Slow Pyramidal Tract Cells Research Articles

Serotonin has different effects on two classes of Betz cells from the cat.

1. Intracellular recording from cat Betz cells in vitro revealed a strong correlation between the dominant effect of serotonin (5-HT) and the Betz cell subtype in which it occurred. In large Betz cells that show posthyperpolarization excitation (termed PHE cells), 5-HT evoked a long-lasting membrane depolarization, whereas 5-HT evoked an initial hyperpolarization of variable duration in smaller Betz cells that show posthyperpolorization inhibition (termed PHI cells). 2. Voltage-clamp studies revealed that 5-HT caused a depolarizing shift of activation of the cation current Ih, which resulted in the depolarization in PHE cells, whereas the hyperpolarization in PHI cells is caused by an increase in a resting potassium conductance. 3. The effect of 5-HT on firing properties during constant current stimulation also differed consistently in the two types of Betz cells. In PHE cells the initial firing rate increased after 5-HT application, but the steady firing was unaffected. The depolarizing shift of Ih activation caused the increase of initial firing rate. 4. In PHI cells 5-HT caused a decrease in spike frequency adaptation. The decrease in adaptation was caused by a combination of two conductance changes. First, 5-HT caused a slow afterdepolarization in PHI cells that could trigger repetitive firing in the absence of further stimulation. The sADP depended on calcium entry through voltage-gated channels and was associated with a decrease in membrane conductance. Second, 5-HT caused reduction of a slow calcium-dependent potassium current that normally contributes to slow adaptation. 5. In conclusion, the effect of 5-HT on excitability differs systematically in Betz cell subtypes in part because they have different dominant ionic mechanisms that are modulated. If we assume that PHE cells and PHI cells represent fast and slow pyramidal tract (PT) neurons respectively, 5-HT will cause early recruitment of fast PT cells and delay recruitment of slow PT cells during low levels of synaptic excitation.

Spontaneous firing patterns and axonal projections of single corticostriatal neurons in the rat medial agranular cortex.

1. Spontaneous fluctuations of membrane potential, patterns of spontaneous firing, dendritic branching patterns, and intracortical and striatal axonal arborizations were compared for two types of corticostriatal neurons in the medial agranular cortex of urethan-anesthetized rats: 1) pyramidal tract (PT) cells identified by antidromic activation from the medullary pyramid and 2) crossed corticostriatal (CST) neurons identified by antidromic activation from the contralateral neostriatum. The ipsilateral corticostriatal projections of intracellularly stained PT neurons as well as contralateral corticostriatal neurons were confirmed after labeling by intracellular injection of biocytin. 2. All well-stained PT neurons had intracortical and intrastriatal collaterals. The more common type (6 of 8) was a large, deep layer V neuron that had an extensive intracortical axon arborization but a limited axon arborization in the neostriatum. The less common type of PT neuron (2 of 8) was a medium-sized, superficial layer V neuron that had a limited intracortical axon arborization but a larger and more dense intrastriatal axonal arborization. Both subclasses of PT neurons had anatomic and physiological properties associated with slow PT cells in cats and monkeys and conduction velocities < 10 m/s. All of the PT cells but one were regular spiking cells. The exception cell fired intrinsic bursts. 3. Intracellularly stained CST neurons were located in the superficial half of layer V and the deep part of layer III. Their layer I apical dendrites were few and sparsely branched. Their axons gave rise to an extensive arbor of local axon collaterals that distributed in the region of the parent neuron, frequently extending throughout the more superficial layers, including layer I. Axon collaterals were also traced to the corpus callosum, as expected from their contralateral projections, and they contributed axon collaterals to the ipsilateral neostriatum. In the neostriatum, these axons formed extended arborizations sparsely occupying a large volume of striatal tissue. All CST neurons were regular spiking cells. 4. Both types of cells displayed spontaneous membrane fluctuations consisting of a polarized state (-60 to -90 mV) that was interrupted by 0.1- to 3.0-s periods of depolarization (-55 to -45 mV) accompanied by action potentials. The membrane potential was relatively constant in each state, and transitions between the depolarized and hyperpolarized states were sometimes periodic with a frequency of 0.3-1.5 Hz. A much faster (30-45 Hz) subthreshold oscillation of the membrane potential was observed only in the depolarized state and triggered action potentials that locked to the depolarizing peaks of this rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential connections by intracortical axon collaterals among pyramidal tract cells in the cat motor cortex.

1. Recurrent EPSPs were produced in fast pyramidal tract (PT) cells in the cat motor cortex by stimulation of the medullary pyramid and/or by the glutamate-induced activity of neighbouring PT cells using the spike-triggered averaging (spike-TA) method. 2. In fast PT cells located lateral to the end of the cruciate sulcus, predominantly the motor cortical representation area of the distal forelimb, two components (fast and slow) of recurrent EPSPs were produced by pyramid stimulation. 3. In response to pyramid stimulation, the appearance of the fast and slow components of recurrent EPSPs correlated with the appearance of N1 and N2 field potentials, respectively. 4. The monosynaptic nature of both the fast and slow components of recurrent EPSPs was demonstrated by a double shock test (interstimulus interval less than 5 ms) and high frequency repetitive stimulation (50-100 Hz). 5. The generation of the fast and slow components of recurrent EPSPs was attributed to the synaptic action of recurrent collaterals of fast and slow PT cells, respectively. 6. The amplitude of the slow component of recurrent EPSPs markedly increased with an increase in the stimulus frequency whereas that of the fast component did not, despite the change in stimulus frequency. 7. Selected spike-triggered averaging also revealed frequency facilitation of recurrent individual EPSPs produced in fast PT cells by the activity of single slow PT cells. 8. In fast PT cells located in the anterior and posterior lips of the cruciate sulcus, the motor cortical representation area of the proximal limb or trunk, only the slow component of recurrent EPSPs was produced by pyramid stimulation. 9. It is concluded that the pattern of recurrent connections between neighbouring PT cells differs depending on the motor cortical representation area, and that frequency facilitation of recurrent EPSPs is caused mainly by the input from axon collaterals of slow PT cells.

Relationships between axonal diameter, soma size, and axonal conduction velocity of HRP-filled, pyramidal tract cells of awake cats

Relationships between axonal diameter, soma size, and axonal conduction velocity were examined in intracellularly recorded pyramidal tract (PT) cells of conscious cats using pressure injection of horseradish peroxidase. Positive linear correlations were found between axonal conduction velocities and axonal diameters as well as between axonal conduction velocities and soma sizes. All PT cells had somata located in layer V. Slow PT cells had high densities of dendritic spines in layer III; however, so did some fast PT cells, making this morphologic feature 4,8 unacceptable for distinguishing between slow and fast conducting PT neurons.

Excitatory synaptic actions between pairs of neighboring pyramidal tract cells in the motor cortex.

1. By spike-triggered averaging, we documented recurrent individual excitatory postsynaptic potentials (EPSPs) produced in 33 pyramidal tract (PT) cells (target) by the activity of axon collaterals of neighboring single PT cells (reference) in the motor cortex of the cat. 2. The computer was triggered by the spontaneous activity of reference PT cells or by current pulses applied to reference PT cells through the extracellular recording electrode. 3. The threshold for direct activation of PT cells was less than 0.1 microA with an anodal current pulse and 0.2-0.3 microA with a cathodal current pulse. 4. Application of an anodal current pulse directly activated only a single reference PT cell, the surface membrane of which was presumably touched by and sucked with the extracellular recording electrode. 5. When a cathodal current pulse was used, simultaneous activation of neurons or axons other than the reference PT cell was checked by changing the stimulus parameters along the characteristic strength-duration curve for the reference PT cell and/or by comparing averaged EPSPs obtained by cathodal stimulation with those obtained from spontaneous spikes of the reference PT cell. 6. Recurrent individual EPSPs were produced in fast PT cells by activation of neighboring slow PT cells and also of neighboring fast PT cells. Some recurrent individual EPSPs were also observed in slow PT cells. 7. The mean latencies of recurrent individual EPSPs produced by the spontaneous activity of reference slow and fast PT cells were 1.61 (n = 12) and 1.12 ms (n = 8), respectively. Their amplitudes ranged between 30 and 390 microV (n = 33). The rise time observed in fast PT cells with activation of slow and fast PT cells ranged from 1.6 to 3.6 ms (n = 20) and from 0.8 to 1.9 ms (n = 10), respectively. 8. The average conduction velocity of axon collaterals of slow and fast PT cells was estimated to be as slow as that of unmyelinated fibers in the cat. 9. It is suggested that axon collaterals of slow PT cells synapse onto more distal dendrites of fast PT cells than axon collaterals of fast PT cells.

Vertical spread of neuronal activity within the cat motor cortex investigated with epicortical stimulation and intracellular recording.

In the encéphale isolé cat preparation the surface of precruciate cortex was electrically stimulated. Intracellular responses underneath the stimulated site were recorded to assess the vertical spread of activities across the cortical layers. To the epicortical stimulation (EPICS) with intensity adjusted to evoke a pure negative wave in the direct cortical response (DCR), only some neurons in relatively superficial layers responded with excitatory postsynaptic potentials (EPSPs). Stimuli intensified to evoke both the negative and subsequent positive waves in DCR produced in all tested cells either EPSPs, inhibitory postsynaptic potentials (IPSPs), or both. Direct or axonal antidromic excitation of the cell was observed only infrequently. Cells with EPSPs distributed through all the layers with two peak populations in laminae II and V-VI. Those with IPSPs were located mainly in the upper half of lamina III with a few in more superficial as well as in deeper layers. Both EPSPs and IPSPs showed mono- or oligosynaptic latencies (0.6-10 msec) that tended to become longer in deep than in superficial layers. Some deep layer cells including fast and slow pyramidal tract cells showed slowly rising monosynaptic EPSPs of dendritic origin. Further late responses consisted of EPSPs, IPSPs, disfacilitation (DF), and disinhibition (DI). DF or DI occurred in some deep layer cells. Two modes of vertical spread of activities were postulated: one the cascade transmissions which increased response repertoire toward the depths, and the other the electrotonic spread of EPSPs along dendrites.

Excitation of slow pyramidal tract cells and their family neurones during phasic and tonic phases of EEG arousal.

1. Intracellular activities of slow pyramidal tract cells and their family neurones were investigated during the EEG arousal of various intensities. 2. By assessing the intensity of midbrain reticular or natural stimuli, the arousal length of EEG and the extent of EEG stage shift, these neurones were identified as the recipient of enduring excitation (E + E) during both the phasic and tonic phases of EEG arousal, and were termed E + E cells. 3. These cells were located in all the cortical laminae. E + E responses took the form of continuous depolarization in most of the deep cortical layer cells, but separated initial and late peaks of depolarization were seen in most of the superficial initial and late peaks of depolarization were seen in most of the superficial layer cells. 4. The E + E response versus stimulus intensity or arousal length relationship consisted of plateau and rising limbs, which would characterize the initial and late E components, respectively. 6. The excitatory tonus was revealed in E + E cells with mean levels of resting membrane potential, being most hyperpolarized during highly synchronized EEG and gradually depolarized according to stage shift towards desynchronization.

Activities of the sodium pump in cat pyramidal tract cell studied with intracellular injection of sodium ions.

Sodium ions were injected into cat pyramidal tract (PT) cells electrophoretically through an intracellular NaCl or Na glutamate-filled microelectrode. Following an injection there were decreases in the maximum rates of rise and fall of the spike potential and there was displacement of the inhibitory postsynaptic potential in a depolarizing direction. These changes recovered with an exponential time course, indicating concomitant changes in the internal sodium, potassium and chloride concentrations under the operation of the sodium pump in extruding excess sodium. From the exponential recovery curve, the rate constant of active sodium extrusion was estimated as about 60 hr−1 in fast PT cells and about 90 hr−1 in slow PT cells. It was suggested that the sodium pump was at least partly electrogenic, since the resting membrane was hyperpolarized by the sodium injection to the degree which depended on the amount of sodium-injecting current. Further support for this possibility was obtained by the experiment of high-frequency activation of PT cells, in which the sodium entry through the active membrane developed a slow post-tetanic hyperpolarization.

Repetitive impulses generated in fast and slow pyramidal tract cells by intracellularly applied current steps.

Responses to current steps were recorded from pyramidal tract (PT) cells of the cat by means of intracellular microelectrodes. PT cells with resting potentials from -60 to -80 mV set up a well sustained repetitive discharge during stimulation. When comparing fast and slow PT cells, quantitative differences were found between them in the pattern of repetitive firing. Thus, (1) the rheobase is lower in slow PT cells (mean and S.D.; 0.53±0.63 nA) than in fast cells (1.57±1.11 nA). (2) Following stimulation with a current step twice rheobase the latency and the successive interspike intervals are shorter in fast PT cells than in slow cells. (3) The interspike interval distribution shows a greater irregularity in fast PT cells than in slow cells. At firing rates around 30 impulses/sec the coefficient of variation has a mean value of 0.243 for fast PT cells and 0.085 for slow cells. (4) Fast PT cells show a greater decrease of firing rate during the initial 300 msec of current stimulation (adaptation) than do slow cells. The mean value of this initial decrease is 1.85 times the later steady firing rate in fast PT cells and 0.56 times in slow cells. (5) The slope constant of the firing rate-current relationship is larger in fast PT cells, being five times or more than in slow cells. These characteristics of firing pattern are termed “kinetic” and “tonic” for fast and slow PT cells respectively, and their functional meanings are discussed in comparison with other neural organs.

Transcallosal excitatory postsynaptic potentials of fast and slow pyramidal tract cells in cat sensorimotor cortex

Transcallosal excitatory postsynaptic potentials of fast and slow pyramidal tract cells in cat sensorimotor cortex

Precise location of fast and slow pyramidal tract cells in cat sensorimotor cortex

Precise location of fast and slow pyramidal tract cells in cat sensorimotor cortex

Accommodative properties of fast and slow pyramidal tract cells and their modification by different levels of their membrane potential

1. Threshold-latency curves were determined by intracellular application of linearly rising currents to cat pyramidal tract (PT) cells under various conditions of impalement. The nature of the curves was found to vary considerably, depending mainly upon the resting potential level. Three different types of curves were distinguished: (1) the ceiling type at relatively high resting potentials, (2) the simple type at moderate levels and (3) the minimal gradient type under depolarized conditions. In the first type, the ceiling increased with increasing membrane potential level. The second type attained an extremely low ceiling. 2. After eliminating the effects of the resting potential, a significant difference was still found between the ceilings of fast and slow PT cells, the ceilings being higher in the former than in the latter. 3. Parameters determining the threshold-latency curve were analyzed by applying current steps intracellularly, as described in previous paper. The variations of the ceiling due to the resting potential level were found to be dominated by the first exponential component of the membrane, while those between fast and slow cells were ascribable to the second exponential component.

Recurrent Facilitation in Cat Pyramidal Tract Cells

Recurrent Facilitation in Cat Pyramidal Tract Cells

Slow and fast groups of pyramidal tract cells and their respective membrane properties.

Slow and fast groups of pyramidal tract cells and their respective membrane properties.

RELATION OF DISCHARGE FREQUENCY TO CONDUCTION VELOCITY IN PYRAMIDAL TRACT NEURONS.

RELATION OF DISCHARGE FREQUENCY TO CONDUCTION VELOCITY IN PYRAMIDAL TRACT NEURONS.