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Results for “Medial Forebrain Bundle”

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At least 19 recordsLinked to original sources

PubMed1977

Effects of lesions of various medial forebrain bundle components on lateral hypothalamic self-stimulation.

Unilateral lesions of various medial forebrain bundle components were assessed for their effects on lateral hypothalamic self-stimulation. Damage of areas containig nigrostriatal dopaminergic or ascending noradrenergic neurons had negligible effects on bar pressing, tail moving and alley running for hypothalamic stimulation. Lesions which appeared to destroy most or all of the catecholaminergic fibers in the posterior medial forebrain bundle virtually eliminated reinforced bar pressing and tail moving, but only partially suppressed alley running. The results suggest that brain stimulation reinforcement of the bar press and tail movement tasks depends upon the integrity of neural tissue in the area of the catecholaminergic pathways of the medial forebrain bundle, but not upon specific dopaminergic or noradrenergic systems. The data further suggest that the reinforcement of alley running is at least partially mediated by different neural tissue (possibly non-catecholaminergic) at the level of the posterior medial forebrain bundle lesions.

Animals↗

PubMed1979

Neural connexions between the medial forebrain bundle, the preoptic area and the basal hypothalamus in the rat: an electrophysiological study.

1. Electrophysiological experiments have been performed on intact cycling female rats to investigate the neural connexions that exist between the medial forebrain bundle, the anterior hypothalamic region, which included the preoptic area, and the basal hypothalamus. Recordings have been made from a total of 351 neurones in the anterior hypothalamus of which 216 were responsive to stimulation of either or both the medial forebrain bundle and basal hypothalamus (arcuate and ventromedial nuclei).2. Forty-six of these cells were responsive to a stimulus applied both to the medial forebrain bundle and the basal hypothalamus with a variety of response combinations. The majority of neurones were orthodromically activated by stimulation in both sites. Inhibition by stimulation of the medial forebrain bundle coupled with orthodromic excitation from the basal hypothalamus, or the reverse situation, was also encountered frequently.3. A few cells were antidromically invaded by the stimulation of the medial forebrain bundle and these received orthodromic or inhibitory inputs from the basal hypothalamus, although one unit outside the anterior hypothalamus was antidromically activated by both stimuli.4. Ninety per cent of all the doubly responsive units that could be antidromically activated by stimulation of the basal hypothalamus received an orthodromic input from the medial forebrain bundle, and no cells in the anterior hypothalamus that projected to the basal hypothalamus were found to receive an inhibitory input from the medial forebrain bundle.5. These results provide electrophysiological evidence for inhibitory and excitatory inputs from the medial forebrain bundle to the preoptic and anterior hypothalamic cells that either project to, or receive connexions from, the basal hypothalamus. Neurones in the preoptic area which project to the basal hypothalamus are implicated in the control of anterior pituitary function, particularly gonadotrophin secretion. These experiments, coupled with functional studies, suggest that there is an excitatory input from the medial forebrain bundle to these preoptic and anterior hypothalamic cells which may modulate adenohypophyseal secretions.

Animals↗

PubMed1979

Light and electron microscopic studies on the medial forebrain bundle in the rat. ii. nerve terminals from the medial hypothalamus.

After the surgical interruption of connections between the medial and lateral hypothalamus of the rat axonal (transient) and nerve terminal degeneration was shown in the medial forebrain bundle (MFB) with light and electron microscopy. Following 1 mm long parasagittal cuts at various rostro-caudal levels the degeneration pattern within the MFB indicated a certain territoral arrangement of terminating fibres from the medial hypothalamus. After a parasagittal cut through the lateral retrochiasmatic area, degeneration was observed in the full length of the MFB. This suggests that a number of axons connect the medial and lateral hypothalamus through this area. With the aid of a parasagittal cut separating totally the medial and lateral hypothalamus, the degeneration of dendrites in the middle portion of the lateral hypothalamus was also revealed. These proved to derive from cells of the ventromedial nucleus.

Animals↗

PubMed1978

Cocaine: acute effects on reinforcement thresholds for self-stimulation behavior to the medial forebrain bundle.

Reinforcing thresholds for self-stimulation behavior to the medial forebrain bundle were determined in rats by means of rate-free psychophysical method. The acute administration of cocaine lowered the reinforcing thresholds independent of motor stimulatory effects. These results indicate that cocaine affects the sensitivity of the reward pathways in the brain, and further demonstrate the utility of rate-independent methods in the assessment of drug effects on self-stimulation behavior.

Animals↗

PubMed1979

Interactions of septal evoked responses to stimulation of the fornix and medial forebrain bundle.

Gross and single unit septal evoked response to stimulation of the fornix and medial forebrain bundle (MFB) were studied in anesthetized, acutely prepared rats. Stimulation of the fornix and MFB produced short-latency antidromic and synaptic activation of localized groups of septal target cells. In addition, stimulation of either pathway produced inhibition of spontaneous single cell activity. The interactions of these responses were studied by delivering paired stimuli to the fornix and/or MFB. A prior stimulus to the fornix potentiated the responses of cell groups synaptically activated by subsequent fornical stimulation, but briefly depressed the sunaptic activation of septal cells by subsequent MFB stimulation. A prior stimulus to the MFB slightly potentiated the synaptic activation of septal cells by a subsequent MFB stimulus, but depressed the responses of cell groups synaptically activated by a subsequent stimulus to the fornix. These results were discussed in terms of their implications for septal organization and function.

Animals↗

PubMed1978

Responses and pharmacological properties of preoptic/anterior hypothalamic neurones following medial forebrain bundle stimulation.

1. The responses of neurones in the anterior hypothalamic and preoptic areas (POA/AHA) to stimulation of the medial forebrain bundle (MFB) have been studied in urethane anaesthetized female rats. Extracellular unit recordings have been made from 150 neurones which were responsive to a single stimulus applied to the MFB at the level of the mammillary nucleus. 2. Forty-five per cent of these cells were orthodromically activated with latencies ranging from 7.5 to 100 msec. However, the majority of cells responded with latencies of less than 40 msec. 3. Marked inhibition of spontaneous activity was observed in 41.5% of the units. Response latencies of up to 40 msec were observed in these cells, the inhibitory periods lasting up to 150 msec. 4. A small proportion of cells (13.5%) were antidromically activated and the average conduction velocity of these neurones in the POA/AHA with axons passing down to the mid-brain was estimated to be 0.3 m sec-1. It is suggested that they represent part of the descending MFB. 5. The experiments did not show any discrete topographical organization of cells in the POA/AHA which could be driven by MFB stimulation although the units tended to be located in more lateral rather than medial areas. 6. The responses to iontophoretically applied dopamine (DA) or noradrenaline (NA) was tested on sixty-one cells. These amines suppressed the activity of the majority of both orthodromically activated and inhibited units; the remaining cells were unresponsive. 7. These results provide electrophysiological evidence for both a direct and indirect input of MFB fibres to cells in the POA/AHA and that these inputs can be either excitatory or inhibitory. The data also indicate that a small number of fibres in the descending MFB originate from cells in the POA/AHA. 8. The sensitivity of these units to NA and DA suggests an inhibitory aminergic input, although this evidence is as yet indirect. 9. These connexions of the MFB, with neurones in the POA/AHA may be part of the neural circuits important for extra-hypothalamic modulation of gonadotrophin secretion.

Animals↗

PubMed1977

Hypothalamic adrenaline synthesis after stimulation of the medial forebrain bundle.

1 The problem of whether locally released noradrenaline can be methylated to adrenaline in the hypothalamus has been investigated. 2 During stimulation of the medial forebrain bundle (MFB) the hypothalamic adrenaline content increased somewhat, but the increase was not statistically significant (13%, mean of 10 experiments). 3 After inhibition of the activity of monoamine oxidase and catechol-O-methyltransferase this increase was much larger (80%, mean of 9 experiments). 4 Adrenalectomy did not prevent the rise in hypothalamic adrenaline after stimulation of the MFB. These results suggest that noradrenaline released during activity of noradrenergic hypothalamic structures may be methylated to adrenaline in the hypothalamus.

Adrenalectomy↗

PubMed1979

Synaptosomal uptake of hypothalamic monoamines and recovery of pituitary-adrenal activity following medial forebrain bundle lesions in rats.

The normal diurnal variation in plasma corticosterone (COR) was abolished and the response to ether stress was enhanced at 3 days following the production of medial forebrain bundle (MFB) lesions in male rats. However, by 7 days following surgery, basal plasma COR levels and the response to ether stress appeared normal. These alterations and subsequent recovery of pituitary-adrenal activity were accompanied by decreasing hypothalamic synaptosomal uptake of serotonin (5HT) and increasing synaptosomal uptake of dopamine (DA), evident at 3 and continuing at 7 days following the lesion. Uptake of norepinephrine (NE) was not affected at 3 days but showed a reduction at 7 days following surgery. The results suggest that disruption of ascending 5HT and NE fibers to the hypothalamus can alter pituitary-adrenal activity but that normal activity recovers by 7 days following the lesion. The correlation between recovery of pituitary-adrenal activity and increases in the normal uptake of hypothalamic DA suggest that DA may interact with 5HT and NE systems in the normal control of adrenocorticotrophin (ACTH) release.

Animals↗

PubMed1979

Light and electron microscopic studies on the medial forebrain bundle in the rat. I. Nerve terminals in the lateral hypothalamus of extrahypothalamic origin.

Degenerated nerve terminals were demonstrated in the lateral hypothalamus of the rat following transection of the rostral and caudal fibres to the medial forebrain bundle (MFB) and a parasagittal cut along the lateral edge of the hypothalamus. In the light of these findings the termination of extrahypothalamic MFB pathways on intrinsic neurons is assumed.

Animals↗

PubMed1979

Evaluation of the non-specific effects of catecholamine and serotonin neurotoxins by injection into the medial forebrain bundle of the rat.

Low doses of 6-hydroxydopamine (6-OHDA), 5,6-dihydroxytryptamine (5,6-DHT) and 5,7-dihydroxytryptamine (5,7-DHT) that have previously been shown to produce behavioral change following intracerebral infusion were injected into the medial forebrain bundle of the rat. This site contains serotonin (5-HT), norepinephrine (NE), and dopamine (DA) fibers whose anatomical locations have been described. Damage to these fiber systems was quantified by measuring depletion of telencephalic 5-HT, NE and DA. The effects of infusions of 6-OHDA, 5,6-DHT and 5,7-DHT were compared to the effects of unequivocally non-specific electrolytic lesions and copper sulfate infusions. Survival time was varied to evaluate the amount of regeneration that could be expected over periods from 8 to 60 days. Amine levels were found to be stable over the time period examined. With the doses used, evidence was found to support the position that non-specific damage caused by general cytotoxic effects of 6-OHDA and 5,7-DHT is minimized sufficiently to permit the acquisition of useful data on the function of central catecholamine and indoleamine systems.

5,6-Dihydroxytryptamine↗

PubMed1978

Failure of medial forebrain bundle or raphe ablation to alter the daily temperature rhythm of the rat.

The data presented in the present study suggest that neither the ascending noradrenergic fibres confined to the MFB nor the serotonergic fibres originating in or passing through the mesencephalic raphe are essential for periodicity in body temperature. Both control and experimental groups, i.e., rats subjected to medial forebrain bundle or raphe ablation presented circadian periodicity in body temperature and neither the phase, amplitude or overall mean of experimentals differed significantly from controls.

Animals↗

PubMed1975

A comparison of drug-induced rotation in rats lesioned in the medial forebrain bundle with 5,6-dihydroxytryptamine or 6-hydroxydopamine.

Drug-induced rotational behaviour was studied in two groups of rats with differing chemical lesion of the right medial forebrain bundle (MFB). 6-hydroxydopamine (6-OH-DA), 3.5 mug, injected in one group, induced a marked lowering of dopamine (DA) and noradrenaline (NA) in the right hemiforebrain. 5,6-Dihydroxytryptamine (5,6-HT), 10 mug, injected in a second group, produced a profound and long-lasting depletion of 5-hydroxytryptamine (5-HT) and DA, but not of NA. Rotational behaviour induced in both groups by DA receptor agonists (apomorphine, piribedil, L-DOPA, ergometrine, ergocornine, 2-bromo-alpha-ergocryptine, ergocristine, methylergometrine) and agents releasing DA (d-methamphetamine, methylphenidate) were qualitatively identical and quantitatively very similar, suggesting a minor role of 5-HT striatal terminals in these experimental conditions. LSD induced contralateral rotation by direct stimulation of the DA receptor, while L-5-hydroxy-tryptophan (L-5HTP) was inactive.

5,6-Dihydroxytryptamine↗

PubMed1978