Short-term synaptic plasticity at the main and vomeronasal olfactory receptor to mitral cell synapse in frog.

Synaptic responses resulting from stimulation of the main olfactory and vomeronasal (VN) nerves were measured in main and accessory olfactory bulb (AOB) of frog, Rana pipiens, to test the hypothesis that properties of these synapses would reflect the distinct differences in the time course of odour delivery to each of these olfactory structures. Paired-pulse depression dominated responses to repetitive stimulation of the main olfactory nerve for interstimulus intervals (ISI) up to several seconds. Inhibition of voltage-gated Ca(2+) channels by GABAb receptors contributes significantly to this inhibition of transmitter release, particularly for ISI > 0.5 s. In contrast, the monosynaptic connection between VN sensory neurons and mitral cells in the AOB showed enhancement with pairs or short trains of stimuli for ISI of 0.5 to > 10 s. A small inhibitory effect of GABAb receptors on presynaptic Ca(2+) influx and release was only evident when a large proportion of the VN axons were stimulated simultaneously but even with inhibition present an overall enhancement of release was observed. Increasing the number of conditioning stimuli from one to five increased residual [Ca(2+)] and enhancement but a direct correlation between residual [Ca(2+)] and either the magnitude or the time course of enhancement was not observed. Enhanced transmitter release from VN afferent terminals results in effective integration of sustained low-frequency activity, which may play a role in the detection of low-intensity odourant stimuli by the VN system.

Ca2+ accumulations in dendrites of neocortical pyramidal neurons: an apical band and evidence for two functional compartments.

Apical dendrites constitute a prominent feature of the microcircuitry in the neocortex, yet their function is poorly understood. Using fura-2 imaging of layer 5 pyramidal neurons from slices of rat somatosensory cortex, we have investigated the Ca2+ influx into dendrites under intracellular, antidromic, synaptic, and receptor-agonist stimulation. We find three spatial patterns of Ca2+ accumulations: an apical band in the apical dendrite approximately 500 microns from the soma, an accumulation restricted to the basal dendrites, soma, and proximal apical dendrite, and a combination of both of these. We show that the apical band can be activated antidromically and synaptically and that, under blocked Na+ and K+ conductances, it generates Ca2+ spikes. Thus, the apical band may serve as a dendritic trigger zone for regenerative Ca2+ spikes or as a current amplifier for distal synaptic events. Our results suggest that the distal apical dendrite should be considered a separate functional compartment from the rest of the cell.

Changes in juvenile coho salmon electro-olfactogram during and after short-term exposure to current-use pesticides.

For anadromous salmonids, olfaction is a critical sense, enabling return migration. In recent years, several pesticides have been identified that interfere with salmonid olfaction at concentrations in the microg/L range; thus, they may pose a risk to species longevity. In the present study, we investigated the acute effects of five agricultural pesticides on juvenile coho salmon (Oncorhynchus kisutch) olfaction using the electro-olfactogram (EOG), a measure of odorant-evoked field potentials. Electro-olfactogram responses to the odorant L-serine were measured during and following a 30-min exposure of the left olfactory rosette to chlorothalonil, endosulfan, glyphosate acid, iodocarb (IPBC), trifluralin, and 2,4-dichlorophenoxyacetic acid. With the relatively insoluble pesticides endosulfan and trifluralin, decreases in EOG amplitude were only apparent at relatively high concentrations (100 and 300 microg/L, respectively) following 20 min of exposure and were absent for chlorothalonil (1 mg/L). With the water-soluble herbicide glyphosate, significant EOG reductions occurred within 10 min of exposure to 1 mg/L and more rapidly with higher concentrations. Recovery of EOG post-glyphosate exposure was concentration-dependent, and complete recovery was not observed with some concentrations at 60 min postexposure. Dichlorophenoxyacetic acid only affected EOG at high concentration (100 mg/L), where it eliminated EOG within 2 min of exposure. With IPBC, EOG was decreased at 25 min of exposure to 1 microg/L; higher concentrations caused decreases to occur more rapidly. Excluding IPBC and glyphosate, all EOG reductions occurred at concentrations greater than the current Canadian water-quality guidelines and reported 96-h lethality values. Our results show that olfactory neurons can be impaired rapidly by some current-use pesticides, even at exposures in the low-microg/L range.

Distributed representation of vibrissa movement in the upper layers of somatosensory cortex revealed with voltage-sensitive dyes.

We have identified large-scale patterns of electrical activity in circuits that occur in response to stimulation of peripheral receptors. Our focus was on primary (S1) vibrissal cortex of anesthetized rat, and we used optical techniques in conjunction with voltage-sensitive dyes to measure depolarization of the upper layers of cortex. Displacement of one vibrissa produced a field of activity that extends over very many cortical columns in S1. There are multiple, focal maxima within this field. A global maximum is located near the center of the field of activity, and, as determined electrically and histologically, this site maps to the cortical column appropriate for the deflected vibrissa. The amplitude of this component attains a steady-state value under continuous stimulation. Additional temporal characteristics are revealed by the response to a single displacement; the signal was triphasic and began with a prompt depolarization that was followed by a transient phase of inhibition and a final phase of long-lasting depolarization. The somatotopy of the other, satellite maxima in the field of activity were established through the reconstruction of the fields of activity produced by individual stimulation of other vibrissae. Local maxima for one vibrissa were seen to overlie the global maximum found for stimulation of nearest- and next-nearest-neighbor vibrissae. In contrast to the amplitude of the global maxima, the amplitude associated with the local maxima was not maintained with either continuous or infrequent but repetitive stimulation. Finally, the field of activity induced by alternate deflection of two neighboring vibrissae was suppressed in amplitude in comparison to the summed amplitudes of the signals elicited by deflection of each vibrissa alone. We suggest that these patterns of activity are a manifestation of the dynamic interaction among neighboring cortical columns.

Mitral cell presynaptic Ca(2+) influx and synaptic transmission in frog amygdala.

Dextran-conjugated Ca(2+) indicators were injected into the accessory olfactory bulb of frogs in vivo to selectively fill presynaptic terminals of mitral cells at their termination in the ipsilateral amygdala. After one to three days of uptake and transport, the forebrain hemisphere anterior to the tectum was removed and maintained in vitro for simultaneous electrophysiological and optical measurements. Ca(2+) influx into these terminals was compared to synaptic transmission between mitral cells and amygdala neurons under conditions of reduced Ca(2+) influx resulting from reduced extracellular [Ca(2+)], blockade of N- and P/Q-type channels, and application of the cholinergic agonist carbachol. Reducing extracellular [Ca(2+)] had a non-linear effect on release; release was proportional to Ca(2+) influx raised to the power of approximately 3.6, as observed at numerous other synapses. The N-type Ca(2+) channel blocker, omega-conotoxin-GVIA (1 microM), blocked 77% of Ca(2+) influx and 88% of the postsynaptic field potential. The P/Q-type Ca(2+) channel blocker, omega-agatoxin-IVA (200 nM), blocked 19% of Ca(2+) influx and 25% of the postsynaptic field, while the two toxins combined to block 92% of Ca(2+) influx and 97% of the postsynaptic field. The relationship between toxin blockade of Ca(2+) influx and synaptic transmission was therefore only slightly non-linear; release was proportional to Ca(2+) influx raised to the power approximately 1.4. Carbachol (100 microM) acting via muscarinic receptors had no effect on the afferent volley, but rapidly and reversibly reduced Ca(2+) influx through both N- and P/Q-type channels by 51% and postsynaptic responses by 78%, i.e. release was proportional to Ca(2+) raised to the power approximately 2.5. The weak dependence of release on changes in Ca(2+) when channel toxins block channels suggests little overlap between Ca(2+) microdomains from channels supporting release or substantial segregation of channel subtypes between terminals. The proportionately greater reduction of transmission by muscarinic receptors compared to Ca(2+) channel toxins suggests that they directly affect the release machinery in addition to reducing Ca(2+) influx.

Presynaptic calcium in transmitter release and posttetanic potentiation.

This review gives some indication of the progress that has been made in understanding synaptic transmission by use of new methods for measuring and controlling presynaptic [Ca2+]i. Many unsolved problems remain. We still do not have a clear idea of the exact relationship between [Ca2+]i and transmitter release and whether this relationship is the same under all circumstances. The apparently different [Ca2+]i-dependence of evoked transmitter release and of PTP suggest multiple molecular sites of calcium action that remain to be identified. A complete and comprehensive model of transmitter release has yet to be devised, and questions raised by our experiments may indicate that it is still too early to try to construct a precise model. We also do not know just how serotonin acts to modulate transmitter release, only that it does not appear to alter either resting or entering calcium. Some of these questions may be approachable with the techniques described here; others are not and require different methods for their resolution. The work continues.

An in vitro preparation of frog nose and brain for the study of odour-evoked oscillatory activity.

An in vitro preparation is described that consists of frog brain rostral to the brainstem connected to the nasal epithelium by the olfactory nerves. Field potential and intracellular recordings from various brain structures can be obtained while stimulating the nasal epithelium with air-borne odours for at least 12 h after removal of the brain. Power spectra, amplitude and duration of odour-evoked and spontaneous field potentials in vitro are similar to those obtained from paralyzed, spinal cord pithed frogs. A brief puff of odorant applied to the olfactory epithelium produces a 1-2 s bout of 7-13 Hz oscillations in the field potential recorded from the ipsilateral bulb and various ventral, lateral and medial telencephalic structures. Odour evoked bulbar oscillations are maintained after removal of the telencephalon. Electrical stimulation of the olfactory nerves will not elicit oscillations like those evoked by odour stimulation. High-pressure puffs of non-odorised, moist air, elicit olfactory bulb oscillations similar to those evoked by lower pressure puffs of odorised air. Intracellular recordings from most mitral cells reveal oscillations in membrane potential that are phase-locked to the field potential. The extent to which these phase-locked oscillations produce action potentials varies, apparently as a function of the strength and duration of a long-lasting inhibitory potential that is superimposed upon the 7-13 Hz oscillations. This preparation is well-suited for the study of the cellular basis of oscillatory activity in vertebrate brain, and the function of sensory-evoked oscillatory responses in processing of sensory information.

Anatomical and functional imaging of neurons using 2-photon laser scanning microscopy.

Light scattering by brain tissue and phototoxicity are major obstacles to the use of high-resolution optical imaging and photo-activation ('uncaging') of bioactive compounds from inactive ('caged') precursors in intact and semi-intact nervous systems. Optical methods based on 2-photon excitation promise to reduce these obstacles (Denk, 1994; Denk et al., 1990, 1994). Here we show a range of imaging modes based on 2-photon laser scanning microscopy (TPLSM) as applicable to problems in neuroscience. Fluorescence images were taken of neurons labeled with ion-sensitive and voltage-sensitive dyes in invertebrate ganglia, mammalian brain slices, and from the intact mammalian brain. Scanning photochemical images with whole-cell current detection (Denk, 1994) show how the distribution of neurotransmitter receptors on the surface of specific cells can be mapped. All images show strong optical sectioning and usable images can be obtained at depths greater than 100 microns below the surface of the preparation.

Neuromodulation of activity-dependent synaptic enhancement at crayfish neuromuscular junction.

Action potential-evoked transmitter release is enhanced for many seconds after moderate-frequency stimulation (e.g. 15 Hz for 30 s) at the excitor motorneuron synapse of the crayfish dactyl opener muscle. Beginning about 1.5 s after a train, activity-dependent synaptic enhancement (ADSE) is dominated by a process termed augmentation (G.D. Bittner, D.A. Baxter, Synaptic plasticity at crayfish neuromuscular junctions: facilitation and augmentation, Synapse 7 (1991) 235-243'[4]; K.L. Magleby, Short-term changes in synaptic efficacy, in: G.M. Edelman, L.E. Gall, C.W. Maxwell (Eds.), Synaptic Function, John Wiley and Sons, New York, 1987, pp. 21-56; K.L. Magleby; J.E. Zengel, Augmentation: a process that acts to increase transmitter release at the frog neuromuscular junction, J. Physiol. (Lond.) 257 (1976) 449-470) which decays approximately exponentially with a time constant of about 10 s at 16 degrees C, reflecting the removal of Ca2+ which accumulates during the train in presynaptic terminals (K.R. Delaney, D.W. Tank, R.S. Zucker, Serotonin-mediated enhancement of transmission at crayfish neuromuscular junction is independent of changes in calcium, J. Neurosci. 11 (1991) 2631-2643). Serotonin (5-HT, 1 microM) increases evoked and spontaneous transmitter release several-fold (D. Dixon, H.L. Atwood, Crayfish motor nerve terminal's response to serotonin examined by intracellular microelectrode, J. Neurobiol. 16 (1985) 409-424; J. Dudel, Modulation of quantal synaptic release by serotonin and forskolin in crayfish motor nerve terminals, in: Modulation of Synaptic Transmission and Plasticity in Nervous Systems, G. Hertting, H.-C. Spatz (Eds.), Springer-Verlag, Berlin, 1988; S. Glusman, E.A. Kravitz. The action of serotonin on excitatory nerve terminals in lobster nerve-muscle preparations, J. Physiol. (Lond.) 325 (1982) 223-241). We found that ADSE persists about 2-3 times longer after moderate-frequency presynaptic stimulation in the presence of 5-HT. This slowing of the decay of ADSE by 5-HT was not accompanied by significant changes in the initial amplitude of activity-dependent components of enhancement 1.5 s after the train. Measurements of presynaptic [Ca2+] indicated that the time course of Ca2+ removal from the presynaptic terminals after trains was not altered by 5-HT. Changes in presynaptic action potential shape, resting membrane potential or postsynaptic impedance after trains cannot account for slower recovery of ADSE. Axonal injection of EDTA slows the removal of residual Ca2+ and the decay of synaptic augmentation after trains of action potentials (K.R. Delaney, D.W. Tank, A quantitative measure of the dependence of short-term synaptic enhancement on presynaptic residual calcium, J. Neurosci. 14 (1994) 5885-5902), but has little or no effect on the 5-HT-induced persistence of ADSE. This also suggests that the time course of ADSE in the presence of 5-HT is not determined primarily by residual Ca2+ removal kinetics. The slowing of ADSE recovery after trains by 5-HT reverses with washing in 5-HT-free saline along with the 5-HT-mediated enhancement of release.

Impacts of carbamate pesticides on olfactory neurophysiology and cholinesterase activity in coho salmon (Oncorhynchus kisutch).

Many freshwater aquatic environments in the Pacific Northwest of North America contain neurotoxic pesticides, an issue of concern given the use of many of these habitats by Pacific salmon (Oncorhynchus sp.). Pesticides such as carbamates are known to affect fundamental physiological systems (such as the enzyme acetylcholinesterase (AChE)), and have been shown to affect salmonid olfactory-mediated behaviors. A neurophysiological measure of olfactory function, the electro-olfactogram (EOG), was used in this study to examine the impacts of acute localized exposure to three carbamates (the insecticide carbofuran, the antisapstain IPBC, and the fungicide mancozeb) on olfactory function in the coho salmon (Oncorhynchus kisutch). We also examine the potential for these pesticides to alter AChE levels in the primary olfactory system and brain with brief exposures (30 min to only the olfactory rosette (OR)). In results, we find that the EOG in coho salmon is highly sensitive to brief localized exposures of two of these three carbamate pesticides. The effective nominal concentration required to cause a 50% reduction in EOG amplitude (EC50) for carbofuran was 10.4 microg/l and for IPBC was 1.28 microg/l. For mancozeb, the EC50 was higher at 2.05 mg/l. All three carbamates also affected AChE activity levels in the OR and brain (BR): carbofuran exposure at 200 microg/l significantly inhibited AChE activity in the OR, and both IPBC and mancozeb significantly increased AChE activity in BR at multiple concentrations with acute localized exposure. These carbamate effects highlight the sensitivity of salmon olfactory neurophysiology to pesticides acting not only potentially via AChE-inhibition, but also by other currently unknown modes of action.

Calming an escalated psychiatric milieu.

On inpatient psychiatric units, nurses control the tone, pace, and activity level of the environment. But under the influence of factors such as high patient acuity and negative group contagion, a milieu can become unacceptably loud and chaotic. A volatile milieu is a potentially dangerous environment because patients' anxiety and agitation can quickly lead to acting out and aggression. This article focuses on how nurses can regain control of a milieu spiralling into chaos by tightening the structure of the routine, anticipating potential problems, and maintaining a confident calm manner. The charge nurse orchestrates the staff group's response to escalation through detailed planning, decisive interventions, and strategic use of every available resource.

Developing a restraint-reduction program for child/adolescent inpatient treatment.

TOPIC: Meeting mandated guidelines to reduce, if not eliminate, the use of restraints with children and adolescents hospitalized on inpatient psychiatric units. PURPOSE: To present eight promising options for restraint reduction with inpatient children and adolescents, and the research that supports their efficacy. SOURCES: Review of the literature. CONCLUSION: By combining what is known about child/adolescent restraint use with restraint-reduction research in the adult field, several options for restraint reduction can be derived.

Parents' perceptions of their child's emotional illness and psychiatric treatment needs.

PROBLEM: The purpose of this study was to describe how parents define their child's emotional illness and psychiatric treatment needs. SUBJECTS: The sample consisted of 19 parents and one grandparent (N = 20) who had recently admitted their child to a short-term psychiatric unit. METHODS: Qualitative methods, utilizing a semistructured interview. Data were analyzed using the constant comparative method. Substantive codes were combined to derive the key concepts and themes in the interviews. FINDINGS: The findings of this study center on themes related to parents' efforts to control the current behavioral crisis, treatment acceptability, family needs, explanatory formulations, and securing the child's future. CONCLUSIONS: Implications for treatment include how nurses might tap into parents' perceptions to facilitate parent' professional communication.

Psychiatric hospitalization and process description: what will nursing add?

1. Inpatient treatment programs operating in the managed care environment must clearly articulate their treatment outcomes and the processes of care that are connected to these outcomes. 2. The work of inpatient psychiatric nurses can be organized and articulated through the therapeutic processes of the Four S Model: Safety, Structure, Support, and Symptom Management. 3. Nurses are vital contributors to the inpatient treatment process, but will be marginalized if they are unable to articulate how their interventions contribute to the positive treatment outcomes.

Milieu therapy: a therapeutic loophole.

TOPIC: The confusion over, and ultimate demise of, milieu therapy. SOURCE: Literature review. GOAL: To chronicle the conceptual problems and other events leading to the decline in the use of milieu therapy. CONCLUSION: Inpatient nurses would do best to leave the concept of milieu therapy behind and focus on clarifying how specific nursing interventions are operationalized and tied to patient outcomes.

Electrophysiological identification of medial and lateral perforant path inputs to the dentate gyrus.

The medial perforant path (MPP) and lateral perforant path (LPP) inputs to the hippocampal dentate gyrus form two distinct laminar inputs onto the middle and distal aspects of granule cell dendrites. Previous evidence indicated that paired stimuli reliably produced paired-pulse depression (PPD) in the MPP and paired-pulse facilitation (PPF) in the LPP. Despite this, several years of practical experience in our laboratory questioned the utility of using paired-pulse administration to reliably differentiate the MPP and LPP in vitro. Using visualized field and whole-cell recordings in male Sprague-Dawley rats, we demonstrate that both pathways show net PPF of the excitatory postsynaptic potential (fEPSP) at 50-ms interpulse intervals. LPP afferents did reliably exhibit greater PPF than MPP afferents. Thus, the LPP reliably exhibits a greater paired-pulse ratio than the MPP. The magnitude of the paired-pulse ratio was reduced in both afferents by raising calcium levels or lowering the temperature of the recording chamber. PPD of MPP-evoked fEPSPs was only reliably detected at moderate to high stimulus intensities when population spike activity was evident. PPD was more evident in whole cell voltage clamp recordings but nonetheless was not completely diagnostic as PPD was occasionally observed with LPP stimulation as well. We found the MPP and LPP could be reliably identified using conventional microscopy with hippocampal slices, and that they could be distinguished through the analysis of evoked waveform kinetics. This work refines our knowledge of electrophysiological differences between MPP and LPP projections and will help to facilitate the selective activation of these pathways.