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PubMed2002

The basolateral complex of the amygdala is necessary for acquisition but not expression of CS motivational value in appetitive Pavlovian second-order conditioning.

The basolateral complex of the amygdala (ABL) is involved in processing information about stimulus motivational value. However, it is not clear whether the ABL is critical for acquisition, maintenance, or expression of this information. Our previous work has shown that ABL lesions made prior to training, block acquisition of an appetitive Pavlovian second-order conditioning task, in which performance is thought to depend on the acquisition of motivational (conditioned reinforcement) value by the first-order conditioned stimulus (CS). The present experiments examined the effects of ABL lesions made after first-order conditioning, when the CS acquires motivational value, but before second-order conditioning, the test for acquired value of that CS. Rats received pairings of a visual CS with a food reinforcer. They then received bilateral sham or excitotoxic lesions of the ABL. After recovery, they received pairings of a second-order auditory CS with the previously conditioned visual CS. In two experiments, both sham and lesioned rats acquired normal second-order conditioned behaviours. Some of the same rats were then given another round of second-order conditioning with novel CSs. In this case, when first-order training occurred after surgery, some second-order conditioned behaviours were impaired in lesioned rats. Tests of the associative underpinnings of second-order conditioned behaviours showed that those behaviours impaired by ABL lesions were based on stimulus-response associations. The results show that although the ABL is critical for second-order conditioning, this role is limited to acquisition of information about the motivational value of the first-order CS, and it is not critical for maintenance of this information or for its use in forming second-order associations.

Acoustic Stimulation↗
PubMed2003

Expression of conditional fear with and without awareness.

Conditional responding during simple Pavlovian conditioning is often characterized as a form of implicit memory. The extent to which this type of associative learning is independent of awareness is an issue of continuing debate. Previous studies have demonstrated conditioning in the absence of awareness. However, their results have been questioned based on methodological concerns with postexperimental questionnaires. In the present study, skin conductance response (SCR) and unconditioned stimulus (UCS) expectancy were measured concurrently as participants were exposed to a differential delay fear conditioning procedure in which one tone (CS+) predicted a loud white noise, whereas a second tone (CS-) was presented alone. UCS predictability was varied on a trial-by-trial basis by presenting conditioned stimuli (CSs) at volumes just above or below the perceptual threshold. Differential UCS expectancy (awareness) was observed only on perceived trials, whereas differential SCR developed on both perceived and unperceived trials. Although perceived stimuli elicited larger SCRs, the magnitude of conditioning, indexed by differential conditioned response expression (conditioned SCR to CS+ minus the SCR to CS-), was not influenced by stimulus perception. These data indicate that conditional fear can be expressed when individuals are unaware of fear-eliciting stimuli and suggest that the degree of conditioning is independent of awareness during differential Pavlovian fear conditioning.

Adult↗
PubMed1999

Operant conditioning of H-reflex increase in spinal cord--injured rats.

Operant conditioning of the spinal stretch reflex or its electrical analog, the H-reflex, is a new model for exploring the mechanisms of long-term supraspinal control over spinal cord function. Primates and rats can gradually increase (HRup conditioning mode) or decrease (HRdown conditioning mode) the H-reflex when reward is based on H-reflex amplitude. An earlier study indicated that HRdown conditioning of the soleus H-reflex in rats is impaired following contusion injury to thoracic spinal cord. The extent of impairment was correlated with the percent of white matter lost at the injury site. The present study investigated the effects of spinal cord injury on HRup conditioning. Soleus H-reflexes were elicited and recorded with chronically implanted electrodes from 14 rats that had been subjected to calibrated contusion injuries to the spinal cord at T8. At the lesion epicenter, 12-39% of the white matter remained. After control-mode data were collected, each rat was exposed to the HRup conditioning mode for 50 days. Final H-reflex amplitudes after HRup conditioning averaged 112% (+/-22% SD) of control. This value was significantly smaller than that for 13 normal rats exposed to HRup conditioning, in which final amplitude averaged 153% (+/-51%) SD of control. As previously reported for HRdown conditioning after spinal cord injury, success was inversely correlated with the severity of the injury as assessed by white matter preservation and by time to return of bladder function. HRup and HRdown conditioning are similarly sensitive to injury. These results further demonstrate that H-reflex conditioning is a sensitive measure of the long-term effects of injury on supraspinal control over spinal cord functions and could prove a valuable measure of therapeutic efficacy.

Animals↗
PubMed1992

No evidence of classical conditioning of electrodermal responses during anesthesia.

Classical conditioning of skin conductance responses was studied in 26 healthy volunteers and 31 patients who received general anesthesia (0.5 MAC isoflurane-70% nitrous oxide) for minor gynecologic surgery to determine whether there was autonomic evidence of new learning during anesthesia. In the conditioning phase, a loud noise was paired with a target word (conditioned stimulus [CS]). Conditioning was established if the CS produced conditioned responses, i.e., greater skin conductance responses than other, "filler words." In the subsequent elicitation phase, we investigated whether it was possible to elicit similar conditioned responses to the CS when it was presented without noise about 3 h later. Conditioning was established in the control group, who received no anesthesia. There were differences in response magnitudes of 0.32 and 0.27 mu siemen between responses to the CS and filler words, P less than 0.001. In contrast, there was no evidence that conditioning was established during anesthesia. In the elicitation phase, conditioned responses to the CS could be elicited in volunteers; i.e., response magnitudes were greater for the CS than other words (during the first two blocks of trials), with differences of 0.19 to 0.48 mu siemen, P less than 0.05 to P less than 0.001. In contrast, responses to the CS could not be elicited in patients after anesthesia. There was also no evidence of recognition of words that were presented during anesthesia in patients, but recognition was manifested in volunteers. Thus, in contrast to our previous demonstration of conditioning in subjects who received 30% nitrous oxide in oxygen, there was no evidence of conditioning in anesthetized patients.

Adult↗
PubMed1995

The effects of AMPA-induced lesions of the septo-hippocampal cholinergic projection on aversive conditioning to explicit and contextual cues and spatial learning in the water maze.

The environmental context of an animal both subsumes and is associated with the explicit cues that guide its behavioural responses. Recent work in this laboratory suggests that learning about the relationship between the cues which comprise a context depends on the hippocampus. In the present study the role of the cholinergic input to the hippocampus in contextual learning was assessed in rats using a conditioned stimulus/context conditioning paradigm and spatial learning in the Morris water maze. In the former, a place preference apparatus provided the context. The subject was confined in the black chamber and a 'clicker' conditioned stimulus was presented five times in a 20 min period. A trace interval of 5 or 30 s, depending on the group, was interposed between the end of the clicker and a footshock. Theory predicts that animals in the 5 s condition will learn more about the clicker as a predictor of shock and become strongly conditioned, while those in the 30 s condition learn relatively more about the context. Conditioning to the clicker (conditioned stimulus) was measured in a separate lick suppression chamber--presentation of the clicker suppresses drinking, and contextual learning was determined by recording the time spent on the black side of the place preference apparatus when both the black and a familiar white chamber were accessible. Lesions of the medial septum/diagonal band induced by RS-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) enhanced contextual learning in this paradigm but disrupted conditioned stimulus conditioning in the 30 s condition. Acquisition of the Morris water maze was largely unimpaired. The results are suggested to reflect a shift towards the use of hippocampal-dependent contextual learning strategies in lesioned animals.

Acetylcholine↗
PubMed2003

Protein synthesis in the amygdala, but not the auditory thalamus, is required for consolidation of Pavlovian fear conditioning in rats.

The amygdala is an essential neural substrate for Pavlovian fear conditioning. Nevertheless, long-term synaptic plasticity in amygdaloid afferents, such as the auditory thalamus, may contribute to the formation of fear memories. We therefore compared the influence of protein synthesis inhibition in the amygdala and the auditory thalamus on the consolidation of Pavlovian fear conditioning in Long-Evans rats. Rats received three tone-footshock trials in a novel conditioning chamber. Immediately after fear conditioning, rats were infused intra-cranially with the protein synthesis inhibitor, anisomycin. Conditional fear to the tone and conditioning context was assessed by measuring freezing behaviour in separate retention tests conducted at least 24 h following conditioning. Post-training infusion of anisomycin into the amygdala impaired conditional freezing to both the auditory and contextual stimuli associated with footshock. In contrast, intra-thalamic infusions of anisomycin or a broad-spectrum protein kinase inhibitor [1-(5'-isoquinolinesulphonyl)-2-methylpiperazine, H7] did not affect conditional freezing during the retention tests. Pre-training intra-thalamic infusion of the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (APV), which blocks synaptic transmission in the auditory thalamus, produced a selective deficit in the acquisition of auditory fear conditioning. Autoradiographic assays of cerebral [14C]-leucine incorporation revealed similar levels of protein synthesis inhibition in the amygdala and thalamus following intra-cranial anisomycin infusions. These results reveal that the establishment of long-term fear memories requires protein synthesis in the amygdala, but not the thalamus, after auditory fear conditioning. Forms of synaptic plasticity that depend on protein synthesis, such as long-term potentiation, are likely candidates for the encoding and long-term storage of fear memories in the amygdala.

Amygdala↗
PubMed2004

Latent inhibition of cued fear conditioning: an NMDA receptor-dependent process that can be established in the presence of anisomycin.

Much of the research examining the biological basis for long-term memories has focused on mechanisms that support the formation of conditioned associations. Less information is available on biological mechanisms which underlie processes that modify the strength of conditioned associations. Latent inhibition is a phenomenon by which pre-exposure to a to-be-conditioned stimulus (CS) weakens subsequent conditioning of that CS to an unconditioned stimulus (US). Here we report that latent inhibition of cued fear conditioning is dependent on NMDA receptor activation. MK-801 (1 mg/kg), an NMDA receptor antagonist, abolished latent inhibition of cued fear conditioning. This dose of MK-801 administered before training did not disrupt cued fear conditioning. Conversely, anisomycin (150 mg/kg), a protein synthesis inhibitor, had no effect on latent inhibition of cued fear conditioning when administered 20 min before, immediately after, or 2, 4, 6, or 8 h after CS pre-exposure. Furthermore, continuous anisomycin administration (50 mg/kg, administered every 2 h for 6 h starting 20 min prior to pre-exposure) did not disrupt latent inhibition of cued fear conditioning. In addition, anisomycin had no effect on a long-lasting version of latent inhibition of cued fear conditioning that was maintained over a 7-day interval. Anisomycin administered before training, however, disrupted learning of the CS-US association. These findings suggest that latent inhibition of cued fear conditioning is a long-lasting NMDA receptor-dependent process that can develop during the inhibition of protein synthesis.

Analysis of Variance↗
PubMed1999

Effects of conditioning horses with lactate-guided exercise on muscle glycogen content.

The effects of 3 different conditioning programmes on muscle glycogen concentration in horses were examined. Speed of exercise was selected according to the blood lactate values for each horse derived from a standardised exercise test before beginning a conditioning programme. Six 2-year-old Haflinger stallions were assigned randomly to one of 3 conditioning programmes according to a 6 x 3 latin square design: 45 min at their individual v1.5 or v2.5 and 25 min at v4. Each conditioning programme lasted 6 weeks (21 exercise sessions), followed by 5 weeks without conditioning (resting period). All exercise was carried out on a treadmill inclined at 17%. Muscle biopsies were taken 5 times from the gluteus medius muscle at 2 cm and 6 cm depth: before the start and in the middle of the conditioning period, then at Days 2, 9 and 35 after the last exercise session. It was found that glycogen concentration was not affected by conditioning until 9 days after finishing conditioning at v1.5 and v2.5 for 45 min (P < 0.05). By this time glycogen concentration in the muscle samples taken at 6 cm depth increased by 47 and 48%, respectively, and remained elevated until the end of the resting period. It was concluded that conditioning at lower intensity and for longer duration seemed to increase glycogen stores in the muscle while faster intensity but shorter duration exercise did not. To increase the likelihood of measuring effects of conditioning programmes on muscle variables, sampling should be done at different depths of a muscle and at several days after finishing a conditioning programme.

Animals↗
PubMed1997

Enhanced synaptic transmission in CA1 hippocampus after eyeblink conditioning.

CA1 field potentials evoked by Schaffer collateral stimulation of hippocampal slices from trace-conditioned rabbits were compared with those from naive and pseudo-conditioned controls. Conditioned rabbits received 80 trace conditioning trials daily until reaching a criterion of 80% conditioned responses in a session. Hippocampal slices were prepared 1 or 24 h after reaching criterion (for trace-conditioned animals) or after a final unpaired stimulus session (for pseudo-conditioned animals); naive animals were untrained. Both somatic and dendritic field potentials were recorded in response to various stimulus durations. Recording and data reduction were performed blind to the conditioning state of the rabbit. The excitatory postsynaptic potential slope was greater in slices prepared from trace-conditioned animals killed 1 h after conditioning than in naive and pseudo-conditioned controls (repeated-measures analysis of variance, F = 4.250, P < 0.05). Associative learning specifically enhanced synaptic transmission between CA3 and CA1 immediately after training. This effect was not evident in the population field potential measured 24 h later.

Animals↗
PubMed1997

Quantal organization of reflex and conditioned eyelid responses.

Quantal organization of reflex and conditioned eyelid responses. J. Neurophysiol. 78: 2518-2530, 1997. Upper lid movements and the electromyographic activity of the orbicularis oculi muscle were recorded in behaving cats during spontaneous and experimentally evoked reflex blinks, and conditioned eyelid responses. Reflex blinks evoked by the presentation of air puffs, flashes, or tones consisted of a fast downward lid movement followed by late, small downward waves, recurring at approximately 50-ms intervals. The latency, maximum amplitude, peak velocity, and number of late waves depended on the modality, intensity, and duration of the evoking stimulus. The power spectra of acceleration records indicated a dominant frequency of approximately 20 Hz for air puff-evoked blinks. Flashes and tones usually evoked small and easily fatigable reflex responses of lower dominant frequencies (14-17 and 9-11 Hz, respectively). A basic approximately 20-Hz oscillation was also noticed during lid fixation, and ramplike lid displacements evoked by optokinetic stimuli. Five classical conditioning paradigms were used to analyze the frequency-domain properties of conditioned eyelid responses. These learned lid movements differed in latency, maximum amplitude, and profile smoothness depending on the modality (air puff, tone), intensity (weak, strong), and presentation site (ipsi-, contralateral to the unconditioned stimulus) of the conditioned stimulus. It was found that the characteristic ramplike profile of a conditioned response was not smooth, but appeared to be formed by a succession of small waves at a dominant frequency of approximately 20 Hz. The amplitude (and number) of the constituting waves depended on the characteristics of the conditioned stimulus and on the time interval until unconditioned stimulus presentation. Thus conditioned responses seemed to be formed from lid displacements of 2-6 degrees in amplitude and approximately 50 ms in duration, which increased in number throughout conditioning sessions, until a complete (i.e., lid closing) conditioned response was reached. It is suggested that a approximately 20-Hz oscillator underlies the generation of reflex and conditioned eyelid responses. The oscillator is susceptible to being neurally modulated to modify the velocity of a given quantum of movement, and the total duration of the lid response. Learned eyelid movements are probably the result of a successively longer release of the oscillator as a function of the temporal-spatial needs of the motor response.

Acoustic Stimulation↗
PubMed2005

The interaction of a new motor skill and an old one: H-reflex conditioning and locomotion in rats.

New and old motor skills can interfere with each other or interact in other ways. Because each skill entails a distributed pattern of activity-dependent plasticity, investigation of their interactions is facilitated by simple models. In a well characterized model of simple learning, rats and monkeys gradually change the size of the H-reflex, the electrical analog of the spinal stretch reflex. This study evaluates in normal rats the interactions of this new skill of H-reflex conditioning with the old well established skill of overground locomotion. In rats in which the soleus H-reflex elicited in the conditioning protocol (i.e., the conditioning H-reflex) had been decreased by down-conditioning, the H-reflexes elicited during the stance and swing phases of locomotion (i.e., the locomotor H-reflexes) were also smaller. Similarly, in rats in which the conditioning H-reflex had been increased by up-conditioning, the locomotor H-reflexes were also larger. Soleus H-reflex conditioning did not affect the duration, length, or right/left symmetry of the step cycle. However, the conditioned change in the stance H-reflex was positively correlated with change in the amplitude of the soleus locomotor burst, and the correlation was consistent with current estimates of the contribution of primary afferent input to the burst. Although H-reflex conditioning and locomotion did not interfere with each other, H-reflex conditioning did affect how locomotion was produced: it changed soleus burst amplitude and may have induced compensatory changes in the activity of other muscles. These results illustrate and clarify the subtlety and complexity of skill interactions. They also suggest that H-reflex conditioning might be used to improve the abnormal locomotion produced by spinal cord injury or other disorders of supraspinal control.

Animals↗
PubMed2004

Differential effects of cerebellar, amygdalar, and hippocampal lesions on classical eyeblink conditioning in rats.

Eyeblink conditioning has been hypothesized to engage two successive stages of nonspecific emotional (fear) and specific musculature (eyelid) learning, during which the nonspecific component influences the acquisition of the specific component. Here we test this notion by investigating the relative contributions of the cerebellum, the amygdala, and the hippocampus to the emergence of conditioned eyelid and fear responses during delay eyeblink conditioning in freely moving rats. Periorbital electromyography (EMG) and 22 kHz ultrasonic vocalization (USV) activities were measured concurrently from the same subjects and served as indices of conditioned eyeblink and fear responses, respectively. In control animals, conditioned EMG responses increased across training sessions, whereas USV responses were initially robust but decreased across training sessions. Animals with electrolytic lesions to their cerebellum (targeting the interpositus nucleus) were completely unable to acquire conditioned EMG responses but exhibited normal USV behavior, whereas animals with lesions to the amygdala showed decelerated acquisition of conditioned EMG responses and displayed practically no USV behavior. In contrast, hippocampal lesioned rats demonstrated facilitated acquisition of conditioned EMG responses, whereas the USV behavior was unaffected. The amygdalar involvement in eyeblink conditioning was examined further by applying the GABA(A) agonist muscimol directly into the amygdala either before or immediately after training sessions. Although pretraining muscimol infusions impaired conditioned EMG responses, post-training infusions did not. Together, these results suggest that, even during a simple delay eyeblink conditioning, animals learn about different aspects associated with the behavioral task that are subserved by multiple brain-memory systems that interact to produce the overall behavior.

Amygdala↗
PubMed2001

Single-cue delay eyeblink conditioning is unrelated to awareness.

We examined the importance of awareness for eyeblink conditioning by directly comparing single-cue delay eyeblink conditioning and single-cue trace eyeblink conditioning. During single-cue delay conditioning, participants who became aware of the stimulus contingencies early in the conditioning session conditioned no better than those who became aware later in the session or did not become aware. Thus, the level of awareness was unrelated to the overall level of conditioning across the session. In contrast, awareness of the stimulus contingencies early in the session predicted the success of single-cue trace conditioning. These data, together with earlier findings, show that awareness is irrelevant to single-cue delay eyeblink conditioning but is critical for single-cue trace eyeblink conditioning. The findings from the present study are related to previous findings for differential (CS+ and CS-) eyeblink conditioning and awareness.

Aged↗
PubMed1985

[Acquisition of audio-visual conditional discrimination in pigeons].

Pigeons were trained on a cross-modal conditional discrimination task in which the subjects were required to select visual comparison stimuli depending upon auditory conditional stimuli. In simultaneous condition, the auditory conditional stimuli were presented until the subjects selected one of the two visual stimuli. All subjects attained above 80% correct responses within 21-64 sessions. After simultaneous condition, all subjects were trained in 0-1-2- and 3-s delayed conditions. They showed above 80%-90% correct responses in zero delayed training. In 1-s and 2-s delayed conditions, the percentage of correct responses was not significantly different in comparison with 0-s delayed condition. The results indicated that pigeons could learn audio-visual cross-modal conditional discrimination task both in simultaneous and delayed conditions and had no greater difficulty learning them than learning visual (unimodal) conditional discrimination.

Acoustic Stimulation↗
PubMed2003

The burden of musculoskeletal conditions at the start of the new millennium.

Musculoskeletal conditions are extremely common and include more than 150 different diseases and syndromes, which are usually associated with pain and loss of function. In the developed world, where these conditions are already the most frequent cause of physical disability, ageing of the most populous demographic groups will further increase the burden these conditions impose. In the developing world, successful care of childhood and communicable diseases and an increase in road traffic accidents is shifting the burden to musculoskeletal and other noncommunicable conditions. To help better prepare nations for the increase in disability brought about by musculoskeletal conditions, a Scientific Group meeting was held to map out the burden of the most prominent musculoskeletal conditions at the start of the Bone and Joint Decade. In particular, the Group gathered data on the incidence and prevalence of rheumatoid arthritis, osteoarthritis, osteoporosis, major limb trauma and spinal disorders. Data were collected and organized by world region, gender and age groups to assist with the ongoing WHO Global Burden of Disease 2000 study. The Group also considered what is known about the severity and course of these conditions, along with their economic impact. The most relevant domains to assess and monitor the consequences of these conditions were identified and used to describe health states for the different stages of the conditions. Instruments that measure these most important domains for the different conditions were recommended. It is clear from data collated that the impact from musculoskeletal conditions and trauma varies among different parts of the world and is influenced by social structure, expectation and economics, and that it is most difficult to measure impact in less developed nations, where the predicted increase is greatest.

Adolescent↗
PubMed1995

Electrolyte and total protein changes in nonheat acclimated horses performing treadmill exercise in cool (20 degrees C/40%RH), hot, dry (30 degrees C/40%RH) or hot, humid (30 degrees C/80%RH) conditions.

Four horses (H, J, N and M) undertook a simulated competition exercise test (CET), designed to simulate physiological and metabolic stresses of the Speed and Endurance (S & E) test of a 3-day-event, under 3 different environmental conditions: 20 degrees C/40% relative humidity (RH) (cool, dry [CD] 2 sessions); 30 degrees C/40% RH (hot, dry [HD]) and 30 degrees C/80% RH (hot, humid [HH]) (Marlin et al. 1995a). Venous blood samples for electrolyte and total protein (TP) determinations were collected from indwelling catheters at predetermined time points throughout each CET and initial 30 min recovery period. Venous blood samples were collected by jugular venepuncture at 2 h and 24 h after the end of the final 8 min canter (Phase D). The effects of exercise, environmental condition and horse on venous TP, sodium (Na+), potassium (K+), chloride (Cl-), calcium (Ca2+), magnesium (Mg2+) and phosphate (PO4(3-)) plasma concentrations were investigated. In addition, the effect of environmental condition on estimated cation loss was evaluated. All horses completed the full CET under the CD and HD conditions, but only one horse completed the full 8 min of the final canter Phase D under HH conditions. Exercise had a significant (P < 0.05) effect on all parameters similar to those reported previously in field competitions. There was a significant (P < 0.05) interaction between time and horse for TP, Na+ and Cl-. Overall, the environmental condition had a significant (P < 0.05) effect on all parameters, but the differences were not considered to be of any physiological relevance, other than for Cl- and TP. There was a significant (P < 0.05) interaction between time and environmental condition for Cl- and TP only. During much of the CET and recovery period, mean Cl- values were higher with the first CD session than the second CD session or under the HH or HD conditions. For TP after 2 min of Phase D and during the initial recovery period, concentrations were higher under the HH conditions and returned to the Pre- values less quickly. There were marked individual variations in the estimated cation losses and no consistent effect of environmental condition was found. Although estimated fluid loss was similar following both HD and HH sessions, restoration of bodyweight was slower following the CET studies under HH conditions.

Acclimatization↗
PubMed1997

N-methyl-D-aspartate receptors in associative eyeblink conditioning: both MK-801 and phencyclidine produce task- and dose-dependent impairments.

The effects of N-methyl-D-aspartate receptor blockade on two major variants of rabbit eyeblink conditioning were evaluated using a selective noncompetitive antagonist, [5R, 10S]-[+]-5-methyl-10, 11-dihydro-5H-dibenzo[a, d] cyclo-hepten-5,10-imine hydrogen maleate; dizocilpine (MK-801) or phencyclidine (PCP), a drug of abuse. Either MK-801 or PCP (given daily) impaired rabbits' ability to associate tone conditioned stimuli with airpuff unconditioned stimuli, with the severity of impairment exhibiting clear dose and task dependencies. Trace-conditioned rabbits given > or = 80 micrograms/kg of MK-801 or > or = 1.0 mg/kg of PCP failed to reach a criterion of 80% conditioned responses during training, with significant impairments seen at intermediate doses. Delay-conditioned rabbits, although dose-dependently slowed, successfully acquired the task, even when given doses of MK-801 or PCP that completely blocked acquisition in trace conditioning. Additionally, even low doses of MK-801 (10 micrograms/kg) or of PCP (0.1 mg/kg) severely altered conditioned response timing in trace but not in delay conditioning, resembling effects observed after hippocampal lesions. Doses of MK-801 or PCP that impaired acquisition also severely impaired extinction of both trace- and delay-conditioned eyeblink responses. However, neither MK-801 nor PCP altered retention or timing of previously learned responses. Higher doses of MK-801 (> or = 200 micrograms/kg) or of PCP (> or = 2.0 mg/kg) dose-dependently impaired unconditioned response performance, although lower doses of MK-801 (< or = 160 micrograms/kg) or of PCP (< or = 1.0 mg/kg) had no effects on unconditioned responses or on non-associative pseudoconditioned responses. The deficits observed indicate that although not necessary for retention, N-methyl-D-aspartate receptor activation may facilitate acquisition of delay-conditioning. N-methyl-D-aspartate receptor activation appears to be necessary for acquisition of trace conditioning, and for extinction in either paradigm.

Animals↗
PubMed1996

Youth with chronic conditions and their transition to adulthood. Findings from a Finnish cohort study.

OBJECTIVE: To explore the effect of chronic health conditions in adolescence on eventual transitional paths and young adult functioning in a cohort of Finnish youths. DESIGN: Survey in school at age 16 years followed by postal questionnaire at age 22 years. METHODS: Youths who had reported persistent chronic conditions at ages 16 and 22 years were compared with peers without chronic health conditions, using two-way analysis of variance for continuous outcomes and logistic regression models for dichotomous outcomes, adjusting for socioeconomic differences. MAIN OUTCOME MEASURES: Health status, chronic conditions, personal characteristics (including self-esteem), health behavior, education, family background, personal relations, and depression. RESULTS: Adolescents with chronic health conditions attained levels of psychosocial well-being, education, and marriage or dating as young adults similar to their peers without chronic conditions. Most of them experienced a successful transition to adulthood. Females with chronic conditions were more likely than women without chronic conditions to have moved away from their family of origin and to be living with a spouse or steady partner. Our findings also suggest that males with chronic conditions from white-collar family backgrounds may be at increased risk for symptoms of depression in early adulthood. Youths with chronic conditions had similar rates of nicotine and alcohol consumption as their healthy peers. CONCLUSION: Our findings suggest that in this cohort, most adolescents with common chronic conditions had a successful transition to adulthood.

Adolescent↗