Neuroscience
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It was previously shown that tyrosine hydroxylase (TH) immunoreactivity in the terminals of the lateral efferents of the cochlea is decreased by acoustic trauma and that sound preconditioning counteracted this decrease [Hear Res 174 (2002) 124]. Here we identify those neurons in the lateral olivocochlear system (LOC) in the brainstem that regulates the peripheral expression of TH in the cochlea. By employing retrograde tracing techniques, dextran-labeled neurons were found predominantly in the ipsilateral LOC system including lateral superior olive (LSO), and the surrounding periolivary regions (dorsal periolivary nucleus [DPO], dorsolateral periolivary nucleus [DLPO], lateral nucleus of trapezoid body [LNTB]). ⋯ Sound conditioning protected against the decrease of TH immunolabeling by acoustic trauma and increased the fiber staining for TH in the LSO and DLPO, but not in the DPO or the LNTB. These results provide evidence that TH positive neurons are present in the LOC system in the guinea-pig. It is now demonstrated that protection against acoustic trauma by sound conditioning has a central component that is governed by TH in the LSO and the surrounding periolivary DLPO region.
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Repeated exposure to stress induces cross-sensitization to psychostimulants. The present study assessed functional neural activation during social defeat stress-induced sensitization to a subsequent amphetamine challenge. Social defeat stress was induced in intruder rats during short confrontations with an aggressive resident rat once every third day during the course of 10 days. ⋯ Amphetamine augmented stress-induced Fos-LI labeling 17 days after the first stress episode in the dorsal striatum, NAc core, and medial amygdala, reflecting a cross-sensitization of Fos response. Amphetamine challenge 70 days after social stress exposures revealed sensitized Fos-LI labeling in the VTA and the amygdala. These data suggest that episodes of repeated social stress induce a long-lasting neural change that leads to an augmented functional activation in the VTA and amygdala, which might represent a neurobiological substrate for long-lasting cross-sensitization of repeated social defeat stress with psychostimulant drugs.
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The present study was designed to investigate the roles of different subtypes of opioid receptors in ventrolateral orbital cortex (VLO) opioid-evoked antinociception in formalin test by using an automatic detection system for recording the nociceptive behavior (agitation) and a manual method for detecting the duration of licking the injected paw in the conscious rat. Formalin (5%, 50 microl) s.c. injected into the hindpaw produced a biphasic agitation response or lengthening duration of licking. Morphine (5 microg) microinjected unilaterally into VLO significantly inhibited the agitation response and the licking time, and these effects were blocked by pre-administration of the non-selective opioid receptor antagonist naloxone (1.0 microg) into the same site. ⋯ Microinjection of selective kappa-receptor agonist (+/-)-trans-U-50488 methanesulfonate salt (1.5 microg) failed to alter the nociceptive behaviors induced by formalin injection. The beta-FNA and naloxone applied into VLO and morphine into the adjacent regions ventral and dorsal to VLO had no effect on the formalin-evoked nociceptive behaviors. These results suggest that mu- but not delta- or kappa-opioid receptor is involved in the VLO opioid-evoked antinociception in formalin test rat.
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This study investigated the relationship between the orexins and patterns of activity in the diurnal Nile grass rat, Arvicanthis niloticus. Some individuals of this species switch to a more nocturnal pattern when given access to a running wheel, while others continue to be most active during the day. In both day- and night-active grass rats, the percentages of orexin A (OXA) and orexin B (OXB) cells expressing Fos were highest when animals were actively running in wheels. ⋯ This study demonstrates that individual differences in the patterns of activation of OXA and OXB cell populations are related to differences in the temporal pattern of wheel running. We also present evidence that orexin cells have projections to the intergeniculate leaflet that appear to make contact with neuropeptide-Y cells. We discuss the possibility that these fibers may be involved in relaying feedback regarding the activity state of the animal to the circadian system through these projections.
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Comparative Study
Potential pathways for intercellular communication within the calbindin subnucleus of the hamster suprachiasmatic nucleus.
In mammals, the suprachiasmatic nucleus (SCN) is the master circadian pacemaker. Within the caudal hamster SCN, a cluster of neurons containing the calcium binding protein, calbindin-D28K (CB), has been implicated in circadian locomotion. However, calbindin-immunoreactive (CB+) neurons in the calbindin subnucleus (CBsn) do not display a circadian rhythm in spontaneous firing [Eur J Neurosci 16 (2002) 2469]. ⋯ Lastly, we show that CB+ neurons are coupled to CB+ and CB- neurons by gap junctions. The current study provides a structural framework for synaptic communication, electrical coupling, and signaling via a growth factor within the CBsn of the hamster SCN. Our results reveal connections that have the potential for integrating cellular communication within a subregion of the SCN that is critically involved in circadian locomotion.