Cohabitation with receptive females under D2-type agonism in adulthood restores partner preference and brain dimorphism in the SDN-POA following neonatal gonadectomy in male rats.

Perinatal testosterone, or its metabolite estradiol, organize the brain toward a male phenotype. Male rodents with insufficient testosterone during this period fail to display sexual behavior and partner preference for receptive females in adulthood. However, cohabitation with non-reproductive conspecifics under the influence of a D2 agonist facilitates the expression of conditioned partner preference via Pavlovian learning in gonadally intact male rats. In the present experiment, three groups of neonatal PD1 males (N = 12/group) were either gonadectomized (GDX), sham-GDX, or left intact and evaluated for social preferences and sexual behaviors as adults. We then examined whether the effects of GDX could be reversed by conditioning the males via cohabitation with receptive females under the effects of the D2 agonist quinpirole (QNP) or saline, along with the size of some brain regions, such as the sexually dimorphic nucleus of the preoptic area (SDN-POA), suprachiasmatic nucleus (SCN), posterior dorsal medial amygdala (MeApd) and ventromedial hypothalamus (VMH). Results indicated that neonatal GDX resulted in the elimination of male-typical sexual behavior, an increase in same-sex social preference, and a reduction of the area of the SDN-POA. However, GDX-QNP males that underwent exposure to receptive females in adulthood increased their social preference for females and recovered the size in the SDN-POA. Although neonatal GDX impairs sexual behavior and disrupts partner preference and brain dimorphism in adult male rats, Pavlovian conditioning under enhanced D2 agonism ameliorates the effects on social preference and restores brain dimorphism in the SDN-POA without testosterone.

Minimally Invasive Treatment of Facet Osteoarthritis Pain in Spine: A Clinical Approach Evaluating Cryotherapy.

BACKGROUND: Chronic pain management remains a challenging aspect of neurosurgical care, with facet arthrosis being a significant contributor to the global burden of low back pain. This study evaluates the effectiveness of cryotherapy as a minimally invasive treatment for patients with facet arthrosis. By focusing on reducing drug dependency and pain intensity, the research aims to contribute to the evolving field of pain management techniques, offering an alternative to traditional pain management strategies. METHODS: Through a retrospective longitudinal analysis of patients with facet osteoarthritis treated via cryotherapy between 2013 and 2023, we evaluated the impact on medication usage and pain levels, utilizing the Visual Analog Scale for pre- and posttreatment comparisons. RESULTS: The study encompassed 118 subjects, revealing significant pain alleviation, with Visual Analog Scale scores plummeting from 9.0 initially to 2.0 after treatment. Additionally, 67 patients (56.78%) reported decreased medication consumption. These outcomes underscore cryotherapy's potential as a pivotal tool in chronic pain management. CONCLUSIONS: The findings illuminate cryotherapy's efficacy in diminishing pain and curtailing medication dependency among patients with facet arthrosis. This study reaffirms cryotherapy's role in pain management and propels the discourse on nontraditional therapeutic avenues, highlighting the urgent need for personalized and innovative treatment frameworks.

Electrophysiological Characterization of Cerebellar Responses during Exploration and Grooming Behaviors in a Rat Model of Parkinsonism.

Parkinson's disease is currently a global public health challenge due to the rapid growth of aging populations. To understand its pathophysiology is necessary to study the functional correlation between the basal ganglia (BG) and the cerebellum, which are involved in motor control. Herein, we explored multiunit electrical activity (MUA) in the cerebellum of rats with induced Parkinsonism as a result of lesions following bilateral placement of electrodes and passing of current in the ventrolateral striatum (VLS). In one control group, the electrodes descended without electrical current, and another group was left intact in VLS. MUA was recorded in Sim B and Crus II lobes, and in the dentate nucleus (DN) during the execution of exploration behaviors (horizontal and vertical) and grooming. The lesioned and sham groups showed a decrease in MUA amplitude in the Crus II lobe compared to the intact group in all recorded behaviors. However, Sim B and DN did not express differences. Both electrical and physical insults to the VLS induced Parkinsonism, which results in less MUA in Crus II during the execution of motor behaviors. Thus, this type of Parkinsonism is associated with a decrease in the amplitude of Crus II.

Neuroinflammation in Parkinson's Disease: From Gene to Clinic: A Systematic Review.

Parkinson's disease is a neurodegenerative disease whose progression and clinical characteristics have a close bidirectional and multilevel relationship with the process of neuroinflammation. In this context, it is necessary to understand the mechanisms involved in this neuroinflammation-PD link. This systematic search was, hereby, conducted with a focus on the four levels where alterations associated with neuroinflammation in PD have been described (genetic, cellular, histopathological and clinical-behavioral) by consulting the PubMed, Google Scholar, Scielo and Redalyc search engines, including clinical studies, review articles, book chapters and case studies. Initially, 585,772 articles were included, and, after applying the inclusion and exclusion criteria, 84 articles were obtained that contained information about the multilevel association of neuroinflammation with alterations in gene, molecular, cellular, tissue and neuroanatomical expression as well as clinical-behavioral manifestations in PD.

Valorisation of the invasive alga Rugulopteryx okamurae through the production of monomeric sugars.

Rugulopteryx okamurae is an invasive brown alga causing severe environmental and economic problems on the western Mediterranean coasts. Thus, in addition to the difficulties caused to the fishing and tourism sectors, there is a need to manage its accumulation on the beaches. This work aims to valorise this waste by using it as raw material for producing monosaccharides through a two-stage sequential process. These sugars could be used for different fermentative processes to obtain high-value-added bioproducts. In this work, biological pretreatment of the previously conditioned seaweed with the fungus Aspergillus awamori in solid-state fermentation (SSF), followed by enzymatic hydrolysis with a commercial enzyme cocktail, was performed. The effect of the extension of the biological pretreatment (2, 5, 8 and 12 days) on the subsequent release of total reducing sugars (TRS) in the enzymatic hydrolysis stage was studied. To analyse this effect, experimental data of TRS produced along the hydrolysis were fitted to simple first-order kinetics. Also, the secretion of cellulase and alginate lyase by the fungus, along with the biological pretreatment, was determined. The results suggest that 5 days of biological pretreatment of the macroalgae with A. awamori followed by enzymatic saccharification for 24 h with Cellic CTec2® (112 FP units/g of dry biomass) are the best conditions tested, allowing the production of around 240 g of TRS per kg of dried biomass. The main sugars obtained were glucose (95.8 %) and mannitol (1.5 %), followed by galactose (1 %), arabinose (0.9 %) and fucose (0.5 %). KEY POINTS: • Five-day SSF by A. awamori was the best condition to pretreat R. okamurae. • Five-day SSF was optimal for alginate lyase production (1.63 ±0.011 IU/g biomass). • A maximum yield of 239 mg TRS/g biomass was obtained (with 95.8 % glucose).

Neurobiology of Maternal Behavior in Nonhuman Mammals: Acceptance, Recognition, Motivation, and Rejection.

Among the different species of mammals, the expression of maternal behavior varies considerably, although the end points of nurturance and protection are the same. Females may display passive or active responses of acceptance, recognition, rejection/fear, or motivation to care for the offspring. Each type of response may indicate different levels of neural activation. Different natural stimuli can trigger the expression of maternal and paternal behavior in both pregnant or virgin females and males, such as hormone priming during pregnancy, vagino-cervical stimulation during parturition, mating, exposure to pups, previous experience, or environmental enrichment. Herein, we discuss how the olfactory pathways and the interconnections of the medial preoptic area (mPOA) with structures such as nucleus accumbens, ventral tegmental area, amygdala, and bed nucleus of stria terminalis mediate maternal behavior. We also discuss how the triggering stimuli activate oxytocin, vasopressin, dopamine, galanin, and opioids in neurocircuitries that mediate acceptance, recognition, maternal motivation, and rejection/fear.

Tumor ENPP1 (CD203a)/Haptoglobin Axis Exploits Myeloid-Derived Suppressor Cells to Promote Post-Radiotherapy Local Recurrence in Breast Cancer.

ABSTRACT: Locoregional failure (LRF) in patients with breast cancer post-surgery and post-irradiation is linked to a dismal prognosis. In a refined new model, we identified ectonucleotide pyrophosphatase/phosphodiesterase 1/CD203a (ENPP1) to be closely associated with LRF. ENPP1hi circulating tumor cells (CTC) contribute to relapse by a self-seeding mechanism. This process requires the infiltration of polymorphonuclear myeloid-derived suppressor cells and neutrophil extracellular trap (NET) formation. Genetic and pharmacologic ENPP1 inhibition or NET blockade extends relapse-free survival. Furthermore, in combination with fractionated irradiation, ENPP1 abrogation obliterates LRF. Mechanistically, ENPP1-generated adenosinergic metabolites enhance haptoglobin (HP) expression. This inflammatory mediator elicits myeloid invasiveness and promotes NET formation. Accordingly, a significant increase in ENPP1 and NET formation is detected in relapsed human breast cancer tumors. Moreover, high ENPP1 or HP levels are associated with poor prognosis. These findings unveil the ENPP1/HP axis as an unanticipated mechanism exploited by tumor cells linking inflammation to immune remodeling favoring local relapse. SIGNIFICANCE: CTC exploit the ENPP1/HP axis to promote local recurrence post-surgery and post-irradiation by subduing myeloid suppressor cells in breast tumors. Blocking this axis impairs tumor engraftment, impedes immunosuppression, and obliterates NET formation, unveiling new opportunities for therapeutic intervention to eradicate local relapse and ameliorate patient survival. This article is highlighted in the In This Issue feature, p. 1171.

Enhanced D2 Agonism Induces Conditioned Appetitive Sexual Responses Toward Non-reproductive Conspecifics.

Brain mechanisms of sexual attraction toward reproductive partners develop from a systematic interrelationship between biology (nature) and learning (nurture). However, the causes of attraction toward non-reproductive partners are poorly understood. Here, we explored the role of Pavlovian learning under dopaminergic agonism on the development of sexual preference and brain activation for young male rats. During conditioning, adult sexually naïve males received either Saline (Saline-Paired) or the D2-receptor agonist quinpirole (QNP-Paired) and cohabited in contingency, or out of contingency (QNP-Unpaired) during 24 h with an almond-scented prepubertal juvenile male (PD25). Conditioning occurred every 4 days for three trials. Social and sexual responses were assessed four days after the last conditioning trial in a drug-free test, and males chose freely between a scented young male (PD37) and a novel receptive female. Four days later, males were exposed to the conditioned odor only and brain Fos-IR and serum testosterone were analyzed. Saline-Paired and QNP-Unpaired males displayed more non-contact erections (NCEs) and genital investigations for females, whereas QNP-Paired males expressed more NCEs and genital investigations for young males. In the QNP-Paired group, exposure to the young male-paired odor evoked more Fos-IR in limbic, hypothalamic and cortical areas, but no differences in serum testosterone were observed. Cohabitation with juvenile males during enhanced D2 agonism results in atypical appetitive sexual responses and a higher pattern of brain response for the young male-paired odor, with no changes in serum testosterone. We discuss the potential implications for the development of pedophilic disorder and perhaps other paraphilias.

Changes in multiunit activity pattern in cerebellar cortex associated to olfactory cues during sexual learning in male rats.

The cerebellum is a structure of the central nervous system which has been previously studied with different techniques and animal models and even humans, so it is associated with multiple functions such as cognition, memory, emotional processing, balance, control of movement, among others. Its relationship with sensory systems has already been explored, however, the role it plays in olfactory processing in the cerebellum is unclear. Several hypotheses have been proposed from work done in humans and animal models with neuroimaging and immunohistochemical techniques. Everything seems to indicate that the cerebellar function is of vital importance for the olfactory perception, being able to be controlling not only the olfactory aspect, but also the olfactory processing. In this study we analyzed the multiunit activity in the granular layer of the cerebellar vermis during olfactory stimulation: a session being sexually naive and during four sessions of sexual behavior learning. The amplitude was compared between male naive and sexual experts, as well as between olfactory stimuli. The amplitude of the sexually experienced rats showed the highest values compared to naive ones. Odor of receptive female causes the greatest amplitudes, however, in the control group the amplitude increased when they were sexually experts. The motor, sensory and associative learning generated by the acquisition of sexual experience modifies the activation pattern in the cerebellum by presenting neutral odors or associated with a reward.

Brain activation associated to olfactory conditioned same-sex partner preference in male rats.

Sexual preferences can be strongly modified by Pavlovian learning. For instance, olfactory conditioned same-sex partner preference can occur when a sexually naïve male cohabits with an scented male during repeated periods under the effects of enhanced D2-type activity. Preference is observed days later via social and sexual behaviors. Herein we explored brain activity related to learned same-sex preference (Fos-Immunoreactivity, IR) following exposure to a conditioned odor paired with same-sex preference. During conditioning trials males received either saline or the D2-type receptor agonist quinpirole (QNP) and cohabitated during 24 h with a stimulus male that bore almond scent on the back as conditioned stimulus. This was repeated every 4 days, for a total of three trials. In a drug-free final test we assessed socio/sexual partner preference between the scented male and a receptive female. The results indicated that QNP-conditioned males developed a same-sex preference observed via contact, time spent, olfactory investigations, and non-contact erections. By contrast, saline-conditioned and intact (non-exposed to conditioning) males expressed an unconditioned preference for the female. Four days later the males were exposed to almond scent and their brains were processed for Fos-IR. Results indicated that the QNP-conditioned group expressed more Fos-IR in the nucleus accumbens (AcbSh), medial preoptic area (MPA), piriform cortex (Pir) and ventromedial nucleus of the hypothalamus (VMH) as compared to saline-conditioned. Intact males expressed the lowest Fos-IR in AcbSh and VMH, but the highest in MPA and Pir. We discuss the role of these areas in the learning process of same-sex partner preferences and olfactory discrimination.

Heterosexual experience prevents the development of conditioned same-sex partner preference in male rats.

Sexual partner preferences can be strengthened, weakened or even drastically modified via Pavlovian conditioning. For example, conditioned same-sex partner preference develops in sexually-naïve male rats that undergo same-sex cohabitation under the effects of quinpirole (QNP, D2 agonist). Here, we assessed the effect of prior heterosexual experience on the probability to develop a conditioned same-sex preference. Naïve or Sexually-experienced males received either Saline or QNP and cohabited during 24h with a male partner that bore almond scent on the back as conditioned stimulus. This was repeated every 4days for a total of three trials and resulted in four groups (Saline-naïve, Saline-experienced, QNP-naïve, QNP-experienced). Social and sexual preference were assessed four days after the last conditioning trial in a drug-free test in which experimental males chose between the scented familiar male and a novel sexually receptive female. Results showed that Saline-naïve, Saline-experienced and QNP-experienced displayed a clear preference for the female (opposite-sex). By contrast, only QNP-naïve males displayed a same-sex preference. Accordingly, QNP-experienced males were not affected by the conditioning process and continued to prefer females. We discuss the effects of copulation and D2 agonists on the facilitation and/or disruption of conditioned partner preferences.

Effect of hyperprolactinemia on PRL-receptor expression and activation of Stat and Mapk cell signaling in the prostate of long-term sexually-active rats.

The abnormal elevation of serum PRL, referred to as hyperprolactinemia (HyperPRL), produces alterations in several reproductive parameters of male rats such as penile erection or decreased tendency to reach ejaculation. Additionally, this situation produces a significant modification of prostate histology, as observed in the epithelial structure and alveolar area, which could reach a level of hyperplasia in the long-term. In this tissue, HyperPRL produces an increase in expression of PRL receptors and activation of the Stat3 signaling pathway that is correlated with the evolution of prostate pathologies. However, the impact of HyperPRL in long-term sexually active male rats is unknown. In this work, using constantly copulating Wistar male rats with induced HyperPRL, we analyzed the level of serum PRL, the effect on prostate PRL receptors, and activation of pStat3, pStat5 and Mapk signaling pathways. Two procedures to induce HyperPRL were employed, comprising daily IP administration or adenohypophysis transplant, and although neither affected the execution of sexual behavior, the serum PRL profile following successive ejaculations was affected. Messenger RNA expression of the short and long isoforms of the PRL receptor at the ventral prostate was affected in different ways depending on the procedure to induce HyperPRL. The ventral prostate did not show any modification in terms of activation of the pStat5 signaling pathway in subjects with daily administration of PRL, although this was significantly increased in ADH transplanted subjects in the second and fourth consecutive ejaculation. A similar profile was found for the pStat3 pathway which additionally showed a significant increase in the third and fourth ejaculation of daily-injected subjects. The Mapk signaling pathway did not show any modifications in subjects with daily administration of PRL, but showed a significant increase in the second and third ejaculations of subjects with ADH transplants. Thus, although sexual behavior was not modified, HyperPRL modified the expression of PRL receptors and the activation of signal pathways in the prostate tissue. Hence, it is probable that prostatic alterations precede the sexual behavioral deficits observed in subjects with HyperPRL.

Androgen receptors in Purkinje neurons are modulated by systemic testosterone and sexual training in a region-specific manner in the male rat.

The androgen receptor (AR) is a widely distributed molecule indicating the spread actions of its ligand steroid, and plays an important role underlying male sexual behavior. Nevertheless, the influence of steroid hormones and their receptors on cerebellar neurons, as foundation of sexual behavior, is largely unknown. We sought to determine the influence of peripheral hormones on the AR expression in Purkinje neurons across cerebellar lobules in the vermis of male rats. First, we found a basal AR expression in Purkinje neurons that was higher in the superficial region than the deep region only in cerebellar lobules 2, 4, 5, 7, 8 and 9. Moreover, only the cerebellar lobule 10 showed a significant difference between the coordinates 0.1, 0.3 and 0.9. Second, males with four sessions of sexual training showed a decreased AR density in cerebellar lobules 7, 8, 9 and 10, but not in lobules 2, 4 or 5 when compared to males with one session of sexual training. However, sexual training did not affect AR expression in Purkinje neurons according to their location in any of the cerebellar lobules studied. Third, castration decreased the AR density in the cerebellar lobules 1, 2, 5 and 9 in the superficial region, while in the deep region all cerebellar lobules, except lobule 6, showed a lower AR density after castration. Finally, testosterone replacement restored AR density to control levels in all cerebellar lobules in the superficial region that were affected by castration. Contrary, in the deep region hormonal replacement failed to restore the AR density to control level in the majority of the cerebellar lobules that were affected by castration. Altogether, our findings indicate that Purkinje neurons in the vermis are influenced by systemic testosterone in a region-dependent manner highlighting a link between the cerebellum and gonads in the male rat. The AR function in Purkinje neurons may be related to cerebellar plasticity since both estrogen and progesterone receptors, members of the nuclear receptor family, regulate plasticity processes in Purkinje neurons. We concluded the cerebellum is an important component of the neural circuit for male sexual behavior.

Thermophilic anaerobic co-digestion of organic fraction of municipal solid waste (OFMSW) with food waste (FW): Enhancement of bio-hydrogen production.

Bio-hydrogen production from dry thermophilic anaerobic co-digestion (55°C and 20% total solids) of organic fraction of municipal solid waste (OFMSW) and food waste (FW) was studied. OFMSW coming from mechanical-biological treatment plants (MBT plants) presents a low organic matter concentration. However, FW has a high organic matter content but several problems by accumulation of volatile fatty acids (VFAs) and system acidification. Tests were conducted using a mixture ratio of 80:20 (OFSMW:FW), to avoid the aforementioned problems. Different solid retention times (SRTs) - 6.6, 4.4, 2.4 and 1.9 days - were tested. It was noted that addition of food waste enhances the hydrogen production in all the SRTs tested. Best results were obtained at 1.9-day SRT. It was observed an increase from 0.64 to 2.51 L H2/L(reactor) day in hydrogen productivity when SRTs decrease from 6.6 to 1.9 days. However, the hydrogen yield increases slightly from 33.7 to 38 mL H2/gVS(added).

Neurobiology of social attachments.

Many types of social attachments can be observed in nature. We discuss the neurobiology of two types (1) intraspecific (with a partner) and (2) parental (with the offspring). Stimuli related to copulation facilitate the first, whereas pregnancy, parturition and lactation facilitate the second. Both types develop as consequence of cohabitation. These events seem to stimulate similar neural pathways that increase (1) social recognition, (2) motivation, reward; and (3) decrease fear/anxiety. Subregions of the amygdala and cortex facilitate social recognition and also disinhibition to decrease rejection responses. The interrelationship between MeA, BNST, LS may mediate the activation of NAcc via the mPOA to increase motivation and reward. Cortical areas such as the ACC discriminate between stimuli. The interaction between OT and D2-type receptors in NAcc shell facilitates intraspecific attachment, but D1-type appears to facilitate parental attachment. This difference may be important for maternal females to direct their attention, motivation and expression of attachment toward the appropriate target.

Cohabitation between male rats after ejaculation: effects on conditioned partner preference.

Male rats display a conditioned ejaculatory preference for females that bear olfactory cues associated with ejaculation+the postejaculatory interval (PEI), or with the PEI alone. This indicates that exposure to a partner during the PEI is necessary and sufficient 'for the development of conditioned sexual partner preference. In the present study we examined the effect of cohabitation between two males during the PEI on the possible development of same-sex partner preference. Males first copulated with an ovariectomized, E+P primed female to one ejaculation and were immediately removed from the female's chamber and placed in another chamber with a conspecific male scented with almond odor as a conditioned stimulus (CS+). Cohabitation lasted for 1 h and started immediately after ejaculation in the PEI group and 7h later in the control group. Conditioning occurred daily for a total of ten trials with different females, but cohabitation during the PEI occurred always with the same stimulus male partner. On trial 11, males were tested for social partner preference with two stimulus male partners. One was the familiar scented male and the other an unfamiliar unscented male. Results indicated that males did not develop any social or sexual preference for the male associated with the PEI. In fact, rats from the PEI group interacted significantly less with the scented male as compared to the unscented male, and displayed more agonistic behaviors towards the scented male than towards the unscented male. These data show that conditioned same-sex preference does not develop as a result of cohabitation during the PEI. We discuss the implications for conditioned hostility in intrasexual competition.

Levels and predictors of HIV risk behavior among Black men who have sex with men.

Black men who have sex with men (MSM) contract HIV at disproportionately high rates, and National HIV/AIDS Strategy goals to reduce HIV incidence cannot be successful without improved HIV prevention among racial minority MSM. A total of 210 Black MSM from three cities (Cleveland, Miami, and Milwaukee) completed measures assessing their sexual behavior and demographic characteristics, as well as AIDS-specific psychosocial scales, broader contextual domains, and substance use. Nearly 50% of men reported recent unprotected anal intercourse (UAI), often with non-main partners, with partners not known to be HIV seroconcordant, or with multiple partners. Thirty-seven percent of men reported being HIV positive. In multiple regression analyses, higher levels of unprotected behavior were predicted by weaker perceived peer norms for condom use, weaker risk reduction behavioral intentions, being HIV negative, and recent use of marijuana, cocaine/crack, and poppers. Greater number of UAI partners was associated with weaker perceived peer condom use norms, lower risk reduction intentions, illicit use of prescribed opiates, and fewer AIDS conspiracy beliefs. These findings suggest important factors that should be targeted in HIV prevention programs for Black MSM.

Testing comprehensive models of disclosure of sexual orientation in HIV-positive Latino men who have sex with men (MSM).

Individuals who disclose their sexual orientation are more likely to also disclose their HIV status. Disclosure of HIV-serostatus is associated with better health outcomes. The goal of this study was to build and test comprehensive models of sexual orientation that included eight theory-informed predictors of disclosure to mothers, fathers, and closest friends in a sample of HIV-positive Latino gay and bisexual men. US acculturation, gender nonconformity to hegemonic masculinity in self-presentation, comfort with sexual orientation, gay community involvement, satisfaction with social support, sexual orientation and gender of the closest friend emerged as significant predictors of disclosure of sexual orientation.

Enhaced D2-type receptor activity facilitates the development of conditioned same-sex partner preference in male rats.

Animal models have shown that the neural bases of social attachment, sexual preference and pair bonds, depend on dopamine D2-type receptor and oxytocin activity. In addition, studies have demonstrated that cohabitation can shape partner preference via conditioning. Herein, we used rats to explore the development of learned same-sex partner preferences in adulthood as a result of cohabitation during enhanced D2 activity. Experimental Wistar males (N=20), received saline or the D2 agonist (quinpirole) and were allowed to cohabitate during 24 h, with a stimulus male partner that bore almond scent on the back as conditioned stimulus. This was repeated every 4 days, for a total of three trials. Four days later they were drug-free tested for partner preference between the scented male partner and a sexually receptive female. Sexual partner preference was analyzed by measuring frequency and latency for appetitive and consummatory sexual behaviors, as well as non-contact erections. Social preference was also analyzed by measuring the frequency and latency of visits, body contacts and time spent together. Results indicated that only quinpirole-treated males displayed sexual and social preference for the scented male over the sexually receptive female. They spent more time together, displayed more body contacts, more female-like proceptive behaviors, and more non-contact erections. Accordingly, conditioned males appeared to be more sexually aroused and motivated by the known male than by a receptive female. We discuss the implications of this animal model on the formation of learned homosexual partner preferences.