Spatial selectivity of rat hippocampal neurons: dependence on preparedness for movement

The mammalian hippocampal formation appears to play a major role in the generation of internal representations of spatial relationships. In rats, this role is reflected in the spatially selective discharge of hippocampal pyramidal cells. The principal metric for coding spatial relationships might be the organism's own movements in space, that is, the spatial relationship between two locations is coded in terms of the movements executed in getting from one to the other. Thus, information from the motor programming systems (or "motor set") may contribute to coding of spatial location by hippocampal neurons. Spatially selective discharge of hippocampal neurons was abolished under conditions of restraint in which the animal had learned that locomotion was impossible. Therefore, hippocampal neuronal activity may reflect the association of movements with their spatial consequences.

Early-life undernutrition impairs the development of the learning and short-term memory processes mediating performance in a conditional-spatial discrimination task

Previously undernourished and well-nourished control rats 23, 30, 40, and 90 days old were compared in a win-shift version of a conditional-spatial discrimination task. Control animals at each age were able to reach criterion on this problem. In contrast, the underfed rats were unable to solve this problem until they were at least 40 days old. The short-term memory of the 40- and 90-day-olds was further evaluated by increasing the interval between the forced run and choice run to 30, 60, and 180 s. Control animals could bridge all intervals; however, the undernourished animals' performance fell to chance when the interval was only 60 s. Thus, early-life undernutrition severely impaired the development of the ability of animals to solve spatial-conditional discrimination tasks and permanently impaired their short-term memory capacity. A simple threshold model relating undernutrition, brain development, and behavior is proposed to account for these data.

Pleuropulmonary actinomycosis associated with a systemic-to-pulmonary artery fistula and contralateral metastatic back mass

We report a case of systemic-to-pulmonary artery fistula associated with thoracic actinomycosis and with metastatic hematogenous dissemination to the soft tissues of the back. The difficulty in diagnosing thoracic actinomycosis may predispose to the increased incidence of hematogenous spread of this disease. Although resection of pulmonary tissue including the infectious mass was required in previous cases, resection of the pleural mass alone was curative in this patient when combined with penicillin therapy.

Early-life malnutrition impairs the performance of both young and adult rats on visual discrimination learning tasks

Previously malnourished young (20-40-day-old) and mature (70-77-day-old) rats were compared on position, brightness, and pattern discrimination problems using an aquatic version of the Lashley jump stand. Malnutrition did not affect performance on the position discrimination. In contrast, previously malnourished 24-34-day-olds failed to solve the brightness discrimination, 40-day-olds were impaired on the brightness problem, and 40-77-day olds were impaired on the pattern problem. The impaired performance of the 40-day-olds on the brightness problem was eliminated by prior training on the pattern discriminations, and the impaired performance of the 70-day-olds on the pattern discrimination could be eliminated if they were first trained on the brightness problem. These impairments were attributed to the effects of early-life malnutrition on the maturation of attention processes that enable the rat to suppress responding to irrelevant cues. The relevance of a contextual-organismic perspective for understanding the effects of early-life malnutrition was discussed.

Early-life malnutrition selectively retards the development of distal- but not proximal-cue navigation

The effects of early-life malnutrition on the distal-cue and proximal-cue versions of the Morris (1981) water maze were studied with different-aged rats. Consistent with the existing literature, malnutrition only mildly influenced the distal-cue navigation of relatively old pups (30 day olds). Pups 20-27 days old, however, displayed no evidence of distal-cue navigation if they had been malnourished previously. Malnutrition had no effect on proximal-cue based navigation by pups at any age. The effect of malnutrition on distal-cue performance could not be attributed to any general debilitating effects, sensory, motor, or motivational deficits. Instead, it appears to selectively influence the development of the neural system (perhaps the hippocampus and related structures) more directly involved in learning to utilize distal cues.