Review: Early and late determinants of puberty in ruminants and the role of nutrition.

This article reviews the scientific literature on puberty with a focus on ruminants and draws inference, where appropriate, from recent findings in transgenic mouse models and human pathology. Early genetic determinants of puberty have been discovered in humans suffering from hypogonadotropic hypogonadism or central precocious puberty. Transgenic mouse models selected on the basis of the causative defective genes helped in discovering the cellular and molecular mechanisms involved. Most of the genes found are involved in the development of neuroendocrine networks during embryo development and early postnatal life. Notwithstanding that the development of neuroendocrine networks takes place early in puberty, a delay or acceleration in the development of Gonadotropin Releasing Hormone (GnRH) neurons has an impact on puberty onset inducing a delay or an advance, respectively. Among the genes discovered in humans and laboratory models, only a few of them displayed polymorphisms associated with advanced sexual maturity, but also marbling, growth traits and callipygian conformation. This could be related to the fact that rather than puberty onset, most research monitored sexual maturity. Sexual maturity occurs after puberty onset and involves factors regulating the maturation of gonads and in the expression of sexual behaviour. The association with growth and metabolic traits is not surprising since nutrition is the major environmental factor that will act on late genetic determinants of puberty onset. However, a recent hypothesis emerged suggesting that it is the postnatal activation of the GnRH neuronal network that induces the acceleration of growth and weight gain. Hence, nutritional factors need the activation of GnRH neurons first before acting on late genetic determinants. Moreover, nutritional factors can also affect the epigenetic landscape of parental gamete's genome with the consequence of specific methylation of genes involved in GnRH neuron development in the embryo. Season is another important regulator of puberty onset in seasonal small ruminants and appears to involve the same mechanisms that are involved in seasonal transition in adults. The social environment is also an underestimated factor affecting puberty onset in domestic ruminants, most research studies focused on olfactory cues, but the genetic basis has not heretofore been adequately tackled by the scientific community. Additionally, there is some evidence to suggest transgenerational effects exist, in that nutritional and social cues to which parents were exposed, could affect the epigenetic landscape of parental gametes resulting in the epigenetic regulation of early genetic determinants of puberty onset in their offspring.

Role of corticosteroid binding globulin in emotional reactivity sex differences in mice.

Sex differences exist for stress reactivity as well as for the prevalence of depression, which is more frequent in women of reproductive age and often precipitated by stressful events. In animals, the differential effect of stress on male's and female's emotional behavior has been well documented. Crosstalk between the gonadal and stress hormones, in particular between estrogens and glucocorticoids, underlie these sex differences on stress vulnerability. We have previously shown that corticosteroid binding globulin (CBG) deficiency in a mouse model (Cbg k.o.) leads, in males, to an increased despair-like behavior caused by suboptimal corticosterone stress response. Because CBG displays a sexual dimorphism and is regulated by estrogens, we have now investigated whether it plays a role in the sex differences observed for emotional reactivity in mice. By analyzing Cbg k.o. and wild-type (WT) animals of both sexes, we detected sex differences in despair-like behavior in WT mice but not in Cbg k.o. animals. We showed through ovariectomy and estradiol (E2) replacement that E2 levels explain the sex differences found in WT animals. However, the manipulation of E2 levels did not affect the emotional behavior of Cbg k.o. females. As Cbg k.o. males, Cbg k.o. females have markedly reduced corticosterone levels across the circadian cycle and also after stress. Plasma free corticosterone levels in Cbg k.o. mice measured immediately after stress were blunted in both sexes compared to WT mice. A trend for higher mean levels of ACTH in Cbg k.o. mice was found for both sexes. The turnover of a corticosterone bolus was increased in Cbg k.o. Finally, the glucocorticoid-regulated immediate early gene early growth response 1 (Egr1) showed a blunted mRNA expression in the hippocampus of Cbg k.o. mutants while mineralocorticoid and glucocorticoid receptors presented sex differences but equivalent mRNA expression between genotypes. Thus, in our experimental conditions, sex differences for despair-like behavior in WT mice are explained by estrogens levels. Also, in both sexes, the presence of CBG is required to attain optimal glucocorticoid concentrations and normal emotional reactivity, although in females this is apparent only under low E2 concentrations. These findings suggest a complex interaction of CBG and E2 on emotional reactivity in females.

Embryonic development of kisspeptin neurones in rat.

Kisspeptins, encoded by the Kiss1 gene, play a key role in the regulation of reproductive function, although very little is known about the ontogenesis of this system. The present study aimed to determine the period of arcuate nucleus (ARC) kisspeptin cell birth and the embryonic stage and neuroanatomical sites of onset of kisspeptin immunoreactivity. Bromodeoxyuridine (BrdU) was administered to female rats at various gestational stages and double immunohistochemistry against kisspeptin and BrdU was performed on brain sections from their offspring. The period of neurogenesis of ARC kisspeptin neurones begun between embryonic day (E) 12.5 and E13.5, reached its peak at E15.5 and was not completely over at E17.5. Kiss1 mRNA was detected in mediobasal hypothalamic punches of embryos aged E14.5, E16.5, E18.5 and E22.5 by real-time reverse transcriptase-polymerase chain reaction. Accordingly, kisspeptin-immunoreactive (-IR) cells were consistently detected in the embryonic ARC from E14.5 and their number increased until E18.5 to reach approximately half the level observed in adults. Between E18.5 and E22.5, the number of kisspeptin-IR cells and hypothalamic Kiss1 expression significantly decreased, regardless of sex, and this decrease persisted until birth. Taken together, these results demonstrate that rat ARC kisspeptin neurones are born locally during an extended embryonic period and are able to synthesise kisspeptins rapidly after their birth, consistent with the hypothesis of a role during embryonic activation of the hypothalamic-hypophyseal-gonadal axis. A sex-independent decrease of kisspeptin-IR cell numbers was observed during the perinatal period, suggestive of important regulations of kisspeptin neurones around birth.

Kisspeptin-immunoreactivity changes in a sex- and hypothalamic-region-specific manner across rat postnatal development.

Kisspeptins are potent secretagogues of gonadotrophin-releasing hormone, playing a key role in puberty onset. These peptides are produced by distinct neuronal populations of the hypothalamus located in the rostral periventricular area of the third ventricle (RP3V) and arcuate nucleus (ARC). The present immunohistochemical study aimed to determine the spatiotemporal onset of kisspeptin-immunoreactivity (-IR) in the neonatal hypothalamus of male and female rats and to evaluate changes in kisspeptin-IR around puberty. Kisspeptin-IR cells and fibres could be detected from the day of birth in the ARC of both males and females. At this stage, only females displayed some kisspeptin-IR fibres in the RP3V. From postnatal day 7 to adulthood, males displayed lower levels of kisspeptin-IR than females in both regions. During infancy, kisspeptin-IR fibre density in the female decreased in the ARC, whereas it increased in the RP3V. A sex-independent decline in RP3V kisspeptin-IR fibre density was observed in the juvenile, followed by a peripubertal increase in RP3V and ARC kisspeptin-IR. These peripubertal increases in kisspeptin-IR occurred at different timings dependent on sex and region. In females specifically, the increase in kisspeptin-IR fibre density occurred first in the ARC and later in the RP3V under constant levels of circulating oestradiol. In conclusion, the present study highlights the expression of hypothalamic kisspeptins soon after birth, as well as the neonatal establishment of a strong and persisting sex difference in ARC kisspeptin-IR in rats. Moreover, a female-specific desynchronisation of the ARC and RP3V was observed with respect to the increase in kisspeptin-IR fibre density around puberty, which was not related to peripubertal variations in circulating oestradiol.

The influence of catecholamine on the migration of gonadotropin-releasing hormone-producing neurons in the rat foetuses.

Catecholamines (CA) play an important role in the regulation of GnRH neurons in adults, and it is probable that they control GnRH-neuron development. Migration of GnRH neurons was evaluated in male and female rats at the 17th embryonic day (E17) and E21, following the daily treatment of their pregnant mothers from the 11th to the 16th and 20th day of gestation with alpha-methyl-para-tyrosine (alphaMPT), an inhibitor of catecholamine synthesis. High-performance liquid chromatography with electrochemical detection (HPLC-ED) was used to specify the alphaMPT-induced CA depletion. There was a 50-70% decrease in dopamine and noradrenaline content in the nose and in the brain of alphaMPT-treated foetuses, proving the efficacy of this pharmacological model. Immunohistochemistry was used to evaluate the percentage (%) of GnRH neurons along their migration pathway from the vomeronasal organ (VNO) in the nose to the septo-preoptic area in the forebrain which is considered as an index of neuron migration. Special attention was paid to the topographic relationships of GnRH neurons with catecholaminergic fibres. These were observed in apposition with GnRH neurons in the entrance to the forebrain. In CA-deficient foetuses, the percentage of GnRH neurons located in the rostral regions extending from the VNO to the septum was greater than in controls. However, no statistically significant difference was found in the forebrain which extended from the septum to the retrochiasmatic area. In conclusion, these data suggest that endogenous catecholamines stimulate the GnRH neuron migration in ontogenesis.

[Catecholamines in regulation of development of GnRH neurons of rat fetuses].

The contents of dopamine, serotonin, and noradrenaline in rat fetuses developing under the conditions of their deficiency induced by administration of alpha-methyl-para-tyrosine to females during 11th to 16th or 20th day of pregnancy and in fetuses, whose mothers were given saline at the same time, were determined using HPLC with subsequent electrochemical detection. Administration of alpha-methyl-para-tyrosine led to decreased levels of dopamine and noradrenaline in the areas of migration of GnRH-neurons in fetuses on days 17 and 21 of prenatal development. The concentration of serotonin remained unchanged, except in the head nasal area in males on day 21. The areas of interaction between the brain catecholaminergic systems and migrating and differentiating GnRH-neurons were determined by double immunohistochemical labeling. Close topographical location of GnRH-immunoreactive neurons and tyrosine hydroxylase-immunoreactive in the area of nucleus accumbens on days 17 and 20, as well as in the median eminence on day 20. The GnRH concentration in the caudal areas of migration of GnRH-neurons under the normal conditions and in the case of catecholamine deficiency was determined using radioimmunoassay. After administration of alpha-methyl-para-tyrosine the GnRH concentration in the anterior hypothalamus decreased in females. The data obtained suggest the involvement of catecholamines in the regulation of development of GnRH-Neurons during prenatal development. In addition, the adequacy and efficiency of the used model of catecholamine deficiency for studying the development of such neurons was confirmed.

[A population of neurons expressing tyrosine hydroxylase and migrating from olfactory placode into forebrain during ontogenesis in rats]. / Populiatsiia neironov, ékspressiruiushchikh tirozingidroksilazu, migriruiushchikh iz oboniatel'nykh plakod v perednii mozg, v ontogeneze u krys.

Olfactory placodes, that give rise to the olfactory and respiratory epithelia during ontogenesis, are a source of many neurons migrating into forebrain in the direction of growth of the olfactory nerves. The neurons expressing gonadotropin releasing hormone (GnRH) are among the best studied in the population in question. This hormone is responsible for the central regulation of reproduction in adult animals. It was already shown that, in addition to the GnRH-immunoreactive neurons, a small amount of neurons expressing tyrosine hydroxylase (TH), the first enzyme of catecholamine synthesis, migrates into the forebrain. Such a transient population of TH-immunoreactive neurons was shown by means of single and double immmunohistochemical labeling. The TH neurons were first found on branches of the olfactory, terminal, and vomeronasal nerves, along the trajectory of migration of GnRH-immunoreactive neurons on day 15 of embryogenesis, which preceded the appearance of GnRH-immunoreactive neurons. On days 17-21 of embryogenesis, both populations of neurons were found in almost the same areas and on day 21 single neurons contained both GnRH and TH. There were no neurons expressing decarboxylase of aromatic acids (DAA), the second enzyme of catecholamine synthesis, among TH-immunoreactive neurons, thus suggesting noncatecholaminergic nature of these neurons. However, single nonenzymatic DAA-immunoreactive neurons were found in the area of anterior olfactory nuclei in the forebrain, which suggests their involvement in local cooperative synthesis of catecholamines in the area where GnRH-immunoreactive neurons penetrate in the forebrain. Thus, the neurons expressing TH, TH and GnRH, and DAA were found in rats during prenatal period in the nasal part of the head along the nerves projecting into the forebrain and in the rostral part of forebrain. The origin and functional significance of these neurons are discussed.

[Effect of catecholamines on migration and differentiation of gonadotropin releasing hormone-neurons in rats]. / Vliianie kateholaminov na migratsiiu i differentsirovku gonadotropin-relizing gormon-neironov u krys.

The GnRH producing neurons are the key link of neuroendocrine regulation of the adult reproductive system. Synthesis and secretion of GnRH are, in turn, under the afferent catecholaminergic control. Taking into account that catecholamines exert morphogenetic effects on target cells during ontogenesis, this study was aimed at investigation of the effects of catecholamines on development of GnRH neurons in rats during ontogenesis. We carried out comparative quantitative and semiquantitative analyses of differentiation and migration of GnRH neurons in fetuses of both sexes under the conditions of normal metabolism of catecholamines (administration of saline) or their pharmacologically induced deficiency (administration of alpha-methylparatyrosine). The inhibition of catecholamine synthesis from day 11 of embryogenesis led to an increasing number of GnRH neurons in rostral regions of the trajectory of their migration over the brain: in the area of olfactory tubercles on day 17 and in the area of olfactory bulb on days 18 and 21. In addition, the optical density of GnRH neurons located in the rostral regions of migration was higher in the fetuses after administration of alpha-methylparatyrosine during embryogenesis, as compared to the control. It has been concluded that catecholamines stimulate the migration of GnRH neurons and affect their differentiation.

Prolonged neurogenesis during early development of gonadotropin-releasing hormone neurones in sheep (Ovis Aries): in vivo and in vitro studies.

Gonadotropin-releasing hormone (GnRH) neurons involved in controlling the reproductive function in vertebrates are derived from the olfactory placode. However, in the sheep and the rat species, GnRH-immunoreactive (GnRH-IR) neurons could not be detected in the olfactory region during the earliest phase of GnRH system development. Using in situ hybridization (ISH) and immunohistochemistry (IHC) in sheep embryos ranging from 26 to 53 days' gestational age (G26-G53), the present work confirmed that GnRH expression could not be detected during the earliest steps of migration. The first ISH+ cells were detected in the nasal septum and at the entrance of the telencephalon at G33 stage. [(3)H]-thymidine pulses applied to in vitro olfactory explant cultures showed that GnRH neuron precursor cells have an extended multiplication period corresponding to G26-G36 before entering the neuronal differentiation process. Therefore, the lack of GnRH neuron detection during the early phase of development in the sheep compared to the mouse and other vertebrates represents a major difference in the early development of GnRH neurons. In the mouse, GnRH neuron precursors have a limited multiplication period in the vomeronasal pit and only postmitotic neurons start migration, whereas in the sheep embryo, the multiplication period is extended to about 10 days as demonstrated in olfactory explant cultures.

Primary culture of neural precursors from the ovine central nervous system (CNS).

The present study demonstrates that bipotential neural precursors isolated from an early developmental stage of the sheep embryo nervous system can be maintained in vitro in an undifferentiated state for a long period. These precursors multiplied under the action of epidermal growth factor and basic fibroblast growth factor and formed free-floating aggregates of nestin-immunoreactive cells, called neurospheres. These precursors can undergo predominantly neural or glial differentiation according to the culture conditions. Medium supplemented with foetal calf serum mainly favoured cell differentiation predominantly into astrocytes, whereas the defined SATO medium favoured neuronal differentiation. Using various immunomarkers of neurones and astroglial cells, we described the course of differentiation of neuronal and astroglial cells in different culture conditions. The ability to grow neural precursors from common laboratory animals has been useful for studying the cellular and molecular mechanisms underlying the development of the central nervous system. Furthermore, neural progenitors are already being used for in vivo cell therapy in various neurodegenerative disorders. The ovine species is a well-known model for prion diseases, since scrapie is endemic in most countries and has been studied for a long time. In this respect, the availability of ovine neural precursors will add a new perspective to the study of the pathogenicity of prion diseases.

Pulsatile GnRH secretion from primary cultures of sheep olfactory placode explants.

The aim of this study was to investigate the development of pulsatile GnRH secretion by GnRH neurones in primary cultures of olfactory placodes from ovine embryos. Culture medium was collected every 10 min for 8 h to detect pulsatile secretion. In the first experiment, pulsatile secretion was studied in two different sets of cultures after 17 and 24 days in vitro. In the second experiment, a set of cultures was tested after 10, 17 and 24 days in vitro to investigate the development of pulsatile GnRH secretion in each individual culture. This study demonstrated that (i) primary cultures of GnRH neurones from olfactory explants secreted GnRH in a pulsatile manner and that the frequency and mean interpulse duration were similar to those reported in castrated ewes, and (ii) pulsatile secretion was not present at the beginning of the culture but was observed between 17 and 24 days in vitro, indicating the maturation of individual neurones and the development of their synchronization.

Early, middle, and late stages of neural cells from ovine embryo in primary cultures.

The utilization of neural cells in culture has importantly increased the knowledge of the nervous system biology. In most studies, the investigations are performed on biological materials coming from common laboratory animals and the extrapolation of the results to other animals is not easy. For some studies, such as developmental biology of the nervous system, prion disease investigations, or agronomical production, the utilization of ovine neural cell cultures presents many advantages. Unfortunately, there are few data on the conditions of culture of such cells. In the present work, we investigated simple ways to obtain neurons and astrocytes from sheep brain. Viable neuronal cell cultures were obtained from 40 to 50 day old fetuses. Their morphologies were quite similar to that of neurons from rodent or chick brain and they were labeled by antineurofilament antibodies. Stages older than 50 days of pregnancy were unable to give viable culture of neurons. The stages of 40 day old fetus to newborn lamb were able to give viable astrocyte cultures. The common protoplasmic astrocytes were obtained and they were labeled by antiglial fibrillary acidic protein antibodies. The astrocytes contained glycogen, thus looking like the common astrocytes from rodents. Neuronal or astroglial cultures can be derived from 26 day old embryos, but the cultures contained contaminating cells. Among the latter cells, there were undifferentiated cells which were flat and epitheloid and which were grouped as islets. These cells could be maintained in culture for a time duration over 7 months, even after two passages. They differentiated principally in astrocytes with a radial configuration. This work shows how some neural cells can be simply and easily cultured from sheep brain. For the first time, neurons were cultured from the sheep embryonic brain. Moreover, stem cells were cultured for more than 7 months and, finally, glycogen accumulation in sheep astrocytes was shown to be the same as that in rodent astrocytes. The oligodendrocyte culture was already documented. Thus, sheep can easily be used as well as other models for neural cell studies.

Primary cell culture of LHRH neurones from embryonic olfactory placode in the sheep (Ovis aries).

The aim of this study was to establish an in vitro model of ovine luteinizing hormone-releasing hormone (LHRH) neurones. Olfactory placodes from 26 day-old sheep embryos (E26) were used for explant culture. Cultures were maintained successfully up to 35 days, but were usually used at 17 days for immunocytochemistry. LHRH and neuronal markers such as neurofilament (NF) were detected by immunocytochemistry within and/or outside the explant. Three main types of LHRH positive cells are described: (1) neuroblastic LHRH and NF immunoreactive cells with round cell body and very short neurites found mainly within the explant, (2) migrating LHRH bipolar neurones with an fusiform cell body, found outside the explant, (3) network LHRH neuron, bipolar or multipolar with long neurites connecting other LHRH neurons. Cell morphology was very similar to that which has been described in the adult sheep brain. These results strongly suggest that LHRH neurones in the sheep originate from the olfactory placode. This mode may represent a useful tool to study LHRH neurones directly in the sheep.

Effect of sulfhydryl oxidation on ionic and gating currents associated with L-type calcium channels in isolated guinea-pig ventricular myocytes.

OBJECTIVE: L-type calcium currents (ICa) and gating currents modification by extracellular application of the selective free sulfhydryl oxidant p-hydroxy-mercuric-phenylsulphonic acid (PHMPS) were studied. METHODS: Both currents were obtained with the whole cell patch clamp technique in guinea-pig ventricular cardiocytes. RESULTS: The main finding was a reduction of ICa clearly differentiable from a "run down" process. This effect was protected, stopped and in some cases partially reversed by dithiothreitol, a protective reagent for -SH groups. We also found a decrease of the gating currents associated with L-type calcium channels. The calcium modulation and cAMP phosphorylation systems of ICa are unaffected by PHMPS. With barium as charge carrier the current-voltage curves of barium currents were shifted by 10 mV to the positive direction by PHMPS. The same effect was obtained with calcium currents using BAPTA as a fast calcium buffer. CONCLUSION: The results indicate that oxidation of -SH groups carried by the channel protein induces dysfunction of the calcium entry to cardiac cells by altering the gating process. A participation of thiol functions on the gating of the calcium channel is proposed.

Novel arylaminopyridazine-GABA receptor antagonists examined electrophysiologically in Ascaris suum.

The structure-activity relationships of 35 novel derivatives of 2-(carboxypropyl)-3-amino-4-methyl-6-phenyl pyridazine (SR 95103) were examined as gamma-aminobutyric acid (GABA) antagonists in the flap preparation of the parasitic nematode, Ascaris suum, using a two-microelectrode current-clamp technique. All but one of the potent antagonists displaced GABA dose-response curves to the right without reduction in the maximum response. The dissociation constants of the more potent competitive antagonists were described using a model which assumed that two molecules of GABA were required to open the ion channel but that only one molecule of antagonist acted on each ion channel. By exploring the structure-activity relationship, the potency of the antagonist was increased from a KB of 64 microM for SR 95103 to a KB of 4.7 microM for NCS 281-93 (2-(3-carboxypropyl)-3-amino-4-phenylpropyl-6-phenyl pyridazine).

Ontogeny of GnRH systems.

In all vertebrate species studied, the main central population of GnRH neurones, which produces the final messages regulating reproduction, originates outside the brain. Early during fetal life, they appear in the olfactory placode epithelium and then migrate toward the base of the telencephalon in close association with the nervus terminalis, penetrate the brain within the nervus terminalis roots, reach their final locations and eventually grow axons toward their targets. Only part of this process is documented in ruminants. In the sheep fetus, the olfactory placode develops between day 22 and day 26 of gestation, but the first GnRH-immunoreactive neurones have been detected only at day 35, associated with the extracerebral part of the nervus terminalis. During the next 30-40 days, the GnRH neuronal systems progressively invade the brain. In both sexes, most of the development, in terms of distribution and morphology of the neurones, appears to be completed by the middle of gestation (term being on day 145). On day 85 GnRH-immunoreactive neuronal systems of male and female fetuses have also been reported to be very similar to GnRH neuronal systems of adult females. Attention should now be focused on the earliest developmental steps.

Antagonist properties of arylaminopyridazine GABA derivatives at the Ascaris muscle GABA receptor.

1. In a previous study, it was shown that the potency order for two arylamino-pyridazine derivatives, SR95531 and SR95103, was different in Ascaris suum when compared to vertebrate preparations. SR95531, the most potent analogue at the vertebrate GABAA receptor, was found to be very weak at antagonizing GABA responses in Ascaris, but SR95103, approximately 20 times less potent than SR95531 in vertebrate preparations, was more potent than SR95531 in Ascaris. These results suggested the existence of different accessory binding sites at the Ascaris GABA receptor. 2. To test this hypothesis, the effects of a series of arylaminopyridazine derivatives of GABA on the GABA response in Ascaris suum muscle were investigated using a two-microelectrode current-clamp technique. 3. The results showed that SR42627, a potent antagonist at the GABAA receptor, was one of the weakest analogues in Ascaris muscle. In contrast, SR95132, virtually inactive in vertebrate preparations, was equipotent to SR95103, the most potent analogue of the series in Ascaris muscle. 4. The three most potent analogues in Ascaris, SR95103, SR95132 and SR42666, displace GABA dose-response curves to the right without decreasing the maximal response. The modified Schild plots for these compounds are consistent with a competitive mechanism involving two molecules of GABA and only one molecule of antagonist interacting with the receptor. The estimated dissociation constants for SR95103, SR95132 and SR42666 are, respectively, 64, 65 and 105 mumol l-1. 5. Structure-activity relationships for this series of compounds were examined in Ascaris and compared to those in vertebrates. Substitution on the pyridazine ring in the 4-position, while detrimental for the antagonist potency at the vertebrate GABAA receptor, appears to be a prerequisite for antagonistic activity on the Ascaris muscle GABA receptor. These results are interpreted in terms of the accessory binding site theory of Ariëns, and suggest the existence of different accessory binding sites on the Ascaris GABA receptor.

The physiology and pharmacology of neuromuscular transmission in the nematode parasite, Ascaris suum.

The organization of Ascaris motoneurones and nervous system is summarized. There is an anterior nerve ring and associated ganglia, main dorsal and ventral nerve cords which run longitudinally, and a small set of posterior ganglia. Cell bodies of motoneurones are found in the ventral nerve cord and occur in 5 repeating 'segments'; each contains 11 motoneurones. Seven morphological types of excitatory or inhibitory motoneurone are recognized. Each Ascaris somatic muscle cell is composed of the contractile spindle; the bag region, containing the nucleus; the arm; and the syncytial region, the location of neuromuscular junctions. The resting membrane potential of muscle is approximately -30 mV and shows regular depolarizing, Ca-dependent 'spike potentials' superimposed on smaller Na(+)- and Ca2(+)-dependent 'slow waves' and even slower 'modulation waves'. The membrane shows high Cl- permeability. Adjacent cells are electrically coupled so that electrical activity in the cells is synchronized. Acetylcholine (ACh) and gamma-aminobutyric acid (GABA) affect the electrical activity. Bath-applied ACh increases membrane cation conductance, depolarizes the cells, alters the frequency and amplitude of spike potentials and produces contraction. Bath-applied GABA increases Cl- conductance, decreases spike activity and causes hyperpolarization and muscle relaxation. The extra-synaptic ACh receptors on the bag region of Ascaris muscle can be regarded as a separate subtype of nicotinic receptor. ACh and anthelmintic agonists (pyrantel, morantel, levamisole) produce a dose-dependent increase in cation conductance and membrane depolarization which is blocked by tubocurarine, mecamylamine but not by hexamethonium. The potency of GABA agonists, with the exception of sulphonic acid derivatives, correlates with the vertebrate GABAa receptor. The potency of antagonists does not. Thus, bicuculline, securinine, pitrazepine, SR95531 and RU5135 are potent vertebrate GABAa antagonists but have little effect on GABA receptors. The potency order of the arylaminopyridazine GABA antagonists: SR95103, SR95132, SR42666, SR95133, SR95531, SR42627 and SR42640 at the Ascaris GABA receptors contrasts with that at vertebrate GABAa receptors. It has been suggested that the receptor is referred to as a GABAn receptor. Patch-clamp studies show that ACh activates a non-selective cation channel which has a main conductance of 40-50pS and apparent mean open time of 1.3 ms; a smaller channel of 20-30 pS with a similar open-time is also activated. Pyrantel and levamisole also produce openings with similar conductances and open-times.(ABSTRACT TRUNCATED AT 400 WORDS)