Endocrine regulation of the establishment of spermatogenesis in pigs.

Somatic and germ cell maturation precedes the start of spermatogenesis and is coordinated, so efficient spermatogenesis will occur in the adults. The present study was conducted to evaluate endocrine regulation of germ and somatic cell homeostasis in the neonatal boar testis associated with the establishment of spermatogenesis. Testis tissue obtained from 3-, 5-, 7- and 14-day-old piglets were ectopically xenografted onto castrated, immunodeficient nude mice. Grafts were removed 22 weeks later and evaluated for growth and the establishment of spermatogenesis. Recipient mouse testosterone biosynthesis and follicle-stimulating hormone (FSH) concentrations were also assayed. Testis tissue graft growth was significantly greater in testis grafts from 3-day donor tissue when compared to all other ages; 5-, 7- and 14-day-old donor tissue weights were not significantly different at removal. Follicle-stimulating hormone concentrations in recipient mice supporting testis grafts from 5-, 7- and 14-day-old donor tissues did not differ and were similar to normal physiological levels in age-matched, intact nude mice. Serum FSH levels were significantly lower in recipient mice supporting testis grafts from 3-day-old donor tissue. Radioimmunoassay and biological assay indicated no differences in testosterone production by testis tissue grafts of varying donor age. Porcine testis tissue obtained from 3-, 5-, 7- and 14-day-old neonatal boars were all capable of producing round and elongate spermatids after 22 weeks of grafting, but testis grafts from 14-day-old donors had a significantly greater (eightfold) percentage of seminiferous tubules with spermatids compared to all other donor ages (p < 0.05). Cryopreservation did not affect the ability of testis tissue grafts to grow, produce testosterone or establish spermatogenesis when compared to controls (p < 0.05). Collectively, these data demonstrate intrinsic differences in the biological activity of germ and somatic cell populations during neonatal boar testis development associated with the establishment of spermatogenesis.

Hydra head activator peptide has trophic activity for eukaryotic neurons.

The synthetic undecameric peptide, pGlu-Pro-Pro-Gly-Gly-Ser-Lys-Val-Ile-Leu-Phe, known as the hydra head activator peptide, present in high concentrations in mammalian hypothalamus and intestine, was tested for neurotrophic activity in a survival assay using cultured chick embryonic sympathetic and dorsal root ganglion cells, and for morphological differentiation activity on neuroblastoma cells. Hydra head activator peptide supported neuron survival. The optimal active concentration, 1 pM, was very similar to the concentration that causes bud and head formation in hydra. Maximal neuron survival obtained with hydra head activator peptide was close to that obtained with nerve growth factor: both substances enhanced survival up to 3 times that of control cultures. Bradykinin, which has some amino acid sequence homology with hydra head activator, was inactive as a neurotrophic factor. Hydra head activator induced rapid morphological differentiation of the mouse neuroblastoma cell line Neuro-2A. Neuro-2A responded to the peptide by process extension, 4 h after its addition to the culture medium. Neurotrophic factors isolated to date have been characterized by their ability to maintain cell viability and enhance neurite outgrowth. Hydra head activator peptide met these two criteria when tested in 3 different neuron culture systems. Our results suggest that the head activator peptide may act as a neurotrophic factor for neurons in other species, including mammals.

A screening method using tissue culture for evaluation of potential retinal adhesives.

Several adhesives have been tested for their potentially toxic effects on embryonic retinal tissue. The authors have characterized the effects of the adhesives on neurofilament extension and also on surgical-wound "re-knitting." While none of the adhesives in the sample (including those in current surgical use) seem to be ideal, the model advanced has application for the continuing development of better 'bio-adhesives'. The most immediate application is within the field of vitreoretinal surgery in situations where conventional procedures currently seem inadequate.

Correlation between histamine-induced neuronal excitability and activation of adenylate cyclase in the guinea pig hippocampus.

In a homogenate of guinea pig hippocampus histamine activated adenylate cyclase and in a hippocampal slice preparation it increased the firing rate of pyramidal cells in the CA3 region. Both activities were apparently mediated by H2 receptors. The concentration of histamine and of the H2 receptor agonist, impromidine, required to stimulate activity was similar in each test preparation with impromidine being about 100-fold more potent than histamine. Moreover, the H2 receptor antagonists, cimetidine and ICIA 5165, each reversed the activation by histamine of the two test preparations, with ICIA 5165 being about 100-fold more potent than cimetidine. Thus, there is a correlation between activation of cyclase and neuronal excitability induced by histamine. These observations support a large body of evidence suggesting that histamine is a neurotransmitter or modulator in the CNS.

Seizures with antidepressants: an in vitro technique to assess relative risk.

The relative potential of various antidepressants to induce seizures while being used at therapeutic doses was studied by examining their action on spike activity in perfused guinea pig hippocampal slices. Within the range of concentration studied, imipramine, amitriptyline, nortriptyline, maprotiline, and desipramine tended to increase spike activity in a descending order of effect. Doxepin and nomifensine increased spike activity at lower concentrations, but reduced it at higher concentrations. Protriptyline and trimipramine reduced spike activity with increasing concentrations, whereas mianserin and viloxazine had little effect at any concentration. These findings are discussed in light of previous clinical and laboratory reports, and the clinical implications of these findings are presented. Finally, results with the antidepressants are compared with those previously observed with neuroleptics. On the basis of this comparison and a review of clinical reports, the assumption that neuroleptics have greater epileptogenic potential than antidepressants is questioned.

Sequence of alcohol presentation is important in the potentiation of long-term events.

Animal and human studies have demonstrated that, depending upon the sequence of alcohol presentation, long-term memory of events can either be enhanced or diminished. In the present study a similar phenomenon is demonstrated in the neuronal excitability of slices of hippocampus from guinea pig brains. Alcohol given after, but not before, 3 days of pentylenetetrazol (PTZ) administration to the intact animal produced kindling equivalent to 5 days of PTZ given by itself. This effect appears to be independent of the known withdrawal effects of alcohol and lasts for at least 14 days after the alcohol and PTZ administration have been discontinued.

Neuroleptic-induced seizures. An in vitro technique for assessing relative risk.

To estimate the relative risk of various neuroleptic medications for patients with epilepsy or likely to have neuroleptic-induced seizures, their action on spike activity in perfused guinea pig hippocampal slices was studied. Within the range of concentrations studied, molindone hydrochloride, butaclamol hydrochloride, pimozide, and fluphenazine dihydrochloride produced the least increase in excitability. There were also differences in the dose-response curves. Chlorpromazine, thioridazine, and pimozide produced an inverted U-shaped curve. For haloperidol and fluphenazine, excitability tended to increase and them plateau. Molindone and butaclamol produced no increase in excitability. Combinations of neuroleptics had synergistic effects, while the anticonvulsant diazepam inhibited neuroleptic-induced excitability. This article discusses the clinical implications of these findings and their effect on theories of which neuroleptics might produce the fewest seizures.

Kindling induces long-lasting alterations in response of hippocampal neurons to elevated potassium levels in vitro.

The cellular basis of kindling was studied electrophysiologically with slices of guinea pig hippocampus. Normally, epileptiform activity can be induced in the slices only by combined exposure to elevated potassium levels and a chemical convulsant such as penicillin. In hippocampal slices from pentylenetetrazole-kindled animals, however, elevated potassium alone can induce seizures. These data suggest that kindling elicits long-term changes in neuronal excitability that may involve ionic mechanisms.

The hippocampal slice: a system for studying the pharmacology of seizures and for screening anticonvulsant drugs.

Interictal spikes with a configuration similar to that occurring in grand mal epilepsy were generated by the application of penicillin to a hippocampal slice preparation. This slice preparation has potential value for screening anticonvulsant drugs and for studying epileptic activity. The effect of anticonvulsant drugs on seizure activity was tested at concentrations comparable to reported clinical serum concentrations. Phenytoin and diazepam were maximally effective at concentrations of 20 microgram/ml and 3-4 microgram/ml, respectively, in good agreement with their effective concentrations in clinical practice. Phenobarbital was more potent (5 microgram/ml) and mesuximide (50% potent at 80 microgram/ml) was least effective.

Effects of putative neurotransmitters on neuronal activity in monkey auditory cortex.

The effects of the putative neurotransmitters norepinephrine (NE), gamma-aminobutyric acid (BAGA), and acetylcholine (ACh) were tested on auditory cortex neurons which were activated acoustically by species-specific vocalizations in awake squirrel monkeys. Five-barrel glass electrodes were used to record the activity single neurons in the superior temporal gyrus and to apply NE, GABA, or ACh microiontophoretically. Poststimulus time histograms and raster displays of neuronal responses to the vocalizations were computed before, during, and after iontophoresis. Dose-dependent inhibition of spontaneous and vocalization-evoked discharge rates was seen with NE and GABA. Generally, excitation was observed with ACh. A given dose of NE or GABA reduced spontaneous activity by a greater proportion than it reduced activity evoked by the vocalizations. During excitatory responses, segments with lower discharge rates were reduced proportionately more than segments with higher discharge rates. Usually, response 'pattern' was not altered by iontophoresis of any of the substances. However, in some cases the differential inhibition of slow activity produced by NE or GABA did result in a 'patern' change. The demonstration that small amounts of locally applied NE and GABA substantially alter the specific neuronal activation produced by vocalizations provides additional evidence that these agents may function as neurotransmitters in this neocortical area and offers clues about their functional significance.