Stimulation In Female Rats Research Articles

Hyperlocomotion induced by inhalation of nicotine and a low dose of Δ9‐Tetrahydrocannabinol in female rats

BackgroundsGrowing availability of e‐cigarette devices permits users to prepare their own cocktail of drugs for inhalation, including polysubstance inhalation. Some individuals use nicotine and (−)‐Δ9‐tetrahydrocannabinol (THC) in combination by smoking tobacco and cannabis together or in sequence; this practice may extend to electronic cigarette users. THC exerts biphasic effects on locomotion in rats, with high doses (e.g., 5 mg kg−1, i.p.) decreasing, and lower doses (e.g., 0.03 mg kg−1, i.p.) increasing, locomotor activity. Nicotine (NIC) also increases locomotor activity in rodents. This study was designed to determine if interactive effects of THC and NIC result from vapor inhalation in rats using a novel e‐cigarette based procedure.MethodsFemale Sprague‐Dawley rats were exposed to vapor produced by the propylene glycol vehicle (PG), NIC (1 mg/mL in PG), THC (12.5 mg/ml in PG) or a combination of NIC with THC for a duration of 15 minutes. Body temperature and locomotor responses were evaluated post‐inhalation using a radiotelemetry system.ResultsLocomotor activity was increased in the rats for the first 60 min after NIC (1 mg/ml) exposure and this effect was blocked by pretreatment with mecamylamine. Activity was also increased 15 min after initiation of THC vapor compared with PG. Female rats did not show any further hyperlocomotion following exposure to the combination of NIC+THC vapor compared with either NIC or THC vapor inhalation, alone. The body temperature was decreased following the THC (12.5 mg/ml) or a combination of THC (12.5 mg/ml) +NIC (1 mg/ml) inhalation with significant effects starting 120 min post‐exposure, while NIC (1 mg/ml) inhalation did not alter the body temperature.DiscussionVapor inhalation of NIC or low dose THC stimulates locomotor activity in female rats. The co‐administration of a lower dose of THC with NIC produced no additive locomotor stimulation in female rats compared to either THC or NIC alone. The observed data provided behavioral evidence to suggest that the effect of nicotine on locomotion might not be modified by the physiological action of cannabinoids.Support or Funding InformationFunding support provided by USPHS grants AA007456, DA035482 and DA041967This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Mapping and neuromodulation of lower urinary tract function using spinal cord stimulation in female rats

Spinal cord epidural stimulation (SCS) represents a form of neuromodulation for the management of spasticity and pain. This technology has recently emerged as a new approach for potentially augmenting locomotion and voiding function in humans and rodents after spinal cord injury. However, the effect of SCS on micturition has not been studied extensively. Here, SCS was first applied as a direct stimulus onto individual segmental levels of the lumbar spinal cord in rats to map evoked external urethral sphincter (EUS) electromyography activity and SCS-induced voiding contractions. SCS of L2-3 inhibited EUS tonic activity, and SCS on L3 (L3/SCS) inhibited EUS tonic activity and elicited EUS bursting. In contrast, SCS of L1 and L4-6 evoked EUS tonic contractions, which resembled the urethral guarding reflex during bladder storage. Next, the effects of a bilateral pelvic nerve crush (PNC) injury on urodynamic function were examined at 14 days post-operatively. The PNC injury resulted in decreased voiding efficiency and maximum intravesical pressure, whereas the post-voiding residual volume was increased, suggestive of an underactive bladder. Finally, L3/SCS was performed to induce a voiding contraction and enable voiding in rats with a PNC injury. Voiding efficiency was significantly increased, and the residual volume was decreased by L3/SCS in rats after the PNC injury. We conclude that L3/SCS may be used to induce micturition reflexes in a partially filled bladder, reduce urethral resistance, and augment bladder emptying after PNC injury.

Cortical electrical stimulation in female rats with a cervical spinal cord injury to promote axonal outgrowth.

Electrical stimulation (ES) to promote corticospinal tract (CST) repair after spinal cord injury (SCI) is underinvestigated. This study is the first to detail intracortical ES of the injured CST. We hypothesize that cortical ES will promote CST collateralization and regeneration, prevent dieback, and improve recovery in an SCI rat model. The CST was transected at the the fourth cervical level in adult female Lewis rats trained in a stairwell grasping task. Animal groups included (a) ES333 (n = 14; 333 Hz, biphasic pulse for 0.2-ms duration every 500 ms, 30 pulses per train); (b) ES20 (n = 14; 20 Hz, biphasic pulse for 0.2-ms duration every 1 s, 60 pulses per train); (c) SCI only (n = 10); and (d) sham (n = 10). ES of the injured forelimb's motor cortex was performed for 30 min immediately prior to SCI. Comparisons between histological data were performed with a 1-way ANOVA or Kruskal-Wallis test, and grasping scores were compared using repeated-measures 2-way ANOVA. Significantly more axonal collateralization was found in ES333 animals compared with controls (p < .01). Axonal dieback analysis revealed ES20 rats to have consistently more dieback than the other groups at all points measured (p < .05). No difference in axonal regeneration was found between groups, nor was there any difference in functional recovery. Cortical ES of the injured CST results in increased collateral sprouting and influences neuroplasticity depending on the ES parameters used. Further investigation regarding optimal parameters and its functional effects is required.

Lateral Hypothalamic Stimulation Reduces Hyperalgesia Through Spinally Descending Orexin-A Neurons in Neuropathic Pain.

No evidence to date shows that lateral hypothalamic (LH) stimulation produces orexin-A-mediated antinociception in the spinal cord dorsal horn (SCDH) in a model of neuropathic pain. We conducted experiments to examine the effect of orexin-A-mediated LH stimulation in female rats with chronic constriction injury (CCI) on thermal hyperalgesia. Rats receiving carbachol into the LH demonstrated antinociception on both the left CCI and right nonligated paws (p < .05). Rats were given carbachol in the LH followed by intrathecal injection of the orexin-1 (OX1) receptor antagonist SB-334867, which blocked LH-induced antinociception compared with control groups (p < .05) in the left paw, but not in the right paw. These findings support the hypothesis that LH stimulation produces antinociception in rats with thermal hyperalgesia from neuropathic pain via an orexin-A connection between the LH and the SCDH. Identification of this pathway may lead to studies using orexins to manage clinical pain.

Inhibition of temporomandibular joint input to medullary dorsal horn neurons by 5HT3 receptor antagonist in female rats

Repeated forced swim (FS) conditioning enhances nociceptive responses to temporomandibular joint (TMJ) stimulation in female rats. The basis for FS-induced TMJ hyperalgesia remains unclear. To test the hypothesis that serotonin 3 receptor (5HT3R) mechanisms contribute to enhanced TMJ nociception after FS, ovariectomized female rats were treated with estradiol and subjected to FS for three days. On day 4, rats were anesthetized with isoflurane and TMJ-responsive neurons were recorded from superficial and deep laminae at the trigeminal subnucleus caudalis/upper cervical (Vc/C1–2) region and electromyographic (EMG) activity was recorded from the masseter muscle. Only Vc/C1–2 neurons activated by intra-TMJ injections of ATP were included for further analysis. Although neurons in both superficial and deep laminae were activated by ATP, only neurons in deep laminae displayed enhanced responses after FS. Local application of the 5HT3R antagonist, ondansetron (OND), at the Vc/C1–2 region reduced the ATP-evoked responses of neurons in superficial and deep laminae and reduced the EMG response in both sham and FS rats. OND also decreased the spontaneous firing rate of neurons in deep laminae and reduced the high-threshold convergent cutaneous receptive field area of neurons in superficial and deep laminae in both sham and FS rats. These results revealed that central application of a 5HT3R antagonist, had widespread effects on the properties of TMJ-responsive neurons at the Vc/C1–2 region and on jaw muscle reflexes under sham and FS conditions. It is concluded that 5HT3R does not play a unique role in mediating stress-induced hyperalgesia related to TMJ nociception.

Effect of prenatal methamphetamine exposure and challenge dose of the same drug in adulthood on epileptiform activity induced by electrical stimulation in female rats

Our previous study demonstrated that chronic prenatal methamphetamine (MA) exposure and a single dose of MA in adulthood decrease focally induced epileptiform activity in adult male rats. As seizures are known to be dependent on sex and female estrous cycle, the goal of the present study was to examine the combined effect of prenatal MA exposure (5mg/kg) and the MA challenge dose (1mg/kg) in adulthood on electroencephalography (EEG) recordings and consequences of brain stimulation in freely moving adult female rats with respect to the estrous cycle. Overall, 12 groups of adult female rats were tested: prenatally MA-exposed, prenatally saline-exposed and rats without prenatal injections, each of these groups was either postnatally challenged with MA or with saline injection (MA–MA, MA–S; S–MA, S–S; C–MA, C–S) and further divided according to the stage of the estrous cycle to metestrus/diestrus (M/D) or proestrus/estrus (P/E). Seizures were induced by repetitive electrical stimulation (15s/8Hz) of sensorimotor cortex. Stimulation threshold, duration of afterdischarges (ADs), and presence and duration of spontaneous ADs (SADs) were evaluated. Additionally, behavior associated with stimulation and ADs, and occurrence of wet-dog-shakes (WDS) were analyzed. The present study demonstrates that the prenatal MA exposure decreased the seizure threshold in females in M/D, but not in females in P/E. In addition, prenatally MA-exposed M/D females injected with saline in adulthood had increased the duration of ADs as well as SADs. The challenge dose of MA also decreased the seizure threshold. Moreover, prenatal as well as adult MA administration decreased the number and occurrence of WDS, respectively. Thus, the present study demonstrates that the effect of prenatal MA exposure and challenge dose of the same drug on focally induced epileptiform activity in adult female rats depends on the estrous cycle.

Spinal neurons activated in response to pudendal or pelvic nerve stimulation in female rats

The overlapping distribution of spinal neurons activated with either pudendal sensory nerve or pelvic nerve stimulation was examined in the female rat using c-fos immunohistochemistry. Pudendal sensory nerve stimulation resulted in a significant increase in fos-positive cells in the ipsilateral dorsal horn and bilaterally in the medial, lateral and intermediate gray of L5-S1. Pelvic nerve stimulation resulted in significant increases of c-fos immunoreactive nuclei in the ipsilateral dorsal horn, lateral and intermediate gray and bilaterally in the medial gray of L5-S1. Co-distribution of fos immunoreactive nuclei with the vesicular glutamate transporters (VGlut2 and VGlut3) and neurokinin I receptors were found in distinct regions of the dorsal horn, medial and lateral gray. Specific areas in the medial dorsal horn, dorsal gray commissure, laminae VI and X and dorsal lateral gray were activated after stimulation of the pudendal sensory and pelvic nerves, suggesting these areas contain spinal neurons that receive both somatomotor and visceral inputs and are part of the intraspinal circuit that regulates sexual and voiding function.

Spinal neurons activated in response to pudendal or pelvic nerve stimulation in female rats

Spinal neurons activated in response to pudendal or pelvic nerve stimulation in female rats

Facilitation of estrous behavior by vaginal cervical stimulation in female rats involves α 1-adrenergic receptor activation of the nitric oxide pathway

In estrogen-primed female rats, vaginal cervical stimulation (VCS) provided by male intromissions or by an experimenter enhances estrous behaviors exhibited by females during subsequent mating with a male. We tested the hypothesis that α 1-adrenergic receptors, acting via the nitric oxide-cGMP-protein kinase G pathway, mediate VCS-induced facilitation of female reproductive behaviors. Ovariectomized, estradiol-primed rats received intracerebroventricular (icv) infusions of vehicle or pharmacological antagonists 15 or 60 min before VCS. Estrous behaviors (lordosis and proceptivity) in the presence of a male were recorded immediately (0 min), and 120 min following VCS. First we verified that VCS, but not manual flank stimulation alone, enhanced estrous behaviors when females received icv infusion of the vehicles used to administer drugs. Increased estrous behavior was apparent immediately following VCS and persisted for 120 min. We then infused prazosin, phenoxybenzamine (α 1-adrenergic receptor antagonists), yohimbine, idaxozan (α 2-adrenergic receptor antagonists), or propranolol (β-adrenergic receptor antagonist) 15 min prior to the application of VCS in females primed with 5 μg estradiol benzoate. Only α 1-adrenergic antagonists inhibited VCS facilitation of estrous behavior, apparent 120 min after VCS. Finally, we administered specific inhibitors of soluble guanylyl cyclase, nitric oxide synthase or protein kinase G icv 15 or 60 min before VCS. All three agents significantly attenuated VCS facilitation of estrous behavior. These data support the hypothesis that endogenously released norepinephrine, acting via α 1-adrenergic receptors, mediates the facilitation of lordosis by VCS, and are consistent with a mechanism involving α 1-adrenergic activation of the nitric oxide/cGMP/protein kinase G pathway.

Estrogen modulation of adrenoceptor responsiveness in the female rat pineal gland: differential expression of intracellular estrogen receptors.

The effect of different doses of 17beta-estradiol (E2) on the pineal response to beta-adrenoceptor stimulation in female rats was examined. Pinealocytes from 21-day-old ovariectomized rats were exposed to different estrogen doses and treated with beta-adrenergic agonists. Estrogen treatment produced a dose-dependent, biphasic response to beta-adrenoceptor-induced accumulation of cAMP. This effect was inhibitory at estrogen doses up to 0.1 nM and fitted to a negative exponential curve, while at doses from 0.1 to 100 nM the effect was stimulatory and fitted to a standard positive hyperbola. For in vivo studies, ovariectomized rats were treated with equivalent estrogen concentrations plus a single dose of progesterone (250 microg per rat), and their pineals exposed in vitro to beta-adrenergic agonists. Low doses of E2 (0.1-100 ng per rat) reduced both pineal cAMP accumulation and N-acetyltransferase activity after beta-adrenoceptor stimulation, while a high dose (10 microg per rat) induced the opposite response. Apparently, the final estrogen target was the pineal beta-adrenergic receptor, as a low dose of E2 (which had diminished cAMP accumulation after beta-adrenoceptor stimulation) also reduced its maximal binding capacity (Bmax) and its dissociation constant (Kd). We also found that the female rat pineal gland contains two different ER subtypes, alpha and beta, which respond to estrogen exposure with nucleocytoplasmic shuttling. These results indicate that, in the female rat, estrogen directly modulates pineal sensitivity to adrenergic stimulation in a complex, dose-dependent manner that may be related to differential expression and activity of two estrogen receptor subtypes within pineal cells.

Activation of a Subset of Lumbar Spinothalamic Neurons after Copulatory Behavior in Male But Not Female Rats

The precise pathways that convey copulation-related information to forebrain regions activated during male and female sexual behavior are poorly understood. Previous work from our laboratory and others has demonstrated the existence of a spinothalamic pathway that is a candidate to relay information to these areas. This pathway originates from a population of spinothalamic neurons in the lumbar spinal cord containing several neuropeptides including galanin, located in laminas 7 and 10 of the lumbar segments 3 and 4. To investigate the involvement of these lumbar spinothalamic neurons in conveying copulation-related information, we tested the hypothesis that these cells are activated after ejaculation in male rats and vaginocervical stimulation in female rats. This was assessed using galanin or cholecystokinin as a marker for this subset of spinothalamic neurons and Fos-immunoreactivity as a marker for neuronal activation. The results demonstrated that activation of these spinothalamic neurons is triggered by stimuli associated with ejaculation. Fos induction was specifically associated with ejaculation, because mounts or intromissions did not trigger expression. Moreover, these spinothalamic neurons were not activated by vaginocervical stimulation in female rats. Spinothalamic neurons have generally been associated with signaling pain and temperature information. The present findings demonstrate that a specific subpopulation of spinothalamic neurons signals information associated with ejaculation.

Differential Effects of Dorsal Raphe Nucleus Lesions on Pseudopregnancy Induced by Reserpine or Vaginal Stimulation in Female Rats.

The role of the dorsal raphe nucleus in the maintenance of pseudopregnancy induced by reserpine and/or vaginal stimulation was investigated in female rats. In order to induce pseudopregnancy, either the vagina was stimulated electrically (VS) on the day of proestrus, or 1 mg/kg b.w. reserpine (R) was injected on the day of diestrus I. In some females, both VS and R treatments (VS+R) were applied. Radiofrequency lesions were made in the dorsal raphe nucleus (DRL) 5 days after VS and 3 days after R. At the same time, the left uterine horn was traumatized in order to induce deciduoma. As a result, positive decidual responses were seen in most control and sham-control rats with VS or R-treatments. In contrast, the incidence of deciduoma in DRL females with R injection was lower than that in control and sham groups, but the incidence in DRL females with VS or VS+R was comparable to that in control and sham females. These results suggest that the dorsal raphe nucleus plays an important role in maintaining the mechanism of pseudopregnancy induced by reserpine, but not in that induced by vaginal stimulation.

An estradiol-induced protein synthesized in the ventral medial hypothalamus and transported to the midbrain central gray

Estradiol (E2) facilitates the lordosis reflex that occurs in response to flank stimulation in female rats. Lordosis appears to be regulated in part by the synthesis of proteins in the ventral medial hypothalamus (VMH) that are transported to the midbrain central gray (MCG). We developed a strategy involving microinfusion of radioactive amino acids, followed by 2-dimensional gel electrophoresis, to identify proteins that may be regulated by E2 in the VMH and transported to the MCG. A mixture of 35S-methionine and 35S-cysteine (2:1, total 500-1000 microCi), suspended in 1 microliter PBS, was infused bilaterally into the VMH over a period of 2 hr into matched pairs of ovariectomized female rats, one of which was given a Silastic implant containing E2 at the beginning of infusion or 1 week earlier. The rats were sacrificed 12 hr after the end of infusion, and several brain regions were obtained by microdissection. Samples were analyzed by 2-dimensional gel electrophoresis, entailing isoelectric focusing in the first dimension and SDS-PAGE (molecular-weight separation) in the second dimension, followed by fluorography. We could routinely separate at least 250 spots. We consistently found a protein spot with an apparent molecular weight of 70 kDa, pI of about 5.9, which almost always appeared in the VMH and MCG of rats given E2 replacement but very rarely in samples from ovariectomized rats given no E2 replacement. A spot immediately acidic to this protein (70 kDa, pl about 5.8) appeared to vary inversely with this E2-induced protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of septal hyperreactivity by testosterone and its reversion by an estrogen antagonist in weanling female rats

Neonatal administration of testosterone inhibits emotional hyperreactivity to capture and tactile stimulation in female rats following septal lesions at 25 days of age. Testosterone, an aromatizable androgen, after metabolization to estrogen interacts with estrogen receptors in neonatal rat brain. In order to investigate whether the testosterone inhibited septal hyperreactivity via estrogen receptors rats were tested after pretreatment with the estrogen receptor antagonist tamoxifen. Weanling female rats pretreated with tamoxifen showed emotional hyperreactivity, while androgenized females showed no change. In addition, estradiol benzoate, neonatally administered, was able to inhibit emotional reactivity displayed after septal lesions. These results suggest that the action of testosterone on septal hyperreactivity might be mediated by estrogen receptors.

Similarity of luteinizing hormone surges induced by medial preoptic stimulation in female rats blocked with pentobarbital, morphine, chlorpromazine, or atropine.

Adult proestrous rats were subjected to either electrochemical or electrical stimulation of the medial preoptic area after ovulation-blocking dosage with either pentobarbital (PTBL), morphine, chlorpromazine, or atropine. For electrochemical stimulation (ECS), 233 microA anodal DC for 30 sec (7000 mu coulombs) was delivered through a unipolar stainless steel electrode. For electrical stimulation (ES), 750 microA biphasic pulse pairs at 30 Hz, on and off each 15 sec, were delivered through a coaxial platinum electrode, in four 5-min bursts equally spaced during 60 min. In PTBL-blocked rats this stimulus produced LH surges equivalent to those after continuous stimulation for 60 min. Blood was collected 60 and 90 min after ECS or after the start of ES. Mean serum LH concentrations (RIA) maximal at 90 min after ECS, were similar under the four blocking agents (1270-1486 ng/ml serum in terms of NIAMDD LH RP-1). Like-wise, after ES there were no significant differences (P greater than 0.05) among the mean LH levels at 60 min (310-571 ng/ml serum). The 90-min values showed a downward, but not significant, trend in the case of PTBL, chlorpromazine, and atropine plus PTBL. Under morphine an apparent upward trend was due largely to an animal having an especially large increase. With rare exception, full ovulation was evident at terminal laparotomy on the morning after stimulation. Thus, whichever of the several drugs was used, medical preoptic area stimulation with given parameters induced section of comparable amounts of LH. None of the drugs appears to have primary suppressive action on the preoptic-tuberal system, on the availability of LHRH or its release into the portal vessels, on the ability of the pituitary to release LH, or on the ovarian response.

Electrophysiological studies on the development and sex differentiation of the brain systems controlling gonadotropin secretion in immature rats (author's transl)

In order to elucidate the process of the development and sex differentiation of the brain systems controlling gonadotropin secretion, electrophysiological studies were performed using immature intact rats of both sexes after endocrinological manipulations. Medial preoptic (MPO) unit responses to the medial amygdala (AMYG) or the dorsal hippocampus (HPC) stimulation (0.1-2.0mA, 0.2msec, 2/3Hz) and hypothalamic arcuate (ARC) unit reponses to the MPO stimulation were examined by means of post-stimulus time histograms, and percentages of neurons responding in a facilitatory or in an inhibitory manner and threshold currents for the induction of the unit response were calculated. Furthermore, the effects of gonadectomy and estrogen administration on serum gonadotropin concentrations were examined in immature female rats of various ages.Intact rats were classified into 4 groups : i.e., 21-25, 26-30, 31-35 and 36-40 days of age. Neither responses of ARC neurons to the MPO stimulation nor thresholds of the MPO stimulation for the induction of the ARC unit responses showed any significant differences during prepuberal growth nor between sexes. In male rats, the percentages of MPO neurons which were facilitated by the AMYG stimulation decreased during the development (x2=11.963), while the change in percentages of MPO units responding to the stimulation in female rats was rather small (x2=4.053). Significant developmental changes were observed in the percentages of MPO units responding to the HPC stimulation in both males (x2 = 39.957, p<0.001) and females (x2=15.628, p<0.02). Moreover, differences in the number of MPO units responding to the HPC stimulation were observed between intact 21-25-day-old male and female rats (p<0.02), between neonatally (at 2 or 3 days of age) gonadectomized 21-25-day-old males and females (p<0.005), and between neonatally gonadectomized and intact 21-25-day-old males (p<0.05), though responsive patterns of the MPO units to the AMYG stimulation were not significantly different between both sexes except at the age of 31-35 days (p<0.05).Thresholds of the AMYG stimulation for the induction of the MPO unit responses were lowered and those of the HPC stimulation elevated during development in both sexes. Estrogen injection at weaning lowered the threshold of the AMYG, and elevated that of the HPC in female rats. Testosterone injection at weaning in male rats lowered the HPC threshold. In rats which had been gonadectomized at weaning, thresholds of the HPC stimulation were significantly lower and those of the AMYG stimulation higher than in intact rats of the same age.Endocrinologically, a simultaneous injection of estrogen with ovariectomy caused a significant and transient increase in serum gonadotropin concentrations 1 day after the treatment in 40-day-old female rats, 2 days after in 30-day-old rats, and 3 days after in 25day-old rats.These results showed the existence of sexual differences and developmental changes in the limbic-preoptic neural transmissions. It was suggested that the AMYG-MPO system might develop after weaning, presumably under the influence of gonadal hormones, and the lowering in thresholds of the AMYG stimulation during maturation or following estrogen treatment in female rats might be related to the development of stimulatory feedback mechanisms of estrogen which induce phasic gonadotropin release indispensable for ovulation in mature female rats. The HPC-MPO system might have a sexual dimorphism before the age of 20 days, and testes at very early periods of life as well as during postnatal growth might have an important role in the development of HPC-MPO mechanisms in the male. In female rats, estrogen might reorganize the role of the HPC, which had been a trigger for the initial FSH release for ovarian growth in the early prepuberal period,