The effect of the duration of adaptation to laboratory conditions on the passive avoidance reflex in rats

Influence of adaptation degree in new conditions on the passive avoidance was studied. The short period of habituation (3 days) positively influenced the rats' ability for memory trace retrieval. A negative correlation between the step through latency and anxiety in the elevated plus-maze, was shown. Prolongation of adaptation up to 9 days reduced levels of anxiety and retrieval of conditioned response. Modulating role of adaptation degree causing various anxiety levels in passive avoidance, is discussed.     

Effects of neurotensin on active and passive avoidance performance in rats with lesions of serotoninergic neurons

After a lesion of serotoninergic neurons performed by administration of 5.7-dihydroxytriptamine into the dorsal raphe nucleus, effects of neurotensin microinjections into the substantia nigra on rat behavior were investigated. Serotoninergic lesions resulted in enhanced fear of rats manifested as an increase in the number of intersignal avoidance reactions and intensification of escape reactions. Neurotensin microinjections into the substantia nigra diminished the neurotoxin action thus increasing the adaptive character of defensive behavior of rats with deficit of functions of serotonin neurons.     

The effect of cortical spreading depression on motor performance and depth avoidance in rats.

Functional decortication induced by cortical spreading depression (CSD) was used to estimate the significance of cerebral cortex for swimming and depth avoidance in arts. In the swimming test (5 gr sinkers, 36 degrees C water) the median swimming time was reduced from greater 120 minutes in the controls to 16 minutes in the bilaterally depressed rats. Depth avoidance in the physical and visual cliff situation (6 cm to the shallow and 48 cm to the deep surface) was unimpaired by unilateral CSF but was abolished by bilateral CSD. Combination of monocular occlusion with ipsilateral CSD deteriorated the visual cliff test but not the physical cliff behaviour. Functional decortication increased descent latencies and decreased the explaration rate in both tests. It is concluded that cerebral cortex plays an important role in the regulation of unlearned, innate activities with the overall behaviour of the organism.     

Involvement of serotoninergic brain structures in the mechanisms of neurotensin effect on passive avoidance in rats

The purpose of the research was to reveal the features of neurotensin (administered in substantia nigra or dorsal raphe nucleus) effect on recall of passive avoidance reactions in rats. It was shown that the effect of neurotensin injected into the substantia nigra was characterized by a sharp reduction of passive avoidance reactions. On the contrary, injection of the substance in the dorsal raphe nucleus led to an intensification of these reactions and delay of their extinction. The effects of microinjections of serotonin 1A receptor agonist, 8-hydroxy-dipropylaminotetralin (8-OH-DPAT), into the mentioned brain structures was similar to that of neurotensin. Changes in the content of serotonin and its metabolite 5- hydroxyindoleacetic acid (5-HIAA) in the caudate nucleus corresponded to various behavioral effects. The conclusion was made that neurotensin effect on the passive avoidance behavior is related to regulation of emotional state of animals mediated by its action on the function of the serotoninergic brain structures.     

Effects of stress and of amphetamine on passive avoidance conditioning in rats

This study examined the effects of immobilization stress combined with water immersion (ICS) and/or amphetamine (AM) on different memory phases in the passive avoidance task in rats. The performance of rats was evaluated in the retention tests 24 and 48 h after a single acquisition trial. ICS exposure lasting 1 h impaired retention of the learned avoidance response if applied 2 to 4 h before or immediately after training. The stressor did not affect retrieval if presented 5 or 2 h before the retention test. AM was used i.p. at the dose of 8 or 1 mg/kg. Neither 8 mg AM administered 4 h before nor 8 or 1 mg doses given after training did not impair the retention performance in unstressed rats. The 1 mg AM prevented the impairment of retention in animals exposed to the stressor 3 or 4 h before training but had no effect when the stronger impairment was induced by ICS 2 h before training. However, when given 1 h before retention testing, 1 mg AM attenuated even the severe impairment induced by the pre-training stressor exposure. Our results suggest that ICS impairs primarily the early phase of memory consolidation and a low dose of AM can prevent this effect.     

Effects of dehydroepiandrosterone on passive avoidance in ovariectomized female rats of different age

The aim of the present work was to study the influence of long-term treatment with dehydroepiandrosterone (DHEA) in doses of 0.1 and 0.7 mg/kg, i.p. on the passive avoidance performance in the ovariectomized female rats of 5- and 18-month old. The results obtained indicated that DHEA administration during 7 days in dose of 0.1 mg/kg normalized the passive avoidance performance in the ovariectomized rats of 5-month old while DHEA administration during 7 days in dose of 0.7 mg/kg restored passive avoidance performance in the ovariectomized rats of 18-month old.     

Pregnene-type steroids and impairment of passive avoidance behavior in rats.

Several pregnene-type steroids, such as progesterone, 19-norprogesterone, dydrogesterone, hydroxydione, corticosterone, deoxycorticosterone, cortisone, and hydrocortisone, were tested on passive avoidance behavior. All steroids except dydrogesterone resulted in an impairment of passive avoidance behavior as shown by decreased avoidance latencies, whereas cortisone appears to have only a weak effect in this respect.     

Naloxone blocks the effect of 5-hydroxy-tryptophan on passive avoidance learning in rats: Implication of endogenous opioid peptides

The synthetic opioid peptide D-Ala²-met-enkephalinamide (DALA) impairs retention performance of rats on a one-trial passive avoidance task. The same effect is observed after administration of 5-hydroxy-tryptophan (5-HTP). Both drugs appear to impair learning by disrupting memory consolidation since similar effects are observed when they are given either peripherally before the acquisition test or intracerebroventricularly immediately after. A moderate dose of naloxone prevents the amnesia produced by DALA or 5-HTP. However, the opiate antagonist does not block the behavioral syndrome induced by clorgyline and 5-HTP. Moreover, bacitracin, a peptidase inhibitor, potentiates the effect of 5-HTP on the passive avoidance task. The results suggest that endogenous opioid peptides are involved in the amnesic effect of 5-HTP.     

Comparison of the effect of serotonin administered into the dorsal hippocampus on conditioned passive and active avoidance in rats

It has been established that intrahippocampal bilateral injection of 5-HT in a dose of 2 micrograms prolonged the time of passive avoidance reflex retention, inhibiting the retrieval of active avoidance reflex and facilitating its extinction. The data obtained show the dependence of 5-HT effect on reinforcing and triggering properties of spatial-environmental and phasic conditioned stimuli. It is suggested that intrahippocampal 5-HT administration was responsible for the retrieval of traces of conditioned reinforced stimuli.     

Intraseptal injection of scopolamine increases the effect of systemic diazepam on passive avoidance learning and emotionality in rats.

This experiment was designed to assess the role of the septo-hippocampal cholinergic (ACh) system in the deleterious effects produced by systemic benzodiazepine injection on learning processes in rats. Retention of a step through passive avoidance task was analysed after systemic injection of increasing doses of either scopolamine or diazepam applied alone 30 min before the acquisition phase. Results indicated a dose related impairment of retention by each drug: in addition, sub-threshold doses of scopolamine and diazepam applied in combination (diazepam: 2mg/kg plus scopolamine: 0.3mg/kg) produced a decrease of retention latencies, thus showing an additive effect of the combined treatment. Secondly, a sub-threshold dose of scopolamine (15microg/0.5microl) was also administered into the medial septal area, together with an i.p. injection of 2mg/kg of diazepam. This combined treatment produced a severe impairment of retention, in parallel with a large reduction in emotionality (number of faeces). The data are consistent with the hypothesis that peripheral administration of behaviorally effective doses of diazepam on passive avoidance learning might act partially via a septal ACh-GABA/benzodiazepine mechanism. It is also suggested that this mechanism subserves both anxiety and the memorisation of contextual stimuli associated with passive avoidance acquisition, through the modification of the septo-hippocampal activity.     

Levels of arginine-vasopressin in cerebrospinal fluid during passive avoidance behavior in rats

The concentration of immunoreactive arginine-vasopressin (IR-AVP) was measured in the cerebrospinal fluid (CSF) during acquisition and retention of passive avoidance behavior. IR-AVP level in CSF of male Wistar rats immediately after the learning trial was increased; the rate of which was related to the intensity of the electric footshock during the learning trial and the avoidance latency as measured 1 day after the learning trial. Immediately after the 24 h retention test IR-AVP levels were significantly increased in rats subjected to the low (0.25 mA) shock intensity during the learning trial, but IR-AVP levels of rats exposed to the high shock (1.0 mA) were under the limit of detection. If the retention test was postponed till 5 days after the learning trial, the increase of IR-AVP level in the CSF was related to avoidance latencies which reflect the intensity of aversive stimulation (electric footshock). The results suggest an association between central AVP release and passive avoidance behavior and may be indicative of the role of this peptide in neuronal mechanisms underlying learning and memory processes.