Paradoxical effects of low dose MDMA on latent inhibition in the rat

Hippocampal Disinhibition Reduces Contextual and Elemental Fear Conditioning While Sparing the Acquisition of Latent Inhibition

Hippocampal neural disinhibition, i.e., reduced GABAergic inhibition, is a key feature of schizophrenia pathophysiology. The hippocampus is an important part of the neural circuitry that controls fear conditioning and can also modulate prefrontal and striatal mechanisms, including dopamine signaling, which play a role in salience modulation. Consequently, hippocampal neural disinhibition may contribute to impairments in fear conditioning and salience modulation reported in schizophrenia. Therefore, we examined the effect of ventral hippocampus (VH) disinhibition in male rats on fear conditioning and salience modulation, as reflected by latent inhibition (LI), in a conditioned emotional response (CER) procedure. A flashing light was used as the conditioned stimulus (CS), and conditioned suppression was used to index conditioned fear. In experiment 1, VH disinhibition via infusion of the GABA-A receptor antagonist picrotoxin before CS pre-exposure and conditioning markedly reduced fear conditioning to both the CS and context; LI was evident in saline-infused controls but could not be detected in picrotoxin-infused rats because of the low level of fear conditioning to the CS. In experiment 2, VH picrotoxin infusions only before CS pre-exposure did not affect the acquisition of fear conditioning or LI. Together, these findings indicate that VH neural disinhibition disrupts contextual and elemental fear conditioning, without affecting the acquisition of LI. The disruption of fear conditioning resembles aversive conditioning deficits reported in schizophrenia and may reflect a disruption of neural processing both within the hippocampus and in projection sites of the hippocampus.

Data showing regional differences in rat brain monoaminergic function

Chemical neurotransmitters (such as dopamine) modulate cognitive function via ascending projections to various cortical and sub-cortical brain regions. This report describes and links to a relatively large dataset (up to N = 112) compiled from control (untreated) brain samples taken during a series of experimental in vivo studies. The dataset is freely available, to explore the normal interrelationships between levels of neurotransmitter (e.g., dopamine, serotonin), across brain regions implicated in both normal reward and drug addiction, as well as in disorders such as schizophrenia (e.g., nucleus accumbens, prefrontal cortex). Most experimental studies run with a relatively small control group, so there is a lack of baseline data on the expected levels of neurotransmitters and their metabolites in different brain regions. Accordingly, the available dataset has been compiled from a number of studies run in the same laboratory, and using closely similar behavioural procedures, sampling selected brain regions of a priori interest. These collated data can be used to explore differences in the distribution of the monoamines and their metabolites, patterns of neurotransmitter intercorrelations, both between and within different brain structures and including some consideration of laterality effects.

MDMA modulates spontaneous firing of subthalamic nucleus neurons in vitro

3,4-Methylene-dioxy-N-methylamphetamine (MDMA, 'ecstasy') has a broad spectrum of molecular targets in the brain, among them receptors and transporters of the serotonergic (5-hydroxytryptamine, 5-HT) and noradrenergic systems. Its action on the serotonergic system modulates motor systems in rodents and humans. Although parts of the basal ganglia could be identified as mediators of the motor effects of MDMA, very little is known about the role of the subthalamic nucleus (STN). Therefore, this study investigated the modulation of spontaneous action potential activity of the STN by MDMA (2.5-20 µM) in vitro. MDMA had very heterogeneous effects, ranging from a complete but reversible inhibition to a more than twofold increase in firing at 5 µM. On average, MDMA excited STN neurons moderately, but lost its excitatory effect in the presence of the 5-HT(2A) antagonist MDL 11,939. 5-HT(1A) receptors did not appear to play a major role. Effects of MDMA on transporters for serotonin (SERT) and norepinephrine (NET) were investigated by coapplication of the reuptake inhibitors citalopram and desipramine, respectively. Similar to the effects of 5-HT(2A) receptor blockade, antagonism of SERT and NET bestowed an inhibitory effect on MDMA. From these results, we conclude that both the 5-HT and the noradrenergic system mediate MDMA-induced effects on STN neurons.