Biomedical subjects

M D Holder

Publications and source records attributed to M D Holder.

24 records · Page 2Linked to original sources

PubMed1985

Time, space and value.

The ability of animals to associate stimuli depends on whether the stimuli are processed by the cognitive system or the affective system. Historically, a distinction was made between "thinking" and "feeling" by the empirical philosophers of the Renaissance. Recent evidence indicates that cognition and affect can be fruitfully applied to animal research. When animals are required to search an external environment for hidden food baits, they display an objective mastery of time and space as if they have acquired a "cognitive map" of the test area. Tests of an animal's ability to span the time between two external events yield intervals which can best be measured in seconds or fractions thereof. When animals consume a food, the affective value of that food is adjusted according to its utility in the internal milieu. If the food is nutritious, visceral feedback raises the preference value of the food. If nausea ensues, the taste becomes disgusting. Tests of an animal's ability to span the time between eating and nausea yield intervals which can best be described in hours or fractions thereof. Cognitive and affective processes are qualitatively distinct and subserved by different neural systems, yet they are both essential for associative learning. We offer a theoretical scheme designed to weld the two components into a single unitary sequence.

Affect↗

PubMed1985

Comparison of timing and classical conditioning.

Four experiments with rats investigated if the timing of a stimulus (sound) correlated with the strength of a conditioned response (CR) to the stimulus. The timing (effective duration) of the stimulus was measured using the peak procedure, similar to a discrete-trials fixed-interval procedure. The rats were trained so that their response rate reached a maximum about 40 s or 60 s after the onset of a light; the time of the maximum measured from the start of the light (peak time) was the measure of timing. On some trials, the light was preceded by a short (5 s) or long (20 s or 30 s) interval of sound. We assumed that the difference in peak time after long and short sounds reflected the timing of the sound--if the sound was timed, the longer sound would produce a lower peak time; if the sound was not timed, the two durations of sound would produce the same peak time. The CR was lever-pressing during the sound. The sound was treated in various ways: presented alone (Experiments 1, 3, and 4), followed by food (Experiments 1, 3, and 4), preceded by food (Experiment 3), and followed by food after 20 s (Experiment 4). Treatments that produced no timing of sound produced no CR, and treatments that increased (or diseased) timing also increased (or decreased) the CR. The results suggest that there is overlap between the mechanisms that produce time discrimination and the mechanisms that produce classical conditioning.

Animals↗

PubMed1984

The function of time discrimination and classical conditioning.

This paper makes three main points: There are many similarities between man-made rules for detecting causality and "laws" of classical conditioning, presumably generated by nature. They suggest that the function of classical conditioning resembles the detection of causality. There are twelve similarities between the clock used by rats to discriminate time and a stopwatch. They suggest that the rat's clock, like a stopwatch, was designed for measuring unknown durations. There are eight similarities between time discrimination and classical conditions. In particular, whether or not a stimulus is timed depends on the signal value of the stimulus. The similarities suggest that time discrimination and classical conditioning - their underlying mechanisms - have similar functions.

Animals↗

PubMed1984

What starts an internal clock?

Five experiments with rats investigated under what conditions a stimulus is timed by the internal clock used in time-discrimination procedures. In Experiments 1-4, we trained rats to time one stimulus (e.g., light) and then asked whether they timed a stimulus from another modality (e.g., sound). The second stimulus was treated in three ways: exposed (presented alone), paired with food, and extinguished. Experiments 1 and 2 used the peak procedure, similar to a discrete-trial fixed-interval schedule, and paired the treated stimulus with food using instrumental training; Experiments 3 and 4 used a psychophysical choice procedure and paired the treated stimulus with food using classical conditioning. All four experiments found that there was cross-modal transfer of the time discrimination after pairing, but not after exposure or extinction. This suggests that the rat's internal clock timed the treated stimulus after pairing, but not after exposure or extinction. Experiment 5 tested a theory of extinction based on the results of Experiments 1-4; the results suggested that the decline of responding observed in extinction is not due to changes in timing. The main conclusion is that the internal clock apparently times stimuli with signal value (associative strength) and does not time stimuli without signal value.

Animals↗

PubMedDate not supplied

Effects of naloxone and cholecystokinin on food and water intake in vasopressin-deficient rats (Brattleboro strain).

Opioid peptides and cholecystokinin (CCK) have been shown to play a role in regulation of feeding behavior. Another neuropeptide that has recently been suggested to be involved in feeding is vasopressin. We explored possible interactions between opiates, CCK and vasopressin in feeding regulation by studying feeding suppression produced by naloxone and CCK in Brattleboro (DI) rats, which are homozygous for diabetes insipidus and lack the ability to synthesize vasopressin. Ten DI and 15 age-matched Long Evans (LE) rats were food deprived for 14 hours on two different days and then injected with naloxone (2.5 mg/kg) on one day or saline on the other. Thirty minutes later the food was returned and food and water consumption were measured after 1, 3 and 4 hr. Naloxone suppressed the food consumption of both DI and LE rats but the suppression was greater for the DI rats. This result was specific to feeding as water consumption was suppressed in LE more than in DI rats. Two weeks later, the same rats were food deprived for 6 hours on two different days and then injected with CCK-8 (2.5 micrograms/kg) on one day and with saline on the other. Food was returned one minute after the injection and food and water consumption were measured 30 and 60 minutes later. Food intake was reduced equally for both DI and LE rats. Water intake was not reduced. The results suggest that the suppression of feeding by CCK does not require an intact vasopressinergic system. The greater feeding suppression by naloxone in DI rats may suggest that opiates are interacting with vasopressin in producing their effects on food intake.

Animals↗

PubMedDate not supplied

Effects of perinatal exposure to aspartame on rat pups.

Possible effects of perinatal exposure to L-aspartyl-L-phenylalanine methyl ester (aspartame) on rat pups were investigated. Adult female rats, and later their pups, were exposed, via their drinking water, to aspartame (0.007%, 0.036%, 0.18% or 0.9% w/v) or phenylalanine (0.45% w/v) for 12 days prior to conception until the pups were 38 days old. Control rats were given plain water. The adults exposed to aspartame consumed an average of 14, 68, 347 and 1614 mg/kg/day of aspartame and those exposed to phenylalanine consumed an average of 835 mg/kg/day of phenylalanine. After weaning the pups given aspartame consumed an average of 32, 154, 836, and 3566 mg/kg/day of aspartame and those given phenylalanine consumed an average of 1795 mg/kg/day of phenylalanine. No effect of aspartame or phenylalanine was detected on either two measures of morphological development (i.e., latencies to pinnae detachment and eye opening) or two tests of reflex development (i.e., latencies for surface righting at 7 days of age and negative geotaxis at 8 days of age). All groups were similar in spatial memory as assessed with two different mazes with pups 30-36 days old. The number of arms before reentry in an 8-arm radial-arm maze and the acquisition curves from a milk maze did not differ between groups. Furthermore, the latencies of mothers to retrieve their litters was also unaffected by the aspartame and phenylalanine. These results indicate that perinatal exposure to aspartame, when voluntarily consumed by mothers (14-1614 mg/kg/day) and later directly by the rat pups (32 to 3566 mg/kg/day) does not affect reflex development, morphological development or spatial memory.

Animals↗