Bengt J. Meyerson

Latency between intravenous injection of progestins and the appearance of estrous behavior in estrogen-treated ovariectomized rats

Abstract The latency of the lordosis response after different progestins and progesterone metabolites given by the intravenous route was studied in spayed rats pretreated with estradiol benzoate (10 μg/kg sc). Progestins with anesthetic capacity (progesterone, medroxyprogesterone) had a longer latency at high doses than at low. It is suggested that the true latency for these progestins is masked by the anesthetic property even at dose levels which did not give an overt sedative effect. In analogous experiments with isopregnenone, which lacks an anesthetic effect, a median latency of 10–30 min was obtained regardless of doses given (0.5, 5.0 mg). The isopregnenone data suggest that a certain time is required between the treatment and the appearance of lordotic behavior which is longer than could be expected to be due only to transport from the circulation to the brain tissue.

Growth hormone replacement in hypophysectomized rats affects spatial performance and hippocampal levels of NMDA receptor subunit and PSD-95 gene transcript levels

Clinical studies have demonstrated that growth hormone (GH) promotes learning and memory processes in GH-deficient (GHD) patients. In animal studies, GH also influences the N-methyl-D-aspartate (NMDA) receptor system in the hippocampus, an essential component of long-term potentiation (LTP), which is highly involved in memory acquisition. This study was designed to examine the beneficial effects of recombinant human GH (rhGH) on cognitive function in male rats with multiple hormone deficiencies resulting from hypophysectomy (Hx). The performance of an rhGH-treated group and an untreated control group was appraised in the Morris water maze (MWM). The rhGH-treated group performed significantly better in the spatial memory task than the control animals on the second and third trial days. Further training eliminated this difference between the groups. Hippocampal mRNA expression of the NMDA subunits NR1, NR2A and NR2B, insulin-like growth factor type 1 receptor (IGF-1R), and postsynaptic density protein-95 (PSD-95) was then measured in the animals by Northern blot analysis. The results suggest that there may be a relationship between the NMDA receptor subunit mRNA expression levels and learning ability, and that learning is improved by rhGH in Hx rats. Furthermore, a link between MWM performance and PSD-95 was also suggested by this study.

Estrus behaviour in spayed rats after estrogen or progesterone treatment in combination with reserpine or tetrabenazine

SummaryEstrus behaviour in ovariectomised rats is normally activated by progesterone after pretreatment with estrogen. It has now been found that progesterone but not estrogen can be replaced by the amine depletors reserpine and tetrabenazine.The effect of reserpine lasted several weeks.ACTH can only partly replace progesterone and the reserpine effect is obtained even after adrenalectomy. This indicates that reserpine does not act by inducing steroid release from the adrenals.The results give further evidence of monoamine dependent central nervous pathways mediating heat inhibition.

Comparison of the effects of β-endorphin and morphine on exploratory and socio-sexual behaviour in the male rat

The socio-sexual and exploratory behaviour profiles were studied in male rats after intracerebral administration of beta-endorphin and morphine. Two social test situations were used, one with a sexually receptive female and one with a castrated male as the stimulus subject. Time (10-60 min)-response and dose (0.25-5.0 millimicron)-response relationships were investigated. A dose of 5 millimicron of beta-endorphin or morphine decreased exploratory activity and socio-sexual approaches. At lower doses (0.5-1.0 millimicron) beta-endorphin produced a more selective inhibitory effect on copulatory behaviour than morphine, which still caused a general depression of both social and sexual behaviours. In contrast to morphine, beta-endorphin increased amicable social contacts at a dose (1 millimicron) which decrease sexual responses. The dissimilarities in morphine and beta-endorphin effects suggest involvement of different brain areas or opiate receptors. The particular behaviour profiles observed after treatment with beta-endorphin indicate the possibility that beta-endorphin influences mechanisms implicated in perception or interpretation of environmental stimuli.

The effect of oestradiol, testosterone and dihydrotestosterone on sexual motivation in the ovariectomized female rat☆

Abstract In two separate tests for the measurement of sexual motivation, the open field and the increasing barrier method, both oestradiol benzoate (10 μg/kg) and testosterone propionate (1 mg/kg) significantly increased the willingness of ovariectomized female rats to seek contact with sexually active males. In contrast, no effect was seen after dihydrotestosterone (1 mg/kg). The oestrogen antagonist MER-25 (150 mg/kg) prevented the increase in the number of grid crossings in response to oestradiol and delayed the response to testosterone. The data are discussed in relation to the role of androgens in controlling sexual motivation.

The Concentric Square Field: a multivariate test arena for analysis of explorative strategies.

In this study, we describe the behavior of laboratory rats in a recently developed observation arena, the Concentric Square Field (CSF). The CSF contains a number of areas designed to provoke exploration and behaviors associated with risk assessment, risk taking and security seeking in an environment not previously experienced. The model includes sheltered, open and elevated areas, a hole board device, areas with different light conditions, and wall-enclosed corridors. The rationale behind the CSF is to meet the demand for multivariate test situations that are not predictive in the sense of previous definition of a specific purpose of measuring a certain mental state. We define multivariate as being a free choice of where to stay in areas of different qualities. In the present study, identification of risky as opposed to safe areas is based on the retrieval behavior in lactating females and hoarding of food pellets in food-deprived males. Furthermore, we describe the effects of pre-trial food deprivation, immobilization, social stress, strain differences (Sprague-Dawley, Wistar and Lister Hooded males), sex differences (Sprague-Dawley) and repeated testing. Besides the conventional statistics, a principal component analysis (PCA) helped to discriminate between the various categories tested. Our conclusion is that the multivariate and non-predictive test situation (CSF) and the use of PCA provide a good tool for ethoexperimental analysis.

Sexual preference in female rats during estrous cycle, pregnancy and lactation

Choice of a male or female social contact was studied in intact female rats in a runway-choice apparatus during estrous cycle, pregnancy, and lactation. The male was chosen significantly more often during proestrus/estrus than during the diestrous days of the cycle. During pregnancy this preference in choice declined only to reappear gradually during the lactation period. The shifts in the level of motivation to seek out the male support previous studies and point to the significance of estrogen in producing the preference for the male.

Neuropharmacology, Neurotransmitters, and Sexual Behavior in Mammals

In this chapter, we discuss the possible relationship between certain neurotransmitters, sexual behavior, and its controlling hormones. The knowledge in this field has accumulated through experiments that have utilized chemical substances that influence transmission processes in the central nervous system. To understand how drugs can be used to investigate different elements of sexual behavior, together with the possibilities and limitations of such an approach, we first survey some basic knowledge and concepts in neuropharmacology in general and behavioral pharmacology in particular. We follow this survey with a review of the experimental data within this area as they relate to the neuroendocrine basis of sexual behavior.

The Behavior of Spontaneously Hypertensive and Wistar Kyoto Rats Under a Paced Fixed Consecutive Number Schedule of Reinforcement

Spontaneously hypertensive (SHR) and Wistar Kyoto rats (WKY) were trained under paced FCN schedules of reinforcement to complete a minimum number of consecutive responses on one lever, before responding on a second. The levers were retracted from the test chamber for a short period after each response to control the speed at which the rats could complete the sequence (paced FCN). Changes in the average chain length may reflect the influence of impulsivity on the execution of behavioral patterns. Although they quickly learned to press the levers, SHR rats performed poorly compared to the WKY rats when the chain length requirement was increased to FCN 6 and FCN 8. Eventually stable performance was obtained under paced FCN 6, although the SHR rats continued to have a consistently lower average chain length. Both strains of rats were treated with imipramine (10 mg/kg), chlordiazepoxide (3 and 10 mg/kg), d-amphetamine (0.4 and 0.8 mg/kg), haloperidol (0.05 and 0.1 mg/kg), 8-OH-DPAT (0.1 mg/kg), WAY-100635 (0.1 mg/kg), and DOI (0.3 and 1.0 mg/kg). The SHR rats were less sensitive to the effects of d-amphetamine, chlordiazepoxide, and DOI and slightly more sensitive to the effects of haloperidol. All of these drugs reduced the average chain length. There was no difference in the response of the two strains to imipramine and 8-OH-DPAT, both of which increased the average chain length. These results support the suggestion that SHR rats may more impulsive than WKY rats. The data with d-amphetamine and haloperidol support biochemical findings that these rats have a deficit in dopaminergic function, and the strain differences in response to chlordiazepoxide and DOI suggest that that there may be differences in GABAergic and 5-HT2-mediated neurotransmission relevant to regulating impulse control in the rat.

Comparison of the action of lysergic acid diethylamide and apomorphine on the copulatory response in the female rat.

The effects of lysergic acid diethylamide (LSD) and apomorphine were compared using female copulatory behavior (lordosis response), in ovariectomized estrogen + progesterone-treated rats. Both serotonin and dopamine are implicated in the inhibition of this behavior. Each compound inhibited lordosis behavior dose dependently and with a similar time-course. Pimozide (0.1; 0.5 mg/kg) blocked the apomorphine (0.2 mg/kg)-induced decrease of lordosis response, while only a certain abbreviation of the LSD (0.10 mg/kg) inhibition was achieved by pimozide (0.5 mg/kg). Chlorpromazine (0.5 mg/kg) in a dose without effects on lordosis of its own had an action similar to pimozide on the LSD effect.It is concluded that the predominant action of LSD on the female coupulatory response is not mediated by increased dopamine receptor activity but that the LSD effect might be modulated by decreased dopaminergic activity.