Acute alcohol intoxication disrupts brightness but not olfactory conditioning in preweanling rats

The present experiments tested the effect of acute alcohol administration on Pavlovian conditioning of 21-day-old rats using conditioned stimuli of two different sensory modalities--olfaction, an early developing sensory capacity functional at birth, and vision, a later developing sensory system not becoming functional until approximately 15 days of age. Conditioning and testing were conducted between 30 and 60 min following gastric infusion with either physiological saline or a mildly intoxicating alcohol dose (1.5 g/kg body weight). Brain alcohol levels were observed to remain at a peak and stable concentration during this period (Experiment 1). Alcohol impaired acquisition or expression of conditioned aversions to a visual cue paired with footshock when presented either as a single-element conditioned stimulus or as part of an odor/visual compound stimulus (Experiment 2), but it had no discernible effect on conditioned aversions to an olfactory stimulus that had similarly been paired with footshock (Experiments 2 and 3). The results suggest that alcohol may impair some aspects of learning but spare others, depending perhaps on the particular sensory modality to be conditioned.     

Long-term regular exercise promotes memory and learning in young but not in older rats

BACKGROUND AND OBJECTIVE: By aging, some functions in nervous system like spatial memory are reduced. It has been shown that short-time physical activity can improve memory but there is much less data on the long-term exercising. In the present study, the aim was to clarify the effect of regular long-term physical activity on spatial memory and learning of young and middle aged and older male Wistar rats. MATERIALS AND METHODS: Sixty 3 months old rats were randomly divided in six equal groups. Experimental groups were treadmill exercised at speed 22m/min for 1h 6 days per week, and the program lasted 3, 6 and 9 months, respectively. At the end of training period, spatial memory of rats was tested using Morris Water Maze. RESULTS: Results indicated that regular physical activity significantly increased spatial memory (p<0.05) in young rats (6 months old) as compared to controls, but not in the older ones (9 and 12 months old). Nonetheless, spatial memory of these rats was significantly better than in younger ones in both groups (p<0.05). CONCLUSION: Spatial memory and learning increased due regular exercise in young rats. With progression of age up to 9 and 12 months the memory improved, but the programmed exercise had no positive effect on learning.     

Sleep modulates word-pair learning but not motor sequence learning in healthy older adults

Sleep benefits memory across a range of tasks for young adults. However, remarkably little is known of the role of sleep on memory for healthy older adults. We used 2 tasks, 1 assaying motor skill learning and the other assaying nonmotor/declarative learning, to examine off-line changes in performance in young (20-34 years), middle-aged (35-50 years), and older (51-70 years) adults without disordered sleep. During an initial session, conducted either in the morning or evening, participants learned a motor sequence and a list of word pairs. Memory tests were given twice, 12 and 24 hours after training, allowing us to analyze off-line consolidation after a break that included sleep or normal wake. Sleep-dependent performance changes were reduced in older adults on the motor sequence learning task. In contrast, sleep-dependent performance changes were similar for all 3 age groups on the word pair learning task. Age-related changes in sleep or networks activated during encoding or during sleep may contribute to age-related declines in motor sequence consolidation. Interestingly, these changes do not affect declarative memory.     

Infant rats can acquire,but not retain contextual associations in object-in-context and contextual fear conditioning paradigms

Context learning in postnatal day (PD) 16–18 rats has been taken by Revillo, Cotella, Paglini, and Arias (2015, Physiology & Behavior, 148 , 6–21) to challenge the view that the ontogeny of contextual learning is related to the development of the hippocampal system (Rudy, 1993, Behavioral Neuroscience, 107 (5), 887–891; Schiffino, Murawski, Rosen, & Stanton, 2011 Neurobiology of Learning and Memory, 95 (2), 190–198). Whether context learning is “incidental” or “reinforcement-driven” may determine the ontogeny and neural systems involved (Rudy, 2009, Learning & Memory (Cold Spring Harbor, N.Y.), 16 , 573–585). However, we have shown differential ontogeny of two different forms of incidental context learning, the context pre-exposure facilitation effect (CPFE; Jablonski, Schiffino, & Stanton, 2012, Developmental Psychobiology, 54 (7), 714–722), which emerges between PD 17 and 21; and object-in-context recognition (OiC, Ramsaran, Westbrook, & Stanton, 2016, Developmental Psychobiology, 58 (7), 883–895; Ramsaran, Sanders, & Stanton, 2016, Behavioural Brain Research, 298 , 37–47), which is present on PD17. We investigated whether this task-dissociation reflects an encoding or a retention deficit, by varying the sample-to-testing intervals for both tasks. Experiment 1A found that PD17 rats were able to perform the OiC task after short (5 min) but not long (24 hr) sample-to-test intervals. Experiments 1B and 1C found that PD17 rats trained on the CPFE are able to acquire and express context-shock associations after short but not long retention intervals. These findings suggest that pre-weanling rats encode contexts but show poor consolidation or retrieval after longer retention intervals.     

Mercaptoacetate decreases latency to initiate independent ingestion,but not suckling,in preweanling rats

Altering oxidation of fatty acids by administration of mercaptoacetate (MA) or methyl palmoxirate has been demonstrated to stimulate independent ingestion in rat pups by 12 to 15 days of age. However, in other work, neither agent has been demonstrated to affect intake in the context of suckling. In the present experiments, we tested the effects of MA on both suckling and independent ingestive behavior by examining changes in latency to initiate suckling or independent ingestion and by measuring intake in short-term (30 min) and longer term (4 hr) suckling and independent ingestion tests in pups aged 12 to 15 days of age. The results demonstrated that (a) MA does not affect suckling intake in short- or longer term tests; (b) MA does not affect latency to attach to a nipple, most likely due to floor effects on latency to attach in control pups; (c) MA stimulates independent ingestion in short-term, but not longer terms tests; and (d) MA reduces the latency to initiate independent ingestion. These results suggest that administration of MA preferentially stimulates the initiation of independent ingestion over suckling, and that this response develops at an age just prior to the time at which independent ingestion is typically first expressed by rat pups.     

Enrichment to odors improves olfactory discrimination in adult rats

The authors tested how prior odor enrichment affects the spontaneous discrimination of both preexposed and novel odors. Experimental rats were exposed to single odors or to pairs of similar or dissimilar odors for 1-hr periods twice daily over 20 days. Spontaneous discriminations between pairs of similar odors were tested before and after the odor exposure period using an olfactory habituation task. The authors found that (a) experimental rats did not spontaneously discriminate similar odor pairs before the exposure period, whereas they spontaneously discriminated them after the enrichment period, and (b) the improvement of performance was not selective for the odors used during enrichment. These results show that odor experience changes perception in the manner predicted based on other groups' electrophysiological experiments.     

Oxytocin selectively increases holding and licking of neonates in preweanling but not postweanling juvenile rats

Preweanling rats exhibit components of maternal behavior (MB) after brief periods of contact with neonates; the latency of onset of MB rises considerably after weaning. Oxytocin (OXT) stimulates MB in adult rats. The effects of intracisternal (IC) administration of OXT (2 micrograms) on pup-directed and other behaviors in preweanling and postweanling juvenile rats were tested. Compared with saline and no treatment, OXT significantly increased active holding of pups in preweanling but not postweanling juvenile rats. No other components of adultlike MB were stimulated by OXT. OXT also decreased inactive touching of pups and robustly increased selfgrooming in juveniles at all ages tested. It is concluded that OXT facilitation of active pup-holding and licking in preweanling rats may be an extension of OXT-induced self-grooming to pups and may also be related to OXT activation of MB in adult rats.     

Perirhinal cortex lesions impair simultaneous but not serial feature-positive discrimination learning

The role of the perirhinal cortex in discriminative eyeblink conditioning was examined by means of feature-positive discrimination procedures with simultaneous (A-/XA+) and serial (A-/X-->A+) stimulus compounds. Lesions of the perirhinal cortex severely impaired acquisition of simultaneous feature-positive discrimination but produced no impairment in serial feature-positive discrimination. The results suggest that the perirhinal cortex plays a role in discriminative eyeblink conditioning by resolving ambiguity in discriminations with overlapping stimulus elements.     

The vomeronasal organ is involved in discrimination of individual odors by males but not by females in golden hamsters

The vomeronasal organ (VNO) has a wide variety of functions in terrestrial vertebrates, some of which involve responses to classical pheromones whereas others do not. We examined the role of the VNO in discrimination of individual differences in odors of male and female golden hamsters using a habituation paradigm. Removal of the VNO resulted in elimination of the ability of male hamsters to discriminate between some individually distinctive odors (e.g., flank gland secretion), but not others (e.g., urine). In females, such lesions had no effect. The type of test trial also influenced the results; in test trials employing a single, novel odor, removal of the VNO in males did have an effect but in test trials in which both the novel and the familiar odor were presented, VNO removal had no effect. It is concluded that (a) there is a sex difference in the role of the VNO in the discrimination of individual odors, (b) the role of the VNO in discrimination of individual odors varies from odor to odor, and (c) deficits due to VNO removal are more readily observed in more difficult tasks.     

Deficient brightness discrimination in hooded but not albino rats given neocortical ablations

Hooded and albino rats with lesions of the neucortex overlying hippocampus and normal rats of both strains were trained in an operant discrimination. Though the normal groups did not differ from one another and the neocortically lesioned albinos did not differ from the unlesioned rats, when compared to the other groups the hooded group was found to be deficient in the acquisition of the task. A greater amount of cell loss and gliosis was observed in the thalamus of the hooded rats.     

Probability discrimination learning in hippocampectomized rats

Rats with hippocampal lesions or neocortical lesions and normal rats were trained on a spatial probability discrimination task where one side of a T maze was reinforced on 70% of the trials and the other side on the remaining 30% of the trials. Training was to a criterion of 39 correct trials out of 40 using a noncorrection procedure. There was no difference between the learning rates of normal rats and with neocortical lesions, but the rats with hippocampal lesions learned the discriminiation more rapidly than the other two groups. These results indicated that the hippocampus does not function as a stimulus gating system, but is probably concerned in the selection and rejection of hypothese (central-sets).     

Cerebellar cortical degeneration disrupts discrimination learning but not delay or trace classical eyeblink conditioning

The authors investigated classical eyeblink conditioning in a relatively rare patient, B.R., with extensive cerebellar cortical atrophy and marked sparing of the dentate nucleus. Patient B.R.'s ability to acquire and extinguish simple associations (delay and trace conditioning tasks) as well as her ability to acquire more complex associations (temporal and simple discrimination tasks) were examined. There are 2 primary findings from this study. First, B.R. showed normal acquisition and extinction in delay and trace conditioning. Second, she demonstrated a complete inability to learn associative discriminations, even in the case of a simple 2-tone discrimination within the context of a delay paradigm. The latter finding was unexpected because of the sparing of her deep cerebellar nuclei. These data suggest that the cerebellar cortex, or pathways traversing cerebellar cortex, play an important role in classical eyeblink discrimination learning.     

Impairments in negative patterning, but not simple discrimination learning, in rats with 192 IgG-saporin lesions of the nucleus basalis magnocellularis

Rats with 192 IgG-saporin lesions of the nucleus basalis magnocellularis (NBM) and sham-operated rats were trained in either a simple discrimination paradigm assessing simple association learning or a negative patterning paradigm assessing configural association learning. In the simple discrimination task, rats were reinforced for responding to a light but were not reinforced for responding to a tone. In the negative patterning discrimination task, rats were reinforced for responding to either a light or a tone presented alone but were not reinforced for responding to both stimuli presented simultaneously. Simple discrimination learning was not affected, whereas acquisition of negative patterning was impaired by NBM lesions. Impaired configural association learning may reflect a loss in the ability of rats with NBM lesions to attend to multiple sensory stimuli or to cope with conflicting response strategies.     

Social learning about ethanol in preweanling rats: role of endogenous opioids

The role of the endogenous opioid system in social learning about ethanol was examined in three experiments using preweanling rats. Experiment 1 showed that interactions with intoxicated siblings in the home cage on postnatal Days (PD) 12, 14, and 16 results in increased voluntary intake of ethanol when subjects are tested 24 hr after the final exposure. The results also suggested that the endogenous opioid system is not involved in acquisition. Administration of naloxone during social exposure to ethanol had no effect on later ethanol intake. Experiment 2 examined the effects of receptor‐selective antagonists administered prior to test. For subjects that had social exposure to ethanol, intake of ethanol was completely suppressed by either naloxone or the δ antagonist naltrindole. For ethanol‐naïve subjects, intake also was completely suppressed by naloxone. However, intake was partially blocked by naltrindole or the μ antagonist β‐FNA. Experiment 3 confirmed the differential involvement of μ and δ receptors in ethanol intake through a more comprehensive dose–response analysis of β‐FNA and naltrindole. Collectively, these data reveal that learning about ethanol from intoxicated conspecifics not only affects voluntary intake of ethanol but also alters the opioidergic response to ethanol consumption. © 2004 Wiley Periodicals, Inc. Dev Psychobiol 44: 132–139, 2004.     

Acquisition and retention of separate elements of a conditioned olfactory discrimination in preweanling rats

Acquisition and retention of separate elements of an olfactory discrimination were tested in 15- and 20-day-old preweanling rats. Four or 8 conditioning trials were given in Experiment 1. Each rat was presented one odor always followed by footshock (CS+) and another never paired with footshock (CS-). Conditioning to both stimuli was assessed through 3 types of olfactory preference tests involving comparison between CS+ and a novel odor, CS- and a novel odor, or CS+ and CS-. The results indicated that for 15- and 20-day-olds, both stimuli become excitatory early in training; further conditioning trials diminished the excitation previously accrued to the CS-, and the olfactory discrimination became apparent. When levels of conditioning were equated, retention was tested after intervals of 4 min, 3 days, or 8 days (Exp. 2). Rate of forgetting was more rapid for the 15-day-olds, but both ages of subjects showed similar patterns of forgetting, which included a progressive decrease in the aversion to the CS+ but an increase in aversion to the CS-.     

Early olfactory learning is influenced by sex in hamsters but not rats

The odor of cedar shavings repels infant and juvenile rats and hamsters reared in pine shavings when animals are tested in a two-choice situation. Housing male and female infants of either species in cedar shavings for 3 days before testing increases preference for both cedar odor and for a mixture of cedar and conspecific odors. Similar exposure of juvenile male and female rats and male hamsters, has little or no significant impact on odor preferences. However, housing female hamsters in cedar at either developmental stage equally influences odor preferences. The data imply that sex differences influence the development of early odor-guided behavior in hamsters but not rats. These species differences may have adaptive significance in that the birth of a litter produces a greater environmental change demanding a larger preference adjustment of solitary female hamsters than colonial female rats.     

l-DOPA improves odor discrimination learning in rats

Using a forced-choice odor discrimination task in rats, we show here that intraperitoneal injections of l-DOPA improve rats' odor discrimination performance in comparison to control rats injected with saline. Although the exact mechanism of l-DOPA and potential action on dopamine receptors remains unclear, the present results indicate that rats injected with the 20-50 mg/kg of l-DOPA performed significantly better in an odor discrimination task than did control rats. In addition, we observed a significant correlation between the concentration of l-DOPA and odor discrimination performance.     

Spatial conditional discrimination learning in developing rats

The present study established an effective procedure for studying spatial conditional discrimination learning in juvenile rats using a T-maze. Wire mesh located on the floor of the maze as well as a second, identical T-maze apparatus served as conditional cues which signaled whether a left or a right response would be rewarded. In Experiment 1, conditional discrimination was evident on Postnatal Day (PND) 30 when mesh+maze or maze-alone were the conditional cues, but not when mesh-alone was the cue. Experiment 2 confirmed that mesh-alone was sufficiently salient to support learning of a simple (nonconditional) discrimination. Its failure to serve as a conditional cue in Experiment 1 does not reflect its general ineffectiveness as a stimulus. Experiment 3 confirmed that the learning shown in Experiment 1 was indeed conditional in nature by comparing performance on conditional versus nonconditional versions of the task. Experiment 4 showed that PND19 and PND23 pups also were capable of performing the task when maze+mesh was the cue; however, the findings indicate that PND19 subjects do not use a conditional strategy to learn this task. The findings suggest postnatal ontogeny of conditional discrimination learning and underscore the importance of conditional cue salience, and of identifying task strategies, in developmental studies of conditional discrimination learning.     

Selective breeding for endurance running capacity affects cognitive but not motor learning in rats

The ability to utilize oxygen has been shown to affect a wide variety of physiological factors often considered beneficial for survival. As the ability to learn can be seen as one of the core factors of survival in mammals, we studied whether selective breeding for endurance running, an indication of aerobic capacity, also has an effect on learning. Rats selectively bred over 23 generations for their ability to perform forced treadmill running were trained in an appetitively motivated discrimination-reversal classical conditioning task, an alternating T-maze task followed by a rule change (from a shift-win to stay-win rule) and motor learning task. In the discrimination-reversal and T-maze tasks, the high-capacity runner (HCR) rats outperformed the low-capacity runner (LCR) rats, most notably in the phases requiring flexible cognition. In the Rotarod (motor-learning) task, the HCR animals were overall more agile but learned at a similar rate with the LCR group as a function of training. We conclude that the intrinsic ability to utilize oxygen is associated especially with tasks requiring plasticity of the brain structures implicated in flexible cognition.