Ontogeny of delay versus trace eyeblink conditioning in the rat

The ontogeny of delay versus trace eyeblink conditioning was examined in 19-, 23-, and 30-day-old rat pups. Pairings of a tone conditioned stimulus (CS) and periocular shock unconditioned stimulus (US; 100-ms) were presented in one of three conditioning paradigms: standard delay [380-ms CS, 280-ms interstimulus interval (ISI)], trace (380-ms CS, 500-ms trace interval), or long-delay (980-ms CS, 880-ms ISI). The results of two experiments indicated that standard delay conditioning emerged between 19 and 23 days of age whereas trace and long-delay eyeblink conditioning emerged more slowly from postnatal Days 19 to 30. Because the acquisition profile for long-delay paralleled that of trace and not standard delay, it appears that the relative deficits in the emergence of trace eyeblink conditioning during development reflect difficulty in forming associations over long ISIs rather than the short-term memory demands of the trace conditioning paradigm.     

The ontogeny of human learning in delay, long-delay, and trace eyeblink conditioning

The ontogeny of associative learning in delay (750-ms conditional stimulus [CS], 650-ms interstimulus interval [ISI]), long-delay (1,350-ms CS, 1,250-ms ISI), and trace (750-ms CS, 500-ms trace interval, 1,250-ms ISI) eyeblink conditioning was examined in 5-month-old human infants and adults. Infants and adults showed different acquisition rates but reached equivalent asymptotes of conditional responses (CRs) in standard delay conditioning. In long-delay and trace conditions, infants exhibited less robust conditioning than adults and minimal ability to appropriately time CRs. During infancy, the ISI, rather than the conditioning procedure, predicted rate and effectiveness of CRs. These findings suggest that higher order cognitive abilities begin emerging early in development. Across ontogeny, however, there are changes in the limits and parameters that support associative learning.     

Impaired delay and trace eyeblink conditioning performance in major depressive disorder

BACKGROUND: Preliminary evidence obtained in our lab has revealed that depressive symptoms impair associative learning, as measured by acquisition of eyeblink classical conditioning (EBCC) tasks. The current study assesses EBCC acquisition in individuals with major depressive disorder (MDD). METHODS: The 17-item Hamilton Rating Scale for Depression (HAM-D(17)) and the 30-item Inventory for Depressive Symptomatology, Self-Report (IDS-SR(30)) were used to quantify severity of depressive symptoms. Participants received 60 trials each in delay 500, trace 500, and trace 1000 conditioning paradigms. A 150-ms, 5-7 psi air puff served as the unconditioned stimulus (US), and an 80-dB, 1-kHz tone as the conditioned stimulus (CS). Mean percent conditioned responses (CRs) served as the primary measure of task acquisition. RESULTS: The MDD group generated significantly fewer CRs on delay 500 and trace 500 tasks, and approached significance on the trace 1000 task compared to healthy controls. Furthermore, presentation of successive trials did not increase CR production in the depressed group, in contrast to progressive increases observed in the control group. LIMITATIONS: The presentation of multiple EBCC tasks precludes some detailed analyses of task-specific performance. Future studies may also benefit from including sufficient numbers of subjects to assess differential characteristics of depression (e.g., length of episode, depressive subtype) and treatment effects. CONCLUSIONS: These data suggest that MDD impairs acquisition of EBCC, providing behavioral support for cerebellar and hippocampal dysfunction in depression. Delineating the neural substrates involved in MDD may aid in future treatment approaches for this pervasive disorder.     

Decremental effects of context exposure following delay eyeblink conditioning in rabbits

The conditioning context arises from the relatively static features of the training environment. In rabbit eyeblink conditioning, procedures that retard acquisition (conditioned stimulus [CS] preexposure, unconditioned stimulus preexposure, blocking manipulations) are attenuated by context changes. In this article the authors investigate the effect of context exposure after initial delay conditioning. After conditioned responses (CRs) were established, one group received 6 sessions of context exposure, whereas control groups either remained in their home cages or received exposure to handling and a novel context. Thereafter, all groups received CS-alone testing. The expression of CRs was substantially reduced following context exposure relative to any retention loss in the home-cage control. Exposure to handling and a novel context facilitated the CRs rather than reducing them. ((c) 2006 APA, all rights reserved).     

Awareness is necessary for differential trace and delay eyeblink conditioning in humans

Squire et al. have proposed that trace and delay eyeblink conditioning procedures engage separate learning systems: a declarative hippocampal/cortical system associated with conscious contingency awareness, and a reflexive sub-cortical system independent of awareness, respectively ( [Clark and Squire, 1998] and [Smith et al., 2005]). The only difference between these two procedures is that the conditioned stimulus (CS) and the unconditioned stimulus (US) overlap in delay conditioning, whereas there is a brief interval (e.g., 1 s) between them in trace conditioning. In two experiments using the same procedure as Clark and Squire's group, we observed differential conditioning only in participants who showed contingency awareness in a post-experimental questionnaire, with both trace and delay procedures. We interpret these results to suggest that, although there may be multiple brain regions involved in learning, these regions are organized as a coordinated system rather than as separate, independent systems.     

Prefrontal control of trace versus delay eyeblink conditioning: role of the unconditioned stimulus in rabbits (Oryctolagus cuniculus)

The conditioned eyeblink (EB) response was studied with trace conditioning procedures in rabbits (Oryctolagus cuniculus) with lesions to the medial prefrontal cortex (mPFC) or sham lesions. Three experiments were performed in which either periorbital shock or a corneal airpuff served as the unconditioned stimulus (US) in separate groups of sham or mPFC-lesioned rabbits. Acquisition of the EB conditioned response (CR) was faster and reached a higher asymptote with the eyeshock US than with the airpuff US. However, mPFC lesion-induced trace conditioning deficits were obtained only in the groups that received the airpuff US. All rabbits showed normal delay conditioning and extinction. These results suggest that mPFC mediates trace EB conditioning when emotional arousal is low. However, in circumstances when emotional arousal may be high (i.e., during exposure to aversive periorbital shock), other structures (such as amygdala) may be activated to permit learning even in the absence of input from mPFC.     

Medial prefrontal lesions and Pavlovian eyeblink and heart rate conditioning: effects of partial reinforcement on delay and trace conditioning in rabbits (Oryctolagus cuniculus)

Effects of continuous (100%) versus partial (25%) reinforcement were studied on Pavlovian delay and trace eyeblink conditioning in rabbits (Oryctolagus cuniculus) with either lesions to the medial prefrontal cortex (mPFC) or sham lesions. Concomitant heart rate changes evoked by the conditioned stimulus were also assessed. Partial reinforcement retarded eyeblink conditioning in both the trace and delay paradigm, but this impairment was greater during trace conditioning and in rabbits with mPFC lesions. Accompanying conditioned stimulus-evoked heart rate slowing was attenuated under all conditions by the mPFC lesions, although this result was not always statistically significant.     

A developmental comparison of trace and delay eyeblink conditioning in rats using matching interstimulus intervals

The effects of conditioning paradigm and interstimulus interval (ISI) were evaluated in this study of the development of associative learning in rats. The acquisition of classical eyeblink conditioning (EBC) was examined in two paradigms (trace vs. delay), with three different ISIs (short, medium, or long) at two ages (postnatal Days 21-23 or 29-31). These data provide the first parametric analysis of ISI in developing animals trained with trace EBC procedures. Further, by comparing trace and delay EBC, it was determined that when ISI is held constant, acquisition is similar for both conditioning paradigms regardless of developmental age. This suggests a similar ontogeny of associative processes for delay and trace EBC that relies on common neural substrates. However, conditioned response timing (onset and peak latencies) was affected by age and paradigm, suggesting that different neural mechanisms may play a role in timing delay versus trace conditioned responses.     

Cortical involvement in acquisition and extinction of trace eyeblink conditioning

Previous studies have implicated 2 cortical regions interconnected with the hippocampal formation, the retrosplenial cortex (RSC) and the medial prefrontal cortex (mPFC), as loci important for the acquisition of hippocampally dependent trace eyeblink conditioning. These loci have also been proposed to serve as long-term storage sites of task critical information. This study used lesions made prior to training to investigate the roles of the RSC, as well as the caudal and rostral subdivisions of the mPFC, in the acquisition and subsequent extinction of trace eyeblink conditioning in the rabbit. The caudal mPFC and rostral mPFC were shown to be critical for acquisition and extinction of the conditioned reflex, respectively. The data indicate that the RSC is not critical for acquisition or extinction of the trace conditioned reflex.     

Ibotenic acid lesions of the medial septum retard delay eyeblink conditioning in rabbits (Oryctolagus cuniculus)

S. Berry and R. Thompson (1979) reported that electrolytic lesions of the medial septum significantly retard eyeblink conditioning. However, these electrolytic lesions were nonselective and may have also damaged the subcortical inputs to the hippocampus via the fimbria-fornix. In the present study, the medial septum was selectively lesioned with ibotenic acid in rabbits (Oryctolagus cuniculus), whose performance in a delay eyeblink conditioning paradigm was compared with that of intact controls. sham-operated controls, and intact controls given a systemic injection of scopolamine. Rabbits with selective medial septal lesions and rabbits receiving systemic scopolamine were significantly slower to condition than were intact and sham-lesioned rabbits. This finding demonstrates that the selective removal of the medial septum retards delay eyeblink conditioning in a manner similar to the disruption seen after systemic administration of scopolamine.     

Assessment of forebrain-dependent trace eyeblink conditioning in chronic cannabis users

While CB1 knockout mice exhibit striking impairments on a cerebellar-dependent task called delay eyeblink conditioning (dEBC), these animals demonstrate intact forebrain-dependent trace EBC (tEBC). Although heavy human cannabis users also show impaired delay EBC, their performance on tEBC is currently unknown. Therefore, 13 heavy cannabis users and 13 cannabis naive controls completed a tEBC procedure. The cannabis group exhibited similar rates of conditioned responding compared to controls in the acquisition and extinction phase. Consistent with reports of overt attentional abnormalities, the cannabis group exhibited decreased N100 ERP amplitudes to the tone CS that were unrelated to mean levels of conditioning across blocks during the acquisition phase. The lack of a significant effect of heavy cannabis use on tEBC reported here, combined with the previous report of impaired dEBC in such users, mirrors the findings observed in CB1 knockout mice, and suggests that the cannabinoid system differentially mediates forebrain- and cerebellar-dependent learning processes in both humans and animals.     

RWJ-22108 — a novel airway tissue — selective calcium channel blocker

RWJ-22108 is a novel calcium entry blocker that has potential therapeutic use as an antiasthmatic agent. Although displaying typical potent inhibition of⁴⁵Ca uptake into aortic rings (IC₅₀=7.1 nM) and displacement of [³H]nitrendipine from cardiac membranes (IC₅₀=137 nM), RWJ-22108 demonstrates tissue selectivity in the inhibition of KCl-induced contractions. RWJ-22108 inhibits the calcium-dependent contraction of canine bronchiolar smooth muscle with an IC₅₀ of 5.7 nM. The IC₅₀ femoral artery/IC₅₀ bronchiolar ratios are 2.85, 8.02, 1.47 and 1.96 for nifedipine, RWJ-22108, verapamil, and gallopamil, respectively. Furthermore, this selectivity ratio (range 2.8–5.5) of RWJ-22108 is also observed when inhibition of other pulmonary and cardiovascular smooth muscles are compared. Using canine tracheal muscle and rabbit aortae, the IC₅₀ aorta/IC₅₀ trachea ratio is 1.75 for RWJ-22108 compared to approximately 0.5 for several calcium blocker standards. These results indicate thatin vitro RWJ-22108 is a bronchoselective calcium channel blocker.     

Antiepileptic effects of IOS-1.1212, a new calcium channel blocker

Research Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Institute of Organic Synthesis, Latvian Academy of Sciences, Riga. (Presented by Academician of the Academy of Medical Sciences of the USSR A. D. Ado.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 112, No. 10, pp. 362–365, October, 1991.     

The N-methyl-D-aspartate (NMDA)-type glutamate receptor GluRepsilon2 is important for delay and trace eyeblink conditioning in mice

The corticosterone (CORT) response to environmental perturbation has been shown to be enhanced by estrogen but inhibited by the androgen dihydrotestosterone (DHT). However, the mechanism of androgen's action has not been identified. This study examined the effects of estradiol benzoate (EB), the non-aromatizable androgen DHT, and the DHT metabolite 5alpha-androstan-3beta, 17beta-diol (3beta-diol) on the corticosterone response to stress. Adult male CBB6/F1 mice were gonadectomized and injected subcutaneously (once a day for 4 days) with the above compounds (controls received oil vehicle injections). Animals (within treatments) were randomly assigned to stress or non-stress conditions. The non-stress animals were taken directly from their home cages and killed. Animals were stressed by a 30 min restraint prior to being killed. Hormone levels were determined in plasma via radioimmunoassay. In agreement with previous studies, the CORT response to immobilization was enhanced by EB and inhibited by DHT. Surprisingly, 3beta-diol inhibited the CORT response similar to the effect of DHT. In a second study, concomitant injections of the androgen receptor antagonist flutamide only partially blocked DHT's, but had no effect on 3beta-diol's, inhibitory action. In contrast, injections with the estrogen receptor antagonist tamoxifen completely blocked the effects of 3beta-diol and partially blocked DHT's effect. Taken together these studies suggest that DHT's inhibitory effects may be, at least in part, via the estrogen receptor, through its conversion to 3beta-diol. These studies also suggest that the DHT metabolites may be functionally relevant when considering hormonal responses to stress.     

Normal delay eyeblink conditioning in mice devoid of astrocytic S100B

S100B is a small calcium binding protein synthesized and secreted mostly by astrocytes. Mice devoid of S100B (S100B-KO) develop without detectable anatomic abnormalities of the brain, but exhibit enhanced hippocampal long-term potentiation and enhanced performance in hippocampus-dependent learning and memory tasks, indicating that S100B has a crucial role in hippocampal neuronal plasticity. In the present study, we examined whether S100B has a similar role in the cerebellar regions, because Bergmann glia, a specialized subset of astrocytes in the cerebellar cortex, express a particularly large amount of S100B under physiologic conditions. Unlike in the hippocampus-dependent tasks, S100B-KO mice were indistinguishable from wild-type mice in both cerebellum-dependent motor coordination and delay eyeblink conditioning, a well-established paradigm for cerebellum-dependent learning and memory. These results suggest that S100B has differential roles in the hippocampus and cerebellum.     

Effect of delay interval on classical eyeblink conditioning in 5-month-old human infants

Associative learning was evaluated in human infants with simple delay classical eyeblink conditioning. A tone conditioned stimulus (CS) was paired with an airpuff unconditioned stimulus (US) at three different delay intervals (250, 650, and 1,250 ms). Independent groups of healthy, full-term 5-month-old human infants were assigned to these three paired conditions and received two identical training sessions 1 week apart. The two longer delays resulted in associative conditioning, as confirmed by comparison with unpaired control groups. However, only at the 650-ms delay were associative eyeblinks adaptively timed to avoid the airpuff. The delay function at 5 months of age appears much sharper than is observed in adults. Together with the findings of A. H. Little, L. P. Lipsitt, and C. Rovee-Collier (1984), the present study suggests a downward shift in the optimal delay interval for associative eyeblink conditioning between 1 and 6 months of age. However, this delay remains longer than what is typically reported in adults.     

Inactivation of sodium channel Scn8A (Na-sub(v)1.6) in Purkinje neurons impairs learning in Morris water maze and delay but not trace eyeblink classical conditioning

To examine the isolated effects of altered currents in cerebellar Purkinje neurons, the authors used Scn8a-super(flox/flox), Purkinje cell protein-CRE (Pcp-CRE) mice in which Exon 1 of Scn8a is deleted only in Purkinje neurons. Twenty male Purkinje Scn8a knockout (PKJ Scn8a KO) mice and 20 male littermates were tested on the Morris water maze (MWM). Subsequently, half were tested in 500-ms delay and half were tested in 500-ms trace eyeblink conditioning. PKJ Scn8a KO mice were impaired in delay conditioning and MWM but not in trace conditioning. These results provide additional support for the necessary participation of cerebellar cortex in normal acquisition of delay eyeblink conditioning and MWM and raise questions about the role, if any, of cerebellar cortex in trace eyeblink conditioning.     

Prevention of diabetic vascular calcification by nifedipine, a dihydropyridine-based calcium channel blocker

Vascular calcification is a common feature in advanced atherosclerosis and also a predictor of future cardiovascular events such as unstable angina and myocardial infarction, especially in diabetes. There is a growing body of evidence that advanced glycation end products (AGEs), senescent macroprotein derivatives formed at an accelerated rate in diabetes, exist within atherosclerotic lesions, thereby being implicated in the pathogenesis of accelerated atherosclerosis in diabetes. Indeed, we have previously shown that AGE - their receptor (RAGE) interaction could induce angiogenesis through autocrine production of vascular endothelial growth factor, suggesting its role for plaque formation and enlargement in diabetes. Furthermore, we have found that AGEs have the ability to induce the osteoblatic differentiation of pericytes, thus contributing to the development of vascular calcification as well. These observations suggest that the inhibition of AGE formation or blockade of the downstream signaling of RAGE may be a novel therapeutic target for the inhibition of vascular calcification in diabetic atherosclerosis. Since we, along with others, have shown that nifedipine inhibits glycation of low-density lipoprotein in vitro and blocks the AGE-induced RAGE expression in endothelial cells through its anti-oxidative properties, nifedipine could inhibit vascular calcification by blocking the AGE formation or the downstream signaling in diabetes. In this paper, we would like to propose the possible ways of testing our hypothesis. Does nifedipine treatment slow down the progression of coronary calcification in diabetic patients? If the answer is yes, is this beneficial effect of nifedipine superior to that of other DHPs with equihypotensive properties? Does nifedipine treatment decrease expression levels of AGEs and RAGE in diabetic atherosclerosis? Is the unique effect of nifedipine on vascular calcification correlated with its AGE or RAGE-suppressing properties? These prospective studies will provide further valuable information whether nifedipine could prevent vascular calcification in diabetic atherosclerosis by blockade the AGE-RAGE signaling in vascular wall cells.     

Pregnancy following discontinuation of a calcium channel blocker in the male partner

The fertility potential of human sperm populations can be assessedby the presence of head-directed mannose ligand receptors (mannose-specificlectin) and the occurrence of spontaneous acrosome reactionsafter incubation under capacitating conditions in vitro. Wehave reported previously on the interaction between anti-hypertensivemedications and their effects on these parameters of male fertilitypotential. In this report we document the effects of cessationof calcium ion channel blocker medication on male fertility.Motile spermatozoa from a 30 year old infertile patient on acalcium ion channel blocker as anti-hypertensive treatment hadsubnormal expression of mannose-specific lectin and did notexhibit spontaneous acrosome reactions. Three months followingdiscontinuation of the medications, complete recovery of boththe expression of head-directed mannose ligand receptors andthe acrosome reaction was documented, though sperm motilityand morphology remained unchanged. The couple had 2 years ofinfertility and previously failed to conceive through sevencycles of Pergonal/intra-uterine insemination. Conception occurredon the second Pergonal/intra-uterine insemination cycle afterthe husband discontinued calcium ion channel blocker medication.Calcium ion channel blockers may adversely affect sperm fertilizingpotential. Discontinuation of such medications enhances thechances for conception.     

Trace eyeblink conditioning in patients with cerebellar degeneration: comparison of short and long trace intervals

To elucidate whether the cerebellar cortex may contribute to trace eyeblink conditioning in humans, eight patients with degenerative cerebellar disorders (four with sporadic adult onset ataxia, three with autosomal dominant cerebellar ataxia type III and one with spinocerebellar ataxia type 6) and eight age- and sex-matched healthy control subjects were investigated. Individual high resolution three-dimensional MRI data sets were acquired. As revealed by volumetric measurements of the cerebellum using ECCET software, patients showed cerebellar atrophy to various degrees. No abnormalities were observed in the control subjects. Eyeblink conditioning was performed twice using a tone of 40 ms as conditioned stimulus, followed by a short (400 ms) and a long (1,000 ms) trace interval and an air-puff of 100 ms as unconditioned stimulus. Using the short trace interval, eyeblink conditioning was significantly impaired in cerebellar patients compared to controls, even in those who fulfilled criteria of awareness. Using the long trace interval no significant group differences could be observed. The present findings of impaired trace eyeblink acquisition in patients with cortical cerebellar degeneration suggest that the cerebellar cortex in humans, in addition to the interposed nucleus, is involved in trace eyeblink conditioning, if the trace interval is relatively short. Using a long trace interval, the cerebellum appears to be less important.