Behavioral Latency Research Articles

Ingestion of amniotic fluid enhances the facilitative effect of VTA morphine on the onset of maternal behavior in virgin rats

Previous research has shown that injection of morphine into the ventral tegmental area (VTA) facilitates the onset of maternal behavior in virgin female rats, and injection of the opioid antagonist naltrexone into the VTA disrupts the onset of maternal behavior in parturient rats. Placentophagia – ingestion of placenta and amniotic fluid, usually at parturition – modifies central opioid processes. Ingestion of the active substance in placenta and amniotic fluid, Placental Opioid-Enhancing Factor (POEF), enhances the hypoalgesic effect of centrally administered morphine, and more specifically, enhances δ- and κ-opioid-receptor-mediated hypoalgesia and attenuates μ-opioid-receptor-mediated hypoalgesia. POEF (in placenta or amniotic fluid) ingestion does not, by itself, produce hypoalgesia. In the present study, we tested the hypothesis that ingestion of amniotic fluid enhances the facilitative effect of opioid activity (unilateral morphine injection) in the VTA on the rate of onset of maternal behavior. Virgin female Long-Evans rats were given one intra-VTA injection of morphine sulfate (0.0, 0.01, or 0.03 μg, in saline) and an orogastric infusion of 0.25 ml amniotic fluid or saline once each day of the first three days of the 10-day testing period. Subjects were continuously exposed to foster pups that were replaced every 12 h; replacement of pups was followed by a 15-min observation period. Maternal behavior latency was determined by the first of two consecutive tests wherein the subject displayed pup retrieval, pup licking in the nest, and crouching over all foster pups, during the 15-min observation. We confirmed the previous finding that the VTA injection, alone, of 0.03 μg morphine shortened the latency to show maternal behavior and that 0.0 μg and 0.01 μg morphine did not. Ingestion of amniotic fluid (and therefore POEF) facilitated the onset of maternal behavior in rats receiving an intra-VTA microinjection of an otherwise subthreshold dose of morphine (0.01 μg).

Peripheral and central determinants of a nociceptive reaction: an approach to psychophysics in the rat.

BackgroundThe quantitative end-point for many behavioral tests of nociception is the reaction time, i.e. the time lapse between the beginning of the application of a stimulus, e.g. heat, and the evoked response. Since it is technically impossible to heat the skin instantaneously by conventional means, the question of the significance of the reaction time to radiant heat remains open. We developed a theoretical framework, a related experimental paradigm and a model to analyze in psychophysical terms the “tail-flick” responses of rats to random variations of noxious radiant heat.Methodology/Principal FindingsA CO2 laser was used to avoid the drawbacks associated with standard methods of thermal stimulation. Heating of the skin was recorded with an infrared camera and was stopped by the reaction of the animal. For the first time, we define and determine two key descriptors of the behavioral response, namely the behavioral threshold (Tβ) and the behavioral latency (Lβ). By employing more than one site of stimulation, the paradigm allows determination of the conduction velocity of the peripheral fibers that trigger the response (V) and an estimation of the latency (Ld) of the central decision-making process. Ld (∼130 ms) is unaffected by ambient or skin temperature changes that affect the behavioral threshold (∼42.2–44.9°C in the 20–30°C range), behavioral latency (<500 ms), and the conduction velocity of the peripheral fibers that trigger the response (∼0.35–0.76 m/s in the 20–30°C range). We propose a simple model that is verified experimentally and that computes the variations in the so-called “tail-flick latency” (TFL) caused by changes in either the power of the radiant heat source, the initial temperature of the skin, or the site of stimulation along the tail.Conclusions/SignificanceThis approach enables the behavioral determinations of latent psychophysical (Tβ, Lβ, Ld) and neurophysiological (V) variables that have been previously inaccessible with conventional methods. Such an approach satisfies the repeated requests for improving nociceptive tests and offers a potentially heuristic progress for studying nociceptive behavior on more firm physiological and psychophysical grounds. The validity of using a reaction time of a behavioral response to an increasing heat stimulus as a “pain index” is challenged. This is illustrated by the predicted temperature-dependent variations of the behavioral TFL elicited by spontaneous variations of the temperature of the tail for thermoregulation.

Anxiolytic-like effect of neuropeptide S in the rat defensive burying

Neuropeptide S (NPS) has been recently identified as the endogenous ligand of a previously orphan G-protein-coupled receptor now named NPSR. Both NPS and its receptor are expressed in the brain, where they modulate different functions. In particular, it has been demonstrated that intracerebroventricular (i.c.v.) injection of NPS in rodents increases wakefulness and promotes anxiolytic-like effects. In the present study we used the defensive burying (DB) test in rats to further investigate the action of human NPS (0.1–10 nmol, i.c.v.) on anxiety-related behaviors. Diazepam (1.5 mg/kg, i.p.) and caffeine (20 mg/kg, i.p.) were used in parallel experiments as standard anxiolytic and anxiogenic drugs, respectively. None of the tested drugs produced statistical differences in the latency to contact the probe, burying behavior latency, number of shocks received or immobility/freezing duration. Caffeine increased cumulative burying behavior and the buried bedding height in a statistically significant manner thus promoting anxiogenic like effects. Opposite results were obtained with diazepam that significantly reduced these behavioral parameters. The anxiolytic-like action of diazepam was mimicked by NPS that reduced cumulative burying behavior in a dose dependent manner. Collectively, robust anxiolytic-like effects were recorded in response to NPS in the DB test. These results are of particular interest since the outcome of this assay is marginally influenced by drug effects on locomotor activity. In conclusion, we provide further evidence that NPS evokes genuine anxiolytic-like effects in the rat; therefore NPSR selective agonists are worthy of development as innovative drugs for the treatment of anxiety disorders.

The progesterone receptor and parental behavior in juvenile rats

Juvenile rats exhibit enhanced parental behavior responses to foster pups from 18 to 25 days of age, compared to virgin adults. Previous studies in adult rats and mice suggest that progesterone can inhibit the display of parental care towards offspring. The present study investigated the role of progesterone in juvenile rat parental behavior. It is hypothesized that the decrease in parental responsiveness as juveniles age is due a progesterone-dependent inhibitory mechanism. Groups of male and female juveniles were subcutaneously implanted with the progesterone antagonist RU486, progesterone, or control implants. All juveniles were then tested for parental behaviors. No significant effects of either RU486 or progesterone treatments on parental behavior latencies were detected in male or female juveniles. The current data support the concept that the mechanisms controlling juvenile and adult parental behavior are divergent. Progesterone does not seem to be involved in the display of parental behavior in juvenile rats.

Anxiolytic‐like effects of the selective metabotropic glutamate receptor 5 antagonist MPEP after its intra‐amygdaloid microinjection in three different non‐conditioned rat models of anxiety

The intercalated islands, clusters of dopamine D1-rich GABAergic neurons, are interposed between the basolateral and central nuclei of the amygdala, and control the traffic of nerve impulses between these two structures. Metabotropic glutamate receptor 5- (mGluR5)-like immunoreactivity was studied by immunohistochemistry in this part of the amygdala and was found to be mainly restricted to the central and basolateral nuclei and to a lesser extent to the medial paracapsular intercalated islands. The role of the metabotropic glutamate receptor 5 in the modulation of anxiety has been studied in this region by microinjection of small volumes of the mGluR5 antagonist 2-methyl-6(phenylethenyl) pyridine (MPEP), with restricted diffusion from its injection site, into the rostral amygdala near the basolateral and central amygdaloid nuclei and the intercalated islands, and the behavior of the animals was evaluated using three non-conditioned models of anxiety. Anxiolytic-like effects were observed after MPEP administration in all tests used. In the White and Black Box test, MPEP (2 nmol per side) significantly increased the time spent in the white compartment of the box. In line with these results, MPEP (8 nmol per side) increased the exploration of the open arms of the Elevated Plus-Maze. Burying behavior latency was increased and burying behavior itself was decreased in the Shock-Probe Burying test. It is suggested that anxiolytic effects of MPEP may be mediated by blockade of mGluR5 in the basolateral and/or central amygdaloid nuclei, reducing glutamate transmission in the basolateral amygdaloid nuclei and glutamate output from the central amygdala.

Wind generated by an attacking bat: anemometric measurements and detection by the praying mantis cercal system

The wind-sensitive cercal system, well-known for mediating terrestrial escape responses, may also mediate insect aerial bat-avoidance responses triggered by wind generated by the approaching bat. One crucial question is whether enough time exists between detection and capture for the insect to perform a successful evasive maneuver. A previous study estimated this time to be 16 ms, based on cockroach behavioral latencies and a prediction for the detection time derived from a simulated predator moving toward a simulated prey. However, the detection time may be underestimated since both the simulated predator and prey lacked certain characteristics present in the natural situation. In the present study, actual detection times are measured by recording from wind-sensitive interneurons of a tethered praying mantis that serves as the target for a flying, attacking bat. Furthermore, using hot-wire anemometry, we describe and quantify the wind generated by an attacking bat. Anemometer measurements revealed that the velocity of the bat-generated wind consistently peaks early with a high acceleration component (an important parameter for triggering wind-mediated terrestrial responses). The physiological recordings determined that the mantis cercal system detected an approaching bat 74 ms before contact, which would provide the insect with 36 ms to perform a maneuver before capture. This should be sufficient time for the mantis to respond. Although it probably would not have time for a full response that completely evades the bat, even a partial response might alter the mantid's trajectory enough to cause the bat to mishandle the insect, allowing it to escape.

Anxiolytic-like actions of testosterone in the burying behavior test: role of androgen and GABA-benzodiazepine receptors

The first objective of the present study was to explore if several androgens, including testosterone propionate (TP) and its reduced metabolites, 5alpha-androstan-3alpha, 17beta-diol (3alpha-androstanediol) and 5alpha-androstan-3alpha-ol-17-one (androsterone), produce an anxiolytic-like effect in the burying behavior paradigm. Additionally, the possible participation of androgen or GABA(A)-benzodiazepine receptors in the anxiolytic-like effect of TP was analyzed. Orchidectomized male rats were treated with four injections of TP (0.25, 0.50, 1.0 mg/rat), 3alpha-androstanediol or androsterone (0.5 and 1.0 mg/rat), and the cumulative burying (denoting anxiety levels) and burying behavior latency (reflecting reactivity) evaluated. Besides, a single injection (0.5 mg/rat, -30 m) of each androgen was also tested in castrated rats. Repeated treatment with TP (0.5 and 1.0 mg/rat), but not a single injection of this androgen, produced an anxiolytic-like effect without changes on reactivity. Neither repeated- nor single-treatment with 3alpha-androstanediol nor androsterone produced a reduction of anxiety-like behavior. For the experiment studying the TP mechanism of action, this androgen (0.5 mg/rat, four injections) was combined with an antagonist for androgen receptors, flutamide (50 mg/kg, SC, 7 injections), or with a benzodiazepine antagonist, flumazenil (15 mg/kg, IP, -30 m). Flutamide, but not flumazenil, blocked the anxiolytic-like effects produced by TP. Results are discussed on the basis of interaction of these steroids with androgen receptors or GABA(A)-benzodiazepine receptors.

Chronic morphine exposure during puberty decreases postpartum prolactin secretion in adult female rats

Opiate use in teenage populations has been increasing in recent years. The potential impact of exposure to high levels of opiates at a time when reproductive systems are maturing has not been well studied, especially in females. The present study used an animal model of adolescent opiate abuse in females to examine the potential impact of high levels of opiates during puberty on several reproductive parameters, including suckling-induced prolactin secretion. Two groups of juvenile female rats were administered increasing doses of morphine sulfate or saline (s.c.) from age 30–50 days, beginning with a dose of 2.5 mg/kg and achieving a maximal dose of 50 mg/kg. As adults, these females were mated and reared either their own or foster pups. On either postpartum day 5 or 10, following a 4 h separation, suckling-induced prolactin secretion was measured. In addition, on postpartum day 5 maternal behavior latencies were determined. The results demonstrate reduced suckling-induced prolactin secretion on postpartum day 5 in females previously exposed to morphine during pubertal development. These effects were observed in females rearing either their own or fostered pups. These effects were not due to any differences in maternal behavior latencies, as retrieval or crouching latencies were unaffected. In summary, chronic morphine exposure during puberty results in changes in the regulation of prolactin secretion during early lactation, which are observed several weeks after cessation of drug treatment. These data suggest that prior opiate use during puberty can continue to affect the regulation of prolactin secretion into adulthood.

Rapid firing rates from mechanosensory neurons in copepod antennules.

Small detection distances coupled with rapid movements require copepods to respond to stimuli with behavioral latencies on the order of milliseconds. Receiving adequate sensory information in such a short time necessitates extremely rapid firing rates of the efferent receptors. Here we show that copepod mechanoreceptors can fire at frequencies up to 5 kHz in response to fluid mechanical stimuli. Neural activity at these frequencies enables these animals to code for a range of fluid velocities thus providing important information regarding the nature of different fluid disturbances.

Maternal memory in adult, nulliparous rats: Effects of testing interval on the retention of maternal behavior

The retention of maternal behavior (i.e., maternal memory) was measured in adult, nulliparous rats induced to respond maternally by continuous exposure to foster pups. Specifically, the effects of the interval duration between the initial induction and the reinduction of maternal behavior were determined. Intact virgin rats were first exposed to foster young to induce maternal behavior. During the initial induction phase, females were required to be fully maternal on 2 consecutive test days. Animals were then assigned to one of three interval groups (10, 20, or 40 days). After being isolated from rat pups for these designated periods, females in each group were tested again for their latencies to induce maternal behavior. Whereas the initial median latencies to display full maternal behavior ranged from 4.5 to 5 days for each group, upon retesting, median latencies for each group declined to 1 to 4 days. The greatest reduction in latency was present in the 10-day group (80%), and the smallest reduction was detected in the 40-day group (20%). A significant negative linear correlation was found between test interval and percentage reduction in behavioral latency. Based upon this relationship and under these test conditions, "maternal memory" in the adult, nulliparous rat would be expected to be nondetectable after about an interval of 50 days between tests. The pattern of maternal memory acquisition and loss appears similar to that reported in parous animals. The present study highlights similarities and possible differences underlying the establishment of the retention of maternal behavior (i.e., maternal memory).

Orchidectomy sensitizes male rats to the action of diazepam on burying behavior latency: role of testosterone

The anxiolytic-like effect of diazepam (0.0, 0.5, 1.0 mg/kg) on the cumulative burying behavior and the burying behavior latency were compared between intact and castrated male rats. In both groups a clear reduction in cumulative burying, denoting an anxiolytic-like response, was observed. However, castrated males were more sensitive to diazepam in the burying behavior latency, a parameter indicating reactivity. Thus, orchidectomized males showed an increase in burying behavior latency after 1.0 mg/kg diazepam treatment. This dose has no effect on burying behavior latency in intact animals. The higher sensitivity to diazepam on reactivity seems to be androgen dependent because it was reversed by chronic treatment with testosterone propionate (TP, 0.0625 mg/rat for 2 weeks). TP (0.0, 0.0625, 0.125, 0.25, 0.5 and 1.0 mg/rat) produced a dose-dependent reduction in burying behavior after chronic treatment (four injections separated 48 h). At no dose did TP affect burying behavior latency. These results indicate that some actions of diazepam vary in males depending upon the endocrine milieu. Results also support the idea of androgens possessing anxiolytic-like actions.

Neuroethology of audition and bat evasion in praying mantises

Many praying mantises have a unique auditory system comprising a single ear located in the ventral midline of the thorax. The hearing is nondirectional, and best frequencies range from 25 kHz to over 100 kHz depending on the species. Bat-like ultrasound triggers complex evasive maneuvers in flying mantises that requires CNS processing in the head. A mirror-image pair of interneurons (501) rapidly (&amp;lt;20 ms ) carries auditory information from the auditory nerve to the brain and these neurons are the best candidates as the primary input to the evasive response. The 501 recordings from an electrode chronically implanted in a mantis while it is being attacked by a flying, echolocating bat show that 501 responds strongly to bat cries and faithfully reports the temporal pattern of the echolocation cries during the early stages of the attack. However, during the last 200–250 ms before capture (beginning in mid-Buzz I), 501 falls silent. Although consistent with several physiological characteristics of 501, the result is surprising behaviorally. However, based on behavioral latencies, the latest that a successful response could be triggered is 200–250 ms before capture, and silencing 501 after that may prevent potentially dangerous habituation of the interneuron.

Effects of sensorineural hearing loss on cortical event-related potential and behavioral measures of speech-sound processing.

To investigate systematically the effects of sensorineural hearing loss on cortical event-related potentials (ERPs) N1, MMN, N2 and P3 and their associated behavioral measures (d' sensitivity and reaction time) to the speech sounds /ba/ and /da/ presented at 65 and 80 dB ppe SPL. Cortical ERPs were recorded to /ba/ and /da/ speech stimuli presented at 65 and 80 dB ppe SPL from 20 normal-hearing adults and 20 adults who are hearing impaired. The degree of sensorineural impairments at 1000 to 2000 Hz ranged from mild losses (defined as 25 to 49 dB HL) to severe/profound losses (75 to 120 dB HL). The speech stimuli were presented in an oddball paradigm and the cortical ERPs were recorded in both active and passive listening conditions for each stimulus intensity. Both ERP amplitudes and behavioral discrimination (d') scores were lower for listeners with sensorineural hearing loss than for those with normal hearing. However, these differences in response strength were evident only for those listeners whose average hearing loss at 1000 to 2000 Hz exceeded 60 dB HL for the lower intensity stimuli and exceeded 75 dB HL for the higher intensity stimuli. In contrast, prolongations in the ERP and behavioral latencies, relative to responses from normal-hearing subjects, began with even mild (25 to 49 dB HL) threshold elevations. The amplitude and latency response changes that occurred with sensorineural hearing loss were significantly greater for the later ERP peaks (N2/P3) and behavioral discrimination measures (d' and RT) in comparison with earlier (N1, MMN) responses. The results indicate that latency measures are more sensitive indicators of the early effects of decreased audibility than are response strength (amplitude, d' or percent correct) measures. Sensorineural hearing loss has a greater impact on higher level or "nonsensory" cortical processing in comparison with lower level or "sensory" cortical processing. Possible physiologic mechanisms within the cortex that may be responsible for these response changes are presented. Lastly, the possible clinical significance of these ERP and behavioral findings is discussed.

Steroid implants in the medial preoptic area or ventromedial nucleus of the hypothalamus activate female sexual behaviour in the musk shrew.

Female musk shrews are induced ovulators that do not exhibit a spontaneous behavioural oestrous cycle. Testosterone produced by the ovaries and adrenal glands, is the major steroid hormone in circulation at times of mating, and as such, regulates sexual behaviour. In the first experiment, we identified the neural site(s) of action for testosterone. Hormone implants were placed in one of three targeted brain regions. The neural sites selected were the medial anterior division of the bed nucleus of the stria terminalis (BNSTMA), medial preoptic area (mPOA) and the ventromedial nucleus of the hypothalamus (VMN). Ovariectomized females who received a unilateral testosterone propionate implant in either the mPOA or VMN, were significantly more likely to display sexual behaviour as compared to females who received an implant in the BNSTMA or any other hypothalamic nucleus. In experiments 2 and 3, we investigated whether the behavioural effects of testosterone propionate were mediated by an oestrogen receptor or the androgen receptor. Ovariectomized females that received oestradiol (E2) implants in either the mPOA or VMN were more likely to display receptivity, and had significantly shorter behavioural latencies, as compared to females implanted with either dihydrotestosterone or cholesterol. These data show that neural aromatization of testosterone to E2 in the mPOA or VMN is necessary for optimal activation of female musk shrew sexual behaviour. This finding implies a degree of neural redundancy in the networks that control the expression of sexual receptivity.

Expression of μ-opioid receptor mRNA in the medial preoptic area of juvenile rats

Previous studies indicate that the latency to initiate parental behavior in both male and female rats increases with age; weanling (21 days old) rats display parental behavior 0–2 days after exposure to newborn pups, while older juveniles (30 days old) require 5–6 days of pup exposure before they express the behavior. Furthermore, activation of μ-opioid receptors inhibits parental behavior in juvenile and adult rats. We hypothesized that the age-related increase in behavioral latency could be modulated by the induction of μ-receptor expression in the medial preoptic area (MPOA), a region in which μ-receptors regulate parental behavior. In situ hybridization histochemistry was used to measure μ-receptor mRNA expression in the MPOA of male and female Sprague–Dawley rats that were 21, 24, 27, 30, or 33 days old. Using autoradiographic film analysis, we observed that neurons within part of the MPOA expressed very dense μ-receptor mRNA. Comparison of mRNA distribution with histological boundaries indicated that neurons within the medial preoptic nucleus (MPN), excluding the central part, exhibited the highest density of μ-receptor mRNA within the MPOA. High densities of μ-receptor mRNA extended dorsolaterally and caudally from the MPN toward the bed nucleus of the stria terminalis. MPN μ-receptor mRNA expression was not altered with age and no sex difference was observed. The dense presence of μ-receptor mRNA in the MPN suggests that ample substrate exists on which μ-receptor ligands could modulate the latency to begin parental behavior in juvenile rats, but such behavioral expression apparently is not mediated by a change in μ-receptor mRNA production.

Interaction of desipramine with steroid hormones on experimental anxiety.

The present study analyzes if estradiol benzoate and/or progesterone interact with desmethylimipramine (DMI) to diminish experimental anxiety. The animal model of anxiety used was the conditioned defensive burying test. Dose response curves for DMI (0.625, 1.25 and 2.5 mg/kg, every 24 h, during 21 days), estradiol benzoate (0.5, 1.0, 2.0 and 4.0 micrograms/rat, 48 h) and progesterone (0.5, 1.0 and 2.0 mg/rat, -4 h) were made in ovariectomized rats. DMI per se decreased dose dependently the cumulative burying time, an effect considered as anxiolytic-like. Progesterone produced a decrease in burying at the highest dose, while estradiol benzoate had no effect on defensive burying. Both, progesterone (0.5 mg/rat) and estradiol benzoate (4.0 micrograms/rat) were able to decrease the cumulative burying behavior when injected with a subthreshold dose of DMI (1.25 mg/kg). In addition, the effect of DMI (1.25 mg/kg) plus the combination of estradiol benzoate and progesterone, sequentially administered (48 h and 4 h before the tests, respectively), also produced a synergistic decrease in burying behavior. In general, the treatments produced no changes in burying behavior latency, neither in spontaneous ambulation or in nociception. It is concluded that DMI synergizes its anxiolytic-like effect when administered with estradiol alone or in combination with progesterone. Present data provide experimental evidence suggesting an interaction between hormones and antidepressants. Results are discussed on the basis of the interaction between steroids and serotonergic or GABAergic receptors.

Physiological Correlates of Maternal–Offspring Behaviour in Sheep: A Factor Analysis

The onset of maternal behaviour in sheep is controlled by levels of oestrogen and progesterone in gestation and the release of oxytocin during delivery. Factor analysis was used to investigate the relationships between maternal behaviour, offspring behaviour, and maternal ovarian hormone levels during gestation in sheep. Ewes gave birth to lambs following embryo transfer between two breeds (Suffolk and Scottish Blackface), which differ in their expression of maternal behaviour. Plasma oestradiol-17β concentration was significantly higher in Blackface ewes in the last 6 weeks of pregnancy, whereas plasma progesterone was higher in Suffolk ewes in early and mid gestation. Factor analysis revealed three factors that accounted for 50% of the total variation between variables. Factor 1 described lamb activity and had positive loadings for lamb behavioural latencies immediately postpartum, and negative loadings for sucking frequency. Factor 2 described some aspects of ewe maternal behaviour, and had positive loadings for ewe–lamb separation and lamb vocalisation, and negative loadings for ewe grooming behaviour and plasma oestradiol concentration. Factor 3 described ewe and lamb-sucking interactions, and had positive loadings for ewe moving as the lamb made sucking attempts, and negative loadings for ewe and lamb vocalisation. Factor 1 scores were significantly affected by lamb breed: Suffolk lambs received positive scores, indicating a longer latency to right and stand, whereas Blackface lambs had negative scores. Maternal progesterone concentration was significantly correlated with Factor 1 scores. Factor 2 and 3 scores were significantly affected by ewe breed. This study has shown that there are two behavioural axes to maternal behaviour in sheep, and that maternal oestradiol concentration is related to affiliative behaviours (e.g., grooming) but only weakly to ewe responsiveness to lamb-sucking attempts.

Sexual differentiation modifies the allopregnanolone anxiolytic actions in rats.

The administration of progesterone (0.0, 1.0 and 2.0 mg/rat, s.c.) and allopregnanolone (5 alpha, 3 alpha dihydroprogesterone) (0.0, 0.5 and 1.0 mg/rat, s.c.) to both, males and females, produced a similar reduction in burying behavior. Only allopregnanolone showed a gender-dependent effect on burying behavior latency. Allopregnanolone actions were established in five groups of animals according to their neonatal hormonal manipulation: intact males and females, neonatally-testosterone propionate-treated female rats (TP, 30 and 120 micrograms/rat, s.c. at day 5) and neonatally (4-12 h after delivery) castrated males. Males and females showed a reduction in anxiety after treatment with allopregnanolone. Both neonatally-androgenized-females and -castrated males were completely insensitive to allopregnanolone anxiolytic action tested in both burying behavior and plus-maze paradigm. The virilizing action of neonatally administered TP was demonstrated by dose-dependent delayed vaginal opening, a persistent estrus in their vaginal smears and the presence of polifollicular ovaries. Results are discussed on the bases of the differences and similarities between males, females, androgenized females and neonatally castrated males to anxiolytic steroids and the underlying possible processes.

Blockade of the anxiolytic-like action of ipsapirone and buspirone, but not that of 8-OH-DPAT, by adrenalectomy in male rats.

The effect of the 5-HT1A agonists ipsapirone (5 mg/kg), buspirone (5 mg/kg) and 8-OH-DPAT (0.5 mg/kg) on experimental anxiety was examined in sham-operated, adrenalectomized and adrenally demedullated male rats. The animal model of anxiety used was the defensive burying test. At the doses selected, all 5-HT1A compounds produced an anxiolytic-like action by reducing the burying behavior in both sham-operated and demedullated rats. However, in adrenalectomized subjects, while 8-OH-DPAT still reduced burying behavior, ipsapirone and buspirone lost their action. Data suggest that adrenocortical secretions play a role in the anxiolytic-like actions of buspirone and ipsapirone, but not in those of 8-OH-DPAT. Buspirone and ipsapirone also produced a reduction in burying behavior latency in sham-operated animals that was not observed in adrenalectomized or adrenally demedullated rats. These data suggest that adrenaline may be participating in the action of these compounds on the burying behavior latency. Present findings support possible direct relationships between the stimulation of 5-HT1A receptors and adrenal secretions.

The effects of broadband noise masking on cortical event-related potentials to speech sounds /ba/ and /da/.

To systematically investigate in normal-hearing listeners the effects of decreased audibility produced by broadband noise masking on the cortical event-related potentials (ERPs) N1, N2, and P3 to the speech sounds /ba/ and /da/. Ten normal-hearing adult listeners actively (button-press response) discriminated the speech sounds /ba/ and /da/ presented in quiet (no masking) or with broadband masking noise (BBN), using an ERP oddball paradigm. The BBN was presented at 50, 60, and 70 dB SPL when speech sounds were presented at 65 dB ppe SPL and at 60, 70 and, 80 dB SPL when speech sounds were presented at 80 dB ppe SPL. On average, the 50, 60, 70, and 80 dB SPL BBN maskers produced behavioral threshold elevations of 18, 25, 35, and 48 dB (average for 250 to 4000 Hz), respectively. The BBN maskers produced significant decreases (relative to quiet condition) in ERP amplitudes and behavioral discriminability. These decreases did not occur, however, until the noise masker intensity (in dB SPL) was equal to or greater than the speech stimulus intensity (in dB ppe SPL), that is, until speech to noise ratios (SNRs) were < or = 0 dB. N1 remained present even after N2, P3, and behavioral discriminability were absent. In contrast to amplitudes, ERP and behavioral latencies showed significant decreases at higher (better) SNRs. Significant latency increases occurred when the noise maskers were within 10 to 20 dB of the stimuli (i.e., SNR < or = 20 dB). The effects of masking were greater for responses to /da/ compared with /ba/. Latency increases occurred with less masking for N1 than for P3 or behavioral reaction time, with N2 falling in between. These results indicate that decreased audibility as a result of masking affects the various ERP peaks in a differential manner and that latencies are more sensitive indicators of these masking effects than are amplitudes.