Carcass merit between and among family groups of Bos indicus crossbred steers and heifers.

Differences in live and carcass traits attributable to increasing Bos indicus breed influence were compared to the differences between families with similar proportions of B. indicus influence. Families of offspring from 1/2 Angus×1/2 B. indicus mated to Angus, B. indicus, and 1/2 Angus×1/2 B.indicus were raised under similar conditions. Average daily gain, slaughter weight, and dressing percentage were measured in addition to USDA yield and quality grade factors. Breed type did not affect average daily gain, slaughter weight, dressing percentage, carcass weight, adjusted 12th-rib fat thickness, estimated percentage kidney, pelvic, and heart fat, or carcass maturity. Predominately (3/4) Angus progeny produced greater (P<0.05) longissimus muscle areas than 3/4 B. indicus animals. Predominately Angus cattle also had greater (P<0.05) marbling scores and USDA quality grades than predominately B. indicus cattle. Families within breed types differed (P<0.05) with regard to all traits measured. This is interesting in light of the lack of differences between breeds for most traits. In some instances, the differences in marbling score and longissimus muscle area between families within a given breed type were similar or greater in magnitude than the differences observed between predominately Angus and predominately B. indicus breed types. Whereas growth and carcass traits varied between levels of B. indicus breeding, the opportunity does exists to improve these traits by selecting within specific family lines.

Beef customer satisfaction: factors affecting consumer evaluations of calcium chloride-injected top sirloin steaks when given instructions for preparation.

The objectives of this study were to evaluate whether instructions can help consumers properly prepare top sirloin steaks and to evaluate the use of calcium chloride injection to decrease the sensitivity of top sirloin steaks to degree of doneness, thereby improving customer satisfaction ratings. An in-home study evaluated top sirloin steaks (gluteus medius) as influenced by calcium chloride injection (injected vs. noninjected), consumer segment (beef loyalists = heavy consumers of beef, budget rotators = cost-driven and split meat consumption between beef and chicken, and variety rotators = higher incomes and education and split meat consumption among beef, poultry, and other foods), degree of doneness, cooking method, and instructions (given vs. not given). Consumers evaluated overall like, tenderness, juiciness, flavor like, and flavor amount using 10-point scales. Beef loyalists consistently rated steaks higher for overall like, juiciness, and flavor when instructions were provided (P < 0.05) and rated top sirloin steaks higher for overall like and tenderness when given instructions for grilling (P < 0.05). Budget rotators and variety rotators rated steaks differently among cooking methods (P < 0.05). Correlation and stepwise regression analyses indicated that flavor like was the most highly correlated with overall like, followed by tenderness, flavor amount, and juiciness. Calcium chloride injection had no effect on consumers' likes or dislikes or on tenderness (P < 0.05). For top sirloin steaks, it was likely that preparation played a major role in consumer satisfaction, and beef loyalists benefited the most from providing cooking instructions.

Beef customer satisfaction: USDA quality grade and marination effects on consumer evaluations of top round steaks.

An in-home beef study evaluated consumer ratings of top round steaks (semimembranosus) as influenced by USDA quality grade (top Choice or high Select), city (Chicago or Philadelphia), consumer segment (beef loyalists = heavy consumers of beef; budget rotators = cost-driven and split meat consumption between beef and chicken; and variety rotators = higher incomes and education and split meat consumption among beef, poultry, and other foods), degree of doneness, cooking method, and marination. Consumers evaluated each steak for overall like, tenderness, juiciness, flavor like, and flavor amount using 10-point scales (1 = dislike extremely, not at all tender, not at all juicy, dislike extremely, and none at all to 10 = like extremely, extremely tender, extremely juicy, like extremely, and an extreme amount of flavor, respectively). Quality grade affected several consumer sensory traits, with top Choice receiving higher (P < or = 0.004) tenderness, juiciness, and flavor like scores than high Select. Consumers in Chicago rated steaks cooked "medium and less" higher for overall like, tenderness, juiciness, flavor like, and flavor amount than those in Philadelphia (city x degree of doneness; P < or = 0.020). Steaks braised by customers in Philadelphia received among the highest scores for overall like, tenderness, juiciness, flavor like, and flavor amount compared with any cooking method used by customers in Chicago (cooking method x city; P < or = 0.026). Overall like and flavor amount ratings were least (P < 0.05) for steaks that were marinated and cooked to "medium and less" degree of doneness (marination x degree of doneness; P < or = 0.014). Braised steaks received among the highest values for overall like, tenderness, juiciness, flavor like, and flavor amount when cooked to "medium and less" or "medium well and more" (cooking method x degree of doneness; P < or = 0.008). Correlation and stepwise regression analysis indicated that flavor like was pivotal in customers' satisfaction with top round steaks, and was the sensory trait most highly correlated to overall like, followed by tenderness, flavor amount, and juiciness. Preparation of top round steaks was crucial in consumers' likes and dislikes, and by improving flavor, higher consumer satisfaction may be achieved.

Interrelationships of breed type, USDA quality grade, cooking method, and degree of doneness on consumer evaluations of beef in Dallas and San Antonio, Texas, USA.

The objective of this research was to evaluate the consumer controlled factors of cooking method and degree of doneness on top loin steaks from different USDA quality grades (Low Choice, High Select or Low Select) and breed-types (English, Continental European Cross or Brahman Cross). In addition, cities within the same region were evaluated for differences in consumer controlled factors and palatability responses. The in-home product test was conducted in Dallas and San Antonio, Texas, USA. Consumers (n=173) evaluated steaks for overall like (OSAT), tenderness (TEND), juiciness (JUIC), and flavor (FLAV) using 23-point hedonic scales. Respondents in Dallas cooked their steaks to higher degrees of doneness than did those in San Antonio. Outdoor grilling was the most frequently used method of cookery for steaks in both cities. Generally, consumers in San Antonio gave higher palatability ratings to Choice steaks and Dallas consumers gave higher ratings to Select steaks. The interactions of city×cooking method, breed-type×cooking method, and degree of doneness×cooking method were significant for all palatability attributes. In addition, the interaction of cooking method×quality grade was significant for TEND, JUIC, and FLAV. Warner-Bratzler shear (WBS) force was determined on a steak from each strip loin. Steaks from Continental European Cross cattle and Low Choice carcasses had the lowest WBS values. Differences in consumer preparation of beef top loin steaks present very unique challenges for the beef industry. Consumer information programs may serve a valuable role in connecting consumer perceptions with the preparation techniques needed to consistently achieve satisfaction.

Transcriptional and post-transcriptional regulation of tyrosine hydroxylase messenger RNA in PC12 cells during persistent stimulation by VIP and PACAP38: differential regulation by protein kinase A and protein kinase C-dependent pathways.

VIP and PACAP38 are closely related peptides that are released in the adrenal gland and sympathetic ganglia and regulate catecholamine synthesis and release. We used PC12 cells as a model system to examine receptor and second messenger pathways by which each peptide stimulates transcriptional and post-transcriptional mechanisms that regulate the level of the mRNA for tyrosine hydroxylase (TH), the rate-limiting enzymatic step in catecholamine synthesis. Concentration-response studies revealed that PACAP38 had both greater efficacy and potency than VIP. The specific PAC1 receptor antagonist PACAP[6-38] blocked the effects of each peptide on TH mRNA content while the PACAP/VIP type II receptor antagonist (N-AC-Tyr(1)-D-Phe(2))-GRF-(1-29)-NH(2) was without effect. At equipotent concentrations, each peptide stimulated a transient increase in TH gene transcription lasting less than 3h. Continuous VIP treatment stimulated a transient increase in TH mRNA lasting less than 24h. In contrast, continuous exposure to PACAP38 stimulated a stable increase in TH mRNA that persisted for 2 days in the absence of elevated transcription, pointing to different post-transcriptional effects of the two peptides. PACAP38 alone had no effect on the magnitude of TH gene transcription or TH mRNA in A126-1B2 PKA-deficient PC12 cells. However, when combined with dexamethasone, PACAP38 produced a synergistic increase in TH mRNA in the absence of PACAP38-stimulated TH gene transcription. In contrast, VIP had no effect on either TH mRNA content or TH gene transcription in this model. PACAP38, but not VIP, stimulated PKC activity. Calphostin C antagonized the effect of PACAP38 on the persistent post-transcriptional elevation in TH mRNA. Thus, the results support the conclusion that VIP and PACAP38 each stimulate PAC1 receptors to increase TH gene transcription through a PKA-controlled pathway, but their divergent post-transcriptional effects result at least partly from differing abilities to stimulate PKC.

Beef customer satisfaction: factors affecting consumer evaluations of clod steaks.

An in-home beef study evaluated consumer ratings of clod steaks (n = 1,264) as influenced by USDA quality grade (Top Choice, Low Choice, High Select, and Low Select), city (Chicago and Philadelphia), consumer segment (Beef Loyals, who are heavy consumers of beef; Budget Rotators, who are cost-driven and split meat consumption between beef and chicken; and Variety Rotators, who have higher incomes and education and split their meat consumption among beef, poultry, and other foods), degree of doneness, and cooking method. Consumers evaluated each steak for Overall Like, Tenderness, Juiciness, Flavor Like, and Flavor Amount using 10-point scales. Grilling was the predominant cooking method used, and steaks were cooked to medium-well and greater degrees of doneness. Interactions existed involving the consumer-controlled factors of degree of doneness and(or) cooking method for all consumer-evaluated traits for the clod steak (P < 0.05). USDA grade did not affect any consumer evaluation traits or Warner-Bratzler shear force values (P > 0.05). One significant main effect, segment (P = 0.006), and one significant interaction, cooking method x city (P = 0.0407), existed for Overall Like ratings. Consumers in the Beef Loyals segment rated clod steaks higher in Overall Like than the other segments. Consumers in Chicago tended to give more uniform Overall Like ratings to clod steaks cooked by various methods; however, consumers in Philadelphia gave among the highest ratings to clod steaks that were fried and among the lowest to those that were grilled. Additionally, although clod steaks that were fried were given generally high ratings by consumers in Philadelphia, consumers in Chicago rated clod steaks cooked in this manner significantly lower than those in Philadelphia. Conversely, consumers in Chicago rated clod steaks that were grilled significantly higher than consumers in Philadelphia. Correlation and stepwise regression analyses indicated that Flavor Like was driving customer satisfaction of the clod steak. Flavor Like was the sensory trait most highly correlated to Overall Like, followed by Tenderness, Flavor Amount, and Juiciness. Flavor Like was the first variable to enter into the stepwise regression equation for predicting Overall Like, followed by Tenderness and Flavor Amount. For the clod steak, it is likely that preparation techniques that improve flavor without reducing tenderness positively affect customer satisfaction.

Chronic administration of pharmacological levels of melatonin does not ameliorate the MPTP-induced degeneration of the nigrostriatal pathway.

An extensive literature suggests that melatonin may protect from the degenerative effects of central neurotoxins by acting as a free radical scavenger. The purpose of this study was to determine if melatonin would protect male C57BL6 mice from the toxicity of methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to nigral dopamine (DA) neurons. Melatonin was initially dissolved in dimethyl sulfoxide (DMSO), diluted to 16 microg/ml and then provided in the drinking water for 4 weeks. Control mice drank the same final concentration of the DMSO diluent. One week before the termination of the experiment, randomly selected mice from the melatonin-treated and the DMSO-treated groups received two, three or four doses of 2.5 mg/kg MPTP free base administered subcutaneously at 2-h intervals. Additional DMSO-treated and melatonin-treated mice did not receive MPTP. Following tissue collection, melatonin concentration was measured in blood plasma collected from each animal and found to be 20-fold higher in melatonin-treated compared to DMSO-treated mice. Tyrosine hydroxylase (TH) activity and the levels of DA and dihydroxyphenylacetic acid (DOPAC) were not different in striata collected from melatonin-treated versus DMSO-treated mice which did not receive MPTP. Treatment with MPTP significantly reduced striatal TH activity, DA and DOPAC, but there were no significant differences in the reductions in any of these parameters observed in the melatonin-treated versus the DMSO-treated control mice that received the same total dosage of MPTP. These results show that the long-term administration of a high pharmacological dose of melatonin was ineffective in protecting nigral dopaminergic neurons from the neurotoxic effects of MPTP.

Interaction of a glucocorticoid-responsive element with regulatory sequences in the promoter region of the mouse tyrosine hydroxylase gene.

The purpose of the work reported here was to determine whether the tyrosine hydroxylase glucocorticoid-responsive element (TH-GRE) interacts with the cyclic AMP pathway and the CRE in regulating mouse TH promoter activity, and whether an additional, previously identified downstream GRE-like element also participates in the function of the TH-GRE and CRE. To determine the role of the cAMP pathway on TH-GRE function, we compared the effects of forskolin and dexamethasone on TH mRNA, TH gene transcription and TH promoter activity in a mutant PC12 cell line (A126-1B2) deficient in cAMP-dependent protein kinase A (PKA) with their effects in the wild-type parental strain. Forskolin treatment increased TH mRNA content, transcriptional activity and the activity of a chimeric gene with 3.6 kb of the TH promoter in wild-type cells, but not in PKA-deficient cells. In contrast, dexamethasone treatment stimulated equivalent increases in TH mRNA, TH gene transcription and TH promoter activity in each cell type. Mutation of the CRE in chimeric constructs containing 3.6 kb of the 5' flanking sequence of the mouse TH gene or coexpression of a dominant-negative mutant of CREB prevented the stimulation of TH promoter activity by forskolin. However, neither the mutation of the CRE nor inhibition of CREB influenced basal or dexamethasone-stimulated promoter activity. Site-directed mutagenesis of the TH-GRE eliminated the response of the promoter to dexamethasone. However, the mutagenesis of a more proximal 15-bp region with a GRE-like sequence had no demonstrable effect on the ability of dexamethasone to stimulate TH promoter activity. Neither mutagenesis of the TH-GRE or the downstream GRE-like sequence had an effect on the ability of forskolin to activate this chimeric gene. Taken together, these results provide evidence that a single GRE is sufficient for maximal induction of transcriptional activity by glucocorticoids and that the CRE is not required for either partial or full activity of this upstream GRE sequence.

A tetracycline-repressible transactivator approach suggests a shorter half-life for tyrosine hydroxylase mRNA.

Long-term increases in catecholamine release result in elevated levels of the mRNA for tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of these compounds. This increase is due, in part, to increased transcription. However, recent evidence suggests that increased stability of TH mRNA may also play a role. One of the problems in studying the stability of the TH message is the limitation of current methods for assessing transcript half-life. In this study the regulation of the expression of the rat TH gene was placed under the control of a tetracycline (Tet)-repressible transactivator (tTA). In the absence of doxycycline (Dox), an analogue of Tet, TH mRNA was synthesized. However, when Dox was present, transcription of TH message was essentially totally suppressed, and the resulting degradation of the TH mRNA provided an index of the half-life of this message. With this approach the computed half-life of TH mRNA was significantly shorter than that determined following actinomycin D administration. This effect was not due to some unique feature of the chimeric gene used to synthesize TH mRNA or to an untoward effect of the Tet analogue used to suppress TH transcription.

Identification of a glucocorticoid-responsive element in the promoter region of the mouse tyrosine hydroxylase gene.

It has been known for nearly 30 years that glucocorticoid receptor stimulation induces increased tyrosine hydroxylase (TH) gene expression. However, the mechanism mediating this effect has remained elusive. Sequences with homology to known glucocorticoid-responsive elements (GRE) have been identified in the 5' flanking region of the TH gene of several vertebrate species, but none has been shown to be functional. To identify the GRE element(s) in the TH promoter, we generated chimeric constructs in which different lengths of the 5' flanking sequences of the mouse TH gene (3.6, 1.1 and 0.8 kb) were ligated to a luciferase reporter gene. Dexamethasone treatment increased luciferase expression only in cells transiently transfected with the construct containing 3.6 kb of the TH 5' flanking DNA. Co-administration of mifepristone (RU486), a glucocorticoid receptor antagonist, blocked this effect. We identified a TH-GRE sequence (5'-GGCACAGTGTGGTCT) in the mouse 5' flanking DNA between -2435 and -2421 from the transcription start. Responsiveness to dexamethasone was lost following deletion of this sequence. To determine the ability of this element to function in a heterologous promoter, we prepared a chimeric construct in which the TH-GRE sequence was cloned just upstream of a minimal thymidine kinase (TK) promoter. Promoter activity was increased 2-fold in dexamethasone-treated PC12 cells transfected with the TH-GRE-TK construct. These results provide strong evidence that the 15 base-pair sequence in the 5' flanking DNA of the mouse TH gene functions as a glucocorticoid response element. This is the first report identifying a functional glucocorticoid response element in the promoter region of the TH gene of any species.

Application of exogenously regulatable promoter systems to transgenic models for the study of aging.

Transgenic mouse and gene knockout technologies offer powerful tools for dissecting the roles of specific genes in the process of aging. Tke interpretation of the results of such studies is limited, however, by the fact that the gene of interest of over- or underexpressed throughout the life span of the animal model. Among other problems, this situation makes it difficult to separate the effects that a specific gene has an embryological development from those that it may exert on the subsequent maturation and aging of the animal. It is also not possible with these methods alone to alter the expression of genes in an age-dependent fashion and to assess the effects of these alterations on the aging process. This capacity would be of particular interest in studying genes which are thought to have a role in regulating physiological homeostasis. Because they offer the opportunity to activate or render inactive the expression of genes at will, exogenously regulatable promoter systems, particularly when used in combination with traditional transgenic or gene knockout approaches, provide a new and potentially very powerful tool for studying the effect of selected genes on aging. This review discusses the merits and limitations of the application of either the tetracycline-regulatable promoter system, the RU 486-inducible promoter system, or the ecdysone-inducible promoter system to exogenously regulate the expression of a transcriptionally linked gene and to thus assess the effect of that gene on aging.

National Beef Quality Audit-1995: survey of producer-related defects and carcass quality and quantity attributes.

The National Beef Quality Audit-1995 was conducted to evaluate the progress of the beef industry since the time of the National Beef Quality Audit-1991 in improving quality and consistency of beef. Nine plants were assigned for auditing to Colorado State University, Oklahoma State University, and Texas A&M University. Personnel from each institution visited three of their nine plants twice, once in the spring/summer and once in the fall/winter. Data were collected on 50% of each lot on the slaughter floor and 10% in the cooler during a single day's production (one or two shifts, as appropriate). Of the cattle audited on the slaughter floor, 47.7% had no brands, 3.0% had a shoulder brand, 16.8% had a side brand, 38.7% had a butt brand, and 6.2% had brands in multiple locations. Data revealed that 51.6% of the carcasses had no bruises, 30.9% had one bruise, 12.8% had two bruises, 3.7% had three bruises, .9% had four bruises, and .1% had more than four bruises. In addition, 7.2% of the bruises evaluated were located on the round, 41.1% were on the loin, 20.8% on the rib, and 30.8% on the chuck. Livers, lungs, tripe, heads, tongues, and whole carcasses were condemned at rates of 22.2, 5.0, 11.0, .9, 3.8, and .1%, respectively. Mean USDA yield grade and quality grade traits were as follows: USDA yield grade, 2.8; carcass weight, 338.4 kg; adjusted fat thickness, 1.2 cm; longissimus muscle area, 81.9 cm2; kidney, pelvic, and heart fat, 2.1%; USDA quality grade, High Select; overall maturity, A60; and marbling score, Small-minus.

Brain POU-er.

Developmental coordination is vital in the temporally coordinated appearance of cell types within the precise spatial architecture of the vertebrate brain and this, combined with the rich interplay between the developing brain and its target organs, is a biological problem of monumental complexity. An example is the genesis and subsequent integration of the neuroendocrine hypothalamus and the pituitary. Two recent papers use the developing hypothalamo-pituitary axis in order to gather a deeper understanding of these integrative mechanisms. In addition, they show that a sub-family of homeodomain factors, the POU-domain proteins, play a critical role in coordinating the respective ontogenies of the hypothalamus and the pituitary.

3.6 kb of the 5' flanking DNA activates the mouse tyrosine hydroxylase gene promoter without catecholaminergic-specific expression.

The tyrosine hydroxylase (TH) gene is expressed exclusively in cells and neurons that synthesize and release L-DOPA or catecholamines. To further understand the molecular genetic mechanisms that regulate this cell-type specific expression, a chimeric gene was prepared by linking 3.6 kb of the 5' flanking DNA of the mouse TH gene, including the +1 initiation site for transcription, to an E. coli beta-galactosidase reporter. This fusion gene (TH3.6LAC) was used to prepare transgenic mice, and the tissue distribution of expression of TH3.6LAC was determined by the measurement of beta-galactosidase enzymatic activity and/or by the detection of the transcription product of the chimeric gene by RNase protection assays. In two separate founder lines, TH3.6LAC expression was observed in every region of the brain that was examined, including the olfactory bulb, brainstem, cerebellum, diencephalon, hippocampus, striatum, and cerebral cortex. Expression of TH3.6LAC was observed in the adrenal gland of one founder line but not in the other. TH3.6LAC activation was undetectable in peripheral organs that were examined, including the liver, heart, salivary gland, kidney, lung, and spleen. Although 3.6 kb of the 5' regulatory DNA of the mouse TH gene is sufficient to activate the TH fusion gene in the mouse, it is not enough to restrict its expression to catecholaminergic cells.

The relative potency of pentobarbital in suppressing the kainic acid- or the N-methyl-D-aspartic acid-induced enhancement of cGMP in cerebellar cells.

Primary cultures of rat cerebellar cells were pretreated with various dosages of pentobarbital before the addition of kainic acid or N-methyl-D-aspartic acid in order to assess effects of this drug on the enhancement of cyclic guanosine-3',5'-phosphate (cyclic GMP) mediated by these excitatory agonists. Pentobarbital significantly suppressed kainic acid-induced increases in this cyclic nucleotide at concentrations as low as 5 microM but was only effective in suppressing the N-methyl-D-aspartic acid enhancement at dosages of 100 microM or greater. These data suggest that this barbiturate is a more effective depressant of the stimulatory effects of kainic acid as compared to N-methyl-D-aspartic acid.

Effect of prolactin replacement on the number of tyrosine hydroxylase expressing neurons in the arcuate nuclei of Ames dwarf and normal mice.

Ames dwarf mice do not synthesize or release growth hormone or prolactin (PRL) and have very poorly developed tuberoinfundibular dopaminergic (TIDA) neurons. An antibody to tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of dopamine, and immunohistochemical procedures were used in this study to compare the numbers of TH-immuno-positive neurons observed in the arcuate nuclei of Ames dwarf mice compared to phenotypically normal mice of the same strain. In female dwarfs, the number of TH-immunopositive neurons in the arcuate nuclei but not the pars compacta was markedly reduced when compared to normal females. The elevation of circulating PRL either by the implantation of a normal pituitary under the kidney capsule or by the daily administration of ovine PRL increased the numbers of arcuate neurons which expressed immunochemically detectable TH to a level comparable to that observed in untreated normal mice. The number of TH-expressing neurons was also reduced in the arcuate nuclei of dwarf males although the deficiency was not as great as in females. Ovine PRL seemed to have little effect on the numbers of TH-immunopositive neurons observed in either dwarf or normal male mice. These results suggest that the postnatal absence of PRL in mice does not result in a major reduction in the total population of TIDA neurons. Rather these neurons appear to be present in nearly normal numbers but are in a dormant state in the absence of circulating PRL.

Abuse liability of barbiturates and other sedative-hypnotics.

The principal action of the sedative-hypnotic drugs, of whom the barbiturates are the most widely known and utilized, is to produce drowsiness and promote sleep. At one time these were also the only drugs available to calm seriously anxious or disturbed people. Unfortunately, in addition to their clinical applications these drugs manifest a very high abuse potential. Experienced drug abusers report feelings of well-being and euphoria while under the influence of these drugs. Self-administration experiments conducted in animals have shown that the barbiturates are potent reinforcing agents. In controlled studies in humans, former drug abusers express a preference for barbiturates over benzodiazepines and will "work" to receive barbiturates. Long term consumption of the sedative-hypnotics, particularly barbiturates, leads to dependence characterized by a severe, potentially life-threatening abstinence syndrome following the abrupt withdrawal of the drug. Withdrawal manifestations include delirium and grand mal seizures. Because of the high abuse potential of these drugs, their manufacture and distribution has been greatly curtailed, and for most clinical applications they have been largely replaced by drugs, e.g., the benzodiazepines, which appear to have much less abuse liability.

Increased response of cerebellar cGMP to kainate but not NMDA or quisqualate following barbital withdrawal from dependent rats.

Female Sprague-Dawley rats were maintained on a diet of powdered food containing barbital for 8 weeks before the drug was abruptly withdrawn. Twenty-four hours later both barbital-dependent and control rats were injected intracerebroventricular (i.c.v.) with saline or one of four doses of kainic acid (KA) or in a separate experiment with saline or one of three doses of N-methyl-D-aspartic acid (NMDA) or of quisqualic acid (QA). After 4.5 min, the animals were killed by focused microwave irradiation, and the cerebella were collected. The levels of cyclic guanosine 3',5' monophosphate (cGMP) were markedly elevated in the cerebella of barbital-withdrawn rats when compared to controls. When compared to saline treatment, KA, at all dosages, resulted in a significantly greater elevation of cerebellar cGMP in the barbital-withdrawn rats than was induced by drug withdrawal alone. Only the two higher dosages of KA produced a significant elevation of this parameter in the control rats. Unlike KA, neither QA or NMDA produced any greater elevations of cGMP in barbital withdrawn rats than were induced by drug withdrawal alone. These collective results suggest that there is an increase in the response to KA but not QA or NMDA following the withdrawal of barbital from dependent rats.

Extra-hypothalamic dopamine is not involved in the effects of hyperprolactinemia on male copulatory behavior.

Experiments were performed to determine if the inhibition of copulatory behavior observed in male rats with chronically elevated serum prolactin levels (hyperprolactinemia) is associated with changes in central dopaminergic function in the nigrostriatal and mesolimbic systems. Chronic hyperprolactinemia, induced by ectopic pituitary grafts, inhibited sexual activity but was not associated with changes in locomotor activity, serotyped behavior in response to various doses of apomorphine, or 3H-spiroperidol binding to striatal homogenates. However, open-field defecation was reduced in the pituitary grafted animals. The results of the present study show that changes in nigrostriatal dopamine receptor sensitivity do not contribute to the inhibition of sexual behavior in hyperprolactinemic male rats. In addition, these results also demonstrate that the effects of hyperprolactinemia are relatively specific to copulatory behavior and appear not to involve general behavioral suppression.