Topographical Fos induction within the ventral midbrain and projection sites following self-stimulation of the posterior mesencephalon

Spiritual care for the management of Parkinson's disease: Where we are and how far can we go

An increasing number of studies have investigated the neural networks and brain regions activated by different aspects of religious faith or spiritual practice. The extent to which religiousness and spirituality are dependent on the integrity of neural circuits is a question unique to neurological illnesses. Several studies have reported that neural networks and brain areas represent the various components of religious faith or spiritual activity in recent decades. In addition to research in healthy people, another strategy is to observe if neurological abnormalities caused by stroke, tumour, brain damage, or degenerative sickness are accompanied by an alteration in religiosity or spirituality. Similarly, Parkinson's disease (PD), an ailment characterized by dopaminergic neuron malfunction, has been utilized to explore the role of dopaminergic networks in the practice, experience, and maintenance of religious or spiritual beliefs. Case-control and priming studies have demonstrated a decline in spirituality and religion in people with PD due to dopaminergic degeneration. These studies could not adequately control for confounding variables and lacked methodological rigour. Using qualitative and quantitative assessments, a mixed-method approach might shed additional light on putative religious beliefs alterations in PD. In the current review paper, we discussed the recent research on the impact of PD on spiritual beliefs and spirituality.

Ventral Midbrain NMDA Receptor Blockade: From Enhanced Reward and Dopamine Inactivation

Glutamate stimulates ventral midbrain (VM) N-Methyl-D-Aspartate receptors (NMDAR) to initiate dopamine (DA) burst firing activity, a mode of discharge associated with enhanced DA release and reward. Blockade of VM NMDAR, however, enhances brain stimulation reward (BSR), the results can be explained by a reduction in the inhibitory drive on DA neurons that is also under the control of glutamate. In this study, we used fast-scan cyclic voltammetry (FSCV) in anesthetized animals to determine whether this enhancement is associated with a change in phasic DA release in the nucleus accumbens. Rats were implanted with a stimulation electrode in the dorsal-raphe (DR) and bilateral cannulae above the VM and trained to self-administer trains of electrical stimulation. The curve-shift method was used to evaluate the effect of a single dose (0.825 nmol/0.5 μl/side) of the NMDAR antagonist, (2R,4S)-4-(3-Phosphopropyl)-2-piperidinecarboxylic acid (PPPA), on reward. These animals were then anesthetized and DA release was measured during delivery of electrical stimulation before and after VM microinjection of the vehicle followed by PPPA. As expected, phasic DA release and operant responding depended similarly on the frequency of rewarding electrical stimulation. As anticipated, PPPA produced a significant reward enhancement. Unexpectedly, PPPA produced a decrease in the magnitude of DA transients at all tested frequencies. To test whether this decrease resulted from excessive activation of DA neurons, we injected apomorphine 20 min after PPPA microinjection. At a dose (100 μg s.c.) sufficient to reduce DA firing under control conditions, apomorphine restored electrical stimulation-induced DA transients. These findings show that combined electrical stimulation and VM NMDARs blockade induce DA inactivation, an effect that indirectly demonstrates that VM NMDARs blockade enhances reward by potentiating stimulation-induced excitation in the mesoaccumbens DA pathway.

Separating analgesia from reward within the ventral tegmental area

Activation of the dopaminergic mesolimbic reward circuit that originates in the ventral tegmental area (VTA) is postulated to preferentially suppress emotional responses to noxious stimuli, and presumably contributes to the addictive liability of strong analgesics. VTA dopamine neurons are activated via cholinergic afferents and microinjection of carbachol (cholinergic agonist) into VTA is rewarding. Here, we evaluated regional differences within VTA in the capacity of carbachol to suppress rats' affective response to pain (vocalization afterdischarges, VADs) and to support conditioned place preference (CPP) learning. As carbachol is a non-specific agonist, muscarinic and nicotinic receptor involvement was assessed by administering atropine (muscarinic antagonist) and mecamylamine (nicotinic antagonist) into VTA prior to carbachol treatment. Unilateral injections of carbachol (4μg) into anterior VTA (aVTA) and posterior VTA (pVTA) suppressed VADs and supported CPP; whereas, injections into midVTA failed to effect either VADs or CPP. These findings corroborate the hypothesis that the neural substrates underlying affective analgesia and reward overlap. However, the extent of the overlap was only partial. Whereas both nicotinic and muscarinic receptors contributed to carbachol-induced affective analgesia in aVTA, only muscarinic receptors mediated the analgesic action of carbachol in pVTA. The rewarding effects of carbachol are mediated by the activation of both nicotinic and muscarinic receptors in both aVTA and pVTA. The results indicate that analgesia and reward are mediated by separate cholinergic mechanisms within pVTA. Nicotinic receptor antagonism within pVTA failed to attenuate carbachol-induced analgesia, but prevented carbachol-induced reward. As addictive liability of analgesics stem from their rewarding properties, the present findings suggest that these processes can be neuropharmacologically separated within pVTA.

Blockade of ventral midbrain NMDA receptors enhances brain stimulation reward: a preferential role for GluN2A subunits

Ventral midbrain (VM) neurons that project to limbic structures play a role in reward and incentive motivation. It has been suggested that a reward-related signal is transmitted when the firing rate of VM dopamine neurons shifts from a tonic to a phasic mode. Since glutamate is necessary for this transduction process, it is likely to play a role in reward signaling. This study was aimed at determining the effect of VM N-Methyl-D-Aspartate (NMDA) receptor blockade on reward induced by electrical brain stimulation. Experiments were performed on rats trained to self-administer an electrical stimulation in the medial posterior mesencephalon. Reward thresholds were measured with the curve-shift paradigm before and after bilateral VM injections of the following NMDA receptor antagonists: R-CPP, 3-(R-2-Carboxypiperazin-4-yl)-propyl-1 phosphonic acid, (0, 20.6, 41.2 and 82.5 pmol/0.5 μl/side), PPPA, (2R,4S)-4-(3-Phosphonopropyl)-2-piperidinecarboxylic acid, (0, 0.825 and 1.65 nmol/0.5 μl/side) orRo04-5595, 1-[2-(4-Chlorophenyl)ethyl]-1,2,3,4-tetrqahydro-6-methoxy-2-methyl-7-isoquinolinol hydrochloride (0, 0.825, 1.65 nmol/0.5 μl/side). R-CPP and PPPA produced a dose and time dependent decrease in reward threshold, an effect that was, at some doses and times after the injection, accompanied by an increase in maximum responses. These effects were not observed with Ro04-5595 over the range of doses tested. While previous studies suggest a role for glutamate in reward signaling, the present results show that VM glutamate exerts a tonic inhibition on the reward-relevant pathway. The selectivity of Ro04-5595 for NMDA receptors composed of GluN2B subunits and the higher affinity of R-CPP and PPPA for GluN2A suggest that the inhibition is mediated by receptors composed of GluN2A subunits.

Opposite modulation of brain stimulation reward by NMDA and AMPA receptors in the ventral tegmental area

Previous studies have shown that blockade of ventral tegmental area (VTA) glutamate N-Methyl-D-Aspartate (NMDA) receptors induces reward, stimulates forward locomotion and enhances brain stimulation reward. Glutamate induces two types of excitatory response on VTA neurons, a fast and short lasting depolarization mediated by α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors and a longer lasting depolarization mediated by NMDA receptors. A role for the two glutamate receptors in modulation of VTA neuronal activity is evidenced by the functional change in AMPA and NMDA synaptic responses that result from repeated exposure to reward. Since both receptors contribute to the action of glutamate on VTA neuronal activity, we studied the effects of VTA AMPA and NMDA receptor blockade on reward induced by electrical brain stimulation. Experiments were performed on rats trained to self-administer electrical pulses in the medial posterior mesencephalon. Reward thresholds were measured with the curve-shift paradigm before and for 2 h after bilateral VTA microinjections of the AMPA antagonist, NBQX (2,3,-Dioxo-6-nitro-1,2,3,4-tetrahydrobenzo(f)quinoxaline-7-sulfonamide, 0, 80, and 800 pmol/0.5 μl/side) and of a single dose (0.825 nmol/0.5 μl/side) of the NMDA antagonist, PPPA (2R,4S)-4-(3-Phosphonopropyl)-2-piperidinecarboxylic acid). NBQX produced a dose-dependent increase in reward threshold with no significant change in maximum rate of responding. Whereas PPPA injected at the same VTA sites produced a significant time dependent decrease in reward threshold and increase in maximum rate of responding. We found a negative correlation between the magnitude of the attenuation effect of NBQX and the enhancement effect of PPPA; moreover, NBQX and PPPA were most effective when injected, respectively, into the anterior and posterior VTA. These results suggest that glutamate acts on different receptor sub-types, most likely located on different VTA neurons, to modulate reward.

Day-night differences in neural activation in histaminergic and serotonergic areas with putative projections to the cerebrospinal fluid in a diurnal brain

In nocturnal rodents, brain areas that promote wakefulness have a circadian pattern of neural activation that mirrors the sleep/wake cycle, with more neural activation during the active phase than during the rest phase. To investigate whether differences in temporal patterns of neural activity in wake-promoting regions contribute to differences in daily patterns of wakefulness between nocturnal and diurnal species, we assessed Fos expression patterns in the tuberomammillary (TMM), supramammillary (SUM), and raphe nuclei of male grass rats maintained in a 12:12 h light-dark cycle. Day-night profiles of Fos expression were observed in the ventral and dorsal TMM, in the SUM, and in specific subpopulations of the raphe, including serotonergic cells, with higher Fos expression during the day than during the night. Next, to explore whether the cerebrospinal fluid is an avenue used by the TMM and raphe in the regulation of target areas, we injected the retrograde tracer cholera toxin subunit beta (CTB) into the ventricular system of male grass rats. While CTB labeling was scarce in the TMM and other hypothalamic areas including the suprachiasmatic nucleus, which contains the main circadian pacemaker, a dense cluster of CTB-positive neurons was evident in the caudal dorsal raphe, and the majority of these neurons appeared to be serotonergic. Since these findings are in agreement with reports for nocturnal rodents, our results suggest that the evolution of diurnality did not involve a change in the overall distribution of neuronal connections between systems that support wakefulness and their target areas, but produced a complete temporal reversal in the functioning of those systems.

Fos expression in arousal and reward areas of the brain in grass rats following induced wakefulness

In the diurnal grass rat nocturnal voluntary wakefulness induces Fos expression in specific cellular populations of arousal and reward areas of the brain. Here, we evaluated whether involuntary wakefulness would result in similar patterns of Fos expression. We assessed this question using male grass rats that were sleep deprived for 6h by gentle stimulation (SD group), starting 2h before lights off (12:12 LD cycle). Then, we examined expression of Fos in cholinergic cells of the basal forebrain (BF), as well as in dopaminergic cells of the reward system, and compared these results to those obtained from an undisturbed control group. Different from previous results with grass rats that were voluntary awake, the BF of SD animals only showed a significant increase in Fos expression in non-cholinergic neurons of the medial septum (MS). These observations differ from reports for nocturnal rodents that are sleep deprived. Thus, our results show that voluntary and induced wakefulness have different effects on neural systems involved in wakefulness and reward, and that the effects of sleep deprivation are different across species. We also investigated whether other arousal promoting regions and circadian and stress related areas responded to sleep deprivation by changing the level of Fos expression. Among these areas, only the lateral hypothalamus (LH) and the ventro lateral preoptic area showed significant effects of sleep deprivation that dissipated after a 2h period of sleep recovery, as it was also the case for the non-cholinergic MS. In addition, we found that Fos expression in the LH was robustly associated with Fos expression in other arousal and reward areas of the brain. This is consistent with the view that the arousal system of the LH modulates neural activity of other arousal regions of the brain, as described for nocturnal rodents.

Brain reward circuitry beyond the mesolimbic dopamine system: a neurobiological theory

Reductionist attempts to dissect complex mechanisms into simpler elements are necessary, but not sufficient for understanding how biological properties like reward emerge out of neuronal activity. Recent studies on intracranial self-administration of neurochemicals (drugs) found that rats learn to self-administer various drugs into the mesolimbic dopamine structures-the posterior ventral tegmental area, medial shell nucleus accumbens and medial olfactory tubercle. In addition, studies found roles of non-dopaminergic mechanisms of the supramammillary, rostromedial tegmental and midbrain raphe nuclei in reward. To explain intracranial self-administration and related effects of various drug manipulations, I outlined a neurobiological theory claiming that there is an intrinsic central process that coordinates various selective functions (including perceptual, visceral, and reinforcement processes) into a global function of approach. Further, this coordinating process for approach arises from interactions between brain structures including those structures mentioned above and their closely linked regions: the medial prefrontal cortex, septal area, ventral pallidum, bed nucleus of stria terminalis, preoptic area, lateral hypothalamic areas, lateral habenula, periaqueductal gray, laterodorsal tegmental nucleus and parabrachical area.

Administration of the GABAA receptor antagonist picrotoxin into rat supramammillary nucleus induces c-Fos in reward-related brain structures. Supramammillary picrotoxin and c-Fos expression

BACKGROUND

Picrotoxin blocks GABAA receptors, whose activation typically inhibits neuronal firing activity. We recently found that rats learn to selectively self-administer picrotoxin or bicuculline, another GABAA receptor antagonist, into the supramammillary nucleus (SuM), a posterior hypothalamic structure localized anterior to the ventral tegmental area. Other drugs such as nicotine or the excitatory amino acid AMPA are also self-administered into the SuM. The SuM appears to be functionally linked with the mesolimbic dopamine system and is closely connected with other brain structures that are implicated in motivational processes, including the prefrontal cortex, septal area, preoptic area, lateral hypothalamic area and dorsal raphe nucleus. Here, we hypothesized that these brain structures are activated by picrotoxin injections into the SuM.

RESULTS

Picrotoxin administration into the SuM markedly facilitated locomotion and rearing. Further, it increased c-Fos expression in this region, suggesting blockade of tonic inhibition and thus the disinhibition of local neurons. This manipulation also increased c-Fos expression in structures including the ventral tegmental area, medial shell of the nucleus accumbens, medial prefrontal cortex, septal area, preoptic area, lateral hypothalamic area and dorsal raphe nucleus.

CONCLUSIONS

Picrotoxin administration into the SuM appears to disinhibit local neurons and recruits activation of brain structures associated with motivational processes, including the mesolimbic dopamine system, prefrontal cortex, septal area, preoptic area, lateral hypothalamic area and dorsal raphe nucleus. These regions may be involved in mediating positive motivational effects triggered by intra-SuM picrotoxin.

Neural activation in arousal and reward areas of the brain in day-active and night-active grass rats

In the diurnal unstriped Nile grass rat (Arvicanthis niloticus) access to a running wheel can trigger a shift in active phase preference, with some individuals becoming night-active (NA), while others continue to be day-active (DA). To investigate the contributions of different neural systems to the support of this shift in locomotor activity, we investigated the association between chronotype and Fos expression during the day and night in three major nuclei in the basal forebrain (BF) cholinergic (ACh) arousal system - medial septum (MS), vertical and horizontal diagonal band of Broca (VDB and HDB respectively) -, and whether neural activation in these areas was related to neural activity in the orexinergic system. We also measured Fos expression in dopaminergic and non-dopaminergic cells of two components of the reward system that also participate in arousal - the ventral tegmental area (VTA) and supramammillary nucleus (SUM). NAs and DAs were compared to animals with no wheels. NAs had elevated Fos expression at night in ACh cells, but only in the HDB. In the non-cholinergic cells of the BF of NAs, enhanced nocturnal Fos expression was almost universally seen, but only associated with activation of the orexinergic system for the MS/VDB region. For some of the areas and cell types of the BF, the patterns of Fos expression of DAs appeared similar to those of NAs, but were never associated with activation of the orexinergic system. Also common to DAs and NAs was a general increase in Fos expression in non-dopaminergic cells of the SUM and anterior VTA. Thus, in this diurnal species, voluntary exercise and a shift to a nocturnal chronotype changes neural activity in arousal and reward areas of the brain known to regulate a broad range of neural functions and behaviors, which may be also affected in human shift workers.