Acute and chronic administration of immunomodulators induces anorexia in Zucker rats

To investigate the possible involvement of leptin signaling in lipopolysaccharide (LPS) anorexia, we compared the anorectic effect of LPS in genetically obese (fa/fa) Zucker rats and in their lean (Fa/?) counterparts. The effects of interleukin-1beta (IL-1beta) and muramyl dipeptide (MDP) were also tested. LPS [100 microg/kg body weight (BW)], IL-1beta (2 microg/kg BW) and MDP (2.2 mg/kg BW) injected intraperitoneally (i.p.) at lights out reduced food intake similarly in obese and lean rats. LPS injection at 500 or 1000 microg/kg BW (i.p.) also reduced food intake and BW similarly in obese and lean rats, but obese regained BW faster than lean rats. LPS (2.45 microg or 9.8 microg/h/rat) administered chronically with i.p. implanted osmotic pumps reduced food intake similarly on experimental day 1, regardless of the genotype. After day 3, the lean rats' anorectic response and recovery were dose-dependent, whereas the anorectic response in obese rats was minimally affected by dose (significant dose effect only on day 3). Again, obese rats regained lost BW faster than lean rats. These results do not support a role for leptin as the sole mediator of anorexia induced by bacterial products (LPS and MDP) and IL-1beta.

A role for cyclooxygenase-2 in lipopolysaccharide-induced anorexia in rats

Because nonselective cycloooxygenase (COX) inhibition attenuated anorexia after lipopolysaccharide (LPS) administration, we tested the ability of resveratrol (2.5, 10, and 40 mg/kg) and NS-398 (2.5, 10, and 40 mg/kg), selective inhibitors of the two COX isoforms COX-1 and -2, respectively, to attenuate LPS (100 microg/kg ip)-induced anorexia. NS-398 (10 and 40 mg/kg) administered with LPS at lights out attenuated LPS-induced anorexia, whereas resveratrol at all doses tested did not. Because prostaglandin (PG) E(2) is considered the major metabolite synthesized by COX, we measured plasma and cerebrospinal fluid (CSF) PGE(2) levels after LPS administration. LPS induced a time-dependent increase of PGE(2) in CSF but not in plasma. NS-398 (5, 10, and 40 mg/kg) blocked the LPS-induced increase in CSF PGE(2), whereas resveratrol (10 mg/kg) did not. These results support a role of COX-2 in mediating the anorectic response to peripheral LPS and point at PGE(2) as a potential neuromodulator involved in this response.

Abnormal patterns of microtubule-associated protein-2 (MAP-2) immunolabeling in neuronal nuclei and Lewy bodies in Parkinson's disease substantia nigra brain tissues

Parkinson's disease (PD) is a neurodegenerative disorder associated with the appearance of cytoplasmic Lewy bodies (LBs) in dopaminergic neurons of the substantia nigra and the progressive loss of these neurons. Cytoskeleton alterations and associated impairments of neuronal transport may contribute to neuronal death. Microtubule-associated protein-2 (MAP-2), a cytoskeleton protein is localized primarily in neuronal dendrites and is known to stabilize microtubule assembly and mediate their interactions with other neuronal cell components. To determine if alterations in MAP-2 morphology are present in PD neurons, we used single and double immunohistochemical and immunofluorescent techniques to characterize MAP-2 in PD neuronal tissues. We report abnormal MAP-2 immunolabeling in some neurons of the substantia nigra of PD brain tissues, which were not observed in the normal, age-matched, control brain tissues. Furthermore, MAP-2 was co-localized with alpha-synuclein and ubiquitin in cytoplasmic LBs of neurons. Surprisingly, MAP-2 was also found to form fibrous aggregates and crystal-like structures within neuronal nuclei. These PD-associated alterations in MAP-2 morphology and distribution suggest that impaired neuronal transport may contribute to the progression of neuronal loss in the brains of PD patients.

Topiramate promotes neurite outgrowth and recovery of function after nerve injury

Topiramate is a structurally novel neurotherapeutic agent with a unique combination of pharmacological properties and currently is available in most world markets for treating several seizure disorders. Because its pharmacological profile was suggestive of possible activity as a neuroprotectant, topiramate was evaluated and found to be active in several animal models of stroke or neuropathic pain. This prompted an evaluation of topiramate as a possible neurotrophic agent. In this study, topiramate enhanced the recovery of facial nerve function after injury when administered orally at therapeutically relevant doses, and significantly increased neurite outgrowth in cell cultures derived from fetal rat cortical and hippocampal tissues.

Disordered food intake and obesity in rats lacking cholecystokinin A receptors

Otsuka Long-Evans Tokushima Fatty (OLETF) rats develop obesity, hyperglycemia, and non-insulin-dependent diabetes mellitus and do not express cholecystokinin A (CCK-A) receptors, the receptor subtype mediating the satiety actions of CCK. In short-term feeding tests, male OLETF rats were completely resistant to exogenous CCK, and their response to bombesin was attenuated. Comparisons of liquid meal consumption in OLETF and control Long-Evans Tokushima (LETO) rats demonstrated that 1) OLETF rats had greater intakes during 30-min scheduled daytime meals and significantly larger and fewer spontaneous night-time meals and 2) although the initial rates of licking were the same, OLETF rats maintained the initial rate longer and the rate at which their licking declined was slower. In 24-h solid food access tests, OLETF rats consumed significantly more pellets than LETO controls, and this increase was attributable to significant increases in meal size. Together, these data are consistent with the interpretation that the lack of CCK-A receptors in OLETF rats results in a satiety deficit leading to increases in meal size, overall hyperphagia, and obesity.

Gustatory neural coding in the amygdala of the alert macaque monkey

1. Neurons in the amygdala are implicated in mediating hedonic appreciation, emotional expression, and conditioning, particularly as these relate to feeding. The amygdala receives projections from the primary taste cortex in monkeys, offering a route by which it could gain access to the gustatory information required to guide feeding behavior. We recorded the activity of 35 neurons in the amygdala of alert rhesus macaques in response to a range of gustatory intensities and qualities to characterize taste-evoked activity in this area. 2. The stimulus array comprised 26 chemicals, including four concentrations of each of the four basic taste stimuli, a series of other sugars, salts, and acids, monosodium glutamate, and orange juice. 3. Neurons responsive to taste stimulation could be found in a 76-mm3 region of the amygdala, centered 9.1 mm lateral to the midline, 14.9 mm anterior to the interaural line, and 25.7 mm below the surface of the dura. They composed 7.2% (35/484) of the cells tested for gustatory sensitivity in the amygdala. 4. The mean spontaneous activity of taste cells was 8.2 +/- 2.3 (SE) spikes per second. This rather high level provided an opportunity for reductions from spontaneous rate that was used regularly in the amygdala. When these negative response rates were included, the mean breadth-of-tuning coefficient of this sample of taste cells was 0.82. There was no strong evidence for gustatory neuron types, nor were functionally similar cells located together in a chemotopic arrangement. 5. Responses across 1.5 log units of stimulus concentration were nearly flat, with increasing excitation in some neurons largely offset by increasing inhibition in others. Taking the absolute value of the evoked activity, concentration-response functions rose monotonically to all basic stimuli except HCl, but were not sufficiently steep to account for human psychophysical data. The neural response to HCl did not rise with stimulus concentration within the range used. 6. Neural patterns representing the taste qualities of the basic stimuli were less sharply separated in the amygdala than at lower-order gustatory relays. Glucose elicited activity patterns that were most distinct from those of the nonsweet chemicals; those associated with NaCl were next most distinct. There was no clear separation between the patterns generated by chemicals that humans describe as sour and bitter. Monosodium glutamate evoked responses that did not correlate well with those of any basic stimulus, implying that its quality cannot be subsumed under the four basic tastes.(ABSTRACT TRUNCATED AT 400 WORDS)

Gustatory neural coding in the monkey cortex: L-amino acids

1. Single-neuron activity in the primary gustatory cortex of the alert cynomolgus monkey (Macaca fascicularis) was analyzed in response to a range of taste stimuli. Tastants included the four prototypical stimuli (glucose, NaCl, HCl, and quinine), fruit juice, and 12 amino acids selected for their chemical characteristics, nutritional significance, and biological importance, as well as for the availability of human psychophysical data on their perceived qualities. 2. Taste-evoked responses could be recorded from a cortical area that measured 3.5 mm in its anteroposterior extent, 2.0 mm mediolaterally, and 6.0 mm dorsoventrally. Gustatory cells constituted 4.8% of the 1,129 neurons tested. Nongustatory cells gave responses associated with mouth movements (11.1%), somatosensory stimulation (3.8%), approach or anticipation of the taste stimulus (2.2%), and tongue extension (0.4%). 3. The most effective taste stimuli were those with qualities that humans describe as salty or sweet: NaCl, monosodium glutamate, glucose, proline, glycine, and fruit juice. The least effective tastants were those rated bitter or insipid: tyrosine, tryptophan, phenylalanine, and leucine. Accordingly, 79% of the gustatory neurons responded best to glucose (46%) or NaCl (33%) among the basic stimuli; only 19% responded best to quinine (13%) or HCl (6%). One cell (2%) responded exclusively to fruit juice. 4. Cortical gustatory neurons showed a moderate breadth of sensitivity, with a mean breadth of tuning coefficient of 0.71 across 54 cells. There was no evidence of chemotopic organization in the taste cortex. 5. The taste quality of each stimulus was inferred from the relative similarity of the profiles they evoked. The clearest distinction among stimuli was between those that humans characterize as sweet versus those with other qualities. Several amino acids that have dominant sweet (glycine and proline), salty (arginine and monosodium glutamate), sour (tryptophan), or bitter (phenylalanine) components to humans evoked activity profiles that were associated with those of the appropriate prototypical stimuli. Others (cysteine and lysine) were not closely related to any single prototype. 6. Conclusions based on the responses of cortical cells in the monkey are in close agreement with those that derive from human psychophysical studies of L-amino acids, reinforcing the value of this neural model for human taste perception.

Gustatory neural coding in the monkey cortex: stimulus quality

1. Extracellular action potentials were recorded from 50 single neurons in the insular-opercular cortex of two alert cynomolgus monkeys during gustatory stimulation of the tongue and palate. 2. Sixteen stimuli, including salts, sugars, acids, alkaloids, monosodium glutamate, and aspartame, were chosen to represent a wide range of taste qualities. Concentrations were selected to elicit a moderate gustatory response, as determined by reference to previous electrophysiological data or to the human psychophysical literature. 3. The cortical region over which taste-evoked activity could be recorded included the frontal operculum and anterior insula, an area of approximately 75 mm3. Taste-responsive cells constituted 50 (2.7%) of the 1,863 neurons tested. Nongustatory cells responded to mouth movement (20.7%), somatosensory stimulation of the tongue (9.6%), stimulus approach or anticipation (1.7%), and tongue extension (0.6%). The sensitivities of 64.6% of these cortical neurons could not be identified by our stimulation techniques. 4. Taste cells had low spontaneous activity levels (3.7 +/- 3.0 spikes/s, mean +/- SD) and showed little inhibition. They were moderately broadly tuned, with a mean entropy coefficient of 0.76 +/- 0.17. Excitatory responses were typically not robust. 5. Hierarchical cluster analysis was used to determine whether neurons could be divided into discrete types, as defined by their response profiles to the entire stimulus array. There was an apparent division of response profiles into four general categories, with primary sensitivities to sodium (n = 18), glucose (n = 15), quinine (n = 12), and acid (n = 5). However, these categories were not statistically independent. Therefore the notion of functionally distinct neuron types was not supported by an analysis of the distribution of response profiles. It was the case, however, that neurons in the sodium category could be distinguished from other neurons by their relative specificity. 6. The similarity among the taste qualities represented by this stimulus array was assessed by calculating correlations between the activity profiles they elicited from these 50 neurons. The results generally confirmed expectations derived from human psychophysical studies. In a multidimensional representation of stimulus similarity, there were groups that contained acids, sodium salts, and chemicals that humans label bitter and sweet. 7. The small proportion of insular-opercular neurons that are taste sensitive and the low discharge rates that taste stimuli are able to evoke from them suggest a wider role for this cortical area than just gustatory coding.(ABSTRACT TRUNCATED AT 400 WORDS)

Gustatory neural coding in the monkey cortex: stimulus intensity

1. We analyzed the activity of single neurons in gustatory cortex of alert cynomolgus monkeys in response to a range of stimulus intensities. Chemicals were deionized water, fruit juice, and several concentrations of the four prototypical taste stimuli: 10(-3)-1.0 M glucose, 10(-3)-1.0 M NaCl, 10(-4)-3 x 10(-2) M HCl, and 10(-5)-3 x 10(-3) M quinine HCl. 2. Taste-evoked responses could be recorded from a cortical gustatory area that measured 2.5 mm in its anteroposterior extent, 6.0 mm dorsoventrally, and 3.0 mm mediolaterally. Taste-responsive cells constituted 62 (3.7%) of the 1,661 neurons tested. Nongustatory cells gave responses associated with mouth movement (10.1%), somatosensory stimulation (2.2%), and approach or anticipation (0.9%). 3. Intensity-response functions were determined across 62 gustatory neurons. Neural thresholds for each stimulus quality conformed well to human psychophysical thresholds. Mean discharge rate was a direct function of stimulus concentration for glucose, NaCl, and quinine HCl. The most effective of the basic stimuli was glucose. 4. Power function exponents were calculated from the responses of neural subgroups most responsive to each basic stimulus. Those for glucose, NaCl, and quinine were within the range of psychophysically derived values. Thus the perceived intensity of each basic quality is presumably based on the activity of the appropriate neural subgroup rather than on the mean activity of all taste cells. 5. The mean breadth-of-tuning (entropy) coefficient for 62 gustatory neurons was 0.65 (range, 0.00-0.98). 6. There was no clear evidence of chemotopic organization in the gustatory cortex. 7. An analysis of taste quality indicated that sweet stimuli evoked patterns of activity that were clearly distinct from those of the nonsweet chemicals. Among the latter group, NaCl was differentiable from HCl and quinine HCl, whose patterns were closely related. 8. The response characteristics of cortical taste cells imply gustatory thresholds and intensity-response functions for the nonhuman primate that conform well to those reported in psychophysical studies of humans, reinforcing the value of this neural model for human taste intensity perception.

The neurosteroids pregnenolone and pregnenolone-sulfate but not progesterone, block Ca2+ currents in acutely isolated hippocampal CA1 neurons

The neurosteroids pregnenolone (PE) and pregnenolone-sulfate (PS) have been shown to interact with the GABAA receptor in the central nervous system. In contrast, nothing is known of any possible modulation of voltage-gated calcium channels (VGCC). We have examined the interaction of PE, PS and progesterone on VGCC in acutely isolated adult guinea-pig hippocampal CA1 neurons using the whole-cell patch clamp technique. PE and PS depressed the calcium current at low micromolar concentrations (0.001-100 microM). The time to peak of the calcium current was slowed by PE and PS. The blocking action of PE and PS occurs in the presence of 10 microM picrotoxin. In contrast, progesterone had no effect on the Ca2+ current, indicating specificity for PE and PS. These results demonstrate a direct and novel membrane site of action for PE and PS, suggesting a possible role influencing brain excitability.

Immunomodulators and feeding regulation: a humoral link between the immune and nervous systems

Cells of the nervous and immune systems have specific receptors for humoral substances that originate in both systems. These elements establish a bidirectional information exchange network between the nervous and immune systems. In particular, neuroregulators (neurotransmitters and neuromodulators) can modulate specific immune system function(s) and immunoregulators (immunomodulators) can modulate specific nervous system function(s). Modulation of immune functions by neuroregulators has been receiving considerable attention; however, modulation of nervous system functions by immunomodulators has been little studied. The presence of immunomodulators in the brain and cerebrospinal fluid may represent local synthesis by astrocytes, microglia, endothelial cells, intrinsic macrophages and blood-derived lymphocytes which cross the blood-brain barrier, or the concentration of substances derived from the peripheral blood. Acute and chronic inflammatory processes, malignancy, and immunological reactions stimulate the synthesis and release of immunomodulators in various cell systems. These immunomodulators have pivotal roles in the coordination of the host defense mechanisms and repair and induce a series of endocrine, metabolic, and neurologic responses. This paper focuses on the effects of immunomodulators (interleukins, tumor necrosis factor, tuftsin, platelet activating factor, and others) on the central nervous system (CNS), in particular, on feeding regulation. It is proposed that an immunomodulatory system regulates food intake by a direct action in the CNS through a specific neuro-immuno interaction. This regulatory system may be operative during acute and chronic disease.

Substance P effects on the dorsal motor nucleus of the vagus

Substance P (SP) was applied by superfusion (0.8 to 3.4 x 10(-6) M) to neurons of the dorsal motor nucleus of the vagus (DMV) in slice preparations of the rat medulla oblongata. Intracellular recordings showed that 18 of 43 (42%) neurons were depolarized and the depolarization was associated with an increase in membrane input resistance; five of 43 (12%) neurons were hyperpolarized and the hyperpolarization was associated with a decrease in membrane input resistance. Both effects were reversible and persisted after blockade of synaptic transmission by Ca2+ free/high Mg2+ solution. These data show that: 1) vagal neurons in the DMV have receptors for SP; 2) SP may modulate vagal output specially by increasing neuronal excitability; 3) although electrophysiological effects of SP have been studied in a variety of central and peripheral neurons, this is the first evidence of SP effects on DMV; 4) DMV is a particular brain target site in which SP may induce depo- or hyperpolarization.

Growth factors, feeding regulation and the nervous system

A variety of growth factors and their receptors are present in the nervous system. Growth factors can modulate specific nervous system functions others than those related to growth, development, and tissue repair. The presence of growth factors in the brain and cerebrospinal fluid is the result of local synthesis (by neuronal, glial, vascular, and mononuclear phagocyte components), and uptake from the peripheral blood through the blood-brain barrier (in specific cases) and circumventricular organs. This paper focuses on the effects of a heterogeneous group of growth factors (acidic and basic fibroblast growth factors, insulin-like growth factors, epidermal growth factor, platelet-derived growth factor, interleukin-1 and others) on the central nervous system (CNS), in particular, on feeding regulation. Recent evidence supporting participation of growth factors in the regulation of feeding by a direct action at the level of the CNS is reviewed. Various growth factors have the ability to suppress short- and long-term food intake (FI), whereas others affect only short-term FI, or do not affect FI. Acute and chronic pathological processes stimulate the synthesis and release of growth factors in various cellular systems, and monitoring of growth factors by the CNS could be part of the regulatory signals that induce FI suppression frequently accompanying acute and chronic disease. Thus, it is proposed that a system regulating FI through growth factor-dependent mechanisms may be operative during specific physiological or pathological conditions.