Carol A. Dudley

The effects of microelectrophoretically applied estrogen, cortisol and acetylcholine on medial preoptic-septal unit activity throughout the estrous cycle of the female rat.

SummaryThe technique of microelectrophoresis was utilized to study the effects of 17β-estradiol hemisuccinate (17βE2S), cortisol hemisuccinate (CS), and acetylcholine (Ach) on medial preoptic-septal (mPOA-S) neurons throughout the estrous cycle in urethane anesthetized rats. A total of 23 cells were identified antidromically as having their projections to the arcuate-median eminence region of the hypothalamus, and 18 of these were tested with 17βE2S. Only four cells showed an inhibition to the gonadal steroid, while the remaining neurons did not respond. Twelve antidromically identified (AI) neurons were tested with CS, none of which responded, and 2 out of 16 AI neurons showed an excitation to Ach. Extracellular potentials were recorded from 273 non-antidromically identified neurons, 138 of which were successfully tested with 17βE2S. Sixty-two of these responded to the steroid. The predominant response on late diestrus I was excitation, and the majority of estrogen-sensitive cells showed an inhibitory response on late diestrus 2, proestrus and estrus. A Chi-square analysis showed that the response varied significantly throughout the estrous cycle.Cortisol hemisuccinate was tested on 154 non-antidromically identified mPOA-S neurons. The response to the corticosteroid also varied significantly throughout the cycle, but further analysis determined that the response was different from that of 17βE2S. Acetylcholine was also applied to 180 mPOA-S neurons, but no significant change in the response was found from one day of the cycle to the next.It is apparent from these studies that (1) 17βE2S can bring about direct and rapid changes in the firing frequency of neurons, (2) the non-antidromically identified neuron is a site for these effects, and (3) the response differs significantly throughout the estrous cycle.

The specificity of the response of preoptic-septal area neurons to estrogen: 17α-estradiol versus 17β-estradiol and the response of extrahypothalamic neurons

SummaryThe purpose of this study was to determine the specificity of the response of medial preoptic-septal neurons (mPOA-S) to microelectrophoresed 17β-estradiol hemisuccinate (17βE2S). In vitro studies were conducted initially to determine the release of the labeled 17βE2S from multibarrel glass micropipettes. Subsequently, an isomer of 17βE2S, 17α-estradiol hemisuccinate (17αE2S), was synthesized and purified. Thirty-six mPOA-S neurons from normal cycling female rats were tested with both 17βE2S and 17αE2S. Twelve of these units responded with inhibition to 17βE2S, while none responded to 17αE2S. Furthermore, fifty extrahypothalamic (cortical, hippocampal, thalamic) neurons were tested with 17βE2S. The majority (N = 45) showed no response, three showed excitation and two inhibition to the microelectrophoresed steroid ester. These findings suggest that a specific receptor mechanism is responsible for the changes in mPOA-S unit activity, and that these effects may be important in the regulation of reproductive events.

Intra- and Extrahypothalamic Luteinizing Hormone-Releasing Hormone (LHRH) Distribution in the Rat with Special Reference to Mesencephalic Sites Which Contain Both LHRH and Single Neurons Responsive to LHRH

In addition to hypothalamic sites known to contain LHRH, several extrahypothalamic structures in both male and female rats were discovered to contain the decapeptide. In the mesencephalon, the fasciculus retroflexus, interpeduncular nucleus and midbrain central grey contained readily detectable quantities of LHRH. Single neurons responsive to microiontophoretically applied LHRH were also discovered in the mesencephalon suggesting a physiological role for the decapeptide in neuronal events at the level of the midbrain.

Releasing Hormones and Sexual Behavior

Publisher Summary This chapter focuses on the role and sexual behavior of releasing hormones. The role of luteinizing hormone-releasing hormone (LHRH) in activating mating behavior was examined in estrone (E)-primed ovariectomized (OVX) and normal proestrous female rats (4-day cycles) as well as in testosterone proprionate (TP)-primed castrated and intact male rats. Research on the subject of releasing factors has focused principally on the elucidation of (1) their chemical structure, (2) the neural and pharmacological determinants of their “release mechanism”, and (3) their involvement in the secretion of anterior pituitary hormones. Hypothalamic control over anterior pituitary function is thought to be mediated by the action of hypophyseotropic hormones—for example, the releasing and inhibiting factors. At first glance, the possibility of an interaction between LHRH and sexual receptivity appears quite unlikely. In most species that show spontaneous ovulatory cycles, the period of behavioral estrus coincides with the ovulatory period; that is, a period of sexual receptivity ensues shortly following the time of preovulatory luteinizing hormone (LH) release.

Direct, Neuronal Action of Atrial Natriuretic Factor in the Rat Brain

The present investigation assessed the ability of atrial natriuretic factor (ANF) to affect hypothalamic neuronal excitability. Single neurons in the rostral septal-preoptic area of the female rat brain were recorded extracellularly and tested for responsiveness to iontophoretically applied and/or pressure-ejected ANF. Neurons responsive to ANF were detected in the lateral septal nucleus, the lateral paraolfactory area, the bed nucleus of the anterior commissure, and the medial preoptic area. The majority of neurons influenced by ANF (16 out of 18) exhibited a decrease in spontaneous firing rate during application of the peptide. In some cases, the inhibitory response outlasted the period of ANF application. When both iontophoretic and pressure ejection techniques were used to apply ANF to an individual neuron, the responses were similar. The results indicate that ANF is capable of modulating the membrane excitability of rat forebrain neurons and suggest that the peptide acts as a neuromodulator/neurotransmitter within the central nervous system.

Facilitation of lordosis in female rats by CNS-site specific infusions of an LH-RH fragment, Ac-LH-RH-(5–10)

Structural alterations of the luteinizing hormone-releasing hormone (LH-RH) molecule have been performed to yield analogs which are more potent than, or which compete with, the parent hormone to increase the release of LH from the pituitary gland. The effects of these analogs on mating behavior, however, do not always parallel their effects on LH release. The present study tested the effectiveness of a pituitary-inactive fragment of LH-RH, namely Ac-LH-RH-(5-10), in potentiating mating behavior in the ovariectomized, estrogen-primed female rat. This fragment, when infused bilaterally into the medial preoptic area (POA), the ventromedial hypothalamus (VMH), or the midbrain central gray (MCG), significantly enhanced lordosis. Infusion of the fragment into the cerebral cortex was ineffective. Elevated lordotic responding was first apparent in the POA at 15 min postinfusion and was maintained for the duration of the testing session (180 min). Ac-LH-RH-(5-10) infused into the VMH or MCG enhanced lordotic behavior at 90 and 180 min postinfusion. The results indicate that only a portion of the LH-RH molecule may be required for behavioral activity and suggest that degradation of the LH-RH molecule is physiologically relevant.

Action of Prolactin, Dopamine and LHRH on Ventromedial Hypothalamic Neurons as a Function of Ovarian Hormones

The effect of iontophoretically-applied prolactin, dopamine, LHRH and LHRH-antagonist analog on the electrical activity of neurons (n = 192) located in the ventromedial nucleus of the hypothalamus (VMH) was studied in untreated and hormone-treated ovariectomized female rats (n = 63). The spontaneous electrical activity of VMH neurons was unaffected by the presence or absence of the ovarian hormones. Neuropharmacological studies indicate that the iontophoretic deposition of prolactin and dopamine produced opposing results, in that prolactin increased the electrical activity of the majority of the VMH neurons tested while dopamine decreased their activity. Finally, the application of LHRH and LHRH-antagonist analog to VMH neurons resulted in a marked suppression of their electrical activity that was even more pronounced in the presence of ovarian hormones. The present work provides evidence at the electrophysiological level of hormonal influences on the responsiveness of VMH neurons to LHRH and its antagonist analog, and demonstrates a relationship between the responsiveness of VMH neurons to prolactin and dopamine.

Facilitation of Sexual Receptivity in the Female Rat by a Fragment of the LHRH Decapeptide, Ac-LHRH5-10

The following fragments of LHRH were administered intraventricularly and tested for their ability to enhance sexual receptivity in ovariectomized, estrogen-primed female rats: LHRH1-6 NH2, Ac-LHRH5-10, des-Tyr5-LHRH and des-Gly10-LHRH. LHRH1-6 NH2 had no effect on sexual behavior compared to saline-infused controls. Ac-LHRH5-10, des-Tyr5 LHRH and des-Gly10-LHRH significantly elevated lordotic responding compared to saline-infused controls. The results suggest that the elements contained in the LHRH structure may be functionally differentiated and indicate that the active sequence for facilitation of mating behavior is contained in the last half of the LHRH molecule.

Hypothalamic polypeptide releasing hormones: modifiers of neuronal activity.

Abstract The deposition of synthetic luteinizing hormone-releasing hormone (LRH), LRH inactive analogue, LRH agonist analogue and thyrotropin releasing-hormone (TRH) in small quantities in the immediate vicinity of neurons, via the technique of microelectrophoresis, has demonstrated the action of these peptides on the electrical activity of neurons throughout the brain. In each area of the central nervous system studied, from the cerebral cortex to the basal hypothalamus, neurons responded to the microelectrophoretic application of these peptides with excitation, or inhibition or failed to respond. The direction of the neuronal response to synthetic LRH and LRH agonist analogue was similar. In some cases, the analogue initiated a greater and longer-lasting effect. In neurons which were excited by LRH, TRH caused either a marked inhibition or no response. In general, the response of sensitive neurons to microelectrophoresis of peptides was produced with successive drug applications, yet there was no effect during application of current control. It is suggested that the presence of peptide-sensitive neurons in the central nervous system raises the possibility of a novel mechanism for chemical information transfer mediating anterior pituitary secretion and endocrine-related behaviour.

Changes in responsiveness of medial preoptic neurons to the microelectrophoresis of releasing hormones as a function of ovarian hormones.

Abstract d -Ala6, des-Gly10-LRH ethylamide were generously provided by Drs. M. Gotz and R. Deghenghi of Ayerst Research Laboratories, Montreal, Canada.Thyrotropin-releasing hormone was supplied by Drs. J. Dorn and J. Weinstein and Mr. C. Flanagan of Abbott Laboratories, North Chicago, Illinois, and Drs. Vale and Rivier of the Salk Institute at San Diego supplied the LRH analog peptides (1) d -Trp6, Pro9NHEt-LRH, agonist analog (LRH+), (2) d -Phe2, d -Trp2, d Trp6-LRH, antagonist analog (LRH-) and (3) des-Pro10-LRH inactive analog (LRH0).