Preliminary findings on the effect of load-carrying to the structural integrity of the cervical spine

Summary Carrying loads on the head is a common practice in rural Zimbabwe. Headloading imposes a considerable amount of strain to the axial skeleton. The cervical spine, being the most cranial and mobile part of the vertebral column, may be susceptible to spondylosis or disc degeneration in headloading. Age as well as the effects of intrinsic factors on cervical spondylosis have been well documented. However, studies on the effect of extrinsic weight bearing to spondylosis on the cervical spine are lacking. In this study, the effect of headloading on the pattern of spondylosis attributed to aging was examined. Results indicated that age led to significant degeneration of the fifth intervertebral disc space (P<0.05) as well as significant straightening of the lordotic curve (P<0.01). Load carrying seems to accentuate the straightening of the curve (P<0.001). The results also suggest that headloading creates a shift in the degeneration from the fifth intervertebral disc space to higher levels. It is concluded that carrying heavy loads on the head alters the pattern of degenerative changes of the cervical spine.

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Etude préliminaire des effets des charges lourdes sur l'intégrité structurale de la colonne cervicale

Résumé Porter de lourdes charges sur la tête est une pratique habituelle au Zimbabwe dans les zones rurales. Le port céphalique de charge impose des contraintes considérables au squelette axial. La colonne cervicale, portion crâniale et mobile de la colonne vertébrale, peut présenter une cervicarthrose ou une altération discale en raison du port de charges sur la tête. L'âge et les facteurs intrinsèques déterminant une cervicarthrose ont été bien étudiés. Cependant, l'action éventuelle d'un poids supplémentaire contribuant à la genèse d'une cervicarthrose n'a pas été étudiée. Dans cette étude, les effets du port céphalique de charge sur l'importance d'une cervicarthrose attribuée au vieillissement, sont examinés. Les résultats indiquent que le vieillissement aboutit à une altération significative du 5ème espace intervertébral (P<0,05) ainsi qu'à un redressement significatif de la lordose (P<0.01). Le port de charge semble accentuer le redressement de la courbe (P<0,001). Les résultats suggèrent également que le port de charge sur la tête réalise un transfert des lésions du 5ème espace intervertébral vers des niveaux sujacents. On en déduit que le port de lourdes charges sur la tête modifie l'aspect des atteintes dégénératives de la colonne cervicale.

     

The role of the uterus in reproductive behavior

The uterus plays a major role in reproductive physiology. Numerous studies have shown that estradiol and progesterone exert their effects by binding to receptors within the cytoplasm of uterine cells and translocating these receptors to the nuclei where they presumably alter genomic activity. The extent of the steroid-receptor interaction in the cytoplasm and the nucleus is well correlated with uterine growth. Other physiological changes that take place in the uterus are also correlated with variations in the cytoplasmic and nuclear steroid receptor levels observed during different stages of reproductive cycle. In the rat, the uterus also exerts an inhibitory effect on the hormone-induced maternal and copulatory behaviors. Hysterectomy shortens the latency for the induction of maternal behavior and enhances sexual receptivity and proceptivity in ovariectomized, hormone treated rats. The mechanism of this inhibitory effect is not fully understood; however, it seems that the steroid binding capacity of the uterus mediates its behavioral influence. Thus when this capacity is reduced, as evidenced by lower levels of cytoplasmic estrogen receptors in long-term gonadectomized animals, the uterus loses its inhibitory effect on copulatory behavior.     

Development of feminine sexual behavior in the rat: Androgenic and temporal influences

The contributions of prenatal and postnatal androgen exposure upon the development of sexual behavior in rats were examined by prenatal treatment of pups with an androgen antagonist (flutamide) and postnatal androgenization or castration. Male and female rats were exposed to the androgen receptor-blocker flutamide (FLU) in utero via prenatal injections to the mother on Days 10 through 22 of gestation. At birth (Day 1) males were castrated. Both males and females were injected with either 100 μg testosterone propionate (TP) or oil on Day 1. In adulthood all gonadectomized animals were tested for the display of feminine sexual behavior (lordosis) in response to a range of estrogen dosages. Prenatal exposure to FLU enhanced lordosis in both sexes when compared to vehicle-treated controls. Postnatal TP treatment decreased lordotic potential as expected. However, in animals given TP postnatally, those receiving prenatal flutamide had higher lordosis quotients than animals receiving vehicle treatment. These data confirm (1) that the development of feminine sexual behavior is inhibited by androgen exposure, (2) that such exposure occurs prenatally, (3) that the potential for feminine behavioral differentiation occurs prenatally as well as postnatally, and (4) that androgen acts perinatally to affect estrogen sensitivity in adulthood.     

Induction of female sexual behavior by GTP in ovariectomized estrogen primed rats

The effect of both intrahypothalamic and systemic administration of guanosine triphosphate (GTP) on lordosis behavior was studied in ovariectomized and ovariectomized-adrenalectomized, estrogen-primed rats (estradiol benzoate, 4 μg). This estrogen dose per se induced only weak or no lordosis behavior. Injection of GTP into the medial hypothalamic area (100 μg in 2.5 μl) elicited lordosis behavior with relatively short latency in 6 out of 7 rats. Systemic administration of GTP in a dose range of 0.8 mg to 5.0 mg to ovariectomized estrogen-primed rats, stimulated intense lordosis behavior in all subjects. Weak lordosis responses were displayed within the first 12 hr after GTP injection, but at 48 hr all rats were highly estrous. Lordosis behavior remained for up to eight days, its duration being related to the dose of GTP administered. GTP (2 mg) induced lordosis behavior in ovariectomized, adrenalectomized estrogen-primed rats, thus excluding the participation of adrenal steroids in this effect. The results are interpreted in terms of the stimulation of adenyl cyclase-cAMP systems by GTP.     

Differential regulation of proenkephalin gene expression by estrogen in the ventromedial hypothalamus of male and female rats: implications for the molecular basis of a sexually differentiated behavior

The ventrolateral aspect of the ventromedial hypothalamic nucleus (VL-VM) contains many estrogen-concentrating neurons which mediate estrogen facilitation of reproductive behavior. Previous studies have shown that estrogen treatment increases proenkephalin (PE) gene expression in neurons of the VL-VM in ovariectomized female rats, and that enkephalin peptides may stimulate lordosis behavior. To determine whether there is a sex difference in steroid hormone regulation of PE gene expression we have examined the effects of estrogen and testosterone on PE mRNA levels in male rats. Slot blot hybridization analysis of RNA isolated from the ventromedial hypothalamus indicated that estrogen treatment increased PE mRNA levels in the VL-VM of ovariectomized female rats (2.2-fold), but had no measurable effect on PE mRNA levels in gonadectomized males. Testosterone treatment of gonadectomized males also had no effect on PE gene expression. To determine whether the sex difference in estrogen-inducibility of PE gene expression is due to the developmental effects of gonadal steroids, we have investigated the effect of estrogen on PE mRNA levels in the VL-VM of neonatally androgenized female rats. Unlike the genetic male, the androgenized females responded to estrogen treatment with a female-typical increase in PE mRNA levels (1.7-fold). Further, although the androgenized rats clearly exhibited signs of defeminization, they did exhibit estrogen-facilitated lordosis behavior when tested with manual stimulation. The PE mRNA induction in estrogen-treated androgenized rats correlated well with the lordosis scores obtained by manual stimulation testing. These results indicate that estrogen regulation of PE gene expression in the VL-VM is sexually differentiated and support the hypothesis that the enkephalinergic neurons of the VL-VM are involved in the regulation of female reproductive behavior.     

Evidence for the involvement of central 5-HT1A receptors in the mediation of lordosis behavior in the female rat

5-Hydroxy-L-tryptophan (5-HTP), 25 mg kg^-1 IP, in combination with the peripheral 5-HTP decarboxylase inhibitor benserazide, 25 mg kg^-1 IP, and the selective inhibitor of neuronal 5-hydroxytryptamine (5-HT) re-uptake, zimeldine, 10 mg kg^-1 IP, suppressed lordosis in ovariectomized female rats, treated with estradiol benzoate (EB) or with EB plus progesterone (P). The suppression of lordosis produced by 5-HTP was antagonized by the -receptor blocker (-)pindolol, which also is a selective 5-HT₁ receptor antagonist, but not by the 5-HT₂ receptor antagonists metitepine or pirenperone, nor by the -receptor blocker betaxolol. The EB-or EB plus P-activated lordosis was also suppressed by administration of the selective 5-HT_1a receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). Together, these observations indicate an important role of central 5-HT_1a receptors in the mediation of lordosis behavior in the female rat.     

GABAergic drugs and sexual motivation, receptivity and exploratory behaviors in the female rat

Female rats were allowed to pace sexual interactions in a bilevel chamber, where a sexually vigorous male was tethered to the bottom level. Exploratory behaviors (sniffing, rearing), locomotor activity (expressed as number of level changes and periods of inactivity) as well as items of sexual motivation (latency to descend to the male’s level, approaches towards the male and genital exploration) were recorded. In addition, sexual receptivity was evaluated in a non-paced situation. A test for motor impairment was also performed. The GABA transaminase inhibitor γ-acetylene GABA reduced exploratory behaviors at doses much lower than those needed to reduce receptivity. The GABA reuptake inhibitor SKF 100330A did not affect any behavior category at doses of 15 and 30 mg/kg, but had a sedative action at 60 mg/kg. This was shown as impaired motor coordination and an almost total absence of activity in the bilevel chamber. Receptivity was not impaired, however. The mixed GABA_A/ GABA_B agonist progabide reduced exploratory behaviors and receptivity without producing motor impairment at a dose of 400 mg/kg. The GABA_A agonist THIP impaired motor coordination and reduced receptivity and exploratory behaviors at a dose of 10 mg/kg. A larger dose, 20 mg/kg, had a strong sedative action. Only a small proportion of the animals descended to the males level. The GABA_B agonist baclofen reduced receptivity at a dose that had no effect on motor coordination or exploratory behaviors. None of the drugs had a specific effect on sexual motivation. Whenever behaviors reflecting motivation were reduced, there were also other behavioral effects indicative of sedation. These data show that GABA receptor agonists, particularly the GABA_B agonist baclofen, reduce sexual receptivity at doses that have only slight effect on motor functions or exploratory behaviors. In contrast, non-specific enhancement of GABAergic activity by a transaminase or reuptake inhibitor have effects on motor functions and exploratory behaviors at doses much lower than those needed to reduce receptivity. Received: 24 June 1996 /Final version: 18 September 1996     

Loss of Reproductive Competence at an Earlier Age in Female Rats Exposed Prenatally to Ethanol

Previous studies have shown that prenatal ethanol exposure can partially masculinize or defeminize neurobehavioral development of female rats. An early age of onset of anovulation is one of the primary characteristics of partial defeminization. Consequently, we examined the occurrence of anovulation in fetal alcohol-exposed (FAE) female rats at 2,6, and 12 months of age using both vaginal cytology as well as wheel-running behavior. We assessed the ability of estrogen and progesterone to elicit proprioceptive behaviors and lordosis at 2 and 17 months of age. Female subjects were derived from Sprague-Dawley dams administered an ethanol liquid diet (35% ethanol-derived calories), a pair-fed isocaloric liquid diet, or fed lab chow from days 14 to 22 of gestation. Litter representatives were placed in a computer-monitored wheel-running apparatus under a 12-hr lighting schedule from 49 to 60 days of age. Vaginal smears were taken from littermates during this same period. This same procedure was conducted again from 180 to 196 and from 380 to 396 days of age, except that vaginal cytology was examined in the same animals immediately after wheel-running behavior was studied. At 2 months of age, a normal cyclical pattern of wheel-running, characteristic of 4- to 5-day estrus cycles, was observed in all animals. No differences were detected in mean activity levels during the wheel-running period. This was accompanied by normal cyclic vaginal cytology and normal proprioceptive behaviors and lordosis. At 6 months of age, FAE females exhibited significantly reduced wheel-running. This was associated with a loss in the cyclical increase in wheel-running in 8 of 16 FAE females compared with 1 of 15 controls. Vaginal cytology confirmed the significant increase in the number of acyclic FAE females compared with controls at this age in these same animals. At 12–13 months of age, wheel-running activity was significantly reduced in all treatment groups compared with earlier ages, with no differences observed between groups. This was accompanied by a loss of cyclicity in 50–70% of controls and 100% of FAE animals. At 17 months of age, proprioceptive behavior and the lordosis quotient in FAE females was not different from that observed in controls. However, the quality of the lordotic response was found to be significantly less in FAE females. Overall, these results indicate that the window of reproductive competence in females may be shortened by prenatal alcohol exposure.     

Bulbectomy and sensitivity to estrogen: Anatomical and functional specificity

In order to clarify the influence of the olfactory system on female sexual behavior, ovariectomized rats were given sham operations (SHAM), total bilateral olfactory bulbectomy (TBULBX), partial bulbectomy (PBULBX), anterior olfactory nucleus lesions (AON) or accessory olfactory bulb lesions (AOB), and tested for lordosis behavior. Only TBULBX resulted in increased sensitivity to estradiol benzoate (EB) in that lordosis quotients (LQ) were increased and rejection behavior decreased following administration of 2, 4 or 8 μg EB/kg/day for 3 days. Only TBULBX group rats were anosmic on 2 postoperative tests. TBULBX group rats showed very mild hyperresponsiveness on an emotionality test. Effects of TBULBX on LQ are not due to general sensory hyperresponsiveness or EB-induced hyperresponsiveness since no differences in the quality of lordosis occurred, and no differences occurred in latency to paw-lift on hot plate tests with or without EB. Heightened EB sensitivity in the TBULBX group is not due to adrenal steroids since following adrenalectomy and 8 μg EB/kg treatment, TBULBX group LQ scores were still elevated relative to those of SHAM controls. The LQ scores of PBULBX group rats were intermediate to those of SHAM and TBULBX group rats. Bulbectomy-induced alterations in sensitivity to EB as measured by the LQ do not appear to be due to alterations in “arousal” mechanisms in general. While deficits in olfactory perception might exacerbate the effect, it is unlikely that anosmia per se is sufficient to induce major alterations in the degree of sexual receptivity following EB. The magnitude of behavioral effects of bulbectomy on EB sensitivity may be related, to some extent, to the amount of bulb tissue removed. It is possible that bulbectomy may enhance behavioral sensitivity to EB by disrupting biochemical responses to EB in limbic system structures which normally exert an inhibitory influence over sexual receptivity.     

Dissociation between female sexual behavior and luteinizing hormone release in old female rats

The relationship between lordosis behavior and LH release as measured by the response to mating or by the positive feedback response to estradiol benzoate (EB)/progesterone was studied in ovariectomized rats of three different age groups: young adult female rats (5 to 8 months old), middle age female rats (15 to 23 months old) and old female rats (over 24 months old). Middle age and old rats showed high levels of lordosis behavior regardless of the pattern of LH secretion in response to mating or the positive feedback response to EB/progesterone. The mean LH rise after mating as well as after EB/progesterone treatment in pooled middle age and old rats is significantly lower than that of young rats. A clear dissociation between lordosis behavior and LH release in middle age and old female rats suggests that they are regulated at least in part by different mechanisms.