The antinociceptive effects of the serotonin (5-HT)1A/7 receptor agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) administered into the medial thalamus were evaluated. Pain behaviors organized at spinal (spinal motor reflexes, SMRs), medullary (vocalizations during shock, VDSs), and forebrain (vocalization after discharges, VADs) levels of the neuraxis were elicited by tailshock. Administration of 8-OH-DPAT (5, 10, and 20 microg/side) into nucleus parafascicularis (nPf) produced dose-dependent increases in VDS and VAD thresholds, but failed to elevate SMR threshold. The increase in VAD threshold was significantly greater than that of VDS threshold. Similar effects were observed with administration of 8-OH-DPAT (20 microg/side) into the rostral portion of the central lateral thalamic nucleus. The bilateral or unilateral administration of 8-OH-DPAT (20 microg) into other thalamic nuclei, or into sites dorsal to nPf, did not elevate vocalization thresholds. Increases in vocalization thresholds produced by nPf-administered 8-OH-DPAT were mediated by both 5-HT1A and 5-HT7 receptors. Intra-nPf administration of the 5-HT1A receptor antagonist WAY-100635 (0.05 or 0.5 microg/side), or the 5-HT7 receptor antagonist SB-269970 (1 or 2 microg/side), but not the dopamine D2 receptor antagonist raclopride (10 microg/side), reversed 8-OH-DPAT induced elevations in vocalization thresholds. These results provide the first reported evidence of behavioral antinociception following the administration of a 5-HT agonist into the medial thalamus.

This study examined differences in the spread of semantic activation within and between the cerebral hemispheres. A lateralised lexical decision task using indirect priming was presented to 58 undergraduates with primes and targets separated by 215 or 750 milliseconds (ms). Prime and target words were presented to the same or opposite visual fields and were either directly related (book-read), indirectly related (lion-[tiger]-stripes), or unrelated (cup-street). At 215 ms participants exhibited significant priming effects to directly related words in all conditions except when primes and targets were both presented to the right hemisphere (RH). In contrast, priming to indirectly related words was effective only when primes and targets were presented to opposite hemispheres. At 750 ms, significant priming occurred for directly related words in all conditions, and for indirectly related words when primes were presented to the RH. Results suggest that priming for directly and indirectly related concepts occurs unilaterally in each hemisphere before 215 ms. Both prime types activate semantic networks in the RH within 750 ms, whereas the LH processes information in a more focused manner. This suggests that activation spreads contralaterally from each hemisphere first to directly and then to indirectly related concepts, indicating the importance of incorporating contralateral priming contrasts in lexical decision tasks.

Cholinergic stimulation of dopamine neurons in the ventral tegmental area (VTA) underlies activation of the brain reward circuitry. Activation of this circuit is proposed to preferentially suppress the affective reaction to noxious stimulation. Vocalization afterdischarges (VADs) are a validated model of the affective response of rats to noxious tailshock. The antinociceptive action of the acetylcholine agonist carbachol microinjected into the VTA on VAD threshold was compared to its effect on the thresholds of other tailshock-elicited responses (VDS = vocalizations during shock, and SMR = spinal motor reflexes). Whereas VADs are organized within the forebrain, VDSs and SMRs are organized at medullary and spinal levels of the neuraxis, respectively. Carbachol (1 μg, 2 μg, and 4 μg) injected into VTA produced dose-dependent increases in VAD and VDS thresholds, although increases in VAD threshold were significantly greater than increases in VDS threshold. Administration of carbachol into VTA failed to elevate SMR threshold. Elevations in vocalization thresholds produced by intra-VTA carbachol were reversed in a dose-dependent manner by local administration of the muscarinic receptor antagonist atropine sulfate (30 μg and 60 μg). These results provide the first demonstration of the involvement of the VTA in muscarinic-induced suppression of pain affect.Perspective-Cholinergic activation of the brain reward circuit produced a preferential suppression of rats' affective reaction to noxious stimulation. The neurobiology that relates reinforcement to suppression of pain affect may provide insights into new treatments for pain and its associated affective disorders.