Taste Responses of Neurons of the Hamster Solitary Nucleus Are Enhanced by Lateral Hypothalamic Stimulation

Abstract

. Taste responses of neurons of the hamster solitary nucleus are enhanced by lateral hypothalamic stimulation. J Neurophysiol 87: 1981-1992, 2002; 10.1152/jn.00765.2001. Gustatory responses in the brain stem are modifiable by several physiological factors, including blood insulin and glucose, intraduodenal lipids, gastric distension, and learning, although the neural substrates for these modulatory effects are not known. Stimulation of the lateral hypothalamus (LH) produces increases in food intake and alterations in taste preference behavior, whereas damage to this area has opposite effects. In the present study, we investigated the effects of LH stimulation on the neural activity of taste-responsive cells in the nucleus of the solitary tract (NST) of the hamster. Bipolar stimulating electrodes were bilaterally implanted in the LH, and the responses of 99 neurons in the NST, which were first characterized for their taste sensitivities, were tested for their response to both ipsilateral and contralateral LH stimulation. Half of the tasteresponsive cells in the NST (49/99) were modulated by LH stimulation. Contralateral stimulation was more often effective (41 cells) than ipsilateral (13 cells) and always excitatory; 10 cells were excited bilaterally. Six cells were inhibited by ipsilateral stimulation. A subset of these cells (n ϭ 13) was examined for the effects of microinjection of DL-homocysteic acid (DLH), a glutamate receptor agonist, into the LH. The effects of electrical stimulation were completely mimicked by DLH, indicating that cell somata in and around the LH are responsible for these effects. Other cells (n ϭ 14) were tested for the effects of electrical stimulation of the LH on the responses to stimulation of the tongue with 0.032 M sucrose, NaCl, and quinine hydrochloride, and 0.0032 M citric acid. Responses to taste stimuli were more than doubled by the excitatory influence of the LH. These data show that the LH, in addition to its role in feeding and metabolism, exerts descending control over the processing of gustatory information through the brain stem.

Modulation of activity of gustatory neurons in the hamster parabrachial nuclei by electrical stimulation of the ventroposteromedial nucleus of the thalamus

“…Electrical stimulation of the BNST modulated taste responses in the NST and PbN (34,74). Activation of the CeA and LH also modulated taste responses of the neurons in the NST and PbN (8,35,36). Modulation of PbN neurons' taste responses by forebrain activation, including the CeA, LH, and GC, has also been demonstrated by Lundy and Norgren (39,40) in the rat.…”

The vagus nerve, food intake and obesity

“…Bereiter and coworkers (Bereiter et al, 1980) were the first to demonstrate that NTS neurons receiving oral input through the chorda tympany nerve are modulated by lateral hypothalamic stimulation. Such facilitation of gustatory responses in NTS neurons by lateral hypothalamic stimulation was recently confirmed in the hamster (Cho et al, 2002). Rogers and coworkers then demonstrated a similar effect of paraventricular nucleus stimulation on the activity of NTS neurons receiving gastrointestinal afferents through the vagus nerve (Rogers and Hermann, 1985).…”

Activity in the Hypothalamus, Amygdala, and Cortex Generates Bilateral and Convergent Modulation of Pontine Gustatory Neurons

“…Prior studies demonstrated that stimulation in the LH and CeA can alter responses of nucleus of the solitary tract neurons (NST) to sapid stimulation (Cho et al 2002a;Li et al 2002), whereas the effects of only CeA stimulation were tested one synapse further centrally in the PBN (Lundy and Norgren 2001). Recent evidence also indicates that descending input from the LH and CeA converge to modulate some of the same NST taste cells (Cho et al 2003).…”

“…All 3 forebrain areas modulate the same system bilaterally (Cho et al 2002a;DiLorenzo and Monroe 1995;Li et al 2002). In fact, contralateral stimulation of the CeA and GC, but not the LH, more effectively suppressed responses in NaCl-best PBN cells than did ipsilateral activation.…”

“…In the medullary nucleus of the solitary tract (NST), electrical stimulation of the LH and CeA is known to modulate both background discharge and taste-evoked responses (Bereiter et al 1980;Cho et al 2002a;Li et al 2002;Matsuo et al 1984;Murzi et al 1986). Cortex stimulation also modulates the spontaneous activity of taste responsive cells, but the effects on sapid stimulus responsiveness have not been tested (Smith and Li 2000).…”