Alfredo Feria-Velasco

Neurogenesis in the subventricular zone following transcranial magnetic field stimulation and nigrostriatal lesions

Neurogenesis continues at least in two regions of the mammalian adult brain, the subventricular zone (SVZ) and the subgranular zone in hippocampal dentate gyrus. Neurogenesis in these regions is subjected to physiological regulation and can be modified by pharmacological and pathological events. Here we report the induction of neurogenesis in the SVZ and the differentiation after nigrostriatal pathway lesion along with transcranial magnetic field stimulation (TMFS) in adult rats. Significant numbers of proliferating cells demonstrated by bromodeoxyuridine‐positive reaction colocalized with the neuronal marker NeuN were detected bilaterally in the SVZ, and several of these cells also expressed tyrosine hydroxylase. Transplanted chromaffin cells into lesioned animals also induced bilateral appearance of subependymal cells. These results show for the first time that unilateral lesion, transplant, and/or TMFS induce neurogenesis in the SVZ of rats and also that TMFS prevents the motor alterations induced by the lesion.

Semen quality of workers occupationally exposed to hydrocarbons

Abstract Objective: To determine whether occupational exposure of men to hydrocarbons has adverse effects on the quality of their semen. Design: Comparative study. Setting: The rubber industry in Mexico City. Patient(s): Forty-eight workers who were exposed to hydrocarbons for 2–24 years and 42 unexposed workers. Intervention(s): None. Main Outcome Measure(s): Environmental hydrocarbon concentrations were determined by continuous air monitoring in all areas of the factory. Analyses of semen samples were performed in accordance with World Health Organization criteria. Result(s): Hydrocarbon concentrations were as follows: ethylbenzene, 220.7–234 mg/m 3 ; benzene, 31.9–47.8 mg/m 3 ; toluene, 189.7–212.5 mg/m 3 ; and xylene, 47–56.4 mg/m 3 . The number of subjects with ejaculates that had normal characteristics was greater in the unexposed group (76%) than in the exposed group (17%). More abnormal characteristics were found in the semen of exposed workers than unexposed workers, including alterations in viscosity, liquefaction capacity, sperm count, sperm motility, and the proportion of sperm with normal morphology. Some abnormal characteristics correlated with the number of years of exposure to the hydrocarbons. Conclusion(s): Damage to the spermatogenic process resulting from hydrocarbon exposure was demonstrated by an increased rate of abnormalities in the semen of exposed workers compared with unexposed workers. This information may be useful for conducting future analyses of reproductive risks related to exposure to high concentrations of hydrocarbons.

Serotonin/dopamine interaction in memory formation

Both serotonin (5-HT) and dopamine (DA) neurotransmitters play a key role in modulating synaptic transmission in the central nervous system. Such 5-HT- and DA-mediated modulatory activity has been shown to influence a wide variety of cerebral functions, both of an instrumental and cognitive nature. Some brain regions strongly involved in cognition such as the prefrontal cortex, hippocampal formation and corpus striatum, are densely innervated by serotonergic and dopaminergic afferents proceeding from the raphe complex and the mesocorticolimbic or nigrostriatal systems, respectively. Learning and memory are strongly modulated by 5-HT and DA neurotransmitter activity, and in some cases they interact interdependently to sustain the psychobiological organization of these cognitive processes. Learning and memory, at least in part, depend on short- or long-lasting synaptic modifications, mainly occurring at dendritic spines. Indeed, the modulatory influence of 5-HT and DA at the synaptic level may affect the codification of mnemonic information on such spines. In fact, several experimental models of neurotransmitter activity have identified a close association between a 5-HT-DA imbalance and cytoarchitectonic changes underlying learning and memory impairment.

Spontaneous long-term remyelination after traumatic spinal cord injury in rats.

The capability of the central nervous system to remyelinate axons after a lesion has been well documented, even though it had been described as an abortive and incomplete process. At present there are no long-term morphometric studies to assess the spinal cord (S.C.) remyelinative capability. With the purpose to understand this phenomenon better, the S.C. of seven lesionless rats and the S.C. of 21 rats subjected to a severe weight-drop contusion injury were evaluated at 1, 2, 4, 6, and 12 months after injury. The axonal diameter and the myelination index (MI = axolemmal perimeter divided by myelinated fiber perimeter) were registered in the outer rim of the cord at T9 SC level using a transmission electron microscope and a digitizing computer system. The average myelinated fiber loss was 95.1%. One month after the SC, 64% of the surviving fibers were demyelinated while 12 months later, only 30% of the fibers had no myelin sheath. The MI in the control group was 0.72 +/- 0.07 (X +/- S.D.). In the experimental groups, the greatest demyelination was observed two months after the lesion (MI = 0.90 +/- 0.03), while the greatest myelination was observed 12 months after the injury (MI = 0.83 +/- 0.02). There was a statistical difference (p < 0.02) in MI between 2 and 12 months which means that remyelination had taken place. Remyelination was mainly achieved because of Schwann cells. The proportion of small fibers (diameter = 0.5 micron or less) considered as axon collaterals, increased from 18.45% at 1 month to 27.66% a year after the contusion. Results suggest that remyelination is not an abortive phenomenon but in fact a slow process occurring parallel to other tissue plastic phenomena, such as the emission of axon collaterals.

Golgi Method without Osmium Tetroxide for the Study of the Central Nervous System

A variant Golgi technique was developed that consisted of substituting osmium tetroxide with formaldehyde as the initial fixative in intracardiac perfusion, along with the addition of glacial acetic acid to the chromating fluid. This procedure avoids disposal of dangerous waste substances into the environment. Other advantages include 1) reduction of cost, danger to lab workers, and risk of disruption of the tissue slices during their handling by eliminating the osmium tetroxide, 2) clear tissue background, 3) greater quantity of impregnated neurons than in the classical procedure, with distinct morphological details easily identified even in gross sections and 4) reduction in processing time.

PYRIDOXAL PHOSPHATE AND GLUTAMATE DECARBOXYLASE IN SUBCELLULAR PARTICLES OF MOUSE BRAIN AND THEIR RELATIONSHIP TO CONVULSIONS

The subcellular distribution of pyridoxal phosphate (PLP) was studied in mouse brain, as well as the effect of pyridoxal phosphate‐γ‐glutamyl hydrazone (PLPGH—a convulsant drug which decreases both PLP levels and glutamate decarboxylase activity [GAD] in whole brain) upon both the PLP concentration and the GAD activity in subcellular fractions. An electron microscopic evaluation of the subcellular particles of control and PLPGH‐treated animals was also carried out. The main findings were the following: (1) PLP was localized mainly in the supernatant and crude mitochondrial fractions; two‐thirds of the amount present in the latter were located in the subfraction containing pure mitochondria, and the remainder was in the synaptosomal fraction. After osmotic disruption of synaptosomes, PLP was found in both the intrasynaptosomal mitochondria and the synaptoplasm. (2) Treatment of mice with PLPGH decreased levels of PLP in several brain fractions, this effect being much more notable in the soluble fractions than in the particulate fractions. After osmotic disruption of the synaptosomes, a specific decrease of PLP in the synaptoplasm was observed. (3) Treatment with PLPGH produced also an inhibition of GAD activity in most of the fractions studied, when this enzyme was assayed in the absence of PLP. In general, the inhibition was greater in those fractions in which levels of PLP were also affected. In synaptosomes, this correlation between the decreased levels of PLP and decreased activity of GAD occurred only in the synaptoplasm. (4) The activation of GAD by PLP added to incubation mixtures was much greater in those fractions from PLPGH‐treated animals which displayed extensive inhibition of GAD, in comparison to the corresponding fractions from control animals. (5) No ultrastructural changes were detected in the subcellular fractions from treated animals. Our results show that the decreases of both the levels of PLP and the activity of GAD (as previously found in whole brain) actually occur in the synaptosomes, a finding that supports the hypothesis that the role of PLP in the mechanisms controlling excitability can be explained, at least in part, by its regulatory action on GAD activity, which in turn determines the rate of GABA synthesis at the nerve endings.

Changes in NMDA-receptor gene expression are associated with neurotoxicity induced neonatally by glutamate in the rat brain.

The N-methyl-D-aspartate receptor (NMDA-R) is fully functional in the rat early in embryogenesis, and diverse neuronal plasticity events are regulated through its activation later in postnatal development. On the other hand, systemic administration of glutamate (Glu) to rats at birth induces neuronal degeneration in glutamatergic central nervous system regions via Glu receptor activation. However, it is not known whether an increase in neonatal Glu levels modifies the gene expression of NMDA-R subunits, or if these putative changes are related to gamma-aminobutyric acid-mediated (GABAergic) neurotransmission. We measured, by means of semi-quantitative reverse transcriptase polymerase chain reaction, changes in gene expression of the NMDA-R subunits: NMDA-R1, NMDA-R 2A and NMDA-R 2B in cerebral cortex (CC), striatum (ST) and hippocampus (HP) in the brains of rats treated neonatally with monosodium L-glutamate (MSG). These studies were supported by histological and quantitative analysis of the glia. Our results showed histological evidence of neuronal damage, and increased glial cell number and activity were detected. This was seen mainly in the ST and HP of MSG-treated animals. Significant increases in NMDA-R1, 2A and 2B subunits gene expression was also observed in ST and HP but not in CC, where only NMDA-R 2B was increased in MSG-treated rats. Our data suggest that increases in Glu levels and activation of Glu-receptors after neonatal administration of MSG induce an increase in glial cell reactivity and important changes in NMDA-R molecular composition, with signs of neuronal damage.

Toxicology of Male Reproduction in Animals and Humans

Environmental contaminants can interfere with the male reproduction function. A review is presented of those pollutants with adverse effects on human reproduction. The possible effects of occupational and environmental exposure to various substances on male reproductive health are evaluated. This analysis considers studies showing damage of men exposed to halogenated hydrocarbons, other organic compounds, heavy metals and some physical agents, and some lifestyles, such as continuous stress, alcohol consumption, cigarette and marijuana smoking, and other addictions. Possible influences of these agents on the neuroendocrine system with the decrease of male fertility during the last decades are also discussed.

MALE FERTILITY OF KIDNEY TRANSPLANT PATIENTS WITH ONE TO TEN YEARS OF EVOLUTION USING A CONVENTIONAL IMMUNOSUPPRESSIVE REGIMEN

The reproductive functions and hormone serum levels of 55 male kidney transplant recipients were assessed. Patients underwent peritoneal dialysis before transplantation and were given immunosuppressive therapy afterward for 1 to 10 years. Spermatobioscopies were performed, and serum urea, creatinine, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), and testosterone (T) levels were determined. Average serum urea and creatinine levels were 54.6 + 1.4 and 3 + 1.3 mg/dL, respectively. The average serum hormone levels were 3.2 + 2 mIU/mL (LH), 6.3 + 1.7 mIU/mL (FSH), 11.7 + 1.5 ng/mL (PRL), and 23 + 1.4 pg/mL (T). Libido reduction was reported in 88% of patients within 8 months following transplantation. Normozoospermia was seen in 47.3% of the patients, asthenozoospermia in 18.2% oligozoospermia in 14.5%, while oligoteratozoospermia, asthenoteratozoospermia, oligoasthenozoospermia, oligoasthenoteratozoospermia, and azoospermia were seen in the rest. Twenty-six patients procreated...

Prenatal-through-postnatal exposure to moderate levels of ethanol leads to damage on the hippocampal CA1 field of juvenile rats: A stereology and Golgi study

Experimental paradigms conducted to assess the neurotoxic effects of ethanol exposure on hippocampus development have yielded controversial findings. Hippocampal CA1 population and some cytoarchitectural parameters of pyramidal cells were studied after exposure to ethanol during early development, in rats. Examination of 30-day-old offspring of rats exposed to moderate levels of ethanol during gestation through lactation showed an increased volume of the hippocampal CA1 field compared to untreated or pair-fed control pups, as well as a reduced number of pyramidal neurons. In addition, the number of spines from surviving CA1 pyramidal neurons was reduced. Furthermore, stubby and wide spines were proportionally increased, while the proportion of mushroom and ramified spines was reduced; no variation in the proportion of thin spines was observed. Because alcoholic women usually drink alcohol before, during, and after pregnancy, a broad-range experimental model of alcohol exposure was used in this study. The present findings show that experimental exposure to moderate levels of ethanol, resembling the human situation in alcoholic mothers, leads to loss of hippocampal CA1 pyramidal neurons, along with several pathological and plastic events in the dendritic arborization of these neurons. Some ethanol-induced excitotoxicity-related mechanisms, which may be underlying these effects, are discussed.