TY - JOUR

T1 - Synaptic Vesicle Depletion in Reticulospinal Axons is Reduced by 5‐hydroxytryptamine

T2 - Direct Evidence for Presynaptic Modulation of Glutamatergic Transmission

AU - Shupliakov, O.

AU - Pieribone, V. A.

AU - Gad, H.

AU - Brodin, L.

PY - 1995/1/1

Y1 - 1995/1/1

N2 - 5‐hydroxytryptamine (5‐HT; serotonin) is known to depress glutamatergic synaptic transmission in the spinal cord of vertebrates. To test directly whether 5‐HT inhibits synaptic glutamate release, we examined its effect on the ultrastructure of synaptic vesicle clusters in giant reticulospinal axons in a lower vertebrate (lamprey; Lampetra fluviatilis). The size of these axons makes it possible to selectively expose only a part of the presynaptic element to 5‐HT, while another part of the same axon is maintained in control solution. Action potential stimulation at 20 Hz for 20 min caused a marked reduction in the number of synaptic vesicles in active zones maintained in control solution, while in the part exposed to 5‐HT (20 μM) the number of synaptic vesicles per active zone was ‐3‐fold higher. In contrast, 5‐HT had no effect on the number of vesicles in resting axons. To examine whether 5‐HT acts by reducing presynaptic Ca2+ influx, intra‐axonal recordings of Ba2+ potentials were performed. No reduction of the axonal Ba2+ potential could be detected after application of 20 or 200 pM 5‐HT. The present results show that 5‐HT reduces the rate of synaptic exocytosis in reticulospinal axons. The effect appears to be mediated by a mechanism distinct from the presynaptic Ca2+ channels.

AB - 5‐hydroxytryptamine (5‐HT; serotonin) is known to depress glutamatergic synaptic transmission in the spinal cord of vertebrates. To test directly whether 5‐HT inhibits synaptic glutamate release, we examined its effect on the ultrastructure of synaptic vesicle clusters in giant reticulospinal axons in a lower vertebrate (lamprey; Lampetra fluviatilis). The size of these axons makes it possible to selectively expose only a part of the presynaptic element to 5‐HT, while another part of the same axon is maintained in control solution. Action potential stimulation at 20 Hz for 20 min caused a marked reduction in the number of synaptic vesicles in active zones maintained in control solution, while in the part exposed to 5‐HT (20 μM) the number of synaptic vesicles per active zone was ‐3‐fold higher. In contrast, 5‐HT had no effect on the number of vesicles in resting axons. To examine whether 5‐HT acts by reducing presynaptic Ca2+ influx, intra‐axonal recordings of Ba2+ potentials were performed. No reduction of the axonal Ba2+ potential could be detected after application of 20 or 200 pM 5‐HT. The present results show that 5‐HT reduces the rate of synaptic exocytosis in reticulospinal axons. The effect appears to be mediated by a mechanism distinct from the presynaptic Ca2+ channels.

KW - exocytosis

KW - presynaptic inhibition

KW - serotonin

KW - spinal cord

UR - http://www.scopus.com/inward/record.url?scp=0029074686&partnerID=8YFLogxK

U2 - 10.1111/j.1460-9568.1995.tb01099.x

DO - 10.1111/j.1460-9568.1995.tb01099.x

M3 - Article

C2 - 7613617

AN - SCOPUS:0029074686

VL - 7

SP - 1111

EP - 1116

JO - European Journal of Neuroscience

JF - European Journal of Neuroscience

SN - 0953-816X

IS - 5

ER -