D1 receptor modulation of memory retrieval performance is associated with changes in pCREB and pDARPP-32 in rat prefrontal cortex

Dopaminergic regulation of inhibitory and excitatory transmission in the basolateral amygdala-prefrontal cortical pathway

Projections from the basolateral amygdala (BLA) and dopamine (DA) input from the ventral tegmental area (VTA) converge in the medial prefrontal cortex (mPFC), forming a neural circuit implicated in certain cognitive and emotional processes. However, the role that DA plays in modulating activity in the BLA-mPFC pathway is unknown. The present study investigated the mechanisms by which DA modulates BLA-evoked changes in mPFC neural activity, using extracellular single-unit recordings in urethane-anesthetized rats. BLA stimulation evoked two distinct types of responses in separate populations of mPFC neurons: monosynaptic, excitatory responses and, more commonly, inhibition of spontaneous firing. Stimulation of the VTA or local iontophoretic application of DA attenuated BLA-evoked inhibition of PFC neuron firing. Administration of selective DA receptor agonists revealed that these effects were mediated by D2 and D4 (but not D1) receptors. In addition, VTA stimulation or DA application attenuated BLA-evoked firing of a separate population of mPFC neurons in a frequency-dependent manner; firing evoked by higher-frequency stimulation of the BLA was less inhibited than that evoked by single-pulse stimulation. Attenuation of BLA-evoked firing was also induced by of D1 (but not D2 or D4) receptor agonists. These data indicate that dissociable DA receptor mechanisms regulate the balance of excitatory and inhibitory transmission in BLA-mPFC circuits, biasing toward an increase in the excitatory influence that the BLA exerts over populations of mPFC neurons. These findings may have important implications for understanding the pathophysiology underlying emotional and cognitive disturbances present in disorders such as depression and drug addiction.

The pharmacology, neuroanatomy and neurogenetics of one-trial object recognition in rodents

Rats and mice are attracted by novel objects. They readily approach novel objects and explore them with their vibrissae, nose and forepaws. It is assumed that such a single explorative episode leaves a lasting and complex memory trace, which includes information about the features of the object explored, as well as where and even when the object was encountered. Indeed, it has been shown that rodents are able to discriminate a novel from a familiar object (one-trial object recognition), can detect a mismatch between the past and present location of a familiar object (one-trial object-place recognition), and can discriminate different objects in terms of their relative recency (temporal order memory), i.e., which one of two objects has been encountered earlier. Since the novelty-preference paradigm is very versatile and has some advantages compared to several other memory tasks, such as the water maze, it has become a powerful tool in current neurophamacological, neuroanatomical and neurogenetical memory research using both rats and mice. This review is intended to provide a comprehensive summary on key findings delineating the brain structures, neurotransmitters, molecular mechanisms and genes involved in encoding, consolidation, storage and retrieval of different forms of one-trial object memory in rats and mice.

Further study of the effects of dopaminergic D1 drugs on place avoidance behavior using pretraining: some negative evidence

Dopaminergic neurotransmission is considered to modulate cognitive processes, including spatial memory. The aim of this study was to further evaluate the role of the D1 receptor system in an active allothetic place avoidance (AAPA) task using pretrained rats. Our previous results showed enhanced AAPA learning after systemic injections of low doses of D1 agonist A77636, and the impairment of AAPA acquisition by D1 blocker SCH23390 [Stuchlik A, Vales K. Effect of dopamine D1 receptor antagonist SCH23390 and agonist A77636 on active allothetic place avoidance, a spatial cognition task. Behav Brain Res 2006;172(2):250-255]. In the present study, we used the intact-pretraining paradigm, in which animals were trained to the task prior to the injections and subsequently retrieval and reacquisition of AAPA while under the effects of the drugs was tested. Results showed that the intact pretraining partly eliminated the effects of A77636 and SCH23390 on AAPA performance, but a higher dose of SCH23390 caused a motor deficit in the retrieval session. We conclude that in the previous study, D1-active drugs may have had influence upon the non-spatial aspects of the AAPA.