Neuroscience
-
Opioid mechanisms are involved in the control of water and NaCl intake and opioid receptors (ORs) are present in the central nucleus of the amygdala (CeA), a site of important facilitatory mechanisms related to the control of sodium appetite. Therefore, in the present study we investigated the effects of the activation of μ-ORs in the CeA on 0.3 M NaCl and water intake in rats. Male Sprague-Dawley rats with stainless steel cannulas implanted bilaterally in the CeA were used. ⋯ Bilateral injections of DAMGO into the CeA did not change urinary volume, sodium urinary excretion and mean arterial pressure, but increased activity. Thus stimulating μ-ORs in the CeA increases hypertonic sodium intake, whereas antagonizing these sites inhibits hypertonic sodium intake. Together, our results implicate μ-ORs in the CeA in a positive regulation of sodium intake.
-
Dorsal horn neurons send ascending projections to both thalamic nuclei and parabrachial nuclei; these pathways are thought to be critical pathways for central processing of nociceptive information. Afferents from the corneal surface of the eye mediate nociception from this tissue which is susceptible to clinically important pain syndromes. This study examined corneal afferents to the trigeminal dorsal horn and compared inputs to thalamic- and parabrachial-projecting neurons. ⋯ Corneal afferent inputs to both groups of projection neurons were also more abundant in the rostral pole of Vc. Finally, by comparing the frequency of corneal afferent appositions to thalamic- versus parabrachial-projecting neurons, we found that corneal afferents preferentially target parabrachial-projecting neurons in trigeminal dorsal horn. These results suggest that nociceptive pain from the cornea may be primarily mediated by a non-thalamic ascending pathway.
-
The role of 5-HT₂A/₂B/₂C receptors in formalin-induced secondary allodynia and hyperalgesia in rats was assessed. Formalin produced acute nociceptive behaviors (flinching and licking/lifting) followed by long-term secondary mechanical allodynia and hyperalgesia. Pre-treatment for five consecutive days with compound 48/80 (1, 3, 10, 10, and 10 μg/paw) prevented formalin-induced secondary allodynia and hyperalgesia. ⋯ Furthermore, ipsilateral pre-treatment (nmol/paw) with ketanserin (1, 10, and 100), RS-127445 (0.01, 0.1 and 1) or RS-102221 (1, 10 and 100) prevented while post-treatment reversed 1% formalin-induced secondary allodynia and hyperalgesia in both paws. In marked contrast, contralateral injection of the greatest tested dose of 5-HT₂A/₂B/₂C receptor antagonists did not modify long-lasting secondary allodynia and hyperalgesia. These results suggest that 5-HT released from mast cells after formalin injection sensitizes primary afferent neurons via 5-HT₂A/₂B/₂C receptors leading to the development and maintenance of secondary allodynia and hyperalgesia.
-
Speech recognition in a multi-talker situation poses high demands on attentional and other central resources. This study examines the relationship between age, cognition and speech recognition in tasks that require selective or divided attention in a multi-talker setting. Two groups of normal-hearing adults (one younger and one older group) were asked to repeat utterances from either one or two concurrent speakers. ⋯ In comparison, speech recognition for tests requiring divided attention could be more strongly determined by neuropsychological probes of fluid intelligence. The findings of this study indicate that - apart from hearing impairment - cognitive aspects account for the typical difficulties of older listeners in a multi-speaker setting. Our results are discussed in the context of evidence showing that frontal lobe functions in terms of working memory and fluid intelligence generally decline with age.
-
Recently, we hypothesized that supraspinal structures may have important functions in discriminating between noxious mechanically and heat mediated nociception through distinct functions: facilitation and inhibition. In this study, conducted in conscious rats, we explored the role of different thalamic nuclei: the mediodorsal (MD) nucleus, the central medial (CM) nucleus, the submedius (SM) nucleus, the ventralmedial (VM) nucleus and the ventral posterolateral (VPL) nucleus, in the descending control of secondary and contralateral mechanical hyperalgesia and heat hypoalgesia occurring in intramuscularly hypertonic (HT, 5.8%) saline-induced muscle nociception. ⋯ This descending facilitatory and inhibitory modulation of nociception was strengthened by glutamate, and weakened by GABA, microinjected into the thalamic MD and VM nuclei. It is suggested that (1) thalamic MD nucleus and VM nucleus form two distinct endogenous systems in the control of noxious mechanically and heat evoked responses, and (2) the strengthening of descending inhibition and the weakening of descending facilitation by means of up regulation and down regulation of appropriate receptor expression in the VM and MD nuclei may provide a new strategic policy in treating pathological pain.