Role of prolonged copulatory behavior in facilitating reproductive success in a competitive mating situation in laboratory rats.

Results of 3 experiments (with 50 female F344/MA, 19 male F344, 12 male Long-Evans, 9 male BN/MA, and 9 male MAXX/MA rats) lend support to the hypothesis that the multiple ejaculatory pattern of male rats is of functional significance in that it increases the proportion of offspring sired by a given male when his female partner subsequently mates with a 2nd male, thus establishing conditions for sperm competition. When each male attained just 1 ejaculatory series, there was little effect of mating order (Exp I). Exp II revealed that when the 1st male completed 5 ejaculatory series, he sired a significantly higher porportion of the offspring relative to a 2nd male than when the 1st male attained just 1 ejaculation. The mechanism underlying the advantage of multiple ejaculations appears to lie in the proportion of sperm from each male in the female's tract rather than in either the mere passage of time or the effects of stimulation per se (Exp III). The multiple ejaculation pattern with a single female can be seen not as "wasted activity" but rather as functional in maximizing the reproductive success of individual males. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distribution of lipochrome pigment in the prostate gland: biological and diagnostic implications

Lipochrome pigment is characteristically found in Wolffian duct-derived structures including seminal vesicles and ejaculatory ducts. The presence of lipochrome pigment is helpful in identifying atypical histological patterns of seminal vesicle or ejaculatory duct that mimic prostatic adenocarcinoma. The authors studied the distribution of lipochrome pigment in 28 radical prostatectomy specimens using a modified Ziehl-Neelson stain and fluorescence microscopy. In all cases secretory epithelium of the central zone contained lipochrome pigment often in significant amounts (2 to 3+). Secretory epithelium from peripheral and transition zones in each of four specimens (14.3%) contained lipochrome pigment. In addition, occasional examples of nodular hyperplasia, prostatic intraepithelial neoplasia, and prostatic adenocarcinoma contained lipochrome pigment. The preferential distribution of lipochrome pigment in central zone epithelium adds further support to the hypothesis that central zone glands are derived embryologically from Wolffian duct (mesoderm) rather than urogenital sinus (endoderm), which gives rise to transition and peripheral zone glands. Furthermore, lipochrome pigment should not be used as the sole diagnostic criterion for separating atypical histological patterns of seminal vesicle and ejaculatory duct from those of prostatic origin.     

Wipe and flexion reflexes of the frog. I. Kinematics and EMG patterns

1. We evaluated the hypothesis that the neural control of complex motor behaviors is simplified by building movement sequences from a series of simple neural "building blocks." In particular, we compared two reflex behaviors of the frog, flexion withdrawal and the hindlimb-hindlimb wipe reflex, to determine whether a single neural circuit that coordinates flexion withdrawal is incorporated as the first element in a sequence of neural circuits comprising the wipe. The neural organization of these two reflexes was compared using a quantitative analysis of movement kinematics and muscle activity patterns [electromyograms (EMGs)]. 2. The three-dimensional coordinates of the position of the foot over time and the angular excursion of hip, knee, and ankle joints were recorded using a WATSMART infrared emitter-detector system. These data were quantified using principal-components analysis to provide a measure of the shape (eigenvalues) and orientation (eigen-vector coefficients) of the movement trajectories. The latencies and magnitudes of EMGs of seven muscles acting at the hip, knee, and ankle were analyzed over the interval from EMG onset to movement onset, and EMG magnitudes during the initial flexion of the limb. These variables were compared during flexion withdrawal and the initial flexion movement of the limb during the hindlimb-hindlimb wipe reflex (before the onset of the frequently rhythmic portion when the stimulus is removed) when the two reflexes were elicited from comparable stimulus locations. 3. In both the flexion reflex and the initial movement segment of the wipe reflex, the foot moves along a relatively straight line. However, the foot is directed to a more rostral and lateral position during flexion than during wipe. All three joints flex during flexion withdrawal, whereas during the wipe, the knee and ankle joints flex but the angular excursion of the hip joint may vary. The different orientations of the movement trajectories are associated with EMG patterns that differ in both timing and magnitude between the two reflexes. 4. The differences in the kinematics and EMG patterns of the two reflexes during unrestrained movements make it unlikely that the neural circuit that coordinates flexion withdrawal is incorporated as the first element in the sequence of neural circuits underlying the wipe reflex. 5. Unlike the wipe reflex, during flexion withdrawal there is no apparent constraint on the accuracy of placement at the end of the movement, yet the animals nevertheless achieved consistent final positions of both the foot and of each joint. The implications of these findings with respect to the controlled variables are discussed.     

Fertility of mating in rats (Rattus norvegicus): Contributions of androgen-dependent morphology and actions of the penis.

Three experiments with Long-Evans hooded rats investigated the roles of the male's penile spines and penile cups (flaring of the distal glans) in the induction of luteal activity in the female and in the removal of copulatory plugs from the vaginal tract. Exp I revealed no role for the cup in luteal induction but suggested that elements of the ejaculatory reflex apart from cup formation contribute to the elicitation of this neuroendocrine response. The origin of this stimulatory effect was not directly determined, but indirect evidence suggested a role for penile spines. In Exps II and III, features of the glans penis that might help effect plug removal were investigated. It was found that penile spines, perhaps in conjunction with penile cups, contributed to the extraction of plugs from the vagina. It is posited that morphological aspects of the penis, together with behavioral factors such as the number of preejaculatory insertions, profoundly influence the fertility of mating. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transurethral resection of partially obstructed ejaculatory ducts: seminal parameters and pregnancy outcomes according to the etiology of obstruction

PURPOSE: We determine how transurethral resection of the ejaculatory ducts performed for infertility affects seminal parameters and pregnancy outcomes in patients with partial ejaculatory duct obstruction due to a congenital or acquired etiological factor. MATERIALS AND METHODS: Based on history and physical examination, hormonal profiles, semen analyses, transrectal ultrasonography and vasography findings partial ejaculatory duct obstruction was diagnosed in 14 men a mean of 30 years old who presented for infertility evaluation. Patients were grouped according to congenital or acquired cause of obstruction. Transurethral resection of the ejaculatory ducts was performed using the standard resectoscope loop technique. Clinical outcome was assessed by postoperative analyses of seminal parameters and pregnancy reports. RESULTS: Transurethral resection of the ejaculatory ducts significantly improved semen quality (ejaculate volume and percentage of sperm motility) in all patients in the congenital group, while all but 1 (83%) had an improved sperm count. Pregnancy was achieved via sexual intercourse by 66% of the patients an average of 5.7 months postoperatively. Of the acquired etiological factor group 37.5% had improved semen quality after transurethral resection of ejaculatory duct and 12.5% achieved pregnancy via sexual intercourse. Postoperative complications occurred at a similar rate in each group (33%). However, complications in the congenital etiology group were minor, while 25% of the men in the acquired group had significant impairment of seminal parameters after transurethral resection of the ejaculatory ducts. CONCLUSIONS: Semen quality improvement and pregnancy outcome after transurethral resection of the ejaculatory ducts for partial ejaculatory duct obstruction differ significantly according to the main etiological cause of obstruction. An equivocal diagnosis of partial obstruction and technical problems during transurethral resection of the ejaculatory ducts may contribute to failure. However, in some cases the reason for failure remains unclear.     

Is transrectal ultrasonography a reliable diagnostic approach in ejaculatory duct sub-obstruction?

We studied the diagnostic predictive power of transrectal ultrasonography (TRUS) coupled with semen volume in cases of distal seminal tract sub-obstruction. As a gold standard for diagnosis we used seminal tract washout (STW). Non-azoospermic subjects (n = 112) were submitted to transrectal ultrasonography because of suspected excretory infertility or other andrological pathologies, before performing STW. STW indicated ejaculatory duct sub-obstruction in 36.6% of the patients. Seminal vesicle enlargement (anterior-posterior diameter > or = 15 mm) and seminal vesicle roundish anechoic areas (stasis) were the ultrasonographic anomalies more often associated with ejaculatory duct sub-obstruction. Stepwise logistic regression (SLR) analysis revealed that the ultrasonographic evidence of stasis was highly diagnostic only in the presence of a low semen volume (< or = 1.5 ml) and that ejaculatory duct sub-obstructions may be present but with no evidence of ultrasonographic anomalies. Therefore, TRUS is a useful approach for the treatment of suspected ejaculatory duct sub-obstruction, but is not a reliable diagnostic tool and, before performing transurethral surgery, STW should be mandatory.     

Factor concentrates for haemophilia in the developing world

A total of 191 patients were evaluated at our department for azoospermia, and 11 were found to have azoospermia due to ejaculatory duct obstruction as proved by normal serum hormones, normal testicular biopsy, low ejaculate volume and absence of fructose in semen. Also transrectal ultrasound was performed, revealing distended seminal vesicles and dilated ejaculatory ducts. All these criteria together suggested ejaculatory duct obstruction as a cause of azoospermia. All patients underwent endoscopic management for treatment of their ejaculatory duct obstruction in the form of resection and/or incision of the ejaculatory duct ostium inside the urethra and patency was checked intraoperatively by injection of sterile methylene blue in the vas and visualizing the efflux of the blue dye endoscopically. Intraoperative patency was documented in 10 patients and postoperative patency by follow-up semen analysis in 7 patients (70% patency rate) of which 2 (20% pregnancy rate) were able to conceive within 2 years of endoscopic treatment. Postoperative complications included acute urinary retention in 1 patient, haematuria in 5 and recurrent epididymitis in 2 patients.     

Olfactory conditioning of sexual behavior in the male rat (Rattus norvegicus).

The role of classical conditioning in the copulatory preferences of male Long-Evans rats (Rattus norvegicus) was examined by pairing a neutral olfactory stimulus (almond odor) with female reproductive status. During training trials, the males were given access to scented or unscented females that were either sexually receptive or unreceptive. Subsequently, copulatory preferences were tested in males given simultaneous access to 2 receptive females, 1 scented and 1 not. Males trained with scented-receptive females displayed an ejaculatory preference for the scented female. Males trained with scented-unreceptive females or with unscented-receptive females displayed an ejaculatory preference for the unscented female. Males displayed no preference when scent and reproductive status were paired randomly. These results demonstrate that classical conditioning produces an ejaculatory preference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relationships among ejaculatory control, ejaculatory latency, and attempts to prolong heterosexual intercourse

Although premature ejaculation (RE) is considered the most common male sexual dysfunction, progress in understanding it has been hampered by the lack of a commonly accepted definition. Several different criteria have been used to assess RE with no attempt to validate the extent to which they are related. The current study assessed, in a sample of university men, the occurrence and relationships among four commonly applied RE criteria: perceived control over the occurrence of ejaculation, latency from vaginal penetration to ejaculation, satisfaction with perceived degree of ejaculatory control, and concern over the occurrence of rapid ejaculation. Other aspects of ejaculatory behavior were also assessed such as the thoughts and techniques men used to prolong intercourse and delay ejaculation. Results indicated that although the four RE criteria were significantly correlated, the magnitudes of these correlations were small. This suggests that these commonly used RE criteria are largely independent and are not interchangeable and that research in this area needs to adopt a multivariate approach to assessment. Men's erotophilia/erotophobia was not related to RE. While use of several ejaculatory delaying techniques were individually and jointly predictive of ejaculatory control and/or ejaculatory evidence, there was no strong support for any specific pattern of behavior that is related to better control and longer latencies. Further, experts were not able to distinguish the ejaculatory delaying techniques of the men with the poorest control and shortest latencies from those of the men with the best control and longest latencies.     

Facilitation and inhibition of male rat ejaculatory behaviour by the respective 5-HT1A and 5-HT1B receptor agonists 8-OH-DPAT and anpirtoline, as evidenced by use of the corresponding new and selective receptor antagonists NAD-299 and NAS-181

1. Ejaculatory problems and anorgasmia are well-known side-effects of the SSRI antidepressants, and a pharmacologically induced increase in serotonergic neurotransmission inhibits ejaculatory behaviour in the rat. In the present study the role of 5-HT1A and 5-HT1B receptors in the mediation of male rat ejaculatory behaviour was examined by use of selective agonists and antagonists acting at these 5-HT receptor subtypes. 2. The 5-HT1A receptor agonist 8-OH-DPAT (0.25-4.00 micromol kg(-1) s.c.) produced an expected facilitation of the male rat ejaculatory behaviour, and this effect was fully antagonized by pretreatment with the new selective 5-HT1A receptor antagonist (R)-3-N,N-dicyclobutylamino-8-fluoro-3,4-dihydro-2H-1-benzopyran-5 -carboxamide hydrogen (2R,3R) tartrate monohydrate (NAD-299) (1.0 micromol kg(-1) s.c.). NAD-299 by itself (0.75-3.00 micromol kg(-1) s.c.) did not affect the male rat ejaculatory behaviour. 3. The 5-HT1B receptor agonist anpirtoline (0.25-4.00 micromol kg(-1) s.c.) produced a dose-dependent inhibition of the male rat ejaculatory behaviour, and this effect was fully antagonized by pretreatment with the 5-HT1B receptor antagonist isamoltane (16 micromol kg(-1) s.c.) as well as by the new and selective antagonist (R)-(+)-2-(3-morpholinomethyl-2H-chromene-8-yl)oxymethylmorphol ino methansulphonate (NAS-181) (16 micromol kg(-1) s.c.). Isamoltane (1.0-16.0 micromol kg(-1) s.c.) and NAD-181 (1.0-16.0 micromol kg(-1) s.c.) had no, or weakly facilitatory effects on the male rat ejaculatory behaviour. The non-selective 5-HT1 receptor antagonist (-)-pindolol (8 micromol kg(-1) s.c.), did not antagonize the inhibition produced by anpirtoline. 4. The present results demonstrate opposite effects, facilitation and inhibition, of male rat ejaculatory behaviour by stimulation of 5-HT1A and 5-HT1B receptors, respectively, suggesting that the SSRI-induced inhibition of male ejaculatory dysfunction is due to 5-HT1B receptor stimulation.     

Spectral frequency and the modulation of the acoustic startle reflex by background noise.

The rat's (Long-Evans) acoustic startle reflex to a high-frequency tone burst (10.5 kHz) was depressed by intense high-frequency band-pass noise (8–26 kHz) but enhanced by low frequency noise (1–2 kHz). However, contrary to the hypothesis that the depression of startle in intense background noise is produced by sensory masking, the reflex to a low-freqency tone burst (at 1 kHz) was depressed by both high- and low-frequency band-pass noise. Two additional hypotheses are offered to supplement sensory masking in order to explain the asymmetry in these data. The first is that the intratympanic reflex, which acts as a high pass filter on acoustic input, is elicited in intense backgrounds. The second is that acoustic startle reflexes elicited by intense low-frequency tones are in part elicited by their high-frequency distortion products and that these distortion products are then masked by high-frequency background noise. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stretch reflex and servo action in a variety of human muscles

1. In the long flexor of the thumb the latency of the stretch reflex and of other manifestations of servo action is some 45 msec, roughly double the latency of a finger jerk. 2. Tendon jerks are feeble or absent in the long flexor of the thumb even in subjects with brisk long-latency stretch reflexes in this muscle. This, and other facts, suggests that the nervous mechanism of the tendon jerk is different from that of the stretch reflex. 3. A muscle that has feeble tendon jerks may show a late component in the response to a tendon tap, with a latency similar to that of the long-latency stretch reflex. 4. On the hypothesis that the excess latency of the stretch reflex over that of a tendon jerk is because the stretch reflex employs a cortical rather than a spinal arc, the excess would be expected to be larger in magnitude for the long flexor of the big toe and smaller for the jaw closing muscles. This is confirmed, 5. An alternative hypothesis that the long latency of stretch reflexes in thumb and toe is because they are excited by slow-conducting afferents is made improbable by the finding that stretch reflexes with an equal or greater excess latency are also found in proximal arm muscles. 6. The long-latency stretch reflex in proximal muscles was seen most distinctly in a healthy subject who happened to have feeble or absent tendon jerks. In ordinary subjects there is often a large, short-latency, presumably spinal component of the stretch reflex in proximal muscles; and short-latency responses to halt and release are also seen, The significance of this spinal latency servo action in proximal muscles remains to be explored. 7. The Discussion argues that the available data on conduction time to and from the cerebral cortex are compatible with the hypothesis that the long-latency component of the stretch reflex uses a transcortical reflex arc, and that none of the experiments described in the present paper are inimical to this view.     

Differential rates of exhaustion and recovery of several parameters of male rat sexual behavior.

Studied sexual exhaustion of 12 sexually experienced Long-Evans male rats with respect to several copulatory measures. The ejaculatory latency, intercouplatory interval, and intromission frequency demonstrated a U-shaped curve, exhibiting high values for the initial ejaculatory series, falling to a minimum at an intermediate ejaculatory series, and again increasing at exhaustion. The absolute refractory period of the postejaculatory interval (measured at vocalization termination) increased linearly, whereas the relative refractory period (the remaining portion of the postejaculatory interval) was a positively accelerating function. Partial recovery tests demonstrate that the preejaculatory measures and absolute refractory period substantially returned to baseline values by Day 6, while the relative refractory period was still extended. The significance of these data to the theoretical modeling of sexual behavior is discussed. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Activation of a distinct arousal state immediately after spontaneous awakening from sleep

In contrast to the many neural studies into the mechanisms of sleep onset and maintenance, few studies have focused specifically on awakening from sleep. However, the abrupt electrographic changes and large brief cardio-respiratory activation at awakening suggest that a distinct, transiently aroused, awake state may exist compared to later wakefulness. To test this hypothesis we utilized the acoustic startle reflex, a standard un-conditioned reflex elicited by a sudden loud noise. This reflex is modulated under specific conditions, one being a diminution of startle when a quieter pre-stimulus is presented immediately before the loud stimulus. This pre-pulse inhibition (PPI) is used as a measure of sensorimotor gating, with smaller PPI indicating less filtering of sensory inputs and increased responsiveness to external stimuli. Eight rats with electrodes for recording sleep-wake state were studied. An accelerometer measured startle responses. The startle reflex was elicited by 115 dB, 40 ms tones. PPI was produced by 74 dB, 20 ms tones preceding the 115 dB tone by 100 ms. Responses within 100 ms were measured. Stimuli were applied either 3-10 s after spontaneous awakenings, or in established wakefulness (> 30 s). Responses to the startle stimuli alone were similar in the different awake states (P = 0.821). However, PPI was smaller at awakening from non-REM sleep compared to established wakefulness (45.4 +/- 7.5% vs. 74.3 +/- 6.1%, P = 0.0002). PPI after awakening from REM sleep (52.8 +/- 17.9%) was not significantly different than established wakefulness (P = 0.297). Reduced PPI of the startle reflex at awakening from non-REM sleep supports the hypothesis that wakefulness immediately after spontaneous sleep episodes is neurophysiologically distinct from later wakefulness and associated with reduced gating of motor responses to sensory inputs. Spontaneous activation of this distinct, transiently aroused, state upon awakening may serve a protective function, preparing an animal to respond immediately to potentially threatening stimuli.     

Cardiovascular effects of amitriptyline in anaesthetized dogs

1. The effect of amitriptyline on cardiovascular variables has been studied in anaesthetized dogs. 2. In small doses (0.25 mg/dg) amitryptyline caused small increases in heart rates, contractility, blood pressure, coronary blood flow and aortic flow. 3. Large doses produced initial depressant effects on myocardial reflex rises in these and rate and blood pressure, which were followed by secondary reflex rises in these measurements. 4. The depressant effects were dose-related and were accompanied by marked increases in coronary flow and smaller increases in ortic flow. 5. The secondary reflex rises in cardiac parameters were abolished by propranolol and that of the blood pressure was much reduced.     

Hormonal modulation of genital reflexes in male and masculinized female dogs.

When testosterone propionate (TP) is administered to adult, neonatally castrated male dogs and to adult females with masculinized genitalia produced by prenatal and neonatal exposure to androgen, both types of animals are unsuccessful in their attempts to copulate with receptive females. In the present experiment, 6 neonatally castrated male and 10 genitally masculinized female beagles were tested before and after TP treatment for responses to manual stimulation of the genitalia. An additional experimental group consisted of 6 males castrated as adults, and there was a control group of 5 normal males. After a series of TP injections (5 mg/kg), neonatally castrated males, adult castrates, and genitally masculinized females exhibited complete and strong erectile and ejaculatory reflexes. Erect penis lengths of neonatally castrated males and masculinized females were significantly shorter than those of normal males or of males castrated as adults. It is suggested that the failure of males castrated at birth, and of genitally masculinized females, to insert and lock when mounting receptive females is due to incomplete penile development and not to incomplete "organization" of spinal reflex mechanisms. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Calcium regulation of basic helix-loop-helix transcription factors

There are clinical and experimental evidences that the cardiopulmonary reflex function is impaired in chronic hypertension, but it could be due to myocardial hypertrophy rather than to hypertension itself. To test this hypothesis we evaluated the Bezold-Jarisch reflex in experimental conditions of myocardial hypertrophy and arterial normotension. Adult male Wistar rats were subjected to myocardial hypertrophy (MHR) treating them with the beta-adrenoceptor agonist isoproterenol (0.3 mg/kg/day, s.c.) for 15 days and compared with vehicle injected control rats (CR). No significant changes in body weight (283+/-14 vs. 299+/-9 g), resting mean arterial pressure (104+/-4 vs. 110+3 mm Hg) or heart rate (330+/-11 vs. 358+/-18 bpm) were observed in MHR compared to CR. As expected, MHR showed left and right ventricular and left atrial hypertrophy when compared to CR. The bradycardia and hypotension that characterizes the Bezold-Jarisch reflex, induced by the 5-HT3, agonist phenyldiguanide (1.5-24.0 microg/kg, i.v.), were significantly decreased in MHR compared to CR. Cardiac muscarinic responsiveness, which was assessed by electrical stimulation of the efferent vagus in anesthetized animals or by stimulation of muscarinic receptors in isolated hearts, was unchanged or increased, respectively, in MHR compared to CR. Additional studies showed that the baroreflex and chemoreflex were also attenuated in MHR compared to CR. These data indicate that cardiac hypertrophy impairs the Bezold-Jarisch reflex probably due to changes at central integrative areas of the reflex.     

Microsatellites reveal heterosis in red deer

The fitness consequences of inbreeding and outbreeding are poorly understood in natural populations. We explore two microsatellite-based variables, individual heterozygosity (likely to correlate with recent inbreeding) and a new individual-specific internal distance measure, mean d2 (focusing on events deeper in the pedigree), in relation to two measures of fitness expressed early in life, birth weight and neonatal survival, in 670 red deer calves (Cervus elaphus) born on the Isle of Rum between 1982 and 1996. For comparison, we also analyse inbreeding coefficients derived from pedigrees in which paternity was inferred by molecular methods. Only 14 out of 231 calves (6.1%) had non-zero inbreeding coefficients, and neither inbreeding coefficient nor individual heterozygosity was consistently related to birth weight or neonatal survival. However, mean d2 was consistently related to both fitness measures. Low mean d2 was associated with low birth weight, especially following cold Aprils, in which foetal growth is reduced. Low mean d2 was also associated with low neonatal survival, but this effect was probably mediated by birth weight because fitting birth weight to the neonatal survival model displaced mean d2 as an explanatory variable. We conclude that in the deer population fitness measures expressed early in life do not show evidence of inbreeding depression, but they do show evidence of heterosis, possibly as a result of population mixing. We also demonstrate the practical problems of estimating inbreeding via pedigrees compared with a direct marker-based estimate of individual heterozygosity. We suggest that, together, individual heterozygosity and mean d2, estimated using microsatellites, are useful tools for exploring inbreeding and outbreeding in natural population.     

Reduced stretch-reflex sensitivity after exhausting stretch-shortening cycle exercise

The stretch-shortening cycle (SSC) is an effective and natural form of muscle function but, when repeated with sufficient intensity or duration, it may lead to muscle damage and functional defects. A reduced tolerance to impact has been reported, which may be partly attributed to a reduced stretch-reflex potentiation. The aim of the present study was to examine the influence of SSC-induced metabolic fatigue and muscle damage on the efficacy of stretch reflexes, as judged by the electromyograph (EMG) response of two shank muscles (lateral gastrocnemius LG, soleus SOL) to controlled ramp stretches. These EMG responses were recorded before and immediately after exhausting SSC-type leg exercise and 2 h, 2 days and 4 days later. Serum concentrations of creatine kinase ([CK]), myoglobin and lactate were measured repetitively along the protocol. Two maximal vertical drop jumps and counter-movement jumps were performed after each reflex test. The exhausting SSC-type exercise induced an immediate reduction (P < 0.05) with a delayed short-term recovery of the LG peak-to-peak reflex amplitude. This was not accompanied by significant changes in the reflex latency. The drop jump performance remained slightly but significantly reduced (P < 0.05) until the 2nd day postexercise. Peak [CK] appeared for all the subjects on the 2nd day, suggesting the presence of muscle damage. The increase in [CK] between the 2nd h and the 2nd day postexercise was found to be negatively related (P < 0.001) to the relative changes in the drop jump height. Furthermore, a significant relationship (P < 0.05) was found between recovery of the stretch reflex in LG and the decrease of [CK] between the 2nd and the 4th day. These findings support the hypothesis of a reduced stretch-reflex sensitivity. While the exact mechanisms of the reflex inhibition remain unclear, it is emphasized that the delayed recovery of the reflex sensitivity could have resulted from the progressive inflammation that develops in cases of muscle damage.