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  1. Tan SZK, Temel Y, Chan AY, Mok ATC, Perucho JAU, Blokland A, et al.
    Brain Struct Funct, 2020 Sep;225(7):1957-1966.
    PMID: 32594260 DOI: 10.1007/s00429-020-02102-w
    Electrical stimulation of the dorsolateral periaqueductal gray (dlPAG) in rats has been shown to elicit panic-like behaviour and can be a useful as an unconditioned stimulus for modelling anticipatory fear and agoraphobia in a contextual fear conditioning paradigm. In this study, we further analysed our previous data on the effects of escitalopram (a selective serotonin reuptake inhibitor, SSRI) and buspirone (a 5-HT1A receptor partial agonist) on dlPAG-induced anticipatory fear behaviour in a rat model using freezing as a measure. We then attempted to unravel some of the interactions with dopamine signalling using tyrosine hydroxylase (TH) immunohistochemistry to probe the effects on dopaminergic neurons. We showed that acute treatment of escitalopram, but not buspirone, was effective in reducing anticipatory freezing behaviour, while chronic administrations of both drugs were effective. We found that the dlPAG stimulation induced increase number of dopaminergic neurons in the ventral tegmental area (VTA) which was reversed in both chronic buspirone and escitalopram groups. We further found a strong positive correlation between the number of dopaminergic neurons and freezing in the VTA and showed positive correlations between dopaminergic neurons in the VTA and substantia nigra pars compacta (SNpc) in escitalopram and buspirone groups, respectively. Overall, we showed that chronic treatment with an SSRI and a 5-HT1A agonist reduced anticipatory freezing behaviour which seems to be associated, through correlative studies, with a reversal of dlPAG stimulation induced increase in number of dopaminergic neurons in the VTA and/or SNpc.
  2. Ng KY, Leong MK, Liang H, Paxinos G
    Brain Struct Funct, 2017 Sep;222(7):2921-2939.
    PMID: 28478550 DOI: 10.1007/s00429-017-1439-6
    Melatonin, through its different receptors, has pleiotropic functions in mammalian brain. Melatonin is secreted mainly by the pineal gland and exerts its effects via receptor-mediated and non-receptor-mediated actions. With recent advancement in neuroanatomical mapping, we may now understand better the localizations of the two G protein-coupled melatonin receptors MT1 and MT2. The abundance of these melatonin receptors in respective brain regions suggests that receptor-mediated actions of melatonin might play crucial roles in the functions of central nervous system. Hence, this review aims to summarize the distribution of melatonin receptors in the brain and to discuss the putative functions of melatonin in the retina, cerebral cortex, reticular thalamic nucleus, habenula, hypothalamus, pituitary gland, periaqueductal gray, dorsal raphe nucleus, midbrain and cerebellum. Studies on melatonin receptors in the brain are important because cumulative evidence has pointed out that melatonin receptors not only play important physiological roles in sleep, anxiety, pain and circadian rhythm, but might also be involved in the pathogenesis of a number of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease and Huntington's disease.
  3. Manan HA, Yahya N, Han P, Hummel T
    Brain Struct Funct, 2022 Jan;227(1):177-202.
    PMID: 34635958 DOI: 10.1007/s00429-021-02397-3
    Brain structural features of healthy individuals are associated with olfactory functions. However, due to the pathophysiological differences, congenital and acquired anosmia may exhibit different structural characteristics. A systematic review was undertaken to compare brain structural features between patients with congenital and acquired anosmia. A systematic search was conducted using PubMed/MEDLINE and Scopus electronic databases to identify eligible reports on anosmia and structural changes and reported according to PRISMA guidelines. Reports were extracted for information on demographics, psychophysical evaluation, and structural changes. Then, the report was systematically reviewed based on various aetiologies of anosmia in relation to (1) olfactory bulb, (2) olfactory sulcus, (3) grey matter (GM), and white matter (WM) changes. Twenty-eight published studies were identified. All studies reported consistent findings with strong associations between olfactory bulb volume and olfactory function across etiologies. However, the association of olfactory function with olfactory sulcus depth was inconsistent. The present study observed morphological variations in GM and WM volume in congenital and acquired anosmia. In acquired anosmia, reduced olfactory function is associated with reduced volumes and thickness involving the gyrus rectus, medial orbitofrontal cortex, anterior cingulate cortex, and cerebellum. These findings contrast to those observed in congenital anosmia, where a reduced olfactory function is associated with a larger volume and higher thickness in parts of the olfactory network, including the piriform cortex, orbitofrontal cortex, and insula. The present review proposes that the structural characteristics in congenital and acquired anosmia are altered differently. The mechanisms behind these changes are likely to be multifactorial and involve the interaction with the environment.
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