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B J Everitt

Publications and source records attributed to B J Everitt.

At least 145 records · Page 8Linked to original sources
PubMed1990

Damage to ceruleo-cortical noradrenergic projections impairs locally cued but enhances spatially cued water maze acquisition.

A series of 4 experiments tested the effects of central catecholamine depletion on acquisition of an escape response in a spatial water maze. In Expt. 1, local infusions of 6-hydroxydopamine (6-OHDA) into the dorsal noradrenergic bundle (DNAB) enhanced efficient acquisition of the spatial water maze in a stressful condition (cold water), but had no effect in warm water. In Expt. 2, lesions of the ventral noradrenergic bundle did not affect acquisition of the maze, indicating that the changes observed in Expt. 1 were unlikely to have been the result of incidental damage to the noradrenergic innervation of the hypothalamus. Measures of core body temperature and plasma corticosterone were taken in parallel with the behavioral experiments and revealed that central noradrenaline (NA) depletion did not alter these responses to cold or warm water swims. Expt. 3 revealed a contrasting pattern of effects following dopamine (DA) depletion from the caudate-putamen: swimming speed was reduced in warm, but not cold water and maze acquisition was impaired, to an equal extent in warm and cold water. Finally, in Expt. 4, rats with 6-OHDA lesions of the DNAB were impaired in discriminating local cues in a simultaneous visual discrimination water maze. These results support the hypothesis that ceruleo-cortical NA depletion broadens the span of attention, particularly under stressful circumstances. In contrast, the results also indicate that striatal DA depletion mainly affects vigour of responding, as measured by swim speed, and that this effect can be reversed by the stressful effects of cold water.

Amygdala↗
PubMed1990

Neuroendocrine anatomy of the hypothalamus.

The hypothalamus is a most complex part of the CNS having rich interconnections with forebrain, limbic and brainstem structures. Its outflow is directed in such a way as to influence the endocrine system (via the neurohypophyseal and adenohypophyseal neurosecretory systems), the autonomic nervous system (via projections to preganglionic cell groups in brainstem and spinal cord) and behavioural responses to physiological and environmental cues via its interaction with limbic and somatomotor systems. The chemical identity of many of its neuronal messengers and those of some of its important afferents, such as the monoaminergic neurons, has opened the way to a form of systematic experimental investigation with chemical tools more powerful than those available to neuroendocrinologists in the past. Much of the information which follows has accrued very rapidly through the use of these methods to reveal the rich complexities of neuroendocrine integration.

Amino Acids↗
PubMed1990

Comparative effects of preoptic area infusions of opioid peptides, lesions and castration on sexual behaviour in male rats: studies of instrumental behaviour, conditioned place preference and partner preference.

The effects on the sexual behaviour of male rats of excitotoxic amino acid-induced lesions of the medial preoptic area-anterior hypothalamic area (mPOA/AHA), infusions of beta-endorphin, alpha-melanocyte stimulating hormone and naloxone into the mPOA/AHA, systemic naloxone and castration were compared using different behavioural paradigms. These included measures of unconditioned copulatory behaviour, instrumental responses for an oestrous female presented under a second-order schedule of reinforcement, conditioned place preference and partner preference. The results demonstrate that manipulations of the mPOA/AHA markedly affect consummatory aspects of sexual behaviour (mounting, intromitting and ejaculating) but tend not to affect appetitive or reward-related aspects of sexual behaviour, although intra-mPOA/AHA alpha MSH did result in a small increase in instrumental responses, while beta-endorphin infused into the mPOA/AHA also abolished preference for an oestrous over an anoestrous female. Systemic naloxone, on the other hand, reduced instrumental behaviour and a place preference conditioned by prior sexual interaction, while the same compound infused into the mPOA/AHA markedly facilitated copulatory responses but did not affect other measures of appetitive sexual responses. Castration caused an extremely rapid attenuation of conditioned place preference which was apparent before the males had experienced reductions in their copulatory performance. This treatment only slowly reduced partner preference. The results indicate that the use of several behavioural procedures can reveal discrete actions of neuroendocrine treatments on separable psychological processes which underly the integrated pattern of masculine sexual behaviour. In particular, they suggest that the mPOA/AHA is especially concerned with the copulatory responses of mounting and intromitting, but is much less important for a variety of appetitive sexual acts as well as sexual reward, as measured in the place preference procedure. The marked effects of castration on conditioned place preference taken together with the lack of effect of lesions of the mPOA/AHA on this measure indicate that testosterone affects sexual reward-related processes by an action at a site other than the mPOA/AHA. The implications of these findings are discussed.

Animals↗
PubMed1990

The effects of excitotoxic lesions of the basal forebrain on the acquisition, retention and serial reversal of visual discriminations in marmosets.

The effects of N-methyl-D-aspartate-induced lesions of the basal forebrain (which included the cholinergic cells of the nucleus basalis of Meynert) were studied on three aspects of visual discrimination; learning, retention and reversal performance, in the marmoset. Neurobiological investigations revealed that the lesion produced large reductions in choline acetyltransferase activity within anterior regions of cortex, particularly prefrontal. In Experiment 1 lesioned animals showed impaired retention, one week after surgery, of a visual discrimination learned immediately prior to surgery and subsequently showed impaired performance over a series of reversals. The reversal deficit could be characterized as a tendency to perseverate on the previously correct stimulus on the first reversal and as a failure to show serial reversal learning on subsequent reversals. Acquisition of a novel discrimination was not impaired five weeks after surgery. As time of testing may have been a confounding factor, in Experiment 2 the effects of the same lesion on new learning were examined immediately following surgery and the effects on retention a month later. The lesion was found to disrupt new learning but did not affect retention. From the two experiments it is clear that, whereas disruption of retention and new learning was relatively transient, the impairments in reversal performance were more long lasting. In addition, lesioned animals exhibited behavioural hyperactivity and elevations in consummatory and schedule-controlled licking. The disinhibitory and preservative effects observed following lesions of the basal forebrain in this study are similar to those following lesions of the orbitofrontal cortex while the disruption of serial reversal learning is commonly seen following damage to the amygdala. Therefore, these results are consistent with the hypothesis that the range of behavioural effects of the lesion result from damage to the cholinergic afferents to orbitofrontal cortex and to the amygdala, two structures intimately connected to one another.

Animals↗
PubMed1990

Sexual motivation: a neural and behavioural analysis of the mechanisms underlying appetitive and copulatory responses of male rats.

Experiments investigating the neural mechanisms underlying the expression of masculine sexual behaviour are discussed in the context of the hypothesis set out by Frank Beach that suggested the existence of separate sexual arousal and performance mechanisms. The results indicate that the medial preoptic area is crucially involved in consummatory aspects of sexual behaviour: lesions and chemical manipulations of the area profoundly affect mounts, intromissions and ejaculation, but tend not to alter appetitive sexual responses. By contrast, ventral striatal dopamine-dependent mechanisms primarily affect appetitive sexual responses, measured in a variety of paradigms, but tend not to alter copulatory behaviour itself. Finally, associative mechanisms, for example those by which arbitrary environmental stimuli come to control appetitive sexual responses through their predictive association with sexual reinforcement, are shown to depend at least in part on interactions between the basolateral amygdala and dopamine-dependent events in the ventral striatum. Thus, diverse neural and behavioural procedures have revealed that separable neural mechanisms appear to be involved more or less selectively with different components of the male rat's sexual response system. It may still be useful to conceptualize separate sexual arousal and intromission/ejaculatory mechanisms when studying the neuroendocrine basis of sexual behaviour. However, a major challenge is to understand the way in which elements of the telencephalic limbic system, the striatum and preoptic area, some of which are targets for the action of sex steroids, interact to produce an integrated pattern of sexual behaviour.

Animals↗
PubMed1990

Enhanced behavioral conditioning to context and impaired behavioral and neuroendocrine responses to conditioned stimuli following ceruleocortical noradrenergic lesions: support for an attentional hypothesis of central noradrenergic function.

This study tested the hypothesis that cortical noradrenaline (NA) depletion induced by 6-hydroxydopamine (6-OHDA) widens attentional span, impairing the acquisition of conditioning to an explicit stimulus while enhancing conditioning to contextual stimuli. Sham-operated and NA-depleted rats were exposed to pairings of an auditory (clicker) CS and (footshock) US in a distinctive environment. Half of the lesioned and half of the control animals were trained with a short trace interval between presentations of clicker and shock, and half with a long trace. Associative learning theory predicts that a long trace interval should bias intact animals towards stronger contextual conditioning and, in contrast, a short trace interval should bias controls towards stronger CS conditioning. During testing, NA-depleted animals showed impaired fear conditioning to explicit cues, compared with controls, indicated by their reduced suppression of drinking when the CS was introduced into a separate, lick-operant chamber. In contrast, the same animals exhibited enhanced fear of contextual cues, as shown by their greater preference for a "safe" environment over the one in which they were shocked. The behavioral and plasma corticosterone responses of individual animals to the CS were positively correlated in both the lesion and sham groups. Corticosterone levels corroborated the impairment in CS conditioning caused by the lesion. In contrast, behavioral and corticosterone responses to contextual stimuli were not significantly correlated in either group, and there was no enhancement of the corticosterone response to contextual stimuli in the lesioned animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1989

Comparative effects of ibotenic acid- and quisqualic acid-induced lesions of the substantia innominata on attentional function in the rat: further implications for the role of the cholinergic neurons of the nucleus basalis in cognitive processes.

Two experiments examined the effects of excitotoxic lesions of the substantia innominata on cholinergic activity in the neocortex and on performance in a paradigm measuring selective attention in the rat. In Expt. 1, ibotenate-induced lesions produced approximately 30% reductions in cortical choline acetyltransferase (ChAT) activity, and damage to wide regions of the substantia innominata and ventral pallidum. The rats were impaired in their ability to localize brief visual targets in a serial reaction time task, as measured by reduced choice accuracy. This impairment was particularly evident at short stimulus durations, but the lesioned rats did not exhibit evidence of primary visual sensory dysfunction and exhibited only minor deficits when the stimuli were presented unpredictably. The deficit was exacerbated when distracting white noise was interpolated into the task. The rats with lesions were also slower to respond correctly, probably resulting partly from the adoption of a speed/error trade-off strategy, and were slower to collect earned food pellets, although they made no more errors of omission than controls. In Expt. 2, quisqualate-induced lesions produced fewer signs of non-specific damage and 50% reductions in cortical ChAT activity. This lesion produced generally qualitatively similar, but weaker effects to those of ibotenate-induced lesions. It was notable that many of the deficits following either ibotenate- or quisqualate-induced lesions lasted for several months after surgery. The results are discussed in terms of the cholinergic hypothesis of cognitive dysfunction. It is argued that lesions of the substantia innominata, including the magnocellular cholinergic neurons of the nucleus basalis of Meynert, produce deficits in attentional processing, which may not result from damage specifically to cholinergic cells. However, the longevity of the effects makes these preparations suitable for further exploration of the restorative effects of cholinergic treatments.

Animals↗
PubMed1989

Effects of excitotoxic lesions of the substantia innominata, ventral and dorsal globus pallidus on visual discrimination acquisition, performance and reversal in the rat.

Rats received infusions of ibotenic acid into the substantia innominata, in the region of the nucleus basalis of Meynert (nbM), before and after training on simple (simultaneous) and conditional visual discriminations. The ibotenate infusions reduced cortical choline acetyltransferase (ChAT) levels by about 20%, destroyed many ChAT-immunoreactive neurons in the nbM, but also caused the loss of many neurons in the substantia innominata and adjacent areas. These lesions did not impair the acquisition and performance of a simple visual discrimination, but did impair reversal of the discrimination and the performance of a conditional visual discrimination. However, the degree of impairment was unrelated to the degree of cortical ChAT loss. Ibotenic acid lesions to the dorsal globus pallidus also impaired reversal of discrimination but left acquisition and performance unaffected. Striatal dopamine depletion produced by 6-hydroxydopamine (6-OHDA) infusions into the mid-ventral caudate nucleus impaired performance of the simultaneous visual discrimination. Cortical noradrenaline depletion produced by 6-OHDA lesions of the dorsal noradrenergic bundle either alone or in combination with ibotenic acid lesions of the substantia innominata had no effect on acquisition of the discrimination. It is concluded that ibotenic acid lesions of the substantia innominata or to the dorsal globus pallidus affect learning and performance of conditional visual discrimination performance and impair reversal learning without affecting the capacity to discriminate visual events. These results are compared to those following cortical noradrenaline depletion or striatal dopamine loss.

Animals↗
PubMed1989

Comparative effects of quisqualic and ibotenic acid-induced lesions of the substantia innominata and globus pallidus on the acquisition of a conditional visual discrimination: differential effects on cholinergic mechanisms.

Two experiments tested the hypothesis that the deficits in conditional discrimination learning produced by ibotenic acid-induced lesions of the ventral pallidum and substantia innominata are produced by loss of the magnocellular cholinergic cells in the nucleus basalis and adjacent regions. Experiment 1 replicated the previously reported deficit in conditional learning produced by ibotenate-induced lesions of the ventral pallidum/substantia innominata, but failed to demonstrate any restoration of learning by a subchronic regimen of the acetylcholinesterase inhibitor physostigmine sufficient to produce significant (30%), but equivalent, degrees of inhibition in the frontal cortex of ventral pallidum/substantia innominata-lesioned or sham-operated rats. Experiment 2 examined the effects of quisqualic acid-induced lesions of the ventral pallidum/substantia innominata. According to most of the measures of learning employed, the quisqualic acid-induced lesion of the ventral pallidum/substantia innominata failed to impair conditional learning, even though the quisqualate-induced lesion produced greater degrees of cholinergic neuron destruction than the ibotenate-induced lesion, as measured in terms of reductions in cortical choline acetyltransferase activity (44% vs 27%). Although consideration of individual data suggested that very high (60%) levels of choline acetyltransferase reduction in Experiment 2 might have detrimental effects of conditional learning, the overall failure of the quisqualate-induced lesions of the ventral pallidum/substantia innominata to impair learning is to be contrasted with the significant behavioural effects of ibotenate-induced lesions. Histological and immunocytochemical analysis showed that the quisqualate-induced lesion, unlike that produced by ibotenate, tended to produce less damage to the overlying dorsal globus pallidus and to parvocellular neurons of the ventral pallidum/substantia innominata, thus implicating these nonspecific effects of ibotenate-induced lesions in their behavioural effects. The present results question previous interpretations of the behavioural effects of ibotenate-induced lesions of the ventral pallidum/substantia innominata in terms of damage inflicted on the cortically-projecting cholinergic cells of the nucleus basalis, and suggest that quisqualic acid, although also nonspecific in its excitotoxic effects, is nevertheless more selective for producing damage to cholinergic neurons in the ventral pallidum/substantia innominata than ibotenic acid.

Animals↗
PubMed1989

Interactions between the amygdala and ventral striatum in stimulus-reward associations: studies using a second-order schedule of sexual reinforcement.

Bilateral, N-methyl-D-aspartate-induced lesions of the basolateral region of the amygdaloid complex in male rats resulted in a marked decrease in instrumental responses maintained by a visual conditioned reinforcer in a paradigm in which sexual reinforcement was presented under a second-order schedule. There were no effects of lesions of the amygdala on the unconditioned sexual behaviour of the males, i.e. on behaviour elicited by primary reinforcers. Infusion of D-amphetamine bilaterally into the nucleus accumbens region of the ventral striatum resulted in a dose-dependent amelioration of the decrease in instrumental behaviour maintained by a conditioned reinforcer which followed lesions of the amygdala. This effect of D-amphetamine critically depended upon the presentation of the conditioned reinforcer (a previously neutral light which had gained reinforcing properties through its prior association with sexual interaction). The results indicate that the basolateral region of the amygdala may interact with dopamine-dependent processes in the ventral striatum in mediating the control by conditioned reinforcers over instrumental behaviour.

Amphetamines↗
PubMed1989

Involvement of the amygdala in stimulus-reward associations: interaction with the ventral striatum.

The involvement of the amygdala in the potentiation of responding for conditioned reinforcers following intra-accumbens amphetamine injections has been studied. Thirsty rats were trained to associate a light-noise compound stimulus with water and then implanted with guide cannulae in the nucleus accumbens. Half of these rats received excitotoxic lesions of the basolateral region of the amygdala by accumbens. Half of these rats received excitotoxic lesions of the basolateral region of the amygdala by infusing N-methyl-D-aspartate, whereas the other half received infusions of the vehicle. In the test phase, water was no longer presented but responding on one of two novel levers produced the light-noise compound (the conditioned reinforcer) whereas responding on the other lever had no effect. The two groups received four counterbalanced intra-accumbens infusions of amphetamine (3, 10 and 30 micrograms /microliter) or vehicle over four test days. Intra-accumbens amphetamine infusions dose-dependently increased responding on the lever providing a conditioned reinforcer but had no significant effect on responding on the lever which did not produce the conditioned reinforcer. Compared with controls, the lesioned group exhibited a significant, selective reduction in responding on the lever providing a conditioned reinforcer, with no change on the lever on which responding had no consequence, irrespective of drug or control treatment. Control experiments showed that the amygdala lesioned animals were not hypodipsic and exhibited similar levels of hyperactivity following intra-accumbens infusions of D-amphetamine. Furthermore, the capacity to discriminate the conditioned stimulus as well as to acquire a new motor task was not altered by the lesion. These results indicate a role for the amygdala in mediating the effects of stimulus-reward associations on behaviour, via an action on dopamine-dependent mechanisms of the ventral striatum.

Amphetamines↗
PubMed1988

Distribution and some projections of cholinergic neurons in the brain of the common marmoset, Callithrix jacchus.

The distribution of choline acetyltransferase-immunoreactive (ChAT-IR) neurons was studied in the brain of the common marmoset by using immunohistochemistry. ChAT-IR neurons were found in the medial septal nucleus, vertical and horizontal limb nuclei of the diagonal band, the nucleus basalis of Meynert, pedunculopontine nucleus and laterodorsal tegmental nucleus, and also in the striatum, habenula, and brainstem cranial nerve motor nuclei. The organization of ChAT-IR neurons in the basal forebrain, midbrain, and pons is consistent with the Ch1-Ch6 nomenclature introduced by Mesulam et al. ('83). The combination of the retrograde transport of HRP-WGA with ChAT immunohistochemistry revealed the distribution of neurons in the Ch4 cell group projecting to the dorsolateral prefrontal cortex. The activity of ChAT was highest in limbic cortical structures, such as the hippocampus, and lowest in association areas of the neocortex. Lesions at various loci in the basal forebrain resulted in differential patterns of ChAT loss in the cortex, which suggests some degree of topographical organization of Ch4 projections to the cortical mantle.

Animals↗
PubMed1988

Lesions of the dorsal noradrenergic bundle simultaneously enhance and reduce responsivity to novelty in a food preference test.

In conclusion, DNAB lesions have been shown to have two, apparently contradictory effects in a food preference test: to increase neophobia to a novel environment, and to increase the tendency to eat novel food in a novel environment. It has been suggested that these two effects occur because, although NA has a common action on neuronal firing in terminal fields, the dissociable consequences reflect the different functions of areas in receipt of these noradrenergic afferents. In addition, it has been shown that DNAB lesions, VNAB lesions, and a benzodiazepine, chlordiazepoxide, all have somewhat different behavioral effects in the food preference test. Taken together with the lack of correlation between the various behavioral measures used in these experiments, this suggests that neophobia does not reflect a single behavioral process, such as anxiety, or reactivity to novelty.

Adrenergic Fibers↗
PubMed1988

The influence of steroid hormones on competing sexual and ingestive behavior in the male rat.

Water replete rats allowed restricted access to a sweet nonnutritive solution (0.2% Acesulfame-K) spend about one third of their time drinking it. This ingestive response is markedly inhibited if the male rat is simultaneously presented with an estrous female, but not an anestrous female or another male, despite the fact that there is sufficient time for both sexual and ingestive behaviors to occur. Castration and the subsequent decline in sexual behavior is accompanied by an increase in Acesulfame ingestion in the presence of a receptive female. Treatment with testosterone reverses both these effects. Similarly treatment of castrate males with DHT and estradiol (the active metabolites of testosterone) maintains both full sexual behavior and suppression of the ingestive response. However, the steroid requirements for sexual activity do not correspond completely with those for the sexually-induced suppression of ingestive behavior. Treatment of castrate males with estradiol alone maintains mounting behavior (but no intromissions or ejaculations) but does not suppress ingestive behavior in the presence of a receptive female--indeed under these suboptimal hormone conditions sexual behavior appears to be reduced in the presence of Acesulfame. Steroid hormones, therefore, have at least two effects upon sexual behavior. They enable certain aspects of sexual behavior such as intromissions and ejaculations, and also alter the animal's priority of response to two competing (ingestive and sexual) stimuli.

Animals↗
PubMed1988

The effects of simultaneous or separate infusions of some pro-opiomelanocortin-derived peptides (beta-endorphin, melanocyte stimulating hormone, and corticotrophin-like intermediate polypeptide) and their acetylated derivatives upon sexual and ingestive behaviour of male rats.

Intraneuronal post-translational cleavage of pro-opiomelanocortin yields a variety of peptides including beta-endorphin, melanocyte stimulating hormone and corticotrophin-like intermediate polypeptide, some of which are subsequently N-acetylated. Such peptides may be co-released from neuronal terminals, and so these experiments explored the effects of co-administration of some of them on sexual behaviour in the male rat, which is known to be sensitive to hypothalamic infusions of beta-endorphin. Peptides were infused into the pre-optic-anterior hypothalamic area bilaterally in doses up to 320 pmol, and males allowed access to a sexually receptive female and/or a sweet solution (0.1% Acesulfame-K) for 15 min, so that both sexual and ingestive behaviour could be studied. beta-Endorphin(1-31) by itself inhibited sexual interaction, confirming our previous data. Acesulfame-K ingestion was inhibited in control-infused rats in the presence of a female, but this inhibition was released when sexual behaviour was itself diminished by beta-endorphin(1-31). Both the acetylated and non-acetylated forms of melanocyte stimulating hormone (alpha-melanocyte stimulating hormone and des-acetyl melanocyte stimulating hormone) stimulate sexual behaviour; latencies both to ejaculation and to resumption of copulatory behaviour after an ejaculation (post-ejaculatory interval) were reduced. However, infusion of either corticotrophin-like intermediate peptide or N-acetylated beta-endorphin (1-31) had no effect on either sexual or ingestive behaviour. Infusion of either acetylated melanocyte stimulating hormone or des-acetyl melanocyte stimulating hormone mixed with beta-endorphin(1-31) prevented the inhibitory effect of the latter on sexual behaviour. Dose-response studies showed that the behavioural effect of such mixtures depended upon the molar ratios of the two peptides, rather than their absolute concentrations. The higher the ratio in favour of alpha-melanocyte stimulating hormone or des-acetyl melanocyte stimulating hormone, the greater the display of sexual behaviour. Infusing either corticotrophin-like intermediate polypeptides or N-acetyl beta-endorphin(1-31) with beta-endorphin(1-31) did not prevent the inhibition of sexual activity expected with beta-endorphin(1-31) alone. These results are discussed in terms of the functional consequences of co-release of proopiomelanocortin peptides from hypothalamic nerve terminals.

Acetylation↗
PubMed1988

Double dissociations of the effects of amygdala and insular cortex lesions on conditioned taste aversion, passive avoidance, and neophobia in the rat using the excitotoxin ibotenic acid.

The results in this article show that although electrolytic amygdala lesions disrupt learning of a conditioned taste aversion (CTA), ibotenic acid-induced, axon-sparing lesions of the amygdala do not. However, ibotenic acid lesions of the insular cortex do disrupt learning of a CTA. Electrolytic, but not ibotenic acid lesions of the amygdala, interrupt axons running between the insular (gustatory) cortex and the brain stem/hypothalamus. It is the destruction of these projections which appear to underly CTA deficits after amygdala lesions. Other results revealed that ibotenic acid lesions of the insular cortex attenuated the reaction to the novel taste of saccharin in a familiar environment but failed to affect the ingestion of a novel food in a novel environment or passive avoidance learning. Conversely, ibotenic acid lesions of the amygdala did not affect the reaction to novel saccharin in a familiar environment but did impair both the reaction to novel food in a novel environment and passive avoidance learning. We conclude that the insular cortex is involved in reactions to the novelty and associative salience exclusively of taste stimuli, whereas the amygdala is probably more concerned with the reaction to more general aspects of novelty in the environment and in fear-motivated behavior.

Amygdala↗
PubMed1987

Oxytocin in the central nervous system and sexual behaviour in male rats.

Concentrations of oxytocin (OT) and vasopressin (AVP) were measured in cerebrospinal fluid (CSF) obtained from the cisterna magna of freely moving rats. Basal levels of OT and AVP were approximately 9 fmol/ml in both male and female. In the male rats this increased to approximately 18 fmol/ml 5 min after ejaculation, and 27 fmol/ml 20 min after ejaculation. No increase from basal levels occurred when males were placed with unreceptive females, or alone in the test environment. AVP levels were unchanged in any condition. Preliminary investigations indicate that discrete electrolytic lesions to the lateral and posterior parvocellular hypothalamic paraventricular nucleus (PVN) abolished this ejaculation-associated increase in CSF OT, prolonged mount and intromission latencies and reduced the absolute postejaculatory interval (PEI). We conclude that intracerebrally projecting OT systems may be activated during coitus and may contribute to the mechanisms underlying postejaculatory refractoriness.

Animals↗