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At least 343 records · Page 19Linked to original sources
PubMed1976

Single unit study of binaural interaction in the auditory cortex of the chinchilla.

The primary aim of this investigation was to systematically compare for various stimulus conditions the relative influences of contralateral and ipsilateral acoustic stimulation on cortical single units in an unanesthetized preparation and to study the effects upon single unit responses of the dominant stimulus cues for sound localization--interaural intensity difference (deltaI) and interaural time difference (deltat). Recordings were obtained from 133 units in chinchillas immobilized by gallamine triethiodide. All units were found to be influenced by input from both ears. Unit thresholds for contralateral stimulation were lower and more discharges were elicited than for ipsilateral stimulation over a range of intensities from unit threshold intensity to 80 dB sound-pressure level. A predominance of contralateral influence was also observed when the number of stimulus-evoked discharges was plotted as a function of the deltaI or deltat. For 62% of the deltaI functions maximal responsiveness occurred for binaural stimuli that were more intense at the contralateral ear. Similarly, of the 36 units that showed sensitivity to deltat parameters for tone stimuli, 22 (61%) were maximally responsive at the contralateral-leading deltat intervals. For click stimuli, maximal responsiveness for all 21 deltat-sensitive units also occured for contralateral-leading stimuli. Certain observations in the study question the generality of the hypothesis that a particular cell invariantly encodes a specific deltat, i.e., that cells have 'characteristic delays'. First, most units tested at more than two frequencies showed maximal responsiveness at different deltat intervals depending upon stimulus frequency. Second, the deltat intervals for maximal responsiveness for half of the units tested were greater than the maximal interaural delays the animal could encounter naturally. Third, deltat functions from the same unit for click and tone stimuli showed poor correspondence. These findings suggest that the encoding of interaural time and intensity might depend on an inter-hemispheric comparison of the activity of neural populations as originally proposed by von Bekesy.

Acoustic Stimulation↗
PubMed1977

Some synaptic inputs and ascending projections of lateralis posterior thalamic neurons.

(1) Some synaptic inputs and telencephalic targets of lateralis intermedius-lateralis posterior (LI-LP) thalamic neurons have been investigated in the encéphale isolé cat by recording extracellular unit discharges and focal slow waves following stimulation of cortical areas 5 and 7, center median (CM) thalamic nucleus and mesencephalic reticular formation (RF). (2) Orthodromic and/or antidromic discharges in LI-LP neurons following anterior suprasylvian stimulation are electrophysiological evidence of thalamocortical reciprocal pathway in this "association" system. A few neurons were backfired from several cortical stimulated foci at different latencies, thus suggesting the existence of LI-LP output cells with branching axons. The numerous cases of cortically elicited synaptic excitation in LI-LP cells, taken together with evidence of an unexpectedly high proportion of corticothalamic neurons found in parallel experiments of this laboratory on areas 5 and 7, support the suggestion that complex functions of the "association" cortex partially depend on its downstrem connections with thalamic integrative structures. (3) Monosynaptic and oligosynaptic excitatory projections link the brain stem reticular core with LI-LP nuclear group. For some neurons, this is a high-security pathway as shown by the ability of thalamic cells to follow at short latencies fast repetitive reticular shocks. The RF-elicited phasic excitation is followed by a period of suppressed spontaneous and evoked discharge. The excitatory projections from the upper brain stem RF to the LI-LP nuclei are discussed in relation to disfacilitatory phenomena in thalamocortical systems due to withdrawal of reticulofugal ascending activation at sleep onset.

Afferent Pathways↗
PubMed1977

Somatosensory properties of spinoreticular neurons in the cat.

(1) Spinal cord neurons projecting to the brain stem were studied in cats prepared by decerebration or anesthetized with barbiturate or nitrous oxide and halothane. Antidromic stimulation from the medial pontomedullary reticular formation (MDRF) and midbrain (MB) was used to identify the site of projection. (2) Receptive fields were mapped using adequate stimuli. A variety of noxious stimuli was employed to establish the capacity of these neurons to transmit nociceptive input. (3) Neurons were found to project bilaterally to the MPRF. Of 46 units tested for a more rostral projection, only 13 were activated from the MB electrode. (4) Neurons fall into three categories based on receptive fields: cutaneous, restricted (SR); deep, restricted (DR); and complex, extensive (CE). All 16 SR neurons were located in the dorsal horn and had low thresholds to mechanical stimulation of the skin. Seven discharged maximally to nociceptive inputs. The 34 DR neurons were widely distributed in the spinal gray and responded to pressure upon subcutaneous structures. Although 13 neurons increased their firing rate as the stimulus intensity was increased into the noxious range, nociceptive input could only be established with confidence in 4 neurons. The 38 CE neurons were located ventrally in the spinal gray and had highly convergent inputs from cutaneous and deep receptors. Ten responded maximally to noxious stimulation.

Afferent Pathways↗
PubMed1978

Centrally programmed feeding in Helisoma: identification and chracteristics of an electrically coupled premotor neuron network.

(1) The oscillatory network underlying centrally programmed feeding in the fresh water pulmonate, Helisoma trivolvis, was studied using intracellular recording and staining techniques. These premotor neurons have been termed cyberchron neurons. (2) Intracellular staining with Procoin yellow has allowed the construction of a soma map and tentative identification of axonal projections of the cyberchron neurons. (3) Cyberchron neurons form a tightly electrically coupled network. Coupling coefficients range from 0.15 to 0.5, and electrotonic junctions allow the passage of Procion dye from cell to cell. Electrical synapses act as low pass filters, and allow spatial and temporal summation. (4) Burst generation within the network is the result of network interaction manifest as regeneration positive feedback from neuron to neuron via attenuating electrical synapses. (5) Decreased coupling between cyberchron neurons during and immediately following a burst is observed, and is discussed as a possible mechanism for burst termination.

Action Potentials↗
PubMed1978

Synaptic connexions and related postsynaptic pharmacology studied in the cerebral ganglion of Aplysia.

Interneuronal connexions have been studied within the cerebral ganglion of Aplysia californica. Excitatory monosynaptic connexions between two groups of cells located on the dorsal surface of the ganglion near the cerebropleural connectives were analyzed in detail. The monosynapticity of these connexions was established not only by the strict one-to-one correlation between presynaptic action potential and excitatory postsynaptic response (EPSP) and the constant latency for any given cell pair, but also by the following criteria: (a) gradual change in the EPSP following tetraethylammonium injection into the presynaptic neurone, (b) sustained EPSP in the presence of a high external calcium ion concentration, (c) sensitivity of the EPSP amplitude to presynaptic polarization. Iontophoretic application of acetylcholine, 5-hydroxytryptamine and glutamate on the postsynaptic cells elicited excitatory responses in many cases. Inhibitory responses were obtained by local iontophoresis of dopamine, gamma-aminobutyric acid and occasionally also by acetylcholine. The only agent found to block the EPSP was bufotenine, which also readily blocked the 5-hydroxytryptamine response. Bufotenine was completely ineffective on the acetylcholine or glutamate excitatory responses. Of the various cholinolytics tested, none had an effect on the EPSP. Our data all point to 5-hydroxytryptamine as a transmitter in the studied synaptic connexions. However, it must be emphasized that in the absence of biochemical and histological evidence the role of the 5-hydroxytryptamine cannot be regarded as conclusive.

Amino Acids↗
PubMed1978

Facilitatory and inhibitory effects of electrochemical stimulation of the amygdala on the release of luteinizing hormone.

The effect of amygdaloid stimulation on the release of luteinizing hormone (LH) was studied in unanesthetized, unrestrained rats. Electrochemical stimulation (anodic D.C.) was applied at 11.30 h through stainless steel electrodes chronically implanted into different amygdaloid nuclei; medial (Men.), cortical (Con.), central (Cn.), or basolateral (Bln.). A plastic cannula inserted into the jugular vein was used for obtaining blood samples at different times of the experimental procedure. In rats on the day of proestrus, stimulation (100 micronA/30 sec) in the Bln. resulted in blockade of spontaneous ovulation and of the preovulatory LH release and that in the Cn. produced a delay in the hormone discharge. On the contrary, stimulation in the Men. was effective in advancing the time of the normal LH surge, while no change of the normal pattern occurred from the Con. Stimulation (100 micronA/60 sec) of ovariectomized estrogen primed rats applied in the Men. or the Con. induced LH release, while that in the Bln. or the Cn. had no effect. The release of LH by Men. stimulation and the blocking effect of Bln. showed a close relationship with the amount of current delivered. Lower thresholds were required for inhibition than for activation. The release of LH induced by stimulation in the Men. of ovariectomized estrogen primed rats occurred at the same time of the day whether the stimulus was applied at 8.30 h, 11.30 h or 14.00 h, indicating a modulatory effect of the amygdala. No changes in serum LH concentration were observed after stimulation of the Men. of castrated estrogen primed male rats or in the Bln. of ovariectomized non-primed rats. The present results indicate that the amygdala exerts a dual effect on the release of LH, the Bln. being inhibitory and the Men. and Con. facilitatory.

Amygdala↗
PubMed1978

A comparison of the inhibitory effects of taurine and GABA on identified Purkinje cells and other neurons in the cerebellar cortex of the rat.

The microiontophoretic application of taurine and GABA was studied in the cerebellar cortex of the rat. Both taurine and GABA produced a dose-dependent depression of spike frequency of cerebellar neurons. GABA (2-42 nA, mean 27 nA) induced an inhibition of spike discharge on all 138 cells tested, including 29 Purkinje cells. Taurine (60-200 nA, mean 108 nA) induced an inhibition of spike discharge on 93 of the 106 cerebellar neurons tested, including inhibition on 22 of 25 Purkinje cells. Iontophoretic application of bicuculline and picrotoxin antagonized the inhibitory effects of both GABA and taurine on Purkinje cells as well as on cerebellar neurons in general. Strychnine did not antagonize the inhibition of either GABA or taurine. Simultaneous application of taurine and GABA produced a synergistic inhibitory effect on the firing rate of Purkinje cells. Taurine, in contrast to GABA, appeared to be more depressant when applied in the Purkinje cell dendritic zone than when applied near the soma. The data are discussed in terms of taurine functioning as a neurotransmitter in the cerebellum of the rat and having receptor sites distinct from those for GABA.

Aminobutyrates↗
PubMed1978

Differential excitatory and inhibitory effects of opiates on non-nociceptive and nociceptive neurones in the spinal cord of the cat.

Morphine, levorphanol, dextrorphan and naloxone were applied microelectrophoretically to cells identified as either having nociceptive inputs or non-nociceptive inputs in the dorsal horn of the cat. Morphine excited non-nociceptive cells and depressed nociceptive cells. Naloxone reversed morphine excitations on non-nociceptive cells, but only reversed about one-third of morphine depressions on nociceptive cells. Levorphanol depressed nociceptive cells, whilst dextrophan ejected with similar currents caused less depression or had no effect. It is concluded that excitation of non-nociceptive cells may constitute a spinal action relevant to the analgesic action of opiates, acting synergistically with a depressant effect on nociceptive neurones.

Animals↗