mA Shock Research Articles

Punishment-induced resurgence

The phenomenon of extinction-induced resurgence is well established, but there is comparatively little experimental evidence for punishment-induced resurgence. Punishment-induced resurgence can by tested by contingent shocks following the alternative response. The purpose of Experiment 1 was to test whether low-intensity shocks, that do not decrease rate of reinforcement, result in resurgence. Four rats served as subjects. Rats were exposed to three sequential conditions: (a) variable-interval (VI) 30-s food delivery for a lever press (target response); (b) VI 30-s food delivery for a nose poke (alternative response) and extinction of the lever press; (c) VI 30-s reinforcement for a nose poke with superimposed VI 60-s shock delivery. In the final condition, shocks increased gradually from 0.1 to 0.5 mA. Experiment 2 evaluated whether an abrupt introduction of a high-intensity shock would result in resurgence. Three rats served as subjects and were exposed to three sequential conditions: (a) VI 30-s food delivery for a lever press; (b) VI 30-s food delivery for a nose poke and extinction of the lever press; (c) continued VI 30-s reinforcement for a nose poke with superimposed VI 60-s 0.6 mA shock delivery. Resurgence was observed in all subjects, including in situations in which rate of responding, but not rate of reinforcement, decreased. The present study provides additional evidence for punishment-induced resurgence, but future studies are warranted to determine the extent to which punishment can produce resurgence with or without decreases in rates of reinforcement.

Effects of environmental and pharmacological manipulations on cocaine-vs-negative reinforcer choice in male and female rats.

The adverse consequences of human addictive drug use could be the result of either addictive drug consumption resulting in punishment (e.g., incarceration) or failure to engage in negative-reinforced behaviors that might compete with drug-maintained behaviors (e.g., contingency management strategies that reset payment amounts for drug free urines). The goal of the present study was to establish a discrete-trial cocaine-vs-negative reinforcer (SNR) choice procedure where rats were presented with a simplified model of this conflict: choose negative reinforcement (i.e., escape or avoid foot shock) or choose an intravenous (IV) cocaine infusion followed by an inescapable shock. Responding was maintained in male and female rats by IV cocaine infusions (0.32-1.8 mg/kg/inf) and a SNR (0.1-0.7 mA shock) under a discrete-trial concurrent"choice" schedule during daily sessions. Following parametric reinforcer magnitude and response requirement experiments, the effects of 12 h extended access cocaine self-administration and acute diazepam (0.32-10 mg/kg, IP) pretreatment were determined on cocaine-vs-SNR choice. Negative reinforcement was chosen over all cocaine doses. Lowering shock magnitude or increasing SNR response requirement failed to promote behavioral reallocation towards cocaine. Extended access cocaine self-administration sessions resulted in high daily cocaine intakes but failed to significantly increase cocaine choice in all (19) but one rat. Acute diazepam pretreatment also did not alter choice behavior up to doses that produced behavioral depression. These results suggest that SNRs may be a source of reinforcement that effectively compete with and mitigate maladaptive addictive drug-maintained behaviors in the general population.

Context-induced renewal of passive but not active coping behaviours in the shock-probe defensive burying task.

Renewal is the return of extinguished responding after removal from the extinction context. Renewal has been extensively studied using classical aversive conditioning procedures that measure a passive freezing response to an aversive conditioned stimulus. However, coping responses to aversive stimuli are complex and can be reflected in passive and active behaviours. Using the shock-probe defensive burying task, we investigated whether different coping responses are susceptible to renewal. During conditioning, male, Long-Evans rats were placed into a specific context (Context A) where an electrified shock-probe delivered a 3 mA shock upon contact. During extinction, the shock-probe was unarmed in either the same (Context A) or a different context (Context B). Renewal of conditioned responses was assessed in the conditioning context (ABA) or in a novel context (ABC or AAB). Renewal of passive coping responses, indicated by an increased latency and a decreased duration of shock-probe contacts, was observed in all groups. However, renewal of passive coping, measured by increased time spent on the side of the chamber opposite the shock-probe, was only found in the ABA group. Renewal of active coping responses linked to defensive burying was not observed in any group. The present findings highlight the presence of multiple psychological processes underlying even basic forms of aversive conditioning and demonstrate the importance of assessing a broader set of behaviours to tease apart these different underlying mechanisms. The current findings suggest that passive coping responses may be more reliable indicators for assessing renewal than active coping behaviours associated with defensive burying.

Electric catfish hearts are not immune to electric bolts

Electricity is at once the heart's best friend and fiercest foe. The heart coordinates its own rhythmic beats with repetitive gentle electrical pulses and a sudden jolt of electricity can shock a stopped heart back into action. However, an accidental electric bolt can trigger irregular heartbeats and even fatal heart attacks; electric shocks are generally best avoided. So, how do the hearts of electric catfish (Malapterurus beninensis) that stun prey with 300 V discharges protect the delicate organ? Having previously discovered that the muscles of the extraordinary fish are somehow immune to their own violent electrical discharges, Georg Welzel and Stefan Schuster from the University of Bayreuth, Germany, wanted to know how vulnerable the catfish heart is to powerful electric currents.The duo removed the still-beating organ from a catfish and placed it in liquid laced with sugar and salts to keep the organ alive as they recorded the heart's ECG to find out whether the resilient fish had somehow modified the electrical impulses that regulate the heartbeat to withstand life-threatening shocks. However, when the pair compared the electric catfish's ECG to that of a goldfish, the charts were virtually indistinguishable. The catfish had not altered its ECG for protection. And, when Welzel and Schuster checked how responsive the electric catfish's heart is when mildly stimulated, a 0.12 mA current was sufficient to trigger a regular heartbeat, identical to the goldfish heart's stimulation threshold. But the real test came when the pair checked how resilient the catfish heart was to more significant electric shocks – sufficient to trigger a life-threatening irregular heartbeat in other fish – and surprisingly, the electric catfish hearts were equally as vulnerable. A 3.03 mA shock was sufficient to send catfish and goldfish hearts racing erratically. Even though electric catfish are immune to the fatal power of their own bolts of electricity, their hearts appear to be as vulnerable as the hearts of any creature they intend to stun.So, how do the extraordinary river dwellers protect their hearts from their own lethal discharges? Schuster suggests that the heart and other vulnerable tissues, such as the brain and sensory organs, could be wrapped in insulation; however, he has yet to find any evidence of such a material. ‘Either the hypothetical insulators are highly efficient or the actual mechanism of how such layers protect the hearts of living electric catfish is more complex’, Welzel says. Meanwhile, electric catfish continue to be immune to their own deadly discharges regardless of vulnerability at the heart of the matter.

Sex‐ and region‐specific consequences of chronic nicotine in the murine hippocampus during fear extinction

In the United States 90% of people experience at least one event in their lifetime that meets the DMS‐5 criteria for a traumatic event, but only 8.3% of Americans develop Post‐Traumatic Stress Disorder (PTSD). While severity and frequency of trauma impact the development of PTSD, there is an increasing emphasis on biological factors explaining why only a subset present with PTSD. We know sex is a major risk factor for PTSD, with women being twice as likely to develop PTSD than men. Additionally, people suffering from PTSD are twice as likely to smoke daily than healthy controls. However, while nicotine dependence is positively correlated with PTSD symptoms in men, this is not true in women, suggesting sex divergence in the neurobiological response to trauma and the resulting increased susceptibility to nicotine use disorder. The hippocampus has a well‐defined regiospecific role in both contextual memory and affective responding, the dorsal hippocampus (DHIPP) and ventral hippocampus (VHIPP) respectively. This places the hippocampus as a nexus point for both memory and emotion, suggesting these subregions are potential targets for mechanistic evaluation of comorbid PTSD and nicotine dependence. In these studies, we chronically treated male and female 7 to 8‐week‐old mice with either saline or intermittent nicotine (18 mg/kg/day) via osmotic minipumps (Alzet 1002 model). On the twelfth day of treatment, the subjects were trained in a fear conditioning paradigm with two CS‐US pairings (CS 89 dB tone and US 0.35 mA shock), then underwent 6 contextual fear extinction sessions. Following behavioral testing, the DHIPP and VHIPP were collected and assessed for genomic, transcriptomic, and proteomic changes. Preliminary results from these experiments suggest that the behavioral sex differences observed likely relate to differences in transcriptional control mechanisms. Further examination of treatment by sex effects in extinction behavior and the genomic and functional alterations underpinning these effects are ongoing.

Parametric Study of Magnetosheath Jets in 2D Local Hybrid Simulations

We perform 2D local hybrid simulations of collisionless shocks in order to study the properties of simulated magnetosheath jets as a function of shock properties, namely their Alfvénic Mach number (MA) and geometry (angle between the upstream magnetic field and the shock normal, θBN). In total we perform 15 simulations with inflow speeds of Vin = 3.3 CA (Alfvén velocity), 4.5 CA and 5.5 CA and θBN = 15°, 30°, 45°, 50°, and 65°. Under these conditions, the shock MA varied between 4.28 and 7.42. In order to identify magnetosheath jets in the simulation outputs, we use four different criteria, equivalent to those utilized to identify subsets of magnetosheath jets, called high-speed jets (Plaschke and Hietala and Angelopoulos, Ann. Geophys., 2013, 31, 1877–1889), transient flux enhancements (Němeček et al., Geophys. Res. Lett., 1998, 25, 1273–1276), density plasmoids (Karlsson et al., J. Geophys. Res., 2012, 117, a–n; Karlsson et al., J. Geophys. Res., 2015, 120, 7390–7403) and high-speed plasmoids (Gunell et al., Ann. Geophys., 2014, 32, 991–1009). In our simulations, the density plasmoids were produced only by shocks with MA ≥5.7, while the high-speed plasmoids only formed downstream of shocks with MA ≥6.97. We show that higher MA shocks tend to produce faster jets that tend to have larger surface area, mass, linear momentum and kinetic energy, while these quantities tend to be anticorrelated with θBN. In general, the increase of θBN to up to 45° results in increased jet formation rates. In the case of high-speed jets in runs with Vin = 3.3 CA and high-speed plasmoids, the jet formation anticorrelates with θBN. The jet production all but ceases for θBN = 65° regardless of the shock’s MA. The maximum distances of the magnetosheath jets from the shocks were ≲140 di (upstream ion intertial lengths), which, estimating 1 di ∼100–150 km at Earth, corresponds to 2.4–3.3 Earth radii. Thus, none of the simulated jets reached distances equivalent to the average extension of the Earth’s subsolar magnetosheath, which would make them the equivalents of geoeffective jets. Higher MA shocks are probably needed in order to produce such jets.

A transient dopamine signal represents the value of avoidance in negative reinforcement

The mesolimbic dopamine (DA) system has traditionally been examined under a reward based context. While accumulating evidence supports that DA release events represent the value of predicted rewards, there is little known about its role in avoidance. To investigate dopamine's role in the valuation of signaled operant avoidance, we developed an economics‐based shock avoidance task in which rats were given the opportunity to avoid (signaled by the presentation of a cue light) electrical foot‐shock across epochs wherein the unit price (response requirement over mA shock) to avoid or escape increases. After developing this task, we first used fast‐scan cyclic voltammetry (FSCV) to measure DA release events in vivo as the animals performed across a range of prices. We observed that the concentration of DA decreased with price, though both DA and avoidance were initially suppressed at session onset. To establish a causal role, we then used optogenetics to augment DA release at either the presentation of the cue signal or upon successful avoidance of the foot‐shock. Increasing release at the cue made avoidance more sensitive to price; whereas increasing release at successful avoidance made it less sensitive to price. We conclude that this is likely because the neural representation of the value to avoid is greater than predicted at successful avoidance, and worse than expected at the cue on trials in which foot‐shock is administered. We will next assess the role of the rostromedial tegmental nucleus (RMTg), a neural structure known to cause prediction errors, in the valuation of avoidance.Support or Funding InformationFunding for the project was provided by NSF grant IOS‐1557755, NIH grant R03DA038734, Boettcher Young Investigator Award and NARSAD Young Investigator Award to EBO and an institutional UROP to KJP.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Assessing Mongolian gerbil emotional behavior: effects of two shock intensities and response-independent shocks during an extended inhibitory-avoidance task.

Despite step-down inhibitory avoidance procedures that have been widely implemented in rats and mice to study learning and emotion phenomena, performance of other species in these tasks has received less attention. The case of the Mongolian gerbil is of relevance considering the discrepancies in the parameters of the step-down protocols implemented, especially the wide range of foot-shock intensities (i.e., 0.4–4.0 mA), and the lack of information on long-term performance, extinction effects, and behavioral patterning during these tasks. Experiment 1 aimed to (a) characterize gerbils’ acquisition, extinction, and steady-state performance during a multisession (i.e., extended) step-down protocol adapted for implementation in a commercially-available behavioral package (Video Fear Conditioning System—MED Associates Fairfax, VT, USA), and (b) compare gerbils’ performance in this task with two shock intensities – 0.5 vs. 1.0 mA—considered in the low-to-mid range. Results indicated that the 1.0 mA protocol produced more reliable and clear evidence of avoidance learning, extinction, and reacquisition in terms of increments in freezing and on-platform time as well as suppression of platform descent. Experiment 2 aimed to (a) assess whether an alternate protocol consisting of a random delivery of foot shocks could replicate the effects of Experiment 1 and (b) characterize gerbils’ exploratory behavior during the step-down task (jumping, digging, rearing, and probing). Random shocks did not reproduce the effects observed with the first protocol. The data also indicated that a change from random to response-dependent shocks affects (a) the length of each visit to the platform, but not the frequency of platform descends or freezing time, and (b) the patterns of exploratory behavior, namely, suppression of digging and rearing, as well as increments in probing and jumping. Overall, the study demonstrated the feasibility of the extended step-down protocol for studying steady performance, extinction, and reacquisition of avoidance behavior in gerbils, which could be easily implemented in a commercially available system. The observation that 1.0 mA shocks produced a clear and consistent avoidance behavior suggests that implementation of higher intensities is unnecessary for reproducing aversive-conditioning effects in this species. The observed patterning of freezing, platform descents, and exploratory responses produced by the change from random to periodic shocks may relate to the active defensive system of the gerbil. Of special interest is the probing behavior, which could be interpreted as risk assessment and has not been reported in other rodent species exposed to step-down and similar tasks.

EFFECTS OF MALNUTRITION AND ENVIRONMENT ON THE ACQUISITION AND EXTICTION OF AVOIDANCE BEHAVIOR IN RATS

Twelve newborn rats were fed by mothers maintained on protein-deficient diet (12% casein, M) during lactation, and 12 rats fed by mothers maintained on a diet containing 25% casein were used as controls (C). After weaning, all animals were standard lab ration. Half of each group was housed individually (MI and CI), while the other half was allowed to live in pairs (MP and CP). When adult, all animals were trained to avoid footshocks by jumping onto a platform. Trainiing sessions consisted of 40 trials starting with a 20 sec light stimulus (CS) and followed by a 2 sec, 0.6 mA shock (US) with an average interval of 54 sec. When all animals displayed consistent avoidance behavior, the extinction phase was initiated. The produce was the same as for the training session except that shock generator was disconnected. Extinction continued until each animal showed a 50% reduction in avoidance performance. During acquisition, MI learned faster than CI and CI showed greater avoidance performance than CP, but no differences were observed between MP and CP. During extinction, group M responded more persistently than group C. The present acquisition results may explain the contradictory data reported in the literature with respect to the effects of malnutrition on avoidance performance, since environmental stimulation was shown to reduce the effects of early malnutrition. Individually housed animals showed greater avoidance performance during both phases. Keywords: Protein malnutrition, avoidance response, acquisition, extinction, environmental stimulation.

Abstract TP98: Moderate Physical Exercise Promotes Cognitive Recovery Following Focal Cerebral Ischemia in Rats

The majority of stroke patients suffer long-term disabilities impacting both motor and cognitive function. Physical exercise has been shown to improve functional recovery following focal cerebral ischemia by facilitating brain plasticity. However, the exercise intensity that promotes optimal cognitive recovery needs closer examination. This study seeks to analyze the effects of forced treadmill exercise at various speeds on spatial memory tests after focal ischemia in rats. We hypothesized that, a moderate intensity treadmill regiment will better ameliorate cognitive deficits and improve functional recovery after focal ischemia compared to the high or mild intensity groups. Three-month-old male Sprague Dawley rats were acclimated to the investigator and treadmill for three days. On day four, rats underwent focal cerebral ischemia using the middle cerebral artery occlusion model for 90 minutes or sham surgery and were randomly assigned to an exercise intensity group. Rats had three days of recovery post-surgery followed by forced treadmill exercise for six days. The rats were exposed to a two-minute warm-up period at 5 m/min and then exercised for a period of 30 minutes at 6 m/min for mild, 10 m/min for moderate, and 18 m/min for heavy. Finally, the rats were subjected to contextual fear conditioning where rats were placed in a fear conditioning chamber for 8 minutes with a 2 second 1.5 mA shock delivered at minute 7.5 then returned to chamber 24 hours later. Fear conditioning data showed that, following a stroke rats froze 16.48 +/- 2.75%, compared to the moderate intensity group where rats froze 63.57 +/- 10.72 % (S.E.M, n = 10, p < 0.01, one-way ANOVA, Bonferroni post-hoc). Mild and heavy exercise groups froze 43.3 +/- 10.75% and 38.26 +/- 10.53% respectively. In conclusion, focal cerebral ischemia impairs cognitive function, however moderate intensity physical exercise has the most beneficial impact on cognitive recovery compared to other exercise intensities.

Interactional effects of corticosterone and stress in the formation of PTSD-like memory impairment rats

Objective To investigate the interactional roles corticosterone and stress played during the PTSD-Like memory impairment. Methods First we established the model of PTSD-like memory using three levels of electric shock: 0 mA, 0.8 mA and 1.4 mA. The freezing time percent of each group were calculated 24 hours later in order to find which group of rats obtained the PTSD-like memory, and generalizing tests was used to verify it. After the model was established, rats received adrenalectomy (ADX) were operated bilaterally in order to investigate the effect of corticosterone and fed with corticosterone in the drinking water 7 days before fear conditioning. These rats were divided into four groups: control group (no corticosterone supplement, 0 mA shock), Cort group (corticosterone supplement, 0 mA shock), shock group (no corticosterone supplement, 1.4 mA shock), Cort-shock group (corticosterone supplement, 1.4 mA shock). A two-way factorial analysis of variance was used to determine whether there was a significant interaction between corticosterone and shock. Results The freezing time percent of group 0.8 mA raised compared with the group 0 mA, whereas the freezing time percent of group 1.4 mA showed reversely and the generalizing effects appeared, compared with group 0.8 mA. In two-way factorial analysis design, the freezing time percent of Cort-shock group significantly increased (P<0.05) compared with other groups, and there was no significant variance among the other groups. Corticosterone (F=6.464, P<0.05) and stress (F=53.419, P<0.01) played parts in the formation of PTSD-like memory impairment, and they interacted with each other (F=11.580, P<0.05). Conclusion PTSD-like memory impairment can be induced on rats with high (1.4 mA) electrical shock, and they have interactional effect with each other in the process. Key words: PTSD-like memory impairment; Stress; Corticosterone; Fear memory

Orexins (hypocretins) contribute to fear and avoidance in rats exposed to a single episode of footshocks

Orexins (hypocretins) are peptides that have been shown to regulate behavioral arousal and wakefulness. Recent evidence indicates that orexin neurons are activated by stress and that orexins play a role in anxiety. The present paper describes a series of experiments that examined whether orexins are involved in the anxiety that resulted from exposing rats to an acute episode of footshocks (5×2s of 1.5mA shocks). We found that prepro-orexin (ppOX) mRNA was elevated in rats at 6 and 14days after exposure to footshock and that ppOX mRNA levels were correlated with fear at 14days post-shock. Systemic injections of the non-selective dual orexin receptor antagonist TCS-1102 (10 and 20mg/kg, i.p.) were found to decrease fear and anxiety in rats 14days after exposure to footshock. We also found that rats that exhibited a high level of immobility to a novel tone the day after the footshock episode (high responders, HR) showed significantly elevated levels of ppOX mRNA at 14days post-shock compared to control rats. Furthermore, TCS-1102 (10mg/kg, i.p.) was found to have anxiolytic effects that were specific for HR when tested in the elevated T-maze. This study provides evidence linking the orexin system to the anxiety produced by exposure of rats to a single episode of footshocks. It also provides preclinical evidence in support of the use of orexin antagonists for the treatment of anxiety in response to an acute episode of stress.

Lesions of the Fasciculus Retroflexus Alter Footshock-Induced cFos Expression in the Mesopontine Rostromedial Tegmental Area of Rats

Midbrain dopamine neurons are an essential part of the circuitry underlying motivation and reinforcement. They are activated by rewards or reward-predicting cues and inhibited by reward omission. The lateral habenula (lHb), an epithalamic structure that forms reciprocal connections with midbrain dopamine neurons, shows the opposite response being activated by reward omission or aversive stimuli and inhibited by reward-predicting cues. It has been hypothesized that habenular input to midbrain dopamine neurons is conveyed via a feedforward inhibitory pathway involving the GABAergic mesopontine rostromedial tegmental area. Here, we show that exposing rats to low-intensity footshock (four, 0.5 mA shocks over 20 min) induces cFos expression in the rostromedial tegmental area and that this effect is prevented by lesions of the fasciculus retroflexus, the principal output pathway of the habenula. cFos expression is also observed in the medial portion of the lateral habenula, an area that receives dense DA innervation via the fr and the paraventricular nucleus of the thalamus, a stress sensitive area that also receives dopaminergic input. High-intensity footshock (120, 0.8 mA shocks over 40 min) also elevates cFos expression in the rostromedial tegmental area, medial and lateral aspects of the lateral habenula and the paraventricular thalamus. In contrast to low-intensity footshock, increases in cFos expression within the rostromedial tegmental area are not altered by fr lesions suggesting a role for non-habenular inputs during exposure to highly aversive stimuli. These data confirm the involvement of the lateral habenula in modulating the activity of rostromedial tegmental area neurons in response to mild aversive stimuli and suggest that dopamine input may contribute to footshock- induced activation of cFos expression in the lateral habenula.

RETRACTED: Acute ethanol administration affects memory reactivation: A look at the neuronal density and apoptosis in the rat hippocampus

This study is an attempt to examine whether administration of ethanol after memory reactivation will modulate expression of memory in rats or not. We further examined whether this administration alters the number of tunnel positive cells in hippocampus. Adult male Wistar rats were trained in a fear conditioning system using two 1s , 0.6 mA shock with an interval of 180 s. 24 h later the rats were returned to the chamber for reactivation, and then they were injected with ethanol (0.5, 1, 1.5 mg/kg) or saline, ip. Again, one, seven and fourteen days after reactivation, the rats were returned to the context for 5 min. The freezing time (absence of all movements except respiration) was scored in seconds. In the second experiment, after test 1, the animals were anesthetized and a transcardial perfuse with phosphate buffer and paraformaldehyde 4% was conducted. After post-fixation of brains 5-μm sections were stained with cresyl violet. Finally, paraffin-embedded sections of 10 μm were cut out throughout the tissue and each sample was processed with TUNEL. The number of apoptotic cells in a 130 μm-long segment of the hippocampal CA1 and CA3 fields and dentate gyrus was counted. The data demonstrate that ethanol exposure impairs post retrieval processes. Rats receiving ethanol (1.5 mg/kg) showed lower freezing levels during the first test. Moreover, ethanol decreases the density of CA1, CA3 and DG cells and increases the density of apoptotic cells in all regions of hippocampus. Therefore, ethanol exposure impairs reconsolidation of contextual fear conditioning probably via decreasing the density of CA1, CA3 and DG cells.

Optimization of a contextual conditioning protocol for rats using combined measurements of startle amplitude and freezing: The effects of shock intensity and different types of conditioning

Contextual conditioning in rats is typically quantified using startle amplitude or freezing time. Our goal was to create a robust contextual conditioning protocol combining both startle amplitude and freezing time as measures of contextual anxiety. Comparison of 0.8mA – 250ms shocks with an established shock configuration (0.3mA – 1s) favoured the first parameters. Subsequently, we systematically investigated the effect of shock intensity (0.6mA, 0.8mA or 1.0mA) and concurrently compared two different contextual conditioning procedures (shocks alone versus unpaired shock–tone presentations). In future experiments, this second type of contextual conditioning may form the optimal contrasting condition for a cued fear conditioning group, trained with explicit cue–shock pairings. The 0.8mA shocks produced significant contextual freezing and startle potentiation, whereas the 0.6mA and 1.0mA shocks only led to a significant increase of freezing time. We found no major differences between the two types of conditioning, implying that these procedures might be equivalent. In conclusion, training with ten 0.8mA – 250ms shocks produced reliable contextual conditioning as measured with both startle amplitude and freezing time.

Functional emergence of the hippocampus in context fear learning in infant rats.

The hippocampus is a part of the limbic system and is important for the formation of associative memories, such as acquiring information about the context (e.g., the place where an experience occurred) during emotional learning (e.g., fear conditioning). Here, we assess whether the hippocampus is responsible for pups' newly emerging context learning. In all experiments, postnatal day (PN) 21 and PN24 rat pups received 10 pairings of odor-0.5 mA shock or control unpaired odor-shock, odor only, or shock only. Some pups were used for context, cue or odor avoidance tests, while the remaining pups were used for c-Fos immunohistochemistry to assess hippocampal activity during acquisition. Our results show that cue and odor avoidance learning were similar at both ages, while contextual fear learning and learning-associated hippocampal (CA1, CA3, and dentate gyrus) activity (c-Fos) only occurred in PN24 paired pups. To assess a causal relationship between the hippocampus and context conditioning, we infused muscimol into the hippocampus, which blocked acquisition of context fear learning in the PN24 pups. Muscimol or vehicle infusions did not affect cue learning or aversion to the odor at PN21 or PN24. The results suggest that the newly emerging contextual learning exhibited by PN24 pups is supported by the hippocampus.

Adult depression-like behavior, amygdala and olfactory cortex functions are restored by odor previously paired with shock during infant's sensitive period attachment learning

Maltreatment from the caregiver induces vulnerability to later life psychopathologies, yet attraction and comfort is sometimes provided by cues associated with early life maltreatment. We used a rat model of early life maltreatment with odor–0.5 mA shock conditioning to produce depressive-like behaviors and questioned whether stimuli associated with maltreatment would restore emotional neurobehavioral function to control levels. Pups received daily novel odor–0.5 mA shock conditioning from postnatal day 8 to 12. This procedure produces a new maternal odor that controls pups’ attachment behaviors. In adulthood, either with or without the infant odor, animals received a Forced Swim Test, Sucrose Preference Test or assessment of amygdala and olfactory system functioning using field potential signal evoked by olfactory bulb paired-pulse electrical stimulation. Following neonatal odor–shock pairings, but not unpaired controls, adults without the odor present showed increased depression-like behavior in the Forced Swim Test and Sucrose Preference Test and a deficit in paired-pulse inhibition in amygdala and piriform (olfactory) cortex. All effects were brought to control levels when the infant conditioned odor was presented during behavioral and neural tests. The ability of cues associated with early life maltreatment to normalize behavior and amygdala activity suggests these cues provide adaptive value in adulthood.

Defining age limits of the sensitive period for attachment learning in rat pups.

Enhanced odor preference learning and attenuated fear learning characterizes rat pups' attachment learning Sensitive Period for learning the maternal odor. This period terminates at 10 days old (PN10) with increasing endogenous levels of the stress hormone, corticosterone. Increasing Sensitive Period pups' corticosterone prematurely terminates the Sensitive Period, while decreasing corticosterone in older pups delays Sensitive Period termination. Here we extend these findings and define the age range corticosterone alters learning and question whether corticosterone permanently terminates the Sensitive Period. Pups were odor-0.5 mA shock conditioned with either corticosterone increased (PN5-6; 4 mg/kg vs. saline) or decreased (PN15-16; naturally by maternal presence or corticosterone synthesis blocker, Metyrapone). Finally, PN7-8 pups were conditioned with corticosterone and reconditioned without corticosterone to assess whether the Sensitive Period was permanently terminated. Results indicate developmental limits for corticosterone regulation of pup learning are PN6 through PN15. Furthermore, inducing precocious corticosterone induced fear learning was not permanent, since reconditioning without corticosterone enabled odor preference learning. Results suggest pups are protected from learning aversions to maternal odor until approaching weaning.

Developing a Neurobehavioral Animal Model of Infant Attachment to an Abusive Caregiver

Both abused and well cared for infants show attachment to their caregivers, although the quality of that attachment differs. Moreover, the infant's attachment to the abusive caregiver is associated with compromised mental health, especially under stress. In an attempt to better understand how abuse by the caregiver can compromise mental health, we explore the neural basis of attachment in both typical and abusive environments using infant rats, which form attachments to the mother through learning her odor. Here, we hypothesize that the neural circuitry for infant attachment differs based on the quality of the attachment, which can be uncovered during stressful situations. We used infant rats to compare infant attachment social behaviors and supporting neurobiology using natural maternal odor, as well as two odor-learning attachment paradigms: odor-stroke (mimics typical attachment) and odor-.5 mA shock conditioning (mimics abusive attachment). Next, to uncover differences in behavior and brain, these pups were injected with systemic corticosterone. Finally, pups were reared with an abusive mother to determine ecological relevance. Our results suggest that the natural and learned attachment odors indistinguishably control social behavior in infancy (approach to the odor and interactions with the mother). However, with corticosterone injection, pups with an abusive attachment show disrupted infant social behavior with the mother and engagement of the amygdala. This animal model of attachment accommodates both abusive and typical attachment and suggests that pups' social behavior and underlying neural circuitry may provide clues to understanding attachment in children with various conditions of care.

Early-Life Stress Disrupts Attachment Learning: The Role of Amygdala Corticosterone, Locus Ceruleus Corticotropin Releasing Hormone, and Olfactory Bulb Norepinephrine

Infant rats require maternal odor learning to guide pups' proximity-seeking of the mother and nursing. Maternal odor learning occurs using a simple learning circuit including robust olfactory bulb norepinephrine (NE), release from the locus ceruleus (LC), and amygdala suppression by low corticosterone (CORT). Early-life stress increases NE but also CORT, and we questioned whether early-life stress disrupted attachment learning and its neural correlates [2-deoxyglucose (2-DG) autoradiography]. Neonatal rats were normally reared or stressed-reared during the first 6 d of life by providing the mother with insufficient bedding for nest building and were odor-0.5 mA shock conditioned at 7 d old. Normally reared paired pups exhibited typical odor approach learning and associated olfactory bulb enhanced 2-DG uptake. However, stressed-reared pups showed odor avoidance learning and both olfactory bulb and amygdala 2-DG uptake enhancement. Furthermore, stressed-reared pups had elevated CORT levels, and systemic CORT antagonist injection reestablished the age-appropriate odor-preference learning, enhanced olfactory bulb, and attenuated amygdala 2-DG. We also assessed the neural mechanism for stressed-reared pups' abnormal behavior in a more controlled environment by injecting normally reared pups with CORT. This was sufficient to produce odor aversion, as well as dual amygdala and olfactory bulb enhanced 2-DG uptake. Moreover, we assessed a unique cascade of neural events for the aberrant effects of stress rearing: the amygdala-LC-olfactory bulb pathway. Intra-amygdala CORT or intra-LC corticotropin releasing hormone (CRH) infusion supported aversion learning with intra-LC CRH infusion associated with increased olfactory bulb NE (microdialysis). These results suggest that early-life stress disturbs attachment behavior via a unique cascade of events (amygdala-LC-olfactory bulb).