AN ASCENDING PATHWAY FOR RELEASE OF PROLACTIN IN THE BRAIN OF THE RABBIT

1969 ◽  
Vol 45 (1) ◽  
pp. 111-120 ◽  
Author(s):  
J. S. TINDAL ◽  
G. S. KNAGGS
Keyword(s):  
Electrical Stimulation ◽  
Medial Geniculate Body ◽  
Posterior Hypothalamus ◽  
Implanted Electrodes ◽  
Oxytocin Release ◽  
Central Grey Matter ◽  
Medial Geniculate ◽  
Monopolar Electrodes ◽  
Milk Ejection Reflex ◽  
The Brain

SUMMARY Rabbits in pentobarbitone anaesthesia were implanted bilaterally with a pair of monopolar electrodes in the brainstem. Approximately 10 days after the operation, pseudopregnancy was induced by i.v. injection of human chorionic gonadotrophin, and 1 week later the rabbits received electrical stimulation with square-wave pulses through the implanted electrodes for two periods of 30 min. daily for 11 days. At autopsy on the following day the mammary glands were inspected for occurrence of lactogenesis and sites of electrode tips in the brain were determined histologically. Lactogenesis, indicating release of prolactin, occurred when electrical stimulation had been applied to sites in the lateral mesencephalic tegmentum and further forward in a region medio-ventral to the medial geniculate body. Passing rostrally, the pathway moved medially and then forwards in association with the extreme rostral central grey matter, and was traced as far forward as the posterior hypothalamus where sites were found close to, but not involving, the mammillo-thalamic tracts. When compared with our previous studies on the afferent path of the milk-ejection reflex in this species, the ascending path for release of both oxytocin and prolactin appears to be the same in the mesencephalon. However, whereas the ascending path for oxytocin release bifurcates on each side into dorsal and ventral paths which reunite in the posterior hypothalamus, that for prolactin release appears to follow only the dorsal path, since stimulation of the subthalamus, through which the ventral path passes, was ineffective. It is proposed that the pathway traced in the present study represents the mesencephalic and posterior diencephalic route by which impulses initiated by the suckling stimulus attain the hypothalamus to evoke release of prolactin from the adenohypophysis.

MESENCEPHALIC AREAS CONTROLLING PULSATILE OXYTOCIN RELEASE IN THE SUCKLED RAT

1981 ◽  
Vol 91 (2) ◽  
pp. 233-244 ◽  
Author(s):  
T. S. JUSS ◽  
J. B. WAKERLEY
Keyword(s):  
Medial Geniculate Body ◽  
Milk Ejection ◽  
Ventral Tegmentum ◽  
Irregular Pattern ◽  
Oxytocin Release ◽  
Medial Geniculate ◽  
Radiofrequency Lesions ◽  
Milk Ejection Reflex ◽  
Bilateral Lesions ◽  
And Control

Experiments were performed on anaesthetized lactating rats to investigate the effects of radiofrequency lesions of the mesencephalon on the milk-ejection reflex. In lesioned and control rats, intramammary pressure recordings were used to estimate oxytocin release (number and relative amplitude of the intermittent milk-ejection responses) during a 3-h suckling test with ten pups. Bilateral lesions (diameter 0·5–1·5 mm) of the lateral tegmentum (near the brachium of the inferior colliculus and medial geniculate body) seriously disrupted the milk-ejection reflex, reducing the number of rats ejecting milk (two out of ten v. all 12 controls, P<0·001) and the amount of oxytocin they released (1·35±0·35 (s.e.m.) v. 15·52±2·19 mu. for controls, P<0·05). Unilateral lesions of the lateral tegmentum also impaired milk ejection and, if the suckling stimulus was restricted only to the contralateral nipples, oxytocin release was virtually abolished. Bilateral lesions placed more medially in the intermediate tegmentum were far less disruptive (eight out of nine rats ejected milk), though the amount of oxytocin released in this group (8·64±1·88 mu.) was still significantly (P<0·05) lower than controls. All rats with lesions of the central grey (nine) or ventral tegmentum (eight) displayed reflex milk ejection, as did those with multiple lesions of the tectum, central grey and ventral tegmentum (seven); in these three groups the amounts of oxytocin released (13·88±2·68, 13·10±1·90 and 11·04±1·95 mu. respectively) did not differ significantly from controls. Damage to the ventral tegmentum produced an irregular pattern of milk ejection characterized by occasional abnormally short (<2 min) milk-ejection intervals, though the overall number of responses in 3 h was less than that of controls (20·83±1·82 v. 14·50±1·30 mu., P<0·05). In conclusion, these results delineate two mesencephalic areas of particular importance in the milk-ejection reflex: (a) the lateral tegmentum, which appears to be concerned with transmission of the suckling stimulus from the contralateral nipples and is indispensable for oxytocin release, and (b) the ventral tegmentum which, although not an essential component of the reflex, may contribute to the timing of the intermittent milk-ejection responses.

THE AFFERENT PATH OF THE MILK-EJECTION REFLEX IN THE BRAIN OF THE GUINEA-PIG

1967 ◽  
Vol 38 (3) ◽  
pp. 337-349 ◽  
Author(s):  
J. S. TINDAL ◽  
G. S. KNAGGS ◽  
A. TURVEY
Keyword(s):  
Guinea Pig ◽  
Medial Geniculate Body ◽  
Pituitary Stalk ◽  
Medial Lemniscus ◽  
Milk Ejection ◽  
Major Pathway ◽  
Ventral Thalamus ◽  
Medial Geniculate ◽  
Milk Ejection Reflex ◽  
The Brain

SUMMARY The afferent path of the milk-ejection reflex has been studied in the brain of the lactating guinea-pig in light pentobarbitone anaesthesia. Square-wave pulses were applied between an indifferent electrode in the scalp and a monopolar electrode inserted stereotaxically in the brain. The brain was transected at the mid-cerebellar level to eliminate activation of the sympathetico-adrenal system, and milk-ejection pressure was monitored to detect release of neurohypophysial hormone(s). The afferent path of the reflex in the caudal midbrain was very compact and lay in the lateral tegmentum. More rostrally, milk-ejection responses were obtained from the tectum and mesencephalic central grey, but the major pathway remained in the lateral tegmentum and passed forward to lie ventromedial to the medial geniculate body, after which it divided into two components which we have termed the dorsal and ventral paths. The dorsal path traversed dorsomedially across the brainstem to reach the parafascicular thalamic nucleus, the extreme rostral central grey and the periventricular region at the meso-diencephalic boundary, and then continued forward to reach the pituitary stalk and the medial and dorsal hypothalamus. The ventral path traversed ventromedially to enter the subthalamus and then the lateral hypothalamus, in which it passed both to the rostral basal diencephalon and to the pituitary stalk. In the diencephalon, milk-ejection responses were obtained after stimulation of part of the ventral thalamus, the lateral, dorsal and anterior hypothalamic areas, the dorsomedial, ventromedial, arcuate, supraoptic and paraventricular nuclei, and the pituitary stalk. It is suggested from these findings that in the guinea-pig the suckling stimulus ascends by the spinothalamic system, and continues rostrally to relay with the medial and ventral thalamus, the dorsal longitudinal fasciculus and the medial forebrain bundle. Other ascending pathways in the medial lemniscus and mammillary peduncle may also be involved, but appear to be of only minor significance.

PATHWAYS IN THE FOREBRAIN OF THE RABBIT CONCERNED WITH THE RELEASE OF PROLACTIN

1972 ◽  
Vol 52 (2) ◽  
pp. 253-262 ◽  
Author(s):  
J. S. TINDAL ◽  
G. S. KNAGGS
Keyword(s):  
Electrical Stimulation ◽  
Orbitofrontal Cortex ◽  
Preoptic Area ◽  
Third Ventricle ◽  
Posterior Hypothalamus ◽  
Bipolar Electrode ◽  
Prolactin Release ◽  
Implanted Electrodes ◽  
Neuronal Systems ◽  
The Brain

SUMMARY Rabbits were implanted unilaterally with a bipolar electrode in the forebrain, and approximately 10 days later pseudopregnancy was induced by i.v. injection of human chorionic gonadotrophin. One week later the rabbits began receiving electrical stimulation with square-wave pulses through the implanted electrodes for two periods of 15 min daily for 11 days. At autopsy on the 12th day the mammary glands were inspected for the occurrence of lactogenesis and sites of electrode tips in the brain were determined histologically. In a preceding study a prolactin-release path, believed to be that normally activated by the suckling stimulus, had been traced from the mid-brain as far rostral as the posterior hypothalamus, and in the present work, lactogenesis, indicating release of prolactin, occurred after electrical stimulation of this same region in the posterior hypothalamus, between the third ventricle and the mammillo—thalamic tract. Further rostrally, effective stimulation sites were found in the medio-dorsal hypothalamus, in the farlateral hypothalamus within the medial forebrain bundle, and in the lateral and medial preoptic area. Sites extended caudally from the last area to the medial anterior hypothalamus. Passing rostrally from the lateral preoptic area, effective sites occurred in, and ventral to, the external capsule, in the claustrum and in the adjacent orbitofrontal cortex which yielded the two maximum lactogenic responses observed in the stimulated group. The role of these rostral structures, in particular the orbitofrontal cortex, is not yet clear, nor is the final mechanism mediating prolactin release, although the results suggest that the ascending pathway for prolactin release approaches the medial hypothalamus by way of the preoptic area. The presence of control electrodes in the brains of pseudopregnant rabbits was found to cause lactogenesis when their tips were in structures associated with prolactin release, as determined from the stimulated group of animals. It was concluded, therefore, that electrical stimulation may have been unnecessary in this work and that the physical irritation caused by the presence of the electrode tip in appropriate neuronal systems may be a sufficient stimulus per se to be used for tracing prolactin-release pathways in the brain.

THE AFFERENT PATH OF THE MILK-EJECTION REFLEX IN THE BRAIN OF THE RABBIT

1969 ◽  
Vol 43 (4) ◽  
pp. 663-671 ◽  
Author(s):  
J. S. TINDAL ◽  
G. S. KNAGGS ◽  
A. TURVEY
Keyword(s):  
Medial Geniculate Body ◽  
Milk Ejection ◽  
Major Pathway ◽  
Arterial Blood ◽  
Neural Substrate ◽  
Indifferent Electrode ◽  
Medial Geniculate ◽  
Milk Ejection Reflex ◽  
The Brain ◽  
Stimulation Technique

SUMMARY The afferent path of the milk-ejection reflex has been studied in the brain of the anaesthetized lactating rabbit. Electrical stimulation was applied between a monopolar electrode in the brain and an indifferent electrode in the scalp. The brain was transected at the mid-cerebellar level to eliminate sympathetico-adrenal activation, and intramammary pressure and arterial blood pressure were monitored to detect release of neurohypophysial hormones. In the mid-brain, the afferent path of the reflex is compact, lying in the lateral tegmentum of each side and passing forwards to lie medio-ventral to the medial geniculate body. On entering the diencephalon, the pathway on each side bifurcates: a dorsal path passing forwards in association with the extreme rostral central grey and periventricular region, and a ventral path ascending through the subthalamus. The dorsal and ventral paths reunite in the posterior hypothalamus. Delineating the pathway further forward in the hypothalamus, using a simple stimulation technique, was not possible because at this level it intermingles with efferent fibres descending from the paraventricular nucleus to the pituitary stalk. The afferent path of the reflex is concerned with the preferential release of oxytocin from the neurohypophysis, is not a major pathway for the release of vasopressin and its neural substrate in the mid-brain is believed to be the spinothalamic system of fibres.

Corticofugal Projection Inhibits the Auditory Thalamus Through the Thalamic Reticular Nucleus

2008 ◽  
Vol 99 (6) ◽  
pp. 2938-2945 ◽  
Author(s):  
Zhuo Zhang ◽  
Chun-Hua Liu ◽  
Yan-Qin Yu ◽  
Kenji Fujimoto ◽  
Ying-Shing Chan ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Medial Geniculate Body ◽  
Thalamic Reticular Nucleus ◽  
Reticular Nucleus ◽  
Inhibitory Effects ◽  
Inhibitory Pathway ◽  
Inhibitory Postsynaptic Potentials ◽  
Medial Geniculate ◽  
Inferior Colliculi ◽  
Stimulation Of

Electrical stimulation of the auditory cortex (AC) causes both facilitatory and inhibitory effects on the medial geniculate body (MGB). The purpose of this study was to identify the corticofugal inhibitory pathway to the MGB. We assessed two potential circuits: 1) the cortico-colliculo-thalamic circuit and 2) cortico-reticulo-thalamic one. We compared intracellular responses of MGB neurons to electrical stimulation of the AC following bilateral ablation of the inferior colliculi (IC) or thalamic reticular nucleus (TRN) in anesthetized guinea pigs. Cortical stimulation with intact TRN could cause strong inhibitory effects on the MGB neurons. The corticofugal inhibition remained effective after bilateral IC ablation, but it was minimized after the TRN was lesioned with kainic acid. Synchronized TRN neuronal activity and MGB inhibitory postsynaptic potentials (IPSPs) were observed with multiple recordings. The results suggest that corticofugal inhibition traverses the corticoreticulothalamic pathway, indicating that the colliculi-geniculate inhibitory pathway is probably only for feedforward inhibition.

PREFERENTIAL RELEASE OF OXYTOCIN FROM THE NEUROHYPOPHYSIS AFTER ELECTRICAL STIMULATION OF THE AFFERENT PATH OF THE MILK-EJECTION REFLEX IN THE BRAIN OF THE GUINEA-PIG

1968 ◽  
Vol 40 (2) ◽  
pp. 205-214 ◽  
Author(s):  
J. S. TINDAL ◽  
G. S. KNAGGS ◽  
A. TURVEY
Keyword(s):  
Blood Pressure ◽  
Electrical Stimulation ◽  
Guinea Pig ◽  
Arterial Blood Pressure ◽  
Pituitary Stalk ◽  
Milk Ejection ◽  
Arterial Blood ◽  
Milk Ejection Reflex ◽  
The Brain ◽  
Stimulation Of

SUMMARY Discrete portions of the afferent path of the milk-ejection reflex have been explored in the brain of the lactating guinea-pig. Both intramammary pressure and arterial blood pressure were recorded to detect release of oxytocin and vasopressin. It was found that the milk-ejection responses which occurred after electrical stimulation of the pathway in the midbrain and hypothalamus were caused by the release of oxytocin without detectable release of vasopressin. A mixture of oxytocin and vasopressin, in the ratio of approximately 3:1, was released only after electrical stimulation of the rostral tuberal region of the hypothalamus adjacent to the pituitary stalk. It is concluded that the afferent path in the brain of the guinea-pig studied is concerned with the preferential release of oxytocin from the neurohypophysis and that it is the pathway of the milk-ejection reflex.

DETERMINATION OF THE DETAILED HYPOTHALAMIC ROUTE OF THE MILK-EJECTION REFLEX IN THE GUINEA-PIG

1971 ◽  
Vol 50 (1) ◽  
pp. 135-152 ◽  
Author(s):  
J. S. TINDAL ◽  
G. S. KNAGGS
Keyword(s):  
Electrical Stimulation ◽  
Lateral Hypothalamus ◽  
Third Ventricle ◽  
Milk Ejection ◽  
Lateral Direction ◽  
Reflex Pathway ◽  
Oxytocin Release ◽  
Far Lateral ◽  
Milk Ejection Reflex ◽  
Stimulation Of

SUMMARY The effect of various types of surgical damage to the forebrain on the release of oxytocin in response to electrical stimulation of the discrete ascending milk-ejection reflex pathway in the mid-brain was investigated in 99 anaesthetized lactating guinea-pigs. Oxytocin release was measured by comparison of experimental milk-ejection responses with the response to i.v. injection of known amounts of synthetic oxytocin. Removal of the entire telencephalon, including cerebral cortex, hippocampi, amygdalae and forebrain rostral to the hypothalamus, did not affect the subsequent release of oxytocin after electrical stimulation of the pathway in the mid-brain, from which it was concluded that the reflex pathway within the forebrain is entirely diencephalic. Transection of the hypothalamus immediately rostral to the paraventricular (PV) nuclei was without effect, while transection immediately caudal to the PV nuclei blocked the release of oxytocin. Destruction of the PV nuclei by a radiofrequency lesion which spared the supraoptic (SO) nuclei blocked the release of oxytocin. Undercutting both PV nuclei so as to isolate them from the ventral hypothalamus blocked the release of oxytocin. Undercutting the PV nucleus ipsilateral to the stimulated side of the mid-brain blocked the release of oxytocin, while undercutting the contralateral PV nucleus had no effect. The PV nuclei, therefore, lie on the ascending path of the milk-ejection reflex, the SO nuclei do not, and, from the mid-brain forwards, the ascending pathway remains uncrossed. The course of the reflex pathway was traced rostrally from the mesodiencephalic junction by making narrow transverse knife-cuts and determining which cuts reduced or blocked the release of oxytocin after mid-brain stimulation. At this level, the pathway on each side of the brain is represented by separate dorsal and ventral paths and in the present study it was found that the ventral path is more important than the dorsal path in terms of oxytocin release. The ventral path passes forward in the medial forebrain bundle, in the far-lateral hypothalamus, while the dorsal path enters the posterior hypothalamus dorsally in the periventricular region at the top of the third ventricle and impinges on the thalamic reuniens nucleus. Shortly afterwards the dorsal path swings abruptly in the lateral direction to join the ventral path in the lateral hypothalamus. The reunited pathway then moves forward in this position until it is level with the PV nuclei, where it swings dorsomedially to relay with the lateral tip of the ipsilateral PV nucleus, and in doing so intermingles with the descending neurosecretory fibres from this nucleus.

The functional anatomy of middle-latency auditory evoked potentials: thalamocortical connections

1992 ◽  
Vol 68 (2) ◽  
pp. 425-431 ◽  
Author(s):  
S. Di ◽  
D. S. Barth
Keyword(s):  
Electrical Stimulation ◽  
Auditory Cortex ◽  
Evoked Potentials ◽  
Linear Combination ◽  
Evoked Potential ◽  
Medial Geniculate Body ◽  
Cortex Area ◽  
Medial Geniculate ◽  
Potential Complex ◽  
Stimulation Of

1. An 8 x 8-channel microelectrode array was used to map epicortical field potentials from a 4.375 x 4.375-mm2 area in the right parietotemporal neocortex of four rats. Potentials were evoked with bilaterally presented click stimuli and with electrical stimulation of the ventral and dorsal divisions of the medial geniculate body. 2. Epicortical responses to click stimuli replicated earlier findings. The responses consisted of a positive-negative biphasic waveform (P1a and N1) in the region of primary auditory cortex (area 41) and a positive monophasic waveform (P1b) in the region of secondary auditory cortex (area 36). Two potential patterns, one at the latency of the N1 and the other at the latency of the P1b, were used to represent activation of cells within areas 41 and 36. A linear combination of these patterns was sufficient to explain from 90 to 94% of the variance of the evoked potential complex at all latencies. 3. In the same animals, epicortical responses to electrical stimulation of the ventral and dorsal divisions of the medial geniculate body were also localized to areas 41 and 36, respectively. A linear combination of potential patterns from these separate stimulation conditions was sufficient to explain from 80 to 93% of the variance of the original click-evoked potential complex at all latencies. 4. These data provide functional evidence for anatomically defined topographical thalamocortical projections to primary and secondary auditory cortex. They suggest that short-latency cortical evoked potentials (10-60 ms poststimulus) are dominated by parallel thalamocortical activation of areas 41 and 36.

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