Innervation and reinnervation of rat inferior olive by neurons containing serotonin and substance P: an immunohistochemical study after 5,6-dihydroxytryptamine lesioning.
Serotonin (5-HT) and substance P (SP) immunoreactive axon terminals were visualized in the inferior olivary complex (IOC) of adult rats, 1 to 2 weeks or 6 to 12 months after cerebro-ventricular injection of 5,6-dihydroxytryptamine (5,6-DHT). In normal or saline-injected controls of the same age, there was some overlap between the respective distributions of 5-HT- and SP-immunostained axonal varicosities among the various subdivisions of IOC. At short time intervals after the 5-HT axotomy, almost as many degenerating axonal profiles showed immunoreactivity to SP as to 5-HT throughout the IOC, suggesting the coexistence of both transmitters within the same fibres. A few areas continued to exhibit characteristic patches of 'normal-looking' SP immunoreactivity, consistent with a distinct innervation by SP fibres without coexistent 5-HT. At prolonged survival times after 5,6-DHT treatment, there was a massive increase in the number-and striking similarity in the distribution-of IOC axonal varicosities immunostained for SP as well as for 5-HT. This neo-innervation involved certain subdivisions of the IOC normally receiving fibres of either type (e.g. dorsal accessory olive), but also others normally poor in 5-HT and/or SP (e.g. medial accessory olive). It remains to be determined if this abundance of 5-HT-SP terminals in the 'hyperinnervated' IOC reflected a particular capacity to express both transmitters in regenerating 5-HT neurons.
D015115:5,6-Dihydroxytryptamine / Q000494:pharmacology*; D000818:Animals; D007124:Immunoenzyme Techniques; D008297:Male; D009473:Neuronal Plasticity; D009847:Olivary Nucleus / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism*
D012701:Serotonin; D013373:Substance P; D015115:5,6-Dihydroxytryptamine