“Habit” gambling behaviour caused by ischemic lesions affecting the cognitive territories of the basal ganglia

Effect of traumatic brain injury on nicotine-induced modulation of dopamine release in the striatum and nucleus accumbens shell

Background

Traumatic brain injury is associated with substantial alterations in reward processing, but underlying mechanisms are controversial.

Objective

A better understanding of alterations in dopamine (DA) release patterns from the dorsal striatum and nucleus accumbens shell (NAc) may provide insights into posttraumatic reward pathology.

Materials and Methods

The patterns of DA release with or without exposure to nicotine in brain slices with striatum and NAc, isolated from Sprague-Dawley rats with 6 psi fluid percussion (FPI) or sham injury were analysis by using fast-scan cyclic voltammetry. Tonic and phasic DA releases were assessed using single pulse and 10 pulses at 25 Hz, respectively. DA release relative to stimulation intensity, frequency, number of pulses, and paired-pulse facilitation was evaluated to determine release probability and response to bursting.

Results

There was a profound suppression in tonic DA release after nicotine desensitization after FPI, and the input/output curve for the DA release based on stimulation intensity was shifted to the right. FPI was associated with a significant decrease in frequency-dependent DA release augmentation, DA release induced by high frequency stimulation trains, and DA release in response to paired-pulse facilitation. The effect of nicotine desensitization was similar in FPI and sham-injured animals, although significantly smaller after FPI. Nicotine desensitization–induced differences between phasic and tonic release concentrations that contrasted with the reward-related signals then became less prominent in NAc after FPI.

Conclusions

TBI blunts DA release from mesolimbic reward centers, and more intense stimuli are required to produce context-dependent DA release sufficient to have a physiological effect.

Implications

The nicotine desensitization-related suppression in tonic DA release was profound with right-ward shift of the input/output curve for DA release after FPI. FPI was associated with a significant decrease in frequency-dependent DA release augmentation, DA release induced by high frequency stimulation trains, and DA release in response to paired-pulse facilitation. Nicotine desensitization–induced differences between phasic and tonic release concentrations that contrasted with the reward-related signals then became less prominent in NAc after FPI. TBI thus blunts DA release from mesolimbic reward centers, and more intense stimuli are required to produce context-dependent DA release sufficient to have a physiological effect.

Selective bilateral lesion to caudate nucleus modulates the acute and chronic methylphenidate effects

The psychostimulant methylphenidate (MPD) is currently the most prescribed drug therapy for attention deficit hyperactivity disorder (ADHD) and is used by students as a cognitive enhancer. The caudate nucleus (CN) is a structure within the motive circuit where MPD exerts its effects, it is known to contain high levels of dopaminergic cells and directly influence motor activity. The objective of this study was to understand the role of CN in response to acute and chronic administration of MPD. Specific and non-specific bilateral ablations were created in the CN using electrolytic lesion and 6-Hydoxydopamine (6-OHDA). Four groups of rats were used: control (n=4), sham (n=4), CN electrolytic lesion group (n=8) and CN 6-OHDA injected group (n=8). On experimental day one (ED 1) all rats received a saline injection and baseline locomotive activity was recorded. On ED 2 and ED 3 CN sham, electrolytic lesion and/or 6-OHDA injected groups were made followed by four to five days recovery (ED 3-7), followed by six daily 2.5 mg/kg MPD injections (ED 9-14), three days of washout (ED 15-17) and an MPD re-challenge of drug proceeding the washout days (ED 18). Locomotor activity was obtained at ED 1, 8, 9, and 18 using an open field assay. The results show that the CN electrolytic lesion group responded to the acute and chronic MPD administration similar to the control and sham group, while the CN 6-OHDA injected group prevented the acute and the chronic effects of MPD administration. One possible interpretation why nonspecific electroyltic lesioning of the CN failed to prevent acute and chronic effects of MPD administration is due to destruction of both the direct and the indirect CN pathways which act as an inhibitory/excitatory balance, electroylticelectroyltic. The selective dopaminergic lesioning prevented the effects of MPD administration suggesting that dopaminergic pathways in CN play a significant role in the effects of MPD.