Distribution and properties of diencephalic neuronal responses to genital stimulation in the female cat

Changes in hypothalamic neuronal function related to hormonal induction of lordosis in behaving hamsters

The hypothalamus is known to be critical for the neuroendocrine control of sexual behavior, but the neural effects of gonadal hormones on behavior-related activity of hypothalamic neurons has received little investigation. The present study examined the effects on single hypothalamic neurons of lordosis-inducing estrogen and progesterone administration to behaving golden hamsters. The lordosis-inducing action of the hormones was associated with rapidly emerging, cumulative changes in the activity level and somatosensory responsiveness of neurons throughout the hypothalamus, as well as the appearance in most neurons of lordosis-correlated firing. This functional reconfiguration of hypothalamic neuronal properties resembled, in time course and other aspects, effects of estrogen and progesterone previously observed in hamster midbrain neurons. Although the firing rates of the hypothalamic neurons were typically low, the lordosis-related activity of these neurons was compatible with a role in the control of individual episodes of lordosis as well as a state-related tendency to exhibit the lordosis response.

Failure of fertilization following abbreviated copulation in the ferret (Mustela putorius furo)

In the first experiment, copulations in 10 domestic ferrets were interrupted 5 minutes after penetration. Ten control females were bred without interruption to the same males. Both control and experimental animals were rebred in the same manner to the same males 24 hours later. Sperm were present in all postcoital washes. We allowed all females from the first experiment to proceed to their expected date of parturition. All females who had been interrupted during copulation failed to conceive, whereas all controls produced litters. In a second experiment, the same procedure was followed; however, in this experiment, ferret oviducts and uteri were flushed 10 days after copulation. Nine control females (one failed to ovulate) averaged 5.2 blastocysts (range 2-10; S.D. = 5.8) per animal. Of nine interrupted copulation ferrets (one failed to ovulate), only one animal produced a single blastocyst. The interrupted copulation group averaged 4.4 unfertilized eggs (range 2-10; S.D. = 5.0) per female. Although ferrets ovulated during short copulations, those eggs are not likely to be fertilized.

L-glutamate stimulation of the zona incerta in the rat decreases heart rate and blood pressure

Microinjections of L-glutamate into the zona incerta of pentobarbital anesthetized rats caused decreases in blood pressure and heart rate. The bradycardic response was reduced by approximately 70% after i.v. administration of atropine methyl nitrate. After combined muscarinic and beta-adrenergic blockade the bradycardic response was reduced to 90% of the control value. This suggests that the bradycardia was mediated primarily by activating the vagal outflow. Blood pressure decreases elicited after pharmacological blockade of the heart with both atropine and timolol were approximately 50% of the control values. This indicates that the zona incerta is also capable of altering stroke volume and/or inhibiting the sympathetic outflow controlling the peripheral blood vessels. By using an injectate containing L-glutamate mixed with [3H]L-glutamate and subsequent analysis of autoradiographic tissue sections, we have determined that the most reactive site is the region of the ventral zona incerta.

Cingulate gyrus of the cat receives projection fibers from the thalamic region ventral to the ventral border of the ventrobasal complex

Direct projections to the cingulate gyrus from the thalamic region lying just ventrally to the ventral border of the ventrobasal complex (VB) were found in the cat by two sets of experiments that used WGA-HRP (wheat germ agglutinin-horseradish peroxidase conjugate). In the first set of experiments, WGA-HRP was injected into the thalamic region around the ventral border of the VB. When the site of injection involved the thalamic region lying ventrally to the ventral border of the VB at the levels of the caudal two thirds of the VB, the cerebral cortex in the rostral part of the cingulate gyrus ipsilateral to the WGA-HRP injection contained fine HRP-positive granules, which indicated anterograde labeling of axon terminals. These labeled presumed axon terminals were mainly distributed to the superficial part of layer I, deep part of layer II, layer IV, and the most superficial part of layer V in the cingulate cortex. In the second set of experiments, WGA-HRP was injected into the cerebral cortex of the rostral part of the cingulate gyrus. When the site of injection involved the region of the cingulate gyrus, where presumed axon terminals had been labeled in the first set of experiments, the thalamic region just ventral to the ventral margin of the caudal two-thirds of the VB ipsilateral to the WGA-HRP injection contained neuronal cell bodies labeled retrogradely. The results indicate that some neurons that are located in the thalamic region just ventral to the ventral border of the caudal two-thirds of the VB send their axons to the cerebral cortex in the rostral part of the cingulate gyrus. The possible significance of the thalamocingulate projection found in the present study is discussed with relation to nociceptive behavior and function.

Ascending fiber projections from the midbrain central gray to the ventromedial hypothalamus in the rat

In 18 urethane-anesthetized ovariectomized female rats, 54 neurons in and around the hypothalamic ventromedial nucleus were transynaptically activated by electrical stimulation of the mesencephalic central gray matter. Ventromedial nucleus afferents from either the dorsal longitudinal fascicle (N = 10) or the medial forebrain bundle (N = 8) were disrupted by a small knife cut. In animals which lacked inputs from the dorsal longitudinal fascicle by a cut posterior to the ventromedial nucleus, transynaptic activation followed central gray stimulation in 20 cells; 26 cells were driven from the central gray in animals deprived of afferents through the medial forebrain bundle by a cut placed laterally to the ventromedial nucleus. Two patterns of synaptic activation followed electrical stimulation at 0.5 Hz: one type of response occurred during a latency range of 4 to 20 ms with fluctuation of each response less than 5 ms, the other type was characterized by diffuse activation for 50 ms following central gray stimulation. It was noted that the former time-locked response occurred in 19 among 20 cells in the posterior-cut animals, and the latter diffuse response was seen in 20 of 26 cells in the lateral-cut animals. Electrical stimulation of the ventromedial nucleus in another group of seven animals with the posterior cut caused antidromic activation of 19 central gray cells at latencies of 4.8 to 21.0 ms. Thus, central gray axons in the medial forebrain bundle were shown to have direct access to the ventromedial nucleus and multisynaptic pathways intervened for those in the dorsal longitudinal fascicle.

Afferents to the zona incerta in the rat: a combined retrograde and anterograde study

In a first set of experiments, the retrograde transport of horseradish peroxidase (HRP) was utilized to investigate the afferent projections to the zona incerta (ZI) in the hooded rat. HRP was introduced in its crystalline form into various sectors of the ZI of seven subjects. The largest contingent of afferents arises from the following centers: the cingulate and somatosensory cortices, central amygdaloid nucleus, ventromedial hypothalamic nucleus, posterior thalamic nucleus, anterior pretectal nucleus, peripeduncular area, deep and intermediate layers of the superior colliculus, dorsal and ventral parabrachial nuclei, principal and interpolar trigeminal subnuclei, and cuneate nucleus. Other centers less systematically or more sparsely labeled were the lateral hypothalamic area, ventrobasal complex, lateral geniculate nucleus pars ventralis, medial geniculate nucleus, interstitial nucleus of Cajal, Darkschewitsch nucleus, perirubral fields, cuneiform, tegmental pedunculopontine, and deep mesencephalic reticular nuclei, pontine reticular nucleus pars oralis, lateral and interpositus cerebellar nuclei, and gracile nucleus. In a second set of experiments, an anterograde tracer (WGA-HRP) was injected in several centers projecting to the ZI in order to localize their terminal fields within this structure. It has been thus possible to distinguish a ventral zone (ventral sector of pars caudalis and pars ventralis) in which the somesthetic (somatosensory cortex, trigeminal complex, and dorsal column nuclei (DCN), collicular, and cerebellar projections terminate, from a dorsal zone (pars dorsalis) to which a limbic input (cingulate cortex and ventromedial hypothalamic nucleus) is directed. In most cases, the labeled terminal fields consisted of well-delimited, narrow bands disposed obliquely, parallel to the cerebral peduncle or the internal capsule. The contingent of somatosensory afferents is relatively large and there is a high degree of overlapping between the different somatosensory terminal fields within the ventral ZI. This suggests a participation of this structure in the treatment of somesthetic information and/or in the transmission of noxious stimuli.

Afferent connections of the zona incerta: a horseradish peroxidase study in the rat

Restricted microelectrophoretic injections either of free horseradish peroxidase or of horseradish peroxidase conjugated with wheat germ agglutinin were given to albino rats in order to study the afferent connections of structures of the subthalamic region. The results suggest that the zona incerta receives its main input from several territories of the cerebral cortex, the mesencephalic reticular formation, deep cerebellar nuclei, regions of the sensory trigeminal nuclear complex and the dorsal column nuclei. Substantial input to the zona incerta appears to come from the superior colliculus, the anterior pretectal nucleus and the periaqueductal gray substance, whereas many other structures, among which hypothalamic nuclei, the locus coeruleus, the raphe complex, the parabrachial area and medial districts of the pontomedullary reticular formation, seem to represent relatively modest but consistent additional input sources. The afferentation of neurons in Forel's fields H1 and H2 appears to conform to the general pattern outlined above. As pointed out in the Discussion, the present results provide hodological support for the classic concept according to which the zona incerta can be regarded as a rostral extent of the midbrain reticular core. Some of the possible physiological correlates of the fiber connections of the zona incerta in the context of the sleep-waking cycle, ingestive behaviors, somatic motor mechanisms, visual functions and nociceptive behavior are briefly discussed.

Localization of forebrain neurons which project directly to the medulla and spinal cord of the rat by retrograde tracing with wheat germ agglutinin

Wheat germ agglutinin (WGA) in a slow-release polyacrylamide gel pellet was implanted in the medulla or spinal cord of the rat. Large numbers of retrogradely labeled cells were visualized by immunocytochemical procedures in specific nuclei of the forebrain mainly ipsilateral to the implant site following implants as far caudal as the sacral segments of the spinal cord. Total average number of labeled forebrain cells (three brains per category; 100 micron per 150 micron of brain tissue were examined microscopically): medulla, 2,115; cervical, 1,878; lumbar, 1,017; sacral, 385. After WGA-gel implants in the medulla or cervical cord the majority of retrogradely labeled neurons were seen in the lateral hypothalamic area, the zona incerta, and in subdivisions of the paraventricular nucleus. A continuum of labeled cells extended from the caudal part of the paraventricular nucleus into the posterior hypothalamus and into the central gray of the midbrain. Labeled cells were also seen in the medial basal hypothalamus and the rostral part of the bed nucleus of the stria terminalis. A few labeled cells were observed in the medial and lateral preoptic areas, the rostral part of the paraventricular nucleus, and in the arcuate nucleus. Following WGA-gel implants in the lumbar or sacral cord many retrogradely labeled cells were observed mainly in the paraventricular nucleus, the lateral hypothalamus, zona incerta, medial basal hypothalamus, and posterior hypothalamic area. The continuum of labeled cells described above was also seen following these implants. Our data indicate that the lateral hypothalamus and zona incerta, as well as specific parts of the paraventricular nucleus, are major loci of neurons which project directly to the medulla and spinal cord of the rat. The consistency with which labeled cells were localized across all brains examined within categories of implant sites and the large numbers of labeled cells counted within these areas appeared to verify the sensitivity of our retrograde tracing method. Therefore, we interpret the paucity or absence of labeled cells in particular brain regions to indicate that cells of these regions do not project to the medulla or spinal cord.

Dorsolateral funiculus and intraspinal pathways mediate vaginal stimulation-induced suppression of nociceptive responding in rats

In rats, stimulation of the vaginal cervix with a glass rod reliably produces analgesia, as measured by the tail-flick test. The present studies sought to identify the neural substrates underlying this potent pain inhibition by examining the effects of decerebration, spinalization and bilateral dorsolateral funiculus (DLF) lesions on vaginal stimulation-produced analgesia (VSPA). These studies indicate that the neural circuitry mediating VSPA is contained within the caudal brainstem and spinal cord, since decerebration did not reduce VSPA when compared with sham-operated controls. A significant though markedly reduced level of analgesia was induced in spinalized rats, indicating that VSPA involves both intraspinal and descending pathways. This descending pathway, originating within supraspinal nuclei of the caudal brainstem, projects to the spinal cord via the DLF, since DLF lesions and spinalization produced equivalent reductions in VSPA compared to sham-operated controls. These results, considered in the light of previous electrophysiological and anatomical findings, indicate that the ventral medullary region may be the source of the descending DLF projection mediating VSPA.

Efferent connections of the subthalamic region in the rat. II. The zona incerta

The efferent connections of the zona incerta (ZI) were studied experimentally in the rat by the aid of the autoradiographic tracer technique. Small microelectrophoretic injections of tritiated proline and leucine practically confined to the ZI were found to label a widespread, predominantly ipsilateral system of descending and ascending fibers distributed to reticular structures of the brain stem (mesencephalic reticular formation, nucleus tegmenti pedunculopontinus pars compacta, parabrachial area, nuclei reticularis pontis oralis, pontis caudalis, gigantocellularis and medullae oblongatae, pars ventralis), precerebellar nuclei (nucleus reticularis tegmenti pontis, pontine nuclei and inferior olivary complex), the middle and deep layers of the superior colliculus, the pretectum (anterior, posterior and medial pretectal nuclei), perioculomotor nuclei (interstitial nucleus of Cajal, nucleus of Darkschewitsch and nuclei of th posterior commissure), the parvocellular portion of the red nucleus, the central gray substance, the nucleus tegmenti dorsalis lateralis, the ventral horn of the cervical spinal cord, non-specific thalamic nuclei (parafascicular, centralis medius, paracentralis, centralis lateralis and ventromedial thalamic nuclei, nucleus reuniens), basal ganglia (entopeduncular nucleus and globus pallidus), hypothalamic structures (posterior hypothalamic nucleus, dorsal and lateral hypothalamic areas), and a subpallidal district of the substantia innominata. Isotope injections centered in Forel's field H1 resulted in the labeling of a similar set of projections. Some of the possible functional correlates of these connections are briefly discussed.