Genetic Enhancement of Visual Learning by Activation of Protein Kinase C Pathways in Small Groups of Rat Cortical Neurons

Abstract

Although learning and memory theories hypothesize that memories are encoded by specific circuits, it has proven difficult to localize learning within a cortical area. Neural network theories predict that activation of a small fraction of the neurons in a circuit can activate that circuit. Consequently, altering the physiology of a small group of neurons might potentiate a specific circuit and enhance learning, thereby localizing learning to that circuit. In this study, we activated protein kinase C (PKC) pathways in small groups of neurons in rat postrhinal (POR) cortex. We microinjected helper virus-free herpes simplex virus vectors that expressed a constitutively active PKC into POR cortex. This PKC was expressed predominantly in glutamatergic and GABAergic neurons in POR cortex. This intervention increased phosphorylation of five PKC substrates that play critical roles in neurotransmitter release (GAP-43 and dynamin) or glutamatergic neurotransmission (specific subunits of AMPA or NMDA receptors and myristoylated alanine-rich C kinase substrate). Additionally, activation of PKC pathways in cultured cortical neurons supported activation-dependent increases in release of glutamate and GABA. This intervention enhanced the learning rate and accuracy of visual object discriminations. In individual rats, the numbers of transfected neurons positively correlated with this learning. During learning, neuronal activity was increased in neurons proximal to the transfected neurons. These results demonstrate that potentiating small groups of glutamatergic and GABAergic neurons in POR cortex enhances visual object learning. More generally, these results suggest that learning can be mediated by specific cortical circuits.

Identified circuit in rat postrhinal cortex encodes essential information for performing specific visual shape discriminations

“…We delivered a constitutively active PKC into several hundred spatially grouped glutamatergic and GABAergic POR cortex neurons via a virus vector (12). This intervention activated PKC pathways, increased activation-dependent neurotransmitter release, and supported faster learning and improved steady-state accuracy for visual shape discriminations learned after gene transfer (12). Further, activity-dependent gene imaging showed increased activity in the genetically targeted circuit during performance (12).…”

“…An alternative approach is to target some essential information to an identified circuit, by genetically modifying the physiology of small groups of neurons in a specific neocortical area. With a suitable genetic intervention, the modified neurons will increase their response to incoming neuronal activity, including that associated with learning (12), likely placing some of the essential information in the circuit containing the modified neurons (SI Text).…”

“…We developed a model system for exploiting this essential information-targeting approach by activating protein kinase C (PKC) pathways in small groups of rat postrhinal (POR) cortex neurons before visual shape discrimination learning (12,13). Rat POR cortex, and specific areas in monkeys and humans, are required for this learning (14), specific PKC genes are required for multiple types of learning (15,16), and a constitutively active PKC is required for specific cognitive learning tasks (17).…”

“…Rat POR cortex, and specific areas in monkeys and humans, are required for this learning (14), specific PKC genes are required for multiple types of learning (15,16), and a constitutively active PKC is required for specific cognitive learning tasks (17). We delivered a constitutively active PKC into several hundred spatially grouped glutamatergic and GABAergic POR cortex neurons via a virus vector (12). This intervention activated PKC pathways, increased activation-dependent neurotransmitter release, and supported faster learning and improved steady-state accuracy for visual shape discriminations learned after gene transfer (12).…”

“…Results Some Essential Information Is in a Specific Circuit. The hypothesis that the genetically targeted circuit encodes some of the essential information for performance on specific image sets was derived by further analysis of published results (12). After gene transfer of a constitutively active PKC (PkcΔ) (12) or controls (PkcΔGG, a point mutation lacking enzyme activity, or wt), rats were either retested on an image set learned before gene transfer (pre-genetransfer image set) or tested on a new image set (post-genetransfer image set).…”