The hypothalamus: Neural systems involved in feeding, irritability, aggression, and copulation in male rats.

In 3 experiments with a total of 58 male hooded rats, cuts of the ventral amygdalofugal pathway resulted in slight aphagia, and cuts anterior to the medial preoptic area resulted in transient hyposexuality. A unilateral posterior medial forebrain bundle (MFB) cut combined with a contralateral parasagittal cut resulted in severe hyposexuality if the parasagittal cut lay lateral to the anterior hypothalamic nucleus, and in irritability if the parasagittal cut lay lateral to the ventromedial hypothalamic nucleus. It is concluded that (a) the medial hypothalamic nuclei exert their effects on irritability and copulation through their lateral connections with those components of the MFB that descend on, or ascend from, the lower brain stem; and (b) the neural pathways mediating the consummatory aspects of feeding, irritability, aggression, and copulation are distinct. (58 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Midbrain and motivated behavior.

Obtained measures of eating, drinking, irritability, aggression, and copulation in 57 hooded male rats before and after they were subjected to midbrain knife cuts or control operations. Slight hypophagia resulted from cuts through the supramammillary and ventral tegmental decussations. Severe-to-moderate hyposexuality resulted from cuts involving either the medial lemniscus and zona incerta or the ventral reticular formation. Cuts through the central gray or dorsal reticular formation produced no significant behavioral effects. It is suggested that the medial lemniscus and the ventral reticular formation convey an ascending sensory-arousal influence that facilitates copulation. (25 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hypothalamic knife cuts: Effects on eating, drinking, irritability, aggression, and copulation in the male rat.

Describes 2 experiments with a total of 43 male hooded rats. In Exp. I, Ss with parasagittal knife cuts that separated the medial from the lateral hypothalamic areas (a) became hyperphagic, hyperdipsic, obese, and irritable; (b) did not change their level of aggressive responses against mice; and (c) copulated at an impaired rate or not at all. In Exp. II, 2 groups of Ss were subjected to coronal cuts restricted between the fornices at levels either anterior or posterior to the ventromedial hypothalamic nuclei. Most of the anterior-cut Ss increased their food and water intake, and some became irritable. Of the posterior-cut Ss, none increased and 1/2 decreased their food intake, some became hyperdipsic, and 1 became irritable. Neither of the coronal-cut groups changed levels of aggressive or sexual responses. It is concluded that the mediolateral hypothalamic connections are important for eating, irritability, and copulation. (42 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The septum: Neural systems involved in eating, drinking, irritability, muricide, copulation, and activity in rats.

Measured eating, drinking, irritability, muricide, and copulation in 45 male albino Wistar rats before and after 1 of 3 coronal knife cuts in the septal region or a control operation. Activity was also measured postoperatively in the 3 experiments. Cuts posteroventral to the septum resulted in slight hypophagia, marked hyperdipsia, irritability, asexuality, and decrease in activity. Cuts of the fornix resulted only in slight decrease in activity. Cuts through the anterior septum resulted in irritability, slight hyposexuality, and slight decrease in activity. No significant correlations between the various behavioral effects were found. It is suggested that the neural pathways mediating eating, drinking, irritability, muricide, copulation, and activity are relatively distinct and that neural activity in the septal region probably does not influence behavior in any unitary fashion. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feeding and drinking pathways between medial and lateral hypothalamus in the rat.

Carried out 3 experiments, using 101 female rats of the CFE strain. Bilateral parasagittal transections were made at different lateral and dorsal-ventral positions in and between the ventromedial hypothalamus (VMH) and lateral hypothalamus (LH). Cuts through or just lateral to the VMH produced hyperphagia and obesity, while cuts through or medial to the LH produced, depending upon their exact position and the diet, either temporary aphagia-hypophagia, mild hyperphagia, or no effect. The cuts medial to the LH, but not the others, abolished insulin-induced eating. All cuts produced deficits in drinking regulation that varied according to their exact position. These deficits included hypodipsia, mild hyperdipsia, and reduced water/food ratios, as well as reduced drinking responses to food deprivation, water deprivation, hypertonic sodium chloride injections, and polyethylene glycol injections. The knife cuts also produced changes in gustatory reactivity. The hypothalamic pathways responsible for these effects are discussed. (54 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple knife cuts between the medial and lateral hypothalamus in the rat: A reevaluation of hypothalamic feeding circuitry.

In 2 experiments single or multiple sets of bilateral knife cuts were made in a total of 73 female CFE rats just lateral to the ventromedial hypothalamus (VMH) and/or just medial to the lateral hypothalmus (LH). The lateral VMH knife cuts by themselves produced greater hyperphagia and obesity than did the medial LH cuts. The lateral VMH knife cuts also significantly increased food intake and body weight in Ss previously given bilateral cuts along the medial LH border. Findings indicate that the feeding inhibitory fibers responsible for the hyperphagia syndrome do not project from the VMH to the LH, and this calls for a reevaluation of hypothalamic circuitry. It was also discovered that sham surgery in 7 Ss had a significant suppressive effect on the hyperphagia syndrome produced by hypothalamic knife cuts. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Destruction of the medial forebrain bundle caudal to the site of stimulation reduces rewarding efficacy but destruction rostrally does not.

Rats with an electrode in the medial forebrain bundle (MFB) in or near the ventral tegmental area and another at the level of the rostral hypothalamus sustained large electrolytic lesions at either the rostral or the caudal electrode. The rewarding efficacy of stimulation through the other electrode was determined before and after the lesion. Massive damage to the MFB in the rostral lateral hypothalamus (LH) generally had little effect on the rewarding efficacy of more caudal stimulation, whereas large lesions in the caudal MFB generally reduced the rewarding efficacy of LH stimulation by 35–60%. Similar reductions were produced by knife cuts in the caudal MFB. These results appear to be inconsistent with the hypothesis that the reward fibers consist either of descending or ascending fibers coursing in or near the MFB. It is suggested that the reward fibers are collaterals from neurons with both their somata and their behaviorally significant terminals located primarily in the midbrain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Septal complex of the telencephalon of lizards: III. Efferent connections and general discussion

The projections of the septum of the lizard Podarcis hispanica (Lacertidae) were studied by combining retrograde and anterograde neuroanatomical tracing. The results confirm the classification of septal nuclei into three main divisions. The nuclei composing the central septal division (anterior, lateral, medial, dorsolateral, and ventrolateral nuclei) displayed differential projections to the basal telencephalon, preoptic and anterior hypothalamus, lateral hypothalamic area, dorsal hypothalamus, mammillary complex, dorsomedial anterior thalamus, ventral tegmental area, interpeduncular nucleus, raphe nucleus, torus semicircularis pars laminaris, reptilian A8 nucleus/substantia nigra and central gray. For instance, only the medial septal nucleus projected substantially to the thalamus whereas the anterior septum was the only nucleus projecting to the caudal midbrain including the central gray. The anterior and lateral septal nuclei also differ in the way in which their projection to the preoptic hypothalamus terminated. The midline septal division is composed of the dorsal septal nucleus, nucleus septalis impar and nucleus of the posterior pallial commissure. The latter two nuclei projected to the lateral habenula and, at least the nucleus of the posterior pallial commissure, to the mammillary complex. The dorsal septal nucleus projected to the preoptic and periventricular hypothalamus and the anterior thalamus, but its central part seemed to project to the caudal midbrain (up to the midbrain central gray). Finally, the ventromedial septal division (ventromedial septal nucleus) showed a massive projection to the anterior and the lateral tuberomammillary hypothalamus. Data on the connections of the septum of P. hispanica and Gecko gekko are discussed from a comparative point of view and used for better understanding of the functional anatomy of the tetrapodian septum.     

Hyperphagia and obesity produced by parasagittal and coronal hypothalamic knife cuts: Further evidence for a longitudinal feeding inhibitory pathway.

Hyperphagia and obesity are produced by parasagittal knife cuts through the medial hypothalamus and by coronal knife cuts through the posterior hypothalamus. Results of the present series of experiments with 91 female CFE rats indicate that the 2 types of cuts produce their overeating effect by severing the same neural pathway. Exp I demonstrated that unilateral parasagittal knife cuts combined with contralateral coronal cuts in either the posterior hypothalamus or the midbrain significantly increased food intake and body weight. Exp II revealed that bilateral parasagittal cuts and bilateral coronal cuts in the hypothalamus produced qualitatively similar effects on food intake, diurnal ingestive pattern, finickiness, and amphetamine anorexia. The 2 types of cuts differentially altered water intake, however. In Exp III, coronal cuts in the posterior hypothalamus, like parasagittal cuts in the medial hypothalamus, increased the food intake and body weight of Ss previously given bilateral parasagittal transections through the lateral perifornical region. The neuroanatomy and neurochemistry of the longitudinal feeding inhibitory pathway suggested by these results are discussed. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prefrontal cortical projections to the hypothalamus in macaque monkeys

The organization of projections from the macaque orbital and medial prefrontal cortex (OMPFC) to the hypothalamus and related regions of the diencephalon and midbrain was studied with retrograde and anterograde tracing techniques. Almost all of the prefrontal cortical projections to the hypothalamus arise from areas within the "medial prefrontal network," as defined previously by Carmichael and Price ([1996] J. Comp. Neurol. 371:179-207). Outside of the OMPFC, only a few neurons in the temporal pole, anterior cingulate and insular cortex project to the hypothalamus. Axons from the OMPFC also innervate the basal forebrain, zona incerta, and ventral midbrain. Within the medial prefrontal network, different regions project to distinct parts of the hypothalamus. The medial wall areas 25 and 32 send the heaviest projections to the hypothalamus; axons from these areas are especially concentrated in the anterior hypothalamic area and the ventromedial hypothalamic nucleus. Orbital areas 13a, 12o, and Iai, which are related to the medial prefrontal network, selectively innervate the lateral hypothalamic area, especially its posterior part. The cellular regions of the paraventricular, supraoptic, suprachiasmatic, arcuate, and mammillary nuclei are conspicuously devoid of cortical axons, but many axons abut the borders of these nuclei and may contact dendrites that extend from them. Areas within the orbital prefrontal network on the posterior orbital surface and agranular insula send only weak projections to the posterior lateral hypothalamic area. The rostral orbital surface does not contribute to the cortico-hypothalamic projection.     

Medial hypothalamic involvement in maternal aggression of rats.

Extensive electrolytic lesions of the medial hypothalamus, or more restricted ones in its ventral division, decreased maternal aggression in rats operated upon on postpartum Days 2 and 3 and tested with female intruders 4 days later. Maternal aggression was attenuated also in mothers receiving intrahypothalamic infusions with ibotenic acid or parasagittal knife cuts along the lateral border of the ventromedial hypothalamic nucleus; in addition, the females with ibotenate lesions or knife cuts showed impaired lordosis behavior. None of the hypothalamic interventions were associated with deficits in pup retrieval. Lactation was impaired in groups with hypothalamic electrocoagulations but not in mothers with ibotenate lesions or knife cuts. The results suggest that the ventromedial hypothalamus and its lateral connections participate in control of maternal aggression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of knife-cut lesions of the medial forebrain bundle in self-stimulating rats.

Unilateral frontal-plane knife-cut lesions were made in the anterior medial forebrain bundle ipsilateral to a lateral hypothalamic self-stimulation electrode. Behavioral effects of the knife cut on self-stimulation reward and operant performance capacity were measured via the reward summation function method. Knife cuts placed at the level of the anterior commissure were ineffective in altering reward or motor/performance capacity, whereas knife cuts just posterior in the caudal lateral preoptic area degraded reward and sometimes impaired motor/performance capacity. In a second experiment, knife cuts placed posterior to the ventral tegmental area were ineffective unless they intruded on the ventral tegmental area itself. Several small knife cuts placed just anterior to the ventral tegmental were effective in reducing self-stimulation reward. The results are discussed in terms of the anatomical substrate of lateral hypothalamic self-stimulation reward and as a first step in a larger mapping study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-stimulation of the habenular complex in the rat.

65 male hooded Long-Evans rats learned to barpress for rewarding electrical stimulation of the medial or lateral habenular nucleus or the fasciculus retroflexus, but not the surrounding thalamic nuclei. Response rates were moderate and steady and were not influenced by food or water deprivation. Habenular self-stimulation was significantly facilitated by placing lesions in the ipsilateral anterior part of the medial forebrain bundle (MFB). Similarly, MFB self-stimulation was enhanced by ipsilateral habenular lesions. Lesions centered in the region of median raphe nucleus suppressed habenular self-stimulation for more than 4 wks. Self-stimulation of median raphe was not affected by habenular lesions. Results show that habenular stimulation can produce a rewarding effect by exciting neurons in the region of the raphe nuclei but apparently without requiring the participation of the well-known MFB reward system. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deficient passive and one-way active avoidance acquisition following medial forebrain bundle lesions in rats.

In 3 experiments with 93 Long-Evans male hooded rats, cathodal electrolytic lesions of the medial forebrain bundle (MFB) at posterior hypothalamic levels produced a mild, transient hypodipsia and lowered jump thresholds to footshock. Lesions produced marked deficits in passive avoidance performance in a paradigm that paired discrete, linearly incrementing footshock intensities with contact of a water spout following 48 hrs of water deprivation. Injections of levo-dextro-5-hydroxytryptophan (75 mg g, ip), the immediate metabolic precursor of serotonin, had no effect on the passive avoidance performance of either experimental or operated control Ss. Lesions of the MFB also resulted in deficient acquisition in a 1-trial step-through passive avoidance paradigm not using motivation to drink and caused a severe acquisition deficit in a 1-way active avoidance task. Lesions of the septal nuclei produced lowered jump thresholds but did not affect acquisition in the 1st passive avoidance task. Results are interpreted as indicating a lesion-induced deficiency in fear learning, independent of the serotonergic functions of the MFB. (45 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increased ipsilateral expression of Fos following lateral hypothalamic self-stimulation

Immunohistochemical labeling of Fos protein was used to visualize neurons activated by rewarding stimulation of the lateral hypothalamic level of the medial forebrain bundle (MFB). Following training and stabilization of performance, seven rats were allowed to self-stimulate for 1 h prior to anesthesia and perfusion. Brains were then processed for immunohistochemistry. Two control subjects were trained and tested in an identical manner except that the stimulator was disconnected during the final 1 h test. Among the structures showing a greater density of labeled neurons on the stimulated side of the brains of the experimental subjects were the septum, lateral preoptic area (LPO), medial preoptic area, bed nucleus of the stria terminalis, substantia innominata (SI), and the lateral hypothalamus (LH). Several of these structures, the LPO, SI, and LH, have been implicated in MFB self-stimulation by the results of psychophysical, electrophysiological, and lesion studies.     

Approach and withdrawal analysis of the effects of hypothalamic stimulation and lesions in rats.

Identified "purely" rewarding lateral hypothalamic and "purely" aversive medial hypothalamic electrodes in a paradigm in which Charles River male rats both initiated and terminated hypothalamic stimulation. Ss were then given a series of tests designed to assess the effects of brain stimulation on approach and withdrawal behaviors. Lateral hypothalamic stimulation facilitated approach behaviors and suppressed withdrawal behaviors, whereas medial hypothalamic stimulation produced largely the opposite effects. No serious motor deficits due to stimulation were detected with either type of electrode. In a 2nd experiment, the approach–withdrawal effects of bilateral lateral hypothalamic lesions were tested and found to suppress approach behaviors and facilitate withdrawal behaviors. Other neurological examinations revealed motor deficits, but these did not account for the specific pattern of results observed on the approach–withdrawal test. These approach–withdrawal phenomena are interpreted in terms of altering a natural balance between approach and withdrawal behavior facilitating systems in the lateral and medial hypothalamus, respectively. (43 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Location of neurons that express regulated endocrine-specific protein-18 in the rat diencephalon

In situ hybridization for regulated endocrine-specific protein-18 messenger RNA showed a distinct and limited pattern of expression in the hypothalamus, midline thalamus, amygdala and hippocampus of the rat. High levels of regulated endocrine-specific protein-18 messenger RNA were found in the magnocellular neurons of the hypothalamic paraventricular, supraoptic and accessory nuclei, in the neurons of the periventricular, medial tuberal, arcuate, lateral and perifornical nuclei, infundibular stalk, and in the ventrolateral division of the ventromedial nucleus and compact division of the dorsomedial nucleus. Lower levels of regulated endocrine-specific protein-18 messenger RNA were found in the parvocellular divisions of the paraventricular nucleus as well as in the bed nucleus of the stria terminalis, median preoptic nucleus, medial preoptic nucleus, medial and lateral preoptic areas, subfornical organ, suprachiasmatic nucleus, anterior hypothalamic area, zona incerta, ventromedial nucleus, dorsomedial nucleus and tuber cinereum. Regulated endocrine-specific protein-18 messenger RNA was also found in thalamic structures including the paraventricular, central medial, intermediodorsal, anterodorsal, rhomboid and reticular nuclei. Signal was also identified in the medial and lateral habenula, in the central, medial, basomedial and anterior cortical nuclei of the amygdala, and in the CA1-CA3 and dentate gyrus of the hippocampus. Dopamine may regulate regulated endocrine-specific protein-18 expression in the CNS because (i) regulated endocrine-specific protein-18 was originally identified in melanotropes based on its regulation by dopaminergic agents and (ii) many of the nuclei that contain regulated endocrine-specific protein-18 also receive dopaminergic input. The localization of regulated endocrine-specific protein-18 in the diencephalon suggests that regulated endocrine-specific protein-18 is involved in regulation of limbic and autonomic function, neuroendocrine control of salt and water balance, reproductive function and feeding behavior.     

Medial preoptic area and maternal behavior in the female rat.

Reports results of 3 experiments with a total of 92 postpartum lactating female Wistar rats. Medial preoptic area lesions severely disrupted maternal behavior, whereas lesions of the stria terminalis and medial cortico-hypothalamic tract knife cuts were without effect. Parasagittal knife cuts that severed the mediolateral connections of the preoptic-anterior hypothalamic continuum also severely disrupted maternal behavior. The lesions and knife cuts which disrupted maternal behavior had no effect on female sexual behavior. It is concluded that the medial preoptic area and its lateral connections are essential for the normal display of maternal behavior in postpartum lactating female rats. Evidence also indicates that independent neural mechanisms for the control of maternal behavior and sexual behavior exist within the hypothalamus of female rats. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A copulatory system in the hypothalamus and tegmentum of the domestic chick

A tract in the chick is described that runs from the posterior nucleus paraventricularis magnocellularis (PVM) through the lateral hypothalamus to a small area of the anterior tegmentum, which is adjacent to the ventral tegmental area. Bilateral lesions of the posterior PVM or of the PVM tract or of its tegmental destination abolish the facilitation of copulation in male chicks by testosterone. The effect is specific in that the facilitation of attack is either unaffected or only slightly depressed by such lesions, while being itself specifically depressed by other hypothalamic lesions. No other hypothalamic tracts were found that were necessary for the facilitation of copulation. An equivalent copulatory system probably exists in the mammal, with a more diffuse distribution in the preoptic area but with similar connections back to the tegmentum.