Effects of midbrain reticular lesions upon aggression in the rat.

Compared behavior of 34 male hooded rats with midbrain reticular formation (MRF) lesions with 17 operated controls in a variety of social interactions. Ss with MRF lesions at the level of the inferior colliculus displayed a marked enhancement of aggressive behavior with another male or female rat. However, Ss with MRF lesions at the superior collicular level did not exhibit alterations in aggressive behavior. Both groups with MRF lesions exhibited infrequent crawling under (a social contact behavior) and pain-elicited threat behavior. It is hypothesized that animals with MRF lesions at the inferior collicular level demonstrate enhanced aggressiveness only with conspecifics attempting to engage in social interaction. (25 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of sensory restriction upon responses to cortical stimulation in rats.

Assigned 43 Long-Evans hooded rats to 7 groups receiving normal, visually restricted, or auditory restricted rearing experience. Ss were then implanted with bipolar pairs of electrodes in the auditory and visual projection areas. Electrical stimulation of the cortex was used as a discriminative stimulus for a lever-pressing response. The ease of using electrical stimulation of visual or auditory cortex as a discriminative stimulus was related to Ss' paranatal sensory experience. Deleterious effects were limited to the restricted cortical projection area, and there were suggestions of facilitated performance in response to stimulation of the nonrestricted cortical areas. These effects were absent when restriction was induced in adulthood. (28 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brain stem reticular units: synaptic responses to stimulation within the ascending reticular pathways

When the ascending reticular axonal system is stimulated, the responses of distal structures (e.g., the cerebral cortex) appear to outlast the stimulus; these longlasting effects could reflect the intrinsic nature of the distal structure, or the response could reflect an interaction among the reticular cells which tends to prolong the effects of stimulation. To examine the latter hypothesis, single units with ascending axons (projecting units) were recorded in the cat rostral rhombencephalon in acute experiments conducted under halothane-nitrous oxide anesthesia. Stimulation of areas to or through which axons of reticular neurons projected (midbrain tegmentum and lower tectum, medial thalamus, and basal forebrain) produced a consistent and specific response which was elicited only from these areas: suppression of spontaneous activity which was typically elicited from several areas having ascending axons. One-half of these responses were accompanied by a short latency-single spike synaptic excitation. Stimulating areas more than 1.0 mm from the ascending trajectory never produced this response, whereas the number of responses was directly related to the number of projecting axons identified in any one experiment from a given site. Thus, the predominant effect of stimulating within the ascending axonal trajectory was suppression of spontaneous activity in the projecting units, not an 'en cascade' activation of these units; on the contrary, the only type of excitation encountered was a single, short latency spike. Therefore, any effects of stimulation within the ascending reticular pathway which appear to outlast the stimulus (as previously described in the literature) cannot be ascribed to a reverberating (excitatory) circuit among projecting units. A possible source of the synaptic responses of projecting units is a retrograde activation of collaterals interconnecting the reticular cells. If such interaction exists, it is specifically distributed among cells with ascending axons, as the responses were only observed in a very few units not identified by antidromic excitation; however, other evidence is adduced to support the belief that these few units were projecting units whose axons were beyond the reach of the stimulating electrodes. Futhermore, the axons may be bundled such that units with axons nearest that of a given projecting unit give rise to the most extensive synaptic interactions; the activation of these nearby axons suppresses spontaneous activity, while axons farther away have a greater possibility of being excitatory in nature. Should such a medium for interaction exist, reticular collateral interactions might be seen to exist specifically for the purpose of decreasing the activity of cells destined for similar rostral target structures.     

Changes in responses of medial pontomedullary reticular neurons during repetitive cutaneous, vestibular, cortical, and tectal stimulation

1. In cats anesthetized with chloralose, responses of medial pontomedullary reticular neurons to stimulation of the body surface, vestibular nerves, superior colliculi, pericruciate cortices, cerebral peduncles, and spinal cord were studied at different stimulus rates. Raising the rate from 1/10 s to between 1/4 s and 2/s caused a significant decrement or increment in the response of most neurons tested. Response decrement typically began near the beginning of the higher frequency stimulus sequence and increased throughout the sequence. Response increment usually began somewhat later, rose to a peak, and then declined. Recovery from response decrement or increment usually occurred within 30-60 s at a 1/10 s stimulus rate.2. Measurements of response latency and of changes occurring in the initial and longer latency portions of responses indicated that all components of a response typically decreased or increased in parallel. Background spontaneous activity did not change during response decrements, but sometimes increased during response increment.3. Where changes could be detected, response decrement usually developed more rapidly when a sequence of repetitive stimulation was repeated.4. Response decrement was most pronounced at the highest stimulation rates and lowest stimulus intensities. Response increment was usually maximal at a stimulus rate of 1/s: at lower rates less increment occurred; at higher rates responses began to exhibit decrement.5. Response changes varied with the type of stimulus applied. Response decrements predominated when the body surface, vestibular nerves, or ipsilateral superior colliculus were stimulated. Approximately equal amounts of response increment and decrement were produced by repetitive stimulation of the cerebral peduncles and contralateral superior colliculus. Stimulation of the surface of the pericruciate cortex or of the spinal cord usually produced a long-lasting response increment.6. Generalization of response decrement and increment was observed in cases where trains of stimuli at a rate of 2/s applied to one point produced changes in the response to stimulation of another point which was tested once per 10 s and where single-shock stimulation of the first point was without effect on the test response. Generalization of response decrement occurred most often when two nearby points were stimulated. Generalization of response increment appeared to spread widely between distant cutaneous points and stimuli of different kinds.7. The response decrement and increment observed in medial pontomedullary reticular neurons displayed most of the parametric features of behavioral habituation and sensitization (8, 33) and therefore appear to represent neural analogs of these latter phenomena. The properties of response decrement suggest that it may occur to a large extent within afferent pathways leading to medial reticular neurons...     

Visceral pain: responses of the reticular formation neurons to gallbladder distension

Visceral projection (gallbladder distension) to the gigantocellular nucleus of the reticular formation of the cat was tested in neurons classified as pain (P), nonpain-pain (NP-P) and nonpain (NP) units, according to their responses to noxious and/or innocuous natural stimuli from the somatic areas. 96% of P neurons (23 out of 24) responded to gallbladder distension. Quantitative criteria showed comparable effectiveness of the somatic and visceral inputs. NP-P neurons reacted to the gallbladder stimulation in 71% of cases (22 out of 31); NP neurons were activated less effectively. Stimulation of either the central tegmental field or "nonspecific" thalamic nuclei evoked direct responses in 38% of P and 26% of NP-P units, which, in most of the P neurons were followed by excitatory and inhibitory phases. The duration of the latter was approximately one second and it greatly affected the responses of the units to somatic as well as to visceral inputs. A large proportion of P neurons responding to a visceral input documents the important role of the reticular formation in the mechanisms of visceral pain. Findings concerning comparable modifying influences upon reactions of P units both in the case of visceral and painful somatic afferentation indicated that similar control mechanisms could be involved.     

Effects of mesencephalic reticular formation lesions on habituation of startle and lick suppression responses in the rat.

In 2 experiments with 43 male albino Holtzman rats, extensive damage to the mesencephalic reticular formation (MRF) altered long-term habituation of the acoustic startle response without disrupting short-term habituation. Ss with MRF lesions, although initially neither more nor less responsive than controls, could not attain as low a long-term asymptote of habituation as could control Ss with repeated presentations of an auditory stimulus. Changing the quality of the auditory stimulus abolished the asymptotic difference in responsiveness. With repeated presentations of the 2nd auditory stimulus, control Ss again reached a significantly lower long-term habituation asymptote than did Ss with MRF lesions. The course of long-term habituation for the 2 groups suggested a disruption of an extrinsic, inhibitory habituation process by the lesions. The effects of MRF lesions were specific to the acoustic startle response. Control Ss and those with lesions showed comparable response levels, short-term habituation, and long-term habituation of the lick suppression response. Responsiveness and habituation to tactile stimuli were comparable for the 2 groups on both lick suppression and startle response measures. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation of flicker discriminability by electrical stimulation of the mesencephalic reticular formation of the rat.

In 4 experiments with 23 male Sprague-Dawley rats, low-intensity, 7 and 10 μA, electrical stimulation of the mesencephalic reticular formation (MFR) in 7 Ss significantly improved the accuracy of a perceptually difficult successive discrimination between a smooth light and a rapidly flickering light. Despite similar baseline conditions, including accuracy, MRF stimulation did not affect accuracy when the flickering light was maintained at an easily detectable 5 Hz. Accuracy of the perceptually difficult discrimination was not affected by changes in water deprivation or by electrical stimulation of the inferior colliculus or the fornical area of the limbic system. These findings suggest that the stimulation-induced improvement in the accuracy of the perceptually difficult flicker discrimination was not due to nonspecific changes in motivation, arousal, or general attention or to the possible cue or alerting function of the stimulation. The failure to implicate nonsensory processes and the finding that accuracy was improved only when the light was flickering rapidly indicate that MRF stimulation increased accuracy by improving the discriminability of the rapidly flickering light. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Post-synaptic activity evoked in the rostral ventrolateral medullary neurones by stimulation of the defence areas of hypothalamus and midbrain in the rat

Neurones in the rostral ventrolateral medulla (RVLM) of the rat were recorded intracellularly (n = 30) and extracellularly (n = 91) in vivo. 91% of them had spontaneous activity with frequencies of 1.1-29.9 Hz. Onset latencies of the excitation induced by the stimulation of the hypothalamic and midbrain defence areas ranged from 1.5 to 44 ms and 2 to 60 ms respectively. There was no statistical difference between two groups. Excitation followed by inhibition or inhibition followed by excitation was observed in these processes. Excitatory post-synaptic potentials (EPSPs) were summated by simultaneous stimulation of both sites and the onset latency was changed with the change of stimulus intensity. It is concluded that projections from the defence areas of hypothalamus and midbrain are relayed to RVLM neurones forming excitatory and inhibitory synapses; one mechanism of the effect summation caused by both sites is via EPSPs.     

Effects of analgesic midbrain stimulation on reflex withdrawal and thermal escape in the rat

Strong analgesia produced by mesencephalic electrical brain stimulation in rats significantly increased escape latencies in two-way escape from a floor heated by hydraulic circulation. Reflective reactions to pinching and needling were abolished or greatly diminished. Individual differences in the strengths of analgesia, as assessed by instrumental and reflex indicants, were highly correlated. Induction of analgesia was demonstrated in the absence of positive reinforcement effects produced by brain stimulation. The findings are discussed in relation to possible neural pain suppression systems with critical components situated in the midbrain.     

Anaesthetics depress the sensitivity of cortical neurones to L-glutamate

1 The effects of general anaesthetics on the responses of neurones to iontophoretically applied L-glutamate have been examined in slices of the guinea-pig olfactory cortex in vitro. 2 Concentrations of pentobarbitone, ether, methoxyflurance, trichloroethylene and alphaxalone that are known to depress synaptic transmission in the prepiriform cortex also depressed the sensitivity of prepiriform neurones to L-glutamate. 3 Halothane, in concentrations that depress synaptic transmission (less than 1%) did not alter sensitivity of neurones to glutamate. Higher concentrations (greater than 1% produced a dose-related depression of the glutamate sensitivity of neurones. 4 All four volatile anaesthetics tested caused some cells to alter their glutamate-evoked firing pattern to one in which the spike discharges were more closely grouped. Pentobarbitone and alphaxalone had no such effect. 5 If the sensitivity of the neurones to the endogenous excitatory transmitter is affected by anaesthetics in the same way as the glutamate-sensitivity, these results suggest that halothane depresses synaptic transmission by decreasing the amount of transmitter released from the nerve terminals, whereas the other anaesthetics depress the sensitivity of the post-synaptic membrane to the released transmitter.     

Interrelationship among multiunit activity of the midbrain reticular formation and lateral geniculate nucleus, thalamocortical arousal, and behavior in rats.

In 3 experiments with a total of 24 male Holtzman albino rats, analyses of multiunit activity of midbrain reticular formation (RF) and lateral geniculate nucleus (LG) revealed marked phasic covariation that conformed to characteristics of behavior. Movement patterns appeared to set the range within which RF activity and thalamocortical arousal (as reflected in LG activity) varied. In tests of spontaneous behavior, sensory stimulation, barpressing for food, and conditioned emotional response, RF activity and thalamocortical arousal conformed to immediate properties of behavior apart from conditions giving rise to the behavior. Other analyses revealed close relationships between RF activity and visual evoked response, but only a general relationship to hippocampal slow-wave rhythms. Findings emphasize the necessity for refining psychological conceptualizations of arousal processes. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of coital stimulation upon behavior of the female rat.

Tested the importance of vagino-cervical stimulation during coitus in 2 experiments, using 16 intact and 48 ovariectomized Sprague-Dawley female rats, in which intromission was prevented by a vaginal mask. The behavior of Ss was compared to that of unmasked females. Behavioral indices included lordosis quotient, a measure of sexual responsiveness, and rejection quotient, a measure of social response toward the males. The rating of lordosis intensity on a 3-point scale provided a mean lordosis intensity. Exp. I investigated long-term effects of coital stimulation by repeated testing of Ss in natural and hormone-induced heat. Coital stimulation generally decreased the probability of subsequent lordosis and increased display of rejection. Exp. II studied the short-term effects of coital stimulation using single 50-mount tests. Coital stimulation decreased intensity as well as probability of subsequent lordosis. (23 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of cortical stimulation on red nucleus neurons in the guinea pig

The aim of the present work was to study the control that the cerebral cortex exerts on red nucleus (RN) neurons in the guinea pig. The experiments were carried out in anaesthetized animals. Electrical stimulation of localized cortical foci was performed by tungsten microelectrodes in frontal and parietal regions containing sensorimotor representations of the body. Single unit RN activity was extracellularly recorded through glass micropipettes, and the encountered RN neurons were recognized by searching their peripheral receptive field. Then, corticorubral influences were tested on RN neurons whose receptive field was located in the same body regions where motor responses were evoked by cortical stimulation. The stimulation with a single pulse evoked complex responses, typically consisting of long lasting inhibitions sometimes preceded by a weak facilitation and always followed by an excitatory rebound. The application of a second pulse modified this pattern, depending on the time interval between the two stimuli. In fact, the reduction of the interval below 300 ms enhanced the excitatory components whereas it shortened the inhibitory component; moreover, an "early" facilitation was evoked but only at intervals as short as 50-150 ms, or less. These results suggest that the corticorubral control may vary according to different levels of cortical activation, becoming more and more facilitatory as the cortical discharges increase from low frequency values (tonic activity) towards high frequency values (phasic activity).     

Effects of erotica upon men's loving and liking responses for women they love.

In 2 studies, the construct validity of the Rubin Love scale and its discriminant validity in relation to the Rubin Liking scale were examined. In Study 1, 51 male undergraduates were asked to describe their loved ones on a series of measures after having been exposed to either erotica or control materials. Analysis of the within-condition correlations revealed convergent and discriminant patterns indicating construct validity. Analysis of covariance also revealed convergent and discriminant patterns: Only scores on the Love measures reliably increased from the control to the erotica condition. In presenting a behavioral analysis of the differential impact of erotica on Love vs Liking scale responses, it was assumed that (a) women are more likely to reinforce suitors for emitting statements more similar to the Love than to the Liking items and (b) men are more likely when sexually aroused than when not aroused to express statements more similar to the Love than to the Liking items to their loved ones. In Study 2, a series of surveys of 77 female and 64 male undergraduates offer support for these assumptions. Overall, results are interpreted as corroborating the construct validity of the Love scale. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of guilt and approachability of examiner upon associative sexual responses

Two sexually attractive female undergraduate examiners each administered the Word Association Test to 12 high- and 12 low-guilt male undergraduates and 12 high- and 12 low-guilt female undergraduates (all of whom had taken the Mosher Forced Choice Guilt Inventory). Results indicate that low-guilt males made more sexual responses when tested by an approachable examiner than an unapproachable examiner. The approachability of the examiner did not lead to differences for the high-guilt males or for the low- or high-guilt females. Ss' perceptions of examiners were consistent with predictions derived from social learning theory; only high-guilt males failed to discriminate between the approachability roles, whereas low-guilt males, and low- and high-guilt females, were able to do so. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Triple projections of neurones located in S1 and S2 segments of the cat spinal cord to the C6 segment, the cerebellum and the reticular formation

We have assessed five signal transduction pathways to determine the role each might play in the malignant transformation of mammary epithelium initiated by neu, heregulin/NDF, TGFalpha, v-Ha-ras and c-myc in transgenic mice. The study involves a molecular and pharmacologic assessment of Erk/MAP kinase, Jnk/SAP kinase, PI 3-kinase, protein kinase C, and the Src-related kinases Lck and Fyn. Our results indicate that oncogenes capable of transforming mammary gland epithelium activate and require specific signal transduction pathways. For example, mammary tumors initiated by neu, v-Ha-ras and c-myc have high levels of active Erk/MAP kinase and their anchorage independent growth is strongly inhibited by PD098059, an inhibitor of Mek/ MAP kinase kinase. By contrast, Erk/MAP kinase activity is weak in tumors initiated by TFGalpha and heregulin/NDF and the corresponding cell lines are not growth inhibited by PD098059. Similarly, PI 3-kinase is strongly activated in neu, TGFalpha and heregulin/NDF initiated tumor cell lines, but not in c-myc or v-Ha-ras initiated tumor cell lines. The anchorage independent growth of all these tumor cell lines are, however, inhibited by the specific PI 3-kinase inhibitor LY294001. Further illustrating this oncogene-based specificity, PP1, a specific inhibitor of the Src-like kinases, Lck and Fyn, blocks anchorage-independent cell growth only in the TGFalpha initiated mammary tumor cell line. Taken together with additional observations, we conclude that certain oncogenes reliably require the recruitment/activation of specific signal transduction pathways. Such specific relationships between the initiating oncogene and a required pathway may reflect a direct activating effect or the parallel activation of a pathway that is a necessary oncogenic collaborator for transformation in the mammary gland. The work points to a molecular basis for targeting therapy when an initiating oncogene can be implicated; for example, because of amplification, increased expression, genetic alteration, or heritable characteristics.     

Effects of sexual arousal and guilt upon free associative sexual responses.

Studied sexual associations given to double-entendre words in relation to individual differences in sex-guilt and differing degrees of sexual stimulation. The Mosher Incomplete Sentences Test was used as a measure of sex-guilt. Ss were 84 college males. Results indicate a significant effect between sex-guilt and sexual stimulation. The stimulation procedure produced sexual response increments for both high- and low-guilt groups, but only the increment for low-guilt Ss was significant. (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)