An associativity requirement for noradrenergic dentate gyrus long-term potentiation in the urethane-anesthetized rat

Glutamatergic activation of the locus coeruleus results in long-term potentiation of dentate gyrus perforant path-evoked population spike amplitude, when paired with perforant path stimulation (.25 Hz). In vitro evidence, however, suggests that this 13-adrenoceptor-rediated effect can also, occur in the absence of perforant path activity. The present study seeks to determine whether pairing of perforant path stimulation and locus coeruleus activation is necessary for norepinephrine-induced population spike potentiation to occur in vivo in urethane-anesthetized rats. Glutamatergic stimulation of the locus coeruleus in the absence of perforant path stimulation resulted in a transient spike and slope increase which returned to baseline by 10 min. In contrast, locus coeruleus activation concurrent with perforant path stimulation resulted in long-lasting potentiation of both spike and slope. These results suggest that, under the conditions of the present study, a temporal pairing of noradrenergic activity with perforant path activity in the dentate gyrus is necessary for the induction of long-term population spike and EPSP slope potentiation.