Cl− conductance increase blocked by LSD, cyproheptadine and mianserin. LSD had little effect on the other responses. We conclude that the symmetrically located cells L1 and R1 have a Cl− channel linked to a cyproheptadine‐ and mianserin‐sensitive serotonin receptor that is selectively labelled by 125I‐LSD. This receptor has many properties in common with the mammalian serotonin 1C receptor.
Effects of serotonergic denervation on the density and plasticity of brain muscarinic receptors in the rat
Authors: Alonso Richard , Soubrie Philippe
Published: December 2004

This study investigated whether serotonergic lesion may affect density, sensitivity, and of muscarinic receptors in hippocampus and cerebral cortex. Intracerebroventricular injection of 5, 7‐dihydroxytryptamine (5, 7‐DHT) in rats produced a 90% reduction in cortical and hippocampal 5‐hydroxytryptamine (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) contents. In these brain areas, the 5, 7‐DHT lesion did not affect the overall density of muscarinic receptors or those of M1 and non‐M1 muscarinic receptor subtypes as assayed using [3H]N‐methylscopolamine ([3H]NMS), [3]pirenzepine, and [3H]NMS in the presence of pirenzepine, respectively. In addition, the binding of the muscarinic agonist [3H]oxotremorine‐M (OXO‐M), taken as an indirect index of coupling efficiency of non‐M1 receptors with G‐proteins, did not change significantly in cortex and hippocampus of 5, 7‐DHT‐lesione rats. Similarly, carbachol‐induced accumulation of [3H]inositol phosphates (InPs) in hippocampal miniprisms showed no significant differences between tissues from 5, 7‐DHT‐lesioned and sham‐operated rats. In sham‐operated rats, an intraperitoneal (i.p) injection of scopolamine (10 mg/kg once daily) during 21 days caused an increased density of [3H]NMS binding sites in cortex (+20%) and hippocampus (+26%). This up‐regulation was restricted to non‐M1 receptors subtypes. In 5, 7‐DHT‐lesioned rats, chronic scopolamine failed to modify significantly the density of cortical or hippocampal M1 or non‐M1 receptors. These results suggest (1) that 5‐HT denervation did not affect the density and sensitivity of muscarinic receptors and (2) that the ability of cortical and hippocampal non‐M1 receptors to up‐regulate following repeated injection of scopolamine requires the integrity of 5‐HT neurons terminating in these brain structures.
GABA depolarizes neurons in the rat striatum: An in vivo study
Authors: Mercuri Nicola Biagio , Calabresi Paolo , Stefani Alessandro , Stratta Francesca , Bernardi Giorgio
Published: December 2004

GABA, applied by iontophoresis to striatal neurons of the rat in an in vivo prepartion, depolarized the membrane potential and decreased the input resistance in a dose‐dependent manner. The null potential of the GABA depolarization was about –50 mV. In addition, a fading of the GABA‐induced response was observed for prolonged and relatively high amino acid application. We conclude that GABA has a depolarizing effect on striatal cells. This is in line with recent in vitro works describing a depolarizing effect of GABA in the rat neostriatum.
Rapid alteration of synaptic number and postsynaptic thickening length by NMDA: An electorn microscopic study in the occipital cortex of postnatral rats
Authors: Brooks William J. , Petit Ted L. , Leboutillier Janelle C. , Lo Robert
Published: December 2004

The N‐methyl‐D‐aspartate (NMDA) receptor has been widely implicated in numerous activity‐dependent models of neural plasticity, learning, and memory. The formation of new synapses is a major assumption of the neural basis of learning. The current research was conducted to determine whether NMDA receptor activation could induce synaptic formation and, if so, whether this ability would mirror developmental changes in NMDA receptors. Rats at various developmental ages were given a single intraperitoneal injection of NMDA and sacrificed at various brief postinjection intervals (0.5–2 hr). The rats showed an age‐dependent decline in the behavioral response to NMDA, as evidenced by reduced seizure activity and duration. Quantitative electron microscopic observations on the molecular layer of the occipital cortex, an area rich in NMDA receptors, revealed a transient increase in the length of postsynaptic thickenings in 17‐ and 35‐day‐old animals, appearing within 0.5 hr of injection. At 1 and 2 hr postinjection, an increase in synaptic density (number of synapses) was observed in 8‐day‐old animals. These results provide evidence that NMDA administration alone is capable of rapidly inducing alterations in synaptic structure and the formation of new synapses, underscoring the importance of the NMDA receptor in synaptogenesis and synaptic structural plasticity.
Age‐related remodeling of glutamic‐acid decarboxylase‐labeled elements in deafferented piriform cortex of rats
Authors: Nousek‐Goebl N. A. , Westrum L. E. , Wu J. ‐Y.
Published: December 2004

Olfactory bulb (OB) removal has been shown to result in plasticity in the piriform cortex (PC) that is age dependent. We are studying this phenomenon using immunoelectron microscopy of glutamic acid decarboxylase immunoreactivity (GAD, the enzymatic precursor for GABA) at selected postnatal ages and in adults with emphasis on short survival times of 4–7 days after OB ablation. Normally GAD‐labeled synaptic terminals form type II symmetric contacts from unlabeled dendrites and GAD‐labeled dendrites receive type I, asymmetric contacts from unlabeled terminals (Westenbroek, el al., 1988a). The OB lesion results in degenerating terminals with type I contacts onto unlabeled and onto GAD‐labeled dendrites. Type I postsynaptic sites may be seen partially contacted by or entirely devoid of degenerating terminals and occasionally may be apposed to variable degrees by normal unlabeled or by GAD‐positive terminals. Subsequently, some GAD‐labeled terminals may form asymmetric type I contacts usually with unlabeled dendrites and rarely with GAD‐labeled dendrites. The findings are most common in the youngest subjects and essentially absent in the adult subjects. A sequence of reinnervation of deafferented type I sites by GAD‐labeled terminals is suggested for the formation of this “atypical” synapse and the sequelae of this reorganization are discussed.
Olfactory deprivation increases dopamine D2 receptor density in the rat olfactory bulb
Authors: Guthrie K. M. , Pullara J. M. , Marshall J. F. , Leon M.
Published: December 2004

Unilateral olfactory deprivation during postnatal development results in significant anatomical and neurochemical changes in the deprived olfactory bulb. Perhaps the most dramatic neurochemical change is the loss of dopaminergic expression by neurons of the glomerular region. We describe here the effects of early olfactory deprivation on other elements of the bulb dopaminergic system, namely the dopamine receptors of the olfactory bulb. Rat pups had a single naris occluded on postnatal day 2 (PN2). On PN20 or PN60, animals were sacrificed and the bulbs were examined for catecholamine levels or D2 and D1 dopamine receptor binding. Receptor densities were quantified by in vitro autoradiography using the tritiated antagonists spiperone (D2) and SCH23390 (D1). Dopamine uptake sites were similarly examined using tritiated mazindol. No significant specific labeling of D1 or mazindol sites was observed in the olfactory bulbs of control or experimental animals at either age. Normal animals displayed prominent labeling of D2 sites in the glomerular and nerve layers. After 60 days of deprivation, deprived bulbs exhibited an average increase in D2 receptor density of 32%. As determined by Scatchard analysis, the mean values for Kd and Bmax were 0.134 nM and 293 fmol/mg protein in normal bulbs, and 0.136 nM and 403 fmol/mg protein in deprived bulbs. The results suggest that, as in the neostriatum, dopamine depletion in the olfactory bulb leads to an upregulation of D2 receptor sites. This change may represent an attempt by the system to adapt neurochemically to reduced dopaminergic activity and thereby maintain bulb function.