Elevation of brain magnesium enhances synaptic plasticity and extinction of conditioned
fear memories. This experiment examined the generalizability of this phenomenon by
studying the effects of a novel magnesium compound, magnesium-L-threonate (MgT), on
conditioned taste aversion (CTA) extinction and spontaneous recovery (SR). Adult male
Sprague-Dawley rats were maintained on a 23-hour water deprivation cycle and acquired
a CTA following the taste of a CS [0.3% saccharin+16 mg/ml MgT (SAC+MgT)] paired with
a US [81 mg/kg (i.p.) lithium chloride (LiCl)]. Following CTA acquisition, rats drank
a water+MgT solution for up to 1 hour/day over the next 31 days. For 14 additional
days, some animals continued water+MgT treatment, but others drank water only to allow
MgT to be eliminated from the body. We then employed 2 different extinction paradigms:
(1) CS-Only (CSO), in which SAC was presented, every-other day, or (2) Explicitly
Unpaired (EU), in which both SAC and LiCl were presented, but on alternate days. EU
extinction procedures have been shown to speed CTA extinction and reduce spontaneous
recovery of the aversion. Throughout extinction, half of the rats in each group continued
to drink MgT (now in SAC or supplemental water+MgT solution), whereas the other half
drank SAC only/water only until SAC drinking reached ≥90% of baseline (asymptotic
extinction). Rats receiving MgT just before/during extinction drank less SAC on the
first day of extinction suggesting that they had retained a stronger CTA. MgT enhanced
the rate of extinction. Furthermore, the MgT-treated rats showed a relatively modest
SR of the CTA 30 days later - indicating that the extinction procedure was more effective
for these animals. Our data suggest that long-term dietary MgT may enhance the consolidation/retention
of a CTA, speed extinction, and inhibit SR of this learned aversion.