Xilu Jiao

Damage of GABAergic neurons in the medial septum impairs spatial working memory and extinction of active avoidance: effects on proactive interference.

The medial septum and diagonal band (MSDB) are important in spatial learning and memory. On the basis of the excitotoxic damage of GABAergic MSDB neurons, we have recently suggested a role for these neurons in controlling proactive interference. Our study sought to test this hypothesis in different behavioral procedures using a new GABAergic immunotoxin. GABA‐transporter‐saporin (GAT1‐SAP) was administered into the MSDB of male Sprague–Dawley rats. Following surgery, rats were trained in a reference memory water maze procedure for 5 days, followed by a working memory (delayed match to position) water maze procedure. Other rats were trained in a lever‐press avoidance procedure after intraseptal GAT1‐SAP or sham surgery. Intraseptal GAT1‐SAP extensively damaged GABAergic neurons while sparing most cholinergic MSDB neurons. Rats treated with GAT1‐SAP were not impaired in acquiring a spatial reference memory, learning the location of the escape platform as rapidly as sham rats. In contrast, GAT1‐SAP rats were slower than sham rats to learn the platform location in a delayed match to position procedure, in which the platform location was changed every day. Moreover, GAT1‐SAP rats returned to previous platform locations more often than sham rats. In the active avoidance procedure, intraseptal GAT1‐SAP impaired extinction but not acquisition of the avoidance response. Using a different neurotoxin and behavioral procedures than previous studies, the results of this study paint a similar picture that GABAergic MSDB neurons are important for controlling proactive interference.

Avoidance perseveration during extinction training in Wistar-Kyoto rats: an interaction of innate vulnerability and stressor intensity.

Given that avoidance is a core feature of anxiety disorders, Wistar-Kyoto (WKY) rats may be a good model of anxiety vulnerability for their hypersensitivity to stress and trait behavioral inhibition. Here, we examined the influence of strain and shock intensity on avoidance acquisition and extinction. Accordingly, we trained WKY and Sprague-Dawley (SD) rats in lever-press avoidance using either 1.0-mA or 2.0-mA foot-shock. After extinction, neuronal activation was visualized by c-Fos for overall activity and parvalbumin immunoreactivity for gamma-aminobutyric acid (GABA) neuron in brain areas linked to anxiety (medial prefrontal cortex and amygdala). Consistent with earlier work, WKY rats acquired lever-press avoidance faster and to a greater extent than SD rats. However, the intensity of foot shock did not differentially affect acquisition. Although there were no differences during extinction in SD rats, avoidance responses of WKY rats trained with the higher foot shock perseverated during extinction compared to those WKY rats trained with lower foot shock intensity or SD rats. WKY rats trained with 2.0-mA shock exhibited less GABAergic activation in the basolateral amygdala after extinction. These findings suggest that inhibitory modulation in amygdala is important to ensure successful extinction learning. Deficits in avoidance extinction secondary to lower GABAergic activation in baslolateral amygdala may contribute to anxiety vulnerability in this animal model of inhibited temperament.

Vulnerability factors in anxiety determined through differences in active-avoidance behavior

The risk for developing anxiety disorders is greater in females and those individuals exhibiting a behaviorally inhibited temperament. Growth of behavioral avoidance in people is a significant predictor of symptom severity in anxiety disorders, including post-traumatic stress disorder. Using an animal model, our lab is examining how the process of learning avoidant behavior may lead certain individuals to develop anxiety. Here we examined whether the known vulnerabilities of female sex and behaviorally inhibited temperament have individual or additive effects upon the acquisition of an active-avoidance response. A discrete trial lever-press escape-avoidance protocol was used to examine the acquisition of behavioral avoidance in male and female Sprague-Dawley (SD) rats and behaviorally inhibited inbred Wistar-Kyoto (WKY) rats. Overall, WKY rats of both sexes were indistinguishable in their behavior during the acquisition of an active-avoidance response, exhibiting quicker acquisition of reinforced responses both between and within session compared to SD rats. Further WKY rats emitted more non-reinforced responses than SD rats. Sex differences were evident in SD rats in both the acquisition of the reinforced response and the emission of non-reinforced responses, with SD females acquiring the response quicker and emitting more non-reinforced responses following lever presses that led to an escape from shock. As vulnerability factors, behavioral inhibition and female sex were each associated with more prevalent reinforced and non-reinforced avoidant behavior, but an additive effect of these 2 factors was not observed. These data illustrate the importance of genetics (both strain and sex) in the assessment and modeling of anxiety vulnerability through the acquisition of active-avoidance responses and the persistence of emitting those responses in periods of non-reinforcement.

Vulnerability factors in anxiety: Strain and sex differences in the use of signals associated with non-threat during the acquisition and extinction of active-avoidance behavior

Rats that exhibit a behaviorally inhibited temperament acquire active-avoidance behaviors quicker, and extinguish them slower, than normal outbred rats. Here we explored the contribution of stimuli that signal periods of non-threat (i.e. safety signals) in the process of acquiring active-avoidance behavior. Utilizing a discrete lever-press escape-avoidance protocol, outbred Sprague-Dawley (SD) rats and inbred, behaviorally inhibited, Wistar-Kyoto (WKY) rats were tested under conditions where a flashing light was either presented or not during periods of non-threat (the inter-trial interval, ITI). For males, we found the absence of the ITI-signal slowed the acquisition of avoidance behavior selectively in WKY rats. However, extinction of the avoidance behavior was not influenced by training with or without the ITI-signal; WKY males extinguished slower than SD males. For females, the presence of the ITI-signal did not affect acquisition in either strain. However, after training with the ITI-signal, females of both strains extinguished quicker in its absence than in its presence. In order to determine if facilitated acquisition of avoidance learning in male WKY rats was due to a paradigm-independent influence of the visual stimulus used as ITI-signal upon associative learning, we conducted eyeblink conditioning in the presence or absence of a similar visual stimulus. No differences in acquisition, as a function of this visual stimulus, were observed within the male WKY rats, but, as was observed in avoidance learning, male WKY rats extinguished slower than male SD rats. Thus, avoidance susceptibility for male WKY rats may be tied both to the presence of non-threat signals as well as a resistance to extinguish Pavlovian-conditioned associations. Female susceptibility to resist extinguishing avoidant behavior is discussed with respect to the possible role of stimuli serving as occasion setters for threat contexts.

The role of the hippocampus in avoidance learning and anxiety vulnerability

The hippocampus has been implicated in anxiety disorders and post-traumatic stress disorder (PTSD); human studies suggest that a dysfunctional hippocampus may be a vulnerability factor for the development of PTSD. In the current study, we examined the effect of hippocampal damage in avoidance learning, as avoidance is a core symptom of all anxiety disorders. First, the effect of hippocampal damage on avoidance learning was investigated in outbred Sprague Dawley (SD) rats. Second, the function of the hippocampus in Wistar-Kyoto (WKY) rats was compared to SD rats. The WKY rat is an animal model of behavioral inhibition, a risk factor for anxiety, and demonstrates abnormal avoidance learning, marked by facilitated avoidance acquisition and resistance to extinction. The results of the current study indicate that hippocampal damage in SD rats leads to impaired extinction of avoidance learning similar to WKY rats. Furthermore, WKY rats have reduced hippocampal volume and impaired hippocampal synaptic plasticity as compared to SD rats. These results suggest that hippocampal dysfunction enhances the development of persistent avoidance responding and, thus, may confer vulnerability to the development of anxiety disorders and PTSD.

Classical and instrumental conditioning of eyeblink responses in Wistar–Kyoto and Sprague–Dawley rats

Wistar-Kyoto (WKY) rats, an animal model of anxiety vulnerability, acquire lever-press avoidance faster than outbred Sprague-Dawley (SD) rats. Faster avoidance acquisition may reflect an inherent ability to acquire cue-outcome associations, response-outcome associations or both. To evaluate cue-outcome learning, acquisition of classically conditioned eyeblink response was compared in SD and WKY rats using a delay-type paradigm (500-ms conditioned stimulus (CS) coterminating with a 10-ms unconditional stimulus (US)). WKY rats demonstrated enhanced classical conditioning, with both faster acquisition and greater asymptotic performance in delay-type training than SD rats. To evaluate response-outcome learning, separate SD and WKY rats were given control over US delivery through imposition of an omission contingency into delay-type training (emitting a conditioned response (CR) prevented delivery of the US). The schedule of US delivery derived by these rats became the training regimen for a separate group of SD and WKY rats, yoked within strain. In SD rats, no differences in acquisition were detected between those given control over US delivery and those trained with the same partial reinforcement schedule. Acquisition rates of those WKY rats with control exceeded those trained with a yoked-schedule of US presentation. Collectively, WKY rats exhibit enhanced classical conditioning and sensitivity to schedules of reinforcement compared to outbred SD rats. Anxiety vulnerability, in particular inhibited temperament, may be traced to active processes in the prediction and control of aversive events.

Deficient proactive interference of eyeblink conditioning in Wistar-Kyoto rats.

Wistar-Kyoto (WKY) rats exhibit behavioral inhibition and model anxiety vulnerability. Although WKY rats exhibit faster active avoidance acquisition, simple associative learning or the influence of proactive interference (PI) has not been adequately assessed in this strain. Therefore, we assessed eyeblink conditioning and PI in WKY and outbred Sprague-Dawley (SD) rats. Rats were pre-exposed to either the experimental context, the conditioned stimulus (CS), the unconditional stimulus (US), or the CS & US in an explicitly unpaired (EUP) manner, to examine latent inhibition (LI), US pre-exposure effect, or learned irrelevance (LIRR), respectively. Immediately following pre-exposures, rats were trained in a delay-type paradigm (500 ms CS coterminating with a 10-ms US) for one session. During training SD rats exhibited LI and inhibition from US pre-exposures without evidence of LIRR. PI was less evident in WKY rats; LI was absent in WKY rats. Even in the context of reduced PI to CS-alone and US-alone pre-exposures, LIRR was not apparent in WKY rats. The more normal acquisition rates exhibited by WKY rats, under conditions which degrade performance in SD rats, increases the overall likelihood for WKY rats to acquire defensive responses. Enhanced acquisition of defensive responses is a means by which anxiety vulnerability (e.g., behavioral inhibition) is translated to anxiety psychopathology.

Preclinical Investigation of the Functional Effects of Memantine and Memantine Combined with Galantamine or Donepezil

Combinations of drugs approved to treat Alzheimers disease (AD) were tested in older rabbits with delay eyeblink classical conditioning, a form of associative learning severely impaired in AD. In Experiment 1 (n=49 rabbits), low doses (0.1, 0.5, 1.0, and 0.0 (vehicle) mg/kg) of memantine (Namenda™) were tested. These three doses neither improved nor impaired acquisition at a statistically significant level. The 0.5 mg/kg dose had the greatest effect numerically and did not cause sensitization or habituation in explicitly unpaired controls. In Experiment 2 (n=56), doses of galantamine (Razadyne™; 3.0 mg/kg) and donepezil (Aricept™; 0.75 mg/kg) that had comparable magnitudes of cholinesterase inhibition were tested alone and in combination with 0.5 mg/kg memantine. Older rabbits treated with galantamine and with galantamine+memantine learned significantly better than vehicle-treated rabbits, but adding memantine did not improve learning over galantamine alone. Older rabbits treated with donepezil or a combination of memantine and donepezil did not learn significantly better than rabbits treated with vehicle. Galantamine has two mechanisms of action: mild cholinesterase inhibition and allosteric modulation of nicotinic acetylcholine receptors (nAChRs). When equated for cholinesterase inhibition, galantamine had significant efficacy in the eyeblink conditioning model system, but donepezil did not, indicating that modulation of nAChRs may be the mechanism that significantly ameliorates learning deficits in this model. In the absence of AD neuropathology in older rabbits, memantine had no efficacy alone or in combination with the other drugs.

Estrus cycle stage modifies the presentation of stress-induced startle suppression in female Sprague-Dawley rats

Tailshock stress causes transient reductions in startle reactivity, associative learning and open field activity in female rats in an ovarian hormone dependent manner. Others have shown estrogen modulation of associative learning by testing across the estrus cycle and pharmacological manipulations. Here we tested whether stress-induced suppression of startle reactivity can be attributed to circulating ovarian hormones. Female rats were tracked across the estrus cycle and subjected to the stressor (2 h periodic tailshock) the morning of diestrus, proestrus, estrus, or metestrus. Startle reactivity was tested 2 h following the cessation of the tailshock. Using a multi-stimulus protocol, we determined there were differences in startle sensitivity and responsivity. Following stressor exposure, estrus females exhibited reduced startle responsivity. In contrast, diestrus females exhibited increased sensitivity to the lowest acoustic stimulus. The results are discussed with respect to ovarian hormone regulation of the immune system and sensory reactivity during and following trauma that may lead to different abnormal behaviors in females in the wake of traumatic stress.

ITI-Signals and Prelimbic Cortex Facilitate Avoidance Acquisition and Reduce Avoidance Latencies, Respectively, in Male WKY Rats.

As a model of anxiety disorder vulnerability, male Wistar-Kyoto (WKY) rats acquire lever-press avoidance behavior more readily than outbred Sprague-Dawley rats, and their acquisition is enhanced by the presence of a discrete signal presented during the inter-trial intervals (ITIs), suggesting that it is perceived as a safety signal. A series of experiments were conducted to determine if this is the case. Additional experiments investigated if the avoidance facilitation relies upon processing through medial prefrontal cortex (mPFC). The results suggest that the ITI-signal facilitates acquisition during the early stages of the avoidance acquisition process, when the rats are initially acquiring escape behavior and then transitioning to avoidance behavior. Post-avoidance introduction of the visual ITI-signal into other associative learning tasks failed to confirm that the visual stimulus had acquired the properties of a conditioned inhibitor. Shortening the signal from the entirety of the 3 min ITI to only the first 5 s of the 3 min ITI slowed acquisition during the first four sessions, suggesting the flashing light (FL) is not functioning as a feedback signal. The prelimbic (PL) cortex showed greater activation during the period of training when the transition from escape responding to avoidance responding occurs. Only combined PL + infralimbic cortex lesions modestly slowed avoidance acquisition, but PL-cortex lesions slowed avoidance response latencies. Thus, the FL ITI-signal is not likely perceived as a safety signal nor is it serving as a feedback signal. The functional role of the PL-cortex appears to be to increase the drive toward responding to the threat of the warning signal. Hence, avoidance susceptibility displayed by male WKY rats may be driven, in part, both by external stimuli (ITI signal) as well as by enhanced threat recognition to the warning signal via the PL cortex.