Gamma-L-glutamyl-L-aspartate, interacting with NMDA receptors, affects appetitive visual discrimination tasks in mice

Blockade of spontaneous posttraining performance improvement in mice by NMDA antagonists

We investigated the effects of immediate post-training systemic administration of gamma-L-glutamyl-L-aspartate (gamma-LGLA) and 3-(2-carboxypiperazine-4-yl)-propyl-1-phosphonate (CPP), antagonists at the N-methyl-D-aspartate receptor, in a lever-press task in two inbred strains of mice. When retention performance was tested in control animals 24 h after partial acquisition of the task. BALB/c mice exhibited a spontaneous performance improvement whereas C57BL/6J mice did not gamma-LGLA at doses of 2.5 and 25 mumol/kg and CPP at doses ranging between 0.025 and 2.5 mumol/kg blocked the spontaneous performance improvement found in BALB/c mice but had no apparent effects on the retention performance of C57BL/6J mice. These data suggest that retention impairment induced by CPP and gamma-LGLA in BALB/c mice results from an interference with posttraining memory processes.

Involvement of AMPA receptors in maintenance of memory for a passive avoidance task in day-old domestic chicks (Gallus domesticus)

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)

Increases in NMDA receptor binding are specifically related to memory formation for a passive avoidance task in the chick: a quantitative autoradiographic study

One-day-old chicks (Gallus domesticus) were trained on a one-trial passive avoidance task in which the aversive stimulus was an unpleasant lasting substance, methylanthranilate (MeA). Control birds were presented with a water (W) coated bead. Five minutes after training a group of McA-trained chicks were given a brief sub-convulsive trans-cranial electric shock, which rendered half amnesic whilst the remainder were able to show recall for the aversive stimulus. Thirty minutes after training birds were killed and quantitative receptor autoradiography was used to determine NMDA sensitive [3H]L-glutamate binding in specific regions of the forebrain of: (i) MeA-trained chicks; (ii) water-control chicks; (iii) MeA-trained electroshocked chicks showing recall; and (iv) MeA-electroshocked chicks amnesic for the aversive stimulus. Increases (805 in the left lobus parolfactorius and 67% in the left intermediate medial hyperstriatum ventrale) in NMDA sensitive [3H]L-glutamate binding occurred in electro-shocked chicks which showed recall of the aversive experience but were absent in MeA-trained chicks rendered amnesic by electro-shock. The increased binding in electroshocked MeA-trained birds which showed recall was similar to that observed previously in MeA-trained birds (without electroshock), compared to water control birds, whereas binding levels in McA-trained electroshocked amnesic birds were not different from those of water control birds. These data argue strongly in MeA-trained electroshocked amnesic birds were not different from those of water control birds. These data argue strongly that alterations in binding to glutamate receptor sub-types are specific to memory formation for the passive avoidance task.

The molecular neurobiology of early learning, development, and sensitive periods, with emphasis on the avian brain

The subcellular processes that correlate with early learning and memory formation in the chick and sensitive periods for this learning are discussed. Imprinting and passive avoidance learning are followed by a number of cellular processes, each of which persists for a characteristic time in certain brain regions, and may culminate in synaptic structure modification. In the chick brain, the NMDA subtype of glutamate receptor appears to play an important role in both memory formation and sensitive periods during development, similar to its demonstrated role in neural plasticity in the mammalian brain. Two important findings have emerged from the studies using chickens. First, memory formation appears to occur at multiple sites in the forebrain and, most importantly, it appears to "flow" from one site to another, leaving neurochemical traces in each as it moves on. Second, the memory is laid down either in different sites or in different subcellular events in the left and right forebrain hemispheres. Hence, we are alerted to the possibility of similar asymmetrical processes occurring in memory consolidation in the mammalian brain. The similarities between early memory formation and experience-dependent plasticity of the brain during development are discussed.