Oral and subcutaneous administration of the glycosaminoglycan C3 attenuates Abeta(25-35)-induced abnormal tau protein immunoreactivity in rat brain

High molecular weight glycosaminoglycans (GAG) and proteoglycans (PG) affect pathological changes of the brain in Alzheimer's disease (AD). PG stimulate the processing and aggregation of amyloid-beta (Abeta), protect the protein from proteolysis, and increase the formation of neurofibrillary tangles by inducing the hyperphosphorylation of tau protein. These effects may be competitively inhibited by GAG. We have studied the effects of orally (by gavage) and subcutaneously (s.c.) administered low molecular weight heparin, C3 (4-10 oligosaccharides; MW = 2.1 kDa; USP value = 12 U/mg), on abnormal tau-2 protein immunoreactivity in the rat hippocampus following a single, unilateral intra-amygdaloid administration of Abeta(25-35). Oral administration of C3 (25 mg/kg; once daily) was initiated 3 days prior to Abeta(25-35) administration, and was continued daily for an additional 14 days. S.c. administration of C3 (2.5 mg/kg, twice daily), was started 3 days prior to, and was continued for 32 days after, Abeta(25-35) administration. Animal brains were subsequently processed for tau-2, ChAT-immunoreactivity, choline acetyltransferase (ChAT) activity and acetylcholinesterase (AChE) activity. Both oral and s.c. administration of C3 attenuated Abeta(25-35) induced appearance of tau-2-immunoreactive (IR) perikarya in the ipsilateral hippocampus (P < 0.05). Hippocampal cholinergic enzyme activity in C3 treated animals was not significantly different from control animals. The present findings suggest that C3 might be used successfully to prevent abnormal tau protein formation in chronic neurologic diseases, such as AD. Moreover, our data demonstrate that the mechanism of this effect does not appear to influence the cholinergic system of the brain.

Amyloid-beta injection in rat amygdala alters tau protein but not mRNA expression

Previously we demonstrated local and distant changes in tau protein immunoreactivity reminiscent of those seen in Alzheimer's disease (AD) following a unilateral injection of amyloid-beta (Abeta)(25-35) into the rat amygdala. To explore the relevance of these findings to AD, we compared the effects of Abeta(1-42) to those of Abeta(25-35). Injections of both Abeta(1-42) and Abeta(25-35) into rat amygdala resulted in increased tau-2 immunolabeling in neurons. To determine whether these alterations were due to changes in the expression of tau, we measured tau protein expression by Western blotting and tau mRNA isoform expression by the reverse transcription-polymerase chain reaction in the amygdala, hippocampus, and cerebellum following a unilateral injection of Abeta(25-35) or vehicle into the amygdala. The levels of tau proteins were increased bilaterally in the amygdala of Abeta(25-35)- compared to vehicle-treated animals 8 and 16 days following treatment. The molecular weights of tau proteins were decreased in the Abeta(25-35)-treated (59-69 kDa) compared to the vehicle-treated (67-72 kDa) animals 8 days following treatment. There were no changes in tau mRNA expression in any brain region examined. In this model, just as in AD, there is an increase in tau protein levels without a change in tau mRNA expression, suggesting that Abeta peptides may influence tau protein stability in both the rat and the human brain.

Neurokinin-3 receptor distribution in rat and human brain: an immunohistochemical study

Autoradiographic and immunohistochemical studies have shown that the neurokinin-3 receptor is widely distributed in the rodent CNS. Expression of the neurokinin-3 receptor in human brain, however, has been debated. These conflicting findings, as well as the poor resolution of autoradiographic images, prompted us to develop a polyclonal antibody against an oligopeptide derived from the carboxy-terminus consensus sequence of both the rat and human neurokinin-3 receptor ([C]ASTTSSFISSPYTSVDEYS, amino acids 434-452 of the rat neurokinin-3 receptor). Western blot analysis of both human and rat brain tissue revealed a major band in the molecular weight range 65,000-67,000, the proposed molecular weight of the neurokinin-3 receptor based on its amino acid sequence and presumed glycosylation state. The distribution of selective high affinity neurokinin-3 receptor agonist [3H]senktide binding and neurokinin-3 receptor immunoreactivity were virtually identical in the brains of male Fischer 344 rats. The highest concentrations of neurokinin-3 receptors were observed in cortical layers IV-V; the basolateral amygdaloid nucleus; the hypothalamic paraventricular, perifornical and supraoptic nuclei; the zona incerta; and the entopeduncular and interpeduncular nuclei. [3H]senktide binding and neurokinin-3 receptor immunoreactivity were compared in homologous cortical areas of the human and rat brain. In contrast to the rat, autoradiographic analysis of normal control human brains (35-75 years) revealed a distinct and predominant superficial cortical labeling in the glia limitans and the cortical layer I. However, neurokinin-3 receptor immunoreactivity could be found not only in the superficial cortical layers, but also on pyramidal neurons and astrocytes in the neuropil and white matter. These findings suggest species differences in both the cellular and anatomical distribution of the neurokinin-3 receptor.

Age and species-dependent differences in the neurokinin B system in rat and human brain

Neurokinin B and its cognate neurokinin-3 receptor are expressed more in the forebrain than in brain stem structures but little is known about the primary function of this peptide system in the central processing of information. In general, few studies have specifically addressed age-related changes of tachykinins, notably the changes in number and/or distribution of the neurokinin B-expressing and neurokinin-3 receptor-bearing neurons. Data on functions and changes of neurokinins in physiological aging are limited and apply mainly to the substance P/neurokinin-1 receptor system. In the present study, we analyzed neurokinin B/neurokinin-3 receptor system in young (5 months) versus middle aged (15 months) and old rats (23-25 months) and also in aging human brains. For the majority of the immunohistochemically examined regions of the rat brain, there was no statistically significant change in neuronal number and size of the neurokinin B and neurokinin-3 receptor staining. In the adult human brain, there was no age-associated change of the number or size of neurokinin-B-positive neurons. However, we found a major decline in number of neurokinin-3 receptor-expressing neurons between young/middle aged (30 years to 69 years) versus old (70 years and older) adults. Interestingly, numbers of neurokinin-3 receptor-positive microglia increased whereas the neurokinin-3 receptor-positive astrocytes remained unchanged in both aging rat and human brains. Finally, in addition to assessing the morphological and quantitative changes of the neurokinin B/neurokinin-3 receptor system in the rat and human brain, we discuss functional implications of the observed interspecies differences.

Effect of d-fenfluramine on the lymphocyte response of HIV+ humans

The objective of this study was to analyse the effect of d-dexfenfluramine (d-FEN) on the human lymphocyte response, in vitro. Experiments were designed to determine whether d-FEN augments specific human immune parameters associated with protection from opportunistic microbial pathogens and particularly focuses on d-FEN as a means by which to augment the function of CD8+ and CD4+ lymphocytes. Lymphocytes were examined for three reasons: (1) for their ability to inhibit the growth of Candida albicans; (2) for their ability to proliferate in response to a mitogen; and, (3) their cytokine profile (vis., production of IL-2, IFN-gamma and TNF-alpha). Peripheral blood mononuclear cells (PBMC) were obtained from 20 HIV+ patients. The patients were diagnosed as HIV+ within the past 0.5-9 years. d-FEN was found to augment the capacity of CD8+ lymphocytes to inhibit the growth of the opportunistic microbial pathogen, C. albicans. d-FEN enhanced the capacity of CD4+ lymphocytes to proliferate in response to the mitogen, Concanavalin A, and to increase the amount of IL-2 produced by CD4+ and CD8+ lymphocytes from AIDS patients. d-FEN increased the number of CD4+ and CD8+ lymphocytes that produced IFN-gamma from either non-AIDS or AIDS patients and increased the number of AIDS patient's CD8+ lymphocytes that produce TNF-alpha. These in vitro data suggest that d-FEN may be effective in enhancing immune function in immunocompromised individuals.

Bilateral injections of amyloid-beta 25-35 into the amygdala of young Fischer rats: behavioral, neurochemical, and time dependent histopathological effects

To examine the time course of the histopathological effects of bilateral injections of amyloid-beta 25-35 (A beta) and to determine if these effects are associated with a reduction in choline acetyltransferase activity and behavioral impairments, we injected A beta (5.0 nmol) into the amygdala of young male Fischer rats. Control rats received vehicle infusions. For histological analysis, animals were sacrificed at 8, 32, 64, 96, and 128 days postoperatively (n = 21-33 per timepoint). A beta induced neuronal tau-2 staining in the right, but not the left amygdala and hippocampus. A beta also induced reactive astrocytosis and neuronal shrinkage within the right hippocampus and amygdala, respectively. As with tau-2, these same brain regions within the left hemisphere in the A beta-treated rats were significantly less affected. In addition, A beta appeared to induce microglial and neuronal interleukin-1beta staining. The histopathological effects of A beta peaked at 32 days postoperatively but were not associated with a reduction in amygdaloid choline acetyltransferase activity. In a separate experiment, behavioral effects of bilateral intra-amygdaloid injections of A beta were analyzed at 34-52 days postoperatively. In an open field test, the treatment groups differed only in the numbers of rears emitted (p = 0.016). There was no effect of A beta in the Morris water maze or in the acquisition and retention of a one-way conditioned avoidance response. These data suggest a laterality in the histopathological effects of A beta and that the effects of single injections are in part transient. These findings also suggest a direct association between plaque and tangle formation in Alzheimer's disease, and support the use of this rat model to screen drugs that may alter the initial pathological events associated with Alzheimer's disease, that occur before the manifestations of extensive behavioral impairments become evident.

Laterality in the histological effects of injections of amyloid-beta 25-35 into the amygdala of young Fischer rats

We have observed that single amyloid-beta 25-35 (A beta) injections (5.0 nmol) into the right amygdala of rats produce progressive cytoskeletal and astrogliotic reactions not only within the amygdala, but also in distal brain regions that project to the amygdala. To determine if these effects are potentiated by bilateral injections, we injected A beta (5.0 nmol) into the left and right amygdala of young male Fischer rats. Animals were sacrificed 32 days postoperatively. Bilateral infusions of A beta induced significant neuronal shrinkage, tau-2 neuronal staining, and reactive astrocytosis within the right amygdala and/or hippocampus, compared with vehicle-treated rats. Surprisingly, the same brain regions within the left hemisphere were significantly less affected even though no differences were observed between the left and right amygdala in the size of Congored-positive A beta deposits. Unilateral injections of A beta into the left amygdala led to significant histological changes in the right amygdala and hippocampus, but not in the same brain regions within the left hemisphere. These results suggest a laterality in the histopathological effects of A beta in male Fischer rats. Identification of the cause for the lateralized effect of A beta may prove valuable for understanding the etiology of Alzheimer disease and provide possible therapeutic strategies designed to slow the progression of the disease.

Androgen inhibits neurotransmitter turnover in the medial prefrontal cortex of the rat following exposure to a novel environment

Previous studies have demonstrated that gonadal steroid hormones affect the neuroendocrine response to a novel environment and other stressors. Introduction to a novel environment also increases neurotransmitter turnover in the medial prefrontal cortex (MPFC). In this study, we examined the possibility that gonadal steroid hormones could similarly modulate the neurotransmitter response to a novel environment in the MPFC of the male rat. Male Fischer 344 rats at 3 months of age were gonadectomized (GDX'd) and implanted with Silastic capsules containing dihydrotestosterone propionate (DHTP, a non-aromatizable form of androgen), 17 beta-estradiol (E), or placebo. Control animals were left intact. Each of these groups was further divided into a group introduced to a novel environment or a home cage control group. Animals exposed to a novel environment were killed after spending 20 min in a novel open field, whereas control animals were killed immediately upon removal from their home cage. Using high performance liquid chromatography, the MPFC was assayed for tissue levels of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylalanine (DOPAC) and homovanillic acid (HVA); norepinephrine (NE) and its metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG); or serotonin (5-HT) and its metabolite 5-hydroxyindole acetic acid (5-HIAA). The introduction to a novel environment caused significant increases in turnover of all three neurochemicals examined as estimated by metabolite/precursor ratios. These increases were characterized by increases in DOPAC, HVA, MHPG and 5-HIAA coupled with decreases in DA, NE and 5-HT. There was no effect of GDX on neurotransmitter turnover, however, treatment of GDX animals with DHTP prevented the open field induced increase in DOPAC/DA, MHPG/NE, and 5-HIAA/5-HT ratio. Treatment of GDX animals with estrogen had the opposite effect of DHTP, DOPAC/DA and MHPG/NE ratios increased to a greater level following the introduction to a novel environment than in GDX or intact animals. Examination of behavior in the open field showed significant decreases in activity in the DHTP-treated group but not in any other behavioral parameter (rears, nose pokes). Since the non-aromatizable androgen, DHTP, is presumably acting via androgen receptors, and E is presumably acting via estrogen receptors, these data suggest that, in the MPFC of male rats, androgen and estrogen receptors act in an opposing fashion to modify neurotransmitter turnover. This suggests that local changes in the relative levels of androgen and estrogen can have profound effects on the neurobiological response of the medial prefrontal cortex to stimuli.

Local and distant histopathological effects of unilateral amyloid-beta 25-35 injections into the amygdala of young F344 rats

To determine if amyloid-beta (A beta) induces tau-immunoreactivity (IR) and reactive astrocytosis in vivo, we injected A beta 25-35 (5.0 nmol) into the right amygdala of rats. At 8 days postinjection, the peptide induced tau-2 IR in neuronal cell bodies and processes ipsilaterally in the amygdala, cingulate cortex, and hippocampus. At 32 days postinjection, the intensity of tau-2 IR was greater than at 8 days in the amygdala and hippocampus, but not in the cingulate cortex. Induction of Alz-50 IR also was progressive but the morphology and distribution was different from tau-2 IR. Beaded fibers with occasional neuronal perikarya were visualized with Alz-50, and the IR was primarily observed in the ipsilateral amygdala. In addition, amygdaloid injections of A beta 25-35 induced reactive astrocytosis, particularly in the ipsilateral hippocampus at 32 days postoperatively. To our knowledge, this is the first study to show that in vivo injections of A beta 25-35 induce progressive transsynaptic cytoskeletal and astrogliotic reactions, that gradually spread from the area of injection to brain regions that have prominent efferent connections with that area. These findings also suggest a direct association between plaque and tangle formation in Alzheimer's disease.

Reduction of calcineurin enzymatic activity in Alzheimer's disease: correlation with neuropathologic changes

Neurofibrillary tangles (NFT), neuritic plaques, and dystrophic neurites are the classic neuropathologic hallmarks of Alzheimer's disease (AD), all of which contain to varying degrees abnormally and/or hyperphosphorylated forms of the microtubule-associated protein tau. Protein phosphatase 2B (calcineurin) dephosphorylates tau isolated from AD brains to control levels in vitro as well as regulates tau phosphorylation and function in vivo. It has been hypothesized that the changes in tau phosphorylation observed in AD may be due to increases in kinase activity and/or decreases in phosphatase activity. In order to investigate the latter possibility, we examined calcineurin enzyme activity using the substrate para-nitrophenyl-phosphate (pNPP) in postmortem brain samples from individuals with moderate to severe AD (n = 8) and age-matched controls (n = 7). The stimulation of calcineurin activity by manganese chloride (1 mM) was reduced by 60% (p < 0.01) in whole-cell homogenates prepared from AD temporal cortex (Brodmann area 38). On the other hand, in P2 membrane fractions, the stimulation of calcineurin activity by manganese chloride as well as nickel chloride (1 mM) was reduced by 37% (p < 0.05) and 79% (p < 0.01), respectively. The manganese-stimulated calcineurin activity in the temporal cortex inversely correlated with both the number of NFT (r = -0.60, p < 0.02) and neuritic/core plaques (r = -0.63, p < 0.02) in whole-cell homogenates, but only with NFT (r = -0.61, p < 0.02) in P2 membrane fractions. The nickel-stimulated calcineurin activity did not correlate with neuropathology measures in either whole-cell or P2 membrane fractions. In striate visual cortex (Brodmann area 17), an area relatively unaffected in AD, neither whole-cell nor P2 membrane calcineurin activity were significantly altered. To our knowledge, this is the first report of a reduction in calcineurin phosphatase activity in AD which correlates with the neuropathological features in a region-, subcellular fraction-, and divalent cation-specific manner.

Responses to novelty stress in female F344 rats: effects of age and d-fenfluramine treatment

To elucidate some of the mechanisms underlying the neuroendocrine and neurochemical changes associated with age in female rats, we administered the serotonin (5-HT) releaser and reuptake inhibitor, d-fenfluramine (d-FEN; 0.0 or 0.6 mg/kg/day, PO) for 30-38 days to young (4 month) and old (21 month) F-344 female rats. Animals were placed into a novel open field (OF) for 20 min before sacrifice. Control animals were sacrificed immediately upon removal from their home cage (HC). Old rats exhibited significantly (p < 0.05) less exploratory behavior and a smaller CORT response to OF than young animals. d-FEN treatment had no effect on plasma ACTH and CORT levels or exploratory behavior. The old HC rats had significantly (p < 0.05) higher plasma levels of prolactin (PRL) than the young HC rats. A stress induced increase in PRL secretion was observed in the old rats only, which was attenuated by d-FEN treatment. In the OF groups, both the young and old rats showed elevated medial frontal cortex (MFC) dopamine turnover (DOPAC/DA ratio), but only the young rats exhibited an elevation in norepinephrine (NE) turnover (MHPG/NE ratio). d-FEN treatment blocked the stress-induced increase in NE turnover in the young rats and the increase in DA turnover in the old rats. These data suggest that 5-HT activity could be involved in the age-related changes in the MFC catecholamine and PRL responses to stress in female rats.

beta-Amyloid 25-35 and/or quinolinic acid injections into the basal forebrain of young male Fischer-344 rats: behavioral, neurochemical and histological effects

beta-Amyloid peptides have been shown to potentiate the neurotoxic effect of excitatory amino acids in vitro. In order to determine if this occurs in vivo, four experiments were performed. We injected beta-amyloid 25-35 (beta A 25-35) and/or quinolinic acid (QA) bilaterally into the ventral pallidum/substantia innominata (VP/SI) of rats. Control rats received vehicle infusions. A high dose of QA (75.0 nmol/3 microliters) increased open field activity and impaired spatial learning in the Morris water maze, but did not affect the acquisition of a one-way conditioned avoidance response. These changes were associated with histological evidence of neurotoxicity and a reduction in amygdaloid but not frontal cortical or hippocampal choline acetyltransferase (ChAT) activity. A lower dose of QA (37.5 nmol/3 microliters) produced no behavioral effects. It reduced amygdaloid ChAT activity to a lesser extent than the higher dose (15% vs. 29-37%), and caused less histological damage. beta A 25-35 (1.0 or 8.0 nmol/3 microliters) failed to produce behavioral, histological or neurochemical signs of toxicity. Neither dose of beta A 25-35 potentiated the effects of QA (37.5 nmol) on behavior or amygdaloid ChAT activity, and did not appear to increase the histological damage caused by QA. These results suggest that in vivo beta A 25-35 is not neurotoxic and does not potentiate the neurotoxicity of QA in the VP/SI. Further, the histological effects of a high dose of beta A 25-35 (8.0 nmol/3 microliters; a cavitation containing a Congo red positive proteinaceous material) are quite distinct from those produced by a high dose of QA (75.0 nmol/3 microliters; widespread neuronal loss and gliosis).

Effect of d-fenfluramine on the local immune response to the opportunistic microbial pathogen Candida albicans

In this study the effects of systemic administration of d-fenfluramine on the local lymphocyte response to Candida albicans was evaluated. Experimental animals were challenged intradermally with Candida albicans and then administered d-fenfluramine (d-FEN 1 mg/kg per day, i.p.) or a balanced salts solution. At successive time intervals, lymphocytes were derived from the draining lymph nodes and from the dermal sites of active microbial challenge. A CD8+ lymphocytosis was observed in all animals challenged with Candida albicans. The CD8+ lymphocytosis was augmented in animals that received d-FEN. Phenotypically, lymph nodes from d-FEN treated animals showed a marked increase in CD3+ and CD8+ lymphocytes, a modest increase in the numbers of NK1.1+ cells and a decrease in Ig+ lymphocytes. Functionally, lymphocytes from the site of active microbial challenge were capable of direct growth inhibition of Candida albicans. The anti-fungal activity was augmented in the animals that received d-FEN. These results suggest that d-FEN augments the local T lymphocyte response to an important microbial pathogen by increasing the number of T lymphocytes draining the site of microbial infection and by increasing the biological activity of the lymphocytes at the site of the infection.

Within-subject decline in delayed-non-match-to-sample radial arm maze performance in aging Sprague-Dawley rats

A within-subject design was used to examine delayed-non-match-to-sample radial arm maze performance in aging (6-18 months) male Sprague-Dawley rats. A decrease in correct choices and an increase in retroactive errors were observed at all retention intervals at 18 months of age compared with performance at 6 or 12 months. No age by retention interval interaction was observed. Neither age nor increasing retention interval influenced proactive errors during the retention test. The observation of an age- and delay-dependent increase in retroactive errors, but not proactive errors, suggests that the deficit relates to a memory dysfunction as opposed to a generalized performance deficit.

Within-subject decline in delayed-non-match-to-sample radial arm maze performance in aging Sprague-Dawley rats

A within-subject design was used to examine delayed-non-match-to-sample radial arm maze performance in aging (6-18 months) male Sprague-Dawley rats. A decrease in correct choices and an increase in retroactive errors were observed at all retention intervals at 18 months of age compared with performance at 6 or 12 months. No age by retention interval interaction was observed. Neither age nor increasing retention interval influenced proactive errors during the retention test. The observation of an age- and delay-dependent increase in retroactive errors, but not proactive errors, suggests that the deficit relates to a memory dysfunction as opposed to a generalized performance deficit.

AF64A affects septal choline acetyltransferase but not parvalbumin immunoreactive cells

Rats received bilateral intracerebroventricular (ICV) infusions of either AF64A (1.5 nmol/ventricle; n = 9) or vehicle (3.0 microliters/ventricle; n = 7). Four weeks later, the animals were anesthetized and their brains processed to visualize and quantify choline acetyltransferase (ChAT) immunoreactive (IR) and parvalbumin-IR GABAergic neurons in the septal complex by immunocytochemistry (PAP method). AF64A significantly reduced the number of ChAT-IR perikarya in the medial septum (28%), ventral limb of the diagonal band of Broca (30%), and horizontal limb of the diagonal band of Broca (20%), but did not affect the number of parvalbumin-containing GABAergic neurons in any of the septal subdivisions. These results provide further evidence that AF64A is a selective cholinotoxin.

Androgen regulation of adrenocorticotropin and corticosterone secretion in the male rat following novelty and foot shock stressors

To examine mechanisms responsible for sex differences in hypothalamo-pituitary-adrenal (HPA) axis responsiveness to stress, we studied the role of androgens in the regulation of the adrenocorticotropin (ACTH) and corticosterone (CORT) responses to foot shock and novelty stressors in gonadectomized (GDX) or intact male F344 rats. Foot shock or exposure to a novel open field increased plasma ACTH and CORT, which was significantly greater in GDX vs. intacts. Testosterone (T) or dihydrotestosterone propionate (DHT) treatment of GDX animals returned poststress levels of ACTH and CORT to intact levels. Estrogen treatment of GDX males further increased poststress CORT secretion above GDX levels. There was no difference in the ACTH response of anterior pituitaries from intact, GDX, and GDX+DHT animals to CRF using an in vitro perifusion system. There were no differences in beta max or binding affinity of type I or II CORT receptors in the hypothalamus or hippocampus of intact, GDX, or GDX+DHT groups. These data demonstrate an effect of GDX on hormonal indices of stress. The increased response in GDX rats appears to be due to the release from androgen receptor mediated inhibition of the HPA axis. This inhibition by androgen is not due to changes in anterior pituitary sensitivity to CRH, nor to changes in type I or type II corticosteroid receptor concentrations.

Spatial learning deficits in the aged rat: neuroanatomical and neurochemical correlates

To assess neurochemical and neuroanatomical correlates of age and spatial learning, aged Sprague-Dawley male rats (20-22 mo) were divided into two groups based on their ability to locate a hidden platform in a Morris water maze. An "old good" group of rats acquired the task as rapidly as young (3-6 mo) animals, whereas an "old poor" group of rats failed to show improvement on subsequent testing days. Age-related changes included (a) a significant decrease in the number of choline acetyltransferase (CHAT) immunoreactive cells in the ventral cell group of the septal complex (28%); (b) a decrease in caudate dopamine levels (-11%); and (c) an increase in 5-HIAA levels in the n. accumbens (+25%) and hippocampus (+18%). Spatial learning related changes in aged rats included: (a) an increase in medial frontal cortex 5-HIAA levels (52%) in the old good learners but not old poor learners with (b) a decrease in medial frontal cortex dopamine levels (-24%) only in the old poor learners group and (c) a decrease in n. accumbens DOPAC (-22%) and HVA (-23%) in the old good learners group only. The present study demonstrates age-related but not spatial learning related decrease in CHAT immunoreactive cells in the ventral cell group of the septal complex. Therefore, either the cholinergic cell loss in the septum is unrelated to the acquisition of spatial learning measured by the Morris water maze, or it is a permissive effect along with specific alterations in forebrain dopaminergic and serotonergic systems, particularly in the medial frontal cortex and n. accumbens. The above findings are consistent with findings seen in Alzheimer's disease where both basal forebrain cholinergic nuclei and cortical projecting brainstem monoamine systems are affected.

Neuroendocrine and neurochemical responses to novelty stress in young and old male F344 rats: effects of d-fenfluramine treatment

To understand some of the mechanisms underlying the neuroendocrine and neurochemical changes associated with aging, we administered the serotonin [5-hydroxytryptamine (5-HT)] releaser and reuptake inhibitor d-fenfluramine (d-FEN; 0.0, 0.2, or 0.6 mg/kg/day, p.o) for 30-38 days to young (4 months) and old (22 months) F344 male rats. Rats were stressed by placement into a novel open field (OF) for 20 min before sacrifice. Control animals were sacrificed immediately upon removal from their home cage (HC). Old rats exhibited less (p < 0.05) exploratory behavior than young rats, which was not altered by treatment with d-FEN. Old HC rats also had higher (p < 0.05) basal plasma levels of adrenocorticotropic hormone (ACTH) and prolactin (PRL) than young HC rats. Old OF rats showed higher (p < 0.05) levels of ACTH and corticosterone (CORT) than young OF animals. A stress-induced increase in PRL secretion was not observed in old rats. Subchronic low-dose d-FEN normalized the enhanced ACTH and CORT responses of old animals to novelty. In addition to these endocrine changes, stress-induced increases in medial frontal cortex (MFC) dopamine (DA) and norepinephrine (NE) turnover also were observed. The increase in NE turnover was greater (p < 0.01) in old than in young rats. d-FEN treatment blocked the stress-induced increase in MFC NE but not MFC DA turnover in both young and old rats. These data support a role for 5-HT and/or NE in some age-related neuroendocrine perturbations and suggest that increased 5-HT neurotransmission can normalize the hyperactivation of the hypothalamo-pituitary-adrenal axis of old male rats.

Preliminary evidence for methamphetamine-induced behavioral and ocular effects in rat offspring following exposure during early organogenesis

Gravid Sprague-Dawley CD (VAF) rats received 50 mg/kg (d,l)-methamphetamine (MA) HCl (expressed as free base, N = 15) or distilled water (N = 6) by SC injection x 2/day in a 3 ml/kg volume on embryonic (E) days 7-12. Control rats were pair-fed to MA-exposed dams on days E7-18. No control dams failed to deliver; however, of 15 MA-exposed dams 4 did not deliver (2 died and 2 had completely resorbed litters). One additional MA litter had all the offspring die shortly after birth. There was no difference between groups on offspring postnatal (P) body weight. The offspring exposed prenatally to MA had significantly lower olfactory orientation scores (P9, 11, 13) to their home cage scent. In a test of early activity (P10, 12, 14) the MA-exposed progeny were marginally less active than controls. MA-exposed offspring exhibited hyperreactivity and marginally shortened response latency on a test of acoustic startle (P27). Motor activity showed no differential response in MA treated or control offspring to MA (P63) or fluoxetine challenge (P70). However, the MA offspring were more active than controls with respect to central and side activity during the second week of testing. No group differences were found for performance in a straight swimming channel or on the number of errors committed or latency to escape in a complex (Cincinnati) water maze (P84). Prenatal exposure to MA also induced eye defects (i.e., anophthalmia, microphthalmia and folded retina) in 16.7% of the progeny. However, MA did not effect hippocampal or neostriatal monoamine levels when measured on P28.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscimol injections into the median raphe nucleus increase serum ACTH and corticosterone concentrations via a nonserotonergic mechanism

Midbrain raphe serotonin (5-HT) neurons can influence the pituitary-adrenal axis. The midbrain raphe nuclei also contain a number of non-5-HT neurons, including gamma-aminobutyric acid (GABA) interneurons which can modulate 5-HT neuronal activity. We investigated the effects of intraraphe injections of the GABAA agonist, muscimol, on serum adrenocorticotropin hormone (ACTH) and corticosterone concentrations. Rats were infused with muscimol (0, 25, 50, and 100 ng in 0.5 microliters saline) into the median raphe nucleus (MR). The animals were killed 30 min later, and trunk blood was collected for measurement of serum concentrations of ACTH and corticosterone by radioimmunoassay. Muscimol dose dependently increased plasma concentrations of these two pituitary-adrenal hormones. In order to determine the role of MR 5-HT neurons in these effects, separate groups of implanted animals were infused with either the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT) or ascorbic acid vehicle into the MR. Two weeks later, the animals were infused with muscimol (100 ng in 0.5 microliters) and sacrificed as above. Treatment with 5,7-DHT, which markedly reduced hippocampal concentrations of 5-HT (-83%) and 5-HIAA (-73%), did not block intra-MR muscimol-induced elevations in ACTH and corticosterone. Thus, 5-HT neurons within the MR apparently do not mediate the increased activity of the pituitary-adrenal axis produced by stimulation of MR GABAA receptors.

Septal choline acetyltransferase immunoreactive neurons: dose-dependent effects of AF64A

Two experiments were performed. In the first, the cholinotoxin, AF64A (0.5, 1.0 or 1.5 nmol/ventricle), or vehicle (3.0 microliters) was injected (ICV) bilaterally into male rats (n = 23). Choline acetyltransferase (ChAT) immunoreactive (IR) perikarya in the four subgroups of the septal complex were visualized by immunocytochemistry (PAP method) 28 days postinjection, and counted using a microprojector (x40). The 0.5 nmol/ventricle dose of AF64A significantly reduced (31%) the number of ChAT-IR cell bodies in the intermediate subgroup (rostral extension of the nucleus basalis/substantia innominata). Higher doses did not produce additional reductions. The highest dose (1.5 nmol/ventricle) of AF64A resulted in significant decreases in ChAT-IR cell bodies in the dorsal (51%) and midline (35%) subgroups (medial septum), but did not affect the number of ventral subgroup (diagonal band of Broca) ChAT-IR neurons. In the second experiment, electrolytic lesions were placed in the corpus callosum, cingulum and overlying cingulate gyrus, in order to simulate the nonselective damage seen following the 1.5 nmol/ventricle dose of AF64A. In comparison to the surgical controls (n = 3), the electrolytic lesions (n = 6) failed to significantly affect the number of ChAT-IR perikarya in any of the septal subdivisions. Thus the distinct subgroups of septal ChAT-IR neurons are differentially sensitive to the toxic effects of ICV administered AF64A: intermediate much greater than dorsal greater than midline much greater than ventral subgroup.

Effects of subchronic d-fenfluramine on splenic immune functions in young and old male and female Fischer 344 rats

The present study was designed to demonstrate age- and sex-related differences in immune functions, and to determine whether subchronic elevations in serotonin (5-HT) availability in vivo would alter immune functions assessed subsequently in vitro. Male and female F344 rats (5 and 21 months of age) were administered the 5-HT releaser and reuptake inhibitor, d-fenfluramine (d-Fen), in their drinking water for 30-38 days then killed. The young animals received a higher dose (1.8 mg/kg/day) of d-Fen than the old rats (0.6 mg/kg/day) in order to compensate for age-related decreases in drug biotransformation and clearance. Brain and spleen d-Fen and metabolite concentrations, however, were considerably higher in the young than in the old rats. d-Fen treatment did not affect body weight or fluid intake. Although substantial sex differences in immune function were not discerned, age-related decreases were observed in absolute splenic cellularity, recombinant interleukin-2 (rIL-2) stimulated natural killer (NK) cytotoxicity, LPS stimulated B-cell mitogenesis, and in the level of Ox19 (CD5) positive cells. d-Fen caused an increase in absolute spleen weight and a decrease in absolute splenic cellularity only in the old rats of both sexes. Spleen cells from young male and old female rats receiving d-Fen had relatively more large granular lymphocytes and enhanced baseline and rIL-2 activated killing of YAC-1 cells than their vehicle matched or opposite sex counterparts. The drug also increased Con A-induced T-cell proliferation in young males and LPS induced B-cell proliferation in old females. d-Fen decreased Ox39 (CD25) levels by 19%, but did not affect any of the other phenotypes examined. The results suggest that 5-HT has a selective stimulatory effect on young male and old female NK activity, and that old female rats are more sensitive to the immunological effects of d-Fen than old male rats.

Intra-midbrain raphe injections of the neurokinin-3 agonist senktide inhibit food and water intake in the rat

Microinjection and lesion studies have implicated the midbrain dorsal (DR) and median raphe (MR) nuclei in behavioral arousal. This behavioral state is manifested as locomotor hyperactivity, hyperphagia, hyperdipsia and increases in plasma corticosteroid release. Intra-midbrain raphe injections of the GABAA agonist muscimol elicit this behavioral activation. We have demonstrated that similar infusions of tachykinins produce locomotor hyperactivity through activation of neurokinin-3 (NK-3) receptors located on serotonin cell bodies. The purpose of the present study was to determine the effects of intra-MR and DR infusions of senktide, an NK-3 agonist, on food and water consumption in nondeprived rats. Male Sprague-Dawley rats were implanted with indwelling intra-MR or intra-DR cannula. Infusions of muscimol (25 ng/0.5 microliters) into the MR increased water intake, while MR and DR infusions increased food consumption. In contrast, intra-MR injections of senktide decreased water intake and intra-MR and DR injections decreased food intake. The results suggest that the behavioral states induced by muscimol and neurokinin infusions into the raphe are distinct and that raphe/neurokinin pathways are involved in consummatory mechanisms.

Aversive properties of bombesin in rats

Aversive properties of bombesin were determined in the conditioned place-preference paradigm in rats and compared with the effects on spontaneous behavior. Bombesin induced excessive grooming and/or scratching behavior at doses of 80 ng, 400 ng, and 2.0 micrograms ICV. In the conditioned place-preference paradigm, doses of 400 ng and 2.0 micrograms ICV induced a profound aversion to the environment in which the animals had received peptide treatment. Eighty ng were partially effective, and 16 ng did not induce a significant change in preference. The grooming/scratching behavior was attenuated by pretreatment with 4 mg/kg morphine-sulfate. These results show that bombesin is strongly aversive at doses that induce grooming/scratching behavior. Although the relationship between these different effects is not known, the similarity in their dose-response relationship suggests that they may be mediated by a common mechanism.

Neuronal sites mediating locomotor hyperactivity following central neurokinin agonist administration

The stable substance P analog, DiMeC7, increases spontaneous locomotor activity after infusion into the lateral ventricles or median raphe nucleus (MRN). The elevated locomotion observed after intracerebroventricular (ICV) infusion of DiMeC7 was attenuated, but not blocked, by bilateral 6-hydroxydopamine (6OHDA) lesions of the ventral tegmental area (VTA). In contrast, bilateral 6OHDA lesions of the nucleus accumbens (NAS) blocked the motor activity induced by ICV administration of DiMeC7. Similar lesions did not affect the increases in motor behavior observed after MRN infusions of DiMeC7. However, the hyperactivity following MRN microinjections of DiMeC7 was attenuated by intraperitoneal administration of the dopamine (DA) antagonist, haloperidol. The results suggest that ICV infusions of DiMeC7 increase locomotor activity by acting directly on neurons in the NAS and in part by influencing, directly or indirectly, the activity of DA cells in the VTA. The increased motor activity seen after MRN administration of DiMeC7 appears to depend on DA neurons but not on projections to the NAS.

Neurochemical, endocrine and immunological responses to stress in young and old Fischer 344 male rats

Two experiments were performed. In the first, a 20 min conditioned emotional response (CER) paradigm was used to compare the neurochemical, endocrine and immunological responses to stress of 7- and 22-month-old Fischer 344 (F344) male rats. In the second, corticosterone levels 20 min following ether stress, and regional brain type I and II corticosterone receptor densities were examined using 7- and 17.5-month-old F344 male rats. Dopamine (DA) metabolism in old nonstressed rats was significantly reduced in the medial frontal cortex, neostriatum, nucleus accumbens and hypothalamus, but not in the amygdala. The CER procedure, nevertheless, increased medial frontal cortical, nucleus accumbens and amygdaloid DA turnover in both the young and old rats. The young and old nonstressed rats did not evidence differences in norepinephrine (NE) and serotonin (5-HT) concentrations. However, stress resulted in a decrease in medial frontal cortical 5-hydroxyindoleacetic acid (5-HIAA) and hypothalamic 5-HT levels in old but not in young animals. These observations suggest age-related differences in the response of central NE and 5-HT systems to stress. Ether and the CER procedure led to exaggerated corticosterone responses in the old rats (17.5 and 22 month, respectively). Hippocampal type I but not type II corticosterone receptors were decreased by 47% in the 17.5-month-old rats. Thus, age-related changes in hippocampal corticosterone receptor types do not occur in unison, and the exacerbated corticosterone response to stress precedes the reported down-regulation of hippocampal type II corticosterone receptors in aged rats. Age-related changes were not observed in the concentrations of corticosterone receptors in other brain regions, or in the prolactin response to stress. The old rats, however, evidenced a reduction in the availability of the renin substrate, angiotensinogen, and in stress-induced renin secretion. Immune function was impaired in the old nonstressed rats, and further compromised by exposure to the CER procedure. In comparison to the young control rats, the old nonstressed rats showed an increased percentage of splenic large granular lymphocytes, reduced splenic natural killer cytotoxicity, and impaired Con-A-stimulated splenic T lymphocyte proliferation. Reductions in T splenic cell proliferation and natural killer cytotoxicity were observed in the young rats subjected to the CER paradigm, but not to the same extent as in the old rats. These observations indicate that aging male F344 rats evidence major alterations in basal central monoamine, endocrine and immune functions, and an increased sensitivity of these systems to stress.

Stress-induced renin and corticosterone secretion is mediated by catecholaminergic nerve terminals in the hypothalamic paraventricular nucleus

Cell bodies in the hypothalamic paraventricular nucleus (PVN) mediate stress-induced increases in renin and corticosterone secretion. Since the PVN has an extensive catecholaminergic innervation, we wanted to determine the role of catecholamines in the neuroendocrine response to stress. The stressor was a conditioned emotional (fear) response paradigm (CER). The catecholamine neurotoxin, 6-hydroxydopamine (6-OHDA), was injected into the PVN 14 days before the rats were subjected to the CER procedure. Damage to noradrenergic nerve terminals was verified immunocytochemically, using an antibody against dopamine beta-hydroxylase. Injection of 6-OHDa into the PVN prevented the stress-induced increase in plasma renin activity (PRA), plasma renin concentration (PRC) and plasma corticosterone concentration, suggesting that intact catecholaminergic innervation of neurons in the PVN is necessary for the stress-induced increase in renin and corticosterone secretion. To determine if beta-adrenoceptors in the PVN mediate the effect of stress on renin and corticosterone secretion, the beta-adrenoceptor antagonist sotalol was injected into the PVN through chronically implanted bilateral cannulae. The injection was performed on the 4th day of the CER paradigm, just before the rats were placed into the CER chamber. Sotalol prevented the stress-induced increase in corticosterone concentration, but did not diminish the stress-induced increase in PRA and PRC. These results suggest that the stress-induced increase in corticosterone concentration is influenced by beta-adrenoceptors in the PVN. The stress-induced increase in PRA and PRC is mediated by different receptors whose ligands might be catecholamines acting at non-beta-receptors or other neuroactive substances colocalized in catecholaminergic nerve terminals.

A dose-response analysis of intra-raphe tachykinin-induced hyperactivity

The nonmammalian (eledoisin, kassinin and physalaemin) and mammalian tachykinins (substance P and neurokinin (NK) A), as well as the metabolically stable neurokinin analogs, DiMe-C7 [( pGlu5, MePhe8, Sar9]substance P (5-11)] and senktide, were infused into the median raphe nucleus of rats via chronically implanted cannulas, and their effects on locomotor activity analyzed. The NK-3 receptor agonists, senktide and DiMe-C7, as well as the endogenous NK-2 receptor ligand, NKA, produced dose-dependent increases in locomotor activity. Substance P, eledoisin, kassinin and physalaemin elevated activity but not dose-dependently. Regression analyses demonstrated that senktide and DiMe-C7 were the most potent and efficacious of the peptides tested. The slopes of the senktide and DiMe-C7 dose-response curves were parallel and differed significantly from the slope of the NKA dose-response curve. Infusions of the endogenous NK-3 ligand, NKB (3.0 pmol in 1.0 microliter), also elicited hyperactivity equivalent to that produced by an equimolar dose of senktide. These and previous findings suggest that activation of NK-2 and NK-3 receptors in the midbrain raphe leads to behavioral arousal through their influence on serotonin neurons.

Effect of selective serotonin (5-HT) agonists and 5-HT2 antagonist on prolactin secretion

The present study was undertaken to determine the involvement of serotonergic 5-HT1 and 5-HT2 receptor subtypes in stimulation of the secretion of prolactin. Several 5-HT agonists were administered, in a dose-response fashion, to conscious rats and the effect on the levels of prolactin in plasma was measured. The 5-HT1A + 5-HT1B agonist RU 24969 (5-methoxy-3[1,2,3,6-tetrahydropyridin-4-yl]-1H-indole succinate) and the 5-HT1 + 5-HT2 agonist MK-212 (6-chloro-2-[1-piperazinyl]pirazine) increased levels of prolactin in plasma in a dose-dependent manner. In contrast, the selective 5-HT1A agonists 8-OH-DPAT (8-hydroxy-2-[di-n-propylamino]tetralin) and ipsapirone (2-[4-[4-(2-pyrimidinyl)-1-piperazinyl]butyl]-1,2-benzisothiazol-3 -(2H) one-1,1-dioxidehydrochloride) did not increase levels of prolactin in plasma at any dose. The 5-HT-releasing drug, fenfluramine, also increased the concentration of prolactin in plasma. Pretreatment with the selective 5-HT2 antagonist, LY53857 (6-methyl-1-[1-methylethyl]ergoline-8-carboxylic acid, 2-hydroxy-1-methyl propyl ester (Z)-2-butenedioate [1:1]), did not significantly diminish an increase in levels of prolactin in plasma, induced by injection of fenfluramine. The antagonist LY53857 inhibited, but did not block the MK-212- and RU 24969-induced increase in the levels of prolactin in plasma. By deduction, these data suggest that 5-HT1B receptors, or as yet undefined 5-HT receptor subtypes may be involved in the stimulation of the secretion of prolactin by endogenously released 5-HT, and that 5-HT2 receptors may play a minor role in the serotonergic regulation of the secretion of prolactin.

Intra-raphe neurokinin-induced hyperactivity: effects of 5,7-dihydroxytryptamine lesions

Rats were implanted with cannulae in the median raphe nucleus (MR). 5,7-Dihydroxytryptamine (5,7-DHT) or vehicle was infused either directly through the MR cannula, or bilaterally into the medial forebrain bundle (MFB). The MR 5,7-DHT lesions completely blocked the hyperactivity elicited by injections into the MR of the neurokinin (NK) 3 agonists, DiMe-C7 and senktide, and the NK-2 agonist, neurokinin A. In contrast, the MFB 5,7-DHT lesions did not affect the locomotor hyperactivity produced by intra-MR administration of DiMe-C7 and senktide, but appeared to attenuate the effects of NKA. The data indicate that intra-raphe neurokinin-induced hyperactivity is mediated by 5-HT neurons, and that 5-HT projections to the forebrain may be involved in the behavioral activation induced by intra-raphe neurokinin A administration, but not that induced by intra-MR NK-3 agonists.

Neuropharmacological characterization of serotoninergic stimulation of vasopressin secretion in conscious rats

In this study we have evaluated a possible role for brain serotoninergic neurons in the regulation of vasopressin secretion using pharmacological methods. In order to accomplish this, we have developed a specific and sensitive vasopressin radioimmunoassay along with a highly reproducible plasma extraction protocol. These tools were used to evaluate the plasma vasopressin response to several pharmacological challenges in conscious rats. Treatment with the serotonin (5-HT) releaser p-chloroamphetamine caused a significant increase in plasma vasopressin concentration. This effect was blocked by posterior hypothalamic deafferentation which separates serotonin cell bodies in the midbrain from their nerve terminals in the hypothalamus. Administration of graded doses of several 5-HT agonists had no effect. However, treatment with MK212, a serotonin agonist with 5-HT1 + 5-HT2 activity, induced a significant increase in plasma vasopressin concentration. The effect of MK212 on plasma vasopressin was completely abolished by the selective 5-HT2 receptor blocker LY53857. These studies confirm and extend studies by others that provide pharmacological evidence for serotoninergic regulation of vasopressin secretion via a selective 5-HT2 receptor mechanism. The specific neuroanatomical site(s) where serotonin exerts this effect are unknown, and the physiological consequences of these studies remain to be established.

Intra-median raphe infusions of muscimol and the substance P analogue DiMe-C7 produce hyperactivity: role of serotonin neurons

Injections into the midbrain median raphe nucleus (MR) of the metabolically stable substance P analogue, DiMe-C7, produce dose-dependent increases in locomotor activity (LMA). Ibotenic acid (8.0 micrograms in 2.0 microliter vehicle) lesions of the MR block the hyperkinetic effects of optimal doses of both DiMe-C7 (1.0 microgram in 0.5 microliter vehicle) and the GABAA agonist, muscimol (100 ng in 0.5 microliter vehicle). This observation indicates that the increases in LMA produced by intra-MR DiMe-C7 and muscimol infusion are not due to diffusion to sites outside the MR. Intra-MR administration of the selective serotonin (5-HT) neurotoxin, 5,7-dihydroxytryptamine (6.0 micrograms in 1.5 microliter vehicle), following pretreatment with the norepinephrine and dopamine reuptake inhibitor, nomifensine maleate (15 mg/kg, i.p.), blocked the hyperactivity induced by intra-MR infusions of DiMe-C7 (1.0 microgram) but not that of muscimol (100 ng). These observations suggest that the LMA effects of intra-MR DiMe-C7 and muscimol administration are mediated by different neural mechanisms. The LMA effects of DiMe-C7 depend on intact 5-HT neurons in the MR, whereas the effects of muscimol depend on intact non-5-HT MR cells.

Differential effects of serotonin (5-HT1A and 5-HT2) agonists and antagonists on renin and corticosterone secretion

The present study was designed to investigate the effect of distinct serotonin (5-HT1A and 5-HT2) agonists and antagonists on renin and corticosterone secretion. Low doses of the selective 5-HT1A agonists 8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT) (5.0-500.0 micrograms/kg, i.p.) and ipsapirone (TVX Q 7821; 0.5-2.5 mg/kg, i.p.), and of the 5-hydroxytryptamine (5-HT) agonist MK-212 (2.0 mg/kg, i.p.), did not elevate plasma renin activity (PRA) and concentration (PRC) 30 min postinjection. Administration of a higher dose of MK-212 (10.0 mg/kg, i.p.) and of higher doses of ipsapirone (5.0-10.0 mg/kg, i.p.), as well as the 5-HT releaser, fenfluramine (5.0 mg/kg, i.p.), resulted in large increases in PRA and PRC. The effects of MK-212 and fenfluramine on PRA and PRC were blocked by pretreatment with the selective 5-HT2 antagonist, LY53857, in a dose-dependent (0.3-1.0 mg/kg, i.p.) manner. LY53857 (1.0 mg/kg, i.p.) by itself did not affect PRA or PRC. LY53857, furthermore, unmasked a renin-suppressive effect of MK-212, since injection of MK-212 (10.0 mg/kg, i.p.) following LY53857 administration led to a reduction in PRA and PRC. MK-212 (2.0 and 10.0 mg/kg), the high doses of 8-OH-DPAT (500.0 micrograms/kg), ipsapirone (1.0-10.0 mg/kg), and fenfluramine (5.0 mg/kg) all produced an increase in plasma corticosterone levels. The effects of MK-212 and fenfluramine on corticosterone were not inhibited by pretreatment with LY53857. These data suggest that 5-HT1A receptors do not play a role in the regulation of renin secretion, whereas stimulation of 5-HT2 receptors enhances renin release.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of acute stress paradigms: hormonal responses and hypothalamic serotonin

The effects of stress on plasma renin activity (PRA), plasma prolactin and corticosterone levels, and hypothalamic 5-HT and 5-HIAA concentrations were investigated using a 3 and 12 min conditioned fear (CER) paradigm; 20 min immobilization; 20 min exposure to shallow or deep cold water; 2, 12 and 22 min of intermittent footshock with or without 20 min recovery; and, a 3 min CER with 0, 10, 30 and 60 min recovery. PRA was increased by all the stressors, except shallow cold water, reaching a maximum after 12 min and returning to control values within 10-20 min post-stress. Prolactin levels also were increased by all the stressors, except shallow and deep cold water. Prolactin levels were maximal after 12 min and returned to baseline within 20-60 min post-stress, depending on the stressor. Corticosterone levels were elevated by all the stressors, but not as rapidly as PRA or prolactin, reaching a maximum after about 20 min and returning to baseline concentrations within 30-60 min post-stress. None of the stressors produced significant changes in hypothalamic 5-HT and 5-HIAA concentrations.

Effect of the anxiolytic drug buspirone on prolactin and corticosterone secretion in stressed and unstressed rats

Buspirone is an atypical anxiolytic drug that exerts its action at a receptor site other than the GABA-benzodiazepine-chloride ionophore complex. The present study examined the effect of buspirone on plasma prolactin and corticosterone levels in both control and stressed rats. In unstressed rats, buspirone produced dose-dependent increases in plasma prolactin and corticosterone levels. The minimal doses of buspirone which led to significant elevations in plasma prolactin and corticosterone levels were 1.0 and 2.0 mg/kg (IP), respectively. The effect of buspirone on both hormones was maximal 30 minutes after injection. The plasma levels of prolactin and corticosterone were significantly elevated in rats that were stressed using a conditioned fear paradigm. Buspirone produced a dose-dependent attenuation of the stress-induced increase in prolactin secretion. The stress-induced increase in corticosterone secretion was inhibited by the 0.5 mg/kg (IP) dose but not by the 2.0 mg/kg (IP) dose of buspirone, which increased corticosterone secretion both in stressed and unstressed rats. These data suggest that the effect of buspirone on plasma prolactin and corticosterone levels may be mediated by two different mechanisms of action.

Serotonin-immunoreactive projections to the hippocampus from the interpeduncular nucleus in the rat

The possibility of a serotonergic projection from the interpeduncular nucleus (IPN) to the hippocampus was examined using a combined immunohistochemical-fluorescence retrograde tracing technique. About one third of the cells in the apical subnucleus of the IPN which projected to the hippocampus could be shown to contain serotonin immunoreactivity, whereas double-labeled cells were only rarely encountered in the lateral subnuclei. These findings suggest that the IPN sends both serotonergic and non-serotonergic projections to the hippocampus and that the serotonergic projections arise primarily from the apical subnucleus.

Pharmacological studies on stress-induced renin and prolactin secretion: effects of benzodiazepines, naloxone, propranolol and diisopropyl fluorophosphate

Stress-induced renin and prolactin secretion was investigated using a conditioned emotional response paradigm. Three minutes after placement in a chamber the rats received an electric shock to their feet via the grid floor, then were immediately returned to their home cage. This procedure was repeated for 3 consecutive days. On the fourth day, instead of receiving an electric shock, they were removed after 3 min and sacrificed by decapitation. Control rats were treated identically with the exception that shock was not administered at any time. There was a significant increase in plasma renin activity and prolactin level in the stressed rats. The administration of the antianxiety drugs chlordiazepoxide (10 mg/kg i.p.) or midazolam (0.125-2 mg/kg i.p.) blocked the stress-induced increase in prolactin levels but not the stress-induced rise in plasma renin activity. Administration of the beta-blocker propranolol (1 mg/kg i.p.) inhibited, but did not completely block, stress-induced rise in plasma-renin activity and had no effect on stress-induced prolactin secretion. The opiate antagonist naloxone (0.1-10 mg/kg i.p.) and the acetylcholinesterase inhibitor diisopropyl fluorophosphate (0.5 mg/kg i.p.) did not block stress-induced renin or prolactin secretion. It is concluded that stress-induced prolactin secretion is regulated by a benzodiazepine-mediated mechanism and that stress-induced renin but not prolactin secretion is mediated in part via beta-receptors.

The non-benzodiazepine anxiolytic buspirone inhibits stress-induced renin secretion and lowers heart rate

The non benzodiazepine drug, buspirone, produces a dose-dependent biphasic effect on plasma renin activity in non-stressed rats. Low doses (0.1 - 2.0 mg/kg i.p.) decrease while high doses (10.0 - 50.0 mg/kg i.p.) increase plasma renin activity. The maximal decrease in plasma renin activity produced by buspirone (1.0 mg/kg i.p.) was observed 30 minutes post-injection. In addition, buspirone (0.5 and 2.0 mg/kg i.p.) blocked the stress-induced rise in plasma renin activity. This effect of buspirone is in contrast to the previously observed failure of the benzodiazepine anxiolytics to alter the effect of stress on plasma renin activity. Administration of buspirone (0.5 mg/kg i.p.) produced a sustained reduction (15%) in heart rate but did not affect mean arterial pressure. The present data support the view that the mechanism of the anxiolytic action of buspirone is different from that of the benzodiazepines.

Role of midbrain raphe in stress-induced renin and prolactin secretion

Stress-induced changes in renin and prolactin secretion were studied using a conditioned emotional response paradigm. Three minutes after being placed in a chamber, the stressed animals received a brief electric shock (1.0 mA for 10 s through the grid floor), then were returned to their home cage. This procedure was repeated for 3 consecutive days. On the fourth day, the rats were placed in the chamber for 3 min, but instead of receiving shock, they were removed and sacrificed. Control animals were treated in the same manner, except that they never received foot shock. The sham-operated stressed rats evidenced significant elevations in plasma renin activity (270%) and prolactin level (550%). Electrolytic lesions in the dorsal raphe nucleus blocked the stress-induced increase in plasma renin activity but did not affect the stress-induced increase in prolactin secretion. Electrolytic lesions in the median raphe nucleus did not affect prolactin levels in either control or stressed animals. However, median raphe lesions led to a significant increase in plasma renin activity in non-stressed rats and potentiated the stress-induced elevation in plasma renin activity. These results suggest that neurons within the dorsal and median raphe nuclei are involved in the regulation of renin but not prolactin secretion during stress. The results also suggest that median raphe neurons play a role in basal renin secretion.

Intra-raphe benzodiazepines enhance rat locomotor activity: interactions with GABA

Intracranial dose response relationships for the water-soluble benzodiazepines, chlordiazepoxide, flurazepam and midazolam, were performed by injecting the drugs through cannulae chronically indwelling in the median raphe nucleus of male albino rats. Drugs were administered in doses of 0.0, 0.22, 0.44, 0.88 and 1.75 nmole in 0.5 microliters saline. Both midazolam and flurazepam produced hyperactivity which was most prominent within the first 30 minutes post-injection. Flurazepam, furthermore, proved twice as potent as midazolam. Chlordiazepoxide, in contrast, was without effect at any of the doses tested. This observation supports the view that chlordiazepoxide is a pro-drug which must be metabolized to form an active metabolite. In another experiment, animals received either saline or a sub-effective dose (0.22 nmole) of flurazepam or midazolam into the median raphe nucleus 5 minutes prior to either a subeffective dose of muscimol (0.22 nmole) or saline. Only the combinations of a benzodiazepine plus muscimol produced hyperactivity. These combinations, moreover, produced effects as robust as those of a 4-fold higher dose of muscimol alone (0.88 nmole). Other animals received either saline or bicuculline methiodide (0.88 nmole). Bicuculline did not affect activity level, but completely blocked the hyperkinetic effects of muscimol. These data suggest that the hyperactivity effect of intra-raphe muscimol is due to activation of GABA receptors within the midbrain raphe, rather than at distant sites. In addition, the data suggest that the intra-raphe administration of certain benzodiazepines produces hyperactivity by facilitating GABA transmission.

Intra-raphe muscimol induced hyperactivity depends on ascending serotonin projections

Acute microinjections of the GABA agonist, muscimol (100 ng), into either the dorsal (DR) or the median (MR) raphe nucleus of etherized rats induced post-anesthesia hyperactivity as measured in photocell chambers. The increased activity counts seen after MR injections, furthermore, were 4 times greater than those following DR injections. In animals implanted with chronically indwelling cannulae, a muscimol (25-400 ng) dose-response analysis confirmed the greater sensitivity of the MR site. Subsequent experiments thus employed only MR cannulae. The benzodiazepine, chlordiazepoxide, in a subataxic dose (3.8 mg/kg, IP) by itself did not affect activity level, but enhanced the locomotor response to low doses (25-50 ng) of muscimol. Conversely, a sub-convulsant dose of the GABA antagonist, bicuculline (1.1 mg/kg, IP), completely blocked the hyperactivity produced by muscimol (50-100 ng). Bilateral electrolytic destruction of the ventral tegmental nuclei of Gudden produced hyperactivity, but failed to alter the effect of muscimol. Forebrain 5-hydroxytryptamine (5-HT, serotonin) depletion following administration of 5,7-dihydroxytryptamine did not affect baseline activity level, but markedly attenuated the locomotor response produced by intra-MR injections of muscimol. These data suggest that midbrain GABA neurons modulate activity level through a direct action on 5-HT neurons, and indicate that intra-MR muscimol induced hyperactivity depends on intact ascending 5-HT fibers.

Effect of selective midbrain and diencephalic 5,7-dihydroxytryptamine lesions on serotonin content in individual preopticohypothalamic nuclei and on serum luteinizing hormone level

Injection of the serotonin neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), into the midbrain dorsal (DR) or median (MR) raphe nucleus of castrated and normal male rats was followed by measurement of serum luteinizing hormone (LH) level and the 5-hydroxytryptamine (5-HT) content of several hypothalamic and amygdaloid nuclei. Only the DR lesions lead to a significant decrease (42%) in serum LH level in normal rats. The elevated LH level in castrated animals was not affected by either lesion. The DR lesions were followed by 5-HT reductions only in the medial preoptic area, the arcuate and ventromedial hypothalamic nuclei, and in the basal and central amygdaloid nuclei. In contrast, the 5-HT reductions produced by MR lesions were much more widespread, being found in all nuclei assayed with the exception of the dorso- and ventromedial hypothalamic nuclei. In a second experiment, degeneration of serotonergic terminals in the ventromedial region of the hypothalamus following intradiencephalic injections of 5,7-DHT led to a significant decrease in serum LH level and a 5-HT reduction in the arcuate, ventromedial and dorsomedial hypothalamic nuclei. 5,7-DHT injections into the medial preoptic area and the anterior hypothalamic area did not affect serum LH level. These results suggest that a serotonergic pathway originating in the midbrain dorsal raphe nucleus and innervating the mediobasal hypothalamus has a stimulatory influence on LH secretion.

Attenuation of pethidine-induced antinociception by zimelidine, an inhibitor of 5-hydroxytryptamine reuptake

1 The effect of selective inhibition of 5-hydroxytryptamine (5-HT) re-uptake by fluoxetine and zimelidine on morphine- and pethidine-induced antinociception was studied in rats. The hot plate (55 degrees C) and tail flick test procedures for measurement of analgesia were employed to assess antinociception. 2 Pretreatment with fluoxetine and zimelidine potentiated the antinociceptive effect of morphine (4.5 mg/kg, as base); zimelidine was without effect on a lesser dose of morphine (3.0 mg/kg, as base). 3 Pretreatment with zimelidine but not fluoxetine, significantly attenuated pethidine-induced antinociception (24 mg/kg, as base) and prevented the expression of pethidine-induced antinociception at a lesser 10 mg/kg (as base) dose of pethidine. 4 These and other results support (a) a role for 5-HT in the expression of morphine-induced antinociception, and (b) a different mode of antinociceptive action of morphine and pethidine. The role of 5-HT in pethidine-induced antinociception remains unclear.

Differential serotonergic innervation of individual hypothalamic nuclei and other forebrain regions by the dorsal and median midbrain raphe nuclei

Lesions in the midbrain median but not in the dorsal raphe nucleus significantly decreased the serotonin (5-HT) content of the hippocampus (61%), medial preoptic area (49%), suprachiasmatic nucleus (70%) and anterior hypothalamic area (60%). Electrolytic lesions restricted to either the median or dorsal raphe nucleus produced significant reductions in the 5-HT concentration of the caudate-putamen, anterolateral hypothalamic area (45%) and arcuate nucleus (48--58%). The fall in caudate-putamen 5-HT level was significantly greater after the dorsal (66%) than after the median (24%) raphe lesion. Neither lesion significantly affected the 5-HT content of the posterolateral hypothalamic area, the ventromedial hypothalamic nucleus or the dorsomedial hypothalamic nucleus. Thus, like their differential projections to the caudate-putamen and hippocampus, the mesencephalic dorsal and median raphe nuclei appear to innervate different preoptico-hypothalamic nuclei and areas. Whereas the median raphe nucleus seems to be the primary source of 5-HT fibers to the suprachiasmatic nucleus, anterior hypothalamic area and medial preoptic area, the 5-HT inputs to the anterolateral hypothalamic area and arcuate nucleus appear to derive from both the dorsal and median raphe nuclei.