Anna W. Lee

Hormone Effects on Specific and Global Brain Functions

The first demonstration of how biochemical changes in neurons in specific parts of the brain direct a complete mammalian behavior derived from the effects of estrogens in hypothalamic neurons that facilitate lordosis behavior, the primary reproductive behavior of female quadrupeds (Pfaff. Estrogens and Brain Function. 1980; Pfaff. Drive: Neurobiological and Molecular Mechanisms of Sexual Motivation. 1999). Sex behaviors depend on sexual arousal that in turn depends on a primitive function: generalized CNS arousal (Pfaff. Brain Arousal and Information Theory. 2006). Here we summarize one of the ways in which a generalized arousal transmitter, norepinephrine, can influence the electrical excitability of ventromedial hypothalamic cells in a way that will foster female sex behavior.

Oxytocin, vasopressin and estrogen receptor gene expression in relation to social recognition in female mice

Inter- and intra-species differences in social behavior and recognition-related hormones and receptors suggest that different distribution and/or expression patterns may relate to social recognition. We used qRT-PCR to investigate naturally occurring differences in expression of estrogen receptor-alpha (ERα), ER-beta (ERβ), progesterone receptor (PR), oxytocin (OT) and receptor, and vasopressin (AVP) and receptors in proestrous female mice. Following four 5 min exposures to the same two conspecifics, one was replaced with a novel mouse in the final trial (T5). Gene expression was examined in mice showing high (85-100%) and low (40-60%) social recognition scores (i.e., preferential novel mouse investigation in T5) in eight socially-relevant brain regions. Results supported OT and AVP involvement in social recognition, and suggest that in the medial preoptic area, increased OT and AVP mRNA, together with ERα and ERβ gene activation, relate to improved social recognition. Initial social investigation correlated with ERs, PR and OTR in the dorsolateral septum, suggesting that these receptors may modulate social interest without affecting social recognition. Finally, increased lateral amygdala gene activation in the LR mice may be associated with general learning impairments, while decreased lateral amygdala activity may indicate more efficient cognitive mechanisms in the HR mice.

Genetic Mechanisms in Neural and Hormonal Controls over Female Reproductive Behaviors

Building on well-established mechanisms that produce the primary female mating behavior, lordosis, research is extending into mechanisms for sexual arousal. Genes and neurochemcal pathways supporting sexual arousal are reviewed, and four neurochemical/biophysical routes by which generalized arousal could influence sexual arousal are charted.

CHAPTER 34 – Hormonal, Neural, and Genomic Mechanisms for Female Reproductive Behaviors, Motivation, and Arousal

This chapter discusses hormonal, neural, and genomic mechanisms for female reproductive behaviors, sexual motivation, and arousal through mammalian researches. The female reproductive behavior depends on estrogen and progestins. The behavioral actions of estrogen affect neurons directly rather than through an obligatory pituitary mechanism because estrogen and progesterone can support female reproductive behavior in hypophysectomized ovariectomized rats. In female monkeys, attractivity and proceptivity clearly change according to the stage of the menstrual cycle or the steroid injected, but there is less agreement among results from different laboratories on the effects of steroid hormones on receptivity. The primary sex behavior of female quadrupeds, lordosis, depends on defined physical signals: cutaneous stimuli and estrogens plus progestins. The neural circuit has been worked out; estrogen-dependent transcription in ventromedial hypothalamic cells allows permissive signals to the midbrain central grey, thus enabling the rest of the circuit. In the absence of fear or anxiety-provoking conditions, females under the influence of estrogens plus progestins demonstrate courtship and then mating behaviors. During the normal female cycle, these behavioral components of reproduction are synchronized with ovulation. Thus, with the mediation of estrogens and progestins, the neural, behavioral, and endocrine preparations for reproduction are harmonized.

Voltage-dependent calcium channels in ventromedial hypothalamic neurones of postnatal rats: modulation by oestradiol and phenylephrine.

Oestradiol actions in the hypothalamus play an important role in reproductive behaviour. Oestradiol treatment in vivo induces α1b‐adrenoceptor mRNA and increases the density of α1B‐adrenoceptor binding in the hypothalamus. Oestradiol is also known to modulate neuronal excitability, in some cases by modulating calcium channels. We assessed the effects of phenylephrine, an α1‐adrenergic agonist, on low‐voltage‐activated (LVA) and high‐voltage‐activated (HVA) calcium channels in ventromedial hypothalamic (VMN) neurones from vehicle‐ and oestradiol‐treated female rats. Whole‐cell and gramicidin perforated‐patch recordings were obtained, with barium as the charge carrier. In the absence of phenylephrine, oestradiol treatment increased the magnitude of LVA currents compared to controls, but had no effect on HVA currents. Phenylephrine enhanced HVA currents in a significantly greater proportion of neurones from oestradiol‐treated rats (76%) than from vehicle‐treated (41%) rats. The L‐channel blocker nifedipine abolished this oestradiol effect on phenylephrine‐enhanced HVA currents. Preincubating slices with the N‐type channel blocker omega‐conotoxin GVIA completely blocked the phenylephrine response, suggesting that the N‐type channel is essential. Phenylephrine also stimulated LVA currents in approximately two‐thirds of neurones in slices from both vehicle‐ and oestradiol‐treated rats. Our data show that oestradiol increases LVA currents in the VMN. Oestradiol also amplifies α1‐adrenergic signalling by increasing the proportion of neurones showing phenylephrine‐stimulated HVA currents mediated by N‐ and L‐type calcium channels. In this way, oestradiol may increase excitatory responses to arousing adrenergic inputs to VMN neurones governing oestradiol‐dependent reproductive behaviour.

Estradiol modulation of phenylephrine-induced excitatory responses in ventromedial hypothalamic neurons of female rats

Estrogens act within the ventromedial nucleus of the hypothalamus (VMN) to facilitate lordosis behavior. Estradiol treatment in vivo induces α1b-adrenoreceptor mRNA and increases the density of α1B-adrenoreceptor binding in the hypothalamus. Activation of hypothalamic α1-adrenoceptors also facilitates estrogen-dependent lordosis. To investigate the cellular mechanisms of adrenergic effects on VMN neurons, whole-cell patch-clamp recordings were carried out on hypothalamic slices from control and estradiol-treated female rats. In control slices, bath application of the α1-agonist phenylephrine (PHE; 10 μM) depolarized 10 of 25 neurons (40%), hyperpolarized three neurons (12%), and had no effect on 12 neurons (48%). The depolarization was associated with decreased membrane conductance, and this current had a reversal potential close to the K+ equilibrium potential. The α1b-receptor antagonist chloroethylclonidine (10 μM) blocked the depolarization produced by PHE in all cells. From estradiol-treated rats, significantly more neurons in slices depolarized (71%) and fewer neurons showed no response (17%) to PHE. PHE-induced depolarizations were significantly attenuated with 4-aminopyridine (5 mM) but unaffected by tetraethylammonium chloride (20 mM) or blockers of Na+ and Ca2+ channels. These data indicate that α1-adrenoceptors depolarize VMN neurons by reducing membrane conductance for K+. Estradiol amplifies α1b-adrenergic signaling by increasing the proportion of VMN neurons that respond to stimulation of α1b-adrenergic receptors, which is expected in turn to promote lordosis.

Functional genomics of sex hormone-dependent neuroendocrine systems: specific and generalized actions in the CNS

Sex hormone effects on hypothalamic neurons have been worked out to a point where receptor mechanisms are relatively well understood, a neural circuit for a sex steroid-dependent behavior has been determined, and several functional genomic regulations have been discovered and conceptualized. With that knowledge in hand, we approach deeper problems of explaining sexual arousal and generalized CNS arousal. After a brief summary of arousal mechanisms, we focus on three chemical systems which signal generalized arousal and impact hormone-dependent hypothalamic neurons of behavioral importance: histamine, norepinephrine and enkephalin.

Presynaptic actions of opioid receptor agonists in ventromedial hypothalamic neurons in estrogen- and oil-treated female mice

Estrogens act upon ventromedial hypothalamic (VMH) neurons, and their effects on female arousal and sexual behaviors mediated by VMH neurons involve several neurotransmitters and neuromodulators. Among these are opioid peptides which might be predicted to oppose estrogenic action on VMH because they tend to decrease CNS arousal. Spontaneous excitatory postsynaptic currents were recorded from VMH neurons from 17beta-estradiol- (E, 10 mug/0.1 ml) or oil-treated control ovariectomized (OVX) mice using whole-cell patch-clamp techniques. To examine the impact of opioidergic inputs, recordings of neurons from both treatment groups were obtained in the presence of the general opioid receptor agonist methionine enkephalin-Arg-Phe (MERF, 3 muM), or mu-receptor specific agonist [d-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO, 1 muM). Compared with oil, E treatment for 48 h significantly increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) without affecting their amplitude. MERF and DAMGO each abolished this E effect, causing significant reductions in sEPSCs. The effect of MERF was abolished by naltrexone (general opioid receptor antagonist, 3 muM) and the effect of DAMGO by d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP) (mu-opioid receptor selective antagonist, 1 muM); in contrast, kappa- and delta-opioid receptor agonists, U69593 (300 nM) and [d-Pen(2),d-Pen(5)]-enkephalin (DPDPE, 1 muM) respectively, had little effect on the sEPSCs compared with DAMGO. To consider presynaptic vs. postsynaptic effects of opioids, miniature excitatory postsynaptic currents (mEPSCs) were investigated in E- and oil-treated VMH neurons and opioid receptor antagonist effects on mEPSCs were observed. Both MERF and DAMGO reduced the frequency of mEPSCs, but had no effect on their amplitude. Our findings indicate that opioids suppress excitatory synaptic transmissions in VMH neurons primarily through mu-receptors and could thereby decrease sexual arousal in mice.