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The suppression of postural muscle tone and its brainstem and spinal cord neuronal mechanisms in acute decerebrate, reflex standing cats
$66 POSTSYNAPTIC POTENTIAL IN SOLEUS ALPHA-MOTONEURON(MN)S THE DORSAL PART OF THE MID-PONTINE TEGMENTAL FIELD.
ELICITED
BY STIMULATING
TAKASHI SAKAMOTO~, KIYOJI ~ T S U Y A ~ * , and KAORU TAKAKUSAKI*, Dept. of Physiol., Asahikawa Med. Coll., 4-5-3-11Nishikagura, Asahikawa 078-11, JAPAN In a precollicular-postmammillary decerebrate, standing cat, stimulation (0.2 ms duration, i0 to 40 uA, 50 Hz, 5 to IOs) of the dorsal part of the mid-pontine tegmental field (P3 to PT, LR0, H-4.5 to H-6) suppresses the tone of hindlimb muscles, with membrane hyperpolarization of soleus alpha~. During the period of mid-pontine stimulation, peak amplitude of la EPSPs, the spike summit level of antidromic action potential and input resistance of }~s decreased in parallel with membrane hyperpolarization. Moreover, the membrane hyperpolarization was reversed by intracellular injection of chloride. All these results indicate that, postsynaptic inhibition plays a major role in eliciting membrane hyperpolarization during mid-pontlne stimulation. To further study postsynaptlc inhibitory mechanisms, we recorded from soleus alpha-MNs (n=10) synaptic potential changes elicited by a single mid-pontine stimulation, in the same preparation. Both early and late membrane hyperpolarization were recorded from these }~s. The former was of a short latency (4.0 to 6.0 ms) and a short duration (i0 to 30 ms), and the latter was of a longer latency (30 to 40 ms) and a longer duration (30 to several tens ms). In the four MNs only early membrane hyperpolarizatlon was recorded. The early and late hyperpolarization were reversed by intracellular injection of direct hyperpolarizing currents. The spike summit level of antidromlcally evoked spike potential was suppressed with a corresponding time course to the early and late membrane hyperpolarization. All these results suggest that a single mid-pontine stimulation elicits different kinds of inhibitory postsynaptic potentials upon soleus alpha-}~s.
THE SUPPRESSION OF POSTURAL MUSCLE TONE AND ITS BRAINSTEM AND NEURONAL MECHANISMS IN ACUTE DECEREBRATE, REFLEX STANDING CATS.
SPINAL
YOSHIHIRO OHTA*, SATOSHI NONAKA~, SHIGEMI MORI Dept. of Physiol., Med. Coll., 4-5-3-11Nishikagura, Asahikawa 078-11, JAPAN
CORD
Asahikawa
Stimulation of the dorsal part of the pons along the midline decreases the tone of the hindlimb extensor muscles in acute precollicular-postmammillary decerebrate, reflex standing cats. The effective stimulus area corresponds to a caudal portion of the nucleus centralis superior, where there are few cell bodies. In order to study the possibility that we are stimulating passing fibers from various origins, we made a mlcrolesion at the effective stimulus area and injected HRP there. Labeled neurons were identified in the dorsolateral tegmental area, including nucleus locus coeruleus, in the pontine reticular formation and in the medullary reticular formation. Testing whether or not these labeled neurons send their axons to the spinal cord, TI2 spinal cord were stimulated. There were neurons among pontine reticular neurons which were activated antidromlcally from the spinal cord and were activated directly or orthodromically by mid-pontine stimulation. There were neurons among medial medullary reticular neurons which were activated from the spinal cord and were activated orthodromically by mld-pontine stimulation. We studied whether or not these medullary neurons exert inhibitory effects upon extensor alpha motoneurons (}~s) innervating hlndlimb muscles. To do this, we selected medial medullary reticular neurons which discharged tonically, and using each spike as a trigger signal, intracellular membrane potentials of a single extensor alpha~ were averaged. It was found that some medial medullary reticular neurons evoked hyperpolarizations of membrane potential with a fixed latency. These results suggest that a part of the pontine-evoked inhibitory effects is mediated to the extensor alpha-MNs by way of medial medullary reticular neurons.
ELICITED
BY STIMULATING
TAKASHI SAKAMOTO~, KIYOJI ~ T S U Y A ~ * , and KAORU TAKAKUSAKI*, Dept. of Physiol., Asahikawa Med. Coll., 4-5-3-11Nishikagura, Asahikawa 078-11, JAPAN In a precollicular-postmammillary decerebrate, standing cat, stimulation (0.2 ms duration, i0 to 40 uA, 50 Hz, 5 to IOs) of the dorsal part of the mid-pontine tegmental field (P3 to PT, LR0, H-4.5 to H-6) suppresses the tone of hindlimb muscles, with membrane hyperpolarization of soleus alpha~. During the period of mid-pontine stimulation, peak amplitude of la EPSPs, the spike summit level of antidromic action potential and input resistance of }~s decreased in parallel with membrane hyperpolarization. Moreover, the membrane hyperpolarization was reversed by intracellular injection of chloride. All these results indicate that, postsynaptic inhibition plays a major role in eliciting membrane hyperpolarization during mid-pontlne stimulation. To further study postsynaptlc inhibitory mechanisms, we recorded from soleus alpha-MNs (n=10) synaptic potential changes elicited by a single mid-pontine stimulation, in the same preparation. Both early and late membrane hyperpolarization were recorded from these }~s. The former was of a short latency (4.0 to 6.0 ms) and a short duration (i0 to 30 ms), and the latter was of a longer latency (30 to 40 ms) and a longer duration (30 to several tens ms). In the four MNs only early membrane hyperpolarizatlon was recorded. The early and late hyperpolarization were reversed by intracellular injection of direct hyperpolarizing currents. The spike summit level of antidromlcally evoked spike potential was suppressed with a corresponding time course to the early and late membrane hyperpolarization. All these results suggest that a single mid-pontine stimulation elicits different kinds of inhibitory postsynaptic potentials upon soleus alpha-}~s.
THE SUPPRESSION OF POSTURAL MUSCLE TONE AND ITS BRAINSTEM AND NEURONAL MECHANISMS IN ACUTE DECEREBRATE, REFLEX STANDING CATS.
SPINAL
YOSHIHIRO OHTA*, SATOSHI NONAKA~, SHIGEMI MORI Dept. of Physiol., Med. Coll., 4-5-3-11Nishikagura, Asahikawa 078-11, JAPAN
CORD
Asahikawa
Stimulation of the dorsal part of the pons along the midline decreases the tone of the hindlimb extensor muscles in acute precollicular-postmammillary decerebrate, reflex standing cats. The effective stimulus area corresponds to a caudal portion of the nucleus centralis superior, where there are few cell bodies. In order to study the possibility that we are stimulating passing fibers from various origins, we made a mlcrolesion at the effective stimulus area and injected HRP there. Labeled neurons were identified in the dorsolateral tegmental area, including nucleus locus coeruleus, in the pontine reticular formation and in the medullary reticular formation. Testing whether or not these labeled neurons send their axons to the spinal cord, TI2 spinal cord were stimulated. There were neurons among pontine reticular neurons which were activated antidromlcally from the spinal cord and were activated directly or orthodromically by mid-pontine stimulation. There were neurons among medial medullary reticular neurons which were activated from the spinal cord and were activated orthodromically by mld-pontine stimulation. We studied whether or not these medullary neurons exert inhibitory effects upon extensor alpha motoneurons (}~s) innervating hlndlimb muscles. To do this, we selected medial medullary reticular neurons which discharged tonically, and using each spike as a trigger signal, intracellular membrane potentials of a single extensor alpha~ were averaged. It was found that some medial medullary reticular neurons evoked hyperpolarizations of membrane potential with a fixed latency. These results suggest that a part of the pontine-evoked inhibitory effects is mediated to the extensor alpha-MNs by way of medial medullary reticular neurons.