ABSTRACT
Sugar consumption is assumed to induce a behavioral state that is similar to the one provoked by addictive substances. Drug withdrawal increases impulsivity, assessed by differential reinforcement of low rate (DRL) performance. The present study investigated the effect of withdrawal from a prolonged period of sugar consumption on DRL performance. Water-deprived rats were trained under a DRL 20s (DRL 20) schedule. The animals were allowed to choose between plain water and a sucrose solution (E group) or water only (C group) for 30 days. The sucrose solution was then removed, and measures of DRL 20 performance were obtained on 3 consecutive days. Results showed that DRL performance in the C group improved after sugar withdrawal, whereas performance in the E group led to the loss of reinforcers. An analysis of variance-type analysis showed that the E group had higher response rates per reinforcer, lower IRTs, and greater differences between baseline and abstinence than the C group after 3 days of sugar withdrawal. Thus, sugar abstinence after a relatively long consumption period resulted in impairment of DRL performance, confirming the parallel effects of addictive drugs and sugar and suggesting an increase in impulsivity as a consequence of sugar deprivation.
Subject(s)
Dietary Sucrose/adverse effects , Reinforcement Schedule , Substance Withdrawal Syndrome/psychology , Analysis of Variance , Animals , Dietary Sucrose/administration & dosage , Drinking Water/administration & dosage , Impulsive Behavior , Male , Rats, Wistar , Water DeprivationABSTRACT
Many lines of evidence indicate that theta rhythm, a prominent neural oscillatory mode found in the mammalian hippocampus, plays a key role in the acquisition, processing, and retrieval of memories. However, a predictive neurophysiological feature of the baseline theta rhythm that correlates with the learning rate across different animals has yet to be identified. Here we show that the mean theta rhythm speed observed during baseline periods of immobility has a strong positive correlation with the rate at which rats learn an operant task. This relationship is observed across rats, during both quiet waking (r=0.82; p<0.01) and paradoxical sleep (r=0.83; p<0.01), suggesting that the basal theta frequency relates to basic neurological processes that are important in the acquisition of operant behavior.
Subject(s)
Conditioning, Operant/physiology , Hippocampus/physiology , Theta Rhythm , Analysis of Variance , Animals , Behavior, Animal , Discrimination, Psychological , Electromyography , Male , Rats , Rats, Wistar , Regression Analysis , Reinforcement Schedule , Reward , Sleep/physiology , Wakefulness/physiologyABSTRACT
Electrical stimulation of deep brain structures, such as globus pallidus and subthalamic nucleus, is widely accepted as a therapeutic tool for patients with Parkinson's disease (PD). Cortical stimulation either with epidural implanted electrodes or repetitive transcranial magnetic stimulation can be associated with motor function enhancement in PD. We aimed to study the effects of another noninvasive technique of cortical brain stimulation, transcranial direct current stimulation (tDCS), on motor function and motor-evoked potential (MEP) characteristics of PD patients. We tested tDCS using different electrode montages [anodal stimulation of primary motor cortex (M1), cathodal stimulation of M1, anodal stimulation of dorsolateral prefrontal cortex (DLPFC), and sham-stimulation] and evaluated the effects on motor function--as indexed by Unified Parkinson's Disease Rating Scale (UPDRS), simple reaction time (sRT) and Purdue Pegboard test--and on corticospinal motor excitability (MEP characteristics). All experiments were performed in a double-blinded manner. Anodal stimulation of M1 was associated with a significant improvement of motor function compared to sham-stimulation in the UPDRS (P < 0.001) and sRT (P = 0.019). This effect was not observed for cathodal stimulation of M1 or anodal stimulation of DLPFC. Furthermore, whereas anodal stimulation of M1 significantly increased MEP amplitude and area, cathodal stimulation of M1 significantly decreased them. There was a trend toward a significant correlation between motor function improvement after M1 anodal-tDCS and MEP area increase. These results confirm and extend the notion that cortical brain stimulation might improve motor function in patients with PD.
Subject(s)
Deep Brain Stimulation/methods , Motor Cortex/physiopathology , Parkinson Disease/therapy , Prefrontal Cortex/physiopathology , Aged , Antiparkinson Agents/therapeutic use , Brain Mapping , Dominance, Cerebral/physiology , Double-Blind Method , Electrodes , Evoked Potentials, Motor/physiology , Female , Humans , Levodopa/therapeutic use , Male , Middle Aged , Motor Activity/physiology , Motor Skills/physiology , Neurologic Examination , Parkinson Disease/physiopathology , Statistics as TopicABSTRACT
The effects of fencamfamine (FCF), an indirect dopamine (DA) agent, were investigated using the latent inhibition (LI) model of schizophrenia. In the LI procedure, rats preexposed (PE) to an unreinforced stimulus show difficulty in subsequent learning of an association in which that stimulus is predictive of an unconditioned stimulus (US). FCF (1.75, 3.5 and 7.0 mg/kg i.p.) yielded an inverse dose-response relationship regarding LI. At 3.5 mg/kg, LI was abolished and no effect was observed at 1.75 and 7.0 mg/kg. The effect of FCF (3.5 mg/kg) on LI was blocked by the antipsychotic risperidone (RIS; 4.0 mg/kg), a D2/5HT2 antagonist. These results confirm the similarity of the behavioral profile of FCF and amphetamine (AMPH). In addition, they provide a further validation of the LI model for psychosis, since RIS was shown to prevent a psychostimulant-induced disruption of LI.
