Expression of activities of two 20 alpha-hydroxysteroid dehydrogenase isozymes in rat corpora lutea.

The rat ovary contains two isozymes of 20 alpha-hydroxysteroid dehydrogenase (HSD-1 and HSD-2). In this study, the expression of activity of each isozyme was investigated in ovaries that contained a single generation of corpora lutea during pseudopregnancy. This condition was induced by cervical stimulation in rats that had been rendered anovulatory by housing them in a continuously lit environment. The total activity of cytosolic 20 alpha-HSD was lower in the ovaries of these pseudopregnant rats than in ovaries containing multiple generations of corpora lutea. In normal pseudopregnancy, HSD-1 activity was low on days 5 and 9 and increased markedly on day 15, whereas HSD-2 was lower than HSD-1 and did not vary throughout pseudopregnancy. However, on days 5 and 9 of continuous-light pseudopregnancy, low activity of HSD-1 only was detected; by day 15, HSD-1 activity had increased sixfold and HSD-2 activity could be detected. Immunohistochemical methods using a specific antibody recognizing both HSD-1 and HSD-2 revealed that the number of 20 alpha-HSD-positive luteal cells increased by day 15. Thus, the increase in total enzyme activity and appearance of HSD-2 activity observed at late pseudopregnancy was accompanied by an increase in the number of 20 alpha-HSD-positive luteal cells.     

Conditions for establishment of reflex ovulation in light estrous rats.

Continual anovulatory state associating with persistent vaginal cornification (light estrus) was induced by placing 4-day cycling rats under continuous lighting (LL). Uterine cervical stimulation was applied at arbitrary solar hours to light estrous rats showing continual vaginal estrus for more than 2 weeks. The ovulation was induced between 14 and 16 hr after the stimulation dissociating entirely with solar hours. Injection of anti-LHRH serum 5 min after the stimulation but not later than 20 min blocked this ovulation. Ovulation thus induced was always followed by pseudopregnancy with continual leucocytic vaginal smear lasting 10.70 days. The change in concentrations of peripheral serum progesterone during this period was almost similar to that of normal pseudopregnancy except extremely low levels observed at the start and end. Effectiveness of the cervical stimulation for induction of ovulation in light estrous rats was related to not only the duration of light estrus but also the time after transfer to LL, suggesting that the neural mechanism of ovulation in light estrous rats shifted from that of the spontaneous to reflex ovulators due to the extinction of environmental photic cue.     

Effect of pelvic endometrial implants on overall reproductive functions of female rats

The effects of pelvic endometrial implants on the overall reproductive potential of female rats were investigated. After homologous transplantation in the peritoneum, the ectopic endometrium developed into highly vascularized nodes that gradually increased in mass until the 9th week postsurgery and then plateaued. In the presence of these implants, overall reproductive function was adversely affected. The effect was of greatest magnitude during 50-70 days posttransplantation. As compared with values in corresponding controls, ovulation was reduced by 43% (6 of 14) (p < 0.05), mating rate was reduced by 44% (12 of 27) (p < 0.025), and premature termination of pregnancy occurred in 34% (5 of 15) of rats. Wastage of pregnancy, which included complete termination or reduction of fetal number, occurred during the postimplantation course of gestation. Furthermore, 100% of the rats with transplants failed to respond to the copulomimetic stimulation for the induction of pseudopregnancy (p < 0.01, compared with corresponding controls). However, on exposure to vasectomized males, 46% (6 of 13) of these rats exhibited development of pseudopregnancy (p < 0.05, compared with corresponding group receiving copulomimetic stimulation). Increased rate of mating failure and differential pseudopregnancy rates after copulomimetic and natural cervical stimulation suggest that the rats with endometrial explants possibly had an absence or a short appearance of behavioral estrus. Hormonal assessment during the preovulatory phase showed a tendency toward lower mean levels of preovulatory estradiol and significantly lower LH (p < 0.01) and progesterone (p < 0.01) concentrations. The adversely affected reproductive functions may be a secondary consequence of these altered endocrine milieus.     

The effects of mating stimulation on c-Fos immunoreactivity in the female hamster medial amygdala are region and context dependent

During mating in hamsters, both tactile and nontactile sensory stimulation experienced by the female affect sexual behavior and progestational neuroendocrine reflexes. To test the interactions of these types of mating stimulation, c-Fos immunohistochemistry measured brain cellular activity during sexual behavior under conditions that included combinations of tactile and nontactile mating stimulation. Test groups received: (1) mating stimulation from a male, females being either fully mated or mated while wearing a vaginal mask, or (2) experimenter applied manual vaginocervical stimulation (VCS)-with or without males present, or (3) handling similar to VCS but without insertions-with or without males present. Numbers of c-Fos immunoreactive cells were counted in specific subdivisions of the posterior medial amygdala (MeP) and ventromedial hypothalamus (VMH). The medial amygdala dorsal and ventral subdivisions responded differentially to components of mating stimulation. The posterodorsal Me (MePD) cellular activation was greatest during mating conditions that included VCS and/or males present. However, the posteroventral Me (MePV) was sensitive to male exposure and not to VCS. Also, MePV and VMH shell responses mirrored each other, both being primarily sensitive to male exposure. In separate tests, manual VCS induced pseudopregnancy, though the procedure was most effective with additional nontactile stimulation from males present. In summary, contextual cues provided by nontactile male stimulation enhance the effect of vaginocervical and other tactile stimulation on reproductive processes. Furthermore, c-Fos expression in the female hamster medial amygdala is region and context dependent.     

Induction of pseudopregnancy in the mongolian gerbil (Meriones unguiculatus) by vaginal stimulation.

In rats, pseudopregnancy has been induced by mating with vasectomized males, by mechanical stimulation of the uterine cervix with a glass rod or vibrator, and by stimulation of the vagina with a tampon. On the other hand, no practical data are available in reports on the induction of pseudopregnancy in Mongolian gerbils. Pseudopregnancy of gerbils has been induced by mating with vasectomized males. But this method was uncertain because the incidence of pseudopregnancy was lower than that obtained in rats by other means. In the present study, two experiments were undertaken as follows. 1) Copulatory behavior of gerbils was observed for one hour to determine the most effective stimulation interval. 2) From the results of Experiment 1, female gerbils in estrus were mechanically stimulated to test the effectiveness of inducing pseudopregnancy by vaginal stimulation at various time intervals. The results of these experiments indicated that, although the frequency of copulatory behavior varied among individuals, on average the most effective method for inducing pseudopregnancy was stimulation of 5 min duration and at 20 or 30 min intervals. Because the incidence of pseudopregnancy induced by such mechanical stimulation (83.3%) was higher than that induced by mating with vasectomized males (30.0%), this method might be useful in inducing pseudopregnancy in Mongolian gerbils.     

The induction of pseudopregnancy and pregnancy by mating in albino rats exposed to constant light

Adult female albino rats anovulatory as a result of exposure to constant light (CL rats) were shown to ovulate in response to limited coital stimulation without necessarily becoming either pseudopregnant or pregnant. A higher level of coital stimulation would induce pseudopregnancy provided that intromission was not prevented. The occurrence of an ejaculation was not essential for the induction of pseudopregnancy but the incidence of pseudopregnancy was higher when a series of intromissions included one or more intromissions associated with ejaculation than when it did not. Similar findings regarding the induction of pseudopregnancy were obtained in experiments on female rats maintained under normal light-dark conditions (LD rats). Increasing the interval between intromissions from less than 1 min to as much as 20 min did not reduce the incidence of pseudopregnancy in CL rats. Splitting a set number of intromissions into two groups separated by up to 180 min did not reduce the incidence of pseudopregnancy in CL or LD rats. Conditions for the induction of pregnancy were more critical than for the induction of pseudopregnancy. CL rats showed only a low incidence of pregnancy and, if pregnant, either had small litters or did not deliver living pups even when a high level of coital stimulation from several males, including multiple ejaculations, occurred over a limited period of time. A high success rate was only observed when CL rats were mated with a single male overnight. LD rats showed a higher incidence of pregnancy than CL rats in response to a restricted amount of coital stimulation over a short time period, especially when an ejaculation was the terminal event in the mating sequence. This dependence on the occurrence of an ejaculation as the terminal event was not observed in CL rats, probably because, unlike LD rats, their uteri were not distended with fluid at the time of mating.     

Stimulation of the Po-shen and Shen-hun scalp-acupuncture bands modifies levels of inhibitory and excitatory amino acids in the immature rat brain

Objective

In the present study, the effect of stimulation of the Po-shen and Shen-hun scalp-acupuncture bands on tissue amino acid concentrations in several brain regions in awake and pentobarbital-sedated immature rats was evaluated.

Materials and methods

Sprague–Dawley rats (aged 15 days) were organized in four groups of at least eight animals: control groups received saline solution 0.9% or sodium pentobarbital at 30 mg/kg dosage via intraperitoneal. Experimental groups received saline solution or sodium pentobarbital plus stimulation in Po-shen and Shen-hun scalp-acupuncture bands for one continuous hour during 10 sessions by using scalp-acupuncture.

Results

As compared to rats receiving saline solution, scalp-acupuncture produced significant changes in amino acid concentrations, depending on the analyzed region, as follows: in inhibitory amino acids, a GABA increase was observed in amygdala and hippocampus (491 and 184%, respectively), but a decrease in the substantia nigra (80%); glycine showed decrease in all the analyzed regions, except for an increase in brainstem(78%); glutamine presented an increase in hippocampus and cortex (42 and 149%, respectively). In the case of excitatory amino acids, glutamate decreased in all the analyzed regions; whereas aspartate decreased in substantia nigra and brainstem (77.08 and 35%, correspondingly) but increased in hippocampus and cortex (32 and 54%, respectively). The combined treatment of scalp-acupuncture and a GABAergic depressant drug like pentobarbital resulted in almost all changes induced in amino acids for scalp-acupuncture alone being significantly reverted.

Conclusion

Stimulation of the Po-shen and Shen-hun scalp-acupuncture bands by using scalp-acupuncture alone might produce depressant activity by changes in amino acids, but the combination with a GABAergic tranquilizer like sodium pentobarbital can interfere with this response.     

Extrahypothalamic control of daily surges of prolactin secretion in pseudopregnant rat

The role of the limbic forebrain structures in controlling twice daily surges of prolactin (PRL) induced by cervical stimulation was investigated after acute or chronic deafferentation of the limbic forebrain afferents to the hypothalamus in rats. The preoptic area-roof section (POA-RS), which interrupted the rostral limbic afferents at the dorsal level of the anterior commissure, induced pseudopregnancy (PSP) and initiated the same nocturnal PRL surges as those initiated by the cervical stimulation. Diurnal PRL surges, however, did not occur following this procedure. The nocturnal PRL surge by POA-RS also occurred in ovariectomized rats. Deafferentation between the diagonal band of Broca and the medial preoptic area (F2-cut) initiated PSP in 37 % of the rats and induced an apparent but small nocturnal PRL surge. The rats with POA-RS or F2-cut showed restoration of their regular estrous cyclicities. Cervical stimulation after POA-RS did not affect the initiation of nocturnal PRL surge induced by POA-RS alone. POA-RS after cervical stimulation also did not affect the initiation of nocturnal PRL surge induced by cervical stimulation, though a diurnal PRL surge was initiated in these rats. The cut made just before the diagonal band of Broca after cervical stimulation did not inhibit the occurrence of either surge. Nocturnal and diurnal PRL surges were manifested after cervical stimulation in the rats with chronic POA-RS or F2-cut and their vaginal cyclicities were resumed. These results suggest that the limbic forebrain structures are not indispensable for the initiation of nocturnal PRL surges induced by cervical stimulation but may modify the hypothalamic mechanism(s) initiating a nocturnal PRL surge through the rostral part of the hypothalamus.     

Hypothalamic potentials evoked by electrical stimulation of the vaginal cervix in the estrous guinea-pig

Summary Evoked potentials were recorded from the hypothalamus of acutely-prepared estrous guinea-pigs responding to electrical stimulation of the vaginal cervix. The latency ranged from 38 to 60 msec. The peak of the first positive wave appeared 50 to 90 msec after the stimulation, usually followed by a negative wave in 120 msec. These responses were obtained from the mid-hypothalamus. The cervical stimulation subsequently induced the release of hypophysial luteotropin (LTH) as indicated by the occurrence of pseudopregnancy. According to the results, the mechanism triggering hypothalamic potential changes was discussed in connection with the LTH secretion.Research Fellow of the Alexander von Humboldt-Foundation in 1967/68.     

Plasma gonadotropins and prolactin in pseudopregnancy in the rat

Radioimmunoassay presented a method of measuring plasma levels of FSH,LH and prolactin in pseudopregnant rats. Plasma prolactin levels doubled 15 minutes following cervical probing (p .01) on the day of estrus. Plasma LH levels were not significantly elevated. Due to the use of ether anesthesia at blood collecting 3 hr before and 15 minutes after stimulation, only 1 of 16 rats developed pseudopregnancy. On Day 4 of pseudopregnancy in rats mated with vasectomized males; plasma LH was lower (p .05) than in normal rats on the first day of diestrus, perhaps due to the suppressive action of ovarian progesterone and some estrogen. FSH was higher than in normal rats (p .05) perhaps due to the lesser sensitivity of FSH to the inhibitory effect of progesterone. Large decidoumata developed by Day 9 in uterine horns traumatized on Day 4 (153 plus or minus 8 mg uterus weight compared to 1510 plus or minus 204 mg). Thus, the corpora remain functional after LH and prolactin are at normal and subnormal levels. On Day 9 plasma prolactin was lower than at Day 1 of diestrus (p .001). Plasma FSH was elevated (p .01). Plasma LH was unchanged. The degree of rise of LH levels 5 days following ovariectomy on Day 4 of psuedopregnancy or on the first day of diestrus was greater in the former group (p .02), perhaps due to rebound of LH from suppression by ovarian steroids. FSH rose equally in both groups. Prolactin remain about the same. Increased prolactin release by the adenohypophysis was briefer than expected.     

Effects of (-)-trans- delta 9-tetrahydrocannabinol on serum prolactin in the pseudopregnant rat

Groups of pseudopregnant rats were injected intravenously with (-)-trans- delta 9-tetrahydrocannabinol (THC) to determine its effects on serum prolactin (PRL) and the maintenance of pseudopregnancy. A single injection of 4 mg THC/kg BW at 2400 h on the first day of leukocytic vaginal smears of pseudopregnancy (D-1) delayed the ensuing nocturnal PRL surge for approximately one hour. When THC (1.0 mg/kg BW) was administered hourly from 2400 h on D-1 through 1700 h on D-2, the nocturnal surge was blocked and serum PRL levels were suppressed until 0600 h on D-2, but not thereafter. Neither treatment altered the duration of pseudopregnancy. These results indicate that the nocturnal surge secretion of PRL during early pseudopregnancy in the rat is sensitive to THC suppression, but that this suppression is not adequate to influence the duration of pseudopregnancy. The mechanism through which THC exerts this action remains unknown.     

Effects of abdominal or cardiopulmonary sympathetic afferents on upper cervical inspiratory neurons

Responses of upper cervical inspiratory neurons (UCINs) to abdominal visceral or cardiopulmonary sympathetic stimulation were studied using extracellular recordings from 213 UCINs in 54 pentobarbital sodium-anesthetized and paralyzed rats. Phrenic nerve activity was used to assess inspiration. The UCINs discharging during inspiration only were mainly in the C(1) segment, whereas phase-spanning UCINs were mostly in the C(2) segment. Phase-spanning activity was typically retained after overventilation or vagotomy. When greater splanchnic nerve (GSN) or cardiopulmonary sympathetic afferent (CPSA) fibers were electrically stimulated, augmented UCIN activity was observed in 65% of cells responding to CPSA stimulation but in only 17% of cells responding to GSN. Response latencies were 10.7 +/- 0.5 and 20.6 +/- 1.5 (SE) ms, respectively. Many augmented responses to CPSA stimulation (64%) and all augmented responses to GSN stimulation were followed by suppression of UCIN discharge (biphasic response). Phrenic nerve activity was suppressed by both GSN and CPSA stimulation, but with shorter latency for the latter (29 +/- 0.7 vs. 14.0 +/- 0.7 ms). Excitation of UCINs using CPSA stimulation occurs more often and by a more direct pathway than for GSN input.     

Effect of naloxone and prolonged preganglionic stimulation on noncholinergic transmission in the superior cervical ganglion of the cat

In cats anesthetized with sodium pentobarbital, a supramaximal 40-Hz, 30-s train to the cervical sympathetic trunk, during block of ganglionic cholinergic transmission with hexamethonium and scopolamine, produced a delayed, slow, small amplitude contraction of the nictitating membrane that persisted for several minutes after the end of the stimulus train. The post-stimulus component of the response was due to afterdischarge of the ganglion cells, since section of the post-ganglionic axons at the end of the train resulted in elimination of this component. The amplitude of the slow nictitating membrane response was enhanced in a dose-dependent manner by i.v. injection of naloxone. The enhancement was detectable at a dose as low as 1 microgram/kg and was maximal at 10 micrograms/kg. During continuous preganglionic stimulation at 40 Hz, the amplitude of the slow nictitating membrane response reached a peak in 2-4 min and then faded with time until it became undetectable. Time for 90% decay was 82 +/- 5 min (n = 18). The nictitating membrane response to postganglionic nerve stimulation was not modified by prolonged preganglionic stimulation. In three cats, the cervical sympathetic trunk was split into two bundles and one bundle was stimulated continuously at 40 Hz until the slow response disappeared. At this time stimulation of the unconditioned bundle evoked a slow response of normal appearance. This suggests that the process underlying the fade involves only the conditioned axons. Recovery from the fade was slow, the response approaching control by 24 h post-stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of olfactory stimulation with jasmin and its component chemicals on the duration of pentobarbital-induced sleep in mice.

The effect of olfactory stimulation with jasmin and its component chemicals on pentobarbital sleep time was investigated using mice. In the present study we sought to determine which component of jasmin influences pentobarbital sleep time via olfactory stimulation. Sleep time was defined as the time elapsed between intraperitoneal pentobarbital administration and the first time that the animal was able to spontaneously right itself. Sleep time was significantly decreased by olfactory stimulation with jasmin, and also by one of the fractions obtained by fractional distillation at 150 degrees C and 0.1 mmHg. The fraction which influenced the sleep time was found to consist of benzyl benzoate, isophytol, geranyl linalool, phytol and phytyl acetate, which were identified using gas chromatography with mass and infrared spectrometry. In experiments using authentic samples of these components, phytol significantly shortened the pentobarbital sleep time, while the others had no effect. We conclude that phytol is the component of jasmin which reduces the duration of pentobarbital-induced sleep.     

Uterine adenylate cyclase activity during the estrous cycle and early progestation in the rat: responses to fluoride activation and decidual induction

Uterine adenylate cyclase (AC) activity of the rat was measured by radiochemical analysis during the estrous cycle and early pseudopregnancy. During the estrous cycle, AC activity increased from 4.6 to 16.9 pmol cAMP formed/min X mg protein between metestrus and proestrus. Although AC was activated 2- to 3-fold at all cycle stages by 10 mM NaF, the resulting pattern of activity was similar to that measured in the absence of fluoride. The results demonstrated that the pattern of AC activity during the cycle was similar to that of other estrogen-sensitive uterine enzymes and that the ovarian hormones probably altered enzyme biosynthesis and turnover to a greater extent than activation and kinetic properties. Following the induction of pseudopregnancy by cervical stimulation, enzymic activity increased from 3.5 to 9.4 pmol between Days 1-4 (Day 1=leukocytic vaginal smear) and declined thereafter. AC activity was increased 2- to 5-fold by NaF on all days. AC activity was similarly increased by a mechanical trauma to the uterus, but only when the trauma was applied on Day 4. Following trauma to the uterus, AC activity was not increased further by NaF. The similarities between the physicochemical characteristics of AC during the estrous cycle and early progestation suggested that the enzyme during all endocrine states had virtually identical properties. However, the transient sensitivity to activation after trauma on Day 4 was unique to progestational uteri. Because the properties of enzyme were not altered by the endocrine state of the tissue, the transient sensitivity to activation by trauma was suggested to be a result of hormone-induced alterations in the membrane in which AC is sequestered.     

Differential Effects of Chloral Hydrate and Pentobarbital Sodium on a Cocaine Level and Its Catecholamine Response in the Medial Prefrontal Cortex: A Comparison with Conscious Rats

Abstract: Adult male Sprague-Dawley rats anesthetized with chloral hydrate and pentobarbital sodium were used as two different treatment groups. Conscious rats were used as a control group. By using baseline (precocaine) concentration as 100%, after cocaine administration (3.0 mg/kg i.v.), the maximal dopamine (DA) increase occurring at the first microdialysis collection period (20 min) in the medial prefrontal cortex was 299 ± 46% for the chloral hydrate group, 168 ± 12% for the pentobarbital sodium group, and 325 ± 23% for the conscious group. At the same time, norepinephrine (NA) increases reached a maximum and were 162 ± 20%, 100 ± 5%, and 141 ± 17%, respectively. The maximal changes of DA and NA in the chloral hydrate group and in the control group were both significantly higher than that in the pentobarbital sodium group. Meanwhile, the cocaine concentration was higher over a 100-min period of time in the chloral hydrate group when compared with the pentobarbital group and the control group. The peak cocaine concentration in dialysate occurred in the same time slot of maximal DA and NA responses, which were 0.65 ± 0.08, 0.30 ± 0.02, and 0.41 ± 0.05 µ M , respectively. Anesthetics suppress the pharmacologic response of neurons, which may explain the difference in catecholamine response between the pentobarbital sodium and the conscious groups. Conversely, because there was no significant difference in DA and NA response between the chloral hydrate group and the conscious group, it may possibly be due to the balancing effect between the higher existing cocaine concentration and the anesthetic suppression on pharmacological response of neurons in the chloral hydrate group. The effect of guide cannula implantation on the cocaine-induced catecholamine response was also evaluated.     

GABA参与兔杏仁体抑制内膝体神经元电活动

本文采用多管微电极胞外记录技术观察了短纯音引起兔内膝神经元的声反应及刺激杏仁体对声反应的影响,并在此基础上观察电泳ＧＡＢＡ及其拮抗剂Ｂｉｃｕｃｕｌｌｉｎｅ的效应。实验结果表明：ＧＡＢＡ可以抑制ＭＧＢ神经元的声反应及自发放电活动,而ＧＡＢＡＡ拮抗剂Ｂｉｃｕｃｕｌｌｉｎｅ的作用则相反;电泳ＧＡＢＡ对ＭＧＢ神经元产生同刺激杏仁体一样的抑制产应,并且这种影响可被Ｂｉｃｕｃｕｌｌｉｎｅ翻转;嗅鼻沟后缘听区农     

Nocturnal surges and reflexive release of prolactin in parentally behaving virgin female and male rats

Maternally behaving virgin rats are capable of releasing prolactin reflexively in response to stimulation by pups, especially during the proestrous/estrous phase of the cycle. When such rats are chronically exposed to pups they usually undergo a state of pseudopregnancy during which prolactin is secreted in a pattern of nocturnal surges. The present series of experiments evaluated the initiation of nocturnal prolactin surges in maternally behaving virgins, the role of estrogen in the reflexive release of prolactin, and the influence of gender on these two modes of prolactin secretion. It was found that the nocturnal surges of prolactin are already present on Days 1 and 2 of pup-induced pseudopregnancy. At this stage, however, the surges are not yet autonomous, seeing that pseudopregnancy is interrupted shortly after removal of the pups on Day 2. Activation by vaginocervical stimulation of the "mnemonic" neurogenic system that controls the autonomous nocturnal prolactin surges did not interfere with the reflexive pup-induced release of prolactin in maternally behaving virgins. The capacity of reflexive prolactin release in the virgin rat was abolished by ovariectomy, restored by estrogen replacement, and persisted for only 24 hr following estrogen removal. Paternally behaving males subjected to chronic exposure to pups were incapable of secreting nocturnal surges of prolactin characteristic of the pseudopregnant female. Such males were also incapable of releasing prolactin reflexively in response to stimulation by pups, even when supplemented with exogenous estrogen. These results indicate that the two modes of prolactin secretion are sex dependent, and that the maternally behaving virgin, unlike the postpartum rat, requires concurrent estrogenic facilitation for releasing prolactin in response to stimulation by young.     

GABAA receptor-related chloride flux of rats receiving continuous intracerebroventricular infusion of pentobarbital

The in vitro receptor-stimulated synaptoneurosomal chloride uptake induced by pentobarbital or muscimol was studied in the brains of rats which had been rendered tolerant to or dependent on pentobarbital. In the chronic study, rats received continuous administration of sodium pentobarbital by intracerebroventricular (i.c.v.) infusion. In rats continuously infused with pentobarbital for 6 days or in rats which had the infusion terminated for 24 h, the basal synaptoneurosomal chloride uptake was not altered in either the cerebral cortex or the cerebellum. On the other hand, pentobarbital (500 µM)-stimulated chloride uptake was significantly decreased in both cerebral cortices and cerebella of rats which received pentobarbital for 6 days as compared with the saline control groups. Twenty-four hours after termination of pentobarbital infusion, this high concentration of pentobarbital-stimulated chloride uptake remained low in both cerebral cortices and cerebella of rats which had been infused with pentobarbital for 6 days. In addition, similar results were also obtained in muscimol (2.5 µM)-stimulated chloride uptake in the cerebral cortices of pentobarbital-infused animals. However, pentobarbital infusion failed to alter muscimol-stimulated chloride uptake in the cerebellum. These results suggest that the GABA_A receptor regulated chloride uptake is downregulated after chronic pentobarbital administration. The results also suggest that down-regulation of the GABA_A receptor chloride channel complex takes place at different recognition sites on the complex. It further substantiates the allosteric effects of GABA and barbiturate recognition sites.     

BOLD signals correlate with ensemble unit activities in rat's somatosensory cortex

Evoked neural activity (ensemble single-unit activity and evoked field potential) and functional magnetic resonance imaging (fMRI) changes of the primary somatosensory cortex in response to electrical stimulation of the hind paw were studied in rats under anesthesia. The effects of stimulation frequency (ranging from 0.3 to 10 Hz) and types of anesthetics (alpha-chloralose and sodium pentobarbital) on blood oxygen level dependent (BOLD) activation and neural activation were compared. Both ensemble single-unit activity and BOLD signal changes achieved maximal activation at 3 Hz of stimulation and responses were significantly stronger under alpha-chloralose anesthesia. The maximal activation of the integral evoked potential (sigmaEP), in contrast, was the highest at 10 Hz; and the values were similar for alpha-chloralose and pentobarbital. These analyses revealed that fMRI image changes were better correlated with ensemble single-unit activity than with sigmaEP during somatosensory stimulations.