Late Discharge Research Articles

Locally evoked potentials in slices of rat neostriatum: A tool for the investigation of intrinsic excitatory processes

Field potentials, extracellular unitary discharges and intracellular potentials evoked by intrastriatal stimulation were recorded from slices (thickness 200-400 micron) of rat neostriatum maintained in an artificial medium. The field potentials consisted of two negative waves appearing at latencies of 0.5-1.5 ms (N-1) and 2-4 ms (N-2). Extracellular unitary records showed two typed of discharges, one with short but constant latencies at threshold level stimulation and the other with longer and variable latencies. In intracellular recordings the late discharge was seen to arise from EPSPs. Based on the intra- and extracellular unitary records, N-1 was identified as the population spike of antidromically or directly activated unitary discharges and N-2 as that of orthodromically activated discharges. This interpretation was substantiated by the fact that the N-2 potential was blocked in a perfusion medium containing a lower Ca++ or a higher Mg++ concentration than the standard solution. Neither interruption of ascending neostriatal inputs nor decortication 14 days prior to recording altered the configuration of the locally evoked potentials or the probability of synaptically driven discharge occurrence. Thus by intrastriatal stimulation, neostriatal neurons are activated antidromically or directly and/or orthodromically through intrinsic excitatroy synapses. Since the intracellular recordings showed that neostriatal neurons can be well preserved, this preparation can be regarded as a useful tool for electrophysiological and neuropharmacological investigations on intrinsic excitatory processes in the neostriatum.

Late long-lasting discharges in hind limb motor nerves and their connection with the locomotor rhythm in thalamic immobilized cats

Effects of stimulation of flexor reflex afferents were studied in decerebrate immobilized cats. Stimulation of ipsilateral afferents evoked late long-lasting discharges in the nerves to the flexors, whereas stimulation of contralateral afferents led to similar discharges in nerves to both extensors and flexors. Compared with spinal animals, early segmental reflexes in thalamic cats were tonically depressed. Similar tonic inhibition of segmental reflexes took place in spinal animals after injection of dopa. Segmental reflexes were clearly modulated during late or rhythmic discharges. The possible central mechanisms of these changes in the segmental reflexes are discussed on the basis of data in the literature.

Transcortical reflexes and focal motor epilepsy

We described in previous papers that, in the monkey with an alumina focus located in the primary motor area, seizures can be triggered by proprioceptive afferents. It is also known that in man as well as in the monkey performing a specific motor task, these afferents may elicit transcortical reflexes involving the primary motor area. This study deals with the possible role of such long-loop reflexes in triggering myoclonic jerks and in extending the seizures. It is shown that selective stimulation of proprioceptive afferents from the limb connected to the focus results in a complex focal response, called on ‘evoked spike’. This cortical response begins with an unaltered evoked potential, followed by a biphasic wave quite similar to a spontaneous epileptic spike. A complex EMG activity is associated with the evoked spike, with an initial burst (40 msec) which is supposed to be the enhancement of a physiological transcortical reflex, and a later discharge (80 msec) which seems closely linked to the pathological wave of the evoked spike. This double activation, at the cortical and at the muscular level, is to be compared with the results of electrical stimulation of motor areas: a single shock on the non-epileptic side is followed by a single motor response, whereas the same stimulus applied within the focal area elicits a double EMG response. The origins of the two components of the evoked spike and their possible relationship to the early and late EMG reflex discharges are discussed.

Long-lasting discharge of postganglionic neurones to skin and muscle of the cat's hindlimb after repetitive activation of preganglionic axons in the lumbar sympathetic trunk.

1. Postganglionic neurones to hairy skin and to skeletal muscle of the cat's hindlimb, probably vasoconstrictor in function, have been investigated for their response characteristics on repetitive stimulation of the preganglionic axons in the lumbar sympathetic trunk in chloralose anaesthetized cats. 2. Repetitive stimulation of the preganglionic axons with 50 stimuli at 25 to 50 Hz and stimulus strengths which excited all classes of preganglionic axons generated eartly short latency responses and late low frequency responses in postganglionic neurones. These late responses occurred predominantly in postganglionic neurones supplying skeletal muscle and in only 30% of postganglionic neurones supplying hairy skin. In most neurones the late discharges could only be elicited by trains of more than 5–10 preganglionic stimuli at frequencies of more than 5–10 Hz. 3. The threshold stimulus strength applied to the preganglionic axons to generate the late discharge was on average 4 times higher than for the early discharge. This finding implies that the late discharge requires the activation of thin preganglionic axons. 4. In most postganglionic neurones, the late discharges could be blocked by atropine, indicating that they were generated by muscarinic action of acetylcholine. The late discharges in a few cutaneous postganglionic neurones were unaffected by atropine. The early discharges were blocked by hexamethonium. 5. The results argue that the transmission of impulses from pre- to postganglionic neurones may be accomplished by two separate pathways acting via nicotinic and muscarinic receptors respectively.

Integration in descending motor pathways controlling the forelimb in the cat. 3. Convergence on propriospinal neurones transmitting disynaptic excitation from the corticospinal tract and other descending tracts.

Extra- and intracellular recording was made from cells in the C3-C4 segments with the aim of finding interneurones of previously described inhibitory pathways to the C3-C4 propriospinal neurones, which may mediate descending feed-forward inhibition and feed-back inhibition from the forelimb, respectively. The lateral interneurones were found in the lateral part of lamina VII interspersed among the C3-C4 PNs and like them they receive convergent monosynaptic EPSPs and disynaptic IPSPs from the cortico-, rubro-, tecto- and reticulospinal tracts. Disynaptic IPSPs, but only rarely monosynaptic EPSPs, are evoked in them from forelimb nerves. The lateral interneurones do not project to the lateral reticular nucleus (LRN). The medial interneurones were found medially in laminae V and VI in a region where volleys in forelimb nerves evoke extracellular monosynaptic focal potentials (Rosen 1969). There is somatotopic organization of the projection from the forelimb to this region. Many neurones are strongly monosynaptically excited from group I muscle or/and cutaneous forelimb afferents. In addition, late discharges are evoked in many cells from cutaneous afferents and high threshold muscle afferents. Corticospinal volleys evoked monosynapic excitation in the great majority of these cells and usually also late EPSPs or IPSPs. Typically, rubrospinal and tectospinal volleys evoked neither monosynaptic excitation nor late effects as those elicited from corticospinal fibres. In some of the interneurones, IPSPs were evoked from forelimb nerves. About 20% of the medial “interneurones” have an ascending projection to the caudal brain stem. Threshold mapping for antidromic stimulation revealed termination in the main cuneate nucleus, the external cuneate nucleus and/or the LRN and also a branch projecting to more rostral levels in the brain. A few of the neurones in the medial region are PNs projecting to the forelimb segments. It is postulated that interneurones both of the lateral and medial type are inhibitory and project to the C3-C4 PNs. It is further postulated that the former are intercalated in the descending feed-forward inhibitory pathway to the C3-C4 PNs and the latter in the feed-back inhibitory pathway from the forelimb to these PNs. The role of feed-forward and feed-back inhibition of transmission from the brain to forelimb motoneurones via the C3-C4 PNs is discussed.

Reticular influences on lateralis posterior thalamic neurons

(1) Spontaneous firing of lateralis intermedius-lateralis posterior (LI-LP) thalamic output cells, as well as excitatory-inhibitory sequences elicited in LI-LP neurons by anterior suprasylvian cortical and center median (CM) thalamic stimulation were studied in ence´phale isole´preparations during control periods of EEG synchronization and during EEG activation induced by stimulating the mesencephalic reticular formation (RF). (2) Mean rates of spontaneous firing of identified thalamocortical neurons increased during spontaneous or RF-induced EEG activation and decreased during EEG synchronization, occuring spontaneously or elicited by hypocapnia. Compared with the sustained firing during EEG activation, discharge patterns of output cells during EEG synchronization were characterized by very short ( < 5msec) and very long ( 1sec) interspike intervals, and by a class of intervals reflecting rhythmic (2.5–4/sec) periods of neuronal silence between high-frequency spike bursts. (3) The following effects were exerted by a short conditioning mesencephalic RF stimulation on cortically evoked events in single LI or LP thalamic neurons: (a) increased probability of the early, antidromically or orthodromically elicited discharges; (b) decreased probability of late (15–25 msec) discharges; (c) shortened latency of the subsequent inhibitory period; (d) reduction in the duration of the first inhibitory phase, and blocking of subsequent, cyclic inhibitory pauses as well as disorganization of postinhibitory clustered excitation.

Spinal cord potentials evoked by cutaneous afferents in the monkey

1. Negative intermediary cord potentials and the equivalent field potentials were recorded from the surface or within the monkey lumbosacral spinal cord in response to stimulation of myelinated afferent fibers in cutaneous or mixed nerves of the hindlimb. 2. Cord potentials resembling the N1 and N2 potentials described in the cat spinal cord were found but, in addition, activation of small myelinated fibers produced a later potential named here the N3-wave. By use of a subtraction technique, it is estimated that the N3-wave has a latency of 11.4 (+/- 3.5 SD) ms from the time of arrival of the volley in the largest affs at 9 (+/- 3) ms after its onset, and the wave lasts 23 (+/- 5.7) ms. 3. The N3-wave is not lost following spinal cord transection, but may instead be enhanced. It is thus due to neural circuitry intrinsic to the lumbosacral spinal cord. 4. The longitudinal distribution of the N3-wave is similar to that of the N1- and N2-waves. 5. The field potential associated with the N3-wave and recorded from within the spinal cord has two negative foci in some animals: near the dorsalmost part of the dorsal horn and in an area equivalent to Rexed's laminae IV-VI. The field potential reverses in sign in the ventral horn. 6. The N3-wave is evoked by Adelta fibers. This was shown by grading the stimulus strength, by measuring the conduction delay for producing the wave when stimuli are applied either proximally or distally on the sural nerve, and by showing that the N3-wave persists when the Aalphabeta fibers are anodally blocked. 7. There is often a late burst discharge in spinal neurons, including spinothalamic tract neurons, which can be attributed to Adelta fibers and which corresponds in time to the N3-wave. 8. It is proposed that the N3-wave can be used as a monitor of the central effects of Adelta fibers in the spinal cord.

Input from trigeminal cutaneous afferents to neurones of the inferior olive in rats.

Extracellular recordings were obtained from inferior olivary neurones of the rat. The responses of fifty neurones evoked by electrical stimulation of a branch of the trigeminal nerve were recorded. Maxillary nerve stimulation was most effective. The response was characterized by an early discharge (single spike and wave, typically with latencies between 16 and 30 msec) and a weak late discharge which followed a period of inhibition of about 100 msec. Half of the neurones responded to one branch of the trigeminal nerve only whereas the other neurons displayed a varying degree of convergence, including sometimes a convergence from limb nerves. Forty-nine olivary neurones were tested for cutaneous receptive fields. Ten out of these had small receptive fields (less than 20% of the contralateral face) and a low threshold to mechanical stimuli. Twenty neurones which had larger receptive fields responded also to low-threshold or to medium-threshold (i.e. non-nociceptive) mechanical stimuli. None of the neurones displayed receptive fields more extensive than half of the contralateral face and some of the larger fields had a small, low-threshold focus. Olivary neurones responding to electrical stimulation of trigeminal nerves or mechanical stimulation of the face were located in the medial segment of the olivary complex (dorsal accessory and principal olive). A few cells only were located in the lateral segment. It is concluded that neurones of the inferior olive receive a substantial input from trigeminal afferents and are capable of transmitting precise somatotopical information to the cerebellum.

Corticofugal modulation of the medial geniculate body

The function of corticothalamic projections in the auditory system was investigated by reversible inactivation of primary auditory cortex. Changes in the discharges of multiple-unit “clusters” within the ventral division of the medial geniculate body were assessed following removal of normal descending influences by cortical cooling. Patterns of neuronal discharges to clicks or tones were classified as either reverberatory or nonreverberatory during precool control sessions. Cortical cooling suppressed the late reverberatory discharges of the former, but had no effect on the discharge rate or pattern of the latter. The short-latency (< 20 msec) response was unaltered for either type. In addition, cooling of primary auditory cortex produced a significant increase in the background activity of nonreverberatory neurons but had no consistent effects on background activity of reverberatory neurons. Two distinct corticothalamic pathways are postulated to account for these results.

Effects of divalent cations and of catecholamines on the late response of the superior cervical ganglion.

The characteristics of the late response of the superior cervical ganglion of dogs were studied by close-arterial injection of catecholamines and divalent cations to the ganglion. 2. Dopamine, noradrenaline and adrenaline inhibit the late response as well as ganglionic activity induced by other means. The effect of dopamine is brief but that of adrenaline is prolonged. 3. Cd2+, Co2+, Ni2+, Zn2+, Hg2+ and Fe2+ markedly potentiate the late response, whereas Mn2+, Ca2+ and Mg2+ inhibit it. 4. may potentiate ganglionic activity triggered by other ganglionic stimulants. The Cd-augmented activity may be blocked by a ganglion-blocker which is specific to the stimulant. 5. CdCl2 may exhibit a direct ganglion-stimulating action on a ganglion which shows prominent late responses and has been conditioned by tetanic preganglionic stimulation. 6. CdCl2 and MnCl2 may inhibit ganglionic transmission by suppressing acetylcholine release from presynaptic nerve terminals. 7. It is concluded that the late response represents the late discharges of ganglion cells, which are very sensitive to inhibition by CaCl2 and MnCl2 and may be potentiated by CdCl2.

Impulse activity and receptor potential of primary and secondary endings of isolated mammalian muscle spindles.

1. An isolated muscle spindle preparation from a tail muscle of cat is described. The afferent response to a ramp-and-hold stretch was recorded in individual axons from identified primary and secondary endings. 2. Primary endings exhibit a prominent dynamic response, including an initial burst. They also show a well-maintained static discharge. Secondary endings also show a well-sustained static discharge but generally have a much lower dynamic sensitivity. The response of primary and secondary endings of the isolated spindle are similar to the typical responses seen in vivo in groups Ia or group II afferent fibres respectively. 3. Following impulse blockade by tetrodotoxin, the receptor potential was recorded from primary and from secondary endings in response to ramp-and-hold stretch. 4. During the dynamic phase the receptor potential of primary endings consists of a depolarization which has two components. (a) An initial component occurs early during ramp stretch, depends in rate of rise and amplitude on velocity of stretch and is reduced on repetitive stretch; it appears to be responsible for the initial burst. (b) A late dynamic component, which follows, is also dependent on stretch velocity and produces the late dynamic discharge. At the end of ramp stretch the receptor potential falls, and may undershoot, the static level. There is a subsequent adaptive fall during hold stretch, then a maintained static level of receptor potential. On release from stretch the membrane is hyperpolarized. 5. Secondary endings usually show a smaller dynamic response, lacking the initial component seen in primary endings. They also generally lack an undershoot following the ramp and have less of a post-release hyperpolarization. 6. Static levels of receptor potential in both primary and secondary endings are related to amplitude of stretch. 7. The receptor potentials of primary and secondary endings account for the major features of the impulse responses of these endings to ramp-and-hold stretch. In primary endings the dynamic frequencies may also depend upon a sensitivity of the impulse initiating site to rate of change of receptor current.

A further study on fast and slow principal cells of rat lateral geniculate body: an analysis of flash-evoked responses.

In the lateral geniculate body (LGB) of urethane-anesthetized and Flaxedil-immobilized rats, unit responses of principal cells (P-cells) were recorded by using flash stimulation of the eyes. By measuring response latencies to electrical stimulation of the optic tract, all P-cells were classified into the fastor slow group according to the criterion established by Fukuda. Flash-evoked unit responses consisted of the two kinds of discharges, i.e. the early discharge (ED) with latencies less than 100 msec and the late discharges of spike burst (LDs) often recurring twice or more (LD1, LD2 and so on). Cells' firings were suppressed during the interval between ED and LD1 and those between successive LDs. The ED- and LD1-latencies, measured in dark with strong flashes, were shorter in the fast cells than in the slow one. The interval between ED and LD1 was shorter in the fast cells than in the slow ones. It was common to the both types of P-cells that as flash intensity was reduced, the ED-latency increased and the LD1-latency decreased. However, the ED-LD1 interval remained shorter in the fast cells than in the slow ones. Upon shifting from dark to light, the LD1-latency markedly increased or decreased in the slow cells, whereas such was not seen in the fast cells. These findings seem to provide a further support for the classification of P-cells into the fast and slow types.

Unit discharges in the mediodorsal nucleus of the rabbit evoked by electrical stimulation of the olfactory bulb

The mediodorsal nucleus of the thalamus (MD) in rabbits was explored with microelectrodes during electrical stimulation of the olfactory bulb and tract. In agreement with previous results in the squirrel monkey, unit responses were located within the medial half of MD. Response patterns included early discharges with latencies of 50 msec or less, late discharges with latencies of more than 100 msec, or dual early and late responses. The interval between early and late responses was characteristically a silent period even in units with spontaneous activity. Units which responded at an early latency were more commonly seen than those which showed only a late response. Latencies to first spike within the former group ranged from 15 to 50 msec (median = 36 msec) when the rostral olfactory bulb was stimulated and from 8 to 36 msec (median = 20m sec) when the stimulating electrode was in the rostral retrobulbar area adjacent to the lateral olfactory tract. Major features of response showed some parallels with results obtained both in the squirrel monkey MD and in the cat prepyriform cortex, a structure reported to have direct anatomical connections with the medial portion of MD.

Relationship between the "late reflex discharge" and locomotor movements in acute spinal cats and rabbits treated with DOPA.

Relationship between the "late reflex discharge" and locomotor movements in acute spinal cats and rabbits treated with DOPA.

Effects of thalamic midline nuclei stimulation upon lateral geniculate transmission in rats: inhibition of principal cells and excitation of internuncial cells.

Effects of low-frequency stimulation of thalamic midline nuclei (MID) upon unitary activities of principal (P) and internuncial (I) cells of the lateral geniculate body were examined in urethane-anesthetized rats. P-cells responsed to single shocks to the optic tract (OT) with single spikes at short latencies (initial spike, IS), followed by a phase of inhibition which lasted for more than 150 msec and ended with a burst of grouped discharges (late discharge, LD). Excitability of P-cells, assessed with the response probability of IS to testing OT shocks, was reduced for about 300 msec after single shock stimulation of MID. Usually this excitability depression became evident about 20 msec after MID shocks and was maximum from 50 to 100 msec. LDs were made more vigorous when MID shocks were given almost simultaneously with testing OT shocks. This was interpreted that MID stimulation induced an inhibition in P-cells and it summed with that induced by OT stimulation. That the MID-induced inhibition of P-cells was due to IPSPs was proved by the quasi-intracellular recording. I-cells, the units fired repetitively by single OT shocks and have been presumed to be inhibitory neurons acting upon P-cells, were found to receive from MID stimulation an excitatory effect followed by an inhibitory one of long duration. It was suggested that the primary inhibition of P-cells by low-frequency stimulation of MID would be a direct consequence of the primary excitation of I-cells.

Influence of l-DOPA on transmission in long ascending propriospinal pathways in the cat

In high spinal cats the influence of an intravenous injection of l-3,4,-dihydroxyphenylalanine (DOPA) has been investigated on the transmission of long ascending propriospinal pathways to certain groups of forelimb motoneurones. The early discharge evoked in pectoralis major and deep radial motoneurones on electrical stimulation of hindlimb afferents, which may be obtained in some high spinal preparations, is facilitated after DOPA. A late discharge (30–80 msec) appears after DOPA in the same forelimb motoneurones and may often last up to 600 msec or more. Facilitation by hindlimb nerves of forelimb mono- and polysynaptic reflexes is similarly prolonged. Ipsilateral hindlimb nerves are more effective than contralateral. Late discharges have also been evoked in forelimb motoneurones on stimulation of forelimb afferents after DOPA and it is concluded that a somewhat similar organization of late reflexes exists in brachial segments as previously reported by Jankowska et al. in the lumbar cord. The influence of DOPA on long ascending propriospinal and forelimb reflexes is ascribed to excitation of the terminals of noradrenergic reticulospinal fibres. The reflex changes are considered to reflect activity in neuronal systems involved in the control of stepping in the cat. A further system modifying long ascending propriospinal transmission could be excited by stimulation of the ventral quadrant of the spinal cord at C 1. The effects on propriospinal transmission could outlast the stimulus by several tens of minutes.

Interaction between picrotoxin and 5-hydroxytryptamine in the superior cervical ganglion of the cat.

1. Electrophysiological techniques were utilized to study the actions of 5-hydroxytryptamine (5-HT) and picrotoxin on the superior cervical ganglion of the cat.2. The intra-arterial administration of 5-HT to the ganglion elicited both depressant and excitatory actions. In low doses (0.01-0.5 mug) the amine produced a depression of ganglionic transmission. In larger doses (2-50 mug) it produced an excitation of ganglion cells (early discharge) and an initial enhancement of transmission, which was followed by depression. Picrotoxin (25-500 mug, i.a.) blocked the initial excitatory effects of 5-HT but did not block the depression. Picrotoxin did not antagonize the excitatory actions of injected cholinomimetic agents or potassium chloride.3. In ganglia conditioned by repetitive stimulation of the preganglionic nerve (30 Hz for 30 s) 5-HT also elicited a late-occurring and very prolonged discharge on certain postganglionic nerves (;spinal') but not on others (external carotid). The late discharge was only partially depressed by picrotoxin.4. Recordings from the surface of the superior cervical ganglion revealed that 5-HT produced three types of ganglionic potentials: (1) an initial transient depolarization which coincided with the early discharge, (2) a late-occurring, prolonged depolarization which coincided with the late discharge, and (3) a hyperpolarization which in some experiments accompanied the depression of transmission. The late depolarization and hyperpolarization were not observed in every experiment. Picrotoxin (25-500 mug) blocked the initial depolarization, but did not block the late depolarization or the hyperpolarization.5. It is concluded the 5-HT can produce three distinct responses in the superior cervical ganglion: a depressant effect and two types of excitation. It seems likely that depression and excitation occur via the activation of different receptors, since picrotoxin selectively blocks the latter. The finding that picrotoxin is a 5-HT antagonist in peripheral ganglia raises the possibility that picrotoxin might also influence tryptaminergic mechanisms in the central nervous system.

Differentiation of principal cells of the rat laternal geniculate body into two groups; fast and slow cells.

In urethane-anesthetized albino rats studies were made on mass potentials and/or unit activities of the lateral geniculate body (LGB) in response to single shock stimulation of optic tract (OT) and visual cortex (VC). The previous finding that LGB mass responses to stimulation of the optic nerve comprise at least two postsynaptic waves (r1 and r2) with different peak times was confirmed by OT stimulation. It was found that the r1 wave had a lower threshold and a more rapid recovery process than the r2 wave. Unit responses of principal (P) cells to maximal OT stimulation consisted of short-latency, single spikes (initial spike, IS), followed by long-latency, grouped discharges (late discharge, LD) repeated more than twice (LD1, LDr2 and so forth). Spontaneous discharges were almost completely suppressed after IS and each LD, suggesting that following these evoked discharges P cells underwent a phase of depressed excitability. The latency histogram of IS based upon 212 P cells had two peaks well-corresponding in time to the peaks of the r1 and r2 waves of the mass response, respectively. P cells were divided into the fast and slow groups according to whether their ISs occurred earlier or later than the trough separating the r1 and r2 waves. Typically, the fast cells had lower thresholds than the slow cells. The duration of the post-excitatory depression following IS and LD1 were shorter in the fast cells than in the slow cells. This same was found true with regard to the duration of depressed excitability following the antidromic firing. Examining the response patterns to OT stimulation of weak intensities, one characteristic difference between the two groups of P cells was found; the fast cells showed the IS without the succeeding LDs whereas the slow cells showed the LDs without the preceding IS. A discussion was made on functional significance of the differentiation of P cells into two types.

Spinal interneurones involved in presynaptic controls of supraspinal origin.

1. Interneurones presenting heterotopic and heterosensory convergence have been identified in laminae VI-VII of the lumbar dorsal horn in the cat. Stimulation of the hind limbs sometimes induced a bimodal response, but we considered only the late convergent discharge.2. The fact that response latencies are longer to hind limb than to forelimb stimulation at this level suggests the intervention of a supraspinal loop in the activation of spinal convergent units. This hypothesis is supported by the relationship between the excitability of supraspinal structures and the discharge intensity of convergent cells as well as by the absence of long latency responses in the spinal preparation.3. Electrophysiological and pharmacological evidence discloses a strong relationship between convergent unit discharges and the occurrence of dorsal root potentials to cortical, heterosegmental and heterosensory stimulation.4. It is suggested that convergent units receive information of supraspinal origin and exert control over sensory input to the cord via primary afferent depolarization.

The action of tetanus toxin on preganglionic sympathetic reflex discharges

1. Tetanus toxin (0.5–1.0 MLD) has been injected in cats into the internal intercostal muscle of the third costal interspace. 2. In spinalized cats, 24 h after toxin injection the early discharge on the tetanus side had an amplitude up to ten times higher than on the control side. The coefficient of variation decreased only slightly. The peak latency remained unchanged. 3. The increase of reflex discharges into the white ramus in local tetanus depended on the dosis of toxin injected. 4. The inhibition exerted on an IC3/WR3 reflex by a preceding stimulus to the IC2 or IC4 nerve was abolished or greatly reduced on the tetanus side only. 5. The disinhibition of sympathetic reflex discharges in local tetanus depended on the dosis of toxin injected. 6. In cats with intact neuraxis, the amplitude of the late discharge was higher on the tetanus side than on the control side. 7. Conditioning experiments in cats with intact neuraxis gave complex results indicating a partial disinhibition.