John W. Davenport

The symmetrical maze: An automated closed-field test series for rats

An automated “intelligence” test for rats is described. Supporting data indicate that this maze-problem series is sensitive to hypothyroidism-induced learning deficit and sex differences. Comparisons between this new problem set and the Rabinovitch-Rosvold (1951) closed-field tests are presented with respect to difficulty, internal consistency, and test-retest reliability.

Hypothyroidism: learning deficit induced in rats by early exposure to thiouracil.

Abstract Two experiments were conducted with rats to investigate long-term behavioral consequences of prenatal and early postnatal exposure to the antithyroid drug thiouracil. In Experiment 1, groups of rats which received varying doses of thiouracil, via transplacental and transmammary passage for 16 prenatal and 16 postnatal days, displayed dose-related performance deficits as adults in a closed-field maze series. When exposure to thiouracil was confined to the prenatal period (Experiment 2), reflexes appearing within the first 3 postnatal weeks were slightly retarded in their development but no maze learning deficit was found in adulthood. The studies indicated that early postnatal thyroid deficiency in rats results in enduring deficits in learning capacity even when overall physical retardation is only temporary, and supported the view that the lower age boundary of the critical period of thyroid deficiency in rats falls at approximately the time of birth.

Environmental Therapy in Hypothyroid and Other Disadvantaged Animal Populations

Bluntly stated, our ultimate concern in this chapter is whether mental deficiency can be alleviated by environmental Stimulation. But since we will restrict our attention to subhuman studies bearing on this question, let us change the language at once from “mental deficiency” to “behavioral deficits,” and let the implications of these studies for the understanding and treatment of human behavioral dysfunctions emerge under their own power. Our focus will be on the question of whether the environmental stimulation conditions which have produced many kinds of brain changes in rodent studies (e.g., Rosensweig et al 1972; Greenough 1975) also result in improved behavioral capacities, particularly those reflected by performance in learning situations. We will examine this question in normal animals of both rodent and primate species, but our major concern will be with animal populations which are disadvantaged in their neural development and adult learning capacities by hormonal abnormalities, undernutrition, genetic factors, or other detrimental conditions in early life.

Temporal persistence of frustration effects in monkeys and rats

Rhesus, stumptail, and squirrel monkeys and rats were tested in various retractable-lever analogues of the double runway commonly used to study the Amsel frustration effect in rats. Variation of the midtrial interval (MTI), analogous to midbox confinement time in the runway, showed response speed in the second half of a trial to be an increasing function of the MTI following first-half reward and to persist at a supernormal level on frustration trials, suggesting the operation of two types of frustration effect which persist beyond 40 sec.

Severity and timing of early thyroid deficiency as factors in the induction of learning disorders in rats

Abstract In Experiment 1 ( N = 277 rats), more extreme deficits in maze learning than heretofore shown appeared in the adult offspring of mothers exposed for 16 pre- and 16 postnatal days to thiouracil-treated mash diets in doses up to 0.3%; the same offspring also displayed deficits in single-alternation pattern learning and a modified operant discrimination task. Surprisingly small maze learning deficits, however, were found in the offspring of mothers which received thiouracil during the 16 postnatal days only, despite previous findings indicating that the postnatal half of the total 32-day perinatal period was the more critical in determining later learning impairments. Reconciliation was provided by Experiment 2 ( N = 54), in which the manipulation of a 0.2% thiouracil diet starting at birth or 3, 6, 10, or 15 days before birth indicated a lower age boundary of the critical period for the induction of maze learning deficit by thyroid deficiency at approximately the fetal age at which thyroid tissue becomes functional-around the 18th day of gestation.

The Amsel frustration effect in monkeys

Four adolescent stumptail macaques were tested in a discrete-trials retractable-lever analogue of the double runway commonly used to study frustration effects in rats. Each trial consisted of fixed-ratio responding on a left lever followed by an identical contingency on a right lever. In agreement with runway data in rats, right-lever responses were faster following nonrein-forcement than following reinforcement of left-lever responses.

Cretinism in Rats: Enduring Behavioral Deficit Induced by Tricyanoaminopropene

Rats reared on diets containing tricyanoaminopropene, the antithyroid compound that stimulates RNA synthesis, showed a deficit in performance on automated closed-field maze tests many weeks after discontinuation of the drug. The rats were also tested while still receiving the drug, and performance deficits were indicated in tests of Y-maze reversal and manual closed-field maze performance; rats treated with the drug and with thiouracil behaved in a highly similar fashion on several tasks. No evidence of facilitation by tricyanoaminopropene appeared in any of the eight learning situations used. Exposure to tricyanoaminopropene before and after birth, at doses sufficient to produce anatomical cretinism, apparently induces an enduring behavioral deficit which is similar to that of neonatal thyroidectomy-induced cretinism in rats and which parallels the mental retardation associated with human cretinism.

Higher-order conditioning of fear (CER)

Stable higher-order conditioning of an emotional response was found in a vast majority of rats given an extension of the CER suppression procedure. The phenomenon was demonstrated under a variety of conditions and frequently took the the form of total suppression in the presence of a stimulus which had never been paired with shock.

Neonatal hyperthyroidism: Maturational acceleration and learning deficit in triiodothyronine-stimulated rats

Rat pups injected on Postnatal Days 2-4 with subcutaneous doses of triiodothyronine (T3 ) up to 4 micrograms/g showed substantial accelerations in the maturation of swimming behavior, righting reflexes, and eye opening which were greater than the accelerations produced by neonatal thyroxine (T4 ) in a previous study. They also showed significantly higher activity in stabilimeter cages on Postnatal Day 13 but not an expected earlier peak than normal rats in the ontogeny-of-arousal functions obtained in stabilimeter testing. As adults, the T3 -treated rats displayed large maze learning deficits which were comparable in size to those produced by fairly severe thyroid deficiency in the perinatal period.

The semiautomatic Wisconsin general test apparatus

A semiautomatic version of the Wisconsin General Test Apparatus is described along with circuitry. Comparison data are provided for the semiautomatic and manual WGTA obtained under comparable procedures and conditions. Response latencies are given for go/no-go object discrimination problems and subsequent retention tests.