Male vole urine changes luteinizing hormone-releasing hormone and norepinephrine in female olfactory bulb.

Female prairie voles (Microtus ochrogaster) exposed to a single drop of male urine on the upper lip showed changes in concentrations of luteinizing hormone-releasing hormone (LHRH) and norepinephrine in olfactory bulb tissue; no such changes occurred in dopamine concentration. The changes were measured in the posterior but not the anterior olfactory bulb tissue of females within 1 hour after they were exposed to urine. These females also showed rapid increases in serum concentrations of luteinizing hormone. Females exposed to water on the upper lip showed none of these changes. These results suggest that in this species LHRH and norepinephrine in the olfactory bulb may mediate luteinizing hormone release in response to external (pheromonal) chemical cues.

Aging and sex differences in striatal dopaminergic function.

In this report the potassium- (30 mM) and amphetamine- (10 microM) stimulated responses of dopamine (DA) and 3,4-dihydroxy phenylacetic acid (DOPAC) from superfused striatal tissue of female and male mice as sampled at 2, 6, 18 and 24 months of age were compared. When assessed relative to responses obtained from 2-month-old female mice, potassium-stimulated DA output of female mice was significantly decreased at 18 months of age and significantly increased at 24 months of age. In male mice, the only statistically significant change was an increase in potassium-stimulated DA in the 24 versus 2-month-old mice. In response to amphetamine-stimulation, DA responses from striatal tissue of 18-month-old females were significantly decreased and that of 24-month-old mice significantly increased relative to that of the 2-month-old females. In the case of male mice, amphetamine-stimulated DA responses of 6- and 18-month-old mice were significantly decreased compared with responses observed in the 2-month-old males. In addition, amphetamine-stimulated DA responses of the 24-month-old females were significantly greater than the 24-month-old males. In general, the response profiles for DOPAC to potassium and amphetamine stimulation were similar to that of DA for male, but not female, mice. These results demonstrate that sex differences in striatal dopaminergic function are differentially affected by age. Overall, striatal DA responsiveness of female mice shows more extreme age-related changes, particularly between the 2- and 6-month versus the 18- and 24-month-old mice and a discord between DA and DOPAC responses. Such extreme changes may be related to the presence (at 2 and 6 months) versus absence (at 18 and 24 months) of estrous cycles/gonadal steroid hormonal functions in female mice.

Sex differences in K+-evoked striatal dopamine output from superfused striatal tissue fragments of reserpine-treated CD-1 mice.

Reserpine inhibits vesicular monoamine transporter-2 (VMAT-2) function and thereby impairs vesicular dopamine (DA) storage within nerve terminals. The present report compared the effects of reserpine treatment upon the striatal dopaminergic system in male and female mice as a means to assess potential sex differences in VMAT-2/DA storage function. After treatment with reserpine, male mice showed significantly greater striatal DA concentrations and K+ -evoked DA output from the striatum compared to females. By contrast, no statistically significant sex differences were observed in methamphetamine-evoked DA output in reserpine-treated mice. These results demonstrate a clear sex difference in the striatal dopaminergic responses to reserpine and suggest that females possess a more active VMAT-2/DA storage capacity, as indicated by the greater degree of deficits observed when VMAT-2/DA storage function is inhibited by reserpine. Such findings have important implications for understanding some of the bases for sex differences in neurotoxicity and neurodegeneration of the nigrostriatal dopaminergic system.

Effects of neonatal and prepubertal hormonal manipulations upon estrogen neuroprotection of the nigrostriatal dopaminergic system within female and male mice.

Estrogen (E) can function as a neuroprotectant of the nigrostriatal dopaminergic (NSDA) system against methamphetamine (MA) neurotoxicity in female, but not male, mice. In the present report we examined whether the organizational effects of gonadal steroid hormones, as exerted in the early postnatal period, or developmental effects, as exerted during the pubertal period, would contribute to this sexually dimorphic neuroprotectant action of E. Neonatal gonadectomy and treatment with testosterone of female mice, retained the ability to show an E neuroprotectant response when tested as adults. However, females not treated with gonadal steroids failed to show an E-dependent neuroprotectant response. Neonatal gonadectomy of male mice, failed to result in the display of an E neuroprotectant response when tested as adults. Prepubertal gonadectomy of female mice, with or without testosterone treatment, abolished the capacity for E to produce neuroprotection against MA-induced NSDA neurotoxicity. Nor did prepubertal gonadectomy enable male mice to show an E neuroprotectant response. Taken together these results demonstrate that none of the manipulations performed within male mice enabled them to show an E-dependent neuroprotective response against MA-induced neurotoxicity of the NSDA system when tested as adults. For the female, it appears that the presences of gonadal steroids at these two developmental periods are needed for the display of an E-dependent neuroprotectant response within the adult.

Inactivation of one copy of the mouse neurotrophin-3 gene induces cardiac sympathetic deficits.

Whether two copies of the neurotrophin-3 (NT3) gene are necessary for proper development of cardiac sympathetic innervation was investigated in mice carrying a targeted inactivation of the NT3 gene. Heterozygous (+/-) and null (-/-) mutant mice had fewer stellate ganglion neurons than did wild-type (+/+) mice at postnatal day 0 (P0 or birth), and this deficit was maintained between adult (P60) +/- and +/+ mice. The sympathetic innervation of the heart matured postnatally in +/+ and +/- mice. Tyrosine hydroxylase (TH)-positive axons were restricted largely to the epicardium at P0, were concentrated around large blood vessels in the myocardium at P21, and were present among cardiac myocytes at P60. Cardiac norepinephrine (NE) concentrations paralleled the growth of the sympathetic axons into the heart. NE concentrations were equivalent among +/+, +/-, and -/- mice at birth, but differences between +/- and +/+ mice increased with age. Adult +/- mice also exhibited lower resting heart rates and sympathetic tonus than +/+ mice. Thus deletion of one copy of the NT3 gene translates into anatomical, biochemical, and functional deficits in cardiac sympathetic innervation of postnatal mice, thereby indicating a gene-dosage effect for the NT3 gene.

In vivo neurotransmitter levels in the anterior pituitary of freely behaving intact and castrated male rats determined with push-pull perfusion and high pressure liquid chromatography coupled with electrochemical detection.

Push-pull cannulae were implanted into the anterior pituitary lobes of intact and castrated male rats, and perfusate samples were assayed for neurotransmitter concentrations with HPLC coupled with electrochemical detection. Epinephrine, which was not obtained in any of the five intact males, was detectable in three of five castrated male rats. Norepinephrine rose from nondetectable to high levels after castration in all animals. In contrast to dopamine, which was significantly decreased in castrated males, levels of 3,4-dihydrophenylacetic acid and 5-hydroxyindolacetic acid were significantly increased in castrated vs. intact male rats. Homovanillic acid was rarely detected in either intact or castrated males. These results demonstrate that the push-pull perfusion technique can be used to measure neurotransmitter levels in the anterior pituitary lobes of living rats. More importantly, after castration a distinct rise in norepinephrine and epinephrine accompanied by a decrease in dopamine was clearly detected, suggesting that these neurotransmitters may play an important role directly at the pituitary.

Transient changes in the in vitro activity of the luteinizing hormone-releasing hormone pulse generator after ovariectomy in rats.

We examined in vitro LHRH release as a function of time after ovariectomy (OVX). Adult female rats (diestrous day 1 and 11-16, 61-68, and more than 120 days post-OVX) were decapitated, and the suprachiasmatic-medial preoptic area-medial basal hypothalamus was removed and superfused in vitro. There was a statistically significant (P less than 0.05) 2-fold decrease in mean in vitro LHRH release 11-16 days post-OVX that returned to levels observed in diestrous day 1 females 60 days post-OVX. LHRH cycle amplitudes of 11- to 16-day ovariectomized rats were reduced and significantly lower (P less than 0.05) than those of more than 120-day ovariectomized rats. These results indicate a complex relationship between ovarian steroid hormone removal and LHRH pulse generator function that is only revealed after direct measurement of LHRH release.

Aging alters opiate inhibition of potassium (K+)-stimulated dopamine release from the corpus striatum of male rats.

The effect of Leu-enkephalin (Leu-ENK), Met-enkephalin (Met-ENK), and naloxone on potassium (K+)-evoked endogenous dopamine (DA) release from striatal tissue fragments was examined in young (2-4 month) and old (20-25 month) male rats. The K(+)-evoked DA release was significantly lower in old compared to young animals. Leu-ENK significantly reduced K(+)-evoked DA release in young animals, but neither opiate affected DA release in old animals. Naloxone, which had no effect in young animals, raised the K(+)-evoked DA response in old animals to levels seen in young control preparations. These results suggest that the age-dependent decrease in K(+)-evoked DA release may in part be due to a stronger opiate inhibitory tonus in the CS of older rats.

Age-related changes in monoamines within the olfactory bulbs of the Fischer 344 male rat.

In this report the olfactory bulbs (OB) were removed from 5-6 month, 15-16 month and 25-26 month male Fischer 344 rats and assayed for concentrations of monoamines and their metabolites using HPLC-EC. Concentrations of norepinephrine were significantly greater in 25-26 and 15-16 compared to the 5-6 month old rats. By contrast, the norepinephrine metabolite, 3-methoxy-4-hydroxyphenyl glycol (MHPG), was significantly lower in the 25-26 vs. the 15-16 and 5-6 month old animals. While OB concentrations of dopamine and serotonin did not differ among the three age groups, their respective metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindole-3-acetic acid (5-HIAA), were significantly reduced in the 15-16 and 25-26 month old animals compared to the 5-6 month old animals. These data show some of the age related changes which occur in the monoamines of the OB of the Fischer 344 rat. The salient bi-directional changes which are observed between norepinephrine and its metabolite, MHPG, are particularly intriguing since they reveal some of the mechanistic alterations that occur in the OB noradrenergic system, which may underlie the age related changes in olfactory related memory/recognition processes.

Estrogen, but not testosterone, attenuates methamphetamine-evoked dopamine output from superfused striatal tissue of female and male mice.

The gonadal steroid hormone, estrogen, has the capacity to function as a neuroprotectant against methamphetamine (MA)-induced neurotoxicity of the nigrostriatal dopaminergic system within female, but not male, mice. In an attempt to understand some of the bases for this effect of estrogen, the incipient effects of MA upon evoked dopamine output from superfused striatal tissue fragments of gonadectomized female and gonadectomized as well as intact male mice were evaluated under conditions where estrogen (or testosterone) was present in the medium. The amount of dopamine evoked by MA was significantly reduced when estrogen was co-infused with MA. This attenuation was obtained with striatal tissue fragments of gonadectomized female and gonadectomized and intact male mice. In contrast to estrogen, co-infusion of testosterone failed to produce an overall statistically significant change in MA-evoked dopamine output within superfused striatal tissue fragments of gonadectomized female and male mice. In this way, the gonadal steroid hormones, estrogen and testosterone, exert differential modulatory effects upon MA-evoked dopamine output from superfused striatal tissue fragments. However, similar effects to these gonadal steroid hormones were observed between gonadectomized female and gonadectomized or intact male mice. These data reveal an absence of a sexual dimorphism in striatal responsiveness with regard to estrogen's ability to alter MA-evoked DA output. Accordingly, the sexually dimorphic capacity for estrogen to function as a neuroprotectant may involve a composite of actions upon the nigrostriatal dopaminergic system involving events/sites other than the initial stimulation of dopamine output.

Tamoxifen abolishes estrogen's neuroprotective effect upon methamphetamine neurotoxicity of the nigrostriatal dopaminergic system.

The effects of 17beta-estradiol and the anti-estrogen, tamoxifen, on methamphetamine-induced neurotoxicity of the nigrostriatal dopaminergic system were examined in ovariectomized CD-1 mice. In Experiment 1, striatal dopamine concentrations from estrogen treated mice were significantly greater than that from non-estrogen treated mice following methamphetamine. Dopamine concentrations from estrogen+tamoxifen+methamphetamine treated mice were decreased compared to estrogen+methamphetamine treated mice and not significantly different from those of tamoxifen+methamphetamine treated mice or mice receiving methamphetamine alone. These results suggest that estrogen is functioning as a neuroprotectant of methamphetamine-induced nigrostriatal dopaminergic neurotoxicity and that this neuroprotective effect of estrogen is abolished in the presence of tamoxifen. In Experiment 2, estrogen administration after methamphetamine treatment did not produce any significant changes in dopamine concentrations compared with methamphetamine treatment alone. The data from Experiment 2 show that estrogen cannot reverse the methamphetamine-induced neurotoxicity upon the nigrostriatal dopaminergic system. Similar results were observed for the potassium-stimulated dopamine outputs from these treatment conditions as evaluated with in vitro superfusion, although a difference between the two measures for the estrogen+methamphetamine treated group was obtained in Experiment 1. These results have important implications for estrogen-tamoxifen interactions upon the nigrostriatal dopaminergic system and the gender differences which are observed in Parkinson's disease and animal models of nigrostriatal dopaminergic neurotoxicity as well as for the proposed use of tamoxifen in pre-menopausal women at risk for breast cancer.

Nisoxetine infusion into the olfactory bulb enhances the capacity for male rats to identify conspecifics.

In the present report, the norepinephrine uptake inhibitor nisoxetine as well as a cocktail of nisoxetine and the alpha-adrenergic receptor antagonist phentolamine were infused unilaterally into the olfactory bulb during microdialysis to assess their effects upon the capacity of male rats to identify conspecifics. A social discrimination test was conducted while simultaneously measuring olfactory bulb norepinephrine output in the dialysate before, during, and after behavioral testing. Nisoxetine significantly increased norepinephrine levels in the olfactory bulb compared with the Ringer's solution control group. Following such increases in olfactory bulb norepinephrine, identification responses were enhanced compared with that observed in the Ringer's control. In the presence of phentolamine, nisoxetine elevated olfactory bulb norepinephrine to levels similar to that obtained in the nisoxetine alone group, however, investigatory responses directed to the conspecifics indicated an absence of identification capacity similar to that observed in the Ringer's control group. These results reveal a direct link between norepinephrine transmission in the olfactory bulb and enhanced identification via its activation of postsynaptic alpha-adrenergic receptors. These results also show that inhibition of norepinephrine uptake may represent an important mechanism involved with the enhancement of social identification and suggest a possible novel effect for the antidepressant nisoxetine.

Age-related changes in nigrostriatal dopaminergic function are accentuated in +/- brain-derived neurotrophic factor mice.

The effects of a deletion for the brain derived neurotrophic factor (BDNF) allele (+/- BDNF) upon age-related changes in nigrostriatal dopaminergic (NSDA) function were assessed. Behavioral (beam crossing and spontaneous activity) and neurochemical (potassium-stimulated dopamine release from superfused striatum) measures were compared among Young (4-5 month), Middle (11-13 month) and Aged (19-21 month) +/- BDNF and their wild type littermate control (+/+ BDNF) mice. No statistically significant differences were obtained between +/+ and +/- BDNF mice at the Young age sampling period for any of the behavioral or neurochemical measures. Behavioral and neurochemical responses indices of NSDA function begin to diverge between +/+ and +/- Middle age BDNF mice and maximal differences were observed at the Aged period. For both movement and stereotypy times, scores obtained from +/+ mice were significantly decreased compared with +/- BDNF mice at the Aged period and center time scores of +/+ mice were decreased at both the Middle and Aged periods compared with +/- BDNF mice. Neurochemically, potassium-stimulated DA release of +/+ mice was significantly greater than +/- BDNF mice with maximal differences obtained at the Aged period. These results demonstrate marked differences in age-related changes of NSDA function between +/+ and +/- BDNF mice and suggest that the deletion of one allele for BDNF may make these mice more susceptible to age-related declines in NSDA function.

In-vivo activity of the LH-releasing hormone pulse generator in castrated and intact male rats.

The in-vivo LH-releasing hormone (LHRH) output from the mediobasal hypothalamus of conscious freely moving sham-castrated, acutely castrated (immediately after castration) and long-term castrated (greater than 20 days after castration) adult male rats has been studied. Five rats in each of the three conditions were perfused for an 8-h period (11.00-19.00 h). One animal in each condition was perfused for a 24-h period. In the sham-castrated and acutely castrated, but not in the long-term castrated rats, apparently random surges of LHRH output (greater than 5.6 pmol/l), separated by periods of non-detectable activity, were observed throughout the perfusion period. The LHRH output of the long-term castrated rats was characterized by an extremely low overall mean release and markedly attenuated pulse amplitudes, with both parameters significantly lower than those of the sham-and acutely castrated rats. These results indicate that the raised blood levels of LH in long-term castrated rats do not appear to be the consequence of high amplitude and high overall release of LHRH.

Para-chlorophenylalanine treatment inhibits the expression of vasoactive intestinal peptide messenger RNA in rat anterior pituitary.

Adult male Sprague-Dawley rats were treated with para-chlorophenylalanine (pCPA) or alpha-methyl tyrosine (alpha-MT) to study the effect of serotonin or catecholamine depletion on the expression of vasoactive intestinal peptide (VIP) messenger RNA in the anterior pituitary. Single injections of pCPA (300 mg/kg) for two consecutive days resulted on the third day in a dramatic depletion of serotonin in the medial basal hypothalamus, and a significant reduction in the pituitary content of VIP mRNA (1.0 and 1.7 kb). The effect of pCPA on VIP mRNA appeared to be relatively specific for the anterior pituitary since VIP message levels in the cerebral cortex did not decrease. alpha-MT treatment, (150 mg/kg) for 2 consecutive days, reduced dopamine concentrations in the MBH but had no significant effect on pituitary VIP levels. In a time-course study, hypothalamic serotonin and pituitary VIP mRNA levels were significantly depressed 1-3 days after initiation of pCPA treatment; however, 12 days after pCPA treatment, serotonin concentrations in the hypothalamus approached control values and pituitary VIP mRNA content increased an average of 2-fold over control levels in an apparent rebound effect. pCPA-treated rats injected i.p. twice a day with 5-hydroxytryptophan (5-HTP; 50 mg/kg) experienced a partial reversal in the decline in the 1.7 kb VIP mRNA seen 24 h after the first pCPA injection. However, at 72 h, supplementation with 5-HTP did not prevent the pCPA-induced decrease of pituitary VIP mRNA. These data indicate that serotonergic pathways have a major role in the control of VIP mRNA expression in the rat anterior pituitary.

Effects of orchidectomy on nigro-striatal dopaminergic function: behavioral and physiological evidence.

Abstract In the present experiments, we examined the effect of castration upon two indices of nigro-striatal dopaminergic function in the male rat. In Experiment I, differences in spontaneous locomotor behavioral activity between intact and castrated male rats were examined. The total distance traveled, horizontal activity and mean revolutions of castrated male rats were significantly greater than that of intact males. No significant differences between intact and castrated males were obtained for vertical activity. In Experiment II, the spontaneous in vitro dopamine release from the corpus striatum of intact and castrated rats as sampled during the light-phase (1500 h) and dark-phase (2400 h) of the photoperiod was examined. At both time periods, the spontaneous in vitro dopamine release of castrated males was significantly greater than that of intact males. Both intact and castrated males showed statistically significant increases in dopamine release at the 2400 h compared to the 1500 h time period. To examine if testicular hormones were responsible for these castration induced changes in dopamine release, in Experiment III we treated castrated male rats with testosterone propionate. Administration of testosterone propionate (0.1 mg/day x 5 days) significantly reduced in vitro dopamine release compared to untreated or castrated male rats receiving vehicle treatment. These results demonstrate that testicular hormones, most likely testosterone, have a markedly suppressive effect upon the nigro-striatal dopaminergic system as evidenced from changes in spontaneous behavioral activity and in vitro dopamine release.

Tamoxifen diminishes methamphetamine-induced striatal dopamine depletion in intact female and male mice.

It has been demonstrated that the nigrostriatal dopaminergic system of male mice is more sensitive to the neurotoxic effects of methamphetamine (MA). The basis for this difference can be related to oestrogen, which has the capacity to function as a neuroprotectant against neurotoxins that target the nigrostriatal dopaminergic system. We examined the effects of the anti-oestrogen, tamoxifen (TMX), upon MA-induced neurotoxicity of the nigrostriatal dopaminergic system in intact female and male CD-1 mice. Striatal dopamine concentrations of TMX-treated female and male mice receiving MA were significantly greater than mice receiving MA alone. In female, but not male, mice, oestrogen treatment also resulted in greater striatal dopamine concentrations compared to mice receiving MA alone. Interestingly, male mice treated with oestrogen were particularly sensitive to the acute toxic effects of MA and displayed no evidence of nigrostriatal neuroprotection. The dihydroxyphenylacetic acid/dopamine ratios following MA for female and male mice treated with TMX or females treated with oestrogen were significantly reduced compared to MA-treated mice and oestrogen + MA-treated male mice. No differences among the treatment groups were obtained for dopamine in the hypothalamus or olfactory bulb. These data demonstrate that TMX treatment of intact female and male mice diminishes striatal dopamine depletions to the nigrostriatal dopaminergic neurotoxin, MA. Oestrogen also displayed this capacity when administered to female, but accentuated acute toxicity in male mice. These effects are relatively specific for the nigrostriatal dopaminergic system. Such data suggest that TMX can function as a nigrostriatal dopaminergic neuroprotectant against MA-induced neurotoxicity in intact female and male mice.

Interactive effects of tamoxifen and oestrogen upon the nigrostriatal dopaminergic system: long-term treatments.

In the present report adult female rats were ovariectomized (OVX) and assigned to one of four treatment conditions. Treatments consisted of administering pellets containing 17beta-oestradiol (E), tamoxifen (TMX), a combination of TMX and E or no further treatment (OVX). Animals received these treatments immediately following OVX and were maintained in these conditions for a 40-day period. Subsequently, the corpus striatum (CS) was dissected from each animal and prepared for determinations of basal and amphetamine stimulated DA output using in-vitro superfusion. No statistically significant differences among the four treatment groups were obtained for basal dopamine output. The highest levels of amphetamine-stimulated dopamine responses were obtained from E treated rats. These values were significantly greater than that obtained from OVX rats and rats treated with a combination of TMX+E. The significance of these findings is that they indicate both a non-traditional central nervous system site and mechanism of action through which tamoxifen-oestrogen interactions can function. Such data may have important implications for administration of tamoxifen to premenopausal women as this anti-oestrogen may compromise nigrostriatal dopaminergic function under conditions where oestrogenic modulation is present.

Tamoxifen alters dopamine output through direct actions upon superfused corpus striatal tissue fragments.

Tamoxifen (10 pg/ml) was infused directly into superfused striatal tissue fragments of ovariectomized rats for a 50 min period. Immediately following the termination of tamoxifen there was a significant increase in dopamine output compared with non-infused controls. No such significant increase was observed with use of a 100 pg/ml tamoxifen dose. Although dopamine output was again increased upon termination of a 2 h infusion of tamoxifen, these levels failed to differ significantly from that of non-infused controls. Similarly, a shorter 10 min duration infusion of tamoxifen failed to alter dopamine output. Finally, we examined whether the tamoxifen-induced, post-infusion increase in dopamine output, as observed following a 50 min infusion of 10 pg/ml, involved a calcium dependent process. To achieve this goal, superfusions were performed with Calcium/Tamoxifen, No Calcium/Tamoxifen, No Calcium/No Tamoxifen and Calcium/No Tamoxifen. A significant increase in dopamine output post-tamoxifen infusion was obtained for the Calcium/Tamoxifen condition compared with the remaining three groups which failed to differ from one another. Taken together these results show that tamoxifen can alter dopamine output through direct, non-genomic effects upon striatal neurons. Responses to this anti-estrogen are intriguing since they are apparent following removal, but not during tamoxifen infusion and represent a calcium-dependent process. These data suggest that tamoxifen may represent an important modulator of nigrostriatal dopaminergic function.

Involvement of olfactory bulb catecholamines and luteinizing hormone-releasing hormone in response to social stimuli mediating reproductive functions.

In this paper we summarize our findings related to the involvement of olfactory bulb (OB) catecholamines and LHRH in response to social stimuli. Previous work from our laboratory had indicated the presence of LHRH within the OB, with localization of this neuropeptide to the posterior dorsal area of this structure. Subsequent work has demonstrated that the presence and localization of LHRH within the OB is an ubiquitous phenomenon characteristic of several rodent species and appears specific for the neuropeptide LHRH, since TRH failed to demonstrate any comparable localization. Analysis of catecholamine concentrations by HPLC-EC revealed that norepinephrine was present in greatest concentrations. Changes in the concentration of LHRH within the OB were obtained following social or chemical cue stimulation. These changes were also localized to the posterior OB, appeared to be specific for LHRH (versus TRH) and were associated with changes in catecholamine concentrations. Recently, we have implanted a push-pull cannula in the OB of male rats and measured the in vivo release of these neuroactive substances in the awake freely moving rat. Release of LHRH from the OB was extremely low with most samples below the detectability of the assay. When detectable, the output of LHRH did not appear to be associated with the introduction of a receptive female. In contrast, norepinephrine output was obtained from all males and demonstrated marked increases in response to the introduction of a receptive female, suggesting that this neurotransmitter may be an important component for processing chemical cue information within the OB.