RESUMO

We examined the behavioural responses and Fos expression pattern of rats that were exposed to snake threats from shed snakeskin and a live snake. We differentiated the behavioural responses and the pattern of Fos expression in response to the odour cues and mild threat from a live snake. Animals exposed to the snake odour alone or to the confined snake showed a great deal of risk assessment. Conversely, the intensification of odour during exposure to the live snake decreased the threat ambiguity, and the animals froze for a significantly longer period. Our Fos analysis showed that a pathway formed by the posteroventral part of the medial amygdalar nucleus to the central part of the ventromedial hypothalamic nucleus appeared to be solely responsive to odour cues. In addition, we showed increased Fos expression in a parallel circuit comprising the lateral amygdalar nucleus, ventral subiculum, lateral septum, and juxtadorsomedial region of the lateral hypothalamic area that is responsive to both the odour and mild threat from a live snake. This path is likely to process the environmental boundaries of the threat to be avoided. Both paths merge into the dorsal premammillary nucleus and periaqueductal grey sites, which all increase Fos expression in response to the snake threats and are likely to organize the defensive responses. Moreover, we found that the snake threat mobilized the Edinger-Westphal and supraoculomotor nuclei, which are involved in stress adaptation and attentional mechanisms.

Assuntos

RESUMO

We examined the behavioral responses and Fos expression pattern of rats that were exposed to snake threats from shed snakeskin and a live snake. We differentiated the behavioral responses and the pattern of Fos expression in response to the odor cues and mild threat from a live snake. Animals exposed to the snake odor alone or to the confined snake showed a great deal of risk assessment. Conversely, the intensification of odor during exposure to the live snake decreased the threat ambiguity, and the animals froze for a significantly longer period. Our Fos analysis showed that a pathway formed by the posteroventral part of the medial amygdalar nucleus to the central part of the ventromedial hypothalamic nucleus appeared to be solely responsive to odor cues. In addition, we showed increased Fos expression in a parallel circuit comprising the lateral amygdalar nucleus, ventral subiculum, lateral septum and juxtadorsomedial region of the lateral hypothalamic area that is responsive to both the odor and mild threat from a live snake. This path is likely to process the environmental boundaries of the threat to be avoided. Both paths merge into the dorsal premammillary nucleus and periaqueductal gray sites, which all increase Fos expression in response to the snake threats and are likely to organize the defensive responses. Moreover, we found that the snake threat mobilized the Edinger-Westphal and supraoculomotor nuclei, which are involved in stress adaptation and attentional mechanisms.

RESUMO

Intracerebroventricular (i.c.v.) or intraperitoneal (IP) administration of saredutant (SR48968), an NK2 receptor antagonist, produces anxiolytic-like effects in rodents in a number of animal models of anxiety. NK2 binding sites are present in several limbic structures in rats, including the hippocampus, thalamus, septum and prefrontal cortex, suggesting involvement in the modulation of emotional processes. The current study investigated the behavioral effects of saredutant infused into the ventral hippocampus (VH), a structure associated with cognitive and emotional processes, to clarify the neural substrate underlying the anxiolytic-like effect of the compound. Saredutant (10, 100 or 500 pmol/0.2 µL) was injected bilaterally into the VH of male CD-1 mice tested in the elevated plus-maze and mouse defense test battery (MDTB). Results from the EPM showed that microinjections of 10 pmol/0.2 µL of saredutant increased entries and time spent in the open arms and enhanced end-arm exploration. In the MDTB, saredutant (500 pmol/0.2 µL) decreased vocalizations and increased escape attempts in mice confronted with a rat. Taken together, these results suggest that hippocampal tachykinin mechanisms are involved in the modulation of anxiety and defensive behaviors.

Assuntos

RESUMO

The midbrain dorsal periaqueductal gray (DPAG) is part of the brain defensive system involved in active defense reactions to threatening stimuli. Corticotrophin releasing factor (CRF) is a peptidergic neurotransmitter that has been strongly implicated in the control of both behavioral and endocrine responses to threat and stress. We investigated the effect of the nonspecific CRF receptor agonist, ovine CRF (oCRF), injected into the DPAG of mice, in two predator-stress situations, the mouse defense test battery (MDTB), and the rat exposure test (RET). In the MDTB, oCRF weakly modified defensive behaviors in mice confronted by the predator (rat); e.g. it increased avoidance distance when the rat was approached and escape attempts (jump escapes) in forced contact. In the RET, drug infusion enhanced duration in the chamber while reduced tunnel and surface time, and reduced contact with the screen which divides the subject and the predator. oCRF also reduced both frequency and duration of risk assessment (stretch attend posture: SAP) in the tunnel and tended to increase freezing. These findings suggest that patterns of defensiveness in response to low intensity threat (RET) are more sensitive to intra-DPAG oCRF than those triggered by high intensity threats (MDTB). Our data indicate that CRF systems may be functionally involved in unconditioned defenses to a predator, consonant with a role for DPAG CRF systems in the regulation of emotionality.

Assuntos