Brachium conjunctivum‐red nucleus synaptic system in the baboon

Abstract

Electrophysiological properties of the brachium conjunctivum-red nucleus (BC-RN) synaptic system were studied in barbiturate-anesthetized baboon (Papio). Topographic recordings from the mesencephalon demonstrated that most of the BC-evoked activity was restricted to an area histologically identified as red nucleus; however, some brachium-evoked activity was recorded from the surrounding mesencephalic reticular formation. Short latency BC-evoked activity was also recorded from the pons in the region of nucleus reticularis tegmenti pontis. The majority of the BC fibers were found to conduct at a rate of 44 m/sec; a second group of BC fibers with a slower conduction velocity of 23 m/sec was also observed. Brachium-evoked responses recorded from magnocellular and pravicellular RN neurons were short latency responses consistent with monosynaptic activation of these RN neurons by the BC fibers. The BC-RN synaptic system was found to be a very secure synaptic system and could transmit activity at high rates of stimulation with little or no failure. The responsiveness of the BC fibers was found to be similar to that of optic nerve fibers and pyramidal tract fibers, both of which have been characterized as being similar to peripheral A fibers. The responsiveness of the BC-RN synaptic system began to decrease 5 msec after a single or repetitive transmission and was reduced to about 50% of normal responsiveness at 34 msec. This period of reduced postsynaptic responsiveness was associated with a reduction in presynaptic input to RN and suggest that a disfacilitation at the level of the deep cerebellar nuclei may be in part responsible for the subnormal responsiveness of the BC-RN synaptic system.

Pharmacology of the brachium conjunctivum: Red nucleus synaptic system in the baboon

“…and indolealkylamines reduced the responsiveness of baboon RN neurons, both magnocellular and parvicellular, to both BC and amino acid activation. These compounds generally were less effective in blocking or reducing BC-RN synaptic transmission than amino acid-evoked firing, a fact most likely explained by the powerful and fairly secure synaptic activation of RN neurons by the BC fibers (Huffman and Davis, 1976) and the remoteness of these synaptic terminations relative to the tip of the microelectrode. The neurochemically demonstrated presence of these putative neurotransmitters in RN together with the pharmacologically demonstrated reduced responsiveness of RN neurons following the iontophoretic application of these substances suggests that NA, DA, and 5HT may play a functional role in RN; whether these substances function as synaptic transmitters in RN or as modulators of RN activity is not clear at the present time.…”

“…Neuronal activity was continuously monitored on an oscilloscope and stored on tape for analysis and photography at a later time. Using a stainless steel electrode, a site was found in the midbrain where short-latency, multineuronal responses could be recorded following an electrical stimulus applied to the BC fibers at the hilum of the contralateral cerebellar nuclei (Huffman and Davis, 1976). Once a suitable recording site was located and the coordinates noted, the steel electrode was replaced with a drug-containing multibarrel electrode.…”

“…Brachium conjunctivum fibers originating from dentate nucleus project to the contralateral RNp, while those BC fibers originating from the anterior interpositus nucleus project to the contralateral RNm (Flumerfelt, Otabe, and Courville, 1973). The electrophysiologic properties of the brachium conjunctivum-red nucleus (BC-RN) synaptic system of the baboon have been reported recently by Huffman and Davis (1976). The responsiveness of feline RN neurons to microiontophoretically applied amino acids, acetylcholine, and biogenic amines has been reported (Davis and Vaughan, 1969;Altmann et al, 1973).…”

Pharmacology of the brachium conjunctivum: Red nucleus synaptic system in the baboon

“…and indolealkylamines reduced the responsiveness of baboon RN neurons, both magnocellular and parvicellular, to both BC and amino acid activation. These compounds generally were less effective in blocking or reducing BC-RN synaptic transmission than amino acid-evoked firing, a fact most likely explained by the powerful and fairly secure synaptic activation of RN neurons by the BC fibers (Huffman and Davis, 1976) and the remoteness of these synaptic terminations relative to the tip of the microelectrode. The neurochemically demonstrated presence of these putative neurotransmitters in RN together with the pharmacologically demonstrated reduced responsiveness of RN neurons following the iontophoretic application of these substances suggests that NA, DA, and 5HT may play a functional role in RN; whether these substances function as synaptic transmitters in RN or as modulators of RN activity is not clear at the present time.…”

“…Neuronal activity was continuously monitored on an oscilloscope and stored on tape for analysis and photography at a later time. Using a stainless steel electrode, a site was found in the midbrain where short-latency, multineuronal responses could be recorded following an electrical stimulus applied to the BC fibers at the hilum of the contralateral cerebellar nuclei (Huffman and Davis, 1976). Once a suitable recording site was located and the coordinates noted, the steel electrode was replaced with a drug-containing multibarrel electrode.…”

“…Brachium conjunctivum fibers originating from dentate nucleus project to the contralateral RNp, while those BC fibers originating from the anterior interpositus nucleus project to the contralateral RNm (Flumerfelt, Otabe, and Courville, 1973). The electrophysiologic properties of the brachium conjunctivum-red nucleus (BC-RN) synaptic system of the baboon have been reported recently by Huffman and Davis (1976). The responsiveness of feline RN neurons to microiontophoretically applied amino acids, acetylcholine, and biogenic amines has been reported (Davis and Vaughan, 1969;Altmann et al, 1973).…”

Pharmacology of the brachium conjunctivum: Red nucleus synaptic system in the baboon

“…and indolealkylamines reduced the responsiveness of baboon RN neurons, both magnocellular and parvicellular, to both BC and amino acid activation. These compounds generally were less effective in blocking or reducing BC-RN synaptic transmission than amino acid-evoked firing, a fact most likely explained by the powerful and fairly secure synaptic activation of RN neurons by the BC fibers (Huffman and Davis, 1976) and the remoteness of these synaptic terminations relative to the tip of the microelectrode. The neurochemically demonstrated presence of these putative neurotransmitters in RN together with the pharmacologically demonstrated reduced responsiveness of RN neurons following the iontophoretic application of these substances suggests that NA, DA, and 5HT may play a functional role in RN; whether these substances function as synaptic transmitters in RN or as modulators of RN activity is not clear at the present time.…”

“…Neuronal activity was continuously monitored on an oscilloscope and stored on tape for analysis and photography at a later time. Using a stainless steel electrode, a site was found in the midbrain where short-latency, multineuronal responses could be recorded following an electrical stimulus applied to the BC fibers at the hilum of the contralateral cerebellar nuclei (Huffman and Davis, 1976). Once a suitable recording site was located and the coordinates noted, the steel electrode was replaced with a drug-containing multibarrel electrode.…”

“…Brachium conjunctivum fibers originating from dentate nucleus project to the contralateral RNp, while those BC fibers originating from the anterior interpositus nucleus project to the contralateral RNm (Flumerfelt, Otabe, and Courville, 1973). The electrophysiologic properties of the brachium conjunctivum-red nucleus (BC-RN) synaptic system of the baboon have been reported recently by Huffman and Davis (1976). The responsiveness of feline RN neurons to microiontophoretically applied amino acids, acetylcholine, and biogenic amines has been reported (Davis and Vaughan, 1969;Altmann et al, 1973).…”

Pharmacology of the brachium conjunctivum: Red nucleus synaptic system in the baboon

“…and indolealkylamines reduced the responsiveness of baboon RN neurons, both magnocellular and parvicellular, to both BC and amino acid activation. These compounds generally were less effective in blocking or reducing BC-RN synaptic transmission than amino acid-evoked firing, a fact most likely explained by the powerful and fairly secure synaptic activation of RN neurons by the BC fibers (Huffman and Davis, 1976) and the remoteness of these synaptic terminations relative to the tip of the microelectrode. The neurochemically demonstrated presence of these putative neurotransmitters in RN together with the pharmacologically demonstrated reduced responsiveness of RN neurons following the iontophoretic application of these substances suggests that NA, DA, and 5HT may play a functional role in RN; whether these substances function as synaptic transmitters in RN or as modulators of RN activity is not clear at the present time.…”

“…Neuronal activity was continuously monitored on an oscilloscope and stored on tape for analysis and photography at a later time. Using a stainless steel electrode, a site was found in the midbrain where short-latency, multineuronal responses could be recorded following an electrical stimulus applied to the BC fibers at the hilum of the contralateral cerebellar nuclei (Huffman and Davis, 1976). Once a suitable recording site was located and the coordinates noted, the steel electrode was replaced with a drug-containing multibarrel electrode.…”

“…Brachium conjunctivum fibers originating from dentate nucleus project to the contralateral RNp, while those BC fibers originating from the anterior interpositus nucleus project to the contralateral RNm (Flumerfelt, Otabe, and Courville, 1973). The electrophysiologic properties of the brachium conjunctivum-red nucleus (BC-RN) synaptic system of the baboon have been reported recently by Huffman and Davis (1976). The responsiveness of feline RN neurons to microiontophoretically applied amino acids, acetylcholine, and biogenic amines has been reported (Davis and Vaughan, 1969;Altmann et al, 1973).…”