Bt. Larson et al., D-2 DOPAMINE-RECEPTOR RESPONSE TO ENDOPHYTE-INFECTED TALL FESCUE AND AN ANTAGONIST IN THE RAT, Journal of animal science, 72(11), 1994, pp. 2905-2910
Effects on rat brain D-2 dopamine receptors by endophyte-infected tall
fescue seed consumption and antagonist injection were characterized.
Forty-eight male Wistar rats (225 g) in three separate trials were exp
osed to either 22 or 32 degrees C. Diets, to maintain similar concentr
ations of ergovaline, contained 10% (Trial 1) or 15% (Trials 2 and 3)
endophyte-infected (E+; 325 average ppb of ergovaline) or uninfected (
E-; 0 ppb of ergovaline) tall fescue seed. Rats were injected i.p. dai
ly with either placebo (PL) or an experimental D-2 dopamine antagonist
(DA, .0375 mg/kg BW). No effects (P > .10) on diet DM intake by E+ in
gestion or DA injection were detected at 22 degrees C. However, ingest
ion of E+ reduced (P < .01) and injection of DA improved (P < .05) DM
intake of rats housed in 32 degrees C (11.1 vs 15.4 g of DM/d for E+ v
s E-, respectively). Whole brain D-2 dopamine receptor density (B-max)
and mRNA were reduced (P < .05) by E+ and increased (P < .05) by DA i
n Trial 1. No treatment effects (P > .10) on cerebral cortex alpha(1)-
and alpha(2)-adrenergic or striatal D-2 dopamine receptor B-max were
measured in Trials 2 and 3. In summary, dietary E+ reduced whole brain
D-2 dopamine mRNA and B-max, whereas injection of DA increased D-2 do
pamine mRNA. Thus, long-term regulation of monoamine receptors seems t
o be affected by E+ ingestion or DA injection.