Effects of intranigral substance P and neurokinin A on striatal dopamine release--I. Interactions with substance P antagonists.
The functional role of striatonigral neurokinins were studied by analysing the effects of intranigral injections of substance P and neurokinin A on the extracellular level of dopamine and dihydroxyphenylacetic acid in the striatum, as measured by in vivo microdialysis in rats. Two substance P antagonists, substance P D-Pro2 D-Trp7,9 and substance P D-Arg1 D-Trp7,9 Leu11 were tested and analysed for their ability to block the neurokinin effects. Unilateral injections of substance P (0.00007-7.0 nmol injected in 0.2 microliter) as well as neurokinin A (0.009-9.0 nmol) into the substantia nigra, pars reticulata of halothane anaesthetized rats produced long-lasting increases in ipsilateral striatal dopamine and dihydroxyphenylacetic acid levels. The dose-response relationship for substance P on dopamine was biphasic, with maximal effects occurring after the middle dose (0.007-0.07 nmol). The dose-response relationship for neurokinin A was monophasic. Intranigral injections of substance P D-Pro2 D-Trp7,9 (0.07-0.7 nmol) or substance P D-Arg1 D-Trp7,9 Leu11 (0.07-0.7 nmol) produced a decrease in striatal dopamine, but an increase in striatal dihydroxyphenylacetic acid. At a low dose (0.07 nmol) substance P D-Pro2 D-Trp7,9 enhanced the dopamine increase produced by intranigral substance P (0.07 nmol) or neurokinin A (0.09), while at a high dose (0.7 nmol) it blocked both substance P and neurokinin A effects. Both doses of substance P D-Arg1 D-Trp7,9 Leu11 (0.07 and 0.7 nmol) blocked the substance P- but not the neurokinin A-induced increase in striatal dopamine. Immunohistochemical analysis revealed that high doses of substance P (7.0 nmol) and neurokinin A (0.9 and 9.0 nmol), as well as substance P D-Pro2 D-Trp7,9 and substance P D-Arg1 D-Trp7,9 Leu11 (0.07 and 0.7 nmol), induced a restricted loss of tyrosine hydroxylase in dendrites and cells, and neuropeptide K in terminals, at the site of injection. Further analysis shows that co-administration of substance P (0.07 nmol) or neurokinin A (0.09 nmol) did not modify the extent of the depletion of both immunoreactivities induced by substance P D-Arg1 D-Trp7,9 Leu11 (0.7 nmol). The extent of the effect produced by substance P D-Arg1 D-Trp7,9 Leu11 (0.7 nmol) was, however, smaller than the spread of intranigral injection of [125I]Bolton-Hunter-labelled substance P D-Arg1 D-Trp7,9 Leu11, and it is suggested that the "neurotoxic" effects of the substance P antagonists are not primarily involved in their abilities to inhibit striatal dopamine release and block the stimulation of dopamine after intranigral substance P and neurokinin A.(ABSTRACT TRUNCATED AT 400 WORDS)
Reid
M S
MS
Department of Pharmacology, Karolinska Institute, Stockholm, Sweden.
Herrera-Marschitz
M
M
Hökfelt
T
T
Ohlin
M
M
Valentino
K L
KL
Ungerstedt
U
U
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D003342:Corpus Striatum / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D004347:Drug Interactions; D005110:Extracellular Space / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D015288:Neurokinin A / Q000378:metabolism / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013373:Substance P / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D013378:Substantia Nigra / Q000378:metabolism*
D010446:Peptide Fragments; D015102:3,4-Dihydroxyphenylacetic Acid; D013373:Substance P; C045505:substance P (4-11), Pro(4)-Trp(7,9)-; D015288:Neurokinin A; D004298:Dopamine