Effects of auricular stimulation on feeding-related hypothalamic neuronal activity in normal and obese rats

It is known that auriculotherapy occasionally affects dramatic body weight reduction for obese patients, although the physiological and anorexigenic functions are not clear. Effects of auricular stimulation on feeding-related lateral (LHA) and ventromedial (VMH) hypothalamic neuronal activity in normal and experimental (hypothalamic and dietary) obese rats were investigated. The LHA and/or VMH neuronal activity were recorded from feeding-related regions in Wistar SPFNAF male and experimental (hypothalamic and dietary) obese rats, anesthetized with urethane-chloralose, under stereotaxic coordination. Recording was through 3 M KCI glass microelectrodes, while stimulating the ipsilateral vagal innervated region of the auricle. This is equivalent to the cavum conchae in the human, and was identified by resistance less than 10–50 kπ The stimulating electrode was a stainless steel ear acupuncture (0.12 x 2.0 mm). The latency of potentials evoked in the LHA by unilateral stimulation of a specific site in the ear was 28.1 ± 3.3 ms (8–92, n = 41). LHA neuronal activity was depressed 45.6% (n = 12, p < 0.01, and VMH activity was excited (60.5%, n = 18, p < 0.01. The auricular acupuncture stimulation clearly modulates feeding-related hypothalamic neuronal activity of experimental (both hypothalamic and dietary) obese rats. These auricle acupuncture stimulation effects were correlated to the degree of obesity. In conclusion, the results suggest that auricular acupuncture stimulation may not reduce appetite, but is more likely concerned with satiation formation and preservation. Thus, auricular acupuncture should be more effective on obese rats than on normal rats.     

An electrophysiological study of amygdalohypothalamic projections to the ventromedial nucleus of the rat.

The influence of the amygdala on the activity of single neurons within the hypothalamic ventromedial nucleus (HVM) was studied in pentobarbital or urethane anesthetized rats. The results are summarized as follows: (1) Stimulation of different amygdaloid nuclei or of the stria terminalis (ST) evoked a prominent field potential within HVM and altered the spike discharge patterns of the majority of HVM neurons. (2) More than 80% of 428 HVM neurons tested with single amygdala shocks exhibited excitation or excitation-inhibition sequences; the remainder displayed inhibitory responses of 100-150 msec duration at latencies slightly longer than for most of the observed excitatory responses. ST stimulation also evoked excitation or excitation-inhibition sequences from 85% of 240 HVM neurons tested; of the remainder, those with spontaneous activity displayed inhibitory responses with durations of 100-150 msec at latencies slightly longer than for most observed excitatory responses. (3) Evoked potential interaction studies suggested that stimulation of either ST or the amygdala activated the same population of HVM neurons. Single cells tested with both amygdala and ST stimulation displayed similar patterns of response. HVM field potentials and single unit responses to amygdala stimulation were markedly diminished by lesions of ST. Thus, in the rat, only one pathway, i.e., the stria terminalis, contains amygdalofugal fibres to the ventromedial hypothalamic nucleus. (4) The orthodromic responses of HVM neurons were dependent on the frequency of amygdala stimulation. Less than 50% of HVM neurons responded to amygdala stimuli at frequencies greater than 33Hz. Many cells could not be activated at stimulation frequencies greater than 10 Hz, and the spontaneous discharges from certain HVM neurons were effectively abolished at this stimulation frequency. (5) Evidence of prominent postsynaptic inhibition was present throughout HVM. Seventeen HVM neurons displayed amygdala evoked unitary activity different from that of the majority of HVM neurons, and these cells were considered to represent possible inhibitory neurons. In contrast to most HVM neurons activated via probable monosynaptic amygdalohypothalamic pathways, these putative inhibitory neurons were apparently activated via polysynaptic pathways. (6) In summary, these results suggest that the amygdala exerts a prominent monosynaptic influence on the activity of many HVM neurons, coupled with polysynaptic activation of powerful local postsynaptic inhibitory mechanism. In the rat, these amygdala evoked events depend on the integrity of the stria terminalis.     

Mechanism of inhibition by the amygdala in the lateral hypothalamic area of rats

OOMURA, Y. AND T. ONO. Mechanism of inhibition by the amygdala in the lateral hypothalamic area of rats. BRAIN RES. BULL. 8(6) 653–666, 1982.—The inhibition of neuronal activity in the lateral hypothalamus (LHA) of the rat by the basolateral nucleus of the amygdala (AL) was investigated by analyzing evoked potentials, single unit discharges and intracellular synaptic potentials. A single volley to the AL induced a negative-positive-wave in the LHA. The negative-wave threshold was lower than that of the positive wave. Analysis of depth profiles showed that the negative- and positive-waves appeared first at the dorsal margin of the LHA, peaked within the LHA, and were clearly different from each other. The effects of acute lesions showed the negative-wave to be conducted through the direct amygdalo-hypothalamic pathway. The positive-wave; through the stria terminalis. Stimulation of the stria terminalis produced positive evoked potentials with latencies shorter than those of the positive-waves. When conditioning and test stimuli were delivered to the AL, the negative-wave was inhibited for about 90 msec by the evoked positive-wave. Single AL stimuli evoked single unit discharges followed by inhibition of spontaneous firing for about 100 msec. Single stria terminalis stimuli inhibited spontaneous firing for the duration of the positive evoked potential. Intracellular LHA recording during single AL stimuli showed the presence of an EPSP followed by a 100 msec long lasting IPSP. The negative and positive extracellular potentials corresponded to these synaptic potentials. Inward current injection of 1 to 1.4 nA reversed the IPSP's indicating a -15 mV hyperpolarization difference between the IPSP reversal potential and the resting potential in LHA cells. The ionic mechanism of the IPSP is also discussed.     

Reciprocal connections between the lateral hypothalamus and the frontal complex in the rat: electrophysiological and anatomical observations

Inputs to rat lateral hypothalamus (LHA) from prefrontal cortex (FC), and vice versa, were studied by intracellular recording, and by retrograde horseradish peroxidase (HRP) method. Stimulation of the FC evoked 3 types of responses: a polysynaptic EPSP-IPSP sequence, IPSPs alone, or antidromic response in LHA neurons. Forty-five per cent of IPSPs were considered to be monosynaptic since the latencies were constant when stimulus intensity was changed. The neurons labeled in the FC following electrophoretic injections of HRP into LHA were located in the medial and sulcal FC. In these cortical areas, not only pyramidal neurons in layer V, but also non-pyramidal neurons in layer VI were labeled. Stimulation of the LHA evoked an EPSP-IPSP sequence, or antidromic response in FC neurons. Some of the fast EPSPs were considered to be monosynaptic. The neurons labeled in the LHA following HRP injection into the FC were either relatively large spherical neurons or small ovoid-shaped neurons. These were distributed diffusely throughout the LHA.     

Selective regulation of thalamic sensory relay nuclei by nucleus reticularis thalami.

Stimulation in the segment of nucleus reticularis thalami adjacent to the lateral geniculate body (RLG), abolished visual evoked potentials for up to 150 msec. Both photic stimulation in the contralateral visual field and electric stimulation in the ipsilateral optic tract elicited primary cortical responses that were markedly reduced or abolished by prior conditioning stimulation in RLG. Stimulation of the segments of nucleus reticularis thalami adjacent to the medial geniculate (RMG) or the ventrobasal complex (RVBC) had the effect of markedly reducing or abolishing unilaterally projected primary evoked responses in the auditory and cutaneous systems, respectively. Only the sensory evoked potentials mediated by the relay nucleus adjacent to the region of R stimulated were affected. The reduction of the cortical evoked potentials was not due to the processes underlying the cortical recovery cycle, because conditioning stimulation on either side of RLG stimulated the primary geniculocortical fibers, but had a minimal or no effect on the visual test evoked response. These results suggest that R functions as a topographically organized inhibitory gate which can regulate the patterns of sensory input from the thalamus to the cortex. The regulatory effects on R by the mesencephalic reticular formation and the mediothalamic-frontocortical system may mediate both generalized and selective control of cortical sensory evoked potentials.     

Postsynaptic potentials evoked in spiny neostriatal projection neurons by stimulation of ipsilateral and contralateral neocortex

Postsynaptic potentials were evoked in neostriatal neurons by stimulation of the ipsilateral and contralateral medial agranular frontal cortical field (AGm) in the rat. This cortical region is known to project bilaterally to the dorsal lateral head of the caudate-putamen of rats. Ipsilateral stimulation of AGm should excite all types of corticostriatal neurons projecting to neostriatal neurons in the corresponding area in neostriatum, while stimulation of the same cortical area on the side contralateral to the recording should evoke synaptic potentials from a more restricted subpopulation of crossed corticostriatal neurons. Neostriatal neuronal responses were recorded intracellularly and spiny projection neurons identified by intracellular staining with horseradish peroxidase. The initial EPSP response to contralateral stimulation was similar to that evoked from the ipsilateral side, except for the absence of a relatively small short latency component responsible for the earliest part of the response to ipsilateral cortical stimulation. Comparison with previous findings indicated that this earliest EPSP component was due to activation of fast-conducting descending cortical efferents with collateral projections exclusively to the ipsilateral neostriatum. Stimulation of contralateral neostriatum evoked responses identical to those obtained using stimulation of contralateral neocortex. Analyses of these responses indicated that both EPSPs arise from activation of the same population of fibers. Stimulation of the contralateral internal capsule just caudal to neostriatum was not effective in evoking the EPSP. Chronic hemidecortication did not change the shape of the EPSP evoked from the intact contralateral side, but reduced its amplitude by approximately one half. These observations indicate that contralaterally projecting corticostriatal neurons in the rat project bilaterally in neostriatum, have axonal branches to the contralateral cerebral cortex as well as neostriatum, and converge onto neostriatal neurons that also receive input from the corresponding cortical region on the ipsilateral side.     

Serial lateral hypothalamic destruction with various interlesion intervals

Mature male or female albino rats sustained unilateral lateral hypothalamic area (LHA) destruction, and 30, 60, or 90 days later, sustained destruction of the intact contralateral LHA, thereby producing bilateral LHA destruction (serial 30, 60, and 90). Other rats sustained either simultaneous bilateral LHA destruction (one-stage), two lesions of the same LHA separated by 60 days (multistage), or unilateral LHA damage followed 60 days later by thalamic-hippocampal damage on the side of the brain opposite the original LHA lesion (thalamic). After brain damage, food and water intakes, body weight, and sensorimotor behaviors were measured. The multistage and thalamic rats displayed only minor and short-term deficits on the variables measured. The one-stage bilateral LHA rats were adipsic and aphagic, and displayed body weight loss, sensory neglect, hypoactivity, and gastric pathology. The serial rats (30-, 60-, and 90-day interlesion intervals) also displayed severe and persistent deficits. The serial rats were equivalent to the one-stage rats for duration of adipsia-aphagia, body weight loss, sensory neglect, hypoactivity, and gastric pathology. The results show that bilateral LHA destruction sustained in two operations (separated by 30, 60, or 90 days) produced behavioral deficits equivalent to deficits produced when the LHA was bilaterally destroyed in a single operation.     

Responses of rat lateral hypothalamic neuron activity to vestibular nuclei stimulation

Effects of lateral vestibular nucleus (LVN) stimulation on neuronal activity in the rat lateral hypothalamic area (LHA), including specific glucose-sensitive neurons, were investigated by extracellular and intracellular recordings in vivo. Stimulation of the contralateral LVN evoked 3 types of response in 46% (111/240) of the neurons recorded extracellularly: long latency (38.1 +/- 23.6 ms) excitation (62/111, 56%), short latency (6.9 +/- 3.1 ms) excitation-inhibition (33/111, 30%), and inhibition with 20.1 +/- 11.1 ms latency (16/111, 14%). Glucose-sensitive neurons, which were identified by electrophoretic application of glucose, did not respond specifically to such stimulation. Neuronal activity was recorded intracellularly from 31 LHA neurons, of which 13 responded to LVN stimulation. Seven of the 13 neurons showed a long latency EPSP (10.4 +/- 5.5 ms) and the remaining 6 exhibited an EPSP-IPSP sequence with shorter latency (4.5 +/- 3.0 ms). The amplitude of these responses was graded with a change in stimulus intensity. The EPSPs of both types of response were considered to be polysynaptic because of shortening of latencies by higher current stimulation. Since the LHA is implicated in the regulation of autonomic nerve activity, the present results showing polysynaptic pathways from the LVN to the LHA suggest functional involvement of the LHA in vestibulo-autonomic responses.     

Evoked potentials and long-term potentiation in the mouse dentate gyrus after stimulation of the entorhinal cortex

When the entorhinal cortex is electrically stimulated, an evoked potential is produced in the ipsilateral dentate gyrus of the mouse which is similar to this response in the rat, rabbit, and other preparations in which it has been recorded. The evoked potential consists of two components: Component I represents an extracellular monosynaptic population EPSP, and Component II represents a population spike due to the synchronous activation of the granule cells. After tetanic stimulation, responses to single-pulse stimuli increased and remained at that level for at least 30 min. This demonstrated long-term potentiation of the evoked potential, phenomenologically similar to that described in other species. A medial and lateral perforant path could be differentiated. Stimulation of the medial perforant path resulted in evoked potentials that had a short peak latency, half-width, and rise time. Conversely, stimulation of the lateral perforant path resulted in evoked potentials that had a long peak latency, half-width, and rise time. The recording electrode depth series were also different after selective activatio of the two paths. Stimulation of the medial perforant path resulted in recording electrode depth series that had their maximum negativities close to the cell body layer, whereas stimulation of the lateral perforant path resulted in depth series that had their maximum negativities farther out along the granule cell dendrites. These results are consistent with the different sites of termination of the two paths. Long-term potentiation was demonstrated in both pathways after administration of tetanic stimuli of various parameters.     

Effect of stimulation of the superior colliculi of the tectum mesencephali on the motor neurons of the neck muscles of the cat

Postsynaptic potentials evoked by stimulation of three points of the superior colliculus in motoneurons of neck muscles were studied in experiments on cats under chloralosenembutal anesthesia. Stimulation of ipsilateral superior colliculus evoked EPSP with latencies ranging from 1.5 to 3.5 ms in 49 motoneurons. Stimulation of contralateral superior colliculus evoked EPSP with latencies ranging from 1.5 to 3.0 ms in 63 motoneurons and IPSP with latencies ranging from 2.6 to 5.0 ms in 10 motoneurons. It is suggested that the recorded postsynaptic potentials are mono- and disynaptic.