Gerbil Hypothalamus Research Articles

Laterally asymmetrical cell number in a sexually dimorphic nucleus in the gerbil hypothalamus is correlated with vocal emission rates.

A lateralized relationship between the total volume of a discrete area in a hypothalamic, sexually differentiated nucleus (SDApc) and stereotyped vocalization exists in male Mongolian gerbils. In this present study, using unbiased stereological methods, two cytoarchitectural estimates of the SDApc's structure, neuron number, and nuclear volume were found to be sexually differentiated and also laterally asymmetrical in adult males. In ovariectomized females receiving exogenous testosterone, no cytoarchitectural component was asymmetrical. Significantly, the estimate of neuron number, but not nuclear volume, in the left SDApc of males was correlated with vocal emission rate. The authors conclude that a specific, sex-related cytoarchitectural SDApc parameter shows left-right asymmetry, suggesting the SDApc has an intimate role in mediating hemispheric specialization rather than just being an end point index of individual structural variability.

Laterally asymmetrical cell number in a sexually dimorphic nucleus in the gerbil hypothalamus is correlated with vocal emission rates.

Laterally asymmetrical cell number in a sexually dimorphic nucleus in the gerbil hypothalamus is correlated with vocal emission rates.

Effects of Androgens and Estrogens on Sexual Differentiation of Sex Behavior, Scent Marking, and the Sexually Dimorphic Area of the Gerbil Hypothalamus

Mating, marking and the sexually dimorphic area (SDA) were studied in male gerbils that were castrated or sham-operated on the day of birth and in females given testosterone (T) propionate or oil 1 day later. Other females received dihydrotestosterone (DHT), R1881, estradiol benzoate (EB), R2858, DHT and EB, or DHT and R2858. Females and control males were castrated as adults. Then half of each group was given T and tested for marking and male sex behavior. They were still exposed to T at perfusion. The rest were given EB and progesterone and were tested for marking and lordosis. They were perfused 1 month after hormone treatment ended. Neonatal castration eliminated mounting, decreased T-induced marking and increased lordosis in males. Neonatal exposure to TP decreased lordosis and increased mounting, intromission patterns and T-induced marking in females. DHT and R1881 did not affect marking or mating when given alone. EB and R2858 decreased lordosis and increased mounting. DHT enhanced the former effect but not the latter. Only combined treatments increased T-induced marking. Total SDA volume was not affected by neonatal treatments, but “dark volume” was largest in control males. The SDApars compacta(SDApc) was seldom seen in females unless they received steroid neonatally but was present in males that were castrated neonatally. SDApcs of neonatal castrates and steroid-treated females differed, though, from SDApcs of control males in that they were smaller in the absence of T and did not enlarge when exposed to T. Another cell group, the cmSDApc, was affected by T neonatally but was not seen consistently in either sex. SDApc volume correlated positively with T-induced marking and an index of male sex behavior. Both SDApc and cmSDApc volumes correlated negatively with lordosis. The correlations with marking and male sex behavior probably reflect constraints on sexual differentiation rather than causal relationships since these behaviors persist when the SDApc is gone. The effects of direct manipulations of the SDApc on lordosis have not been studied.

Telencephalic connections of the sexually dimorphic area of the gerbil hypothalamus that influence male sexual behavior.

The sexually dimorphic area (SDA) of the gerbil hypothalamus is essential for mating in male gerbils. To determine if it affects mating through its connections with the ventral part of the lateral septal nucleus (LSv), the caudal part of the medial bed nucleus of the stria terminalis (caudal BSTm), or the medial amygdala-amygdalohippocampal area (MA-AHi), these connections were severed. Unilateral cell-body lesions were made in the SDA and in the contralateral LSv, caudal BSTm, or MA-AHi. Controls received the same lesions ipsilaterally. Other gerbils received lesions in the caudal BSTm and contra- or ipsilateral MA-AHi. Only contralateral lesions of the SDA and caudal BSTm severely impaired mating. Because contralateral lesions of the SDA and MA-AHi, or BSTm and MA-AHi, did not mimic this effect, the BSTm neurons that are needed for male sexual behavior through their connections with the SDA do not simply relay information to or from the MA-AHi.

Hypothalamic knife cuts that disrupt mating in male gerbils sever efferents and forebrain afferents of the sexually dimorphic area.

The sexually dimorphic area (SDA) of the gerbil hypothalamus is essential for male sexual behavior. To determine (a) if the SDA can affect mating via laterally projecting axons and (b) which SDA afferents might affect mating, male gerbils were given bilateral, parasagittal knife cuts lateral to the medial or lateral SDA. Others were given cuts with a knife coated with horseradish peroxidase to label cells of which axons were cut. Medial cuts eliminated mating and consistently labeled cells in the medial SDA. Lateral cuts did neither. Medial cuts also labeled more cells in the ventral part of the lateral septal nucleus, the encapsulated part of the bed nucleus of the stria terminalis, the medial nucleus of the amygdala, the amygdalohippocampal area, and the ventral premammillary nucleus than lateral cuts did. Thus, medial cuts may disrupt mating by severing SDA efferents or by severing SDA afferents from 1 or more of these 5 sites.

Projection of the sexually dimorphic area of the gerbil hypothalamus to the retrorubral field is essential for male sexual behavior: role of A8 and other cells.

To determine if the sexually dimorphic area (SDA) of the gerbil hypothalamus affects male sexual behavior through its projections to the retrorubral field (RRF) or ventrolateral periaqueductal gray (PAGvl), these pathways were lesioned asymmetrically. Unilateral radio frequency lesions of the lateral SDA (ISDA), the major source of the pathways, impaired mating when combined with contralateral RRF, but not PAGvl, lesions. N-methyl-D-aspartate (NMDA) lesions of the medial SDA, ISDA, and the area between them (the total pathway source) eliminated mating when combined with contralateral, but not ipsilateral, NMDA lesions of the RRF. To determine if A8 cells contributed to these effects, males received NMDA in the SDA and NMDA or 6-hydroxydopamine in the contralateral RRF. When combined with large SDA lesions, A8 lesions impaired but did not eliminate mating. Thus the SDA-RRF pathway, but not an SDA-A8 pathway, is essential for sexual behavior in male gerbils.

Sexually dimorphic cell groups in the medial preoptic area that are essential for male sex behavior and the neural pathways needed for their effects

The research summarized here shows that the two major cell groups of the sexually dimorphic area (SDA) of the gerbil hypothalamus are essential for male sex behavior. Bilateral cell-body lesions of either the medial or lateral SDA virtually eliminate mating in sexually experienced male gerbils given exogenous testosterone. Similar deficits occur when the SDA is bilaterally disconnected from the retrorubral field (RRF) as a result of unilateral cell-body lesions in the SDA and contralateral RRF. The A8 cells of the RRF do not account for this effect. Bilaterally disconnecting the SDA from the caudomedial part of the bed nucleus of the stria terminalis (caudal BSTm) also eliminates sexual activity. Disconnecting the SDA from the medial amygdala does not mimic this effect. Neither does disconnecting the medial amygdala from the caudal BSTm. Thus, caudal BSTm neurons that are essential for mating via connections with the SDA do not simply relay information from the medial amygdala.

Projection of the sexually dimorphic area of the gerbil hypothalamus to the retrorubral field is essential for male sexual behavior: Role of A8 and other cells.

Projection of the sexually dimorphic area of the gerbil hypothalamus to the retrorubral field is essential for male sexual behavior: Role of A8 and other cells.

Telencephalic connections of the sexually dimorphic area of the gerbil hypothalamus that influence male sexual behavior.

Telencephalic connections of the sexually dimorphic area of the gerbil hypothalamus that influence male sexual behavior.

The medial and lateral cell groups of the sexually dimorphic area of the gerbil hypothalamus are essential for male sex behavior and act via separate pathways

Male reptiles, birds and mammals do not copulate if the medial preoptic area (MPOA) is destroyed but the MPOA cell groups necessary for male sexual behavior were not known. Here, two cell groups essential for copulation are identified in the sexually dimorphic area (SDA) of the gerbil ( Meriones unguiculatus) MPOA. Bilateral cell-body lesions of either the medial or lateral SDA eliminated mating in sexually experienced male gerbils given testosterone. Nearby MPOA lesions did not. The medial and lateral SDA affect sex behavior via separate pathways since lesioning the medial SDA on one side of the brain and the lateral SDA on the other did not stop sexual behavior.

Ontogeny of the sexually dimorphic area of the gerbil hypothalamus

The sexually dimorphic area (SDA) of the gerbil hypothalamus is a set of cell groups in the medial preoptic area that is essential for masculine sexual behavior and implicated in the hormonal control of scent marking and ultrasound production. The adult SDA shrinks after gonadectomy unless the gerbils receive testosterone. So does the SDA pars compacta, a small cell group in the SDA of males that is seldom seen in females. Here, development of the SDA and SDApc, and of a second, small, compact cell group, the cmSDApc, that lies caudal and medial to the SDApc, is described. Development of the SDApc and cmSDApc was studied quantitatively by assessing their incidence and volume in both sexes from birth (PND 1) to adulthood (PND 150). The volume of the entire SDA was studied from PND 45 to 150. In male gerbils, puberty begins around PND 40 and is complete by PND 90–120. The male SDA enlarged relative to the cross-sectional area of the hypothalamus as puberty began, but the female SDA did not. The SDApc was present in virtually all gerbils at birth and was the same size in both sexes. Over the next two weeks, the SDApcs of females disappeared while those of males persisted and doubled in size. Like the SDApc, the cmSDApc was larger and more common in males than in females, but it became smaller and less prevalent in both sexes during the first two weeks after birth.

γ-Aminobutyric acid, catecholamine and indoleamine determinations from the same brain region by high-performance liquid chromatography with electrochemical detection

A new procedure for the measurement of γ-aminobutyric acid, norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid from the same brain region was developed. In general, two separate high-performance liquid chromatographic runs were performed, one for the γ-aminobutyric acid determination and one for the determination of the monoamines. The electrochemical detection of γ-aminobutyric acid was determined by a new procedure that utilized a small aliquot of the brain sample prepared for monoamine measurement. This assay was linear and parallel between 6 and 200 ng per 20-μl injection with 5-aminovaleric acid utilized as an internal standard. Inter-assay variability averaged 5% throughout the assay with γ-aminobutyric acid values in the gerbil hypothalamus of 344 μg/g. The catecholamine assay has been characterized previously and utilizes 3,4-dihydroxybenzylamine as an internal standard with less than 5% variability. Norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid levels in the gerbil hypothalamus averaged 2922, 729, 797 and 272 ng/g, respectively. This new protocol allows a wide range of neurochemicals to be determined and evaluated from the same brain region.

Atropine infusions near the sexually dimorphic area of the gerbil hypothalamus facilitate hormonal induction of scent marking

The sexually dimorphic area (SDA) of the gerbil hypothalamus contains cells in which acetylcholinesterase activity is stimulated by testosterone. These cells are probably cholinoceptive. Because cholinoceptive cells and the SDA are both implicated in hormonal control of gerbil scent marking, marking was studied in castrated males given a low dose of testosterone systemically, and atropine, a cholinergic antagonist, near the SDA. Controls received saline near the SDA or atropine in the thalamus. Subjects were also tested for male sexual behavior, since it is also affected by the SDA. Infusing 25–35 μg atropine methyl nitrate near the SDA twice a week facilitated marking but did not affect mating. Experimental males marked more, whereas controls marked less, while receiving infusions, than they did before castration. The two control groups did not differ from each other. After infusions stopped, marking by experimental males decreased, though residual effects were detected in one test setting. The data suggest that a cholinoceptive system in or near the SDA participates in hormonal control of gerbil scent marking.

Afferent connections of the sexually dimorphic area of the hypothalamus of male and female gerbils

We studied neural inputs to the sexually dimorphic area (SDA) of the gerbil hypothalamus by injecting wheat-germ agglutinin-horseradish peroxidase into its medial or lateral components in males and females. To confirm the topography of SDA afferents, we injected Phaseolus vulgaris-leucoagglutinin into areas where retrograde labeling from the medial and lateral SDA differed. Both methods indicated that the medial SDA received stronger inputs from the medial part of the bed nucleus of the stria terminalis, the ventral part of the lateral septal nucleus, the medial amygdaloid nucleus, and the amygdalohippocampal area, than the lateral SDA does. In contrast, the rostrodorsal part of the lateral septum, the lateral part of the bed nucleus of the stria terminalis, the anterior and posterior hypothalamic areas, and the dorsomedial hypothalamic nucleus project more heavily to the lateral than to the medial SDA. In addition, retrograde labeling suggested that the ventral part of the premammillary nucleus projects more strongly to the medial than to the lateral SDA, whereas the infralimbic area of the cortex and the lateral preoptic area project more strongly to the lateral than to the medial SDA. The densities of cells in the bed nucleus of the stria terminalis and medial amygdaloid nucleus that could be retrogradely labeled from the medial SDA were greater in males than in females. This was not true of labeling in the arcuate nucleus or in the ventral part of the lateral septal nucleus. Since the medial SDA receives strong inputs from areas with many steroid-accumulating cells, it could respond to steroids directly and via these afferents. In contrast, hormonal effects on the lateral SDA are more likely to occur locally.

Pars compacta of the sexually dimorphic area of the gerbil hypothalamus: postnatal ages at which development responds to testosterone

The sexually dimorphic area (SDA) of the gerbil hypothalamus contains a dense cell group in males, the SDA pars compacta (SDApc), that is absent in females and that develops under the influence of testosterone. To determine how long SDApc development remains sensitive to testosterone and if it can be fully masculinized, female gerbils were injected with testosterone propionate on various days after birth. Control females and males received the vehicle. SDApc development was assessed when subjects were 2 weeks old. Exposing females to testosterone before they were 3 days old increased both the incidence and the size of the SDApc. Delaying exposure until 3 days after birth prevented these effects. In females that received testosterone daily for 5 days, starting on the day they were born, the incidence and size of the SDApc were the same as in males.

Resistance of the gerbil hypothalamus to gold thioglucose lesion formation

Mongolian gerbils do not develop ventromedial hypothalamic (VMH) lesions, as seen in mice, when challenged with gold thioglucose (GTG, 800, 1600 and 3600 mg/kg IP). Insulin administration or bilateral adrenalectomy, procedures which sensitize nonresponsive mice to GTG, have no effect in the gerbil given GTG. These findings suggest that the gerbil VMH differs significantly in structure and/or function compared with the mouse by not possessing glucoreceptive cells sensitive to GTG.

Phlorizin inhibition of hypothalamic necrosis induced by gold thioglucose.

Phlorizin inhibition of hypothalamic necrosis induced by gold thioglucose.

Gold thioglucose damage to the satiety center: inhibition in diabetes.

Gold thioglucose damage to the satiety center: inhibition in diabetes.