Preproenkephalin mRNA is regulated by an interaction between steroid hormones and nociceptive stimulation.

The expression of preproenkephalin (PPE) mRNA has previously been shown to be regulated by steroid hormones in the ventromedial nucleus of the hypothalamus (VMH) and to be regulated by noxious stimuli in the dorsal horn of the spinal cord (DH). The present in situ hybridization study in ovariectomized rats showed that PPE mRNA expression in both the VMH and the lumbar DH, responds to the interaction between a noxious peripheral stimulus and ovarian steroid hormones. In the VMH, either estradiol or estradiol + progesterone increased the mean PPE mRNA content per cell by 100% compared with vehicle-treated rats. Unilateral hindpaw injection of 5% formalin, as compared to saline, significantly increased mean PPE mRNA content per VMH cell in rats treated with vehicle or estradiol but not those treated with estradiol + progesterone. Regression analysis for mean PPE mRNA content per VMH cell as a function of intensity of hindpaw inflammation showed a significant positive correlation coefficient after vehicle and estradiol treatment (P < 0.02) but a strong trend towards a negative correlation coefficient after estradiol + progesterone treatment (P < 0.06). ANOVA for homogeneity of regression coefficients showed a significant difference across hormone groups (P < 0.01). In the lumbar DH, mean PPE mRNA content per cell was greater in rats injected with formalin than with saline and was greatest in rats given steroids + formalin. Mean PPE mRNA content per DH cell was greater ipsilateral than contralateral to the formalin injection in estradiol-treated rats, but no laterality difference was seen in the other hormone groups. No significant differences in mean PPE mRNA levels per DH cell were found among the rats treated with saline + hormone, saline + vehicle, formalin + vehicle, or uninjected rats. For all hormone groups combined, mean PPE mRNA per DH cell showed a significant positive regression on intensity of hindpaw inflammation (P < 0.05). Taken together these data are consistent with reports of increased pain threshold during pregnancy, descending control of antinociception from the basomedial hypothalamus and positive correlations between VMH levels of PPE mRNA and lordosis, a behavior evoked by somatosensory stimulation below nociceptive threshold.

The medullary reticular formation is a site of muscle relaxant action of diazepam on deep back and neck muscles in the female rat.

We tested the hypothesis that the effect of systemic injections of diazepam (DZ, 125 mg/kg) to reduce the quality of the reproductive behavior, lordosis, and to reduce the EMG of lumbar back muscles involved in lordosis (Schwartz-Giblin et al., 1984) is exerted through a reticulospinal pathway with cells of origin in the nucleus gigantocellularis that excites lumbar motoneurons indirectly (Robbins et al., 1990, Robbins et al., 1992). In contrast, DZ facilitates lordosis behavior when infused into the midbrain central gray (McCarthy et al., 1995). Direct deposits of crystalline mixtures of DZ (20-80 ng) in dextrose were delivered to the medullary reticular formation (MRF) by diffusion from a cannula inserted through a guide to which a bipolar stimulating electrode was attached. The multiunit EMG response evoked by 20 (300 ms long) stimulus trains was recorded in back and neck muscles, lateral longissimus and splenius before and 5, 15, 30 and 60 min after local DZ deposits. There was a significant reduction in EMG response over this time period when stimulus intensities were within the range of 1.2-1.5 times threshold (Friedman two-way non-parametric test, P < 0.002). Large amplitude motor units that provide large tensions were the most sensitive to DZ-induced inhibition. Control deposits of dextrose had no significant effect. Systemic injections of progesterone (1 mg, i.p.) 60 min after DZ deposits, but not after dextrose deposits, further reduced the MRF-evoked EMG responses over the course of 1 h. As predicted, DZ infusions into the midbrain central gray did not reduce the reticulospinal-evoked axial muscle response, consistent with the facilitatory effect of midbrain central gray infusions of DZ on the lordosis quotient. The results suggest that benzodiazepine agonists (if endogenous) acting at sites in the MRF would be effective muscle relaxants during pregnancy, prior to the fall in progesterone that precedes labor.

Estrogen modulation of mRNA levels for the two forms of glutamic acid decarboxylase (GAD) in female rat brain.

Two separate forms of glutamic acid decarboxylase, now termed GAD65 and GAD67, are the rate limiting enzymes for synthesis of gamma-aminobutyric acid (GABA). Because of the significance of GABA to neuroendocrine processes, numerous attempts have been made to determine the impact of gonadal steroids on enzyme functioning with inconclusive results. Therefore, we attempted to determine the impact of estradiol on mRNA levels for each form of GAD by quantitative in situ hybridization histochemistry in various brain regions. Ovariectomized rats were treated with estradiol benzoate or oil vehicle on 2 consecutive days and the brains collected on the third day. DNA probes specific for GAD65 and GAD67 were radiolabeled with CTP32 using asymmetric polymerase chain reaction. Results of in situ hybridizations for each probe on alternate sections from the same animals were analyzed for magnocellular preoptic area (McPOA), dorsal medial nucleus of the hypothalamus (DMN), zona incerta (ZI), and midbrain central gray (MCG). In the McPOA, estradiol exerted opposite effects on the frequency distribution of pixels per cell for two GAD mRNA probes, significantly increasing GAD65 (P < .05) and decreasing GAD67 (P < .01; Kolmogorov-Smirnov). In the DMN, estradiol treatment significantly increased GAD67 by 60% (P < .05; two-way ANOVA) but decreased GAD65 mRNA by 73% (P < .01). Note the direction of effects are opposite between McPOA and DMN. In MCG, analysis showed no estradiol effect on GAD mRNA levels/cells, but the proportion of cells expressing detectable levels of GAD65 or GAD67 increased by 33-40% in estradiol-treated rats (chi 2, P < .001).

Infusions of diazepam and allopregnanolone into the midbrain central gray facilitate open-field behavior and sexual receptivity in female rats.

We have previously shown that blocking GABAA receptors with bicuculline in the dorsal and lateral quadrants of the rostral two-thirds of the midbrain central gray (MCG) in rats reduces the lordosis quotient (LQ) and proceptive behaviors without increasing the defensive index (McCarthy, Pfaff, and Schwartz-Giblin, 1991b), indicating that tonic release of endogenous GABA in the MCG has a primary facilitatory effect on reproductive behaviors. The present study tests whether two modulators of the GABAA-benzodiazepine-receptor complex, diazepam and the progesterone metabolite, allopregnanolone, facilitate female receptivity as well as open-field behavior. Ovariectomized estradiol benzoate (EB)-treated rats were bilaterally infused in the MCG with vehicle, diazepam, or allopregnanolone and tested 20 min after diazepam and 12 min after allopregnanolone. Animals were tested once each for both receptive or open-field behavior with testing sessions being at least 1 week apart in a crossover design between vehicle and one of the two drugs. Both diazepam and allopregnanolone significantly increased the lordosis quotient in a dose-dependent manner, the lowest effective dose tested being 100 and 250 ng, respectively. In the open-field test, infusion of diazepam (100 ng) in EB-treated rats significantly increased the ratio of central squares entered to total squares entered (C/T) without a change in total activity. Rats without EB elicited comparable C/T ratios when tested with five times as much diazepam. Diazepam infusions at more dorsal sites in the midbrain and in overlying cortex were without effect on C/T ratios in EB-treated rats. Allopregnanolone (500 ng) infusions in MCG of EB-treated rats did not alter C/T ratios compared to animals without EB. Our results are consistent with diazepam and allopregnanolone acting through the GABAA receptors of the MCG to enhance female sexual receptivity and with estradiol potentiating the effect of diazepam in the MCG to increase open-field behavior.

Intracerebral administration of antisense oligodeoxynucleotides to GAD65 and GAD67 mRNAs modulate reproductive behavior in the female rat.

Increased GABA activity in the medial hypothalamus (HYP) and midbrain central gray (MCG), but not the preoptic area (POA), facilitates sexual receptivity in the female rat [40]. In the current experiments, ovariectomized females were chronically treated with estrogen (via silastic capsules) to maintain a continuously high level of lordosis response. Administration of crystalline antisense oligodeoxynucleotide to the GABA synthetic enzyme, GAD67, into the HYP and MCG significantly and reversibly reduced lordosis response for 1-2 days, but did not inhibit lordosis when administered into the POA. Administration of a control oligonucleotide, consisting of the same nucleotide bases but in a scrambled sequence, did not significantly modulate behavior when infused into any brain areas. When oligodeoxynucleotide antisense to GAD67 was suspended in oil and then infused into the HYP or MCG it was more effective and resulted in less inter-animal variability. Subsequent experiments involving infusions into the MCG compared the effectiveness of antisense oligonucleotides to the two different forms of GAD, known as GAD65 and GAD67. Oligodeoxynucleotides antisense to the mRNA for either gene were effective at reducing lordosis behavior but with a different time course. Oligonucleotide antisense to GAD67 significantly reduced behavior within 24 h of infusion and there was full recovery by 4 days post-infusion. GAD65 antisense oligonucleotide did not significantly reduce behavior until 48 h post infusion and animals did not fully recover to pretest levels of lordosis until 5 days post-infusion. When antisense oligonucleotide for the two genes was administered simultaneously, the inhibition of lordosis was maximal at 24 h and stayed depressed for 4 days. There did not appear to be an additive effect of the two different antisense oligonucleotides when administered together. Tissue GABA levels in HYP and MCG of individual rats assayed by HPLC were no longer correlated with lordosis score after antisense oligonucleotide infusion but were after infusions of scrambled control oligos. Immunoblotting for the two forms of GAD revealed that GAD67 antisense oligonucleotide infusion led to significant decreases in both GAD67 and GAD65 protein levels as compared to infusions of scrambled control oligo. In addition, the levels of a neuronal marker, neuron-specific enolase, also decreased (although nonsignificantly) suggesting either a temporary shutdown of protein synthesis or a degeneration of GABAergic neurons after GAD67 antisense oligonucleotide infusion.

Catalepsy induced by muscimol infused into the hypothalamus can be sensitized and is modulated by ovarian steroids.

Muscimol (25 ng), but not saline, infused into the region of the zona incerta and lateral hypothalamus induced significant catalepsy in female rats. Daily administration of muscimol for 5 days resulted in a sensitization of the cataleptic response such that there was a significantly greater response to the same dose of muscimol beginning on Day 3 and continuing to increase up to Day 5. It was determined that the increase in catalepsy across days was not the result of conditioning after an initial exposure to muscimol. The endocrine condition of the female affected the degree of catalepsy induced by the first exposure to intrahypothalamic muscimol. Ovariectomized rats pretreated with estradiol benzoate (EB) exhibited significantly greater catalepsy than did females untreated or treated with progesterone or combined EB and progesterone. Weekly administration of muscimol also produced significant sensitization of the behavioral response, and the degree of sensitization was again affected by endocrine condition. Specifically, although females treated with EB for 2 days before muscimol infusion showed a significantly greater catalepsy after the first infusion than did ovariectomized females, they failed to show any increase in catalepsy scores across the 4 weeks of treatment. The greater catalepsy induced by muscimol infusion in EB-treated females may be related to changes in dopaminergic transmission. In contrast, females pretreated with progesterone 4 hr before muscimol infusion (with or without prior EB) exhibited highly significant increases in cataleptic response across the 4 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Axial muscle EMG responses evoked by cutaneous flank nerves in the female rat: effects of spinal transection, steroid hormones, and anesthesia.

In the lateral longissimus muscle (LL) of ovariectomized, female rats anesthetized with low surgical doses of urethane (1.0 g/kg), cutaneous reflexes with similar EMG and response patterns could be elicited from CNS-intact rats and from rats 24 h after complete thoracic spinal cord transection. The probability of eliciting a response to contralateral cutaneous nerve stimulation alone is much lower in rats with complete spinal transections compared to CNS-intact rats. For both CNS-intact and spinal-transected rats, responses to ipsilateral cutaneous nerve stimulation had a shorter latency and required significantly less current on average than responses to contralateral stimulation. The respective currents for eliciting threshold responses to ipsi- and contralateral stimulation are less for CNS-intact than spinal-transected rats. For both CNS-intact and spinal-transected rats, responses to bilateral cutaneous nerve stimulation were inconsistent in the same animal from run to run. With the variability of response at this anesthetic level, no consistent effects of progesterone (acute, i.v.) or estrogen (acute, i.v. and pretreatment, s.c.) were observed in spinal-transected rats. Intravenous progesterone reduced early, unilateral responses in CNS-intact rats anesthetized with 1.0 g of urethane/kg. For both CNS-intact and spinal-transected rats, additional anesthesia during EMG recording produced a gradual decline in response magnitude which could be recovered with a modest increase in stimulus intensity. However, spinal-transected rats appear to require less anesthesia to reduce comparable responses. The results suggest that supraspinal input is especially effective for facilitating contralateral cutaneous reflexes in back muscles, whereas it contributes more equally with afferent input and segmental circuitry to the efficacy of ipsilateral cutaneous reflexes.

Reticulospinal and reticuloreticular pathways for activating the lumbar back muscles in the rat.

These experiments tested hypotheses about the logic of reticulospinal and reticuloreticular controls over deep back muscles by examining descending efferent and contralateral projections of the sites within the medullary reticular formation (MRF) that evoke EMG responses in lumbar axial muscles upon electrical stimulation. In the first series of experiments, retrograde tracers were deposited at gigantocellular reticular nucleus (Gi) sites that excited the back muscles and in the contralateral lumbar spinal cord. The medullary reticular formation contralateral to the Gi stimulation/deposition site was examined for the presence of single- and double-labeled cells from these injections. Tracer depositions into Gi produced labeled cells in the contralateral Gi and Parvocellular reticular nucleus (PCRt) whereas the lumbar injections retrogradely labeled cells only in the ventral MRF, indicating that separate populations of medullary reticular cells project to the opposite MRF and the lumbar cord. In the second series of experiments the precise relationships between the location of neurons retrogradely labeled from lumbar spinal cord depositions of the retrograde trace, Fluoro-Gold (FG) and effective stimulation tracks through the MRF were examined. The results indicate that the Gi sites that are most effective for activation of the back muscles are dorsal to the location of retrogradely labeled lumbar reticulospinal cells. To verify that cell bodies and not fibers of passage were stimulated, crystals of the excitatory amino acid agonist, N-methyl-D-aspartate (NMDA) were deposited at effective stimulation sites in the Gi. NMDA decreased the ability of electrical stimulation to activate back muscles at 5 min postdeposition, indicating a local interaction of NMDA with cell bodies at the stimulation site. In the third series of experiments, electrical thresholds for EMG activation along a track through the MRF were compared to cells retrogradely labeled from FG deposited into the cervical spinal cord. In some experiments, Fast Blue was also deposited into the contralateral lumbar cord. Neurons at low threshold points on the electrode track were labeled following cervical depositions, indicating a direct projection to the cervical spinal cord. The lumbar depositions, again, labeled cells in MRF areas that were ventral to the locations of effective stimulation sites, primarily on the opposite side of the medulla. In addition, the lumbar depositions back-filled cells in the same cervical segments to which the Gi neurons project. These results suggest that one efferent projection from effective stimulation sites for back muscle activation is onto propriospinal neurons in the cervical cord, which in turn project to lumbar cord levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Steroid regulation and sex differences in [(3) h]muscimol binding in hippocampus, hypothalamus and midbrain in rats.

The gonadal steroids estradiol and progesterone have previously been shown to modulate the specific binding of the GABA(A) agonist, [(3) H]muscimol, in the CA1 region of the hippocampus, the ventromedial nucleus of the hypothalamus and the midbrain central gray of ovariectomized female rats. In this report we show a sex difference in the level of binding in the very caudal ventromedial nucleus of the hypothalamus. In contrast to females, there is no steroid modulation of [(3) H]muscimol binding in the ventromedial nucleus of the hypothalamus and midbrain central gray of males. These effects may be functionally related to GABAergic control of female sexual behavior. In contrast, steroid modulation of [(3) H]muscimol binding in the CA1 region of the hippocampus occurred to the same degree in males and females, and there was no difference in the level of binding in any region of the hippocampus between gonadectomized males and females. Incubation of brain slices with progesterone or its metabolite 5α-3α-pregnanolone dissolved in ethanol, produced a significant increase in [(3) H]muscimol binding in most brain regions as compared to control brain slices treated with ethanol alone. Moreover, there was also a marked increase in [(3) H]muscimol binding in all brain areas in the control condition which contained 100 mM ethanol, as compared to brain slices not preincubated with ethanol. The increase in binding after in vitro treatment with either progesterone or 5α-3α-pregnanolone is notably different from that seen after progesterone given in vivo 4 h prior to assay in that it is not site-specific, does not depend on prior treatment with estradiol and shows no sex difference. These results suggest different mechanisms for progesterone effects on the GABA(A) receptor when administered in vivo as compared to in vitro.

Ovarian steroid modulation of [3H]muscimol binding in the spinal cord of the rat.

[3H]Muscimol binding was measured in the lumbar spinal cord of female rats by in vitro quantitative autoradiography. Ovariectomized rats were treated subcutaneously with either oil, estradiol benzoate (EB) or EB plus progesterone (P) in a regime known to reliably induce sexual receptivity. The level of [3H]muscimol binding was highest in laminae I-III and in the region around the central canal. Binding was lower in laminae IV-VI and was frequently undetectable in the ventral horn. There was a significant increase in the level of binding in laminae I-III after EB treatment. There was also a significant increase after treatment with EB+P in comparison to both the ovariectomized and EB-treated groups in this same region of the spinal cord.

Midbrain central gray GABAA receptor activation enhances, and blockade reduces, sexual behavior in the female rat.

The inhibitory neurotransmitter, GABA, has been implicated in the control of lordosis behavior. Previous studies indicate that modulation of GABAA transmission can have dual effects on lordosis, being facilitative in the ventromedial hypothalamus and inhibitory in the preoptic area. The midbrain central gray (MCG) is also known to be an important neural site for regulating lordosis as well as defensive and escape behaviors, and plays an integral role in the control of nociception. Because of the multitude of behaviors regulated at the level of the MCG, we utilized a two-chamber testing apparatus that allowed simultaneous measurement of the females' proceptive (hopping and darting), receptive and rejection behaviors, as well as an index of nociception and general motor activity. We found that microinfusion of the GABAA antagonist, bicuculline, into the MCG of steroid-primed female rats resulted in a significant decrease in lordosis and proceptive behaviors at 5 min post-infusion. There was full recovery to pretest levels by 60 min. Furthermore, microinfusion of the GABAA agonist, muscimol, to estrogen-treated females that displayed low levels of receptivity and high levels of rejection behavior during a pretest, resulted in a significant increase in lordosis responding and a decrease in rejection behaviors. Neither drug significantly affected time spent in the vicinity of the male, motor activity or vocalizations. It is concluded that the decrease in lordosis resulting from blockade of GABA transmission is not solely due to the induction of antagonistic behaviors since there was no increase in rejections after bicuculline administration. The current findings are consistent with the interpretation that GABA facilitates lordosis in the MCG via disinhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Ipsilateral and contralateral effects on cutaneous reflexes in a back muscle of the female rat: modulation by steroids relevant for reproductive behavior.

1. Multiunit EMG recordings of cutaneous reflexes--evoked in the back extensor, lateral longissimus (LL), by bilateral stimulation of nerves to dorsal flank skin--were studied in ovariectomized female rats with and without estrogen pretreatment. 2. Poststimulus time (PST) histograms of data from rats with and without estrogen pretreatment show that the axial EMG response (10-30 ms) to ipsilateral (ipsi) flank skin nerve stimulation is significantly shorter in latency (1.4 ms) and 67% larger than the response to contralateral (contra) flank skin nerve stimulation recorded at the same site (n = 29 pairs). 3. When late EMG responses were also evoked at 50-120 ms in 37% of ipsi and 29% of contra cutaneous reflexes, the incidence of multiunit activity in the late peak was significantly greater in rats pretreated with silastics containing 100% estradiol (E) compared with 10% E or cholesterol controls. 4. When an ipsi cutaneous reflex in LL was conditioned by a stimulus to the contra flank skin nerve at a condition-test interval of 30 ms (C-T 30 ms), the average number of discharges in the early peak of the histogram was double that in the histogram obtained from the unconditioned ipsi reflex, independent of estrogen pretreatment. 5. In 12 out of 19 cases in which a contra cutaneous reflex was conditioned by a stimulus to the ipsi flank skin nerve (C-T 30 ms), the number of discharges in the early peak of the histogram was less than that in the early peak of the histogram derived from the unconditioned contra response, independent of estrogen pretreatment. 6. Intravenous injections of progesterone (P) or its metabolite 5 alpha-pregnane-3 alpha-ol-20-one (tetrahydraprogesterone, THP) decreased the magnitude of the early peak of the ipsi cutaneous reflex and the contra cutaneous reflex in LL, independent of estrogen pretreatment. At the same time, it did not reduce the magnitude of the early peak evoked by either ipsi or contra nerves after conditioning from the other side at C-T 30 ms. 7. As a consequence, the percentage facilitation of ipsi cutaneous reflexes by contra cutaneous conditioning was significantly increased after P or THP. This suggests that these steroids can selectively enhance behaviors involving bilateral inputs. 8. An unchanged axial motoneuron pool output to bilateral cutaneous inputs after P and THP, in spite of reduced motoneuron responses to cutaneous inputs from each side of the body, implies an increased gain in the reflex circuit.(ABSTRACT TRUNCATED AT 400 WORDS)

Hypothalamic effects on medullary reticular activation of deep back muscle EMG.

Medullary reticular stimulation can activate deep back muscle EMG in urethane-anesthetized female rats. Midbrain central gray stimulation can facilitate brainstem reticular control over deep back muscles. Since these deep back muscles lateral longissimus (LL) and medial longissimus (ML) execute the vertebral dorsiflexion of lordosis behavior, and since the motor control hierarchy sketched above parallels lordosis behavior circuitry, we tested the hypothesis that medial hypothalamic lesions (which, in behavioral experiments, decrease lordosis) can also reduce medullary reticular activation of deep back muscle EMG. Urethane-anesthetized rats were tested systematically for amplitude of lateral longissimus (LL) and medial longissimus (ML) EMG responses to electrical stimulus trains applied to the nucleus gigantocellularis (NGC) of the medullary reticular formation, before and after electrolytic lesions of the ventromedial hypothalamus (n = 18) or control sites (n = 30). Bilateral ventromedial hypothalamic lesions were able to greatly reduce EMG responses in LL and ML, often with a time course similar to previous lordosis behavioral results. Surprisingly, lesions at the anterior ventromedial nucleus pole were particularly effective, and may reflect importance of intraventromedial local neurons. Although, on the average, various control lesions were less effective, the ventromedial hypothalamic effect was not unique. For example, it was possible to see an EMG decrease following lesions of the dorsomedial thalamus. Nevertheless, EMG loss was not well correlated with changes in the cortical EEG, and thus does not appear to be a simple consequence of changes in "arousal." In conclusion, it appears that ventromedial hypothalamic neurons can affect medullary reticular control of back muscle EMG, but must share this role with other forebrain elements.

Ascending and descending projections to medullary reticular formation sites which activate deep lumbar back muscles in the rat.

The purpose of this study was to determine ascending and descending afferents to a medullary reticular formation (MRF) site that, when electrically stimulated, evoked EMG activity in lumbar deep back muscles. In anesthetized female rats, the MRF was explored with electrical stimulation, using currents less than 50 microA, while EMG activity was recorded from the ipsilateral lateral longissimus (LL) and medial longissimus (ML). MRF sites that evoked muscle activity were located in the gigantocellular nucleus (Gi). At the effective stimulation site, the retrograde fluorescent tracer, Fluoro-Gold (FG), was deposited via a cannula attached to the stimulating electrode. In matched-pair control experiments, FG was deposited at MRF sites that were ineffective in producing EMG activity in LL and ML, for comparison of afferent projections to effective versus ineffective sites. Labeled cells rostral to FG deposition at effective MRF sites were located in the preoptic area, hypothalamus, limbic forebrain and midbrain, with particularly high numbers in the ipsilateral midbrain central gray, tegmentum, paraventricular nucleus and amygdala. At medullary levels, there was a heavy projection from the contralateral Gi. FG labeled cells were also located in the contralateral parvocellular reticular nucleus, and lateral, medial and spinal vestibular nuclei. Labeled cells with ascending projections were observed in greatest number in the rostral cervical spinal cord, with fewer cells at mid cervical levels and even fewer in the lumbar spinal cord. These labeled cells were located primarily in lamina V, VII, VIII and X. Locations of labeled cells following FG deposition at ineffective MRF sites were similar. However, there was a striking difference in the number of cells retrogradely labeled from the effective MRF sites compared to ineffective MRF sites. Significantly greater numbers of labeled cells were observed in the contralateral MRF, the midbrain, and the cervical spinal cord from the FG deposition at effective stimulation sites. These results suggest that one characteristic of MRF sites that activate epaxial muscles is a larger amount of afferent input, from the midbrain central gray and from contralateral Gi, compared to ineffective MRF sites. Ascending and descending inputs converge at the effective MRF sites, and the larger number of descending projections suggests a more powerful contribution of these afferents to deep lumbar back muscle activation.

Steroid hormone effects on picrotoxin-induced seizures in female and male rats.

Picrotoxin (1 mg/kg, i.p.), evoked a single generalized seizure in 75% of ovariectomized rats. Pretreatment of matched pairs with silastic implants containing 100% estradiol had an anticonvulsant effect; it protected all rats against such seizures. Implants containing 10% estradiol in cholesterol were less effective in protecting against picrotoxin-induced seizures. With 2 mg/kg picrotoxin, 85% of the seizure-affected ovariectomized controls had multiple seizures. The incidence of seizures and the ratio of single to multiple seizures induced by the higher dose of picrotoxin were unaffected by estradiol silastic implants, intraperitoneal injections of progesterone (0.5 mg, 4-5 h before convulsant) or the combination of both hormones. At the 2 mg/kg dose, 8/8 intact males had no seizures while all paired ovariectomized females had seizures. By contrast, the incidence of seizures in pairs of gonadectomized males and females did not differ. Testosterone treatment improved the ratio of single to multiple seizures in males but not in females. Males had statistically fewer multiple seizures than did females after testosterone treatment. The distribution of latencies to a single seizure is statistically different from the distribution of latencies to the first of multiple seizures irrespective of dose, sex and hormone treatment. This suggests that the population of rats responding with a single seizure at the higher dose of picrotoxin have a higher threshold for acquiring multiple seizures and that testosterone predisposes males but not females to this population.

Effects of in vivo estradiol and progesterone on tritiated flunitrazepam binding in rat spinal cord.

Tritiated flunitrazepam binding was measured in autoradiograms of lumbar spinal cord from control ovariectomized female rats and from ovariectomized females treated with either estradiol-silastic implants or one subcutaneous injection of 500 micrograms progesterone 4-5 h before being killed or both estradiol and progesterone. Four areas of spinal cord were analyzed: the substantia gelatinosa, the region leading to and around the central canal, the remainder of the dorsal horn and the ventral horn. Specific flunitrazepam binding was greatest in the substantia gelatinosa and in the region around the central canal and was weakest in the ventral horn. Estradiol had no effect on flunitrazepam binding in the spinal cord despite estradiol concentrating cells in the substantia gelatinosa and around the central canal. In vivo progesterone enhanced flunitrazepam binding in the substantia gelatinosa while 10(-8) M progesterone in vitro was without effect. One day after spinal transection flunitrazepam binding in endocrine controls and estradiol-treated animals was unchanged but a progesterone injection 4-5 h before being killed had no effect on binding in the substantia gelatinosa.

Brainstem reticular stimulation facilitates back muscle motoneuronal responses to pudendal nerve input.

In urethane or pentobarbital anesthetized female rats, stimulation with bipolar electrodes in the medullary reticular formation evoked activity in lateral longissimus muscle nerves, when trains of pulses were applied. Combined stimulation of the medullary reticular formation and the pudendal nerve revealed a marked mutual facilitation of their two separate effects on the excitability of the lateral longissimus muscle nerves. These results match previous conclusions based on the effects of spinal column transection on the pudendal nerve-evoked response, and are consistent with a role for this mutual facilitation in the control of lordosis behavior.

Effects of total and partial spinal transections on the pudendal nerve-evoked response in rat lumbar axial muscle.

The pudendal nerve-evoked activity in lumbar axial muscle nerves 24-48 h following spinal transections was studied in order to examine the supraspinal control of the pudendal nerve-evoked response (PNER). After total transections of the spinal cord in the thoracic region the overall activity in the muscle nerves was much reduced; the evoked responses consisted only of a single peak in activity 19.8 ms (+/- 1.4 ms) following the last shock of a 3-shock pudendal nerve stimulus demonstrating that some of the earliest responses previously described for the PNER are segmental in origin. To help identify supraspinal inputs to the PNER a series of partial transections were made to cut selectively different fiber columns within the cord. Four different surgical procedures were performed: transections of the entire dorsal half of the cord; ablations of all of the medial columns; combined lesions of the dorsal half and medial columns, sparing the tracts within the ventrolateral columns and bilateral transections of the lateral columns. Following all partial transections except those of the lateral columns, the PNER was similar to that seen in intact animals. After lateral column transections however, the responses were like those seen in the totally transected animals. The combined results suggest that supraspinal influences upon the PNER are conveyed primarily via the ventrolateral columns of the spinal cord. Bilateral convergence of afferent information was evident in the totally transected animals, indicating that such convergence can occur at segmental levels. The lesions which substantially altered the PNER closely paralleled those which eliminated lordotic responsiveness in behaving female rats.