A hypothalamic-thalamostriatal circuit that controls approach-avoidance conflict in rats.

Survival depends on a balance between seeking rewards and avoiding potential threats, but the neural circuits that regulate this motivational conflict remain largely unknown. Using an approach-food vs. avoid-predator threat conflict test in rats, we identified a subpopulation of neurons in the anterior portion of the paraventricular thalamic nucleus (aPVT) which express corticotrophin-releasing factor (CRF) and are preferentially recruited during conflict. Inactivation of aPVTCRF neurons during conflict biases animal's response toward food, whereas activation of these cells recapitulates the food-seeking suppression observed during conflict. aPVTCRF neurons project densely to the nucleus accumbens (NAc), and activity in this pathway reduces food seeking and increases avoidance. In addition, we identified the ventromedial hypothalamus (VMH) as a critical input to aPVTCRF neurons, and demonstrated that VMH-aPVT neurons mediate defensive behaviors exclusively during conflict. Together, our findings describe a hypothalamic-thalamostriatal circuit that suppresses reward-seeking behavior under the competing demands of avoiding threats.

A projection from the ventral tegmental area to the periaqueductal gray involved in cardiovascular regulation.

Experiments were done in alpha-chloralose-anesthetized rats to determine a pathway mediating the cardiovascular depressor responses elicited from stimulation of the ventral tegmental area (VTA). The magnitude of the depressor responses elicited by glutamate stimulation (0.1 M/30 nl) of the VTA was examined after neuronal block produced by microinjections of lidocaine into ascending fiber bundles leaving the VTA to innervate the forebrain and thalamus. Bilateral microinjections of 1 microl of 4% lidocaine in the medial forebrain bundle (n = 6) and in the periventricular fibers of the midbrain (n = 5) did not attenuate the depressor response from stimulation of the VTA. Experiments were done using the anterograde tracer biotinylated dextran amine to identify descending projections from the VTA to cardiovascular centers in the brain stem. Examination of the nucleus of the solitary tract, ventrolateral medulla, and A5 catecholaminergic cell group revealed few or no fibers or terminals. Occasional fibers and some terminals were observed in the nucleus of raphe magnus, parabrachial nucleus, and locus ceruleus. A very dense bilateral projection was found to the ventrolateral periaqueductal gray (PAGvl) and dorsal raphe nucleus adjacent to the PAGvl. Bilateral injections of 4% lidocaine (n = 4) or 10 mM cobalt chloride (n = 5) into the PAGvl region attenuated the depressor responses elicited by stimulation of the VTA by approximately 50%. These experiments indicate that the depressor responses elicited from activation of the VTA are mediated in part by a pathway to a cardiovascular depressor area located in the PAGvl.

Identification of barosensitive neurons in the mediobasal forebrain using juxtacellular labeling.

Previous investigations suggest a possible role in cardiovascular regulation for neurons of the mediobasal forebrain. The present study was designed to determine the location and morphology of basal forebrain neurons that respond to acute changes in arterial blood pressure. Extracellular recordings of single units were done in alpha-chloralose- or urethan-anesthetized rats. The effect of cardiovascular pressor (phenylephrine, 1-2 microgram/kg iv) and depressor (sodium nitroprusside, 0.5-1 microgram/kg iv) events on the discharge rates of units was determined. Some of the neurons tested were subsequently filled with biocytin using the juxtacellular method. Brain sections were processed using the avidin-biotin complex reaction to reveal a Golgi-like appearance of the neuron. Of 32 neurons located in the horizontal limb of the diagonal band of Broca (hDB), 13 (41%) were found to be excited by depressor events. Barosensitive biocytin-labeled cells were located in all regions of the hDB and had small- to medium-sized cell bodies with sparse and simple dendritic morphology. Only 2 of 47 neurons tested in the region of the olfactory tubercle, islands of Calleja (IC), and ventral pallidum responded to changes in arterial blood pressure. The results of the present investigation suggest a role in the regulation of cardiovascular function for neurons of the hDB. The findings also suggest that most neurons in the olfactory tubercle, including the IC complex, do not respond to acute changes in arterial blood pressure.

Cardiovascular responses to glutamate stimulation of diagonal band of Broca.

Experiments were done in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of L-glutamate stimulation of the diagonal band of Broca (DBB) on arterial pressure (AP) and heart rate (HR). Stimulation of the horizontal limb of the DBB (hDB) elicited decreases in both mean AP (MAP; -32.3 +/- 2.5 mmHg; n = 37) and HR (-32.5 +/- 3.8 beats/min; n = 33) at 84% of the sites stimulated. Stimulation of the vertical limb of the DBB (vDB) elicited significantly smaller decreases in MAP (-9.7 +/- 1.0 mmHg; n = 19) and HR (-13.5 +/- 1.8 beats/min; n = 7) at approximately 13% of the sites stimulated. Intravenous administration of the muscarinic receptor blocker atropine methylbromide had no effect on the magnitude of the MAP and HR responses to stimulation of the hDB. In contrast, administration of the nicotinic receptor blocker hexamethonium bromide abolished both the depressor and the bradycardic responses elicited by stimulation of the hDB. These data indicate that the hDB contains neurons that exert cardiovascular depressor effects and that these circulatory effects are mediated by the inhibition of sympathetic vasoconstrictor fibers to the vasculature, and cardioacceleratory fibers to the heart.

Cardiovascular afferent inputs to ventral tegmental area.

Extracellular single-unit recording experiments were done in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of selective activation of arterial baroreceptors and stimulation of cardiovascular depressor sites in the nucleus of the solitary tract (NTS) on the discharge rate of neurons in the ventral tegmental area (VTA). Electrical stimulation of the aortic depressor nerve (ADN), which is known to carry aortic baroreceptor afferent fibers only, excited 12 of 21 (mean onset latency 42.4 +/- 8.8 ms) and inhibited 2 of 21 (mean onset latency 42.5 +/- 6.5 ms) single units in the VTA. The discharge rate of VTA units was also altered during the reflex activation of arterial baroreceptors by the acute rise in arterial pressure (AP) to systemic injections of phenylephrine (10 micrograms/kg i.v.): 12 of 44 units were excited and 15 of 44 were inhibited. Units that responded to either ADN stimulation or the reflex activation of the baroreflex also responded to stimulation of depressor sites in the NTS. An additional 12 units that were found in barodenervated controls to be responsive to NTS stimulation were nonresponsive to selective activation of arterial baroreceptors. These data indicate that cardiovascular afferent inputs modulate the activity of neurons in the VTA and suggest that changes in systemic AP may exert an effect on the activity of neurons involved in mesolimbic and mesocortical function.

Cardiovascular depressor responses to stimulation of substantia nigra and ventral tegmental area.

Experiments were done in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of L-glutamate (Glu) stimulation of the substantia nigra (SN) and ventral tegmental area (VTA) on arterial pressure (AP) and heart rate (HR). Glu stimulation of the SN pars compacta (SNC) elicited decreases in both mean AP (MAP; -18.9 +/- 1.3 mmHg; n = 52) and HR (-26.1 +/- 1.6 beats/min; n = 46) at 81% of the sites stimulated. On the other hand, stimulation of the SN pars lateralis or pars reticulata did not elicit cardiovascular responses. Stimulation of the adjacent VTA region elicited similar decreases in MAP (-18.0 +/- 2.6 mmHg; n = 20) and HR (-25.4 +/- 3.8 beats/min; n = 17) at approximately 74% of the sites stimulated. Intravenous administration of the dopamine D2-receptor antagonist raclopride significantly attenuated both the MAP (70%) and the HR (54%) responses elicited by stimulation of the transitional region where the SNC merges with the lateral VTA (SNC-VTA region). Intravenous administration of the muscarinic receptor blocker atropine methyl bromide had no effect on the magnitude of the MAP and HR responses to stimulation of the SNC-VTA region, whereas administration of the nicotinic receptor blocker hexamethonium bromide significantly attenuated both the depressor and the bradycardic responses. These data suggest that dopaminergic neurons in the SNC-VTA region activate a central pathway that exerts cardiovascular depressor effects that are mediated by the inhibition of sympathetic vasoconstrictor fibers to the vasculature and cardioacceleratory fibers to the heart.

Medullary inputs to nucleus accumbens neurons.

Extracellular single-unit recording experiments were done in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect of stimulation of the nucleus of the solitary tract (NTS) and the ventrolateral medulla (VLM) in the region of the A1 noradrenergic cell group on the activity of neurons in the nucleus accumbens (NA). In addition, the response of NA neurons to activation of the arterial baroreceptors was investigated. Electrical or glutamate (Glu) stimulation of the ipsilateral NTS excited 47 of 99 (48%) and inhibited 10 of 99 (10%) of the units tested in the NA. Similarly, electrical or Glu stimulation of the ipsilateral VLM excited 24 of 97 (24.7%) or inhibited 7 of 97 (7.2%) of the units tested. Approximately 22% (17 of 77) of these units responded to stimulation of both the NTS and VLM. Simultaneous stimulation of both the NTS and VLM potentiated the response of the NA neuron tested. CoCl2 injection into the ipsilateral NTS did not alter the response of NA neurons to stimulation of the VLM. Similarly, CoCl2 injections into the ipsilateral VLM did not alter the response of NA neurons to NTS stimulation. The discharge rate of some of the units (6 of 49) that were activated by both NTS and VLM was also increased during the activation of arterial baroreceptors by the acute rise in systemic arterial pressure to phenylephrine injection. Units that responded to stimulation of the NTS and VLM and to baroreceptor activation were located in the shell region of the NA. These data indicate that afferent inputs from the NTS and VLM converge onto NA neurons and suggest that visceral and cardiovascular afferent inputs may influence the output of neurons in the shell region of the NA.

Cholecystokinin-induced release of dopamine in the nucleus accumbens of the spontaneously hypertensive rat.

Changes in dopamine neurotransmission in the nucleus accumbens of the spontaneously hypertensive rat (SHR) may be involved in the pathogenesis of hypertension. This investigation tested the hypothesis that the sulfated octapeptide cholecystokinin (CCK8S) induced release of dopamine is greater in the SHR than in its normotensive control, the Wistar-Kyoto rat (WKY). Dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were sampled using microdialysis in the caudal half of the nucleus accumbens of 10-week-old anesthetized SHRs and WKYs. Samples were collected in the following order: 3 baseline, 3 CCK8S (10 mumol/l), and 3 postdrug samples. The samples were then analyzed using high pressure liquid chromatography with electrochemical detection. CCK8S increased dopamine and DOPAC levels in both the SHR and WKY with a larger increase in basal dopamine in the SHR (greater than 200%). Perfusion of the nucleus accumbens with 1 mumol/l of CCK8S or the nonsulfated form of CCK8 (CCK8US, 10 mumol/l) produced no significant increase in the release of dopamine in the SHR. These results indicate that CCK8S-induced release of dopamine in the nucleus accumbens is greater in the SHR. Changes in CCK8S neurotransmission/receptor function may be responsible for the alterations in dopaminergic function of the SHR and the pathogenesis of hypertension.

Topographical organization in the nucleus accumbens of afferents from the basolateral amygdala and efferents to the lateral hypothalamus.

The basolateral region of the amygdala and the lateral hypothalamic area are involved in cardiovascular regulation. The aim of the present investigation was to determine if the terminal field of afferent projections from the basolateral nucleus of the amygdala to the nucleus accumbens overlap with the origin of the efferent projections from the nucleus accumbens to the lateral hypothalamic area. Neurons projecting from the nucleus accumbens to the lateral hypothalamic area were labeled by injecting the retrograde tracer Fluoro-Gold in the lateral hypothalamus of rats. In the same rats, fiber terminals from the amygdala to the nucleus accumbens were labeled by injecting the anterograde tracer Fluoro-Ruby in the basolateral region of the amygdala. Injections of Fluoro-Gold in the lateral hypothalamus labeled neurons in the posteromedial portion of the nucleus accumbens. Injections of Fluoro-Ruby in the basolateral amygdala labeled fibers and terminals in all parts of the nucleus accumbens with the highest density being found in the posteromedial part of the nucleus accumbens where Fluoro-Gold-labeled neurons were located. When regions of the posteromedial nucleus accumbens were examined under high-magnification, Fluoro-Ruby-labeled terminals appeared to make contact on Fluoro-Gold-labeled dendrites and cell bodies. This investigation demonstrates that there is a distinct overlap in the posteromedial region of the nucleus accumbens between the terminal field from neurons originating in the amygdala and neurons which project to the lateral hypothalamus. In addition, neurons in the basolateral amygdala appear to make synaptic contact with neurons in the nucleus accumbens that project to the lateral hypothalamic area.(ABSTRACT TRUNCATED AT 250 WORDS)

Up-regulation of cholecystokinin receptors in the nucleus accumbens of the young prehypertensive spontaneously hypertensive rat.

We employed receptor autoradiography to test the hypothesis that changes in cholecystokinin neurotransmission in the striatum of the young spontaneously hypertensive rat (SHR) is involved in the development of hypertension. The binding density of 125I-Bolton Hunter labelled cholecystokinin octapeptide (125I-BH-CCK8) in the striatum of 5-week-old prehypertensive SHRs and its normotensive control the Wistar-Kyoto rat (WKY) was determined using computer-assisted densitometry. We found a significant increase in 125I-BH-CCK8 binding density in the nucleus accumbens of the SHR. No difference between the binding density of 125I-BH-CCK8 was found in the caudate-putamen and the prefrontal cortex of SHRs and WKYs. These results suggest that changes in CCK8S neurotransmission or receptor function are not secondary to an increase in arterial blood pressure and, therefore, may be involved in the development of hypertension.

Cholecystokinin receptor density in the striatum of the spontaneously hypertensive rat.

The possibility that cholecystokinin in the striatum may be involved in hypertension was investigated using in vitro receptor autoradiography. The binding density of 125I-Bolton Hunter labeled cholecystokinin octapeptide (125I-BH-CCK8) was determined using computer-assisted densitometry in the striatum of the spontaneously hypertensive rat (SHR) and its control the Wistar-Kyoto rat (WKY). A significant increase in 125I-BH-CCK8 binding density was found in the lateral part of the caudate-putamen of the SHR. In contrast, a significant decrease in 125I-BH-CCK8 binding density was found in the posteromedial nucleus accumbens of the SHR. These results indicate that CCK8 receptor density is altered in the striatum of the SHR and suggest a role for CCK8 receptors in the pathophysiology of hypertension.

Up-regulation of dopamine receptors in the brain of the spontaneously hypertensive rat: an autoradiographic analysis.

Recent evidence points to a dysfunction of brain dopaminergic mechanisms in the spontaneously hypertensive rat. Using in vitro receptor autoradiography, we assessed the density of D1 and D2 dopamine receptors in the brain of spontaneously hypertensive rats and their normotensive controls the Wistar-Kyoto rat. Brain sections from five- and 15-week-old rats were incubated with 1 nM [3H]SCH 23390 (D1 receptor antagonist) or 15 nM [3H]sulpiride (D2 receptor antagonist), and exposed along with radioactive standards to 3H-Hyperfilm. The binding density of selected brain regions (anteromedial prefrontal cortex, cingulate cortex, lateral septal nucleus, nucleus accumbens, caudate-putamen, globus pallidus, amygdaloid complex) were quantified using computer-assisted densitometry. These experiments showed a significant increase in the binding density of [3H]SCH 23390 in the nucleus accumbens and caudate-putamen of five- and 15-week-old spontaneously hypertensive rats. The binding density of [3H]SCH 23390 was increased in the lateral septal nucleus of five-week-old and globus pallidus of 15-week-old spontaneously hypertensive rats. The binding density of [3H]sulpiride was also greater in the nucleus accumbens of five-week-old spontaneously hypertensive rats. The present investigation demonstrates an up-regulation of D1 dopamine receptors in spontaneously hypertensive rats with established hypertension. More importantly, up-regulation of D1 and D2 dopamine receptors in the striatum of young prehypertensive spontaneously hypertensive rats suggests that dopamine may be involved in the pathogenesis of hypertension in this strain of genetically hypertensive rats.