Long term neurodevelopmental and behavioral effects of perinatal life events in rats

Modern neurosciences are now able to open new avenues concerning an experimental approach to clinical neurosciences and psychiatry. Detection and prediction of potential vulnerabilities such as behavioral disturbances and neurodegenerative diseases, are urgent tasks leading to prevention that must be encouraged in parallel to the enormous efforts displayed for treatments. Besides possible genetic origins of diseases, environmental factors are now coming under scrutiny, and especially deleterious and challenging life events and stress occurring during prenatal and postnatal critical periods may orient brain functions towards deleterious developments. The hypothesis that will be examined is that early events might be at the origin of pathological transformations and symptoms after long periods of apparent normal abilities and behavioral homeostasis. We used models of prenatal stress and postnatal manipulations such as cross-fostering. It will be demonstrated that such events induce long-term changes, cognitive and emotional modifications appearing first, when offspring are adults, followed by cognitive defects later in life. Increased sensitivity of the hypothalamic pituitary-adrenal axis (HPA), the endocrine system controlling the secretion of stress hormones (corticoids), appears to be a major element of pathogenesis. HPA axis dysfunction appears very early after birth (3 days) and lasts for months. Cumulative exposure to high levels of hormones seems to be detrimental for some brain regions, especially the hippocampus and major neurotransmitter systems such as dopamine neurons. We evidenced that neuronal modifications in hippocampal region are correlated with behavioral and cognitive defects, relating environment, stress in early life, hormonal changes, long-term neuropathological processes and impaired cognition in aging. Moreover appears in offspring, when adults, a proneness to engage in drug dependence. These data emphasize the need to consider early environmental life events as etiological factors for delayed neuropsychiatric disturbances, neurodegenerative defects included. Moreover, they strengthen the interest for a longitudinal approach to promote experimental psychopathology.

Influence of environment on the efficacy of intrastriatal dopaminergic grafts

Functional recovery is influenced by experience. The aim of the present work was to examine the effects of "enriched" environment (EE) versus an "impoverished" environment on the anatomical and functional integration of intrastriatal dopaminergic grafts. These influences were studied using a paradigm where grafting was performed before the dopamine-depleting lesion. Dopaminergic grafts were implanted into the left neostriatum of adult male rats. In the enriched group, grafted rats were housed collectively and were trained on different behavioral tests following grafting. In contrast, impoverished grafted rats were housed individually and not further manipulated. Ten weeks after grafting, the mesotelencephalic dopaminergic pathway was destroyed unilaterally to the grafted side and different behaviors were followed for 7 months. Grafting prior to lesioning had no prophylactic effects on the performance as the graft did not prevent the onset of the lesion-induced impairments. However, under EE conditions, a graft effect was manifested in the reduction of drug-induced rotation and on the indices of bias as tested by a spatial alternation test. No positive graft effects were observed in the skilled paw reaching test. Grafted rats raised under impoverished conditions performed in a fashion indistinguishable from the control lesioned animals on most measures of behavior. A beneficial effect of EE conditions was observed on survival of TH-positive neurons within the grafts. The results suggest that survival of grafted neurons, and the reduction of the magnitude of particular behavioral impairments, can be optimized by increasing the complexity of the subject's environment.

[Corticosteroid hormones and the brain]

The anatomical and functional links between the hormone stress axis and the cortico-limbic brain regions which integrate emotion and motivation are well documented. It is important, considering the consequences of stress on the brain, to take into account the regulatory buffer capacities of the personality-cognitive processes. Another point of interest is evaluation of the long term effects of repeated life events on chronic environmental pressures which induce brain negative feedback defects and, subsequently, insidious cellular changes in regions such as the hippocampus that lead to memory or adaptive impairments. An example is provided by perinatal stress that induces, later in life, both hormonal and cognitive deleterious changes.

Increased locomotor response to novelty and propensity to intravenous amphetamine self-administration in adult offspring of stressed mothers

It is suggested that drug addiction is more likely to develop in individuals who are particularly sensitive to the reinforcing effects of drugs. Animal studies of intravenous drug self-administration (SA) have shown that rats display a large range of individual differences in the propensity to develop drug-seeking. Predisposed animals are characterized by a higher locomotor reactivity to both novelty and psychostimulants. In this report, we show that prenatal stress (restraint of the mother during the last week of pregnancy) may contribute to an individual's vulnerability to develop amphetamine self-administration. The adult offspring of stressed mothers exhibited: (i) a higher locomotor response to novelty and to an injection of amphetamine (0.3 mg/kg, i.v.); (ii) a higher level of amphetamine self-administration. The data indicate that individual predisposition to drug-seeking in the adult may be induced by prenatal events.

Importance of catecholamine release for the functional action of intrastriatal implants of adrenal medullary cells: pharmacological analysis and in vivo electrochemistry

The aim of the present experiments was to test whether adrenal chromaffin cells implanted into the striatum of rats could exert a functional effect through a release of catecholamines. A cell suspension obtained from bovine adrenal medulla was implanted unilaterally into the striatum. The striatal dopaminergic input was extensively destroyed beforehand to preclude the possibility of reinnervation of the striatum by endogenous dopaminergic neurons. The functional influence of the implant was tested through the measurement of drug-induced rotation, while catecholamine release was measured subsequently in the same animals by in vivo electrochemistry. Transplant survival, as shown by the immunohistochemical analysis performed at the end of the in vivo experiments, was highly variable. Surviving chromaffin cells maintained their endocrine morphology and no reinnervation of the host striatum could be detected. Rotation of the animals evoked by apomorphine (0.1 mg/kg, sc) or amphetamine (5.0 mg/kg, ip) following the lesion was left uninfluenced following transplantation, even when a large transplant was recovered. On the other hand, nicotine (0.5 mg/kg, sc) evoked a strong contraversive rotational response in the transplant-bearing animals. This response could not be ascribed to the central effect of substances released peripherally and entering the nervous system through the blood-brain barrier opened by the implantation procedure, as it could not be found in animals bearing implants of other peripheral endocrine tissue, viz, pituitary. The effect of nicotine was not blocked by the pretreatment of the animals with either the opiate antagonist naloxone (2.5 mg/kg, 10 min) or the dopamine receptor blocker pimozide (0.5 mg/kg, 1 h), although the latter pretreatment blocked the amphetamine-evoked rotation. No spontaneous catecholamine release could be detected from the implanted chromaffin cells by in vivo electrochemistry, while treatment with amphetamine or nicotine did evoke a release. The results suggest that the functional effects of such intrastriatal grafts of chromaffin cells, reported in previous studies, cannot be explained by the secretion from the grafted cells of catecholamines into the denervated striatum. On the other hand the results obtained following the pharmacological stimulation of these cells indicate that adrenal grafts can, under suitable conditions, influence the functioning of the host nervous system.

Intrastriatal dopaminergic grafts restore inhibitory control over striatal cholinergic neurons

The aim of the study was to examine the influence of intrastriatal dopaminergic grafts on the functioning of striatal cholinergic neurons using an in vitro superfusion method. Rats bearing unilateral 6-hydroxydopamine lesion of the nigrostriatal dopaminergic system received a cell suspension obtained from ED 14 rat embryonic mesencephali which was injected into the denervated striatum. Lesioned animals displayed an ipsilateral rotation in response to amphetamine (5 mg/kg i.p.). This rotational response disappeared following grafting and there was even a significant contralateral rotation in response to the drug. Apomorphine (0.1 mg/kg s.c.) induced a contralateral rotation following the lesion. This latter response was attenuated in the grafted group. Three months after grafting 350 microns thick slices were prepared from striata from the control and experimental sides of lesioned and graft-bearing animals. The slices were preincubated either with 3H-dopamine (10(-7) M) or 3H-choline (10(-7) M) and then superfused with an oxygenated Krebs-Ringer solution. Stimulation with electrical pulses following preincubation with 3H-dopamine elicited a marked increase of tritium outflow from control slices. Stimulation-evoked overflow was of similar magnitude from slices from striata containing the graft, while it was much reduced in slices from lesioned striata. Amphetamine markedly potentiated the effect of electrical stimulation in slices obtained from control and graft-containing striata. Nomifensine (a dopamine uptake blocker) led to a significant decrease of the overflow of 3H-acetylcholine evoked by electrical stimulation from control striatal slices. This inhibition was antagonized by domperidone, a D2 dopamine receptor blocker, a finding which indicates that the action of nomifensine was indeed due to a potentiation of the action of endogenous dopamine released by the electrical stimulation. A similar, although somewhat attenuated, action of nomifensine and domperidone was observed for striatal slices containing the graft. Amphetamine inhibited the stimulation evoked overflow of 3H-acetylcholine in a dose-dependent manner from striatal slices obtained both from the intact and experimental sides of graft-bearing animals, while it had no action on slices from denervated striata. Finally, the dose-response curve for the inhibition of 3H-acetylcholine release by apomorphine was significantly shifted to the left for slices from the lesioned striata as compared with control slices. This leftward shift was totally abolished in the slices from the graft-containing striatum.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracerebral dopaminergic transplants are not activated by electrical footshock stress activating in situ mesocorticolimbic neurons

Male rats received a dopaminergic implant aimed either at the nucleus accumbens or the ventral tegmental area (VTA) following 6-hydroxydopamine lesion of their mesocorticolimbic dopaminergic system. Exposure to electrical footshock stress 6 months later markedly activated the mesocorticolimbic neurons in control animals as shown by the increase of dihydroxyphenylacetic acid (DOPAC) levels both in the nucleus accumbens and the VTA. However, no stress-induced activation was seen for the grafted neurons, irrespective of the area of implantation. These results indicate the lack of reinnervation and modulation of the grafted dopaminergic neurons by one of the important afferent systems regulating the activity of endogenous mesencephalic dopaminergic neurons.

Development of intracerebral dopaminergic grafts: a combined immunohistochemical and autoradiographic study of its time course and environmental influences

The aim of the study was to obtain a description of some aspects of the development of intracerebral dopaminergic grafts, namely, the time course of the glial reaction and its relation to cell division on one hand, and the development of graft-originated innervation and its dependence on adequate matching of the implanted neurons and target site on the other hand. Cell suspensions obtained from the mesencephalon or hypothalamus of embryonic day (ED) 14 rat embryos were implanted into the striatum or lateral hypothalamus of adult rats following the destruction of the nigrostriatal system of the hosts. Animals were sacrificed at different postimplantation times, and the development of the graft was followed by immunohistochemistry by using antisera directed against tyrosine hydroxylase (TH) or glial fibrillary acidic protein (GFA). Furthermore, the existence of cell division at various times following implantation was examined by performing autoradiography on immunostained sections after prior intraventricular administration of 3H-thymidine to the host. The first stage of the development of intracerebral grafts was characterized by the existence of intense cell division within the grafted tissue, lasting about 2 weeks, and also in the host tissue surrounding the graft, lasting only about 6 days. The cell division in the host tissue was paralleled by the existence of a strong glial reaction which, however, did not extend into the graft itself. Glial reaction in the host tissue gradually decreased at later times and disappeared by 4 weeks postimplantation without leaving behind a noticeable glial scar. The graft itself was, however, transiently filled with a population of reactive astroglial cells between 3 and 6 weeks postimplantation. Within grafts of mesencephalic tissue located in the striatum TH-positive neurons were distributed evenly at short times postimplantation (2-6 days). At later time a compartmentation could be observed, with TH-positive neurons being aligned along the graft-host interface or clustered within the graft itself. Innervation of the host tissue by TH-positive fibers increased between 1 and 6 weeks postimplantation. On the other hand, no compartmentation and reinnervation of surrounding host tissue was observed for intrahypothalamic grafts of mesencephalic tissue or intrastriatal grafts of hypothalamic tissue. This last observation indicates that adequate matching of implanted neurons and target tissue plays an important role in the development of intracerebral dopaminergic grafts.

Effects of intra-accumbens dopaminergic grafts on behavioral deficits induced by 6-OHDA lesions of the nucleus accumbens or A10 dopaminergic neurons: a comparison

Local lesion of the dopaminergic (DA) terminals of the nucleus accumbens have been described to reproduce part of the behavioral deficits evoked by the lesion of the whole mesocorticolimbic DA system. The most straightforward interpretation of these results would be that the DA innervation of the nucleus accumbens is necessary for and critically involved in the normal performance of the given behaviors. However, while giving some indication as to the necessity of the integrity of this DA innervation for normal behaviors, such an approach cannot reveal whether the presence of the DA innervation of other mesocorticolimbic areas (e.g. amygdala, septum, etc.) is also required. In order to approach this question, the behavioral effects of DA grafts implanted into the nucleus accumbens of rats were evaluated following two different 6-hydroxydopamine-induced lesions: a lesion restricted to the anterior DA field (DA terminals of the nucleus accumbens and to a lesser degree the frontal cortex and anteromedial striatum) or a lesion of the whole mesocorticolimbic DA system. The latter lesion induces a disappearance of the DA innervation of the nucleus accumbens as well as the amygdala, septum, etc. Both kinds of lesions led to locomotor hypoactivity, loss of locomotor activation by amphetamine, increased locomotor stimulation to apomorphine, decrease of exploratory activity and loss of hoarding behavior. These deficits were not seen in grafted animals bearing a local lesion of the DA innervation of this structure. For some of these recoveries, however, a pharmacological stimulation of the grafted neurons was required to reveal the effect of the graft. In the case of the total lesion of the mesocorticolimbic DA system, only locomotor dysfunctions were compensated by the intra-accumbens DA implants, while the other deficits remained intact, irrespective of a stimulation of the graft. These results indicate that the re-establishment of the DA innervation of the nucleus accumbens is a sufficient condition for the compensation of locomotor deficits, irrespective of the presence of the DA terminals in more posterior limbic structures, while for deficits of more complex behaviors the simultaneous presence of posterior DA innervations is also required. This latter requirement suggests the existence of some cooperativity between the different central DA terminal areas for the normal performance of behaviors.

Distorted development of intracerebral grafts: long-term maintenance of tyrosine hydroxylase-containing neurons in grafts of cortical tissue

Cortical cells obtained from rat embryos (ED14 to ED20) were implanted in various regions of rat brain and the presence of tyrosine hydroxylase (TH)-, neuropeptide Y (NPY)- and Met-enkephalin (ENK)-immunoreactive neurons within the grafts were tested using an immunohistochemical approach. TH-like immunoreactive (TH-LI) neurons were present within the implants obtained from ED14, but not ED18 or ED20, embryos up to 10 months post-implantation and their presence was not dependent on the age of the host (adult or neonate) at the time of implantation. Furthermore, the density of such cells varied with the site of implantation, being the highest in the dorsomedial corner of the striatum. This distorted development seems to affect also other cell populations, such as NPY-LI neurons which could be observed within the implants in a density much higher than that found in the normal cortex and which presented generally a rather immature morphology. It has been described that the rat cortex contains TH-LI neurons only during a limited period of development. The survival of such neurons within intracerebral grafts of cortical tissue indicates that their disappearance during normal cortical development is dependent upon environmental cues. The survival of TH-LI cells in grafts implanted to neonatal hosts suggests that these cues are not some humoral factors appearing postnatally. On the other hand, the present observations are compatible with several other hypothesis concerning the nature of such cues: humoral factors present during the late embryonic period, signals dependent on neuronal connectivities (input and/or outputs) established during embryonic or postnatal life.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin parallels thyrotropin-releasing hormone actions on prolactin release from rat anterior pituitary cells

Bradykinin (BK), a nonapeptide, originally discovered in blood, is also present in neurons and fibers of the hypothalamus. We tested the putative releasing factor properties of BK on prolactin (PRL) release from anterior pituitary cells in vitro. BK stimulated the release of PRL in a dose-dependent manner, the threshold concentration being in the range. 0.1-1.0 nM. The release of PRL induced by BK at 1 nM concentration was about 2-fold, delayed and sustained over many minutes. Higher concentrations of BK stimulated PRL release in two phases. The shape of the BK-induced PRL release was superficially similar to that induced by thyrotropin-releasing hormone (TRH). 10 nM BK and 10 nM TRH induced about a 4-fold increase in PRL release within 5 min, followed by a gradual recovery to basal secretion. These results indicate that this peptide can act directly at the anterior pituitary gland to release PRL. Phorbol ester also promoted PRL release over the range of 1-10 nM, but the time course of the release was somewhat different.