Use-dependent modification of a slow NMDA receptor-mediated synaptic potential in rat amygdalar slices

A single stimulus applied to the endopyriform nucleus evoked in 35 of the 101 basolateral amygdaloid (BLA) neurons a slow excitatory postsynaptic potential (s-EPSP) of varying latencies. The s-EPSP could be graded by changing the stimulus intensity and, on reaching the threshold, triggered action potentials. At stimulus intensity just subthreshold for evoking a spike, the s-EPSP has an average amplitude of 16.3 +/- 1.4 mV, a time to peak of 25.7 +/- 3.8 ms, and a duration of 124 +/- 14 ms. The s-EPSP was reversibly blocked by DL-2-amino-5-phosphonovaleate (DL-APV) or ketamine, indicating its mediation through N-methyl-D-aspartate (NMDA) receptor activation. However, the s-EPSP was not able to follow stimulus frequency of 1 Hz, suggesting that APV-sensitive s-EPSP is probably generated by a polysynaptic pathway. The s-EPSP was greatly enhanced by synaptic stimulation in the presence of bicuculline or in Mg(++)-free solution leading to the genesis of paroxysmal depolarizing shift (PDS). The s-EPSP can undergo robust long-term potentiation (LTP) following tetanic stimulation. These results suggest that the NMDA receptor-mediated s-EPSP may play an important role in epileptogenesis and synaptic plasticity in the amygdala.

Potential bile acid metabolites. 19. The epimeric 3 alpha,6,7 beta-trihydroxy- and 3 alpha,6,7 beta,12 alpha-tetrahydroxy-5 alpha-cholanoic acids

Syntheses by a new procedure of the known 3 alpha,6 alpha,7 beta- and 3 alpha,6 beta,7 beta-trihydroxy-5 alpha-cholanoic acids, and of the once-reported analog 3 alpha,6 alpha,7 beta,12 alpha-, as well as the new 3 alpha,6 beta,7 beta,12 alpha-tetrahydroxy-5 alpha-cholanoic acids, are described. Key intermediates of the syntheses are the 6-oxo-7 beta-ols of the respective 5 alpha-cholanoic acids (and their methyl esters) prepared by allomerization at C-5 of appropriate 6-bromo-7-oxo derivatives of the corresponding 5 beta-acids. Successful reduction of the 6,7-ketols to the desired products depended on the proper choice of reagents, either Zn(BH4)2 or Li/NH3/MeOH.

Long-term enhancement of EPSP and NMDA receptor-mediated synaptic transmission in the amygdala

An in vitro slice preparation of rat amygdala was used to study the long-term modifications of synaptic efficacy following high-frequency stimulation of the ventral endopyriform nucleus. Delivery of brief tetani to the afferent fibers led to a long-term potentiation (LTP) of the amplitude and the initial slope of excitatory postsynaptic potential (EPSP). Pretreatment the slices with DL-2-amino-5-phosphonovaleate (DL-APV, 50 microM) blocked the induction of LTP, indicating that N-methyl-D-aspartate (NMDA) receptor activation is required for induction. NMDA receptor-mediated component of synaptic response (EPSPNMDA) was isolated by application of a solution containing 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX, 10 microM) and bicuculline (20 microM). Tetanic stimulation led to a lasting potentiation of the EPSPNMDA. These results suggest that brief repetitive stimulation of afferent pathway produces forms of LTP that share many properties of LTP seen in the CA1 region of the hippocampus.

Pharamacological characterization of excitaory synaptic potentials in rat basolateral amygdaloid neurons

The pharmacological properties of synaptic responses in rat basolateral amygdaloid (BLA) neurons were studied using intracellular recording techniques. Three distinct types of synaptic potential were evoked by stimulation of the adjacent ventral endopyriform nucleus: 1) a fast excitatory postsynaptic potential (f-EPSP); 2) a late EPSP (1-EPSP) following the f-EPSP; and 3) a multiphasic hyperpolarization following the initial depolarizing potential. Superfusion of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a selective non-N-methyl-D-aspartate (non-NMDA) receptor antagonist, blocked the f-EPSP in a concentration-dependent manner. The ED50 for this effect was around 4 microM. In the presence of CNQX, however, a small depolarizing potential remained. This residual depolarizing component was markedly enhanced on removing Mg++ from the perfusing medium and could subsequently be abolished by DL-2-amino-5-phosphonovaleate (DL-APV, 50 microM) indicating its mediation via NMDA receptor-coupled ionophore. The l-EPSP was reversibly blocked by DL-APV. These results suggest that the pyriform cortex-amygdala pathway is mediated through excitatory amino acids acting on non-NMDA as well as NMDA receptors located on the BLA neurons.

Modification of medullary respiratory-related discharge patterns by behaviors and states of arousal

The modulatory influences of behaviors and states of arousal on bulbar respiratory-related unit (RRU) discharge patterns were studied in an unanesthetized, freely behaving guinea pig respiratory model system. When fully instrumented, this model system permits concurrent monitoring and recording of (i) single units from either Bötzinger complex or nucleus para-ambiguus; (ii) electrocorticogram; and, (iii) diaphragmatic EMG. In addition to being used in surveys of RRU discharge patterns in freely behaving states, the model system also offered a unique opportunity in investigating the effects of pentobarbital on RRU discharge patterns before, throughout the course of, and during recovery from anesthesia. In anesthetized preparations, a particular RRU discharge pattern (such as tonic, incrementing or decrementing) typically displayed little, if any notable variation. The most striking development following pentobarbital was a state of progressive bradypnea attributable to a significantly augmented RRU cycle duration, burst duration and an increase in the RRU spike frequencies during anesthesia. In freely behaving states, medullary RRU activities rarely adhered to a fixed, immutable discharge pattern. More specifically, the temporal organization (such as burst duration, cycle duration, and the extent of modulation of within-burst spike frequencies) of RRU discharge patterns regularly showed complex and striking variations, not only with states of arousal (sleep/wakefulness, anesthesia) but also with discrete alterations in electrocorticogram (ECoG) activities and a multitude of on-going behavioral repertoires such as volitional movement, postural modification, phonation, mastication, deglutition, sniffing/exploratory behavior, alerting/startle reflexes. Only during sleep, and on occasions when the animal assumed a motionless, resting posture, could burst patterns of relatively invariable periodicity and uniform temporal attributes be observed. RRU activities during sniffing reflex is worthy of further note in that, based on power spectrum analyses of concurrently recorded ECoG activities, this particular discharge pattern was clearly associated with the activation of a 6-10 Hz theta rhythm. These findings indicated that bulbar RRU activity patterns are subject to change by not only behaviors and sleep/wakefulness cycles, but also a variety of modulatory influences and feedback/feedforward biases from other central and peripheral physiological control mechanisms.

Preparation of glycine-conjugated bile acids and their gas/liquid chromatographic analysis on an aluminum-clad flexible fused silica capillary column

This paper describes a method for the direct gas/liquid chromatographic (GC) analysis of 46 glycine-conjugated bile acids, which differ from one another in the number, position and configuration of the hydroxyl groups at positions C-2, C-3, C-4, C-6, C-7 and/or C-12. Free bile acids were converted quantitatively on a micro scale to ethyl ester-trimethylsilyl (Et-TMS) and methyl ester-dimethylethylsilyl (Me-DMES) ether derivatives of the corresponding glycine conjugates. The Et-TMS and Me-DMES ethers of the glycine conjugates were chromatographed on an aluminum-clad flexible fused silica capillary column coated with a thin film (0.1 micron) of chemically bonded and cross-linked methylpolysiloxane. Relative retention time (RRT) and methylene unit (MU) values were determined for the 46 compounds and their GC behaviour was discussed. The derivatization procedure and the retention data would be useful for the direct GC identification of unknown glycine-conjugated bile acid mixtures extracted from biological samples.

Bursting discharges in disinhibited amygdala slices: the role of excitatory amino acid receptors

The involvement of N-methyl-D-aspartate (NMDA) and non-NMDA receptors in the epileptiform activity, induced by bicuculline, was studied in slices of amygdala in the rat, using intracellular recording techniques. Stimulation of the ventral endopyriform nucleus evoked an excitatory postsynaptic potential (EPSP). After exposure to bicuculline (20 microM), the same stimulus evoked burst firing. Occasionally, spontaneous bursts similar in waveform to synaptically triggered bursts also occurred in disinhibited slices. Superfusion of DL-2-amino-5-phosphonovalerate (DL-APV, 50 microM) or 3-((+)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acids (CPP, 10 microM), rapidly blocked the late component of the paroxysmal depolarizing shift. The spontaneous and evoked bursts were never completely abolished in the presence of DL-APV or CPP. These results suggest that NMDA receptors may contribute to but are not required for the generation of these bursts. In contrast, application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) largely abolished the bursts, indicating that activation of non-NMDA receptors is of primary importance in this model of epilepsy.

Ketamine suppresses synchronized discharges in the disinhibited amygdala slice

The effect of ketamine on the paroxysmal depolarizing shift (PDS) induced by bicuculline was studied in rat amygdala slices using intracellular recording techniques. Stimulation of the ventral endopyriform nucleus evoked an excitatory postsynaptic potential (EPSP). After exposure to bicuculline (20 microM), the same stimulus intensity evoked burst firing. Superfusion of ketamine reversibly reduced the duration of PDS. Pretreatment of amygdala slices with DL-2-amino-5-phosphonovaleate (DL-APV, 50 microM) occluded the effect of ketamine suggesting that ketamine shortened the burst duration via its blocking action on the NMDA receptors. In all neurons tested, a large depolarizing shift remained in the presence of ketamine. The ketamine-resistant component was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 8 microM) indicating its mediation by the non-NMDA receptors.

Potential bile acid metabolites. XVIII. Synthesis of stereoisomeric 3,6,12 alpha-trihydroxy-5 beta-cholanoic acids

Two new 6-hydroxylated bile acids, 3 beta, 6 alpha, 12 alpha- and 3 beta, 6 beta, 12 alpha-trihydroxy-5 beta-cholanoic acids, were synthesized from deoxycholic acid. In addition, their C-3 epimers, 3 alpha, 6 alpha, 12 alpha- and 3 alpha, 6 beta, 12 alpha-trihydroxy acids, were prepared by a new route. The principal reactions used were 1) 6 beta-hydroxylation of 3-methoxy-3,5-dienes with m-chloroperbenzoic acid in aqueous dioxane; 2) catalytic hydrogenation of the resulting 6 beta-hydroxy-3-oxo-4-enes to the 6 beta-hydroxy-3-oxo-5 beta compounds with palladium on calcium carbonate catalyst in ethanol; and 3) stereoselective reduction of appropriate 3-oxo derivatives with potassium tri-sec-butylborohydride and tert-butylamine-borane complex. The thin-layer chromatographic, gas-liquid chromatographic, and high performance liquid chromatographic mobilities, and 1H- and 13C-nuclear magnetic resonance spectroscopic data of the four stereoisomers are presented. With this work all the 6-hydroxylated derivatives of lithocholic, deoxycholic, chenodeoxycholic, ursodeoxycholic, and cholic acids in the 5 beta series are now known and have been synthesized.

Potential bile acid metabolites. 17. Synthesis of 2 beta-hydroxylated bile acids

The 2 beta-hydroxylated derivatives of lithocholic, chenodeoxycholic, deoxycholic, and cholic acids were synthesized from the respective parent bile acids by established procedures. The principal reactions involved were (1) bromination of 3-oxo formylated bile acids in N,N-dimethylformamide, (2) rearrangement and substitution of the resulting 4 beta-bromo-3-oxo derivatives to the 2 beta-acetoxy-3-oxo compounds with potassium acetate, and (3) reduction to the 2 beta-acetoxy-3 alpha-hydroxy compounds with tert-butylamine-borane complex. As for the prepared 2 beta-hydroxylated bile acids with a diequatorial trans-glycol structure, proton and carbon-13 nuclear magnetic resonance spectroscopic and gas-liquid chromatographic/mass spectrometric properties are discussed.

Characterization of a monoclonal antibody (RJ5) against the immunodominant 41-kD antigen of Candida albicans

A 41-kD component of Candida albicans was identified to be the major antigen radioimmunoprecipitated by antibodies with increased titers in the sera of patients with invasive candidiasis. A mouse monoclonal antibody (RJ5) was generated which, by immunoblotting, showed positive reactivity to the immunoprecipitated 41-kD component. By two-dimensional gel electrophoresis and immunoblotting, MoAb RJ5 was shown to react with different isoforms of the 41-kD component with pI values from 6.1 to 6.9. Furthermore, MoAb RJ5 showed positive reactivity to cytoplasmic antigens of C. albicans by frozen section and immunoperoxidase staining. By SDS-polyacrylamide gel electrophoresis and immunoblotting, MoAb RJ5 showed no cross-reactivity to antigens of Candida tropicalis and Candida parapsilosis. The epitope of the 41-kD molecule recognized by MoAb RJ5 was susceptible to treatment of proteinase K at concentrations of greater than or equal to 5 micrograms/ml, and was relatively resistant to periodate oxidation with concentration of NaIO4 up to 20 mM. This MoAb may be useful in the purification and characterization of the immunodominant 41-kD antigen of C. albicans, and as a probe in the detection of Candida antigens in the sera of patients with invasive candidiasis.

Effects of pentobarbital on respiratory functional dynamics in chronically instrumented guinea pigs

Respiratory effects of sodium pentobarbital (35 mg/kg; IP) were studied in guinea pigs chronically instrumented to permit concurrent recordings of bulbar respiratory-related units (RRUs), diaphragmatic electromyogram (DEMG), and electrocorticogram (ECoG). RRU activities were recorded from either the Bötzinger Complex (BOT; expiratory) or Nucleus para-Ambiguus (NpA; inspiratory). Pentobarbital-induced changes in respiratory-related activities were evaluated before, throughout the course of, and during recovery from, anesthesia. The most notable development following pentobarbital was a state of progressive bradypnea which was accompanied by a variety of complex changes in the amplitude and temporal attributes of RRU, DEMG and ECoG activities. As anesthetic effects progressed, the activity profiles of both BOT and NpA units underwent striking transformations from a behavioral and state-dependent wakefulness pattern to an activity profile characterized by i) a significantly augmented RRU cycle duration, burst duration and spike frequency; and, ii) an alteration to the pattern of within-burst spike frequency modulation. Along with changes in RRU activity, pentobarbital also produced a marked attenuation of the amplitudes of diaphragmatic activity as well as a discrete, time-dependent alteration in the amplitude and spectral characters of ECoG activities. Differences in BOT and NpA unit responses to alveolar CO2 loading (ramp; 2% and 5%) across wakefulness and anesthesia states were also considerable. In addition to a depressed responsiveness to CO2, the temporal attributes of BOT and NpA activity profiles also indicated an asymmetrical change under pentobarbital anesthesia. Taken together, these findings indicate that pentobarbital causes not only a fundamental alteration in bulbar rhythmogenic mechanisms, but also a differential influence on bulbar respiratory system components that are involved in the definition of the shape and the amplitude of central respiratory drive. In conclusion, this study offers, for the first time, direct evidence from physiologically and structurally intact preparations that the functional dynamics of respiratory system components are profoundly altered during pentobarbital anesthesia.

Potential bile acid metabolites. 16. Synthesis of stereoisomeric 3 alpha,6,7,12 alpha-tetrahydroxy-5 beta-cholanoic acids

New synthetic routes to the four possible stereoisomeric 3 alpha,6,7,12 alpha-tetrahydroxy-5 beta-cholanoic acids (and their methyl esters), one of which (3 alpha,6 alpha 7 beta,12 alpha) is new, and some related compounds are described. In addition, the 5 alpha-epimer of the new acid was obtained. The final products were obtained in high purity for use as reference compounds in the analysis of bile acids in human biologic samples. The results of analysis of the prepared stereoisomers by proton and carbon 13 nuclear magnetic resonance spectroscopies are briefly discussed along with the thin-layer and gas-liquid chromatographic properties.

Respiratory and cardiovascular effects of tetrodotoxin in urethane-anesthetized guinea pigs

Cardiorespiratory effects of tetrodotoxin (TTX) (15 micrograms/kg, i.p.) were investigated in urethane-anesthetized guinea pigs acutely instrumented for the recording of medullary respiratory-related units (RRUs), diaphragm electromyogram (DEMG), electrocorticogram (ECoG), electrocardiogram (ECG), blood pressure (BP), endtidal CO2, and arterial O2 and CO2. Respiratory system responses showed a hyperventilatory profile during the initial stage of intoxication. This was followed by an abrupt onset of a progressive decrease in the respiratory frequency, and a respiratory rate depression-related respiratory failure. The average time to TTX-induced respiratory arrest and death was 10.3 +/- 4.2 min. Concurrently recorded inspiratory and expiratory RRU activities indicated that respiration invariably failed in an end-expiratory position as manifested by a sustained period of expiratory RRU discharge. The progressive rate depression prior to respiratory arrest was temporally correlated only to a concomitantly augmenting expiratory RRU discharge duration. Inspiratory RRU discharge duration, on the other hand, did not display any significant change throughout the course of intoxication. The asymmetry in RRU response patterns indicates either an expiratory network component's particular sensitivity to perturbation by TTX or a dissociative trend in some bulbar respiratory rhythmogenic mechanisms. Peripheral cardiorespiratory changes were also quite profound. These included a gradual and steadfast decline in BP, a steadily decreasing amplitude in DEMG oscillations, and a state of progressive hypercapnia and hypoxemia. Changes in heart rate and ECG waveform attributes prior to respiratory arrest were not appreciable. In conclusion, in addition to a variety of TTX-induced peripheral cardiorespiratory effects, findings from this study have revealed a central respiratory system component that appears to show an unusual sensitivity to perturbation by TTX. The significance of this unique phenomenon as it relates to the nature and extent of TTX-induced central respiratory depression is discussed.

Epileptiform activity induced by 4-aminopyridine in rat amygdala neurons: the involvement of N-methyl-D-aspartate receptors

The involvement of the N-methyl-D-aspartate (NMDA) receptor in the epileptiform activity induced by 4-aminopyridine (4-AP) was studied in rat amygdala slices using intracellular recording techniques. Stimulation of the ventral endopyriform nucleus evoked an excitatory postsynaptic potential (EPSP). After exposure to 4-AP (200 microM) the amygdala slices usually exhibited spontaneous and evoked epileptiform activity. The epileptiform events had an average duration of 522 +/- 78 ms with a frequency of 0.5-8.5 bursts/min. Superfusion of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a selective non-NMDA receptor antagonist, practically abolished the epileptiform bursting. However, there remained a residual depolarizing component in 13 out of 18 neurons. This CNQX-resistant component was markedly enhanced both in amplitude and duration when extracellular Mg2+ was removed and could be reversibly blocked by the specific NMDA receptor antagonist, DL-2-amino-5-phosphonovaleate (DL-APV). Compared with the CNQX-sensitive component, the APV-sensitive component had a much smaller amplitude shorter duration. These data suggest that the NMDA receptor is likely to play only a minor role, and activation of the NMDA receptor may contribute to but is not required, for the generation of these bursts.

Neurophysiological concomitants of soman-induced respiratory depression in awake, behaving guinea pigs

Soman-induced respiratory failure was investigated in awake, behaving guinea pigs chronically instrumented to allow concurrent recordings of medullary respiratory-related unit (RRU) activity, diaphragm electromyogram (DEMG), and electrocorticogram. Responses to soman typically began with hyperpnea. Loss of consciousness, as indicated by the development of seizure activities, took place shortly after the onset of hyperpnea. This was followed by dyspnea, hypopnea, and finally, respiratory failure. The most profound respiratory dysfunctions were seen during the development of dyspnea characterized by a progressively degenerative RRU-DEMG phase relationship (phase anomalies) and mixed patterns of ataxic breathing. Electrophysiographic records indicated that the anomalous RRU-DEMG phase phenomenon is attributable to a state of functional dissociation in some brainstem mechanisms that are normally involved in the orchestration of a synchronous respiratory drive. The failure of bulbar rhythmogenic mechanisms to maintain an orderly and synchronous recruitment of respiratory drive, which led to untimely and chaotic activations of respiratory muscles, was apparently the underlying cause of various ataxic breathing patterns and a reduced ventilatory efficiency. Spectral analyses of DEMG activities showed that, despite episodic muscle fasciculations and signs of fatigue, the functional integrity of the diaphragm was not significantly compromised by soman at a dose sufficient to produce respiratory failure. These findings not only support the notion of a relatively more important involvement of central respiratory mechanisms in soman-induced respiratory failure, but also identify a state of functional dissociation of central respiratory timing mechanisms as being a significant component in soman intoxication.

Potential bile acid metabolites. XV. Synthesis of 4 beta-hydroxylated bile acids; unique bile acids in human fetal bile

The 4 beta-hydroxylated derivatives of lithocholic, deoxycholic, chenodeoxycholic, and cholic acids were synthesized from their respective parent compounds. The principal reactions employed were 1) beta-face cis-dihydroxylation of delta 3 intermediates with osmium tetroxide-N-methylmorpholine N-oxide, 2) selective cathylation of vicinal 3 beta,4 beta-diols followed by oxidation of the resulting 4 beta-monocathylates, or direct selective oxidation at C-3 of 3 beta,4 beta-diols with pyridinium chlorochromate, and 3) stereoselective reduction of the 3-oxo compounds with tert-butylamine-borane complex. The results of analysis of the prepared 4 beta-hydroxylated bile acids with a diequatorial trans-glycol structure and their 3 beta-epimers by proton and carbon-13 nuclear magnetic resonance spectroscopies are briefly discussed along with the mass spectrometric properties.