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Monkeys could either postpone shock by pressing a lever or pull a chain to produce a period of time out from the avoidance procedure. The period of time out proved to be an effective positive reinforcer. Certain features of the animals' behavior were attributed to interactions between the two responses.
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Several examples of functional recovery of instrumental responding after cerebral lesions are reviewed. Small incision on the boundary between the sensory and the motor cortex of a dog changed the saliency not only of the tactile but also of the auditory conditioned stimuli, eliciting the preoperatively acquired alimentary instrumental response. Prefrontal lesions in cats affected differently each of the several learning processes involved in the performance of the avoidance response: they enhanced the classically conditioned component, attenuated the motivational role of fear but left the motor component intact. Preoperatively acquired interrelations of these components underwent substantial changes, leading to the restoration of the previous level of avoidance of pain. However, a highly adaptive mode of behavior, namely avoidance of the state of fear, was permanently impaired. After small electrolytic lesions of amygdalar nucleus centralis cats were handicapped in the acquisition of escape from pain responses. The responses to low shock intensities were especially diminished. Improvement of the escape from pain responses was observed after a prolonged increase of the intertrial response frequency. The effectiveness of both escape and avoidance learning depended on the duration of the postoperative recovery period prior to instrumental training. All these data indicated that cerebral lesions changed the interactions between different parts of the neuronal circuitry participating in the learning and performance of a given instrumental response.
The hippocampus and the amygdala are involved in avoidance learning in mammals. The medial and lateral pallia of actinopterygian fish have been proposed as homologous to the mammalian pallial amygdala and hippocampus, respectively, on the basis of neuroanatomical findings. This work was aimed at studying the effects of ablation of the medial telencephalic pallia (MP) and lateral telencephalic pallia (LP) in goldfish on the retention of a conditioned avoidance response previously acquired in two experimental conditions. In the first experiment, fish were trained in nontrace avoidance conditioning. In the second experiment, fish were trained in trace avoidance conditioning in which temporal cues were crucial for the learning process. An MP lesion affected the retention of the avoidance response in both procedures; in contrast, an LP lesion impaired the retention only in the trace-conditioning procedure. These data support the presence of two different systems of memory in fish, based on discrete telencephalic areas: the MP, involved in an emotional memory system; and the LP, involved in a spatial, relational, or temporal memory system. Moreover, these differential effects were similar to those produced by amygdalar and hippocampal lesions in mammals. We conclude that these specialized systems of memory could have appeared early during phylogenesis and could have been conserved throughout vertebrate evolution.
The present study investigated the effects of post-trial systemic injections of the neurokinin substance P (SP) on inhibitory avoidance learning in rats treated with naloxone before conditioning and/or test trials. Rats were trained in a step-down or uphill inhibitory avoidance task and tested 24 h later. The animals received, 30 min before training and/or testing an i.p. injection of saline or naloxone (Nx) at doses of 0.5; 1.0; 5.0 or 50 mg/kg. Immediately after training they were administered SP 50 micrograms/kg or vehicle. Animals that received Nx both before conditioning and test trials (5.0 and 50 mg/kg), in combination with SP, showed better test performance for the uphill and step-down avoidance then those treated only with SP. Nx administered only before training (5.0 and 50 mg/kg) or before test (0.5 to 50 mg/kg) reduced the effects of SP. These data are discussed in terms of the possibility that Nx produces a state-dependent learning when combined with SP.
In Experiment 1, rats drank strychnine solution followed by an injection of LiCl. Generalization of learned strychnine avoidance to 4 non-toxic flavors was then assessed. Additional conditioning and generalization trials followed until 24 flavors had been presented. In Experiment 2, rats were conditioned to avoid individual flavors, or flavor mixtures concocted on the basis of avoidance generalization observed in Experiment 1. Tests followed for generalization of learned avoidance from the simple flavors to the mixtures, from the mixtures to the simple flavors, and from either to strychnine. In Experiment 3, two concentrations of NaCl were mixed with strychnine or one of the flavors (SOA) used in the previous experiments. These stimuli, as well as SOA alone, strychnine alone, and each of the NaCl concentrations, were presented to rats during conditioning. Generalization followed, as in the previous experiments. In Experiment 1, strychnine avoidance generalized to 'bitter' flavors (ps less than 0.01). In Experiment 2, avoidance of flavor mixtures generalized more strongly to strychnine than did learned avoidance of simple flavors (ps less than 0.01). In Experiment 3, NaCl masked or otherwise suppressed the 'bitter' flavor of strychnine or SOA insofar as no groups conditioned with a 'bitter'-salt mixture generalized avoidance to 'bitter' alone (ps less than 0.01). Rats are therefore capable of recognizing the flavor components of strychnine. Moreover, when these components are mixed in proportion to the degree of generalized avoidance, a mimic (either in terms of flavor characteristics or perceived intensity) of strychnine is obtained. Avoidance learning appears useful in the development of rodenticide baits and pre-bait formulations.
Intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) biphasically affects performance in tests of learning and memory. In the present study, we used CRF, urocortin (Ucn), a recently cloned CRF homologue, and CRF receptor antagonists, to determine which CRF receptor subtype(s) mediate the memory modulating effects of CRF receptor agonists in male Wistar rats. Under difficult learning conditions (massed trials), i.c.v. pretreatment with CRF or Ucn facilitated the acquisition of spatial navigation in the Morris water maze in a non-dose-dependent fashion (optimal doses of 0.1 and 0.03 microg, respectively). Under less difficult learning conditions (spaced trials), both peptides impaired water maze performance. In addition, with i.c.v. posttraining treatment, the peptides were equipotent (1.0 microg) in facilitating the consolidation of passive avoidance learning. The performance-enhancing effects of Ucn in both water maze and passive avoidance paradigms were reversed by i.c.v. pretreatment with D-Phe CRF(12-41) (2.5, 5 microg), a broad CRF(1)/CRF(2) receptor antagonist, or antalarmin (10 microg), a potent, nonpeptide, CRF(1) selective receptor antagonist. Thus, Ucn shares CRF's memory-modulating effects, and these effects appear to be mediated via the CRF(1) receptor. These findings are consistent with the hypothesis that CRF receptor agonists affect performance in tests of learning and memory by increasing arousal.
Systemic injections of 3-nitropropionic acid (3-NP) in Sprague-Dawley rats have led to (1) hypoactivity that resembles juvenile onset and advanced Huntington's disease (HD), and (2) impairment in contextual retention of passive avoidance. Since it has been established that 3-NP exerts its primary effects in the striatum, we selected intrastriatal injections to more thoroughly understand the direct behavioral effects of 3-NP. Each 14-week old rat received bilateral intrastriatal injections of one of the following: 500 and 750 nmol of 3-NP or vehicle (0.9% saline). At seven days following surgery, the animals were tested for spontaneous locomotor behavior and passive avoidance behavior. Results revealed deficits in both locomotor activity and passive avoidance learning. The animals injected with 500 and 750 nmol of 3-NP were significantly hypoactive compared with control animals. Similarly, the 2 groups of animals were severely impaired in the retention of passive avoidance compared with control. The 3 groups, however, did not differ in their acquisition of this learning task. Macroscopic analyses of brains of these animals revealed that 500 and 750 nmol of 3-NP caused severe loss of neuronal cell bodies and marked glial infiltration in the medial aspect of the striatum. Larger lesions showed a necrotic cavity at the injection site. In comparison with systemic administration of 3-NP, intrastriatal injections resulted in more profound hypoactivity, greater loss of passive avoidance retention, and more severe striatal damage.(ABSTRACT TRUNCATED AT 250 WORDS)
Changes in learning and memory processes that occur with senescence were investigated in male and female Fischer 344 rats, 3-26 mth of age. Age-related impairments were seen in retention of inhibitory avoidance learning, acquisition of a Y-maze discrimination task, and in a swim escape task with short intertrial training intervals. In contrast, old animals performed better than the young rats in an active avoidance task. No age differences were observed in either open field activity or in flinch or jump thresholds to footshock. These results indicate that impairments in learning and memory processes of aged rats are task-specific, and that memory deficits in old rats are best seen following one-time-only events or with weak training. The behavioral baselines described will help in the design of further research to correlate memory and neurobiological changes observed during the aging process in the rat.
Intracerebroventricularly (ICV) injected streptozotocin (STREP) decreases central glucose metabolism and energy metabolism, which has also been observed in patients with dementia. In the present study we examined the behavioral (open-field behavior and two-way active avoidance learning) and biochemical (hippocampal ChAT activity) effects of STREP treatment in old Lewis rats. The results suggest that hippocampal function was affected by STREP. STREP-treated rats acquired the two-way active avoidance task faster than the control rats, which indicates that STREP treatment does not lead to a general learning deficit. Hippocampal ChAT activity was decreased in STREP-treated rats. The present results suggest also that susceptibility to STREP may not be related to age in Lewis rats.
Pharmacological agents known to stimulate monoamine systems improve memory, and destruction of the dopaminergic systems or dopamine depletion lead to impairments in various learning-related tasks. These reported effects of the central dopaminergic system imply the involvement of D2 receptors. The aim of the present study was to investigate changes in [3H]spiroperidol binding in seven areas of rat brain following informal and active avoidance learning. Littermate male and female rats were reared until 3 months of age in standard colony conditions and treated as active controls or in enriched environmental conditions and exposed to pole-jump active avoidance trials. Female rats acquired avoidance behavior more rapidly than males. Among the brain regions, only the hippocampus showed significant variations in D2 receptor binding between the groups; sex differences and learning-sex interaction were observed in the corpus striatum. There was an inverse correlation between learning performance and hippocampal D2 receptor binding. Our results show that learning affects hippocampal D2 receptors in a sexually dimorphic pattern.
The persistence of Müllerian mimicry and geographically distinct wing patterns, as observed in many Heliconius species (Lepidoptera: Nymphalidae), is difficult to explain from a predator's perspective: predator selection against locally rare patterns must persist despite avoidance learning. Maintaining spatial color-pattern polymorphism requires local pattern avoidance, fine-scale discrimination among similar wing patterns, and repeated attacks on novel color patterns. I tested for these behaviors by presenting 80 adult rufous-tailed jacamars (Galbula ruficauda) with three morphs of Heliconius butterflies, and then presenting the same suite of butterflies to 46 of these jacamars between four and 429 days later. These trials offer the first direct evidence of the selective predator behavior required to maintain aposematic polymorphism: jacamars avoid local aposematic morphs while repeatedly attacking similar but novel morphs over time.
There is evidence that inhibitory avoidance learning is still possible after removal of the telencephalic forebrain. However, it is not known whether subtelencephalic storage of such a conditioned response takes place when the brain is intact. To investigate this possibility, rats received one training trial in the "up-hill avoidance" task, and 8 h later the entire forebrain except the hypothalamus was bilaterally ablated. When tested 24 h later, the decerebrate rats still exhibited the learned response, demonstrating a transfer of the conditioned response from the intact to the postlesion state. This result indicates that memory-storage for this avoidance task takes place, at least in part, subtelencephalically.
cAMP/cAMP-dependent protein kinase (PKA) signaling pathway has been recently proposed to participate in both the late phase of long term potentiation in the hippocampus and in the late, protein synthesis-dependent phase of memory formation. Here we report that a late memory consolidation phase of an inhibitory avoidance learning is regulated by an hippocampal cAMP signaling pathway that is activated, at least in part, by D1/D5 receptors. Bilateral infusion of SKF 38393 (7.5 microg/side), a D1/D5 receptor agonist, into the CA1 region of the dorsal hippocampus, enhanced retention of a step-down inhibitory avoidance when given 3 or 6 h, but not immediately (0 h) or 9 h, after training. In contrast, full retrograde amnesia was obtained when SCH 23390 (0.5 microg/side), a D1/D5 receptor antagonist, was infused into the hippocampus 3 or 6 h after training. Intrahippocampal infusion of 8Br-cAMP (1.25 microg/side), or forskolin (0.5 microg/side), an activator of adenylyl cyclase, enhanced memory when given 3 or 6 h after training. KT5720 (0.5 microg/side), a specific inhibitor of PKA, hindered memory consolidation when given immediately or 3 or 6 h posttraining. Rats submitted to the avoidance task showed learning-specific increases in hippocampal 3H-SCH 23390 binding and in the endogenous levels of cAMP 3 and 6 h after training. In addition, PKA activity and P-CREB (phosphorylated form of cAMP responsive element binding protein) immunoreactivity increased in the hippocampus immediately and 3 and 6 h after training. Together, these findings suggest that the late phase of memory consolidation of an inhibitory avoidance is modulated cAMP/PKA signaling pathways in the hippocampus.
The neurotoxic effects of prenatal organosolvent inhalation were studied in rats, because of the expectation that a developing organism may be more sensitive than the adult to the induction of functional deficits. The aim was to determine whether prenatal exposure to the new organosolvent mixture, Aromatol, and the well known neurotoxic carbon disulphide, would impair reflex ontogeny or produce neurobehavioural dysfunctions in the offspring. Development of gait, motor coordination, and activity, avoidance learning and swimming were tested in the offspring of CFY rat mothers, exposed to CS2 inhalation (0, less than 10, 700 and 2000 mg/m3) and to Aromatol (0, 600, 1000 and 2000 mg/m3) on days 7-15 gestation. Prenatal CS2 inhalation induced dose related perinatal mortality of pups. Eye opening and the auditory startle were retarded. There were immature gait, motor incoordination, diminished open field activity and altered behavioural patterns on day 21 and 36 but they were nearly age-appropriate on day 90. As signs of disturbed learning ability, there were diminished performance and lengthened latency of the conditioned avoidance response, related to the concentrations administered. Contrary to expectations, prenatal Aromatol inhalation had no effect on maturation of gait, behaviour patterns, or learning ability.
The effects of prenatal aflatoxin B1 (AFB) exposure on eight behavioral parameters in Jcl:Wistar rat offspring were assessed. Pregnant rats were injected subcutaneously with 0.3 mg/kg/day of AFB dissolved in dimethylsulfoxide on days 11-14 (Group A) or 15-18 (Group B) of gestation. Controls received the vehicle similarly on days 11-18 of gestation. Before weaning, the offspring were examined using the cliff avoidance response (5 days of age), the negative geotaxis reflex (7 days), and swimming development (6, 8, and 10 days). After weaning, animals were examined using the rotarod test (5 weeks of age), the open field test (6 weeks), a conditioned avoidance learning test (14 weeks), an underwater T-maze test (15 weeks), and a reproduction test (16 weeks). The preweaning offspring in the AFB-A group showed significantly lower success rates than controls in cliff avoidance responses. In swimming development, the offspring in the AFB-A group had significantly lower scores than controls for swimming direction. In the rotarod test, the AFB-A group remained on the rod for a significantly shorter time than the controls at 15 rpm on both the first and second trial days. The avoidance performance of the rats in AFB-A and AFB -B groups was significantly poorer than that of controls. These results indicate that prenatal exposure to AFB produced a delay of early response development, impaired locomotor coordination, and impaired learning ability in the offspring of rats exposed to AFB during middle pregnancy, and the early gestational exposure appears to produce more effects than latter exposure.