Prenatal exposure of male mice to androgen increases neuron number in the hypogastric ganglion

Sex differences of brain and their implications for personalized therapy

Nowadays, it is known that the sex differences regard many organs, e.g., liver, vessels, pancreas, lungs, bronchi and also the brain. Sex differences are not just a matter of ethical and moral principles, as they are central to explain many still unknown diseases and their understanding is a prerequisite to develop an effective therapy for each individual. This review reports on those sex differences that are not only macroscopic and morphological, but also involve molecular and functional dimorphism in the brain. It will recapitulate the main structural differences between male and female brain including the neurotransmission systems; in particular, the main objective is to identify a correlation, already known or to be investigated in the future, between the differences that characterize male and female brains from a morphological and biochemical point of view and neurological syndromes. This correlation could provide a starting point for future scientific research aimed to investigate and define a personalized therapy.

Translational Perspective on the Role of Testosterone in Sexual Function and Dysfunction

INTRODUCTION

The biological importance of testosterone is generally accepted by the medical community; however, controversy focuses on its relevance to sexual function and the sexual response, and our understanding of the extent of its role in this area is evolving.

AIM

To provide scientific evidence examining the role of testosterone at the cellular and molecular levels as it pertains to normal erectile physiology and the development of erectile dysfunction and to assist in guiding successful therapeutic interventions for androgen-dependent sexual dysfunction.

METHODS

In this White Paper, the Basic Science Committee of the Sexual Medicine Society of North America assessed the current basic science literature examining the role of testosterone in sexual function and dysfunction.

RESULTS

Testosterone plays an important role in sexual function through multiple processes: physiologic (stimulates activity of nitric oxide synthase), developmental (establishes and maintains the structural and functional integrity of the penis), neural (development, maintenance, function, and plasticity of the cavernous nerve and pelvic ganglia), therapeutically for dysfunctional regulation (beneficial effect on aging, diabetes, and prostatectomy), and phosphodiesterase type 5 inhibition (testosterone supplement to counteract phosphodiesterase type 5 inhibitor resistance).

CONCLUSION

Despite controversies concerning testosterone with regard to sexual function, basic science studies provide incontrovertible evidence for a significant role of testosterone in sexual function and suggest that properly administered testosterone therapy is potentially advantageous for treating male sexual dysfunction.

Sex Differences in Brain and Behavior: Hormones Versus Genes

Sex determination is the commitment of an organism toward male or female development. Traditionally, in mammals, sex determination is considered equivalent to gonadal determination. Since the presence or the absence of the testes ultimately determines the phenotype of the external genitalia, sex determination is typically seen as equivalent to testis determination. But what exactly does sex determine? The endpoint of sex determination is almost invariably seen as the reproductive structures, which represent the most obvious phenotypic difference between the sexes. One could argue that the most striking differences between males and females are not the anatomy of the genitals, but the size of the gametes-considerably larger in females than males. In fact, there could be many different endpoints to sex determination, leading to differences between the sexes: brain sexual differences, behavioral differences, and susceptibility to disease. The central dogma of sexual differentiation, stemming initially from the gonad-transfer experiments of Alfred Jost, is that sexual dimorphisms of all somatic tissues are dependent on the testicular secretion of the developing fetus. In this chapter, we will take the example of sex differences in brain and behavior as an endpoint of sex determination. We will argue that genetic factors play a role in sexually dimorphic traits such as the number of dopaminergic cells in the mesencephalon, aggression, and sexual orientation, independently from gonadal hormones.

Plasticity of pelvic autonomic ganglia and urogenital innervation

Pelvic ganglia contain a mixture of sympathetic and parasympathetic neurons and provide most of the motor innervation of the urogenital organs. They show a remarkable sensitivity to androgens and estrogens, which impacts on their development into sexually dimorphic structures and provide an array of mechanisms by which plasticity of these neurons can occur during puberty and adulthood. The structure of pelvic ganglia varies widely among species, ranging from rodents, which have a pair of large ganglia, to humans, in whom pelvic ganglion neurons are distributed in a large, complex plexus. This plexus is frequently injured during pelvic surgical procedures, yet strategies for its repair have yet to be developed. Advances in this area will come from a better understanding of the effects of injury on the cellular signaling process in pelvic neurons and also the role of neurotrophic factors during development, maintenance, and repair of these axons.

Unusual autonomic ganglia: connections, chemistry, and plasticity of pelvic ganglia

The pelvic ganglia provide the majority of the autonomic nerve supply to reproductive organs, urinary bladder, and lower bowel. Of all autonomic ganglia, they are probably the least understood because in many species their anatomy is particularly complex. Furthermore, they are unusual autonomic ganglia in many ways, including their connections, structure, chemistry, and hormone sensitivity. This review will compare and contrast the normal structure and function of pelvic ganglia with other types of autonomic ganglia (sympathetic, parasympathetic, and enteric). Two aspects of plasticity in the pelvic pathways will also be discussed. First, the influence of gonadal steroids on the maturation and maintenance of pelvic reflex circuits will be considered. Second, the consequences of nerve injury will be discussed, particularly in the context of the pelvic ganglia receiving distributed spinal inputs. The review demonstrates that in many ways the pelvic ganglia differ substantially from other autonomic ganglia. Pelvic ganglia may also provide a useful system in which to study many fundamental neurobiological questions of broader relevance.

Neuroendocrine asymmetry

The information available at present clearly indicates that asymmetry exists from the level of elementary particles to the human cerebral cortex, the latest stage of evolution. Cerebral lateralization is one of the well-known asymmetries. This paper summarizes the data published in the past decades on the asymmetry of the neuroendocrine system. The information on the sided-differences between the gonads, adrenals, and thyroid lobes and that on the lateralization of hypothalamic, limbic, and other brain structures participating in the control of the endocrine glands as well as relevant clinical observations are reviewed here. The innervation of the peripheral endocrine glands is also briefly summarized because the afferent and efferent fibers of these glands may represent one part of the pathway involved in neuroendocrine asymmetry. The data reviewed clearly indicate that some kind of asymmetry (morphological, biochemical, physiological, pathological) is evident at different levels of the neuroendocrine system (at limbic, hypothalamic, peripheral endocrine glands and their innervation) and there are species, sex, and age differences. Most of the information accumulated deals with the CNS-gonadal system. A majority of the observations suggest that in both male and female rats there is a predominance of the right half of brain structures controlling gonadal function. The asymmetry, however, is not restricted to CNS structures: it also exists at the level of the gonads, including their innervation. It appears that the characteristic pattern of the CNS-gonadal system becomes fixed only after sexual maturation. Very few reports are available suggesting some kind of asymmetry of the CNS-adrenal cortex and the CNS-thyroid system. There are convincing findings consistent with the view that in addition to the hypothalamo-adenohypophyseal system acting via the general circulation on the peripheral endocrine glands, there is also a pure neural link between the CNS and the gonads, the CNS and the adrenal gland, and also between the CNS and the thyroid. This link contains afferent and efferent pathways and is able to modulate the functional activity or the responsiveness of the gland. It may also serve as a neural reflex arc. It is assumed that the neuroendocrine asymmetry expresses itself through (i) hypophysiotrophic neurohormones and hormones of the peripheral endocrine glands, (ii) neural pathways, or (iii) a combination of (i) and (ii). The authors hope that this publication, in addition to providing an overview, will also stimulate research, both basic and clinical, in this exciting area of neuroendocrinology.

NADPH-diaphorase-positive ganglion cells of the rat adrenal gland: age- and sex-related changes in their number, size, and distribution

The rat adrenal gland contains ganglion cells able to synthesize nitric oxide (NO). This messenger molecule controls and modulates adrenal secretory activity and blood flow. The present study analyzed the number, size, and distribution of NO-producing adrenal neurons in adulthood and during postnatal development by means of beta-nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. This method reliably visualizes the enzyme responsible for NO generation. The reactive neurons per adrenal gland were 350-400 in both male and female adult rats. The positive nerve cell bodies were mostly located in the medulla, few being detected within the cortex and the subcapsular region. Dual labeling with anti-microtubule-associated protein 2 antibody, specific for neuronal elements, confirmed this distribution. Anti-microtubule-associated protein 1b antibody identified a subset of NADPH-d-positive neurons, displaying different degrees of maturation according to their position within the adrenal gland. At birth, there were about 220 NADPH-d-labeled neurons per adrenal gland in both sexes. As confirmed by dual immunocytochemical labeling, their great majority was evenly distributed between the cortex and the subcapsular region, the medulla being practically devoid of stained neurons. After birth, the number of adrenal NADPH-d-positive ganglion cells displayed a strong postnatal increase and reached the adult-like distribution after 1-2 months. During the period of increase, there was a transient difference in the numbers of these cells in the two sexes. Thus we present here evidence of plasticity in the number, size, and distribution of NADPH-d-positive adrenal neurons between birth and adulthood; in addition, we describe transient sex-related differences in their number and distribution during the 2nd postnatal week, which are possibly related to the epigenetic action of gonadal hormones during this period.

Transient expression of estrogen-receptor-like immunoreactivity (ER-LI) in the facial nucleus of the neonatal rat

Estrogen receptor-like immunoreactivity (ER-LI) was detected in the medial subnucleus of the facial nucleus by immunocytochemistry in both male and female neonatal rats, but not in the adult rat. Identity of the motoneurons in this subnucleus projecting to the corresponding facial muscles and the cells with ER-LI positive signals was examined by retrograde tracing. The majority of the cells marked with the tracer did not carry ER-LI signals.

Laterality associated with sexual dimorphism in the volume of the mouse hypogastric ganglion

The volume of the hypogastric ganglion was investigated in male, female, and prenatally androgen-exposed female newborn mice. Two milligram testosterone propionate was injected into pregnant ICR mice from days 14 to 16 of gestation. The volume of the ganglia on both sides in intact male neonates was significantly larger than that in female neonates. The volume of ganglia in testosterone-exposed females was significantly larger than those in intact females, but did not attain the male volume. In intact males, the ganglion on the left side was significantly larger than on the right. This left-right difference in the volume of the ganglia was not recognized in the intact or TP-exposed females. These results suggest that sex difference and lateralization of the volume of the hypogastric ganglion were highly dependent on the prenatal sex hormone environment.