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Biomedical subjects

C A Dudley

Publications and source records attributed to C A Dudley.

At least 37 records · Page 2Linked to original sources
PubMed1988

Immunocytochemical localization of hypothalamic luteinizing hormone-releasing hormone in male ferrets.

LHRH-containing neurons within the hypothalamus were immunocytochemically identified in adult male ferrets that were either gonadally intact, castrated, or castrated and treated with testosterone. The distribution of LHRH-immunopositive neuron cell bodies was similar in the three treatment groups. The majority of these cells was located mediobasally in the retrochiasmatic area, including some within the ventrolateral aspects of the arcuate nucleus. These soma were associated with a dense basal LHRH fiber plexus which extended to the median eminence. A smaller number of cell bodies was found slightly more dorsal and lateral to the major concentration at the base and midline. Isolated LHRH perikarya were occasionally observed in dorsal areas of the hypothalamus. There were no differences in the mean total number of hypothalamic LHRH cell bodies identified in the three treatment groups. These results indicate that the documented negative feedback effects of testosterone on LH secretion in male ferrets are not the result of an alteration in the absolute number of neurons capable of synthesizing LHRH.

Animals↗
PubMed1987

Effects of a behaviorally active LHRH fragment and septal area stimulation on the activity of mediobasal hypothalamic neurons.

The effect of Ac-LHRH, an LHRH fragment capable of facilitating lordosis, and LHRH on the firing rate of mediobasal hypothalamic neurons receiving input from the septal area, (a site containing the majority of LHRH perikarya) was studied via conventional extracellular recording techniques. A multibarrelled glass electrode assembly was lowered through the dorsomedial and ventromedial hypothalamus to detect single units responsive to septal area stimulation, and to iontophoretically apply Ac-LHRH and LHRH. Ovariectomized rats were primed with estradiol benzoate (EB; n = 21) or left untreated (n = 34) to determine if the neuronal responsiveness to septal area stimulation and/or to the two peptides was subject to estrogenic modulation. Of the total number of 228 neurons recorded in the study, 51 units (22.4%) were orthodromically responsive to septal area stimulation. The orthodromic responses in EB-primed animals (n = 20) were characterized by a short-latency, short-duration increase in membrane excitability. When spontaneous activity was sufficiently high, the excitatory response was followed by, or superimposed upon, an inhibitory response of longer duration. Similar orthodromic excitatory and inhibitory response characteristics were observed in 21 of the 31 neurons recorded in nonprimed animals. In the remaining ten neurons, however, the excitatory component was absent. Iontophoretic application of both Ac-LHRH and LHRH was found to produce predominantly an inhibitory effect on cell firing. Most neurons responded to the two peptides in a similar manner (i.e., inhibited by both peptides, excited by both peptides, or not effected by either peptide).(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

A1 noradrenergic input to medial preoptic-medial septal area: an electrophysiological study.

The effects of electrical stimulation of the A1 noradrenergic cell group on the extracellular activity of medial preoptic-medial septal (MPO-S) neurons were studied in ovariectomized (OVX) female rats under different hormonal conditions [estrogen and progesterone (E-P)-primed or unprimed] via conventional electrophysiological techniques. In addition, MPO-S neurons responding to the A1 noradrenergic cell group stimulation were characterized by examining their connections with the arcuate nucleus/median eminence (ARC/ME). With respect to stimulation of the A1 noradrenergic cell group, a large proportion of MPO-S neurons exhibited one of the following three types of orthodromic responses: orthodromic excitation (OD+), orthodromic inhibition (OD-), or complex orthodromic response (OD comp). The predominant type of response was OD+. Although E-P-priming did not change the relative proportion of neurons displaying a specific type of orthodromic response, it did increase the overall percentage of MPO-S neurons orthodromically responding to A1 stimulation (39% of MPO-S neurons responded to A1 stimulation in the E-P-primed group whereas only 25% of the neurons did so in the unprimed group). Neurons responsive to A1 stimulation were more likely to respond orthodromically to ARC/ME stimulation than were those neurons which were unresponsive to A1 stimulation. About one fifth of MPO-S neurons identified as projecting to the ARC/ME [putative luteinizing hormone-releasing hormone (LHRH) neurons] orthodromically responded to A1 stimulation. The predominant type of response was OD+. The present study indicates that A1 noradrenergic input to MPO-S neurons is predominantly excitatory.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Estrogen priming affects the sensitivity of midbrain central gray neurons to microiontophoretically applied LHRH but not beta-endorphin.

In vivo single-unit extracellular recording was used to assess neuronal membrane sensitivity at the level of the midbrain central gray (MCG) to the iontophoresis of luteinizing hormone releasing hormone (LHRH) and beta-endorphin (beta-END). The percentage of change in firing rate was evaluated to determine the effect of exogenously administered estradiol benzoate (EB) and EB plus progesterone (EB + P) on the membrane sensitivity of these MCG neurons to LHRH and beta-END. Ovariectomized adult female rats were primed with EB or EB + P, or nonprimed, 24-48 h prior to recording. EB priming significantly altered the membrane sensitivity of neurons in the MCG to LHRH by increasing the number of cells excited compared to the EB + P group and the nonprimed controls (p less than 0.005). The addition of P appeared to negate this effect. Hormonal priming did not alter the response profile for beta-END iontophoresis. The results suggest an estrogen-dependent sensitivity to LHRH at the MCG which translates into an increased electrical output, ultimately facilitating lordosis behavior. P treatment dampens this excitation. beta-END's effect on neuronal membrane excitability at the MCG was not distinctly characterized under the hormonal conditions our study evaluated and may reflect a regulatory role under physiological extremes.

Action Potentials↗
PubMed1986

Effect of beta-endorphin on sociosexual proclivity in a choice paradigm.

Intraventricularly-administered beta-endorphin (beta-END) suppresses receptive and proceptive behaviors of the ovariectomized, estrogen-progesterone-primed rat. This rat model was used in a four-way choice paradigm to investigate the behavioral specificity and motivational aspects of sexual suppression by beta-END. The experimental females showed a preference to associate with a sexually active 'stud' male over the other incentive animals as shown by significantly more approaches to and nose pokes into the stud male compartment. beta-END did not alter that choice preference. Rather, there was a decrease in overall social interaction after beta-END treatment, as shown by decreased total nose pokes. This overall decrease in social motivation, which was blocked by subcutaneous naloxone injection, was not specific to the stud male. It was not a result of akinesia, since total movement among the inner alleys was significantly higher after beta-END treatment, an effect also reversed by naloxone. These data suggest that intraventricular beta-END may act to suppress sociosexual motivation as a whole rather than sexual activity specifically.

Animals↗
PubMed1986

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.

Action Potentials↗
PubMed1985

Hyperprolactinemia: its electrophysiologic and pharmacologic effect on neurons of the ventromedial nucleus of the hypothalamus.

Extracellular action potentials were recorded from 691 neurons in the ventromedial hypothalamus (VMH) of urethane anesthetized female rats under acute and chronic sham-operated and hyperprolactinemic conditions. Hyperprolactinemia was produced by transplanting pituitaries under the kidney capsules. Neuronal excitability was recorded and analyzed during spontaneous, baseline activity and following the iontophoretic application of prolactin, dopamine (DA) and luteinizing hormone-releasing hormone (LH-RH). No statistically significant changes were observed in the spontaneous electrical activity of VMH neurons under the conditions tested. Of the responsive neurons, approximately 90% of the neurons recorded and tested with prolactin displayed an increase in firing activity while DA produced a decrease, independent of the endogenous plasma prolactin levels (basal or elevated). However, the response to LH-RH was modified in the chronic hyperprolactinemic animal. The predominant response of VMH neurons to LH-RH in acute sham-operated and hyperprolactinemic as well as in chronic sham-operated animals was one of inhibition, while in the chronic hyperprolactinemic animal, the application of LH-RH initiated excitation rather than inhibition. These results provide evidence that chronic (long-term) exposure to elevated prolactin levels is a sufficient stimulus to modify the neuronal response pattern of VMH nerve cells to iontophoretically applied LH-RH but not to prolactin nor to DA.

Action Potentials↗
PubMed1985

LHRH and mating behavior: sexual receptivity versus sexual preference.

Sexual behavior and sexual preference measurements were obtained from ovariectomized female rats treated with estrogen, estrogen and progesterone, or estrogen followed by third ventricular infusion of luteinizing hormone releasing hormone (LHRH) or saline. The lordosis-to-mount ratio and the occurrence of receptive and proceptive behaviors were scored to assess total sexual receptivity. Sexual preference was determined by placing the test female in the center of a four-winged choice box apparatus in which each of the outer wings contained one of the following incentive animals: a sexually active male (SM), a castrate male (CM), a female in proestrus (PF), and an ovariectomized female (OF). Time spent in close proximity to the incentive animals was measured as an index of sexual preference. Estrogen and progesterone treatment resulted in high sexual receptivity and a marked preference for SM. Estrogen alone or in combination with saline also produced a significant preference for SM. Animals treated with estrogen and LHRH exhibited high levels of sexual receptivity compared to estrogen saline treated controls, but no enhancement of preference for SM was detected. The results indicate that fractionation of sexual receptivity and sexual motivation occurs following estrogen-LHRH treatment.

Animals↗
PubMed1985

Hormonal modulation of the responsiveness of midbrain central gray neurons to LH-RH.

The spontaneous firing rate of midbrain central gray (MCG) neurons and the effect of iontophoretically applied prolactin and luteinizing hormone releasing hormone (LH-RH) on the electrical activity of these neurons was studied in untreated and estrogen-progesterone-treated ovariectomized female rats. The spontaneous firing rate of MCG neurons as well as the neuronal membrane responsiveness to iontophoretically applied prolactin was unaffected by the presence or absence of ovarian hormones. In both treated and untreated rats, the majority of neurons were not responsive to prolactin. On the other hand, the responsiveness of MCG neurons to iontophoretically applied LH-RH was influenced by hormonal treatment. A significantly larger number of MCG neurons were inhibited by LH-RH in hormone-treated animals than in untreated rats. The present work provides evidence at the electrophysiological level that ovarian hormones do not affect the firing rate of MCG neurons but do modulate the responsiveness of MCG neurons to LH-RH.

Action Potentials↗
PubMed1984

Dopaminergic neurons in the mediobasal hypothalamus of old rats: evidence for decreased affinity of tyrosine hydroxylase for substrate and cofactor.

The effect of aging on the activity of tyrosine hydroxylase (TH) and on the number of TH-positive perikarya in the hypothalamus was studied in old and young female rats. The activity of TH in the mediobasal hypothalamus (MBH) of old rats was significantly (P less than 0.025) less than that in young rats. In old rats, the Km of TH for tyrosine as well as cofactor, 6-methyl-5,6,7,8-tetrahydropterine (6MPH4), was markedly greater than the Km in young rats. The maximal velocity was only slightly reduced in old animals. Contiguous coronal sections of the brain of an old and a young female rat were immunocytochemically stained for TH, and the TH-positive perikarya in the hypothalamus were counted. In the circumventricular region, 6793 TH-positive perikarya were present in the young brain and 6632 in the old brain. In the arcuate region, 2868 and 2760 TH-positive perikarya were counted in the young and old brain, respectively. It is concluded that the reduced TH activity in the MBH of old rats is not a consequence of a reduction in the number of TH-positive perikarya in the arcuate or circumventricular regions of the hypothalamus but is due to a reduction in the affinity of TH for its substrate and cofactor.

Age Factors↗
PubMed1984

Hormonal and chemical modulation of ventromedial hypothalamic neurons responsive to vaginocervical stimulation.

Neurons of the ventromedial hypothalamus (VMH) in female rats were electrophysiologically recorded via multibarrelled glass micropipettes and tested for responsiveness to vaginocervical stimulation as well as to a variety of other peripheral stimuli. A small percentage of VMH neurons were found to be specifically responsive to vaginocervical stimulation (type I response) in the ovariectomized animal. Priming the rats with estrogen (E) and progesterone (P) significantly increased the percentage of neurons responding specifically to vaginocervical stimulation but had no effect on the percentage of nonspecifically responding (type II) and nonresponding (type III) neurons. Pharmacological testing of all three types of VMH neurons was accomplished by iontophoretic application of luteinizing hormone releasing hormone (LHRH), prolactin (PRL), and dopamine (DA) to the cell membrane. PRL excited the majority of neurons tested and DA inhibited the majority of tested units regardless of the hormonal condition of the animal or the response elicited by vaginocervical and peripheral stimulation, LHRH, however, produced changes in firing rate which were related to the type of response evoked by vaginocervical stimulation. In E-P-primed animals, neurons which were specifically or nonspecifically affected by vaginocervical stimulation responded to LHRH in a similar manner whereas a different LHRH response profile was obtained in those neurons which were not effected by vaginocervical stimulation. The results indicate that an afferent pathway from the vaginocervix to the VMH exists, that E-P priming in some manner increases the probability that a VMH neuron will respond specifically to vaginocervical probing, and that the effect of LHRH is different in neurons responding to vaginocervical stimulation than in nonresponding neurons.

Animals↗
PubMed1983

Construction of a simple spike counter for analysis of electrophysiological recording data.

A method for constructing a simple spike counter from a conventional calculator by taking advantage of the "adding display to memory" function [(M+) key] is described. The modification involves connecting the (M+) key to a dissecting pin and to a metallic notebook binder which is taped on to a transparent plastic sheet. The plastic sheet can then be placed on top of a polygraph record. After entering "1" into the calculator, a spike can be counted by making a single contact between the pin and the metal fastener. The total number of spikes counted can be displayed on the calculator by pressing the key for memory recall. The spike counter described herein is suitable for counting extracellular action potentials recorded on chart paper as well as other biological signals such as the rate of contraction of muscle.

Animals↗
PubMed1983

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.

Animals↗
PubMed1983

Facilitation of sexual receptivity in the female rat by a fragment of the LHRH decapeptide, Ac-LHRH.

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.

Animals↗
PubMed1982

Inhibition of lordosis behavior in the female rat by intraventricular infusion of prolactin and by chronic hyperprolactinemia.

The role of prolactin (PRL) in the control of the lordosis reflex of female rats was investigated. In the initial series of experiments, the normal high level of sexual receptivity observed in the ovariectomized, estrogen-progesterone (E-P) primed female rat was suppressed by intraventricular infusion of 100 ng PRL. Mating behavior remained suppressed 2, 3, and 5 hours following a single infusion of PRL into the third ventricle. In contrast, infusions of either an equal volume of the solvent vehicle (saline) or 100 ng of adrenocorticotropic hormone (ACTH) were ineffective in modulating the level of mating behavior in hormone-primed female rats. In a second series of experiments, chronic hyperprolactinemia was induced by pituitary transplants under the renal capsule in intact, normal cycle diestrus rats (N=12). A significant decrement in E-P induced mating behavior was observed at 12 and 14 weeks posttransplantation but not at 4 weeks. Sham-operated animals (N=12) displayed the characteristic pattern of behavior normally observed under exogenous E-P therapy. In summary, transient exposure as well as chronic exposure to high levels of PRL can suppress mating behavior, thus suggesting a possible role for PRL in the mediation of reproductive behavior in the female rat.

Adrenocorticotropic Hormone↗
PubMed1981

The effect of LHRH antagonist analogs and an antibody to LHRH on mating behavior in female rats.

The action of two antagonist analogs and an antibody to luteinizing hormone-releasing hormone (LHRH) on sexual receptivity was studied in avariectomized, estrogen-progesterone primed female rats. Small amounts of each LHRH substance or saline was infused through a cannula positioned in either the third ventricle or arcuate-ventromedial (ARC-VMH) area of the hypothalamus. Infusions were carried out at the time of progesterone priming, which was 42 hrs post-estrogen treatment, and sexual receptivity, as denoted by the lordosis-to-mount ratio, was measured six hrs later. One antagonist analog, [D-pGlu1, D-Phe2, D-Trp3,6]-LHRH[1], had little or no effect on sexual receptivity when tested in either site. Similarly, an antibody to LHRH, tested only in the ARC-VMH, had no observable effect on lordotic behavior. However, the second and the most potent antagonist analog, [Ac-dehydro-Pro1, pCl-D-Phe2, D-Trp3,6]-LHRH[2], produced a marked and significant decrement in lordotic behavior when infused into either the third ventricle or ARC-VMH. These results suggest that this potent and long-acting, competitive antagonist analog of LHRH prevented endogenous LHRH from exerting its normal role in the induction of sexual receptivity and provide evidence to support the contention that the role of LHRH in mediating receptivity in the female rat is physiologically relevant.

Animals↗