Involvement of AMPA Receptors in Maintenance of Memory for a Passive Avoidance Task in Day‐old Domestic Chicks (Gallus domesticus)

Abstract

Day-old chicks (Gallus domesticus) were trained on a one-trial passive avoidance task where the aversive stimulus was an unpleasant tasting substance, methyl anthranilate. Chicks were killed 6.5 h after training. The kinetic parameters of [3H] alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]AMPA) binding were determined using quantitative receptor autoradiography and Scatchard analyses in 15 discrete forebrain regions of trained and control (water-trained) chicks, revealing two components of binding in each. KD values showed some regional variation, but were 22.2 +/- 1.1 nmol l-1 for the high-affinity component and 685 +/- 25 nmol l-1 for the low-affinity component of binding to whole forebrain sections from control chicks. Analyses also revealed that Hill coefficients were significantly less than 1 in all regions measured. A significant decrease in KD for the low-affinity component occurred bilaterally in the intermediate and medial hyperstriatum ventrale (IMHV; left, 34.8%; right, 33.3%), a region that has previously been shown to be implicated in the processes of memory formation, following passive avoidance training. A significant decrease in KD for the high-affinity component occurred in the right palaeostriatum augmentatum (19.5%). Significant decreases in Bmax accompanied the KD alterations in both cases. Additionally, bilateral intracerebral injections (administered 4.5-5.5 h after training) into the IMHV of 500 nmol l-1 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a selective antagonist of non-NMDA glutamate receptors (particularly AMPA receptors), resulted in amnesia for one-trial passive avoidance training in day-old chicks tested 6.5 h after training.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of NMDA and AMPA Receptor Antagonists on Corticosterone Facilitation of Long‐term Memory in the Chick

“…In addition, bilateral injections of CNQX into the IMHV 4.5 or 5.5 h after training induced amnesia for the avoidance response (Steele and Stewart, 1995). These findings are in agreement with our study, where we show that the AMPA receptor antagonist effectively blocked the steroid effect on retention when administered several hours after training and corticosterone treatment (5.5 and 5 h respectively).…”

“…Therefore, our results on the pretraining administration of the antagonists are in agreement with reports implicating NMDA receptors in the early phases of memory formation (Burchuladze and Rose, 1992;Rickard et al, 1994), but are in contrast with the lack of early involvement reported for AMPA receptors (Burchuladze and Rose, 1992;Stewart et al, 1992;Steele and Stewart, 1995). Such a discrepancy is difficult to explain, although previous reports used either lower doses of CNQX (Burchuladze and Rose, 1992) or different times of injection of CNQX (Steele and Stewart, 1995) compared with the injection regimes in our study. However, the strong and weak passive avoidance learning tasks share most training factors, except for the respective intensity of both the aversant and the subsequent stress response (Sandi and Rose, 1997a).…”

“…On the other hand, whereas no changes were found in AMPA receptor properties at early times after training (Stewart et al, 1992;, a recent report has shown increased affinity of the low-affinity component of [3H]AMPA binding in the IMHV 6.5 h after training (Steele and Stewart, 1995), which has also been reported after certain types of mammalian learning (Tocco etal., 1992). In addition, bilateral injections of CNQX into the IMHV 4.5 or 5.5 h after training induced amnesia for the avoidance response (Steele and Stewart, 1995).…”

“…A concentration of 500 nM (5 plhemisphere) of the AMPA antagonist CNQX (Sigma) was injected. This dose was selected since it has been shown to be effective by previous studies in our laboratory (Steele and Stewart, 1995). Bilateral intracranial injections (5 plihemisphere) of either vehicle or the corresponding drug were made using a Hamilton syringe fitted with a plastic sleeve as a stop and a Plexiglas headholder designed to direct the injection into the IMHV (Davis et al, 1979).…”

“…However, AMPA receptors have been implicated in a later phase of the mechanisms of memory consolidation in this memory model. Thus, increased affinity of the low-affinity component of r3H]AMPA binding in the LMHV modulation was shown 6.5 h after training (Steele and Stewart, 1995), and injections of the antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) into the IMHV 4.5 or 5.5 h after training induced amnesia for the avoidance response (Steele and Stewart, 1995).…”