The effects of mild maternal stress during pregnancy on the behavior of rat pups

Mild maternal stress in the form of chronic daily subcutaneous injections of saline or the vehicle for diazepam to pregnant rats was shown to result in some long term, subtle but reliable, changes in the behavior of the offspring. The same vehicle given for the same period of time in the dam's drinking water, without injection had no effect on the development of later behavior of rat pups. Chronic prenatal injections of saline or vehicle for diazepam, used in many experiments as controls for the evaluation of drug effects were shown to have some long lasting behavioral effects in the offspring of the treated dams. The series of experiments reported here compared the offspring of saline or vehicle injected dams to those of uninjected dams on a variety of developmental measurements, an open field behaviour and on learning performance in a complex brightness discrimination maze.     

Prenatal cocaine alters dopamine transporter binding in postnatal day 10 rat striatum

The effect of in utero cocaine exposure on the postnatal binding of the radiolabeled dopamine (DA) uptake inhibitor [₃H]GBR 12935 to the DA uptake complex was examined in male rats. One set of pregnant Sprague-Dawley rats was given subcutaneous (s.c.) injections of cocaine (40 mg/kg) or 0.9% saline from gestational day (GD) 8–21. Another set of animals received bilateral s.c. Silastic implants, each containing 60 mg cocaine base dissolved in polyethylene glycol (PEG) or PEG only, from GD 18-21. The density of[₃H]GBR 12935 binding to the DA transporter in striatum and mesencephalon was assessed by quantitative autoradiography on postnatal day (PND) 1, 10, 30, and 60. Both treatment methods resulted in a decrease of [₃H]GBR 12935 binding in dorsal lateral striatum of cocaine-exposed offspring on PND 10. There were no significant differences in [₃H]GBR 12935 binding between offspring of cocaine and vehicle-treated dams at any other time points examined. Thus, prenatal cocaine exposure by either daily injection from GD 8–21 or continuous infusion from GD 18–21 resulted in a transient decrease in DA transporter binding in the dorsal lateral striatum that was apparent on PND 10. © 1996 Wiley-Liss, Inc.     

Reduced serotonin release and serotonin uptake sites in the rat nucleus accumbens and striatum after prenatal cocaine exposure

This study was designed to assess the effects of prenatal cocaine exposure on the development of the serotonergic system. Pregnant Sprague-Dawley rats received daily sc injections of either cocaine (30 mg/kg) or saline from gestation day 7 (GD 7) to GD 20. At 1 week postnatal, all pups were killed and tissues containing the striatum and nucleus accumbens dissected out. In superfusion experiments, tissue slices were incubated with [3H]serotonin ([3H]5-HT) for 30 min and then superfused. The [3H]5-HT release was induced by exposures to the following treatments: electrical stimulations (20 mA or 40 mA, 0.5 Hz, 4 min), the medium containing 15 or 30 mM potassium (2 min), fenfluramine (1 or 2 microM for 2 min), para-chloroamphetamine (1 or 2 microM for 2 min), methiothepin (1 or 2 microM for 2 min), and fluoxetine (1 or 2 microM for 2 min). The results showed that the treatment-induced [3H]5-HT releases were all significantly less pronounced in the pups prenatally exposed to cocaine than in those prenatally exposed to saline regardless of the mechanisms by which the treatment increases extracellular 5-HT. Saturation analysis showed that the Bmax of [3H]citalopram binding sites was also significantly lower in the pups prenatally treated with cocaine than in those prenatally treated with saline. The results are consistent with the concept that less serotonergic innervation may exist in the examined brain areas of cocaine-treated offspring at 1 week postnatal, and support the hypothesis that prenatal cocaine exposure affects the postnatal development of the serotonergic system.     

Prolonged sojourn of developing pyramidal cells in the intermediate zone of the hippocampus and their settling in the stratum pyramidale

In radiograms of rat embryos that received a single dose of [3H]thymidine between days E16 and E20 and were killed 24 hours after the injection, the heavily labeled cells (those that ceased to multiply soon after the injection) form a horizontal layer in the intermediate zone of the hippocampus, called the inferior band. The fate of these heavily labeled cells was traced in radiograms of the dorsal hippocampus in embryos that received [3H]thymidine on day E18 and were killed at different intervals thereafter. Two hours after injection the labeled proliferative cells are located in the Ammonic neuroepithelium. The heavily labeled cells that leave the neuroepithelium and aggregate in the inferior band 1 day after the injection become progressively displaced toward the stratum pyramidale 2-3 days later, and penetrate the stratum pyramidale of the CA1 region on the 4th day. In the stratum pyramidale of the CA3 region, farther removed from the Ammonic neuroepithelium, the heavily labeled cells are still sojourning in the intermediate zone 4 days after labeling. Observations in methacrylate sections suggest that two morphogenetic features of the developing hippocampus may contribute to the long sojourn of young pyramidal cells in the intermediate zone: the way in which the stratum pyramidale forms and the way in which the alveolar channels develop. The stratum pyramidale of the CA1 region forms before that of the CA3 region, which is the reverse of the neurogenetic gradient in the production of pyramidal cells. We hypothesize that this is so because the pyramidal cells destined to settle in the CA3 region, which will be contacted by granule cells axons (the mossy fibers), have to await the formation of the granular layer on days E21-E22. Concordant with this is the observation that the hippocampal intermediate zone, which contains the sojourning young pyramidal cells, greatly enlarges between days E16 and E20, then suddenly diminishes and disappears by day E22. The other factor that may contribute to the prolonged sojourn of pyramidal cells, specifically those destined to settle in the CA1 region, is the pattern of alveolar channel development. This transient extracellular matrix begins to form several days after the onset of pyramidal cell neurogenesis, grows in a direction opposite to the settling of pyramidal cells in the stratum pyramidale, and does not reach the subicular end of Ammon's horn until day E21.(ABSTRACT TRUNCATED AT 400 WORDS)     

Activation of metabotropic glutamate receptor 5 is associated with effect of amphetamine on brain neurons

The role of metabotropic glutamate receptor 5 (mGluR5) was explored in mechanisms underlying the action of amphetamine (AMPH). The activity of mGluR5 was monitored by measuring the level of [3H]inositol monophosphates in brain neurons, in response to stimulation of 2-choloro-5-hydroxyphenylglycine (CHPG), a selective agonist of mGluR5. Treatment with 1 microM of AMPH for 1 h or 7 days increased the CHPG (1 mM, 30 min)-evoked phosphoinositide turnover by 46% or 92% and 26% or 84% in cultured cortical and hippocampal neurons, respectively, from that of CHPG-only treated cells. When AMPH was present during CHPG application post-1 h or 7 day AMPH incubation, the rate of phosphoinositide hydrolysis in cortical neurons became 121% or 142% higher than that treated with CHPG only. The postnatal day (P) 21 (juvenile) and P60 (adult) rats received three intraperitoneal injections of 5 mg/kg of AMPH or saline daily for 6 days. They were challenged on the eighth day with one dosage and sacrificed 3 h later. Reversible 3H-glutamate binding detected increases of 22-89% in the binding levels of cortex and hippocampus of both ages following the AMPH injections. Increases of 13-18% in the levels of mGluR5 mRNA were seen in the juvenile pyramidal neurons of hippocampal CA1-4, granular cells of dentate gyrus, and ventral thalamic nuclei, as shown by in situ hybridization. The AMPH-induced altered activity of mGluR5 is probably associated with changes in the expression of the glutamate receptors, including mGluR5. AMPH may modify the sensitivity of mGluR5 or interact with the receptor itself.     

Post- and presynaptic lesions in the CA1 region of hippocampus: Effect on [3H]forskolin and [3H]phorboldibutyrate ester binding

Summary The effect of transient cerebral ischemia and intraventricular injection of kainic acid on adenylate cyclase and protein kinase C as labeled by [³H]forskolin ([³H]FOR) and [³H]phorboldibutyrate ester ([³H]PDBU) in several rat brain microregions was investigated in a quantitative autoradiographic study. Four days after transient four vessel occlusion a 80% loss of [³H]FOR and a 35% loss of [³H]PDBU binding could be measured in the CA1 stratum radiatum of operated Wistar rats as compared to control rats. Four days after intraventricular injection of kainic acid only a marginal loss of [³H]FOR and a 30% increase of [³H]PDBU binding was seen in the CA1 stratum radiatum while in the CA3 stratum lucidum and radiatum respectively a 30% loss of [³H]FOR and no significant change in [³H]PDBU binding was observed. As transient cerebral ischemia and intraventricular kainic acid injection are depleting the hippocampal CA1 region of CA1 pyramidal cells and axons of CA3 pyramidal cells respectively in rat brain, these findings strongly suggest that both adenylate cyclase and protein kinase C are localized in CA1 pyramidal cells of rat hippocampus.Part of this study has been presented at the 16th C.I.N.P. Congress, Munich, August 15–19, 1988.     

Loss of striatal somatostatin neurons following prenatal methylazoxymethanol

Prenatal administration of methylazoxymethanol acetate (MAM), which kills neuroblasts undergoing mitosis, was used to lesion striatal somatostatin neurons. Previous [3H]thymidine autoradiographic studies had indicated that striatal somatostatin neurons undergo their final mitotic division at Gestational Days (G) 15 and 16. Therefore, pregnant Sprague-Dawley rats received an intraperitoneal injection of MAM (25 mg/kg) on G15. Neurochemical and histological examination of the mature offspring indicated the loss of half the striatal aspiny interneurons in which somatostatin, neuropeptide Y, and NADPH diaphorase coexist, with relative sparing of the cholinergic interneurons and medium spiny projection cells. This prenatal MAM treatment was without apparent effect on the patch-matrix organization of the striatum.     

Concurrent changes in regional cholinergic parameters and nest odor preference in the early postnatal rat after lead exposure.

The effect of pre- and postnatal lead ingestion on choline acetyltransferase (ChAT) activity, muscarinic cholinergic receptors (mACHR) and on nest odor preference, was investigated in the early postnatal male rat. Long Evans dams were given either 0.15% [LL = low lead] or 0.25% [ML = moderate lead] lead acetate (controls, 0.125% or 0.075% sodium acetate) in their drinking solution from the first day of pregnancy and during lactation. Mean blood lead levels were 55 micrograms/100ml at postnatal day [PN] 6 in ML-treated offspring and 35 micrograms/100ml at PN 9 in LL-treated pups. General health of pups and dams was not affected. Lead-treated offspring showed a reduced preference for or ability to identify the smell of home bedding, when tested at PN 9. A decrease in binding (Bmax) of [3H]N-methyl- scopolamine (NMS) was detected in olfactory bulb and in visual cortex of LL-treated rats at PN 9; the affinity (KD) was unchanged. On the other hand, ChAT-activity of ML-treated offspring was significantly increased in olfactory bulb at PN 6. These results suggest that stage-specific behaviors depending on sensory functions and cholinergic projection systems in related brain areas are sensitive to pre- and postnatal lead exposure.     

Prenatal cocaine exposure decreases brain-derived neurotrophic factor proteins in the rat brain

The pregnant rats received daily sc injections of cocaine (30 mg/kg) or saline from the gestational day (GD) 7 to GD 20. At 1 week postnatal, all pups were killed and the hippocampus, cortex and striatum were dissected out. Levels of brain-derived neurotrophic factor (BDNF) under the basal condition and depolarization with high potassium (40 mM) were measured. The results showed that hippocampal BDNF levels under basal and depolarization conditions were all significantly lower in the pups prenatally exposed to cocaine than those exposed to saline. There were no significant differences in basal BDNF levels between the cocaine and saline groups in the cortex or striatum. However, the prenatally cocaine-treated pups showed significantly less BDNF release following high potassium depolarization than the saline-treated animals did in both these regions. The results support the suggestion that prenatal cocaine exposure decreases BDNF expression in the offspring.     

Regional variations in particulate cyclic AMP dependent-protein kinase binding activity in the gerbil hippocampus following transient forebrain ischemia by [3H]cyclic AMP binding.

Changes in the binding of [3H]cyclic AMP as an indicator of particulate cyclic AMP-dependent protein kinase (AMP-DPK) binding activity following transient forebrain ischemia were studied in the gerbil using in vitro autoradiography. [3H]Cyclic AMP binding in the strata pyramidale and lacunosum-moleculare of the hippocampal CA1, the stratum pyramidale of the CA3, and the dentate gyrus decreased transiently in the early postischemic phase but then recovered. However, [3H]cyclic AMP binding in the strata pyramidale and radiatum of the CA1, the granular layer of the dentate gyrus, and the upper layer of the cortex decreased again 7 days after ischemia. In the CA4 subfield and the lower layer of the cortex, the binding showed no significant alterations after ischemia. Administration of pentobarbital prior to the induction of ischemia prevented the decrease in [3H]cyclic AMP binding in the CA1 subfield 6 h and 7 days after ischemia, and showed protective effects against neuronal death of the CA1 pyramidal cells 7 days after ischemia. These results indicate that marked alteration of intracellular signal transduction precedes neuronal damage in the hippocampal CA1 subfield. Furthermore, postischemic reduction of [3H]cyclic AMP binding in the histologically intact cerebral cortex, CA3, and dentate gyrus may be the reflection of cellular dysfunction after energy failure.     

Autoradiographic visualization of adenosine A1 receptors in the gerbil hippocampus: changes in the receptor density after transient ischemia

N6-cyclohexyl-[3H]adenosine [( 3H]CHA) was used for the in vitro visualization of the hippocampal adenosine A1 receptors in the gerbil. The strata radiatum and oriens of the hippocampus showed particularly high binding activity. Depletion of pyramidal cells and consequent severe decrease in [3H]CHA binding activity in the CA1 subfield were observed after transient ischemic insult. These results suggest that most adenosine receptors in the CA1 region are localized in association with pyramidal cells.     

Mapping second messenger systems in the rat hippocampus after transient forebrain ischemia: in vitro [3H]forskolin and [3H]inositol 1,4,5-trisphosphate binding

Autoradiographic imaging demonstrated predominant and reciprocal localization of forskolin and inositol 1,4,5-trisphosphate (IP3) binding sites in synaptic areas in the hippocampus. We produced selective damage to the CA1 pyramidal cells in the rat hippocampus by means of transient forebrain ischemia and analyzed the alteration of the intracellular signal transduction using quantitative autoradiography of these second messenger systems. The dendritic fields (stratum oriens, radiatum and lacunosummoleculare) in the CA1 showed 20% decrease in [3H]IP3 binding activity 3 h after ischemia, when no morphological abnormalities were obvious. Thereafter, grain density in these layers decreased and half of the binding sites were lost 2 days after ischemia. By contrast, the stratum pyramidale of the CA1 showed no significant change until 2 days after recirculation. Seven days after ischemia, when CA1 pyramidal cells were depleted, all layers in the CA1 subfield lost 85% of [3H]IP3 binding sites. In the CA3 subfield, only a small and transient alteration in the [3H]IP3 binding was noticed during recirculation. Postischemic reduction of [3H]forskolin binding sites was obvious in the CA1 only 1 h after ischemia followed by loss of 50% of binding activity 7 days after recirculation. These results suggest that forskolin and IP3 binding sites are predominantly distributed on the pyramidal cells in the CA1 subfield and that marked alteration of intracellular signal transduction precedes the delayed CA1 pyramidal cell death.     

Selective retrograde transport of D-aspartate in spinal interneurons and cortical neurons of rats

Retrograde labeling of neuronal elements in the brain and spinal cord has been investigated by autoradiographic techniques following injections of D-[3H]aspartate (asp), [3H] gamma-aminobutyric acid (GABA) or horseradish peroxidase (HRP) in the medulla and spinal cord of rats. Twenty-four hours after D-[3H]asp injections focused upon the cuneate nucleus, autoradiographic labeling is present over fibers in the pyramidal tract, internal capsule and over layer V pyramids in the forelimb representation of the sensorimotor cortex. After [3H]GABA injections in the same nucleus no labeling attributable to retrograde translocation can be detected in spinal segments, brain stem or cortex. Conversely, injections of 30% HRP in the cuneate nucleus label neurons in several brain stem nuclei, in spinal gray and in layer V of the sensorimotor cortex. These observations give further support to the proposed existence of a selective retrograde transport of D-[3H]asp and are consistent with the available evidence which indicates that the corticodorsal column nuclei path use glutamate and/or aspartate as neurotransmitter(s). D-[3H]Asp injections focused on the dorsal horn at cervical segments label a fraction of perikarya of the substantia gelatinosa and a sparser population of larger neurons in laminae IV to VI for a distance of 3-5 segments above and below the injection point. No brain stem neuronal perikarya appear labeled following spinal injections of D-[3H]asp although autoradiographic grains overlie pyramidal tract fibers on the side contralateral to the injection. This labeling however has not been observed rostral to lower pontine levels nor over cortical neurons at any of the survival times used in the present experiments (6-72 h). As in cases with cuneate injections this pattern of labeling contracts with that obtained after spinal injections of either [3H]GABA or HRP. Although labeling of neocortical neurons has not been observed after spinal injections of D [3H]asp, possibly as a result of the length of corticospinal axons, retrograde labeling of these elements for at least some distance may be taken as suggestive of a special affinity of their terminals for glutamate and/or aspartate.     

Maternal exercise during pregnancy ameliorates the postnatal neuronal impairments induced by prenatal restraint stress in mice

Clinical and preclinical studies have demonstrated that prenatal stress (PS) induces neuronal and behavioral disturbances in the offspring. In the present study, we determined whether maternal voluntary wheel running (VWR) during pregnancy could reverse the putative deleterious effects of PS on the neurodevelopment and behavior of the offspring. Pregnant CF-1 mice were randomly assigned to control, restraint stressed or restraint stressed + VWR groups. Dams of the stressed group were subjected to restraint stress between gestational days 14 and delivery, while control pregnant dams remained undisturbed in their home cages. Dams of the restraint stressed + VWR group were subjected to exercise between gestational days 1 and 17. On postnatal day 23 (P23), male pups were assigned to one of the following experimental groups: mice born from control dams, stressed dams or stressed + VWR dams. Locomotor behavior and pyramidal neuronal morphology were evaluated at P23. Animals were then sacrificed, and Golgi-impregnated pyramidal neurons of the parietal cortex were morphometrically analyzed. Here, we present two major findings: first, PS produced significantly diminished dendritic growth of parietal neurons without altered locomotor behavior of the offspring; and second, maternal VWR significantly offset morphological impairments.     

An autoradiographic study of gliogenesis in the rat lateral geniculate nucleus (LGN).

Rats pregnant for 14, 16, 18 and 20 days, as well as 1-, 3-, 7-, 12-, 16- and 21-day-old offspring, received a single injection of [3H]thymidine and were killed at postnatal ages of 22-27 days. An autoradiographic study of DNA synthesis revealed that proliferation of non-neuronal matrix cell precursors destined for the dorsal part of the lateral geniculate nucleus had already started by gestational day 14. Quantiative evaluation of the incidence of labelled cells revealed 2 peaks occurring in both groups of non-neuronal cells at postnatal days (PD) 7 and 16. It has been assumed that the accelerated production of ectodermally derived glial cells, observed towards PD 7, relfects the enhanced growth of the neuronal surface covered with glial cell processes, and that at PD 16 formation of myelin sheaths. Changes in the number of labelled cells of mesodermal origin in the course of development can probably be attributed to the rate of vasculogenesis of the studied region.     

Time-dependent changes in distribution of basic fibroblast growth factor immunoreactive cells in hippocampus after kainic acid injection in rat pups

Five-day-old Wistar albino rats were injected with kainic acid (KA) or saline i.p. to investigate time-dependent alterations in morphology and number of basic fibroblast growth factor (bFGF) immunoreactive (-ir) astrocytes and neurons in hippocampus at 15, 30, and 90 days after the injections. Sections were stained with cresyl violet for morphological evaluation and bFGF immunohistochemistry was used for quantitative evaluation of bFGF-ir cell density. Fifteen days after KA injection, there was gliosis but no neuronal loss although disorganization in CA1, CA3, CA4 pyramidal layers and neuronal loss were evident 30 and 90 days after the injection. KA injected rats demonstrated significantly increased number of bFGF-ir astrocytes throughout the hippocampus and pyramidal neurons in CA2 after 15 days and decreased number of bFGF-ir cells after 30 and 90 days. The decrease in the number of bFGF-ir astroglia and neurons in long term after KA injection may indicate a decrease in the production of bFGF and/or number of bFGF-ir cells suggesting that protective effects of bFGF may be altered during epileptogenesis in hippocampus.     

Prenatal and postnatal hypothyroidism abolishes lesion-induced noradrenergic sprouting in the adult rat

The effects of altered thyroid states on regeneration in the central nervous system are equivocal. This work was undertaken to examine the influence of propylthiouracil-induced (PTU-induced) pre- and postnatal hypothyroidism on collateral sprouting of noradrenergic (NA) axons in the habenula (Hb), following lesions in the stria medullaris (SM) of the adult rat. Ten pregnant dams were divided into control and PTU-treated groups. Control rats had free access to food and water and the hypothyroid group received, in addition, 0.05% (w/v) of PTU in their drinking water, beginning on day 12 of gestation and continuing post partum through lactation until the offspring were weaned at age 22 days. The pregnant dams received, in addition, daily injections of thyroxine (25 micrograms/kg, ip) and only male pups were used in the study. At weaning the pups were removed from the dams and placed in cages with free access to food and water. The hypothyroid offspring received 0.05% (w/v) PTU in the drinking water until sacrificed at 10 weeks of age. At 6 weeks, some rats in each group received bilateral lesions in the SM and the remainder were sham-operated. All rats were sacrificed 4 weeks after operation. Thus, four groups were formed: 1) control/sham, 2) control/lesion, 3) PTU/sham, 4) PTU/lesion. Sprouting of NA fibers in discrete regions of the Hb was identified by norepinephrine (NE) levels and by fluorescence histochemistry. Blood levels of thyroid stimulating hormone (TSH) were determined. The results show that pre- and postnatal induced chronic hypothyroidism abolished NA sprouting in the partially deafferented Hb. Furthermore, lesions of the SM resulted in a marked decrease in serum TSH levels.     

Localization of hippocampal muscarinic receptors after kainic acid lesion of CA3 and fimbria-fornix transection

Bilateral intraventricular injections of 0.5 μg of kainic acid were used to selectively destroy CA3 hippocampal pyramidal neurons, in an effort to clarify the possible localization of muscarinic cholinergic receptors in the rat hippocampal formation. Thirty days after treatment, there was 43% decrease in the total number of [³H] -QNB binding sites per hippocampus, with no change in affinity. Histological examination confirmed the selective loss of pyramidal neurons in subareas CA3a–b while other regions of the hippocampal formation were spared. The unilateral transection of the fimbria-fornix, done 14 days after kainic acid, produced a further reduction in binding in relation to control hippocampi (−57%).The results demonstrate that in the pyramidal cells of CA3 there is a high concentration of postsynaptic muscarinic receptors. However, the slight further decrease, found after fimbria-fornix transection, suggests the possible existence of a small population of presynaptic receptors that, hitherto, had only been demonstrated indirectly by physiological methods.     

Selective vulnerability of the hippocampal pyramidal neurons to hypothyroidism in male and female rats.

Thyroid hormone deficiency has long been considered to affect profoundly such cognitive functions as learning and memory, which are known to depend on the structural integrity of the hippocampal formation. Since we previously found that the number of granule cells of the dentate gyrus is reduced in hypothyroid animals, we decided to extend our observations to the pyramidal cells of the hippocampus in order to gain further insight into the effects of hypothyroidism upon the other neuronal links of the hippocampal trisynaptic circuitry, inasmuch as CA1 neurons are known to be particularly vulnerable to aggressive agents. Groups of 6 male and 6 female rats aged 30 and 180 days were analysed separately after being treated as follows: (1) hypothyroid from day 0 until day 30 (30-day-old hypothyroid group); (2) respective 30-day-old control; (3) hypothyroid from day 0 until day 180 (180-day-old hypothyroid group); (4) hypothyroid until day 30 and thenceforth maintained euthyroid (recovery group); (5) hypothyroid since day 30 (adult hypothyroid group); and (6) respective 180-day-old control. The volume of the pyramidal cell layer of the CA1 and CA3 regions and the numerical density of the respective neurons were evaluated, thereby allowing us to estimate the total number of pyramidal cells in each hippocampal region. The areal density and the mean nuclear volume of CA1 and CA3 pyramidal cells were also estimated. In the CA3 region, we found that hypothyroidism, whatever its duration and time of onset, induces a reduction in the volume of the pyramidal cell layer and a parallel increase in the numerical density of its neurons, without interfering with the total number of pyramidal cells. Conversely, in the CA1 region, thyroid hormone deficiency started either neonatally or during maturity was found to lead to a decrease in the total number of pyramidal cells. Reductions ranging between 14.2 and 22.5% were found in 30 and 180-day-old hypothyroid groups. The reestablishment of a euthyroid state did not ameliorate the referred neuronal loss. The present results support the view that hypothyroidism induces small alterations in the structural organization of the hippocampal CA3 region, contrary to what happens in CA1 in which neuronal death occurs. Furthermore, the data presented herein demonstrate that the total number of CA1 pyramidal cells displays sexual dimorphism that is not affected by thyroid hormone manipulations.(ABSTRACT TRUNCATED AT 400 WORDS)     

Selective retrograde transport of d-aspartate in spinal interneurons and cortical neurons of rats

Retrograde labeling of neuronal elements in the brain and spinal cord has been investigated by autoradiographic techniques following injections of d-[³H]aspartate (asp), [³H]γ-aminobutyric acid (GABA) or horseradish peroxidase (HRP) in the medulla and spinal cord of rats.Twenty-four hours after d-[³H]asp injections focused upon the cuneate nucleus, autoradiographic labeling is present over fibers in the pyramidal tract, internal capsule and over layer V pyramids in the forelimb representation of the sensorimotor cortex. After [³H]GABA injections in the same nucleus no labeling attributable to retrograde translocation can be detected in spinal segments, brain stem or cortex. Conversely, injections of 30% HRP in the cuneate nucleus label neurons in several brain stem nuclei, in spinal gray and in layer V of the sensorimotor cortex. These observations give further support to the proposed existence of a selective retrograde transport of d-[³H]asp and are consistent with the available evidence which indicates that the corticodorsal column nuclei path use glutamate and/or aspartate as neurotransmitter(s).d-[³H]Asp injections focused on the dorsal horn at cervical segments label a fraction of perikarya of the substantia gelatinosa and a sparser population of larger neurons in laminae IV to VI for a distance of 3–5 segments above and below the injection point. No brain stem neuronal perikarya appear labeled following spinal injections of d-[³H]asp although autoradiographic grains overlie pyramidal tract fibers on the side contralateral to the injection. This labeling however has not been observed rostral to lower pontine levels nor over cortical neurons at any of the survival times used in the present experiments (6–72 h). As in cases with cuneate injections this pattern of labeling contrasts with that obtained after spinal injections of either [³H]GABA or HRP. Although labeling of neocortical neurons has not been observed after spinal injections of d [³H]asp, possibly as a result of the length of corticospinal axons, retrograde labeling of these elements for at least some distance may be taken as suggestive of a special affinity of their terminals for glutamate and/or aspartate.