Spinal Preparation Research Articles

Some observations on habituation of the flexor reflex in the rat: the influence of strychnine, bicuculline, spinal transection, and decerebration.

The involvement of inhibition in habituation of the flexor reflex was investigated in intact, spinal, and decerebrate rats. Strychnine and bicuculline were administered in order to determine the contribution of certain forms of central inhibition to the development of habituation. Both strychnine and bicuculline reduced habituation in the intact rat but did not do so in the spinal preparation. Strychnine, in fact, caused a facilitation of habituation in the spinal rat. The impairment of habituation by strychnine was related to the intensity of stimulation used to elicit the reflex. Thus, the effect of strychnine was only demonstrable when relatively high intensities were used. Flexor reflex habituation was shown to be more pronounced in the decerebrate than in the spinal preparation. This difference could be demonstrated only when stimuli of high intensity were given. It is concluded that, in the absence of supraspinal influences, habituation of the flexor reflex does not require inhibitory mechanisms. However, inhibition may play a role in habituation of the component of the reflex that utilizes descending influences.

Further analyses of reflex movements in the hind limbs of the terrapin,Pseudemys scripta elegans

1. Studies of the control of reflex (scratching) movements of the rear limb of the terrapin were made on spinal preparations and chronic preparations where the spine was transected at the D3–D4 levels. 2. The mechanism in the spinal cord which controls this movement does not obviously compensate either for external frictional forces acting on the limb or to effects of gravity if the preparation is placed in a non-horizontal position. 3. EMG patterns are not modified if an obstacle prevents the limb from reaching its target. 4. Peripheral information is not continuously used to control this movement. The control mechanism is probably a generator which can adjust to different stimulus places. 5. Extensor activity can be inhibited by afferent inflow from the limb. 6. Generation of new cycles of movement in response to a single stimulus can be inhibited by afferent inflow.

Some physiologic characteristics of the electrodermal reflex in the cat

BERNTHAL, P. J. AND M. C. KOSS. Some physiologic characteristics of the electrodermal reflex in the cat. BRAIN RES. BULL. 3(5)437–441, 1978.—The amplitudes of electrodermal reflexes evoked in intact cats were compared under a variety of anesthetic conditions. Electrodermal reflexes were elicited in both decerebrate and spinal preparations with and without anesthesia. Reflex amplitude was significantly depressed in the anesthetized preparation after decerebration or spinal transection. In contrast, spinal transection performed after decerebration in unanesthetized preparations significantly increased the amplitude of the reflex. The evidence presented in this study supports the concept of a primarily inhibitory lower brainstem system with regard to this reflex. The relative stability of the reflex amplitude in the anesthetized cat suggests that this reflex system could be useful in the analysis of the effects of drugs acting on the central nervous system.

Recovery of shivering in spinal cats

Normal adult cats and acute and chronic spinal preparations were studied for shivering responses in the hind limbs to spinal cord cooling. A U-shape polyethylene tube was positioned peridurally so that it would lie from L7 to T5–8. Spinal cord transections were made just rostral to the tubing. The tubing was injected with progressively cooler water to cool the cord and induce shivering. There is a significant increase ( P < 0.01) in the threshold for the initiation of shivering to spinal cord cooling in the acute spinal animal (11.0 ± 5.5°C) compared to that in the intact animal (30.6 ± 3.9°C). Recovery of the threshold for initiation of shivering to a value of 31.0 ± 4.2°C occurs by postoperative Day 2. The recovered threshold is not significantly different from that of the intact animal. The pattern of shivering in the intact cat has both phasic (burst-like) and tonic (fine tremor) components. In the acute spinal cat, the shivering pattern to spinal cord cooling is twitch-like and lacks the pattern of the intact cat. Unlike the threshold for shivering, the pattern of shivering changes gradually with time until postoperative Day 15 when it is almost normal. The elevated threshold for initiation of shivering and the diminished pattern of shivering which are observed initially after spinal cord transection are comparable to the depression of many cutaneous reflexes during the period of spinal shock. In addition, the threshold and pattern of shivering recover from spinal shock. Unlike cutaneous reflexes, however, neither the threshold nor the pattern of shivering becomes hyperactive with recovery.

Swimming movements elicited by electrical stimulation of the turtle spinal cord: The high spinal preparation

1. The movements of each limb of the turtle,Pseudemys scripta elegans, are out-of-phase with the movements of its ipsilateral neighboring limb during normal swimming. Protraction of one limb coincides with retraction of an adjacent limb. The period of the movement cycle in one limb is equal to that of its neighbor. This coordination pattern is termed 1∶:1 or absolute coordination. 2. Swimming movements of the limbs are not produced spontaneously in a turtle with an acute section of the spinal cord at the first cervical segment. This “high spinal” turtle can produce swimming movements in several limbs, however, in response to unpatterned, i.e. constant frequency, electrical stimulation applied to the dorsolateral funiculus (DLF) caudad to the spinal transection. On many occasions, it was possible to place a stimulating electrode in the DLF so that the swimming movements exhibited the normal pattern of absolute coordination (Figs. 2, 4, 5, 8). 3. On a few occasions, it was possible to place a stimulating electrode in the DLF so that the swimming movements elicited by electrical stimulation displayed an abnormal pattern of coordination. In these cases, protraction of the hindlimb coincided with every second occurrence of retraction of the forelimb. The period of the movement cycle of the hindlimb was twice as long as that of the ipsilateral forelimb. This coordination pattern is termed 2∶:1 coordination, and is an example of one type of relative coordination (Figs. 7, 11). 4. These results are consistent with the hypotheses (i) that each limb has its neural control center resident mainly in the spinal cord and (ii) that the neural elements necessary for interlimb coordination are not dependent upon supraspinal connections.

Modulation of response threshold in frog spinal cord: dependence upon descending influences

Response thresholds to von Frey hair stimulation of intact and spinal frogs (Rana pipiens and Rana catesbeiana) were determined. While the response threshold of spinal frogs remained constant over test sessions, thresholds of intact frogs showed a progressive decline. This decline appears due to habituation to the testing procedure rather than to situational factors. Thus the intact frog, in contrast to the spinal preparation, is able to modulate segmental reflex activity. Implications of these behavioral findings for neuronal mechanisms are discussed.

Reflex activation of sympathetic pathways to vesical smooth muscle and parasympathetic ganglia by electrical stimulation of vesical afferents.

1. Activation of the sympathetic input to the urinary bladder by electrical stimulation of afferent fibres in the pelvic nerve evoked three responses: (1) an initial transient rise in intravesical pressure, (2) an inhibition of neurally evoked bladder contractions and (3) an inhibition of transmission in vesical parasympathetic ganglia. Similar responses were elicited by stimulation of the hypogastric nerve. 2. The reflex responses were observed in acute spinal preparations (T10-T12) and in cats with intact spinal cords, but were abolished by bilateral transection of the hypogastric nerves. 3. The inhibition of bladder contractions was antagonized by the administration of propranolol (200-400 mug, I.A.), a beta-adrenergic blocking agent. The inhibition of ganglionic transmission was antagonized by dihydroergotamine (30-75 mug, I.A.), an alpha-adrenergic blocking agent. The initial rise in intravesical pressure was not antagonized by either agent. 4. Electrical stimulation of other afferents (carotid sinus nerve and sciatic nerve) did not consistently elicit responses in the urinary bladder. However, stimulation of these afferents as well as pelvic nerve afferents evoked reflex firing in nerve filaments on the surface of the urinary bladder. The firing was abolished by transection of the ipsilateral hypogastric nerve. 5. It is concluded that stimulation of vesical afferents activates a spinal sympathetic reflex which results in closing of the internal urethral sphincter and a depression of bladder activity. The latter occurs by a direct depression of detrusor smooth muscle as well as a block of the neural input to the bladder. This vesico-sympathetic reflex represents a negative feed-back mechanism which may have an important role in the maintenance of urinary continence.

Reflex figures in the decerebrate and spinal state

The flexors and extensors of the hind limb of the cat were simultaneously activated by stretch of a homolateral flexor muscle or by a nocuous stimulus to the homolateral paw under the conditions of the present experiments, in which the muscles under investigation were maximally retracted after detachment of the tendons from their insertions. The simultaneous activation of flexors and extensors was observed in acute and chronic spinal preparations, and sometimes in decerebrate animals. However, when in such preparations the extensor muscle was made to contract by loading its tendon, stretch of the antagonistic flexor muscles and pinching of the toes of the homolateral leg usually resulted in extensor inhibition and flexor excitation, in agreement with the classical tenet of reciprocal innervation. The reflex figure seems to be to an important extent the result of the inflow of afferent impulses.

Nociceptor-driven dorsal horn neurones in the lumbar spinal cord of the cat

Single dorsal horn neurones have been recorded extracellularly in the lumbar spinal cord of cats anaesthetized with chloralose. Cold block at L 1 was used to provide reversible spinalization. The location of the units in the dorsal horn was marked by the electrophoretic deposition of pontamine sky blue from the recording microelectrode. There was a clear somatotopic representation of the ventrolateral surface of the foot in the L 6 segment. Thirty-five of the 46 units recorded in the marginal zone of the L 6 dorsal horn (lamina I) could only be excited by volleys in small afferent fibres and by noxious stimulation of the skin in the foot regions and were termed class 3 cells. The remaining 11 units could, in addition, be excited by sensitive cutaneous mechanosensitive afferent units — they were class 2 units. The ‘specific’ nociceptor-driven neurones could be divided into 2 subclasses on the basis of their excitability by afferent fibres. Class 3 (a) were excited only by Aδ cutaneous afferents and class 3 (b) by both Aδ and C cutaneous afferents. Some of the latter were also excited by Aδ and C afferent fibres in the lateral gastrocnemius nerve. When tested by natural stimulation all class 3 cells were excited by noxious mechanical stimuli, but only the 3 (b) units were effectively excited by heating the skin. This discharge in 3 (b) units could be suppressed by electrical stimulation of large (group II) cutaneous myelinated afferent fibres and a similar effect could be produced in responses evoked by Aδ and C afferent volleys. Additional inhibition was accomplished by electrical stimulation of the slower myelinated cutaneous (Aδ or group III) afferent fibres. The excitability of the class 3 cells was greater in spinal preparations but the tonic descending inhibition was weaker than the apparently similar descending tonic inhibition of class 2 cells. The results are discussed with reference to pain mechanisms.

The response of alpha-motoneurons of different size to stretch and vibration of extensor muscles after injection of 5-hydroxytryptophan in spinal cats.

1. Vibration of the GS muscle at 100/sec, and the peak-to-peak amplitude of about 100 mu, produced slight reflex activity of homonymous and heteronymous alpha-motoneurons in the spinal, unanesthetized cat. 2. Intravenous injection of the 5-HT precursor 5-HTP (25 mg/kg, L-form) performed in the spinal preparation facilitated the responses of single extensor alpha-motoneurons to both vibration and stretch of the corresponding muscle. The 5-HT antagonist methysergide (0-5 mg/kg i. v.) blocked almost completely the facilitation of the vibration and stretch induced motoneuronal discharges produced by 5-HTP in the spinal cat, indicating that the facilitation was 5-HT specific. 4. A comparison of the types of alpha-motoneurons participating in the reflex responses elicited by the different stimuli in the spinal cat following injection of 5-HTP showed that both small-tonic and large-phasic alpha-motoneurons take part in both stretch and vibration reflexes. 5. It is concluded that the alpha-motoneuron pool of the GS muscle represents an homogenous population, no matter what kind of synaptic drive is used for its activation, and that the susceptibility of a motoneuron to discharge depends on the amount of the afferent excitatory input rather than on the modalities of sensory stimulation.

EFFECTS OF INDOMETHACIN AND THE OTHER ANTIINFLAMMATORY AGENTS ON ACTIVATION OF DORSAL HORN CELL IN THE SPINAL CORD INDUCED BY INTRA-ARTERIAL INJECTION OF BRADYKININ

AbstractBradykinin (1-2 μg) injected into the femoral artery of the rabbit induced a marked increase in the firing rates of the dorsal horn cells (lamina V cells). This response was markedly inhibited by intravenous administration of indomethacin (1.0 mg/kg), acetylsalicylic acid (20 mg/kg), aminopyrine (50 mg/kg) and oxyphenbutazone (20 mg/kg) in both intact and spinal preparations. Moreover, the intra-arterial injection of these agents depressed the response in lower doses. With these same low doses, no significant suppression occurred when the intravenous route was used. These results indicate that indomethacin and other anti-inflammatory agents tested suppress the bradykinin-induced response of the dorsal horn cell at the periphery, probably at the paravascular sensory nerve.

Locus of central depressant action of flunitrazepam

Flunitrazepam has been reported to be a very potent muscle relaxant (12). The dose-response relationship for depressant action of this drug on contralateral extensor reflexes was studied in midcollicular decerebrate and acute spinal cats. The reflex response was more sensitive to the depression of the drug in midcollicular than in acute spinal preparations. The dose required to reduce the reflex response by 50% was about 3 μg/kg in midcollicular preparations, whereas a dose of 15 μg/kg was required to depress the response to the same degree in spinal cats. The stimulation experiments showed that this drug also depressed the facilitation and inhibition of the knee jerk produced by activating the brain stem reticular system. The dose-response curve of the effects of this drug on mesencephalic reticular and spinal internuncial neuronal activity revealed that depression occurred at both levels. These findings suggest that the higher potency of flunitrazepam is attribulable not only to its highly potent depressant action on the mesencephalic reticular system but also to its substantial depressant action on the spinal interneurons.

Inhibition des activit�s spinales � caract�re locomoteur par une modalit� particuli�re de stimulation somatique chez le lapin

In decerebrate rabbit preparations, a gentle pressure exerted on the dorsal skin area can completely suppress the rhythmic, locomotor-like movements or the corresponding nerve discharges which easily develop in such preparations. This inhibition can also be obtained on spinal preparation (and thus does not depend upon supraspinal levels); its maximal effect (i.e. minimal pressure threshold) is located at the lumbar level. It involves tonic receptors belonging both to the skin and to muscle and/or joints. This phenomenon probably plays a role in the so-called “hypnotic akinesia” which, as is well known, can easily be elicited in rabbits put in dorsal decubitus.

Thermoregulatory responses of decerebrate and spinal cats

Cooling the spinal cord of the unanesthetized cat elicited shivering, piloerection, and vasoconstriction. A high-level decerebration abolished these effects. Lowering the decerebration to the level of the lower pons or medulla reinstated these responses to spinal cord cooling. In unanesthetized chronic spinal cats, cooling the spinal cord below the level of a T6 transection produced similar thermoregulatory effects limited to the hind limbs, although it was of less intensity and without piloerection. A high-level decerebration abolished shivering in the forelimbs to whole body cooling, while permitting shivering below the level of transection to spinal cord cooling. Lowering the level of decerebration to the lower pons or medulla reinstated shivering, vasoconstriction, and piloerection in the forelimbs. The data suggest that there is a region in the midbrain and upper pontine tegmentum which exerts tonic inhibition on lower regions in the lower pons, medulla, and spnal cord. When released from inhibition these lower regions are capable of facilitating thermoregulatory responses. Such an organization resolves contradictory reports on the abolition of thermoregulation after decerebration and answers the question of why spinal cord cooling produces shivering in spinal preparations but not in decerebrate preparations.

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.

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.

脊髄の電気活動(自発々射,誘発電位)に対するCardiazolの作用 Cardiazolは抗Pentobarbital剤たりうるか

It has been observed that cardiazol acts facilitatorily, and that the facilitation is provided by suppression of inhibitory mechanisms. The effects of this compound on the spinal cord reflexes have been investigated by this author. The results are as follows: Cardiazol depressed the dorsal activities in all preparations. Regarding ventral activities, the compound accelerated the S. B. S. reflex response, but did not vary either the M. S. R. or the P. S. R. to any great extent in the unanesthetized, immobilized preparation. S. B. S. reflex response was never observed in the spinal preparation. Cardiazol acts not only on the spinal cord itself, but also on the supraspinal mechanisms. The main site of action, however, appeared to be at the supraspinal level, and the mode of action is presumably the suppression of presynaptic inhibition. S. B. S. reflex can be induced according to the depression of presynaptic inhibition and by means of a decrease in the postsynaptic inhibition. Cardiazol may be classified as superior to diazepam-like antagonist drugs, rather than to pentobarbital-like compounds.

The inhibition of sympathetic preganglionic neurons by somatic afferents.

The inhibitory effect of sciatic and ulnar nerve afferent stimulation on the firing frequency of sympathetic preganglionic neurons was studied in anesthetized or unanesthetized decerebrate cats, with intact spinal cords or with spinal cords sectioned at C2. The spontaneous firing and the firing evoked by antidromic stimulation, by iontophoretic glutamate, and by mechanical injury could be depressed, in the preparations both with intact and sectioned spinal cord. The depression was not preceded by excitation. The minimum stimulus strength required for the inhibition was, on average, 15 times the nerve threshold. The inhibition elicited by single shocks lasted several hundred milliseconds and was longer in the intact than in the spinal preparation. The results show that the neural pathway used by high threshold somatic afferents for inhibition of the sympathetic preganglionic neurons is complete within the spinal cord and suggest that the inhibition is probably acting on the preganglionic neuron membrane.

Effects of stimulation of efferent fibres of the vagus on the reticulo-omasal orifice of the sheep.

1. The reticulo-omasal orifice has been observed and its activity recorded in decerebrate and spinal preparations of lambs and in lambs and sheep anaesthetized with chloralose.2. Spontaneous closure movements at about 6/min were seen, or recorded from balloons placed in the orifice in all types of preparation when both vagus nerves had been cut and after atropine, hexamethonium, phentolamine and propranolol had been given I.V.3. The effects on the reticulo-omasal orifice of stimulation in the neck of efferent fibres of the vagus nerves on either side differed according to the form of the stimulus applied.4. Threshold stimulation of the vagus nerve caused closing of the orifice which was blocked by atropine.5. Opening of the orifice and disappearance of spontaneous closing movements followed more intense stimulation of the vagus nerves.6. Vagal opening effects were obtained after atropine was given and after adrenergic opening and closure effects had been blocked with phentolamine and propranolol.

The effects on primary and secondary spindle afferents of fusimotor reflex during ramp and sinusoidal muscle stretch.

Tetanic stimulation of ipsilateral Triceps surae afferents leads to a reflex increase in the “initial burst” from the primary spindle afferents during ramp stretch in both intercollicular decerebrate and spinal preparations. The dynamic index does not change significantly.