Psychological pain and opioid receptors: Reward downshift is disrupted when tested in a context signaling morphine.

A sucrose downshift causes a temporary suppression of consumption accompanied by psychological pain, a negative emotion triggered by reward loss. When administered systemically before downshift sessions, opioid agonists reduce and opioid antagonists enhance such behavioral suppression. However, little is known about the effects of signals of opioid drugs on behavior during a reward downshift episode.

Sensitivity to amphetamine in prepulse inhibition response requires a mature medial prefrontal cortex.

Prepulse inhibition (PPI) refers to the modulation of the startle response by the presentation of a weaker stimulus prior to the onset of the startle stimulus. This response is consolidated along the maturation process of the mesocortical system, where the dopamine neurotransmitter plays an important role. In fact, it has been reported that agonist and antagonist dopaminergic drugs are able to change PPI expression.

Haloperidol-based conditioned increase in locomotor activity is disrupted by latent inhibition and extended interstimulus interval.

Previous research have shown that repeated administration of 0.5 mg/kg of haloperidol in a given context gives rise to an increase in activity when spontaneous locomotor activity is recorded in a drug-free test conducted in such context. In order to confirm whether this type of response is based on processes of a Pavlovian nature, we conducted two experiments involving two manipulations that disrupt conditioning in typical classical conditioning procedures: preexposure of the to-be-conditioned stimulus (latent inhibition), and an increase in the length of the inter-stimulus interval.

Conditioned increase of locomotor activity induced by haloperidol.

Dopamine antagonist drugs have profound effects on locomotor activity. In particular, the administration of the D2 antagonist haloperidol produces a state that is similar to catalepsy. In order to confirm whether the modulation of the dopaminergic activity produced by haloperidol can act as an unconditioned stimulus, we carried out two experiments in which the administration of haloperidol was repeatedly paired with the presence of distinctive contextual cues that served as a Conditioned Stimulus.

Reward devaluation disrupts latent inhibition in fear conditioning.

Three experiments explored the link between reward shifts and latent inhibition (LI). Using consummatory procedures, rewards were either downshifted from 32% to 4% sucrose (Experiments 1-2), or upshifted from 4% to 32% sucrose (Experiment 3). In both cases, appropriate unshifted controls were also included.

Reduced Prepulse Inhibition as a Biomarker of Schizophrenia.

The startle response is composed by a set of reflex behaviors intended to prepare the organism to face a potentially relevant stimulus. This response can be modulated by several factors as, for example, repeated presentations of the stimulus (startle habituation), or by previous presentation of a weak stimulus (Prepulse Inhibition [PPI]). Both phenomena appear disrupted in schizophrenia that is thought to reflect an alteration in dopaminergic and glutamatergic neurotransmission.

Effect of stress and attention on startle response and prepulse inhibition.

The startle reflex magnitude can be modulated when a weak stimulus is presented before the onset of the startle stimulus, a phenomenon termed prepulse inhibition (PPI). Previous research has demonstrated that emotional processes can modulate PPI and startle intensity, but the available evidence is inconclusive. In order to obtain additional evidence in this domain, we conducted two experiments intended to analyze the effect of induced stress and attentional load on PPI and startle magnitude.