Brain areas activated after ejaculation in healthy young human subjects.

Brain mechanisms for the refractory period that characteristically follows ejaculation in animals and human are poorly understood. The possibility of active inhibition of brain areas being responsible for the post-ejaculatory inhibitory state has not been ruled out. Using Blood Oxygen Level Dependent (BOLD) functional magnetic resonance imaging (fMRI) we have mapped brain areas in healthy young volunteers immediately after ejaculation. Functional imaging of the brain for 30 minutes beginning after three minutes of ejaculation induced by masturbation showed spatio-temporal activation in amygdala, temporal lobes and septal areas. The septal areas were observed to be active for a shorter duration than the amygdala and the temporal lobe. Thus the temporal sequence of involvement of the above neural structures may contribute to temporary inhibition of sexual arousal/penile erection during the post-ejaculatory refractory period in humans.

Sleep changes during chronic cold exposure showed that the homeostatic requirement of sleep is reduced in the medial preoptic area lesioned rats.

The effects of chronic exposure to a mildly cold ambient temperature (T(a)) of 18 degrees C on sleep wakefulness (S-W) and brain temperature (T(br)) were studied in the medial preoptic area (mPOA) lesioned male Wistar rats. Electroencephalogram (EEG), electrooculogram (EOG) and electromyogram (EMG) electrodes were chronically implanted to assess S-W, and a thermocouple above the dura to record the T(br). After three recordings (24 h each) of S-W and T(br) at 24 degrees C, N-methyl D-aspartic acid (NMDA) was intracerebrally injected to produce bilateral destruction of neurons in the mPOA. There was decreased sleep and increased T(br) even four weeks after the mPOA lesion. T(a) of the environmental chamber was then reduced to 18 degrees C, and the S-W and T(br) were again recorded for 24 h each on the 1st, 7th, 14th, 21st, and on 28th days of continuous exposure to the mild cold T(a). Exposure to the cold produced further decrease in sleep and increase in the T(br). However, sleep came back to the pre-exposure level by the 14th day. An increase in the duration of sleep episodes was responsible for the restoration of sleep during chronic cold exposure. The study showed that the requirement of sleep was reset at a lower level in the mPOA lesioned rats. The mPOA lesion affected the sleep maintenance and sleep initiation, though the latter became evident only during chronic cold exposure. The magnitude of the acute changes in T(br) and S-W were less in the lesioned rats, as compared to those observed in the normal rats exposed to similar cold T(a). On the basis of these observations, it could be proposed that the mPOA plays some role in cold induced changes in thermoregulation and sleep regulation. The T(br) remained elevated throughout the period of cold exposure. Resetting of the T(br), at a higher level may be part of the homeostatic readjustment to restore sleep.

Role of catecholaminergic terminals in the preoptic area in behavioural thermoregulation in rats.

This study was conducted to find out the role of the catecholaminergic terminals in the preoptic area (POA) in selection of ambient temperature in rats. The adult male Wistar rats (n = 6) were allowed to choose between three ambient temperatures (24 degrees C, 27 degrees C and 30 degrees C). Rats could move about freely from one ambient temperature to another, in a specially designed environmental chamber having three interconnected compartments, which were maintained at the above mentioned temperature. The results show that the normal rats preferred to stay at 27 degrees C both during day and night. After the lesion of catecholaminergic terminals in the POA with 6-hydroxydopamine (6-OHDA), the animals preferred 24 degrees C on the third and seventh day and 27 degrees C on the fourteenth and twenty first day after lesion. The alteration in thermal preference was associated with an elevation of rectal temperature. The study suggests that the catecholaminergic terminals of the POA play an important role in integrating behavioural and non-behavioural thermoregulatory responses, but in its absence the rest of the brain takes over some of its functions.

Effect of ambient temperature on brain temperature and sleep-wakefulness in medial preoptic area lesioned rats.

The changes in brain temperature and sleep-wakefulness were studied in rats during their exposure to different ambient temperatures of 18 degrees C, 24 degrees C and 30 degrees C, before and after N-methyl D-aspartic acid lesion of the medial preoptic area. The medial preoptic area lesion produced a decrease in sleep, and increase in brain temperature except at 30 degrees C. Increase and decrease in brain temperature with slow wave sleep and paradoxical sleep respectively, were observed both in normal and lesioned rats. Sleep-wakefulness and brain temperature cycle durations were increased and their frequencies decreased at higher ambient temperature in normal rats. After the medial preoptic area lesion, sleep-wakefulness cycle duration was decreased and frequency increased at 30 degrees C. There was no significant change in brain temperature cycles at higher ambient temperature in lesioned rats. The medial preoptic area, in normal rats, possibly interlinks the neuronal circuits involved in regulating brain temperature and sleep-wakefulness cycles. The medial preoptic area is essential for increasing the sleep-wakefulness cycle duration with higher ambient temperature. The possible contribution of the increased brain temperature variation in producing sleep-wakefulness changes cannot be ruled out. The results of the study show that this area may serve as a fine tuning mechanism which helps to interlink the sleep-wakefulness with the thermoregulation.

Role of the medial preoptic area in thermal preference of rats.

This study was conducted to find out whether the medial preoptic area (mPOA) plays a role in the selection of ambient temperature by rats. Adult male Wistar rats were kept in an environmental chamber having three interconnected compartments, maintained at three different temperatures (18 degrees, 24 degrees and 30 degrees C) in which the animals could move freely from one compartment to the other. Normal rats preferred to stay at the chamber maintained at 24 degrees C for most of the time, during day and night. The temperature preference shifted to 30 degrees C after the mPOA of these rats had been lesioned by local administration of 5 micrograms of N-methyl D-aspartic acid (NMDA) in 0.2 microliter distilled water. The results of the study suggest that the mPOA acts as a fine tuning center for homeostatic regulation of thermal balance, including selection of appropriate thermal environment. It is proposed that after the mPOA lesion, the animal cannot assess properly the energy status of the body and thereby prefers a higher ambient temperature.

Asymmetrical effects of the unilateral implant of pilocarpine on the preoptic-anterior hypothalamic area on spontaneous ovulation of the adult rat

The effects on ovulation at the next strus after unilaterally implanting pilocarpine in the preoptic-anterior hypothalamic area (POA-AHA) of rats on each day of the estrous cycle were analyzed. Implantation on the left side of POA-AHA on the day of estrus blocked ovulation in all animals, whereas implantation on the right side did not (0/5 vs. 4/4, p<0.05). Implantation on diestrus 1 or 2 on either side of the POA-AHA blocked ovulation. Implatation on the righ side of the POA-AHA at the day of proestrus blocked ovulation (1/6 animals ovulated), while 10/12 with pilocarpine on the left side ovulated (p<0.05).The administration of 3.7 µg of GnRH at 13:00 h o the expected day of proestrus induced ovulation in 36/42 treated animals. In rat with a pilocarpine implant, the injection of estradiol benoznate on diestrus 2 restored ovulation only in those animals with the pilocarpine implant placed in the left side of the POA-AHA, performed on the day of estrus. The results support the previous estatements that in the adult rat POA-AHA, the cholinergic mechanism regulating preovulatory GnRH release, is lateralized. In addition, at the beginning of the estrous phase, the PAO-AHA-cholinergic system needs to remain undisturbed for normal ovulation to take place at the next estrus

Preoptic-periventricular tissue (AV3V): central cholinergic-induced hydromineral and cardiovascular responses, and salt intake

The periventricular tissue of the anterior ventral portion of the third ventricle (AV3V) is an important area for the control of hydromineral balance and of cardiovascular function. The present work discusses the importance of the integrity of the AV3V for multiple responses to central cholinergic activation (water intake, hypertension, natriuresis, salivation) and for the control of salt intake.

Heart rate in female rat in response to snout contact by normal, gonadectomised and testosterone--pretreated gonadectomised male.

The question whether or not there will be an enhanced autonomic response in terms of heart rate in female rat, during sexual encounter with male rat was investigated. The heart rate recorded from partially restrained estrous female rat before and after the snout contact by the normal male rat showed a significant rise. There was no such rise in response to the snout contact by neonatally gonadectomised male rat of the same age as that of normal male. Treatment of testosterone propionate given to the gonadectomised male twelve hours prior to the experiment did not bring about significant rise in the heart rate of the estrous female. It is apparent that the perturbation in the structure of sexually dimorphic medial preoptic area (MPOA) in the male rat as a result of neonatal gonadectomy obliterates certain essential cues such as pheromone(s), visual and ultrasound communications which normally elicit a rise in the heart rate of the estrous female during sexual encounter.

Central angiotensin converting enzyme-blockade and thirst

1. The effect of lisinopril, a potent inhibitor of angiotensin converting enzyme (ACE), injected into the medial preoptic area (MPOA) on water intake was investigated in male Holtzman rats (200-250 g). 2. Injection of lisinopril (2 micrograms/microliters) into the MPOA abolished the water intake induced by subcutaneous (sc) injection of isoprenaline (100 per cent ) and water deprivation (90 per cent ) and drastically reduced the water intake induced by sc injection of polyethyleneglycol (60 per cent ). A small reduction of water intake induced by lisinopril was also observed 90 and 120 min after sc hypertonic saline (N = 10 for each group). 3. These results suggest that central ACE activation, particularly in the MPOA, plays an important role in the dipsogenic responses induced by the agents studied

Possible action of intracerebroventricular thyrotropin on Brobeck's hypothesis.

The effect of ICV administered TSH on Brobeck's thermostatic hypothesis was evaluated by recording chronological changes in electrical activity of precise loci (POA, VMN and CO) coupled by rectal temperature changes in dogs. The study revealed 1. TSH action on thermoregulation is biphasic in nature. 2. This action of TSH is not an independent act but depends on the reaction of satiety centre.

Ethanol induced electroencephalographic changes from certain central loci of canine brain.

Effect of intracerebroventricular (i.c.v.) ethanol on pre-optic area (POA) and hippocampus (HPC) was investigated by recording chronological changes in their electroencephalographic (EEG) activity, through chronically implanted cannulae and bipolar electrodes, in five conscious male beagle dogs. Recordings were made for two hours after microinjection and compared with cortical (CO) tracings. The predominant pattern of EEG activity from subcortical loci was high voltage discharges though synchronization was also observed. Cortical EEG depicted slow waves with some potentiation. The study demonstrated similar type of response form POA and HPC, which was different from CO, suggesting that ethanol produces different actions at subcortical and cortical level.

Evidence for adrenal medulla involvement in cold adaptation of preoptic-lesioned rats

The cold-adaptation process was examined in preoptic-lesioned (PO, 18 rats) and adrenaldemedullated-preoptic-lesioned rats (ADPO, 16 rats). PO rats and ADPO female Wistar rats wee cold acclimatized to 5-C for 2 h a day for 2 weeks, or maintained at 25C, starting one week after the operation. Control animals (20 rats) were sham-operated and then treated exactly like the lesioned rats. Lesions int he PO region caused a decrease in the ability to maintain normal body temperature in a cold environment (5-C for 2h). Theri colonic temperature fell even by the end of the 2nd h of cold exposure (-1.1-C for PO rats and -1.25-C for ADPO rats, P<0.01). However, after 2 weeks of cold acclimattion the PO rats, but not the ADPO rats were able to thermoregulate in the cold and showed a normal increase in interscapular brown adipose tissue weight (79%, P < 0.01). These data suggest that the PO is not an essential link for cold adaptation when a mild col-adaptation methods is used. Furthermore, the data show that increased adrenal medullary activity is required for the cold adaptation process in PO rats

Metabolic adjustments during adaptation to high ambient temperature by preoptic-lesioned rats

Metabolic adjustment was studied in male Wistar rats weighing 180-200 g with bilateral electrolytic lesions in the preoptic area which were acclimatized to a hot envirnment (34-C, 30 rats) and to normal temperature (25-C, 20 rats) for 60 days. Oxygen consuption at 34-C and body weight were measured periodically. Preoptic-lesioned rats (POrats) showed a reduction in metabolic rate (from 46.2 ñ 2 to 33 ñ 2 Cal/m2 per h, P < 0.05) regardless of the temperatures to which they were adapted. Although the reduced metabolic rate of PO rats living at 25-C or 34-C could be an indicator of adaptation to heat, only the PO rats living at 25-C showed a weight gain (101 ñ 13 g) similar to that observed for the sham-operated control (75 ñ 11 g). In fact, the PO rats living at 34-C failed to increase their body weight during 60 days of exposure to heat. These data indicate that the preoptic area is essential to integrate the thermal imput with the energy-linked metabolic process involved in adaptation to hot environments

Metabolic adjustment induced by exposure to elevated ambient temperature is impaired in rats bearingt lesions in the preoptic area

Metabolic adjustment was studied in rats with bilateral electrolytic lesions in the preoptic area which were exposed to heat (34-C) anda to normal temperature (25-C) for 60 days. The metabolic rate measured at neutral temperature (29-C) in preoptic-lesioned rats living at 25- or 34-C was reduced to 80% the rate of sham-operated controls. The increase in metabolic rate induced by heat (30 min at 34- or 37-C) in preoptic-lesioned rats, living at 25-C, was markedly reduced to 10% the rate of sham-operated controls living at 25-C. In preoptic-lesioned rats, the increased metabolic rate induced by heat exposure (34- or 37-C) was impaired, regardless of the living ambient temperature (25- or 34-C) of the animal. These data demonstrate the participation of the preoptic area in heat-induced invreased oxygen consumption and provide additional evidence for its role in the integration of thermal imputs with energy-linked metabolic processes

Substance P injected into the medial preoptic area inhibits sodium, potassium and water urinary excretion: putative modulation of the cholinergic system

Substance P (SP, 1.5 nmol) injected into the medial preoptic area (MPOA) of conscious, unrestrained, water-loaded male rats induced a significant decrease in urinary sodium, potassium and water excretion. In contrast, a significant natriuretic effect was observed after injection of 0.3 nmol of a specific competitive SP antagonist ([D-Pr**2, D-Trp**7,**9]-substance P). SP partially blocked the carbachol-induced natriuresis in a time-dependent manner. These data indicate a tonic inhibitory action of SP on sodium excretion and suggest a putative modulatory action of SP on the cholinergic system

Correlation of preoptic neuronal activity with spontaneous and induced cortical EEG changes.

Preoptic area has neurons which change their firing rate along with spontaneous alterations of the cortical EEG between synchronization and desynchronization. The cortical EEG synchronization and desynchronization could be induced by stimulation of the caudal and the rostral brain stem respectively. This study was aimed at finding out whether stimulation of the brain stem structures produce the same change in the unit activity as that occurring during spontaneous alteration of the EEG. The changes in unit activity showed some concordance and dissociation between spontaneous and induced EEG alterations. The possible interaction of inputs from cortex and brain stem at the level of the preoptic area is discussed.

Role of medial preoptic area (MPOA) in the reproductive function and feeding behavior in rats.

Adult female rats were given ad lib access to two pairs of specially prepared diets containing the three macro-nutrients, protein, fat and carbohydrate, in such proportion that both pairs were isocaloric but one pair varied in protein content (45% and 5%) and the other pair in carbohydrate content (70% and 25%). Body weights, food intake and selectivity were noted daily. Following lesions of Medial Preoptic Area (MPOA), there was an increase in the total food and protein intake and disruption of the regular estrus cycles. In the second series, the total food intake increased after ovariectomy and decreased following intracranial estrogen instillation in the MPOA. A change in the selectivity of the diets was also noted. The observations are suggestive of the role of MPOA in the food intake and selectivity and this is probably effected through the estrogen receptors situated therein.

Experimental dissociation of hypothalamic functions: an analysis of neural structural components for prolactin release control in the male rat

Disociación experimental de funciones hipotalámicas: Análisis de componentes nerviosos estructurales involucrados en el control de la liberación de prolactina en la rata macho. En el presente trabajo se analizan datos experimentales relativos a posibles componentes nerviosos involucrados en el control de la liberación de prolactina en la rata macho, así como la posibilidad de disociar experimentalmente la liberación de prolactina y LH inducida por estimulación aplicada en una área determinada del cerebro. Se formula el siguinte grupo de proposiciones: 1) la región preóptica-supraquiasmática (POA-Sch) incluye elementos nerviosos que participan en el control inhibitorio y facilitatorio de la liberación de prolactina; 2) en su aspecto dorsal esta región se comporta, en repuesta a varios tipos de pertubaciones, como si incluyera elementos predominantemente inhibitorios para la liberación de prolactina, mientras que en su aspecto más ventral aparenta estar compuesta predominantemente por elementos facilitadores de dicha liberación; 3) mientra los primeros estarían representados predominantemente por procesos neuronales que transcurren vecinos a la comisura anterior, los segundos (facilitadores) tomarían origen en la región ventral de la POA-Sch; 4) aunque la estimulación eléctrica aplicada en dicho aspecto ventral de la POA-Sch habitualmente resultan en la liberación de prolactina y LH, es posible disociar tales respuestas modificando la estructura temporal del estímulo aplicado