Testosterone-induced changes of choline acetyl-transferase and cholinesterase activities in rat levator ani muscle

Occupational use of agrochemicals results in inhibited cholinesterase activity and altered reproductive hormone levels in male farmers from Buea, Cameroon

The efficiency of agro pesticides and fertilizers in eliminating pests and scaling up crop yield has motivated farmers to increase their use. Unfortunately, health hazards caused on farmers by these agrochemicals are of growing concern, though not well elucidated. In order to evaluate the effects of occupational exposure to agrochemicals on some key parameters of male farmers' health in Buea Subdivision, Cameroon, a total of 101 men, including 62 farmers using the agrochemicals and a reference population of 39 men not involved in occupational utilization of the agrochemicals, were interviewed on use of protective equipment, exposure symptoms and reproductive health status. Thereafter, serum cholinesterase [acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)] activities, total antioxidant capacity and reproductive hormones [follicle-stimulating hormone (FSH), luteinizing hormone and testosterone] were assessed. Results revealed that farmers mainly used insecticides followed by fungicides, herbicides and fertilizers, but with inadequate protective measures. The use of agrochemicals resulted in several exposure symptoms including weakness, itches, burning sensation, headache, sneezing, coughing and vomiting, as well as decrease in serum AChE activity when compared to the reference population. The agrochemicals impacted negatively on the farmers' reproductive health as evidenced by increased FSH levels. Taken altogether, these results suggested that exposure to agrochemicals adversely affects farmers' health. Therefore, there is a need to further sensitize the farmers on the use of protective equipment to mitigate the exposure and resulting health hazards.

Evaluation of the isokinetic muscle strength, balance and anaerobic performance in patients with young male hypogonadism

Hypogonadism is a clinical condition that occurs due to infrequent abnormalities in the hypothalamic-pituitary-gonadal (HPG) axis in adolescence. Symptoms include weakening of muscle and bone strength. 30 young male patients with congenital hypogonadotropic hypogonadism (CHH) and 20 healthy young males were included in the present study. Quadriceps and hamstring muscle strength, balance and anaerobic performance capacities of the study group were measured both before and six months after Testosterone replacement therapy (TRT). The strength of the extensor and flexor muscles of both legs showed a statistically significant increase in the isokinetic test values at 60(0)/sec and 180(0)/sec angular velocity (p < 0.05). When the parameters related to balance were investigated, a statistically significant difference was found for stability indices of left and right between pre-TRT and post-TRT (p = 0.001 for both comparisons). According to the patients' anaerobic performance measurement results, a statistically significant improvement (p < 0.001) was also found between pre-TRT and post-TRT values for each parameter. It was shown that TRT significantly increases muscle strength, balance, and anaerobic performance of patients with male CHH. As a result, we absolutely recommend the use of TRT in patients with male CHH.

Estrogen alters excitability but not morphology of a sexually dimorphic neuromuscular system in adult rats

In rats, motoneurons of the spinal nucleus of the bulbocavernosus (SNB) innervate the bulbocavernosus (BC) muscle, which surrounds the base of the penis. The SNB/BC is a sexually dimorphic, steroid-sensitive neuromuscular system, which is critically important in male reproductive behavior. Androgens are necessary for the development, morphology, and function of the SNB/BC system. However, estradiol (E) is also necessary for the development of the SNB/BC system, and E is capable of maintaining BC EMG activity in adulthood. In this study, we used electrophysiological and anatomical methods to examine estrogenic effects on BC EMG activity. We used a modified H-reflex testing method to investigate polysynaptic reflex characteristics in intact males, castrates, and castrates treated short term with estradiol benzoate (EB). Measures of EMG activity, response latency, and spike count were altered in castrates, but maintained in EB-treated castrates to the levels of intact males. Furthermore, estrogenic effects were found in EMG activity that could be isolated to the periphery of the SNB/BC system. BC NMJ size and muscle fiber area have been demonstrated to be hormone sensitive, and we examined these for possible correlates of E's effects on BC EMG activity. BC muscles of intact males, castrates, and short-term EB-treated castrates were fixed and stained with zinc iodide and osmium tetroxide. NMJ size and muscle fiber area did not differ between groups. Together, these data suggest that E treatment results in changes in the neuromuscular periphery that maintain BC EMG activity, but this effect cannot be accounted for by changes in NMJ size or muscle fiber area.

Effects of sex hormones, forskolin, and nicotine on choline acetyltransferase activity in human isolated placenta

The activity of choline acetyltransferase (ChAT) was investigated in the human placenta before and after long-term incubation (24 h) to test the effects of sex hormones, nicotine and forskolin. ChAT activity differed considerably between the amnion (0.03 micromol/mg protein/h) and the villus (0.56). After long-term incubation, ChAT activity persisted in the latter but declined in the amnion. Neither sex hormones (beta-estradiol, testosterone, progesterone; 10 or 100 nM each) nor follicle stimulating hormone and luteinizing hormone (FSH/LH; 8.4 U/ml each) modified ChAT activity. Also nicotine (1 nM-100 microM) did not affect ChAT activity. Forskolin, an activitor of adenylyl cyclase, reduced ChAT activity in the villus but not in amnion. The present model offers the possibility to investigate ChAT regulation in intact tissue under long-term incubation. The risks of maternal smoking during pregnancy cannot be attributed to an effect of nicotine on placental ChAT activity. Differences in the regulation of ChAT appear to exist between neuronal and nonneuronal cells.

Testosterone-induced increase in muscle size in healthy young men is associated with muscle fiber hypertrophy

Administration of replacement doses of testosterone to healthy hypogonadal men and supraphysiological doses to eugonadal men increases muscle size. To determine whether testosterone-induced increase in muscle size is due to muscle fiber hypertrophy, 61 healthy men, 18-35 yr of age, received monthly injections of a long-acting gonadotropin-releasing hormone (GnRH) agonist to suppress endogenous testosterone secretion and weekly injections of 25, 50, 125, 300, or 600 mg testosterone enanthate (TE) for 20 wk. Thigh muscle volume was measured by magnetic resonance imaging (MRI) scan, and muscle biopsies were obtained from vastus lateralis muscle in 39 men before and after 20 wk of combined treatment with GnRH agonist and testosterone. Administration of GnRH agonist plus TE resulted in mean nadir testosterone concentrations of 234, 289, 695, 1,344, and 2,435 ng/dl at the 25-, 50-, 125-, 300-, and 600-mg doses, respectively. Graded doses of testosterone administration were associated with testosterone dose and concentration-dependent increase in muscle volume measured by MRI (changes in vastus lateralis volume, -4, +7, +15, +32, and +48 ml at 25-, 50-, 125-, 300-, and 600-mg doses, respectively). Changes in cross-sectional areas of both type I and II fibers were dependent on testosterone dose and significantly correlated with total (r = 0.35, and 0.44, P < 0.0001 for type I and II fibers, respectively) and free (r = 0.34 and 0.35, P < 0.005) testosterone concentrations during treatment. The men receiving 300 and 600 mg of TE weekly experienced significant increases from baseline in areas of type I (baseline vs. 20 wk, 3,176 +/- 186 vs. 4,201 +/- 252 microm(2), P < 0.05 at 300-mg dose, and 3,347 +/- 253 vs. 4,984 +/- 374 microm(2), P = 0.006 at 600-mg dose) muscle fibers; the men in the 600-mg group also had significant increments in cross-sectional area of type II (4,060 +/- 401 vs. 5,526 +/- 544 microm(2), P = 0.03) fibers. The relative proportions of type I and type II fibers did not change significantly after treatment in any group. The myonuclear number per fiber increased significantly in men receiving the 300- and 600-mg doses of TE and was significantly correlated with testosterone concentration and muscle fiber cross-sectional area. In conclusion, the increases in muscle volume in healthy eugonadal men treated with graded doses of testosterone are associated with concentration-dependent increases in cross-sectional areas of both type I and type II muscle fibers and myonuclear number. We conclude that the testosterone induced increase in muscle volume is due to muscle fiber hypertrophy.

Exogenous testosterone treatment decreases diaphragm neuromuscular transmission failure in male rats

The effect of chronic exogenous testosterone (T) treatment on neuromuscular transmission in the diaphragm (Dia) muscle of adult male rats was determined. The contribution of neuromuscular transmission failure (NTF) to Dia fatigue was evaluated by superimposing intermittent direct muscle stimulation on repetitive nerve stimulation of isometric contraction in vitro. T treatment significantly reduced the contribution of NTF to Dia fatigue by approximately 20% (P < 0.001). Fiber type-specific effects on NTF were determined by measuring Dia fiber glycogen levels subsequent to repetitive nerve or muscle stimulation. T treatment had no effect on glycogen depletion in Dia type I and IIa fibers regardless of stimulation route. In the control group, type IIx fibers demonstrated significantly less glycogen depletion after nerve stimulation compared with direct muscle stimulation (P < 0.05), suggesting the presence of NTF. In contrast, T treatment increased glycogen depletion of type IIx fibers during nerve stimulation to levels similar to those after direct muscle stimulation. These data indicate that testosterone treatment substantially improves neuromuscular transmission in the Dia.

Anabolic-androgenic steroid induced alterations in choline acetyltransferase messenger RNA levels of spinal cord motoneurons in the male rat

The effect of chronic supraphysiological doses of anabolic-androgenic steroids, such as those illegally used by recreational, amateur and professional athletes to increase muscle mass and strength, on motoneurons has not been established. The choline acetyltransferase activity levels of perineal muscles in the male rat are modulated by plasma testosterone levels. These muscles are innervated by the sexually dimorphic motoneurons of the spinal nucleus of the bulbocavernosus. Since the primary source of choline acetyltransferase in muscle is motoneuronal, testosterone may modulate perineal muscle choline acetyltransferase activity by regulating choline acetyltransferase messenger RNA levels in motoneurons. The purpose of this study was to determine if choline acetyltransferase messenger RNA levels in cervical and lumbar spinal motoneurons are affected by chronic (four weeks) changes of plasma testosterone levels in the adult male rat. Using in situ hybridization, choline acetyltransferase messenger RNA levels were analysed in four motor columns: the spinal nucleus of the bulbocavernosus, the retrodorsal lateral nucleus of the lumbar spinal cord, and the lateral motor columns of the cervical and lumbar spinal cords. Chronic exposure to supraphysiological levels of testosterone (five- to ten-times physiologic levels) significantly increased choline acetyltransferase messenger RNA in all four motor columns. Subsequent to castration, choline acetyltransferase messenger RNA levels decreased in motoneurons of the spinal nucleus of the bulbocavernosus and the retrodorsal lateral nucleus. This observation suggests that the decrease in choline acetyltransferase activity levels of muscles innervated by spinal nucleus of the bulbocavernosus motoneurons may be due to changes in choline acetyltransferase protein levels. Indeed, testosterone replacement therapy of castrated males prevented the decline of choline acetyltransferase messenger RNA levels in motoneurons. The results of this study demonstrate that anabolic-androgenic steroids can affect the levels of specific messenger RNAs in motoneuron populations throughout the spinal cord suggesting that motoneuronal characteristics are modulated by circulating anabolic-androgenic steroid levels regardless of the purported "androgen sensitivity" of the specific neuromuscular system.

Axotomy of developing rat spinal motoneurons: cell survival, soma size, muscle recovery, and the influence of testosterone

During the period of synapse elimination, motoneurons are impaired in their ability to generate or regenerate axonal branches: following partial denervation of their target muscle, young motoneurons do not sprout to nearby denervated fibers and after axonal injury, they fail to reinnervate the muscle. In the rat levator ani (LA) muscle, which is innervated by motoneurons in the spinal nucleus of the bulbocavernosus (SNB), synapse elimination ends relatively late in development and can be regulated by testosterone. We took advantage of this system to determine if the end of synapse elimination and the development of regenerative capabilities by motoneurons share a common mechanism, or, alternatively, if these two events can be dissociated in time. Axotomy on or before postnatal day 14 (P14) caused the death of SNB motoneurons. By P21, toward the end of synapse elimination in the LA muscle, SNB motoneurons had developed the ability to survive axonal injury. Altering testosterone levels by castration on P7 followed by 4 weeks of either testosterone propionate or control injections did not change the ability of SNB motoneurons to survive axonal injury during development, although these same treatments alter the time course of synapse elimination in the LA muscle. Thus, we dissociated the inability of SNB motoneurons to recover from axonal injury from their developmental elimination of synaptic terminals. We also measured the effect of early axotomy on motoneuronal soma size and on target muscle weight. Axotomy on P14 caused a long-lasting decrease in the soma size of surviving SNB motoneurons, whereas motoneurons axotomized on P28 recovered their normal soma size. Axotomy on or before P7 caused severe atrophy of the target muscles, matching the extensive loss of motoneurons. However, target muscle recovery after axotomy on P14 was as good as recovery after axotomy at later ages, despite greater motoneuronal death after axotomy on P14. This result may reflect an increase in motor unit size, a decrease in polyneuronal innervation by SNB motoneurons that survive axotomy on P14, or a combination of the two.

Prejunctional regulatory actions of androgens on a hormone sensitive muscle

The influence of androgens and time course of effects induced by hormone deprivation were examined on the spontaneous transmitter release in the levator ani (LA) muscle of 30-180-day-old male rats. The resting membrane potential (RMP) and miniature endplate potentials (mepps) were recorded intracellularly from LA muscle fibers of intact animals or gonadectomized at different ages. In intact animals, the frequency of mepps increased proportionately to the muscle fiber growth up to 60 days, stabilizing thereafter. Gonadectomy at any age did not affect the RMP, but increased the frequency of mepps by 65% to 140%. The effect was detected after 15 days and was unrelated to the degree of muscle atrophy. Independently of the age of gonadectomy control values of mepp frequency were restored after 90 days, while the accompanying postjunctional changes persisted. These results indicate that androgens exert a prejunctional inhibitory influence on the spontaneous transmitter release in the rat LA muscle. The transient nature of the prejunctional effect induced by hormone deprivation indicates an adjustment of nerve terminals to persistent postjunctional alterations.

Testosterone control of endplate and non-endplate acetylcholinesterase in the rat levator ani muscle

The time course of effects of castration (5-60 days) and testosterone treatment (15-60 days) of adult male rats were examined on the endplate (+EP) and non-endplate (-EP) acetylcholinesterase (AChE) of the androgen-dependent levator ani (LA) muscle. The thiocholine method was used to determine the enzyme activity. Castration caused LA muscle atrophy within 5 days but reduced the -EP and +EP AChE after 10 and 20 days, respectively. Following 30 days castration -EP and +EP AChE reached respectively 41% and 35% of control activity. Testosterone retrieval restored the control values of both muscle weight and total AChE after 15 and 60 days, respectively. Recovery of the +EP AChE preceded that of -EP AChE by 30 days. The results showed that in the rat LA muscle, +EP and -EP AChE depend on a continuous testosterone regulation that predominates at +EP region spreading thereafter to -EP region. Those data suggest a hormone regulation of AChE exerted indirectly through the synthesis and release of neurotrophic substances.

Effects of prepubertal castration on the spinal motor nucleus of the ischiocavernosus muscle of the rat

The location, number and size of the motoneurons innervating the ischiocavernosus muscle, identified by means of horseradish-peroxidase (HRP) retrograde transport, were studied (1) in adult untreated male rats, (2) in adult male rats castrated before puberty, and (3) in adult male rats castrated before puberty and injected with testosterone from the day of castration. After injection of HRP into the ischiocavernosus muscle, labeled motoneurons were found in the dorsolateral and dorsomedial columns of the lamina IX, at the level of L6 and S1 segments of the spinal cord. Morphometric analysis demonstrated that prepubertal castration induces a statistically significant reduction in the somatic and nuclear areas (40% and 35%, respectively, if compared to those of the control rats) of both the dorsolateral and dorsomedial motoneurons, but does not affect their number. The effects of castration are prevented by exogenous testosterone.

Sexual activity and the morphology of steroid-sensitive rat spinal motoneurons

In adult male rats, differential sexual experience has been shown to alter plasma androgen titers. Alterations in androgen levels have also been shown to significantly alter the structure of neurons in the spinal nucleus of the bulbocavernosus (SNB), a spinal motor nucleus that innervates perineal muscles involved in copulatory behavior. To determine if experientially induced alterations in androgen levels might alter SNB structure, male rats were assigned to one of three groups: sexually active, sexually inactive but exposed to inaccessible cycling females, and isolated. After 4 weeks of differential sexual experience, the soma size, total arbor, density, maximal fiber length, and frequency distribution of lengths of dendrites were examined in SNB motoneurons. No differences in motoneuron morphology were observed, suggesting that these motoneurons are not sensitive to socially induced alterations in androgen titers.

Hormonal control of neuron number in sexually dimorphic spinal nuclei of the rat: I. Testosterone-regulated death in the dorsolateral nucleus

Adult male rats have substantially more motoneurons than do females in two motor nuclei in the lumbar spinal cord: the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). Previous studies of the development of the SNB revealed that the sex difference in SNB motoneuron number is established through a differential motoneuron death which is under the control of androgens. In this study the development of the sexually dimorphic DLN was examined to test the hypothesis that early androgen action also determines the sex difference in DLN motoneuron number by regulating normally occurring motoneuron death. Because SNB motoneurons may migrate from the DLN, quantitative examination of DLN development was necessary in order to understand more completely the cellular mechanisms contributing to the establishment of dimorphic motoneuron number. At 5 days before birth, the number of motoneurons in the DLN is significantly higher than in adulthood in both sexes, and no sex difference is present. There is a decrease in motoneuron numbers prenatally in both sexes, which is consistent with the emigration of presumptive SNB motoneurons. Motoneuron number declines differentially through the first week of postnatal life and by postnatal day 10 motoneuron numbers are in the adult range and the sex difference is fully expressed. Females lose significantly more DLN motoneurons than males through a differential death as revealed by the higher incidence of degenerating cell profiles. Females treated with testosterone propionate have a male-typical motoneuron loss and incidence of degenerating cells. These results indicate that steroid hormones establish the sex difference in DLN motoneuron number by regulating normally occurring cell death.

Trophic control of cholinesterase activity in a testosterone-dependent muscle of the rat. II. Effects of testosterone administration

The effects of testosterone on the weight, protein content, and acetylcholinesterase (AChE) activity were investigated in the hormone-dependent levator ani and nondependent extensor digitorum longus and soleus muscles from normal or castrated male rats. In either group some muscles were also chronically denervated. Testosterone propionate treatment (3 mg/week for 2 weeks, s.c.) of normal rats increased the weight and protein content of the levator ani, respectively, by 19% and 63%; the muscle AChE was not affected. Protein content, but not the weight of the normal extensor digitorum longus and soleus was also increased after testosterone; AChE was reduced by 20% in the extensor digitorum longus and unaltered in the soleus. In castrated rats, testosterone reversed the levator ani atrophy and slowed down the decay of AChE, but it did not restore the normal enzyme activity. Testosterone did not prevent the atrophy and AChE decrease induced by denervation of either muscle. The weight and protein content of the denervated levator ani from castrated rats were increased by testosterone to the values found in denervated muscles from normal rats; AChE in the same muscles was not increased. The results confirm that separate mechanisms regulate protein synthesis and AChE in the rat levator ani. AChE is mainly regulated by neural factors which in turn appear to be influenced by circulating androgens. Similar hormonal influence on the muscle AChE was not detected in the extensor digitorum longus and soleus muscles.

Trophic control of cholinesterase activity in a testosterone-dependent muscle of the rat: effects of castration and denervation

The effects of testosterone withdrawal and chronic denervation on muscle weight and acetylcholinesterase (AChE) activity were studied in the hormone-sensitive levator ani muscle of the rat. Castration of adult male rats for 7 to 60 days caused a linear decrease of the weight, protein content, and AChE activity of the muscle, which stabilized after 30 days. Muscle weight and protein content decreased 2.3% per day. The total AChE activity decreased 7 days later 3.2% per day, reaching 37% of control at day 30. AChE activity per unit weight was increased in all castrated groups. Muscle weights and AChE activity of the extensor digitorum longus and soleus muscles were not altered after castration. Denervation of all three muscles caused 50% reduction of the muscle weight and protein content after 15 days. Total AChE activity decayed exponentially with a rate of 0.12 per day to 15 to 18% of control values. AChE activity per unit weight in the denervated muscles was always lower than in the control muscles. Combined castration and denervation intensified only the levator ani protein loss. The different onset and time course of the effects induced by castration and denervation indicate distinct mechanisms involved in the trophic control of muscle proteins and AChE activity. Chronic muscle denervation decreased total AChE activity to 15% of normal, whereas castration reduced the enzyme to 40% of the control values. The results indicate that neuronal and hormonal influences on AChE activity of the levator ani are not additive but overlap.

Androgens regulate the dendritic length of mammalian motoneurons in adulthood

Sex steroid hormones have been thought to alter behaviors in adulthood by changing the activity of neural circuits rather than by inducing major structural changes in these pathways. In a group of androgen-sensitive motoneurons that mediate male copulatory functions, decreases in androgen levels after castration of adult rats produced dramatic structural changes, decreasing both the dendritic length and soma size of these motoneurons. These changes were reversed by androgen replacement. These results imply a surprising degree of synaptic plasticity in adult motoneurons and suggest that normal changes in androgen levels in adulthood are associated with significant alterations in the structure and function of these neurons.

Testosterone increases acetylcholine receptor number in the "levator ani" muscle of the rat

The "levator ani" muscle of male rats provides a neuromuscular system in which both the muscle and its motoneurons have high levels of androgen receptors. Two weeks of castration caused a 48% loss of acetylcholine receptors in this muscle. One week of testosterone propionate injections initiated on week after castration increased receptor number by 27% over untreated castrate levels. These changes paralleled changes in muscle protein content. In contrast, castration and testosterone treatments of castrates had no effect on total. Triton X-100-extractable acetylcholinesterase activity. This system may provide a useful model of synaptic plasticity.

Androgen affects cholinergic enzymes in syringeal motor neurons and muscle

We examined the role of testosterone (T) in regulating the weight of the songbird syrinx and the activity of two cholinergic enzymes, choline acetyltransferase (CAT) and acetylcholinesterase (AChE). Castration of adult male zebra finches or neonatal canaries results in a lowering of syringeal weight and CAT and AChE activity. Administration of T for 1-4 weeks restores syringeal weight and AChE to intact levels in male zebra finches. Activity of CAT in muscle is not fully restored. Ovariectomy of female zebra finches and canaries does not affect these syringeal parameters, but T administration to ovariectomized females for 1 month increases syringeal weight and AChE activity. In the zebra finch tracheosyringealis nerve, activity of CAT and AChE is decreased one month after castration. T administration to castrates maintains nerve AChE activity but not CAT. In contrast to changes in the syrinx, tongue muscles do not change in weight or enzyme activity when circulating T levels are altered. Effects of muscle use and disuse were found on syringeal weight and AChE activity, but an androgenic effect also operates in addition. Results suggest that one mechanism for T regulation of singing in passerine birds is through induction of specific enzymatic proteins in androgen target neurons and muscles.

Acetylcholine synthesis and its dependence on nervous activity

The findings discussed in this paper mainly derived from studies on salivary glands, serving as model organs, indicate that the capacity to form the neurotransmitter acetylcholine, as judged by the activity of choline acetyltransferase, is influenced by the traffic of nerve impulses, as a long term effect. In the glands, choline acetyltransferase seems to be exclusively localized to the cholinergic nerves. In the postganglionic parasympathetic nerves of the glands, the activity of choline acetyltransferase decreases when the flow of secretory impulses in these nerves is abolished or reduced either by isolating the nerves from the central nervous system, surgically or pharmacologically, or by diminishing the reflex activation of the glands from the mouth. The opposite occurs when the reflex activation of the salivary glands is enhanced, i.e. the activity of choline acetyltransferase increases. Observations on various other organs are quoted in support of the view that the traffic of nerve impulses is of importance for the activity of the enzyme. An increase in choline acetyltransferase activity also occurs in some salivary glands after sympathetic denervation. This puzzling observation is discussed in relation to impulse traffic. Increased nerve impulse traffic and collateral sprouting seem to be responsible for the rapid restitution of choline acetyltransferase activity from a low level in an organ partially deprived of its cholinergic nerve supply.

Effect of castration and testosterone administration on the neuromuscular junction in the levator ani muscle of the rat

The ultrastructure of the neuromuscular junction (n.m.j.) of the androgen-sensitive levator ani muscle was studied in normal adult male rats, in 8-month-old rats castrated at the age of one month and in castrated rats treated with testosterone propionate (TP). Castration does not result in significant changes of the n.m.j. The density of synaptic vesicles and the postsynaptic junctional folds remain practically normal inspite of marked atrophy of the muscle. TP administration for 7 days results in marked changes in pre- and postsynaptic structures. There is slow progressive depletion of synaptic vesicles, appearance of cisternae and coated vesicles in axon terminals, and coalescence of coated vesicles with the plasma membrane. Coated vesicles are also found inside Schwann cells and among junctional folds. Dense core vesicles appear both in the axon terminals and in the postsynaptic area. Collateral sprouting of terminal axons with the formation of new immature junctions is observed. After 35 days of TP administration depletion of synaptic vesicles continues. Glycogen beta-particles, mostly freely dispersed, occasionally seen in axon terminals 7 days after TP administration, subsequently increase in number. In the endplate zone of the muscle fibre increased protein synthesis is indicated by a rapid increase in ribosomes and irregularly located myofilaments and myofibrils. The appearance of n.m.j. after testosterone administration resembles that described after nerve stimulation; the degree of change is however less pronounced.

Electrophysiological and contractile properties of the levator ani muscle after castration and testosterone administration

Electrical and contractile properties of the levator ani muscle were studied in normal rats, in castrated rats and in castrated rats treated with testosterone. 2. No significant changes in the frequency of miniature end-plate potentials were found 6 months after castration. The frequency increased already 6 h after testosterone treatment; an increase of about 100% was observed after 7 days of testosterone treatment. 3. Castration led to a 2-fold increase of the input resistance of the muscle fibres. After 7 days of testosterone treatment the input resistance was only slightly higher than normal. 4. The weight of the muscle was decreased to 18% of the control value after 6 months castration. It increased to 46% after 7 days of testosterone treatment. 5. The muscles of castrated animals revealed a prolongation of contraction time and marked changes in maximal rate of tension development and half relaxation time. Partial recovery of these parameters was found after 7 days of testosterone treatment. 6. Long-term castration did not induce any denervation-like changes of action potential parameters, and no tetrodotoxin resistance was found in spite of marked muscle atrophy.

Effects of castration, testosterone and immobilization on the activities of choline acetyltransferase and cholinesterase in rat limb muscles

Thirteen months after castration of male rats the weight of their soleus muscles was lowered to 82% and their choline acetyltransferase (ChAc) activity to 83% of control values. The administration of testosterone lasting 5 weeks increased the weight of the soleus muscles of castrated animals by 19% and their ChAc activity bu 37%. Changes in the activity of cholinesterase occurring after castration and testosterone treatment were not statistically significant. It is assumed taht the effect of testosterone on the activity of ChAc was mainly due to an increase in the functional activity of the motoneurones innervating the muscle. Rapid developmental increase of ChAc activity was observed in the muscles of intact rats between the age of 48 and 82 days. During this period of development the activity of ChAc rose faster than the weight of the muscles. Testosterone had no effect on the weight and ChAc activity of the soleus and extensor digitorum longus muscles of non-castrated rats after 1 week's administration; after 5 weeks' administration the weight of the muscles and their ChAc activity were diminished. After the soleus muscles of non-castrated rats had been immobilized for 10 days, their ChAc activity was 56% and their weight 51% of control values. The administration of testosterone did not alter the effect of immobilization on the ChAc and weight of the muscle.