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Lesions of periaqueductal gray dissociate-conditioned freezing from conditioned suppression behavior in rats - PubMed

Lesions of periaqueductal gray dissociate-conditioned freezing from conditioned suppression behavior in rats

P Amorapanth et al. Learn Mem. 1999 Sep-Oct.

Abstract

It is commonly assumed that suppression of an ongoing behavior is an indirect measure of freezing behavior. We tested whether conditioned suppression and freezing are the same or distinct conditioned responses. Rats were trained to press a bar for food and then given fear-conditioning sessions in which a tone was paired with a foot shock (two pairings a day for 2 days). They then received either sham or electrolytic lesions of the periaqueductal gray (PAG). Post-training PAG lesions blocked freezing to the conditioned stimulus (CS), but had no effect on the suppression of operant behavior to the same CS. Thus, conditioned suppression and freezing, which both cause a cessation in activity, appear to be mediated by separate processes.

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Figures

Figure 1
Figure 1

A schematic representing coronal sections through the rostrocaudal extent of the PAG lesions (A–D, rostral to caudal). The hatched areas show representative examples of PAG lesions made in this study. (Aq) Aqueduct; (bic) brachium inferior colliculus; (CnF) cuneiform; (cp) cerebral peduncle; (DLL) dorsal nucleus of lateral lemniscus; (DTgP) dorsal tegmental nucleus, pericentral; (IC) inferior colliculus; (MG) medial geniculate body; (ml) medial lemniscus; (MnR) median raphe; (MRF) midbrain reticular formation; (RN) red nucleus; (SC) superior colliculus; (scp) superior cerebellar peduncle; (VTg) ventral tegmental nucleus.

Figure 2
Figure 2

Coronal image of Sham (A)- and PAG (B)-lesioned animals. (Arrowheads) The tips of the electrodes.

Figure 3
Figure 3

(A) Effects of post-training lesions of the PAG on conditioned freezing behavior. (B) Effect of lesions of PAG on conditioned suppression. The suppression ratio is calculated as CS/preCS + CS, where preCS is the number of presses in a 20-sec period prior to CS onset and CS is the number of presses during the 20-sec CS. The first name of the group refers to whether rats received paired or unpaired fear conditioning. The second word refers to whether animals received electrolytic or sham lesions of the PAG. Bars represent group mean ± +s.e.m.−.

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