Brain research
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Comparative Study
Nitric oxide pathway in the nucleus raphe magnus modulates hypoxic ventilatory response but not anapyrexia in rats.
Nucleus raphe magnus (NRM) is one of the cellular groups of the brainstem that is involved in the physiologic responses to hypoxia and contains nitric oxide (NO) synthase. In the present study, we assessed the role of NO pathway in the NRM on the hypoxic ventilatory response (HVR) and anapyrexia (a regulated decrease in body temperature). To this end, pulmonary ventilation (VE) and body temperature (Tb) of male Wistar rats were measured before and after microinjection of N-monomethyl-L-arginine (L-NMMA, a nonselective nitric oxide synthase inhibitor, 12.5 microg/0.1 microl) into the NRM, followed by hypoxia. ⋯ Typical hypoxia-induced hyperventilation and anapyrexia were observed after saline treatment. L-NMMA into the NRM reduced the HVR but did not affect hypoxia-induced anapyrexia. In conclusion, the present study indicates that NO in the NRM is involved in HVR, exerts an inhibitory modulation on the NRM neurons but does not mediate hypoxia-induced anapyrexia.
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Comparative Study
Dynamic processing of taste aversion extinction in the brain.
While substantial advances have been made in discovering how the brain learns and remembers, less is known about how the brain discards information, reorganizes information, or both. These topics are not only relevant to normal brain functioning but also speak to pathologies in which painful memories do not wane but are evoked time and again (e.g., post-traumatic stress disorder; PTSD). Here, we measured brain activity (as indicated by the regional expression of c-Fos protein) in rats during acquisition and throughout extinction of a conditioned taste aversion (CTA). ⋯ Finally, as almost full reacceptance of the taste is achieved, the gustatory neocortex (GNC) expresses enhanced levels of c-Fos protein. Thus, extinction of a CTA is not represented by a simple reversal of the c-Fos activity evoked by CTA conditioning. Rather, the data demonstrate that extinction of conditioned responses is a dynamic process in which the activity levels of particular nuclei along the brain's taste pathway change depending on the extent to which the conditioned response has been extinguished.
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Comparative Study
Separate populations of neurons in the rostral ventromedial medulla project to the spinal cord and to the dorsolateral pons in the rat.
Activation of neurons in the rostral ventromedial medulla (RVM) directly modulates spinal nociceptive transmission by projections to the spinal cord dorsal horn and indirectly by projections to neurons in the dorsolateral pons (DLP) that project to the spinal cord dorsal horn. However, it is not known whether the same neurons in the RVM produce both direct and indirect modulation of nociception. Deposits of the retrograde tracers Fluoro-Gold (FG) in the spinal cord dorsal horn and DiI in the DLP were used to determine whether the same RVM neurons project to both of these regions. ⋯ In addition, spinally projecting RVM neurons were significantly larger than RVM neurons that project to the DLP. Finally, spinally projecting neurons were found predominantly on the midline and within the RVM; neurons that project to the DLP had a wider distribution and were present both within and outside of the RVM. Thus, separate and morphologically distinct populations of RVM neurons appear to modulate nociception by direct and indirect descending pathways.
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Comparative Study Clinical Trial
The effects of muscle vibration on anticipatory postural adjustments.
The current study investigated the influence of changes in sensory information related to postural stability on anticipatory postural adjustments (APAs) in standing subjects. Subjects performed fast arm movements and a load release task while standing on a stable force platform or on an unstable board. We manipulated sensory information through vibration of the Achilles tendons and additional finger touch (contact forces under 1 N). ⋯ Small changes in the other index related to reciprocal activation (R-index) were found only in trunk muscles. Light touch and vibration induced opposing changes in the C-index, suggesting their opposite effects on the stabilization of a reference point or vertical. We conclude that the central nervous system deploys patterns of adjustments in which increased co-contraction of distal muscles and reciprocal adjustments in trunk muscles are modified to ensure equilibrium under postural instability.
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Comparative Study
Intra-amygdalar injection of DAMGO: effects on c-Fos levels in brain sites associated with feeding behavior.
It is well known that the mu opioid agonist, Tyr-D-Ala-Gly-(me) Phe-Gly-ol (DAMGO), increases food intake in rats when injected into a variety of brain sites including the central nucleus of the amygdala (CeA). Immunohistochemical studies measuring c-Fos immunoreactivity (IR) suggest that the CeA contributes to opioid-related feeding. In the current study, we injected 2 nmol of DAMGO and measured food intake, c-Fos IR levels in various brain sites involved in feeding behavior, and mu opioid receptor internalization. ⋯ Administration of DAMGO into the CeA increased c-Fos IR levels in the shell of the nucleus accumbens (NAcc), but not in 17 other brain sites that were studied. We also found that intra-CeA injection of DAMGO, prior to LiCl injection, decreased c-Fos IR levels in the CeA compared to vehicle-injected rats. Thus, intra-CeA administration of DAMGO may increase feeding, in part, by activating neurons in the shell of the nucleus accumbens and by inhibiting activity of selected neurons in the CeA.