Neocortical transplants in the micrencephalic rat brain: morphology and behavior

Behavioral Effects of Neural Transplantation

Considerable evidence suggests that transplantation of fetal neural tissue ameliorates the behavioral deficits observed in a variety of animal models of CNS disorders. However, it is also becoming increasingly clear that neural transplants do not necessarily produce behavioral recovery, and in some cases have either no beneficial effects, magnify existing behavioral abnormalities, or even produce a unique constellation of deficits. Regardless, studies demonstrating the successful use of neural transplants in reducing or eliminating behavioral deficits in these animal models has led directly to their clinical application in human neurodegenerative disorders such as Parkinson's disease. This review examines the beneficial and deleterious behavioral consequences of neural transplants in different animal models of human diseases, and discusses the possible mechanisms by which neural transplants might produce behavior recovery.

Postnatal haloperidol eliminates the deficit in circling behavior produced by prenatal exposure to the same drug

Up to 35% of pregnant women take psychotropic drugs at least once during gestation [Austin and Mitchell, 1998]. From concurrent animal and human evidence, it has been proposed that exposure to several psychoactive medications in utero or during lactation increases the risk for permanent brain disorders. Present preventive or therapy practices applied on humans for this type of long-lasting behavioral alterations are mainly based on empirical results. Here, we test an experimental approach designed to counteract a circling performance deficit that appears in Sprague-Dawley rats at puberty on exposure to the dopaminergic blocker haloperidol (HAL) during gestation [J.L. Brusés, J.M. Azcurra, The circling training: A behavioral paradigm for functional teratology testing, in: P.M. Conn (Ed.), Paradigms for the study of behavior, Acad. Press, New York, 1993, pp. 166-179. Method Neurosci. 14]. Gestational exposure to HAL (GD 5-18, 2.5 mg/kg/day ip) induced the expected circling activity decrease in the offspring at the fifth week of life. When prenatal exposure to HAL was continued through lactation (PD5-21, 1.5 mg/kg/day ip), rats otherwise showed a control-like circling performance. No difference was yet found between lactation-only, HAL-exposed pups and saline (SAL)-treated controls (n=8 each group). We further performed saturating (3H)-spiroperidol (SPI) binding assays on striatal P2 membrane fractions 2 months later. The dopamine-type D2-specific binding results suggested that above circling behavior findings could be partially explained by enduring HAL-induced neurochemical changes. The role of critical periods of sensitivity as transient windows for opportunistic therapies for behavioral teratology is discussed.

Protective effects of fetal neocortical transplants on cognitive function and neuron size in rats with congenital micrencephaly

The rat with micrencephaly, produced by prenatal exposure to methylazoxymethanol, provides a useful model to study neurobehavioral abnormalities associated with congenital brain defects. The micrencephalic animals have a life-long learning impairment. As they age, their already impaired learning competence deteriorates further. To determine whether the aging-associated functional deterioration could be ameliorated by a neural transplant, micrencephalic rats bearing solid transplants of normal fetal neocortical tissue since infancy were evaluated on a visual pattern discrimination learning at 15 months and a spatial navigation test at 24 months of age. The transplant-bearing rats learned both tasks significantly better than the micrencephalic rats without transplants. Morphometric analyses revealed that cortical pyramidal neurons were larger in the transplant-bearing rats than in micrencephalic rats without transplants. The life-long presence of a transplant appeared to have protected the micrencephalic brain against aging-associated deterioration. This is the first demonstration that a neural transplant, placed in a congenitally defective infant brain, can ameliorate aging-associated cognitive deficits.

Fluoresein diacetate uptake to determine the viability of human fetal cerebral cortical cells

We investigated the accuracy of fluorescein diacetate uptake as an indicator of the viability of human fetal cerebral cortical cells. Cortical cells from 16-26-week-old normal fetuses were studied. The cortices were dissociated mechanically with normal saline to make a suspension. Fluorescein diacetate uptake and trypan blue exclusion were compared as methods for examining cell viability. Our results show that fluorescein diacetate uptake is a simple and sensitive method for examining human fetal cortical cell viability.

Anatomical and functional characteristics of fetal neocortex transplanted into the neocortex of newborn or adult rats

In humans, the cerebral cortex can be affected by a variety of diseases (vascular, traumatic, neurodegenerative, etc.) and, therefore, several experimental studies have been undertaken to determine to what extent transplantation of cortical neurons could prove a useful treatment for cerebral cortical damage. The purpose of this review is to give an evaluation of the different attempts of neocortical tissue transplantation which have been undertaken, mostly in rodents, during the last decade. First, we examine the functional effects of neocortical tissue transplantation in various tasks designed to assess different aspects of behavior depending upon the localization and function of the cortical area under investigation. Second, a variety of mechanisms have been proposed by which the graft would improve host behavioral capacities. Two of these are considered in this review: trophic action on the host brain and reconstruction of cortical circuitry. Most behavioral studies in rodents seem to indicate that better synaptic integration and larger functional improvements are achieved when the embryonic neocortical tissue is transplanted into immature host neocortex, i.e. in newborn recipients. Transplantation of embryonic neocortex into an adult damaged cortex seems to provide only partial functional improvement. In adult hosts, the synaptic integration of the transplanted neurons is incomplete since, in most instances, long distance projections are not re-established. It seems, therefore, that transplantation of embryonic cortex into adult hosts would prove a useful therapeutic method only if there is a possibility of neutralizing the growth inhibitory factors of the mature host CNS.