Antinociception Elicited by Aversive Stimulation of the Inferior Colliculus

Role of benzodiazepine and serotonergic mechanisms in conditioned freezing and antinociception using electrical stimulation of the dorsal periaqueductal gray as unconditioned stimulus in rats

“…Some other reports have shown that the conditioned antinociception obtained following exposure to stimuli associated with foot-shocks can be blocked by opioid antagonists (Mayer and Liebeskind 1974;Fanselow and Bolles 1979;Fanselow and Baackes 1982;Fields 1984, 1989;Helmstetter and Landeira-Fernandez 1990;Bellgowan and Helmstetter 1998). These effects have been attributed to opioid mechanisms of other mesencephalic regions, such as the ventral periaqueductal gray (Miczek et al 1985;Fardin et al 1984b;Fang et al 1997), whereas the present results are in agreement with studies showing that the unconditioned antinociception induced by electrical stimulation of the midbrain tectum is not mediated by opioid mechanisms Coimbra and Brand¼o 1997;Castilho et al 1999).…”

“…Our results are coherent with several reports showing that the administration of benzodiazepines inhibits the conditioned antinociception to stimuli associated with footshocks (Fanselow and Helmstetter 1988;Maier 1990;Fanselow 1991;Wetbrook 1995, 1996;Johnston 1996;Fendt and Fanselow 1999). The present findings differ from those obtained with the unconditioned aversive responses induced by electrical stimulation of the midbrain tectum, since previous administration of anxiolytic compounds, such as diazepam and midazolam, attenuated only the behavioral defense response without affecting the unconditioned antinociception (Morgan et al 1987;Le¼o-Borges et al 1988;Castilho et al 1999).…”

“…The unconditioned responses induced by stimulation of the midbrain tectum are also accompanied by antinociception (Fardin et al 1984a(Fardin et al , 1984bBrand¼o et al 1994Brand¼o et al , 1999. This unconditioned antinociception is mediated by 5-HT acting at 5-HT 2A receptors Coimbra and Brand¼o 1997;Castilho et al 1999). In the same way, recent studies of our laboratory pointed to a similar role of 5-HT mechanisms in the conditioned antinociception to the neutral stimulus previously associated with the electrical stimulation of the dPAG, since microinjections of 5-HT antagonists into this structure blocked this response (Castilho and Brand¼o 2001).…”

Apomorphine Enhances Conditioned Responses Induced by Aversive Stimulation of the Inferior Colliculus

“…The inferior colliculus (IC) is a midbrain tectum structure primarily involved in auditory information processing; it also integrates sensory information of aversive nature. Indeed, electrical or chemical stimulation of this structure induces responses such as freezing and flight responses that mimic fearful behavior elicited by environmental challenges (Schmitt et al, 1986;Brandão et al, 1988Cardoso et al, 1994;Troncoso et al, 1998;Castilho et al, 1999). Several studies have suggested modulatory roles for GABA, serotonin, opioids, excitatory amino acids and neuropeptides at the so-called brain aversion system, which includes the dorsal periaqueductal gray and IC (Brandão et al, 1982.…”

Papel dos mecanismos GABAérgicos do colículo inferior e da substância cinzenta periaquedutal na interface sensoriomotora do medo e ansiedade

“…Cortical DA projections are also activated by a wide variety of aversive stimulation (Thierry et al, 1976;Deutch et al, 1985;Feenstra and Botterblom, 1996;Goldstein et al, 1996). Relevant to the present study, reductions of DA activity reduce conditioned escape responses in paradigms that use light as the conditioned stimulus (CS) and electrical stimulation of the IC as the UCS (Troncoso et al, 1998(Troncoso et al, , 2003Castilho et al, 1999;. One surprising finding was that sulpiride, a D 2 receptor antagonist, increased switch-off responses in the light-dark test of unconditioned fear.…”