Midbrain Transection Research Articles

Bilateral midbrain transection induced hyperphagia accelerates the development of diabetes in Spontaneously Diabetic Torii (SDT) rats

Spontaneously Diabetic Torii (SDT) rat is a model of severe type 2 diabetes and its complications. These characteristics of SDT rat are very useful to research diseases; however, the slow onset of diabetes may limit the usefulness of this animal model. To solve this problem, we performed bilateral midbrain transection on SDT rats and evaluated whether hyperphagia accelerates the onset of diabetes. By severing ascending fibers from the nucleus tractus solitarius to limbic regions through ventral and dorsal tegmental regions, food consumption was significantly increased in SDT rats and the onset of diabetes was accelerated. Cumulative incidence of diabetes in midbrain transected SDT rats was 88.9% at 7 weeks after surgery (14 weeks of age), while sham operated rats was 20.0%. Increased food consumption was correlated to body weight, plasma glucose level, plasma triglyceride level, and plasma insulin level. In conclusion, the overeating caused by blocking anorexigenic signal in brain significantly accelerates the onset of diabetes in SDT rats. The early development of type 2 diabetes may accelerate microvascular complications and is considered useful in the study of the disease in SDT rats.

Insulin-Resistance-Associated Compensatory Mechanisms of Pancreatic Beta Cells: A Current Opinion

Insulin-Resistance-Associated Compensatory Mechanisms of Pancreatic Beta Cells: A Current Opinion

Intestinal fatty acid infusion modulates food preference as well as calorie intake via the vagal nerve and midbrain–hypothalamic neural pathways in rats

The intestine plays important roles in the regulation of feeding behavior by sensing macronutrients. Intestinal fatty acids strongly suppress food intake, but little is known about whether intestinal fatty acids affect food preference. We investigated the effects of jejunal fatty acids infusion on food preference by conducting two-diet choice experiments in rats fed a high-fat diet (HFD) and a high-carbohydrate diet (HCD). Jejunal linoleic acid (18:2) infusion reduced HFD intake dose-dependently, while HCD intake increased with the middle dose of the infusion we examined (100 μL/h) and reduced to the control level with the higher doses (150 and 200 μL/h). α-Linolenic acid (18:3), but not caprylic acid (8:0), altered the food preference and total calorie intake in the same manner as linoleic acid. Linoleic acid infusion dose-dependently increased plasma glucagon-like peptide-1, peptide YY and cholecystokinin levels, but not ghrelin levels. Subdiaphragmatic vagotomy or midbrain transection prevented the change in food preference and total calorie intake by linoleic acid infusion. Jejunal linoleic acid infusion increased norepinephrine turnover in the paraventricular hypothalamic nucleus, while intracerebroventricular injection of idazoxan, an α2-adrenergic receptor (AR) antagonist, suppressed the increased HCD intake, but did not affect the decreased HFD intake. These findings indicated that intestinal long-chain fatty acids modulated food preference as well as total calorie intake via the vagal nerve and midbrain–hypothalamic neural pathways. The effects of the α2-AR antagonist in the brain suggested that the brain distinctly controlled HCD and HFD intake in response to jejunal linoleic acid infusion.

Is the periaqueductal gray an essential relay center for the micturition reflex pathway in the cat?

The periaqueductal gray (PAG), especially in a region between the levels the oculomotor nucleus and the trochlear nucleus, was suggested to be the essential relay center that conveys information of bladder fullness to the pontine micturition center (Barrington's nucleus). The present study examined this hypothesis by transecting the brainstem in anesthetized cats. In eight cases of the midbrain transection, all ( n = 3) or most ( n = 5) of the PAG between the levels the oculomotor nucleus and the trochlear nucleus was separated from the intact side of the brain. Furthermore, in the former three cases, the PAG at the level caudal to the trochlear nucleus was separated from the intact brain by more than half ( n = 2) or completely ( n = 1). In all these cases, there were no remarkable differences in the amplitude of the micturition contraction (80–98% of that before transection), irrespective of the levels of the transection. In the cases of the pontine transection, micturition contraction disappeared after transecting through the caudal part of Barrington's nucleus ( n = 1) or through regions caudal to this nucleus ( n = 5). In the one case that received a transection through the rostral part of Barrington's nucleus, the amplitude of the micturition contraction was 43% of that before transection. This study demonstrates that Barrington's nucleus is essential, but the PAG is not essential, for evoking micturition. Our results suggest that the information of bladder fullness in the cat is conveyed to Barrington's nucleus either directly from the lumbosacral neurons or indirectly via relay neurons located below the midbrain.

In the flicker of an eye

In the flicker of an eye

The vagal afferent pathway does not play a major role in the induction of satiety by intestinal fatty acid in rats

Intestinal infusion of long-chain fatty acids (LCFAs) strongly suppresses food intake and gut motility. Vagal afferents and cholecystokinin (CCK) signaling pathway are considered to play important roles in intestinal LCFA-induced satiety. Here, we first investigated the influence of vagus nerve on satiety following intestinal LCFA infusion in rats. Jejunal infusion of linoleic acid (LA) at 200 microL/h for 7 h suppressed food intake and the effect lasted for 24 h. The satiety induced by jejunal LA infusion occurred in a dose dependent manner. In contrast, the anorectic effect induced by octanoic acid, a medium-chain fatty acid, was weaker than that induced by LA. The reduction in food intake induced by jejunal LA infusion was not attenuated in rats treated with vagotomy, the ablation of bilateral subdiaphragmatic vagal trunks. Jejunal LA-induced satiety could also be observed in rats with bilateral midbrain transections, which ablates fibers between the hindbrain and hypothalamus. These findings suggest that the vagus nerve and fibers ascending from the hindbrain to the hypothalamus do not play a major role in intestinal LCFA-induced satiety. Jejunal LA infusion also reduced food intake in CCK-A receptor-deficient OLETF rats, suggesting that CCK signaling pathway is not critical for intestinal LCFA-induced anorexia. In conclusion, this study indicates that the vagus nerve and the CCK signaling pathway do not play major roles in conveying satiety signals induced by intestinal LCFA to the brain in rats.

Role of midbrain in the control of breathing in anuran amphibians

The present study was designed to explore systematically the midbrain of unanesthetized, decerebrate anuran amphibians (bullfrogs), using chemical and electrical stimulation and midbrain transections to identify sites capable of exciting and inhibiting breathing. Ventilation was measured as fictive motor output from the mandibular branch of the trigeminal nerve and the laryngeal branch of the vagus nerve. The results of our transection studies suggest that, under resting conditions, the net effect of inputs from sites within the rostral half of the midbrain is to increase fictive breathing frequency, whereas inputs from sites within the caudal half of the midbrain have no net effect on fictive breathing frequency but appear to act on the medullary central rhythm generator to produce episodic breathing. The results of our stimulation experiments indicate that the principal sites in the midbrain that are capable of exciting or inhibiting the fictive frequency of lung ventilation, and potentially clustering breaths into episodes, appear to be those primarily involved in visual and auditory integration, motor functions, and attentional state.

Chronic hypoxia attenuates central respiratory-related pH/CO2 chemosensitivity in the cane toad

This study examined the effects of chronic hypoxia (CH) and mid-brain transection on central respiratory-related pH/CO(2) chemosensitivity in cane toads (Bufo marinus). Toads were exposed to 10 days of CH (10% O(2)) following which in vitro brainstem-spinal cord preparations, with the mid-brain attached, were used to examine central pH/CO(2) chemosensitivity. A reduction in artificial cerebral spinal fluid (aCSF) pH increased fictive breathing frequency (fR) and total fictive ventilation. CH reduced fictive fR and total fictive ventilation, compared to controls. Mid-brain transection caused an increase in fictive fR, at the lower aCSF pH levels, in both control and CH preparations. In the CH preparations, mid-brain transection restored fictive breathing to control levels. In both groups, mid-brain transection eliminated fictive breath clustering. The data indicate that CH attenuates central pH/CO(2)-sensitive fictive breathing but a mid-brain transection in the middle of the optic lobes abolishes this attenuation. The results suggest that CH induces inhibition of central pH/CO(2) chemoreceptor function via descending inputs from the mid-brain region.

Peripheral ghrelin transmits orexigenic signals through the noradrenergic pathway from the hindbrain to the hypothalamus

Ghrelin, a gastrointestinal peptide, stimulates feeding when administered peripherally. Blockade of the vagal afferent pathway abolishes ghrelin-induced feeding, indicating that the vagal afferent pathway may be a route conveying orexigenic ghrelin signals to the brain. Here, we demonstrate that peripheral ghrelin signaling, which travels to the nucleus tractus solitarius (NTS) at least in part via the vagus nerve, increases noradrenaline (NA) in the arcuate nucleus of the hypothalamus, thereby stimulating feeding at least partially through alpha-1 and beta-2 noradrenergic receptors. In addition, bilateral midbrain transections rostral to the NTS, or toxin-induced loss of neurons in the hindbrain that express dopamine beta hydroxylase (an NA synthetic enzyme), abolished ghrelin-induced feeding. These findings provide new evidence that the noradrenergic system is necessary in the central control of feeding behavior by peripherally administered ghrelin.

Chronic hypercapnia modulates respiratory-related central pH/CO2 chemoreception in an amphibian,Bufo marinus

Anuran amphibians have multiple populations of pH/CO2-sensitive respiratory-related chemoreceptors. This study examined in cane toads (Bufo marinus) whether chronic hypercapnia (CHC) altered the pH/CO2 sensitivity of central respiratory-related chemoreceptors in vitro and whether CHC altered the acute hypercapnic ventilatory response (HCVR; 5% CO2) in vivo. Toads were exposed to CHC (3.5% CO2) for 9 days. In vitro brainstem-spinal cord preparations were used to examine central respiratory-related pH/CO2 chemosensitivity. CHC augmented in vitro fictive breathing as the pH of the superfusate was lowered from 8.2 to 7.4. Midbrain transection in vitro (at a level known to reduce the clustering of breaths) did not alter this augmentation. In vivo, CHC did not alter the acute HCVR but midbrain transection changed the breathing pattern and increased the overall level of ventilation. CHC did not alter the effect of olfactory CO2 chemoreceptor denervation on the acute HCVR in vivo but did alter the response when returned to normal air. The results indicate that CHC increases the response of central pH/CO2 chemoreceptors to changes in cerebrospinal fluid pH in vitro yet this increase is not manifest as an increase in the HCVR in vivo.

The Role of the Vagal Nerve in Peripheral PYY3–36-Induced Feeding Reduction in Rats

Peptide YY (PYY), an anorectic peptide, is secreted postprandially from the distal gastrointestinal tract. PYY(3-36), the major form of circulating PYY, binds to the hypothalamic neuropeptide Y Y2 receptor (Y2-R) with a high-affinity, reducing food intake in rodents and humans. Additional gastrointestinal hormones involved in feeding, including cholecystokinin, glucagon-like peptide 1, and ghrelin, transmit satiety or hunger signals to the brain via the vagal afferent nerve and/or the blood stream. Here we determined the role of the afferent vagus nerve in PYY function. Abdominal vagotomy abolished the anorectic effect of PYY(3-36) in rats. Peripheral administration of PYY(3-36) induced Fos expression in the arcuate nucleus of sham-operated rats but not vagotomized rats. We showed that Y2-R is synthesized in the rat nodose ganglion and transported to the vagal afferent terminals. PYY(3-36) stimulated firing of the gastric vagal afferent nerve when administered iv. Considering that Y2-R is present in the vagal afferent fibers, PYY(3-36) could directly alter the firing rate of the vagal afferent nerve via Y2-R. We also investigated the effect of ascending fibers from the nucleus of the solitary tract on the transmission of PYY(3-36)-mediated satiety signals. In rats, bilateral midbrain transections rostral to the nucleus of the solitary tract also abolished PYY(3-36)-induced reductions in feeding. This study indicates that peripheral PYY(3-36) may transmit satiety signals to the brain in part via the vagal afferent pathway.

The brain stem but not forebrain independently supports morphine tolerance and withdrawal effects in cats

We employed polygraphic recordings and behavioral measures to study the effects of chronic morphine use upon the isolated forebrain and the decerebrate animal in cats with a midbrain transection. Cats received morphine for 12 days, and 24 h recording sessions were conducted on days 1 and 11. For the decerebrate cat, the percent time of rapid eye movement (REM) sleep was reduced during the 24 h period on both days 1 and 11. However, the values on day 11 were consistently higher than the values on day 1. Other tolerance indicators were decreases in the number of early behavioral signs and in the onset delay for REM sleep, together with an increase in onset time for motor activation. After naloxone (day 12) all cats displayed “wet shakes,” tachypnea and eye squinting, as well as either pyloerection, elevated tail, salivation, licking, micturition, and yawning. In the isolated forebrain, the percent time for waking increased through the first 18 h post-morphine on both days 1 and 11. Conversely, the duration of non-REM (NREM) sleep and of drowsiness decreased. But importantly, the duration of sleep–waking states did not vary between days 11 and 1, indicating absence of tolerance. Additionally, after naloxone, the isolated forebrain entered NREM sleep, contrasting with opposite findings in intact cats. Therefore, while we could not demonstrate chronic use effects in the isolated forebrain, the decerebrate cat still displayed typical tolerance/withdrawal manifestations. This suggests that the effects of chronic opiate use are deeply seated in the brain stem, which might help understanding the ingrained nature of physical dependence.

Sympathoexcitation to intravenous interleukin-1beta is dependent on forebrain neural circuits.

We investigated the contributions of forebrain, brain stem, and spinal neural circuits to interleukin (IL)-1beta-induced sympathetic nerve discharge (SND) responses in alpha-chloralose-anesthetized rats. Lumbar and splenic SND responses were determined in spinal cord-transected (first cervical vertebra, C1), midbrain-transected (superior colliculus), and sham-transected rats before and for 60 min after intravenous IL-1beta (285 ng/kg). The observations made were the following: 1) lumbar and splenic SND were significantly increased after IL-1beta in sham C1-transected rats but were unchanged after IL-1beta in C1-transected rats; 2) intrathecal administration of DL-homocysteic acid (10 ng) increased SND in C1-transected rats; 3) lumbar and splenic SND were significantly increased after IL-1beta in sham- but not midbrain-transected rats; and 4) midbrain transection did not alter the pattern of lumbar and splenic SND, demonstrating the integrity of brain stem sympathetic neural circuits after decerebration. These results demonstrate that an intact forebrain is required for mediating lumbar and splenic sympathoexcitatory responses to intravenous IL-1beta, thereby providing new information about the organization of neural circuits responsible for mediating sympathetic-immune interactions.

Sleep–waking states develop independently in the isolated forebrain and brain stem following early postnatal midbrain transection in cats

We report the effects of permanently separating the immature forebrain from the brain stem upon sleeping and waking development. Kittens ranging from postnatal 9 to 27 days of age sustained a mesencephalic transection and were maintained for up to 135 days. Prior to postnatal day 40, the electroencephalogram of the isolated forebrain and behavioral sleep–wakefulness of the decerebrate animal showed the immature patterns of normal young kittens. Thereafter, the isolated forebrain showed alternating sleep–wakefulness electrocortical rhythms similar to the corresponding normal patterns of intact, mature cats. Olfactory stimuli generally changed forebrain sleeping into waking activity, and in cats with the section behind the third nerve nuclei, normal correlates of eye movements–pupillary activity with electrocortical rhythms were present. Behind the transection, decerebrate animals showed wakefulness, and after 20 days of age displayed typical behavioral episodes of rapid eye movements sleep and, during these periods, the pontine recordings showed ponto-geniculo-occipital waves, which are markers for this sleep stage, together with muscle atonia and rapid lateral eye movements. Typically, but with remarkable exceptions suggesting humoral interactions, the sleep–waking patterns of the isolated forebrain were dissociated from those of the decerebrate animal. These results were very similar to our previous findings in midbrain-transected adult cats. However, subtle differences suggested greater functional plasticity in the developing versus the adult isolated forebrain. We conclude that behavioral and electroencephalographic patterns of non-rapid eye movement sleep and of rapid eye movement sleep states mature independently in the forebrain and the brain stem, respectively, after these structures are separated early postnatally. In terms of waking, the findings strengthen our concept that in higher mammals the rostral brain can independently support wakefulness/arousal and, hypothetically, perhaps even awareness. Therefore, these basic sleeping–waking functions are intrinsic properties of the forebrain/brain stem and as such can develop autochthonously. These data help our understanding of some normal/borderline sleep–waking dissociations as well as peculiar states of consciousness in long term patients with brain stem lesions.

Mesopontine contribution to the expression of active ‘twitch’ sleep in decerebrate week-old rats

Myoclonic twitching is a ubiquitous feature of infant behavior that has been used as an index of active sleep. Although the active sleep of infants differs in some ways from the REM sleep of adults, their marked similarities have led many to view them them as homologous behavioral states. Recently, however, this view has been challenged. One avenue for resolving this issue entails examination of the neural substrates of active sleep. If the neural substrates of active sleep were found to be similar to those of REM sleep, then this would support the view that the two states are homologous. Therefore, in the present study, decerebrations were performed in the pons and midbrain to determine whether the mesopontine region is important for the expression of active sleep in infants, just as it is for the expression of REM sleep in adults. It was found that, in comparison to controls, caudal pontine decerebrations reduced myoclonic twitching by 76%, rostral pontine decerebrations reduced twitching by 40%, and midbrain transections had no significant effect on twitching. Moreover, analysis of the temporal organization of twitching indicated that pontine decerebrations predominantly affected high-frequency twitching while leaving unaffected the low-frequency twitching that is thought to be contributed by local spinal circuits at this age. These results indicate that the mesopontine region plays a central role in the expression of active sleep in infant rats.

Secondarily generalized seizures

To the Editor: In their study of secondarily generalized tonic-clonic seizures, Theodore et al [1] carefully documented heterogeneity in the clinical manifestations of the transition from partial seizure to generalized convulsion. The EEG correlate of this transition is also variable in humans and experimental animals [2]. The authors suggest that their results indicate that multiple cortical and subcortical routes of spread may exist. A more precise hypothesis accounting for these findings is suggested by a large body of experimental literature on the neural systems mediating generalized seizures [2-6]. This work demonstrates that generalized convulsions result from activation of a specific brainstem neural substrate, which can be triggered by many types of partial and generalized (absence or myoclonic) forebrain seizures via numerous different descending pathways. For example, Browning and Nelson [3] demonstrated that GTCS can be readily elicited by electroshock or systemic pentylenetetrazol in rats with complete midbrain transections, indicating that the forebrain …

Forebrain rhythm generators influence sympathetic activity in anesthetized cats

Autospectral and coherence analyses were used to study the frequency-domain relationships between frontal-parietal cortical activity [electroencephalogram (EEG)] and the discharges of the interior cardiac and renal sympathetic nerves of baroreceptor-denervated and vagotomized cats anesthetized with either alpha-chloralose or pentobarbital sodium. Delta slow-wave activity in the EEG was correlated to sympathetic nerve discharge (SND) as shown by sharp peaks between 0.5 and 4 Hz in the coherence function. The relationship was stronger in chloralose- than in pentobarbital-anesthetized cats. Coherence of the two signals could be attributed to descending influences of forebrain delta slow-wave generators on sympathetic circuits, since midbrain transection preferentially reduced the power in SND at frequencies that cohered to the EEG before transection. In contrast, the power in the EEG was not reduced by midbrain transection. The relationship between cortical delta slow-wave activity and SND was stronger during than between cortical spindlelike events that lasted 1-3 s and recurred once every 5-10 s. These events were similar to cortical spindles observed during the early stages of sleep and under light barbiturate anesthesia. These observations raise the possibility that the influences of forebrain delta slow-wave generators on SND are gated by thalamic mechanisms normally involved in the sleep-wake cycle.

Diencephalic regions contributing to sympathetic nerve discharge in anesthetized cats.

We reported that the forebrain is responsible for a significant component (38%) of inferior cardiac postganglionic sympathetic nerve discharge (SND) in baroreceptor-denervated cats anesthetized with alpha-chloralose [Huang et al., Am. J. Physiol. 252 (Regulatory Integrative Comp. Physiol. 21): R645-R652, 1987]. The current study was initiated to assess the contribution of various diencephalic regions to the forebrain-dependent component of SND in this preparation. For this purpose, the reductions in inferior cardiac SND and blood pressure produced acutely by midbrain transection at stereotaxic plane A3 in nonlesioned control cats were compared with those in cats in which diencephalic lesions were made with radio-frequency current. Lesions of the anterior medial hypothalamus including the paraventricular nucleus failed to attenuate the decreases in SND and blood pressure produced by midbrain transection. In contrast, the effects of midbrain transection were significantly attenuated by lesions of the lateral hypothalamus (including medial forebrain bundle), posterior medial hypothalamus, or the medial thalamus. We conclude that both the hypothalamus and medial thalamus contribute to SND in anesthetized cats.

Forebrain contribution to sympathetic nerve discharge in anesthetized cats

We tested the hypothesis that the forebrain is responsible for a component of basal sympathetic nerve discharge (SND) in the anesthetized cat. For this purpose integrated postganglionic inferior cardiac SND and blood pressure were measured before and after serial transections of the midbrain at stereotaxic planes A3 and AP0. In the first series of experiments on baroreceptor-denervated cats anesthetized with alpha-chloralose, A3 transection significantly reduced SND to 62 +/- 7% of control. Blood pressure was reduced 33 +/- 4 mmHg. SND and frontal-parietal cortical activity were temporally related prior to A3 transection in many of these animals. Recovery of SND and blood pressure to control levels occurred within 30 min after A3 transection. A second midbrain transection at AP0 failed to affect SND and blood pressure at this time. This observation suggests that the effects of A3 transection were due to the loss of a component of SND of forebrain origin rather than to generalized trauma. The effects of A3 transection were not attributable to cataleptic anesthesia with alpha-chloralose, since SND and blood pressure were significantly reduced by midbrain transection in baroreceptor-denervated cats anesthetized with diallylbarbiturate-urethan. A3 transection also reduced SND and blood pressure in some baroreceptor-innervated cats. Finally, medial diencephalic ablation prevented the effects of A3 transection. We conclude that the forebrain is responsible for a significant component of sympathetic tone in anesthetized cats. Recovery from the loss of this component, however, occurs rapidly even in animals deprived of their compensatory baroreceptor reflex mechanisms.

Tyrosine Hydroxylase in Magnocellular Neurosecretory Neurons

Tyrosine hydroxylase (TH) immunoreactivity is present in a few magnocellular neurons in the supraoptic and paraventricular nuclei of normal Sprague-Dawley and heterozygous Brattleboro rats. Manipulations commonly used to enhance immunostaining of cell bodies, such as colchicine treatment or lesioning of efferent fibers, induced only a slight increase in TH of magnocellular neurons in Sprague-Dawley rats. Seven days after bilateral midbrain transections, which destroyed ascending afferents to paraventricular and supraoptic nuclei from the lower brainstem, there was a substantial increase in TH immunoreactivity in magnocellular neurons. The lesions resulted in a marked increase in the intensity of the staining and in the number of stained cells. Similar increases were induced by giving animals 2% NaCl to drink for 5 days. Neurons in the supraoptic and paraventricular nuclei of homozygous Brattleboro rats show markedly more TH staining than those of normal rats. Vasopressin treatment lowered TH immunoreactivity in magnocellular neurons of Brattleboro rats to normal levels. These observations suggest that extracellular factors, probably afferent inputs, regulate the level of TH immunoreactivity in magnocellular neurons.