Biomedical subjects

H F Carrer

Publications and source records attributed to H F Carrer.

At least 19 recordsLinked to original sources

PubMed2001

Nongenomic mechanism mediates estradiol stimulation of axon growth in male rat hypothalamic neurons in vitro.

The purpose of the present work was to investigate the participation of estradiol receptors (ER) in estrogen-induced axon growth in vitro. Hypothalamic neurons from 16 day (E16) male rat fetuses were cultured with or without 17-beta-estradiol at 1 x 10(-7) M in basal medium or medium conditioned by astroglia derived from ventral mesencephalon (CM). After 48 hr in vitro, neurite outgrowth was quantified by morphometric analysis. An axogenic effect could be demonstrated for estradiol added to CM. With RT-PCR, the mRNA transcript for ERalpha was found in the donor tissues as well as in the neuron cultures. In this model two specific nuclear ER blockers (tamoxifen and ICI 182,780) were ineffective in blocking the neuritogenic effect, and a membrane-impermeable estrogen-albumin construct (E2-BSA) was as effective as estradiol. These results indicate that the axogenic effect of estradiol at E16 is not exerted through the classical intracellular receptor signal transduction system and suggest the possibility of a membrane-mediated mechanism. The data are discussed in light of our previous findings pointing to the interdependent activation of the estrogenic and the trophic factor signaling pathways that mediate stimulated axon growth.

Animals↗

PubMed2000

Differential effect of oestradiol and astroglia-conditioned media on the growth of hypothalamic neurons from male and female rat brains.

To determine whether soluble products from different CNS regions differ in their ability to support oestrogen-stimulated neurite growth, hypothalamic neurons from sexually segregated embryos were cultured with astroglia-conditioned medium (CM) derived from cortex, striatum and mesencephalon, with or without 17-beta-oestradiol 100 nM added to the medium. After 48 h in vitro, neurite outgrowth was quantified by morphometric analysis. Astroglia-CM from mesencephalon (a target for the axons of hypothalamic neurons) induced the greatest axogenic response in males and in this case only a neuritogenic effect could be demonstrated for oestradiol. On the other hand, astroglia-CM from regions that do not receive projections from ventromedial hypothalamus inhibited axon growth. A sexual difference in the response of hypothalamic neurons to astroglia-CM and oestradiol was found; growth of neurons from female foetuses was increased by astroglia-CM from mesencephalon, but no neuritogenic effect could be demonstrated for oestradiol in these cultures. Blot immunobinding demonstrated the presence of receptors for neurotrophic factors in cultures of hypothalamic neurons; Western blot analysis of these cultures demonstrated that oestradiol increased the concentration of trkB and IGF-I Rbeta, whereas trkA was not detected and the concentration of trkC was not modified. These results support the hypothesis that target regions produce some factor(s) that stimulate the growth of axons from projecting neurons and further indicate that in the case of males this effect is modulated by oestradiol, perhaps mediated through the upregulation of trkB and IGF-I receptors.

Animals↗

PubMed1999

Peripeduncular lesion alters expression of c-fos induced in the female rat brain by male mounting.

In order to investigate the role of the peripeduncular nucleus (PP) in the control of lordosis in female rats, activation of neurons after mounts without intromission was investigated by means of FOS immunoreactivity (FOS-IR). Ovariectomized rats were injected with estradiol and progesterone and submitted to approximately 50 mounts by the male. The vaginal area was covered with masking tape to prevent intromission and vaginocervical stimulation. This limited stimulation produced FOS-IR in the ventrolateral division of the ventromedial hypothalamic nucleus (VMHVL), in the lateral periaqueductal grey (LPAG), in the peripeduncular nucleus (PP), and in the posterior intralaminar thalamic nucleus (PIL). No significant differences were found in the anterodorsal or posterodorsal parts of the medial amygdaloid nucleus, in the medial part of the medial preoptic nucleus, in the dorsomedial periaqueductal grey and in the medial division of the posterointermediate part of the bed nucleus of the stria terminalis. The same experiment was performed in rats with unilateral lesion of the PP. Both VMHVL and LPAG activation were significantly reduced in the ipsilateral PP lesion side, leading to the conclusion that those structures are primary targets for the somatic stimuli that trigger lordotic reflexes and which are relayed in the PP. Taking into account what is known about the function of the target structures, it is proposed that afferences relayed in the PP reaching the VMHVL would contribute to control the long range level of sexual receptivity, whereas stimuli reaching the LPAG would serve to control lordotic responses in a moment to moment fashion.

Animals↗

PubMed1997

Estrogen facilitates induction of long term potentiation in the hippocampus of awake rats.

In order to test the hypothesis that circulating levels of estrogen modulate synaptic plasticity in the hippocampus, we have studied the induction of long term potentiation (LTP) in awake rats. Ovariectomized animals, chronically implanted with a recording electrode in the cell body layer of CA1 and a stimulating electrode in stratum radiatum, were used to record evoked field potentials (population spike (PS) and summed EPSP) daily for at least 4 days before injection of sesame oil or 100 microg of estradiol benzoate per kg b.w. (E2). Basal levels of response to single square pulses (0.01 ms pulse width) delivered at 0.05 Hz through the stimulating electrode were recorded daily for 2 days after injection. To induce LTP a high-frequency 'theta pattern' stimulation was administered. Basal recordings at low-frequency stimulation did not change after injection. After high-frequency stimulation all (7/7) E2 injected animals showed LTP whereas only 1/6 oil injected controls did so; the mean increase in amplitude of the PS and slope of the EPSP after high-frequency stimulation were significantly greater in E2 treated rats. Input/output curves did not change significantly after E2 administration. These results show that at low-frequency stimulation, transynaptic responses of pyramidal neurones in CA1 are not affected by changes in levels of circulating estrogen, while synaptic plasticity -- which is at the basis of proposed hebbian associative memory -- is facilitated by estrogen treatment.

Animals↗

PubMed1995

Neuritogenic effect of estradiol on rat ventromedial hypothalamic neurons co-cultured with homotopic or heterotopic glia.

In sexually segregated cultures of dissociated neurons taken from ventromedial hypothalamus of rat fetuses at embryonic day 16 (E16), it is demonstrated that only neurons from males respond with increased axonal growth to the addition of 17-beta-estradiol 100 nM (E2) to the culture medium. Moreover, this response is contingent upon co-culture with heterotopic glia from a target region (amygdala), whereas in the presence of homotopic glia or in cultures without glia, E2 has no effect. It is concluded that before neurons are exposed to gonadal steroids in utero there is a sexual difference in the response to E2, probably explained by earlier maturation of neurons from males as compared to females. The possibility that the observed axogenic effect may be the consequence of an interaction among E2, cells equipped with specific receptors, and glia-producing trophic factors is discussed.

Animals↗

PubMed1992

The learning capacity of high or low performance rats is related to the hippocampus NMDA receptors.

The hippocampal synaptic plasticity of rats with an inborn high (HP) or low (LP) learning capacity to perform in a shuttle box is closely related to their percentage of conditioned responses (Crs). HP rats show less sensitivity to the blocking effect of 2-aminophosphonopentanoic acid (AP5) on the generation of long-term potentiation (LTP) than do LP rats. Results described in the present report are indicative of an increased density of N-methyl-D-aspartate (NMDA) receptors in HP rats compared to control and LP rats. We postulate that the differential pharmacological sensitivity of LTP in these rats is a reflection of this biochemical difference. Also, from these results we suggest that the learning capacity may be related to the density of glutamate NMDA receptors of HP, LP and control rats.

2-Amino-5-phosphonovalerate↗

PubMed1992

Time lapse study of neurite growth in hypothalamic dissociated neurons in culture: sex differences and estrogen effects.

Cultures of dissociated hypothalamic cells taken from rat fetuses of 19 days of gestation were studied using time-lapse recording and sequential microphotography from 1 to 5 days in vitro (DIV) and at 7 and 21 DIV. Cultures were seeded with cells taken from fetuses grouped by sex or sexually mixed; experimental cultures were raised in medium containing 17-beta-estradiol 100 nM (E2). Cells were plated on poly-D-lysine-coated coverslips at a culture density of approximately 4,000 cells/cm2. Immunocytochemistry of cell cultures was performed using a Tau monoclonal antibody (clone Tau-1 PC1C6) and a monoclonal antibody against MAP-2 (clone AP-20). Cells started to produce lamellipodia and neuritic processes approximately 4 hr after plating. Forty-eight hours later a few neurons had defined their morphological polarity by the differentiation of an axon-like process that grows faster than the others; at 5 DIV almost all neurons had defined their axons. At this time, monoclonal antibody against MAP-2 clearly stained soma and dendrites, but not axons. Tau immunoreactivity (lots CCA101 and CCA101N from Boeringher Mannheim) was differentially distributed, with a clear predominance in axon and soma. Results on the morphometric analysis of control and E2 treated neurons provide direct evidence for the existence of sex related differences in the neurite outgrowth response of hypothalamic neurons, since cultured neurons taken from female fetuses differentiated axons later and had fewer primary neurites and shorter dendrites than neurons taken from male fetuses or sexually mixed cultures. Also, it was demonstrated in living neurons that E2 effectively enhances outgrowth and elongation in axons. The frequency distribution curves of axonal length for control and E2 treated cultures was unimodal, suggesting that the effect of E2 was a uniform increase in the axonal length of all neurons. The structural differences between neurons from both sexes and the changes induced by E2 may contribute to explain the differences in brain function found between the sexes.

Animals↗

PubMed1991

Differences in hippocampal synaptic plasticity in rats with inborn high or low learning ability may be related to different sensitivity of aspartate receptors.

Rats with an inborn high (HP) or low (LP) learning capacity were used to study the sensitivity to the blocking effect of 2-amino-phosphonopentanoic acid (AP5; 10 and 20 microM) on long-term potentiation (LTP) produced in hippocampal slices by a 1-s tetanus at 200 Hz. The potential evoked by stimulation of the perforant path was recorded from the granule cell layer of the dentate gyrus in 400 microns slices perfused with standard Krebs' solution or the AP5. Under perfusion with 10 microM of AP5, in 100% of slices from HP rats, LTP generation was not blocked; when AP5 20 microM was used, in 85% of the cases LTP was not blocked. In 60% of slices from LP rats, AP5 10 microM and in 100% of the cases at 20 microM AP5 blocked LTP generation. These results are coherent with the hypothesis that the different inborn learning ability of HP and LP rats is related to the different population or sensitivity of N-methyl-D-aspartate (NMDA) receptors.

2-Amino-5-phosphonovalerate↗

PubMed1990

Rat organum vasculosum laminae terminalis in vitro: responses to changes in sodium concentration.

Extracellular action potentials were recorded from the organum vasculosum laminae terminalis (OVLT) in rat brain slice preparations; the effect of different concentrations of NaCl on spontaneous firing frequency was studied. From 72 neurons, 67 (93%) were responsive to various perfusion media, while 5 neurons (7%) were not responsive. The change from the standard medium (SM; 124 mM NaCl) to 99 mM, decreased the firing frequency in 24 (65%) and increased it in 13 (35%) out of 37 responsive cells. The change from the SM to 149 mM evoked an increase in the firing rate in 33 (73%) and a decrease in 12 (27%) of 45 responsive neurons; the change to 174 mM, increased the firing rate in 5 (100%) neurons tested. The excitatory effect of increasing [NaCl] in the perfusion medium persisted even in low Ca2+ and high Mg2+ medium. Mannitol (55 mM) added to the SM increased the firing rate of cells; no significant decrease in the firing rate was seen with sodium mannitol 99/55 mM. Ouabain (OUA) (0.1 x 10(-3) mM) added to the SM increased the firing rate in 16 (84%) and decreased it in 3 (16%) out of 19 cells. Diphenylhydantoin (DPH) (1 mM) added to the SM decreased the firing rate in 12 (67%) and increased it in 6 (33%) of 18 cells tested. Hypo- or hypertonic NaCl solutions had no consistent effect on the spontaneous activity of 14 pyramidal cells recorded from the hippocampus (area CA3). The results emphasize the importance of intracellular Na content as a physiological trigger regulating the activity in neurons of the OVLT.

Action Potentials↗

PubMed1990

Gangliosides improve synaptic transmission in dentate gyrus of hippocampal rat slices.

The effect of perfusion with gangliosides (1 x 10(-6) M) on the response evoked in the granule cell layer of dentate gyrus by stimulation of perforant path in hippocampal rat slices was studied. Gangliosides induced both a decrease in the frequency threshold of stimulation necessary to generate long-term potentiation (LTP) and greater potentiation than under control conditions. It is proposed that gangliosides improve the mechanisms responsible for synaptic plasticity which generate LTP.

Action Potentials↗

PubMed1990

Differentiation of rat hippocampal neurons induced by estrogen in vitro: effects on neuritogenesis and Na, K-ATPase activity.

To gain insight into the mechanisms responsible for differentiation of hippocampal neurons growing in vitro, the effects of estrogen on neuritic development and on activity and distribution of isoforms of the Na, K-ATPase, were evaluated. Dissociated cells from hippocampi of 19-day-old rat fetuses were raised for 5 days in the presence or absence of 100 nM estradiol-17 beta (E2) in minimum essential medium supplemented either with 10% untreated fetal calf serum (MEM-10) or with 10% fetal calf serum previously adsorbed with dextran-activated charcoal (MEM-10-Cha). Cultures in MEM-10 showed larger neuritic length and increased levels of Na, K-ATPase activity than cultures in MEM-10-Cha. In cells cultured in MEM-10 medium, the addition of E2 resulted in selective enhancement of axonal length with a concomitant increase in the alpha-2 isoform of the Na, K-ATPase, whereas a decrease was found in the form most sensitive to ouabain; the total enzymatic activity remained unchanged. Conversely, in cultures raised in MEM-10-Cha, E2 did not affect Na, K-ATPase activity or neuritogenesis. These results show that two presumably independent probes of cellular differentiation of hippocampal neurons (i.e., neuritogenesis and patterns of Na, K-ATPase activity) were concurrently regulated by E2 and that such regulation depended on interaction with factor(s) present in calf serum. The well-known neuritogenic effect of E2 is hereby extended to hippocampal neurons, although for these cells it seems to be restricted to axons.

Animals↗

PubMed1990

Participation of the olfactory system in the control of approach behavior of the female rat to the male.

The amounts of time spent by females in the sector of an open field close to the cage housing a normal male or a castrated male were measured in order to quantitate the tendency of the female to reach physical proximity to a sexually active male (androtropism). Intact proestrous or ovariectomized females primed with 100 micrograms of estradiol benzoate/kg b. wt. (EB) or EB plus 2 mg progesterone/kg b. wt. (P) spent significantly more time close to the sexually active (intact) male than in the proximity of the orchidectomized male. In order to determine whether olfactory clues were sufficient for female rats to distinguish between intact and castrated males, the males were removed from the stimulus cages, leaving the soiled bedding in place. Ovariectomized rats primed with EB or EB plus P clearly preferred proximity to the cage where the intact male had been living. No preference was evident after transection of olfactory nerves in proestrous rats or in ovariectomized rats primed with EB plus P. Resection of the vomeronasal organ also suppressed preference. These results indicate that olfactory input is necessary and sufficient for androtropism to occur, and suggest that the accessory olfactory system is involved in the analysis of olfactory signals used by female rats to identify the endocrine status of prospective sexual partners. In a different group of animals, it was demonstrated that destruction of the posteromedial cortical amygdaloid nucleus also suppressed preference for the intact male. It is proposed that this structure serves as a relay station for the analysis and integration of olfactory input significant for the motivational control of sexual behavior in the female rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Amygdala↗

PubMed1989

Correlation between threshold to induce long-term potentiation in the hippocampus and performance in a shuttle box avoidance response in rats.

The relationship between the learning ability of normal rats and the facility to induce long-term potentiation (LTP) in the same animals was investigated. Behavioral performance was measured in a shuttle box avoidance paradigm, using a buzzer as conditioned stimulus. Three days later animals were sacrificed; frequency threshold necessary to induce LTP was determined in transverse hippocampal slices taken from these animals and maintained in vitro. A linear regression analysis on the behavioral and electrophysiological data showed a negative correlation (Spearman rank correlation coefficient rs = -0.705; P less than 0.001) between percent of conditioned responses in the shuttle box and threshold frequency necessary to induce LTP in gyrus dentatus in response to tetanic stimulation of the perforant path. It is concluded that learning ability of normal rats in a shuttle box avoidance paradigm is correlated with hippocampal synaptic plasticity.

Animals↗

PubMed1989

Sexual receptivity after destruction of serotonergic terminals in hypothalamus or amygdala.

In order to localize the sites in the brain where serotonergic (5-HT) input may affect the performance of lordotic responses, the serotonin neurotoxin 5-7-dihydroxytryptamine was injected in the ventromedial hypothalamic nucleus (VMN) or in the medial amygdala (AM) in ovariectomized rats. Estrogen induced receptivity as measured by the lordotic quotient was significantly greater in animals injected in AM, but it was smaller in animals injected in the VMN, as compared to controls or animals injected with the vehicle. No differences were found when the same animals were injected with progesterone. It is proposed that serotonergic afferents exert facilitatory influences in the hypothalamus and inhibitory influences in the amygdala, as concerns estrogen-induced sexual receptivity. The integrity of 5-HT terminals in VMN and AM is not necessary for progesterone to exert its potentiating effects.

Amygdala↗

PubMed1988

Differential threshold for long-term potentiation in the hippocampus of rats with inborn high or low learning capacity.

Threshold of stimulation frequency in the perforant path to induce long-term potentiation (LTP) in dentate gyrus was determined in hippocampal slices obtained from two different lines of rats inbred for 30 generations according to their performance in an avoidance escape test in a shuttle box. High-performance (HP) rats were defined as those giving at least 70% conditioned responses (CRs) and low-performance (LP) rats as those giving less than 15% CRs. LTP was defined as a 30% or more increase in the amplitude of the evoked population spike (PS), lasting at least 20 min. Stimulation frequency threshold was determined by stimulating with a train of pulses of 0.5 ms duration during 1 s. The same slice was stimulated with trains of increasing frequency from 5 to 400 Hz, each train separated by an interval of at least 20 min. HP rats showed a lower threshold (13 +/- 4 Hz) than LP rats (92 +/- 42 Hz) for the induction of LTP; there were no differences in the magnitude of LTP. The greater learning ability of HP rats may be related to the plasticity of hippocampal synaptic transmission.

Action Potentials↗

PubMed1988

Verapamil injections in the peripeduncular nucleus suppress multiunit evoked activity and sexual receptivity in female rats.

Using a combination of injection cannula and recording electrode, the effect of 1 microliter of 3 mM verapamil upon the multiunit responses evoked in the peripeduncular nucleus (PPN) by electric stimuli applied to the pudendal nerves in urethane anesthetized proestrous female rats was studied in 9 experiments. It was observed that in 6 cases responses were suppressed after the injection and in 2 other cases there was a marked decrease, whereas no change was observed in 1 case. Similar injections of vehicle (saline) produced no change (7 rats) or small and short lasting depression of evoked activity (4 rats). Similar injections of verapamil applied to a region of the mesencephalic reticular formation caudal to the PPN, presumably containing fibers that carry evoked activity towards the PPN, had no effect on evoked multiunit activity in the PPN. Injection of 2% Xylocaine in the same site in the same animal eliminated the evoked responses. These experiments support our hypothesis that verapamil suppressed evoked responses in the PPN blocking Ca++-dependent release of neurotransmitter at local synapsis, without interfering with fiber conduction of neural activity. Based on this assumption we used identical injections to test the hypothesis that activation of neurons in the PPN is necessary for the performance of lordotic behavior in ovariectomized rats primed with estradiol benzoate. Guide cannulae aimed at the PPN were implanted in castrated females which were then primed with enough estradiol benzoate to induce sexual receptivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Gamma aminobutyric acid mediates ventromedial hypothalamic mechanisms controlling the execution of lordotic responses in the female rat.

To study the participation of gamma-aminobutyric acid (GABA) in the control of sexual behavior in the female rat, the effect of GABA and picrotoxin injections in the ventromedial hypothalamic nucleus (VMN) upon lordosis frequency and multiunit spike activity (MUSA) was determined. Infusion of 100 micrograms GABA into conscious rats reduced lordotic responsiveness within 15 min after injection; with a similar time course, the same dose markedly reduced MUSA in urethane anesthetized rats. Forty-five min after injection lordotic responsiveness recuperated to preinjection levels; at this time MUSA showed a rebound increase in neuron firing frequency. The possible relation between ventromedial hypothalamic neuronal activity and capacity for lordotic responses was further tested with injections of a local anesthetic: 1 microliter of 2% Xylocaine infused into the VMN produced similar results, suppressing MUSA and lordotic responsiveness for ca. 45 min beginning immediately after injection. Microinjections of GABA antagonist picrotoxin had the opposite effects: 0.1 microgram increased MUSA and lordotic responsiveness at 5 and 45 min; however at 20 min, when MUSA was at its highest, lordosis frequency was not elevated. Injections of solvent had no consistent effects on either measure. Two conclusions many be tentatively drawn from these data: (a) the VMN is the origin of a neural signal which exerts a moment-to-moment gating control on the execution of lordosis, and (b) the generation and/or the output of this signal is under the control of a GABAergic hypothalamic mechanism which normally exerts an inhibitory effect on the display of lordotic responses.

Action Potentials↗

PubMed1985

Further studies on peripeduncular-hypothalamic pathways involved in sexual behavior in the female rat.

A series of preliminary experiments demonstrated that injection of 22 mM sodium pentobarbital in the brain of the rat blocked synaptic transmission at the site of injection; the same concentration of pentobarbital did not block fiber conduction. Based on the latter information, 22 mM pentobarbital was applied to different parts of the peripeduncular-hypothalamic pathways responsible for the conduction and generation of potentials evoked in the ventromedial nucleus (VMN) by stimuli applied to the peripeduncular nucleus (PPN), to determine whether participation of the amygdala and bed nucleus of the stria terminalis involves the transynaptic activation of neuron somas at these places or the operation of passing fibers only. We determined that potentials evoked in the VMN by PPN stimulation involves synaptic activity in both the lateral amygdaloid nucleus and the bed nucleus of the stria terminalis. Both structures receive PPN-originated activity independently, and both structures contribute to the generation of PPN-VMN evoked responses, presumably through temporal or spatial summation of inputs in the VMN. We also showed that activity in the lateral amygdaloid nucleus is conducted toward the VMN along fibers in the stria terminalis. We propose that the synaptic interactions thus demonstrated serve as integrating relays for different sensory modalities and hormone actions regulating sexual behavior.

Amygdala↗