Excessive intakes of vitamin B-6 can produce peripheral nervous system
abnormalities, but few reports of central nervous system effects exis
t. We measured startle response, a central nervous system reflex, in r
ats fed excess pyridoxine to determine if subtle effects on central ne
rvous system function could be detected. Female Long-Evans rats (218 g
; n = 12) were fed either 1, 10, 100, 200 or 300 times the requirement
of pyridoxine HCI (7 mg/kg) for 7 wk. Startle behavior was assessed w
eekly in chambers that allowed quantification of movement in response
to stimuli. Food intake and body weights did not differ among groups (
P > 0. 1), and urinary vitamin B-6 excretion reflected intake (P < 0.0
01). Overt toxicity was not observed. There was a marginally significa
nt effect of pyridoxine intake over time (P = 0.053) on the amplitude
of response to a startling acoustic stimulus (117 dB, 40 ms) administe
red alone; the response appeared attenuated at the three highest pyrid
oxine concentrations. When the same stimulus was preceded by either a
70- or 75-dB prepulse (40 ms), responses of groups fed the two highest
pyridoxine concentrations were significantly reduced relative to thos
e fed the two lowest concentrations (P < 0.05). No effect of diet was
seen with a startling tactile stimulus. Changes in central nervous sys
tem function were detected in rats fed excess vitamin B-6 using techni
ques of startle behavior measurement.