Effects of repeated 9 and 30-day exposure to extremely low-frequency electromagnetic fields on social recognition behavior and estrogen receptors expression in olfactory bulb of Wistar female rats.

OBJECTIVE: We investigated the short- and long-term effects of extremely low-frequency electromagnetic fields (EMF) on social recognition behavior and expression of α- and ß-estrogen receptors (ER). METHODS: Rats were exposed to 60-Hz electromagnetic fields for 9 or 30 days and tested for social recognition behavior. Immunohistochemistry and western blot assays were performed to evaluate α- and ß-ER expression in the olfactory bulb of intact, ovariectomized (OVX), and ovariectomized+estradiol (E2) replacement (OVX+E2). RESULTS: Ovariectomization showed impairment of social recognition after 9 days of EMF exposure and a complete recovery after E2 replacement and so did those after 30 days. Short EMF exposure increased expression of ß-ER in intact, but not in the others. Longer exposure produced a decrease in intact but an increase in OVX and OVX+E2. DISCUSSION: Our findings suggest a significant role for ß-estrogen receptors and a lack of effect for α-estrogen receptors on a social recognition task. ABBREVIATIONS: EMF: extremely low frequency electromagnetic fields; ERs: estrogen receptors; OB: olfactory bulb; OVX: ovariectomized; OVX + E2: ovariectomized + estradiol replacement; IEI: interexposure interval; ß-ER: beta estrogen receptor; E2: replacement of estradiol; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; WB: Western blot; PBS: phosphate-buffer saline; PB: phosphate-buffer.

Effect of photoperiod on the mechanical response of the pregnant rabbit uterus to oxytocin.

We present findings suggesting that photoperiod is important in determining the sensitivity of the late-pregnant rabbit uterus to oxytocin (OT). Longitudinal myometrial strips were taken from term-pregnant and estrous rabbits and mounted in an organ bath for isometric myographic recording at different times during a 16:8-h light-dark cycle (lights on 0600-2200; n = 5/group), and the strength of contractions was registered in response to the application of OT or KCl. Strength of contractions was dose dependent and was up to 200 times greater at doses three to four orders of magnitude lower in tissue taken from pregnant animals during the light phase (0700 and 1300) than during the dark phase (2400 and 0400). Strips from nonpregnant estrous females also showed greater sensitivity and contractile force when taken in the light (0700) than in the dark (0400), although the differences were not significant. Consistent with the influence of photoperiod on uterine sensitivity to OT, strips taken from two groups of pregnant females (n = 5/group) maintained on a light-dark cycle advanced 12 h showed significantly greater sensitivity and force in response to OT during the new subjective light than during the new subjective dark phase. The photoperiod-dependent contractile response to OT was specific and not simply the result of a change in general mechanical properties of the muscle, because administration of KCl resulted in dose-dependent contractions of similar magnitude in both the light and dark phase. These results are consistent with the fact that rabbits, like other nocturnal mammals, typically give birth during the day.

Release of classical transmitters and nitric oxide in the rat olfactory bulb, evoked by vaginocervical stimulation and potassium, varies with the oestrus cycle.

In vivo microdialysis was used to investigate the effects of ovariectomy and the oestrus cycle on vaginocervical stimulation-evoked classical transmitter and nitric oxide release in the olfactory bulb of anaesthetized (urethane) and conscious rats. During pro-oestrus/oestrus, vaginocervical stimulation (1 or 10 min) significantly increased concentrations of glutamate, aspartate, GABA, noradrenaline, dopamine and nitric oxide (citrulline) but failed to do so in met-oestrus/di-oestrus or following ovariectomy. Potassium chloride-evoked GABA, noradrenaline and nitric oxide release in the olfactory bulb was also significantly enhanced during pro-oestrus/oestrus. The effects of vaginocervical stimulation on olfactory bulb transmitter release during pro-oestrus/oestrus were significantly reduced by pelvic or vagus nerve section. Basal concentrations of classical transmitters and nitric oxide in the olfactory bulb did not vary across the oestrus cycle although noradrenaline and dopamine levels were reduced following ovariectomy. These results confirm our previous electrophysiological data showing that the olfactory bulb mitral cells are only excited by vaginocervical stimulation during pro-oestrus/oestrus. They also suggest that sex hormones acting primarily at the level of the olfactory bulb dramatically enhance the ability of vaginocervical stimulation to evoke release of both classical transmitters and nitric oxide in this region. Such alterations in neurochemical release in the olfactory bulb may be important for mediating plasticity changes underlying olfactory recognition of mates or offspring.

The Cartesian clock metaphor for pineal gland operation pervades the origin of modern chronobiology.

In theoretical descriptions formulated during the 1600s, R. Descartes attributed a clock-like role to the pineal gland. He established the belief that pineal function underlies the laws of the universe that determine the cyclic sleep-awake states in man. Recent reports about pineal circadian pacemakers now validate the brilliant accuracy of Cartesian thought, in relation to the relevant role of the pineal gland.

Effect of the estrous cycle on olfactory bulb response to vaginocervical stimulation in the rat: results from electrophysiology and Fos immunocytochemistry experiments.

To determine whether the stage of the estrous cycle modified the response of olfactory bulb neurons to vaginocervical stimulation, (1) vaginocervical stimulation was applied to animals in proestrus-estrus and metestrus-diestrus and the extracellular electrophysiological response of units in the mitral cell layer of the main olfactory bulb was compared, and (2) the effect of vaginocervical or sham stimulation and the effect of the estrous cycle on the number of neurons stained immunocytochemically for Fos in the main and accessory olfactory bulb was examined. Animals in proestrus-estrus had basal firing rates of 21.8 +/- 1.8 spikes per 5 s and vaginocervical stimulation produced an increase in firing rate. In contrast, animals in metestrus-diestrus had a slower basal firing rate (14.3 +/- 2.3 spikes per 5 s) and vaginocervical stimulation produced a decrease in the firing rate. For animals in proestrus-estrus, vaginocervical stimulation increased the number of Fos-stained cells in the granular cell layer of the accessory olfactory bulb, and in the glomerular and in external plexiform layers of the main olfactory bulb. In contrast, the number of Fos-stained cells decreased in the granular cell layer of the main olfactory bulb after stimulation was applied to animals in proestrus-estrus. The number of Fos-stained cells in the granular layer of the accessory olfactory bulb and the granular and glomerular cell layers of the main olfactory bulb was modulated by the estrous cycle. Therefore, olfactory bulb activity, measured both electrophysiologically and by Fos staining, was affected by the estrous cycle and vaginocervical stimulation, and the two variables interacted. It is likely that integration of interoceptive and environmental stimulation is important for the normal expression of sexual behavior in the female rat.

Protocerebral deafferentation effects on crayfish glycemic response: a protocerebral circadian pacemaker regulates the hemolymph sugar concentration.

Similar to intact crayfish animals with an isolated protocerebrum exhibit a competent control for circadian variations of glucose concentration in the hemolymph. However, the sudden increase in glucose concentration induced by stressing influences in intact or partially deafferented animals dropped or became totally suppressed in the preparations with isolated protocerebrum.

[Effects of asphyxia on the visual activity of the crayfish with neural deafferentation of the eyestalks]. / Efectos de la asfixia sobre la activadad visual del camarón de río con desaferentación neural de sus tallos oculares.

Centripetal migration of distal pigments of the crayfish compound eye, is induced by light, by a protocerebral circadian pacemaker and among many other influences by asphyxia. The adaptive migration of those pigments, in this case, is accompanied by a clear neural hyperexcitability which can be suppressed by experimental deafferentation of the eyestalks.

Protocerebral circadian pacemakers in crayfish: evidence for mutually coupled pacemakers.

Similar to intact crayfish, animals with an isolated protocerebrum-eyestalk complex, exhibit competent circadian rhythms in the electroretinogram (ERG). The ERG rhythms of the two eyes remain in phase after isolation of the protocerebrum but can be desynchronized after surgical bisection of the protocerebrum. The desynchrony of the two ERG rhythms reveals the existence of at least two circadian pacemakers in the eyestalk-protocerebrum complex. In addition, the fact that desynchrony of the ERG rhythms only occurs in bisected preparations suggests that pathways between the protocerebral lobes normally couple the two pacemakers.

Visual circadian rhythmicity in splitbrain crayfish: a plastic behavioral expression of symmetric circadian pacemakers.

Electroretinographic evoked potentials (ERG's) were continuously recorded in dark-adapted, splitbrain crayfishes Procambarus bouvieri. Pulses of light (0.95 cd/m2) illuminating the left or the right eyes were alternatively applied every 15 or 30 min. As compared to intact crayfish, uni or bilateral damping or suppression of circadian retinal sensitivity rhythm could be caused by surgical bisection of cerebral ganglion in these crustaceans. The damped ERG circadian rhythm was rapidly reversed by reduction or elimination of the test light stimulus to the contralateral eye. Given the redundant processing of pacemaking information coming from bilaterally positioned cephalic circadian pacemakers to the central nervous system in splitbrain crayfish, photodependent damping of ERG rhythm revealed a plastic potential of central circadian pacemakers. The possibility that a strong but reversible inhibitory influence acts simultaneously upon the left and right protocerebral circadian pacemakers while receiving bilateral photic stimulation is considered.

The role of protocerebrum in the modulation of circadian rhythmicity in the crayfish visual system.

Dark-adapted crayfishes with protocerebrum only, were submitted to continuous recordings of electroretinogram (ERG) and of eye glow area (EGA) during several days. Circadian variations of ERG amplitude similar to that of intact animals, were revealed by means of restrained test light stimuli (0.2 Cd/ft2) bilaterally applied to each eyestalk. The period (24.6-38 hr) and range (40-80%) value of ERG oscillations always resulted quite similar to one another side. As in intact animals retinal shielding pigments (RSP) position as measured as EGA size showed a clear circadian rhythm, and also a clear consensual reflex in these preparations. We found a loss of both: circadian and consensual mobilization of distal RSP in animals with complete removal of cerebral ganglion. Our proposition is that the crayfish protocerebrum plays a major role in the modulation of circadian retinal sensitivity, probably through the control-release of hormonal neurosecretions from the sinus gland along the day.

Electrophysiological evidences of mutual modulatory influences on the retinal activity of the crayfish Procambarus bouvieri (O).

Electroretinographic evoked potentials (ERGs) were recorded in dark adapted crayfish by the application of pulses of light (0.09 Cd/ft2) presented every 2.5 min. Heterolateral illumination (HI) for sixty min (0.06-0.3 Cd/ft2) induced up to 50% decrease in ERG after a latency of 12-25 min. ERG depression was proportional to the intensity of HI and also showed a circadian rhythm. During the alpha phase the ERG recovery started 3-10 min after HI was turned off. In contrast it started only after 10-20 min during the rho phase. The time course of the ERG depression, which was abolished in splitbrain animals, strongly suggests that a mutual modulatory influence, probably of neuroendocrine nature, is present in the crayfish visual system.

Habituation of mechanoreceptive interneurons in the crayfish.

The effect of repetition of sensory stimuli was studied on the responses of mechanoreceptive interneurons in the optic tract of the crayfish (Procambarus bouvieri (Ortmann)). The number of spikes recorded from a given unit gradually decreased during a train of stimuli. The decrease showed a negative exponential time course, with a curvature dependent upon the frequency of stimulation, the intensity of stimuli, and the hour of the day. Habituation is selective for the intensity and rate of stimulation, and the particular spot of receptive field stimulated. Locomotor excitation results in a dimminution of the rate of decay. The effect of a single train of stimuli when leading to pronounced habituation may persist for periods longer than 24 hr.