Cognitive Functioning in Adults with Phenylketonuria in a Cohort of Spanish Patients.

The early introduction of a low phenylalanine (Phe) diet has been demonstrated to be the most successful treatment in subjects with phenylketonuria (PKU), especially for preventing severe cognitive and neurological damages. However, it still concerns that even if treated in the first months of life with supplements and following a diet, they can show slight scores below people without PKU in neuropsychological assignments. We investigated 20 adults with classical PKU aged 19-48 years (mean age 29 years) and 20 heathy controls matched by age, gender, and years of education. Patients and controls were assessed with an extended neuropsychological battery, as well as psychological aspects and quality of life, also the last Phe level result was obtained. Results showed that the most affected cognitive domains are processing speed, executive functioning, memory, and also theory of mind, but very well-preserved verbal fluency, language, and visuospatial functioning. In quality of life, some significant results were seen specially in anxiety of Phe levels, anxiety of Phe levels during pregnancy, guilt if poor adherence to supplements, and if dietary protein restriction not followed. No significant results were obtained for the psychological variables. In conclusion, it has been shown that a combination of a low Phe diet, supplement intake, and keeping Phe levels in a low range seems appropriate to have the most normal and alike cognitive performance to persons without PKU.

Evidence for regulated expression of neuropeptide Y gene by rat and human cultured astrocytes.

A series of studies from our laboratory have established that fetal rat and human neuropeptide Y (NPY) cortical neurons in aggregate cultures are differentially regulated. In a preliminary study we found that primary astrocytes produce substantial amounts of immunoreactive (IR) NPY. We addressed the question: Is astrocyte production of NPY-IR a regulated process? The effects of brain-derived neurotrophic factor (BDNF, 50 ng/ml), basic fibroblast growth factor (bFGF), substance P (1 microM), forskolin (10 microM), or phorbol 12-myristate-13-acetate (PMA, 20 nM) on NPY-IR production was tested on rat and human primary astrocyte cultures. Of these agents, PMA and bFGF markedly induced NPY-IR production by rat as well as human astrocytes, forskolin induced NPY-IR production by human but not rat astrocytes, and neither BDNF nor substance P induced NPY-IR production by rat or human astrocytes. The molecular size of PMA-induced NPY-IR was found to be consistent with that of proNPY. Moreover, PMA induced the accumulation of mRNA corresponding in size to the neuronal NPY-mRNA. Immunocytochemical analysis of human post-mortem neocortex revealed co-existence of NPY-IR with astrocyte markers. These results indicate that cultured astrocytes express NPY gene in a regulated manner and they support our proposition that in situ reactive astrocytes may express NPY gene under some physiological/pathological conditions.

Opposite effects of astrocyte-derived soluble factor(s) on the functional expression of fetal peptidergic neurons in aggregate cultures: enhancement of neuropeptide Y and suppression of somatostatin.

Previous studies established that fetal rat and human neuropeptide Y (NPY) cortical neurons in aggregate cultures are differentially regulated. Whereas brain-derived neurotrophic factor (BDNF) or phorbol 12-myristate-13-acetate (PMA) induces NPY production in rat cultures, only PMA does so in human cultures. We addressed these questions: 1) Do soluble products of rat or human astrocytes (conditioned medium; rCM and hCM, respectively) enhance the functional expression of cultured NPY neurons and if so, do they enhance the expression of somatostatin (SRIF) neurons as well? 2) Is the NPY-enhancing activity (EA) in the CM species specific? rCM enhanced (approximately 2-fold) both basal and BDNF-stimulated production of NPY and coculture of rat aggregates and astrocytes did not prevent this NPY-EA. Likewise, the hCM enhanced (approximately 2.5-fold) basal and PMA-stimulated production of NPY by human aggregates. Moreover, the hCM enhanced NPY production by rat aggregates and rCM enhanced NPY production by human aggregates. In addition, rCM and hCM each enhanced BDNF-, forskolin-, or PMA-stimulated NPY production by rat aggregates. Under each of the above conditions, the rCM/hCM suppressed (approximately 50%) production of SRIF by rat aggregates. In summary, secretory products of rat and human astrocytes exert opposite effects on the functional expression of NPY and SRIF neurons in culture: enhancement of NPY and suppression of SRIF. By the criteria evaluated in this study, these astrocyte-derived activities do not exhibit species specificity.

Differential potencies of cocaine and its metabolites, cocaethylene and benzoylecgonine, in suppressing the functional expression of somatostatin and neuropeptide Y producing neurons in cultures of fetal cortical cells.

Using aggregate cultures derived from 17-day-old fetal rat cortex, we addressed the question: Does cocaine alter the functional expression of neuropeptide Y (NPY) and somatostatin (SRIF) neurons and, if so, are cocaethylene (CE) and benzoylecgonine (BZE) as active as cocaine? NPY/SRIF production in response to brain-derived neurotrophic factor (BDNF) or phorbol-12-myristate-13-acetate (PMA) was used as a functional criterion. A 5-day exposure to cocaine did not affect basal or stimulated (BDNF or PMA) production of NPY but it markedly suppressed BDNF- or PMA-stimulated production of SRIF. Exposure to CE led to a drastic suppression of basal as well as stimulated (BDNF or PMA) production of both NPY and SRIF. These effects of cocaine and CE were concentration dependent (1-100 microM). BZE did not alter any of these functional parameters. Next, we evaluated the fate of cocaine, CE, and BZE in the culture medium. Cocaine was converted to BZE, whereas BZE was not converted to cocaine. CE was converted to cocaine and BZE, with substantial amounts of cocaine and CE remaining in the medium after 72 hr (approximately 20% each). In summary, cocaine, CE, and BZE exhibited differential potencies in suppressing the expression of cultured NPY and SRIF neurons: CE was more potent than cocaine and BZE was inactive. SRIF neurons were more susceptible than NPY neurons to the effects of cocaine. The higher potency of CE may be due to a property of the compound and/or to CE serving as a source for a slow, continuous formation of cocaine by the brain cells themselves.

Comparison of neurotrophin regulation of human and rat neuropeptide Y (NPY) neurons: induction of NPY production in aggregate cultures derived from rat but not from human fetal brains.

Previous studies established that brain-derived neurotrophic factor (BDNF) induces neuropeptide Y (NPY) production and accumulation of NPY-mRNA in cultures of rat fetal brain tissues. In this study, we addressed the question: Are cultured human NPY neurons regulated by BDNF and/or by another member of the neurotrophin (NT) family of growth factors? Using aggregate cultures derived from human fetal cortical hemispheres, we assessed the effect of BDNF on NPY production varying the following experimental conditions: fetal and culture age; medium composition (with and without serum), dose and duration of exposure to BDNF, and neurotrophin species tested (BDNF, NT-4/5, NT-3 or NGF). Under none of these conditions did BDNF, NT-4/5, NT-3 or NGF induce an increase in NPY production. This was in contrast to forskolin + phorbol 12 myristate 13-acetate (PMA) which were highly effective in inducing NPY production, verifying that expression of NPY is a regulated process in these cultures. None of these neurotrophins enhanced the response to forskolin + PMA. By comparison, using aggregate cultures derived from rat fetal cortices, BDNF and NT-4/5 were equipotent in inducing NPY production but NT-3 and NGF were essentially ineffective. Moreover, the effects of BDNF or NT-4/5 and forskolin + PMA on NPY production were additive, indicating the involvement of distinct intracellular signalling pathways. Western blot analyses of human- and rat-derived aggregates indicated the presence of full-length Trk receptors which are tyrosine-phosphorylated in response to either BDNF, NT-4/5 or NT-3. Primary cultures of astrocytes (rat as well as human) were devoid of a functional TrkB receptor, strongly suggesting a neuronal expression of TrkB in the aggregates. Thus, a functional TrkB receptor is expressed by both the human and rat aggregates, but only the rat aggregates responded to BDNF or NT-4/5. These results are consistent with a difference in a post TrkB-receptor event(s) mediating BDNF action in the cultured human and rat fetal NPY neurons.

Human fetal brain cells in aggregate culture: a model system to study regulatory processes of the developing human neuropeptide Y (NPY)-producing neuron.

Neuropeptide Y (NPY) is one of the most abundant neuropeptides in the brain and it has been implicated in a wide range of brain functions, including mentation. The aim of this study was to establish a culture system of human fetal brain cells expressing NPY in a regulated manner. The NPY production in response to forskolin and phorbol 12-myristate 13-acetate (PMA) was taken as a criterion for regulated expression of NPY. Aggregates were formed from dissociated cells derived from the cerebral hemispheres of human fetuses (12.5-19 weeks' gestation) by constant rotation and were maintained in serum-free medium. A 24 hr exposure to 10 microM forskolin + 20 nM PMA led to a 2-6-fold increase in NPY content of the cultures, most of which (80-90%) was secreted into the medium. The latter consisted of two substances differing in size: one corresponding in size to proNPY and the other to NPY. Thus, forskolin + PMA led to an increased production of NPY. Exposure to PMA alone led to an increase in NPY production comparable to that seen after forskolin + PMA and this effect of PMA was dose-dependent. In contrast, forskolin alone did not induce NPY production. Conditioned medium, derived from monolayer cultures enriched with human astrocytes, enhanced NPY production in response to forskolin+PMA in an age-dependent manner. The NPY production by aggregates derived from a 12.5 week-, 14-week- and 18-week-old fetus was enhanced 3-3.6-fold, 1.6-2-fold and 1.1-fold, respectively. Thus, expression of the NPY neurons in this culture system is a regulated process. The NPY production is enhanced markedly by activation of the protein kinase C pathway and by an astrocyte-derived soluble substance(s). Based on these results, we propose that this culture system can serve as a model for the study of regulatory processes of the human developing NPY neuron.

Expression of tyrosine hydroxylase gene in cultured hypothalamic cells: roles of protein kinase A and C.

In hypothalamic cells cultured in serum-free medium, the quantity of tyrosine hydroxylase mRNA increases after treatment with an activator of the protein kinase A pathway (8-bromoadenosine cyclic AMP, 3-isobutyl-1-methylxanthine, or forskolin) or an activator of protein kinase C (12-O-tetradecanoylphorbol 13-acetate or sn-1,2-diacylglycerol). The tyrosine hydroxylase mRNA level decreases in the cells after inhibition of protein kinase C with calphostin C or after depletion of protein kinase C by extended phorbol ester treatment. These data suggest that both protein kinase pathways regulate tyrosine hydroxylase gene expression in hypothalamic cells. As simultaneous activation of both pathways has less than an additive effect on the tyrosine hydroxylase mRNA level, they appear to be interrelated. Compared with the rapid and dramatic increase of the tyrosine hydroxylase mRNA level in pheochromocytoma cells, activation of the protein kinase A or protein kinase C pathway in the cultured hypothalamic cells induces slow changes of a small magnitude in the amount of tyrosine hydroxylase mRNA. The slow regulation of tyrosine hydroxylase gene expression in hypothalamic dopaminergic neurons corresponds to the relatively high stability of tyrosine hydroxylase mRNA (half-life = 14 +/- 1 h) in these cells.

Localization of a defect in hypothalamic dopaminergic neurons of the aged brain that results in impaired PKA-dependent activation of tyrosine hydroxylase.

Using an in vitro incubation system, the role of the cyclic AMP-dependent protein kinase A (PKA) pathway in the regulation of the in situ activity of tyrosine hydroxylase (TH) was studied in the hypothalamuses of young and aged ovariectomized rats. Hypothalamic tissue was incubated for 60 min in medium containing 3-hydroxybenzylhydrazine dihydrochloride, a dihydroxyphenylalanine (DOPA) decarboxylase inhibitor, and various agents that modify the activity of the PKA pathway. At the end of the incubation, the tissue was homogenized and analyzed for DOPA and TH mass. The in situ molar activity of TH was expressed as the moles of DOPA accumulating in the tissue per mole of TH per hour. Forskolin, an activator of adenylyl cyclase and the cyclic AMP agonist, (Sp)-cyclic adenosine 3',5'-monophosphothioate, significantly (P < .01) increased the in situ molar activity of TH in the hypothalamic dopaminergic (DAergic) neurons of both young and aged rats. Theophylline, a phosphodiesterase inhibitor, did not affect the TH molar activity in the hypothalamuses of aged animals but did significantly (P < .001) increase its activity in those of young rats. When vasoactive intestinal peptide was evaluated, the TH molar activity was significantly (P < .005) increased in the hypothalamuses of young rats but not in those of aged rats. It was suggested that the deficiency of DA secretion by hypothalamic DAergic neurons of aged rats may be the result of insufficient activation of PKA caused by failure of transduction of an extracellular signal to activate adenylyl cyclase and produce cyclic AMP.

Tyrosine hydroxylase expression in hypothalamic cells: analysis of the roles of adenosine 3',5'-monophosphate- and Ca2+/calmodulin-dependent protein kinases in the action of pituitary cytotropic factor.

We investigated the involvement of second messenger systems in the control by pituitary cytotropic factor (CTF) of tyrosine hydroxylase (TH) expression in primary cultures of hypothalamic cells. Forskolin, an activator of adenylyl cyclase, as well as Sp-cAMP[S] [(Sp)-cyclic adenosine 3',5'-monophosphothioate], a cAMP agonist, and theophylline, an inhibitor of phosphodiesterase activity, stimulate the secretion of dihydroxyphenylalanine (DOPA) and dopamine (DA), suggesting a role for cAMP-dependent protein kinase in the secretion of catecholamines by hypothalamic dopaminergic cells. When cells were cultured with either CTF or forskolin for 14 days, a progressive increase in the secretion of DOPA and DA was observed throughout the period of incubation. At the end of the 2-week culture period, the amount of TH in the cells, determined by immunoblot analysis, was appreciably increased compared to controls. When the cells were analyzed immunocytochemically for TH, the TH-positive cells that had been incubated with CTF or forskolin for 2 weeks were found to have neurites that appeared larger than those of TH-positive cells in the controls. The diameters of the perikarya of TH-positive cells in cultures incubated with CTF also appeared larger than the controls. After incubation of hypothalamic cells with CTF for 96 h, the amount of TH mRNA in the cultures was significantly increased. When membranes isolated from PC12 cells were incubated for 10 min with 50 microM forskolin, the specific activity of adenylyl cyclase was increased 20-fold; CTF had no effect on adenylyl cyclase activity of PC12 cell membranes. Yet, CTF significantly (P less than 0.001) stimulated the secretion of DOPA and DA by PC12 cells. When hypothalamic cells were incubated with both forskolin and CTF, using doses of each that stimulated maximal secretion, the secretion of DOPA and DA was equal to sum of the secretions with each stimulant alone. These additive actions of forskolin and CTF and the failure of CTF to activate adenylyl cyclase in membranes of PC12 cells suggest that forskolin and CTF stimulate catecholamine secretion by hypothalamic dopaminergic cells through different mechanisms, perhaps through different protein kinases. When hypothalamic cells were incubated with CTF and W-7 [N-(6-aminohexyl)5-chloro-1-naphthalenesulfonamide], an inhibitor of calmodulin, the secretion of DOPA was significantly (P less than 0.001) less than that in cultures that were not incubated with W-7. The findings of this study suggest that TH expression in hypothalamic dopaminergic cells is controlled by redundant protein kinases, including cAMP-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase.

Testicular inhibition of tyrosine hydroxylase expression in tuberoinfundibular and nigrostriatal dopaminergic neurons.

We have investigated, in young and aged rats, tuberoinfundibular dopaminergic (TIDA) and nigrostriatal neurons of the brain, and the role of the testes and anterior pituitary (AP) on 1) the in situ activity of tyrosine hydroxylase (TH), 2) translation of TH mRNA, as reflected by the mass of TH, and 3) transcription of the TH gene, as revealed by the mass of TH mRNA. The median eminence (ME) and corpus striatum (CS) were used as the sources of proximal neurites of the TIDA neurons and nigrostriatal neurons, respectively. The arcuate-periventricular nuclei of the ventral hypothalamus were used as the source of perikarya of the TIDA neurons, and substantia nigra (SN) nuclei of the midbrain were used as the source of perikarya of nigrostriatal neurons. The in situ activity of TH was calculated using the rate of accumulation of dihydroxyphenylalanine after pharmacological inhibition of dihydroxyphenylalanine decarboxylase activity. TH mass and TH mRNA were measured using an immunoblot assay and an S1 nuclease protection assay, respectively. Compared to intact animals, orchidectomized young and aged male rats had significantly (P less than 0.001) increased in situ activity of TH in the ME and CS, but not the SN. Orchidectomy also caused a significant (P less than 0.01) increase in the quantity of TH in the ME and a 2- to 3-fold increase in TH in the CS and SN. In contrast to castration, AP grafts, implanted in the lateral ventricles of the brain, caused a significant (P less than 0.001) increase only in TH activity in the ME. No effect of AP grafts was seen on TH activity of the CS or SN. AP grafts had no effect on the amount of TH in the ME, CS, or SN. In the TIDA neurons of young males and in the nigrostriatal neurons of young and aged castrates, the amount of TH mRNA was not different from that in intact males. AP grafts had no effect on TH mRNA in these dopaminergic neurons. These studies show that TIDA neurons and nigrostriatal neurons share some common aspects in their regulation and are dissimilar in others. AP grafts stimulate TH activity in young as well as aged TIDA neurons, but not in nigrostriatal neurons. Castration leads to an increase in TH mass in both TIDA and nigrostriatal neurons. The increase in TH mass is not associated with an increase in the amount of TH mRNA. It is suggested that castration results in increased translation of TH mRNA, but not transcription of the TH gene.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of cerebroventricular anterior pituitary grafts on in situ expression of tyrosine hydroxylase in dopaminergic neurons of the aged animal.

The effect of cerebroventricular anterior pituitary (AP) grafts on brain tyrosine hydroxylase (TH) expression in the median eminence (ME), substantia nigra (SN), and corpus striatum (CS) has been investigated in young and aged female rats. TH expression was studied using the following indices: in situ TH activity, TH mass, and quantity of TH mRNA. The rate of synthesis of dihydroxyphenylalanine (DOPA) was evaluated by measuring its accumulation in the ME, SN, and CS. TH mRNA and TH mass were quantified by an S1 nuclease protection assay and an immunoblot assay, respectively. Viability of the grafts was demonstrated by histological examination and by their ability to secrete PRL into the cerebrospinal fluid (CSF). Liver grafts served as controls. In castrated young and castrated aged animals with AP grafts, the PRL concentrations in the CSF were 204 +/- 49 (mean +/- SE) and 345 +/- 83 ng/ml, respectively, compared to control values of 14 +/- 9 and 23 +/- 9. In intact aged animals, the concentration of PRL was 729 +/- 180 ng/ml in CSF of rats with AP grafts and 223 +/- 62 ng/ml in the controls. DOPA synthesis in the ME of castrated young rats and castrated aged rats with AP grafts was significantly (P less than 0.01) greater than that in controls with liver grafts. AP grafts did not stimulate DOPA synthesis in the ME of intact aged animals. The synthesis of DOPA in the SN and CS was not affected by AP grafts, regardless of the status of the animal. The amount of TH mRNA and the quantity of TH were not influenced by the AP grafts in any of the animal models. However, the in situ molar activity of TH in the ME was significantly greater in castrated young rats and castrated aged rats bearing AP grafts than in animals with liver grafts. The in situ molar activity of TH in the ME of castrated young rats was greater than that of castrated or intact aged animals. It is concluded that AP grafts secrete a substance that stimulates DOPA synthesis in the ME of young as well as aged castrated animals, but not in the nigrostriatal system. This stimulation is due to increased catalytic activity of a fixed number of TH molecules rather than an increase in the mass of TH.

Expression of tyrosine hydroxylase in cultured brain cells: stimulation with an extractable pituitary cytotropic factor.

Expression of tyrosine hydroxylase (TH) in cultured cells of the ventral hypothalamus-midbrain of fetal rats has been investigated. TH mRNA and TH were quantified by an S1 nuclease protection assay and an immunoblot assay, respectively. Dihydroxyphenylalanine (DOPA) and dopamine secretion were evaluated using their rates of accumulation in the culture medium. The rate of accumulation of DOPA was 2-3 times that of dopamine. Inhibitors of TH activity caused a dose-dependent reduction in DOPA secretion. During an 11-week culture of dissociated cells, TH mRNA increased from 1.6 to 2.8 attomole/well between the first and fourth week of culture, remained steady to the ninth week, and then declined. TH increased from 12 to 105 fmol/well between the first and seventh week and then declined. DOPA secretion increased until the sixth week and then remained steady to the tenth week. An extract of rat pituitaries stimulated DOPA secretion by the cultures in a dose-dependent manner. This activity, attributed to a cytotropic factor (CTF), was inactivated by heating for 10 min in a boiling water bath, but was unaffected by trypsin digestion. Incubation with CTF for 24, 48, 72, and 96 h resulted in a day by day increase in the secretion of DOPA. After 96 h of culture with CTF, the amount per well of TH mRNA, but not TH, was significantly (P less than 0.01) greater than the control value. Pituitary CTF is probably not PRL, since rat PRL did not appreciably affect DOPA secretion or the amount of TH mRNA or TH in the cells. Withdrawal of CTF from CTF-stimulated cells resulted in a marked reduction in DOPA secretion as well as a decrease in TH mRNA. These results support the hypothesis that the pituitary gland contains a cytotropic factor that stimulates TH expression in fetal brain cells of the hypothalamus-midbrain.

The tuberoinfundibular dopaminergic neurons of the brain: hormonal regulation.

The role of prolactin and of estradiol and progesterone in the control of the biosynthetic and secretory activity of TIDA neurons has been investigated in the following animal models: young female rats, aged female rats, and young male rats. The indices of TIDA neuronal function employed were a) mass of TH in neurites in the ME, b) total in situ activity of TH in the ME, c) in situ molar activity of TH in the ME, and d) secretion of dopamine into hypophysial portal blood. It was found that prolactin in high concentration in the circulation and in the CSF had little, if any, effect on the mass of TH in the ME. However, a high concentration of prolactin in either the circulation or in the CSF stimulated significantly the in situ TH activity in the ME whether expressed in terms of total activity per ME or activity per mole of TH. The stimulation of TH activity with prolactin was prevented by immunoneutralization of circulating prolactin. A high concentration of prolactin in the CSF was as effective in stimulating TH activity in the ME of rats with intact pituitary glands as in hypophysectomized rats. In addition to prolactin, treatment of animals with intact pituitaries with a combination of estradiol and progesterone markedly stimulated the total in situ activity of TH of the ME as well as the in situ molar activity of TH of the ME, but neither estradiol nor progesterone alone had an effect on TH activity. Hypophysectomy abolished the stimulatory action of estradiol and progesterone on TH activity of the ME. In addition to the in situ activity of TH in the ME, estradiol-progesterone treatment stimulated the secretion of dopamine into hypophysial portal blood. Neither estradiol nor progesterone alone affected dopamine secretion by TIDA neurons. We conclude that exposure to high concentrations of prolactin or to both estradiol and progesterone stimulate the biosynthetic and secretory activity of TIDA neurons. These hormones are effective in old rats and well as young rats and in males as well as females.

Hormonal control of tyrosine hydroxylase in the median eminence: demonstration of a central role for the pituitary gland.

In intact male rats the concentration of dopamine in hypophysial portal plasma of animals treated simultaneously with estradiol and progesterone was twice that of animals treated with the solvent vehicle. Treatment with estradiol or progesterone alone had no effect on dopamine in portal plasma. The rate of synthesis of dihydroxyphenylalanine (DOPA), the precursor of dopamine, in tuberoinfundibular dopaminergic (TID) neurites in the median eminence (ME) was 15 +/- 1.0 (mean +/- SE) pmol DOPA/ME.h in estradiol-progesterone-treated animals compared to 3.2 +/- 0.02 in vehicle-treated controls. Treatment with estradiol or progesterone alone gave a result similar to that seen in controls. In hypophysectomized animals treated with estradiol and progesterone, DOPA synthesis in the ME was greatly attenuated compared to that in intact rats. The in situ activity of tyrosine hydroxylase (TH; expressed as moles of DOPA per mol TH/h) in the ME was 178 +/- 16.5 in estradiol-progesterone-treated intact rats, but was 27 +/- 2.4, 52 +/- 4.2, and 35 +/- 2.5 in animals treated with the solvent vehicle, estradiol, and progesterone, respectively. In hypophysectomized rats the in situ activity of TH in the ME of animals treated with estradiol and progesterone was 53 +/- 8.4, which was significantly (P less than 0.01) less than that in similarly treated intact animals. The circulating PRL level in vehicle-treated animals was 35 +/- 4.6 ng/ml compared to 121 +/- 16 in estradiol-treated animals and 133 +/- 12.2 in estradiol- and progesterone-treated rats, indicating that the difference in the effects of estradiol and estradiol-progesterone on dopamine release, DOPA synthesis, and in situ TH activity was not solely due to a difference in circulating PRL levels. Maintenance for 7 days of anterior pituitary tissue as a graft in a lateral ventricle of intact rats resulted in a 2-fold increase in the synthesis of DOPA and TH activity in the ME compared to that in animals with liver implants. Results obtained in hypophysectomized animals with implants were similar to those in intact animals. The concentrations of PRL in cerebrospinal fluid of intact rats and hypophysectomized rats with anterior pituitary implants in the lateral ventricles were 96 +/- 32 and 127 +/- 35 ng/ml, respectively, which was significantly (P less than 0.001) greater than those in animals with liver implants. We suggest that a factor of pituitary origin stimulates TH activity in TID neurons. This stimulation may be due to PRL, but the existence of another stimulatory substance secreted by pituitary cells cannot be excluded.