Several studies have focused on the neuroanatomical and neuropharmacological substrates of the pa... more Several studies have focused on the neuroanatomical and neuropharmacological substrates of the panic syndrome and phobias. Using a prey/predator paradigm the present study investigated the involvement of the opioid peptidesmediated system in the modulation of fear-induced responses. Rats (Rattus norvegicus, Rodentia, Muridae) were pretreated with an intraperitoneal administration of either physiological saline or naloxone (1 mg/kg, 3 mg/kg, and 5 mg/kg), and were then put into confrontation with a natural predator (Crotalus durissus terrificus, Reptilia, Viperidae). The aggressive encounter took place in a rectangular arena, consisting of semitransparent walls, made of acrylic (5 mm in width), with the inner face covered with light reflector film, kept in a cooled environment illuminated by a fluorescent lamp (Reptisun, 20 W). The animals' defensive behaviour (defensive attention, defensive immobility, escape behaviour, flat back approaches, startle, and neurovegetative responses, such as micturition and defecation) were recorded twice: during 15 min of exposure to the predator; and 24 h after the confrontation, while exposed to the experimental enclosure without the snake. Innate fear-induced antinociception was studied after 5-min of confrontation in independent group of rodents pretreated with physiological saline or naloxone. The non-specific blockade of opioid receptors decreased defensive attention, defensive immobility (freezing), risk assessment and startle reaction elicited in the presence of rattlesnakes, and caused impairment in the fear-induced antinociception organization. The defensive attention and the defensive immobility decreased drastically in the contextual fear-paradigm after the pretreatment with naloxone at different doses. There was a statistically significant increase in exploratory behaviour, with an intensification of crossing and rearing in the fist 10 min, and of the resting state and grooming in the following periods after naloxone pretreatment. These findings suggest an antipanic (antiaversive) effect of opioid antagonism on innate and conditioned fear. Financial support: CNPq, FAEPA, FAPESP.
Several studies have focused on the neuroanatomical and neuropharmacological substrates of the pa... more Several studies have focused on the neuroanatomical and neuropharmacological substrates of the panic syndrome and phobias. Using a prey/predator paradigm the present study investigated the involvement of the opioid peptidesmediated system in the modulation of fear-induced responses. Rats (Rattus norvegicus, Rodentia, Muridae) were pretreated with an intraperitoneal administration of either physiological saline or naloxone (1 mg/kg, 3 mg/kg, and 5 mg/kg), and were then put into confrontation with a natural predator (Crotalus durissus terrificus, Reptilia, Viperidae). The aggressive encounter took place in a rectangular arena, consisting of semitransparent walls, made of acrylic (5 mm in width), with the inner face covered with light reflector film, kept in a cooled environment illuminated by a fluorescent lamp (Reptisun, 20 W). The animals' defensive behaviour (defensive attention, defensive immobility, escape behaviour, flat back approaches, startle, and neurovegetative responses, such as micturition and defecation) were recorded twice: during 15 min of exposure to the predator; and 24 h after the confrontation, while exposed to the experimental enclosure without the snake. Innate fear-induced antinociception was studied after 5-min of confrontation in independent group of rodents pretreated with physiological saline or naloxone. The non-specific blockade of opioid receptors decreased defensive attention, defensive immobility (freezing), risk assessment and startle reaction elicited in the presence of rattlesnakes, and caused impairment in the fear-induced antinociception organization. The defensive attention and the defensive immobility decreased drastically in the contextual fear-paradigm after the pretreatment with naloxone at different doses. There was a statistically significant increase in exploratory behaviour, with an intensification of crossing and rearing in the fist 10 min, and of the resting state and grooming in the following periods after naloxone pretreatment. These findings suggest an antipanic (antiaversive) effect of opioid antagonism on innate and conditioned fear. Financial support: CNPq, FAEPA, FAPESP.
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